Resumo

The aim was to identify predictive traits of relatively easy measurement and which can be recorded early in life (age at first conception - AFCo), besides estimating its genetic correlations with growth and carcass traits in Nellore cattle. Age at first conception was considered the age at which the female had the first positive diagnosis for pregnancy. The estimation of (co)variance components and genetic parameters was performed using a linear animal model in two-trait analysis. The estimates of heritability were moderate, enabling genetic selection for growth-, carcass-, and sexual precocityrelated traits. The genetic correlation obtained between AFCo and age at first calving (AFCa) was high (0.88), indicating the feasibility of using AFCo as a selection criterion for early calving heifers. Genetic correlation estimates between AFCo and AFCa with weight at 120, 210, 365, and 450 days of age and carcass traits were moderate and negative (-0.33 to -0.62). Thus, genetic selection for animals with early AFCo and AFCa would enhance carcass yield, fat deposition, and growth performance, despite not affecting birth weight or daily weight gain. The results of this study encourage the use of AFCo in Nellore cattle since this trait displayed enough genetic variability in Nellore cattle, and can be used as selection criteria to improve sexual precocity. When the objective of genetic selection is to increase heifer sexual precocity, we could use the first trait as a criterion, as the measurement of this trait occurs at a lower AFCa.

Objetivou-se identificar características indicadoras de precocidade sexual de fácil mensuração e que podem ser registradas em menor idade (idade à primeira concepção - IPC), além de estimar as correlações genéticas dessa característica com aquelas de crescimento e carcaça em bovinos Nelore. A IPC foi considerada a idade em que a fêmea apresentou o primeiro diagnóstico positivo de prenhez. A estimativa dos componentes de (co)variância e dos parâmetros genéticos foi realizada usando modelo animal linear em análises bicaracterísticas. As estimativas de herdabilidade foram moderadas, indicando viabilidade de seleção genética para características de crescimento, carcaça e precocidade sexual. As correlações genéticas obtidas entre o IPC e a idade ao primeiro parto (IPP) foram altas (0,88), indicando a viabilidade do uso de IPC como critério de seleção para parto em idade precoce de novilhas. As estimativas de correlações genéticas entre IPC e IPP com peso aos 120, 210, 365 e 450 dias de idade e características de carcaça foram moderadas e negativas (-0,33 a -0,62). Assim, a seleção genética para animais com IPC e IPP precoces aumentaria o rendimento de carcaça, a deposição de gordura e o peso corporal, embora não afete o peso ao nascer e o ganho de peso diário. Os resultados deste estudo encorajam o uso de IPC em bovinos Nelore, uma vez que esta característica apresentou variabilidade genética em bovinos Nelore, podendo ser utilizada como critério de seleção para melhorar a precocidade sexual. Quando o objetivo de seleção genética é aumentar a precocidade sexual das novilhas, indica-se o uso de IPC como critério, pois a mensuração desta característica ocorre em idade menor IPP.

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The objective of this study was to identify parameters, before the start of the breeding season, that affect the conception rate of precocious Nelore heifers through ultrasonographic ovarian evaluation and evaluation of weight and body condition score (BCS). A total of 407 heifers aged 404±69 days (≈14 months old), weighing 267.1±31.2 kg, and with mean BCS of 3.1±0.5, were used. Heifers were subjected to hormone treatment to induce cyclicity and, 30 days later, to a fixed-time artificial insemination (FTAI) program with three managements. Morphometric measurements of ovaries and ovarian structures were performed by transrectal ultrasonographic evaluation, as well as weighing and evaluation of BCS on D −30 and D0. Conception rate was evaluated 30 days after FTAI. The conception rate of heifers did not vary according to ovary diameter, weight, BCS, and age at first calving. However, heifers with the presence of follicle with a diameter > 6 mm at D −30 and D0 had a higher conception rate at the first FTAI. The presence of a dominant follicle greater than 6 mm at D −30 is an efficient complementary criterion to identify 14-month-old Nelore heifers with greater ability to conceive at the first FTAI before the breeding season. Antral follicle count performed on D −30 is not a good tool to predict fertility at the first FTAI, and the weight may not be a limiter to select heifers under good nutritional and health management.(AU)

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This observational study describes the short- and long-term effects of maternal factors in 226 Holstein heifers and their offspring. We obtained maternal data and information from the dairy register. Young heifers were assessed in the window of 60 to 105 days of life to perform the Calf Health Scoring System and performance index, and blood samples to measure inflammatory biomarkers. Prospective data on reproduction were obtained from dairy farm registers. The eutocic weight was higher than the dystocic calving heifers. Plasma total protein and weight were higher in the offspring of multiparous dams than in those of primiparous dams. Calves that were born lighter and in summer had lower concentrations of total protein and performance indices. The punctuation of the fecal score was higher in calves born in summer and cold months for BRD. Offspring from multiparous dams born at term exhibited greater precocity in terms of age at first artificial insemination and first parturition. Finally, seasonality at birth affected pregnancy loss and age at first calving. Heifers born in winter had lower rates of pregnancy loss than those born in summer. In addition, these animals were more precocious than animals born during the cold seasons.

Este estudo observacional descreve os efeitos de curto e longo prazo de fatores maternos em 226 novilhas Holandesas e suas proles. Foram obtidos dados maternos e informações do registro leiteiro. Novilhas jovens foram avaliadas, na janela de 60 a 105 dias de vida, com o escore de saúde, índice de desempenho e amostras de sangue para medir biomarcadores inflamatórios. Dados prospectivos sobre reprodução foram obtidos dos registros da fazenda. O peso das novilhas eutócicas foi superior ao das novilhas que nasceram de parto distócico. A proteína total plasmática e o peso foram maiores nas proles de vacas multíparas do que nas proles das primíparas. Bezerras que nasceram mais leves e no verão apresentaram menores concentrações de proteína total e índices de desempenho. A pontuação do escore fecal foi maior em bezerras nascidas no verão e nos meses frios para DRB. A prole de vacas multíparas nascidas a termo apresentou maior precocidade em relação à idade à primeira inseminação artificial e ao primeiro parto. Finalmente, a sazonalidade ao nascimento afetou a perda de prenhez e a idade ao primeiro parto. As novilhas nascidas no inverno tiveram menores taxas de perda de gestação do que as nascidas no verão. Além disso, esses animais eram mais precoces do que os nascidos nas estações frias.

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Potential variables for the reproductive success of beef cows were evaluated. Included in the model were the age of the cow at calving; the interval between the Julian calving date and the end of the breeding season; the body weight and conditions at calving, at 75 days post-partum and at the end of the breeding season; and the mean daily variation in weight between these dates. Logistic regression was used in the analysis, with the parameters evaluated using the odds ratio statistic, estimating the chance of pregnancy. The mean rate of pregnancy was 84% and 55% for early and late-weaned cows, respectively. For early weaned cows, the regression variables were the Julian calving date, age of the cow, weight gain from calving to 75 days post-partum, and from 75 days post-partum to the end of the reproductive period. For late-weaned cows, there were only two regression variables, weight at calving and weight gain from calving to the end of the reproductive period. For every year above the average age of the herd, early weaned cows have an 80.9% greater chance of pregnancy, while a reduction of one year reduces the chance of pregnancy by 44.7%. In early weaned cows, every seven days after the mean Julian calving date reduces the chances of pregnancy by 22.6%, whereas every seven days before the mean calving date increases pregnancy by 29.2%. Greater gains in cow body weight, from calving to the end of the reproductive period, determine a greater probability of pregnancy.(AU)

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A pecuária de corte brasileira se consolidou no ranking mundial de produção e exportação de carne bovina, possuindo então grande relevância econômica. Porém, a criação extensiva e o baixo investimento tecnológico comprometem os índices zootécnicos, necessitando, assim, de inovações em reprodução animal e melhoria genética para aumento da produtividade. A rentabilidade da atividade de cria se baseia na parição de um bezerro por vaca por ano, sendo crucial que a fêmea se torne gestante precocemente. Assim, a idade em que ocorre a primeira concepção é determinante para a produtividade e a idade à puberdade é o principal fator que estabelece a competência da fêmea em sua primeira estação de monta. Para otimizar os resultados reprodutivos de novilhas, sugere-se a realização da indução de puberdade, feita através de protocolos farmacológicos com intuito de induzir a ciclicidade das fêmeas, para que estejam cíclicas no início da estação reprodutiva e, possivelmente, conceberem. Como auxílio à indução de puberdade, a ultrassonografia transretal possibilita a avaliação da eficácia do protocolo e responsividade da fêmea. Portanto, estudos acerca da precocidade sexual e indução de puberdade são fundamentais, visto a importância econômica das características reprodutivas e a necessidade de redução da idade ao primeiro parto das fêmeas do rebanho nacional. Esta revisão de literatura está dividida em parte 1 e parte 2, na primeira abordou-se Idade ao primeiro parto (IPP) no atual cenário da pecuária de corte, puberdade, principais fatores que interferem na antecipação da puberdade (genética e raça; nutrição e peso corporal) e eficiência reprodutiva e utilização de novilhas precoces. Na segunda parte abordou-se o Impacto do melhoramento genético na precocidade de novilhas, influência da condição corporal sobre a ciclicidade reprodutiva de fêmeas, avaliação do trato reprodutivo com auxílio de ultrassonografia transretal e protocolos de indução de ciclicidade.(AU)

The brazilian beef cattle breeding has consolidated itself in the world ranking of production and export of beef, having then great economic relevance. However, extensive breeding and low technological investment compromise zootechnical rates, thus requiring innovations in animal breeding and genetic improvement to increase productivity. The rentability of breeding is based on the calving of one calf per cow per year, so it is crucial that the female becomes pregnant early. Therefore, the age at which the first conception occurs is a determining factor for productivity, and age at puberty is the main factor that establishes the competence of the dam in the first breeding season. To optimize reproductive results of heifers, it is suggested the induction of puberty, done through pharmacological protocols in order to induce cyclicity of females, so that they are cyclic in the reproductive season and possibly conceive. As an aid to the induction of puberty, transrectal ultrasonography allows the evaluation of the protocol efficacy and female responsiveness. Therefore, studies on sexual precocity and induction of puberty are fundamental, given the economic importance of reproductive characteristics and the need to reduce the age at first calving of females in the national herd. This literature review is divided into first part and second part. The first part deals with Age at first calving in the current beef cattle scenario, puberty, the main factors that interfere with early puberty (genetics and breed; nutrition and body weight) and reproductive efficiency and utilization of precocious heifers. The second part dealt with the impact of genetic improvement on heifer precocity, the influence of body condition on female reproductive cyclicity, evaluation of the reproductive tract using transrectal ultrasound and cyclicity induction protocols.(AU)

Resumo

A pecuária de corte brasileira se consolidou no ranking mundial de produção e exportação de carne bovina, possuindo então grande relevância econômica. Porém, a criação extensiva e o baixo investimento tecnológico comprometem os índices zootécnicos, necessitando, assim, de inovações em reprodução animal e melhoria genética para aumento da produtividade. A rentabilidade da atividade de cria se baseia na parição de um bezerro por vaca por ano, sendo crucial que a fêmea se torne gestante precocemente. Assim, a idade em que ocorre a primeira concepção é determinante para a produtividade e a idade à puberdade é o principal fator que estabelece a competência da fêmea em sua primeira estação de monta. Para otimizar os resultados reprodutivos de novilhas, sugere-se a realização da indução de puberdade, feita através de protocolos farmacológicos com intuito de induzir a ciclicidade das fêmeas, para que estejam cíclicas no início da estação reprodutiva e, possivelmente, conceberem. Como auxílio à indução de puberdade, a ultrassonografia transretal possibilita a avaliação da eficácia do protocolo e responsividade da fêmea. Portanto, estudos acerca da precocidade sexual e indução de puberdade são fundamentais, visto a importância econômica das características reprodutivas e a necessidade de redução da idade ao primeiro parto das fêmeas do rebanho nacional. Esta revisão de literatura está dividida em parte 1 e parte 2, na primeira abordou-se idade ao primeiro parto (IPP) no atual cenário da pecuária de corte, puberdade, principais fatores que interferem na antecipação da puberdade (genética e raça; nutrição e peso corporal) e eficiência reprodutiva e utilização de novilhas precoces. Na segunda parte abordou-se o Impacto do melhoramento genético na precocidade de novilhas, influência da condição corporal sobre a ciclicidade reprodutiva de fêmeas, avaliação do trato reprodutivo com auxílio de ultrassonografia transretal e protocolos de indução de ciclicidade.(AU)

The brazilian beef cattle breeding has consolidated itself in the world ranking of production and export of beef, having then great economic relevance. However, extensive breeding and low technological investment compromise zootechnical rates, thus requiring innovations in animal breeding and genetic improvement to increase productivity. The rentability of breeding is based on the calving of one calf per cow per year, so it is crucial that the female becomes pregnant early. Therefore, the age at which the first conception occurs is a determining factor for productivity, and age at puberty is the main factor that establishes the competence of the dam in the first breeding season. To optimize reproductive results of heifers, it is suggested the induction of puberty, done through pharmacological protocols in order to induce cyclicity of females, so that they are cyclic in the reproductive season and possibly conceive. As an aid to the induction of puberty, transrectal ultrasonography allows the evaluation of the protocol efficacy and female responsiveness. Therefore, studies on sexual precocity and induction of puberty are fundamental, given the economic importance of reproductive characteristics and the need to reduce the age at first calving of females in the national herd. This literature review is divided into first part and second part. The first part deals with Age at first calving in the current beef cattle scenario, puberty, the main factors that interfere with early puberty (genetics and breed; nutrition and body weight) and reproductive efficiency and utilization of precocious heifers. The second part dealt with the impact of genetic improvement on heifer precocity, the influence of body condition on female reproductive cyclicity, evaluation of the reproductive tract using transrectal ultrasound and cyclicity induction protocols.(AU)

Resumo

The use of morphological traits assessed using visual scores as indirect selection criteria in cattle has the advantage of evaluating young animals regarding potential productive and reproductive performance. This enables breeders to make earlier decisions compared to later measurements, such as scrotal circumference at 450 days (SC450) and stayability (STAY). The aim of this study was to estimate the genetic parameters for visual score traits and their associations with reproductive traits: scrotal circumference at 365 days of age (SC365), SC450, STAY, probability of precocious calving (PPC30) and age at first calving (AFC) in Nellore cattle. Visual score data from 4,175 Nellore cattle, with an average age of 22 months, and reproductive data from 3,075 cattle belonging to the HoRa Genetics Provada herd were used. The morphological traits were evaluated by the MERCOS methodology. The heritability estimates obtained ranged from 0.15 to 0.28 for visual scores and 0.10 to 0.54 for reproductive traits. Genetic correlations between visual scores and reproductive traits were generally low, except between: muscularity and PPC30; structure and STAY; racial and SC450; conformation and SC365, SC450, STAY, and AFC; navel and STAY and AFC; and sacrum and SC365, STAY, and AFC, which were moderate to high. The identification of animals with flat sacral bone (not protruding or sloping) can also be an efficient characteristic in the identification for early pregnancy, and together with the musculature score, they can be related to animals with lower age at the first calving.(AU)

A utilização de características morfológicas de bovinos, pelo uso de escores visuais como critério de seleção indireta tem como vantagem a avaliação em animais jovens quanto ao potencial desempenho produtivo e reprodutivo, antecipando a tomada de decisão em comparação a medidas tomadas de forma tardia, como perímetro escrotal aos 450 dias (PE450) e stayability (STAY). Objetivou-se estimar os parâmetros genéticos para características de escores visuais e a associação dessas com características reprodutivas, perímetro escrotal aos 365 (PE365) dias de idade, PE450, STAY, probabilidade de parto precoce (3P) e idade ao primeiro parto (IPP) em bovinos Nelore. Foram utilizadas informações de escores visuais e de reprodução de 4.175 e 3.075 bovinos, respectivamente, com idade média de 22 meses, pertencentes a fazenda HoRa Genética Provada. As características morfológicas foram avaliadas pela metodologia MERCOS. As estimativas de herdabilidade obtidas apresentam grande amplitude, variando de 0,15 a 0,28 para escores visuais e 0,10 a 0,54 para características reprodutivas. As correlações genéticas entre característica de escores visuais e reprodução foram, de maneira geral baixas (0.03-0.66), com exceção entre a musculosidade e 3P, estrutura e STAY, racial e PE450, conformação com PE365, PE450, STAY e IPP, ônfalo com STAY e IPP, e sacro com PE365, STAY e IPP, que foram moderadas a altas. A identificação de animais com melhor osso sacro (mesmo nível das ancas), ou seja, não saliente ou inclinado pode ser uma característica eficiente na identificação para prenhez precoce, e juntamente ao escore de musculatura poderão ser relacionados a animais com menor idade ao primeiro parto.(AU)

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This study examines the impact of the body mass index (BMI) at calving on the development and postpartum efficiency of cows of Zebu origin. The study involved 87 cows and their calves [pure Nellore (N) or predominant Nellore composition in a cross with Charolais (C) (3/4N1/4C and 5/8N3/8C)]. The mothers were grouped into classes according to their BMI at calving, namely, 'small', 'moderate' and 'large'. Body mass index was determined by dividing the body weight of the cows by their length and by hip height and then dividing the result by 10. Cows were weighed at calving, at weaning, at the end of the breeding period and at the diagnosis of pregnancy. Calves were weighed at birth, at early weaning (63 days) and at 210 of age. To evaluate milk yield and quality, milk was collected at 21, 42 and 63 days after calving. Milk yield was measured by the direct method, with manual milking, followed by analysis of the lactose, fat, total solids and crude protein contents. Pregnancy rate was similar between the three BMI groups; however, cows with a lower BMI were more efficient at calving in producing kilograms of calf per kilogram of cow kept. Higher BMI provide higher milk yields, without affecting its quality, as well as heavier calves at early weaning and at 210 days of age.(AU)

O objetivo dessa pesquisa foi avaliar o impacto do índice de massa corporal (IMC) ao parto no desenvolvimento e eficiência pós-parto de vacas de origem zebuína. Utilizou-se 87 vacas e seus bezerros [Nelore (N) puros ou com predominância em cruzamento com Charolês (C) (3/4N1/4C e 5/8N3/8C)], agrupadas em classes segundo o seu IMC ao parto, em 'pequenas', 'moderadas' e 'grandes'. O índice de massa corporal foi determinado através da divisão do peso corporal das vacas pelo seu comprimento e pela altura de quadril e posteriormente o resultado dividido por 10. As vacas foram pesadas no parto; ao desmame; final da monta e no diagnóstico de gestação. Os bezerros foram pesados ao nascimento, na desmama precoce (63 dias) e aos 210 dias de idade. Para a avaliação da produção e qualidade do leite das vacas foram realizadas três coletas aos 21, 42 e 63 dias após o parto. A medida da produção de leite foi realizada pelo método direto, com ordenha manual, seguida de análise do teor de lactose, gordura, extrato seco total e proteína bruta. A taxa de prenhez foi similar para os três índices de massa corporal, no entanto vacas de menor IMC foram mais eficientes ao parto na produção de quilogramas de bezerros por quilograma de vaca mantida. O IMC alto propicia maior produção de leite sem que a qualidade seja alterada e bezerros mais pesados no desmame precoce e no peso aos 210 dias.(AU)

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The objective of this study was to evaluate the breed and heterosis effects on reproductive traits, test-day milk yield, and 305-day milk yield in different lactations of crossbred Girolando cows. Data consisted of test-day milk yield records of first (118,831 records), second (63,227), and third lactation (44,512) and their relative productive (test-day milk yield, 305-day milk yield, and lactation length) and reproductive (age at first calving, calving interval, days open, and dry period) records of 35,582 Girolando cows from Brazil, collected from 1998 to 2014. The heterosis effect of the evaluated traits in Girolando cattle was estimated by MIXED procedure in SAS. Girolando cows showed a negative (favorable) and significant heterosis effect for reproductive traits. The dry periods between the first and second calving and between the second and third calving showed the greatest gains in heterosis (21.93 and 10.41%, respectively). All the evaluated productive traits showed a significant and similar heterosis effect between the three lactations. The use of crossbreeding strategies between the Holstein and Gyr breeds, instead of using the pure breed, is indeed a good alternative to increase the economic efficiency of the dairy activity in the different production systems in tropical environments.(AU)

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We aimed to estimate genetic parameters for growth, reproductive, and carcass traits in Tabapuã cattle. Phenotypic data were collected between 1990 and 2019 in 1,218 farms, and the pedigree file had 340,868 animals. The traits evaluated were body weight at 120 (W120), 210 (W210), 365 (W365), and 550 (W550) days of age; age at first calving (AFC), scrotal circumference at 365 days of age (SC365), ribeye area (REA), backfat thickness (BF), and rump fat thickness (RF). The (co)variance components were estimated using the restricted maximum likelihood method, considering single and two-traits animal models. For all traits, the models considered fixed, direct additive genetic, and residual random effects. In addition, for W120 and W210, the maternal additive genetic and maternal permanent environmental effects were also included. Heritabilities for W120, W210, W365, W550, SC365, REA, BF, and RF were of moderate magnitude (0.15, 0.16, 0.23, 0.19, 0.22, 0.36, 0.31, and 0.27, respectively). Low heritability was observed for AFC (0.07). The genetic correlations between growth traits were higher than 0.90, while AFC and SC365 presented negative moderate correlation (−0.66). The REA showed low genetic correlations with BF (0.07) and RF (0.07), whereas BF and RF were highly correlated (0.77). Considering the heritability estimates, selection for AFC would result in limited genetic gain, while for the other traits, it would be satisfactory. Based on the high genetic correlations between growth traits, selection of Tabapuã animals can be performed at younger ages. Additionally, animals can be indirectly selected for AFC through SC365, and only one fat thickness trait may be used in the selection process considering the high genetic correlation and similar heritability values for BF and RF.(AU)

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Reproductive characteristics directly reflect on productive performance, as they determine the number of calves born annually and the interval between generations, thereby affecting the selection intensity. This allows for the determination of the most important economic variables that directly affect the production system. The present study is a literature review of somatotropic axis gene polymorphisms that are associated with reproductive functions in heifers and cows (Bos taurus taurus and Bos taurus indicus). The following characteristics were analyzed from the various studies reviewed: number of services per pregnancy (Nº services/ pregnancy), age at first calving (AFC), calving interval (CI), and period of service calving conception interval (CCI). The research was conducted during the period from 2011 to 2021, and associations were found among all indicators of reproductive efficiency evaluated in heifers and cows, with 27 single nucleotide polymorphisms (SNPs): 18 in GHR, 5 in IGF-I, and 4 in STAT5A. This study revealed the relationships between SNPs and the reproductive efficiency indicators and demonstrated that molecular genetic techniques enhance the animal selection process, resulting in more profitable systems that are sustainable in the long term.

Características reprodutivas refletem diretamente no desempenho produtivo visto que são capazes de determinar o número de bezerros nascidos anualmente, além de afetar o intervalo entre gerações e, consequentemente, a intensidade de seleção, fazendo com o que tais atributos sejam apontados como variáveis econômicas das mais importantes que afetam diretamente o sistema de produção. O presente estudo propõe realizar uma revisão de literatura de polimorfismos de genes do eixo somatotrópico associados a funções reprodutivas em novilhas e vacas (Bos taurus taurus e Bos taurus indicus), indicadas pelos índices: número de serviços por gestação (Nº serviços/gestação), idade ao primeiro parto (IPP), intervalo de partos (IP) e período de serviço, como também denominado de intervalo parto-concepção (IPC). As pesquisas encontradas durante o período de 2011 a 2021 demonstraram associações entre todos os indicadores de eficiência reprodutiva analisados de novilhas e vacas com 27 polimorfismos de nucleotídeo único (SNPs), sendo 18 em GHR, 5 em IGF-I e 4 em STAT5A. Dessa forma, este estudo mostrou relação entre os SNPs e os indicadores de eficiência reprodutiva, demonstrando que técnicas de genética molecular potencializam o processo de seleção dos animais, resultando em sistemas mais lucrativos e que se sustentam a longo prazo.

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The objective was to evaluate the existence of heterogeneity of variances and its impact on the genetic evaluation of ponderal performance in sires of the Nellore breed. We used records of adjusted body weights at 210 (W210), 365 (W365), and 450 (W450) days of age. Both W365 and W450 were combined by principal component analyses using the first component (PC). Average daily gain (ADG) was obtained by difference between W450 and W210. The classes of standard deviations (SD) for W210, PC, and ADG were obtained by the standardization of means of herd-year means subclasses, with positive values composing the high SD and values equal and less than zero composing the SD. The model included the fixed effects of contemporary group and age at calving as a covariate, random genetic additive, and maternal genetic (except for PC) effects, and the permanent maternal environment. Variance components were obtained by Gibbs sampling. Posterior means of heritability in analyses without considering heterogeneity of variances ranged from 0.15±0.01 to 0.31±0.01. Posterior means of genetic correlations between the two classes of SD for W210, PC, and ADG were equal to 0.85±0.04, 0.83±0.03, and 0.71±0.08, respectively. Spearman correlation to breeding values of sires for ADG as the selection intensity increased in them, and the correlations between breeding values in general analyses were more correlated with those predicted in the high DP. Therefore, when there is a higher selection intensity on the sires only for the ADG criterion, there is a significant presence of the heterogeneity of variances and impact on the genetic evaluation of the sires. Thus, for ADG, the predictions of breeding values obtained by the genetic evaluation model in which the heterogeneity of variances are not considered are more weighted by the class of greater heterogeneity.(AU)

Resumo

We aimed to evaluate the effects of sex and the linear and quadratic components of age of dam at calving, as well as apply a mixed model including maternal effect for the genetic evaluation of weaning (WW) and yearling (YW) weights. The phenotypic database was composed by Charolais, Caracu, Aberdeen Angus, and Canchim purebred and crossbred animals. Single-trait analyses were performed using models that included the maternal effect for WW and YW traits, and a model ignoring this effect on YW (YWNM). The Deviance Information Criterion (DIC), model posterior probabilities (MPP), accuracy of breeding values (ACC), and Spearman's rank correlation were applied to compare the models including and ignoring the maternal effect on YW. Sex and age of dam at calving had significant effects on WW and YW. The direct heritability estimates were 0.21±0.03 and 0.05±0.02, and the maternal heritabilities were 0.11±0.02 and 0.02±0.01 for WW and YW, respectively. The heritabilities estimated for YW may have been influenced by the several genetic groups in the population and by used conventional animal model, which may not have been the better fit model to evaluate YW in this population. The DIC, MPP, and ACC values indicated that YW outperformed the YWNM model, but the rank correlation and percentages of individuals selected in common suggested that the best animals would be selected independently of the model chosen.

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The Colombian creole cattle breed Blanco Orejinegro (BON) is an important zoogenetic resource, but there is little knowledge about the genetic parameters and trends of its reproductive traits. Therefore, the aim of this study was to estimate parameters for the reproductive traits calving interval (CI), age at first calving (AFC), gestation duration (GD) and genetic trends for CI in the BON breed. Genealogy information from 7,799 animals was used, and employing the MTDFREML program, the components of the variance, heritability (h2), repeatability (rep), and estimated breeding values (EBV) for CI (n=3308), AFC (n=729), and GD (n=306) were estimated, in addition to the inbreeding coefficient (F) of the population. Genetic trends were established through linear regression using R software. Finally, the animals were classified as inbred (F > 0) and noninbred (F=0), and the effect of inbreeding on reproductive performance was established through a generalized linear model using the R program. An average F value of 4.41%±0.06 was observed. The h2 for CI was 0.11±0.03 with a rep of 0.15±0.04; for AFC, h2 was 0.00±0.05; and for GD, h2 was 0.00±0.08. The genetic trend for CI was -0.01 days/year. Finally, for CI, inbreeding depression was evident; this trait increased when inbreeding increased. These results indicate an important environmental influence on reproductive traits. The heritability estimate for CI suggests that little genetic progress could be achieved through selection. The evidence of inbreeding depression raises the need to control inbreeding to conserve this genetic resource.(AU)

O gado crioulo colombiano Blanco Orejinegro (BON) é um importante recurso zoogenético, mas ainda há desconhecimento sobre os parâmetros e tendências genéticas das características reprodutivas dessa raça. Portanto, o objetivo deste estúdio foi estimar parâmetros e tendências genéticas para características reprodutivas intervalo de partos (IDP), idade ao primeiro parto (IPP) e duração da gestação (DG) na raça BON. A informação da genealogia de 7,799 animais foi usada. Utilizando o programa MTDFREML foram estimados os componentes de variância, herdabilidade (h2), repetibilidade (rep) e valores genéticos (VGE), para IDP (n=3308), IPP (n=729) e DG (n=306), além do coeficiente de endogamia (F) na população. As tendências genéticas foram determinadas por regressão linear usando o software R. Finalmente, os animais foram classificados como endogâmicos (F > 0) e não endogâmicos (F=0) e o efeito da endogamia no desempenho reprodutivo foi determinado usando um modelo linear generalizado usando R. Observouse um F médio de 4,41%+0,06. A h2 para IDP foi 0,11±0,03 com uma repetibilidade de 0,15±0,04; para IPP a h2 foi 0,00 ± 0,05; e para DG a h2 foi 0,00 ± 0,08. A tendência genética para IDP foi -0,01 dias/ano. Finalmente, para o IDP, a depressão por endogamia foi evidente, aumentando o IDP com o aumento da endogamia. Os resultados indicam uma importante influência ambiental nas características reprodutivas. A herdabilidade estimada para o IDP sugere que pouco ganho genético pode ser alcançado através da seleção, embora a depressão endogâmica evidencie a necessidade de controlar a consanguinidade para conservar o recurso genético.(AU)

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The replacement program in a dairy farm represents the second or third largest cost in a dairy operation. This study aimed to characterize and typify the practices related to the dairy heifer replacement program and describe the growth, development, and health parameters during this period in commercial dairy herds in Trenque Lauquen. A cross-sectional observational study was carried out, including 54 randomly selected dairy farms that were visited once to collect data about facilities and management through a semi-structured survey. Cluster and principal coordinates analysis were applied to classify the farms based on all variables collected, grouped in four main areas: pre-fresh cows, colostrum management, pre-weaning calf 's management, and personnel. Additionally, growth, development, and health status were also recorded and described for calves and breeding heifers. Two similar-sized farm clusters were identified with differences in management and facilities in different areas of calves rearing. In one cluster there was a greater proportion of farms having a pre-fresh group, implementing appropriate health (colostrum, vaccination) and feeding management. Also, differences in personnel and technical support were relevant. The estimated body gain was 452 and 774 g/d for calves younger or older than 60 d of age, respectively. The age and weight farm averages in breeding heifers were 21.0 mo (range: 16.7-27.5) and 416.3 kg (range: 336.7-519.3), respectively. Diarrhea and respiratory affections were the major problems in pre-weaning calves and heifer rearing, respectively. The median mortality was 7.3, 7.6, and 2.9% at the calving, pre-weaning, and heifer rearing period, respectively. The results showed an improvement opportunity for producers, the design of precise and high impact programs that could lead to an improved replacement program.(AU)

Nos rebanhos leiteiros, o programa de reposição representa o segundo ou o terceiro maior custo da atividade de produção de leite. O objetivo do presente trabalho foi caracterizar e tipificar as práticas relacionadas ao programa de reposição de novilhas leiteiras e descrever o crescimento, desenvolvimento e parâmetros de saúde durante este período em rebanhos leiteiros comerciais localizados em Trenque Lauquen, oeste de Buenos Aires, Argentina. Foi realizado um estudo observacional transversal incluindo 54 fazendas de produção de leite selecionadas ao acaso e visitadas uma única vez para a colheita de dados relacionados a instalações e manejo empregando-se um questionário semi-estruturado. Foi efetuada a análise dos agrupamentos e das coordenadas principais para classificar as fazendas com base em todas as variáveis colhidas e agrupadas em quatro principais áreas: vacas pré-parto, manejo de colostro, manejo pré-desmame de bezerros e recursos humanos. Os dados referentes ao crescimento, desenvolvimento e estado de saúde dos animais também foram registrados e descritos para bezerros e novilhas. Dois grupos de fazendas de tamanho semelhante foram identificados com diferenças no manejo e instalações em distintas áreas de recria de bezerros. Em um grupo houve uma maior proporção de fazendas que tinham um grupo de vacas pré-parto, com implementação de adequado manejo de saúde (colostro, vacinações) e manejo alimentar. Também foram relevantes as diferenças em termos de pessoal e suporte técnico. O ganho de peso estimado foi de 452 e 774 gramas por dia, respectivamente, para os bezerros jovens e os com idade superior a 60 dias. As médias das fazendas da idade e do peso das novilhas de reprodução foram, respectivamente, 21,0 meses (variação de 16,7 a 27,5) e 416,3 kg (variação de 336,7 a 519,3). A diarreia e as afecções respiratórias foram os maiores problemas de saúde, respectivamente, nos bezerros em pré-desmama e novilhas em recria. A média de mortalidade foi de 7,3; 7,6 e 2,9%, respectivamente, ao parto, na pré-desmama e durante a recria de novilhas. Os resultados obtidos demonstraram a existência de oportunidades de melhoria para os produtores, com o delineamento de programas precisos e de alto impacto que poderão propiciar um programa de reposição aprimorado.(AU)

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B-spline functions have been used in random regression models (RRM) to model animal weight from birth to adulthood because they are less vulnerable to common difficulties of other methods. However, its application to model growth traits of Polled Nellore cattle has been little studied. Therefore, this study aimed to evaluate polynomial functions of different orders and segment numbers to model effects associated with the Polled Nellore cattle growth curve. For this purpose, we used 15,148 weight records of 3,115 animals aged between 1 and 660 days and reared in northern Brazil and born between 1995 and 2010. Random effects were modeled using B-spline polynomials. As random effects, we considered the direct and maternal genetic additives, as well as direct and maternal permanent environments. As fixed effects were included contemporary group, cow age at calving (linear and quadratic) and fourth-order Legendre polynomials to represent average growth curve. The residue was modeled by considering seven age classes. The bestfitted model was the one that considered cubic B-spline functions with four knots for direct additive genetic effects and three knots for maternal genetic, animal permanent environment, and maternal permanent environment effects (C6555). Therefore, covariance functions under B-spline polynomials are efficient and can be used to model the growth curve of Polled Nellore cattle from birth to 660 days of age.(AU)

Os modelos de regressão aleatória (MRA) aplicando funções B-spline são uma alternativa para modelar pesos do nascimento até a idade adulta dos animais, pois estas funções são menos vulneráveis as dificuldades constantemente observadas em outras metodologias. No entanto, são escassas pesquisas sobre aplicação destas funções sobre as características de crescimento em bovinos Nelore Mocho. Funções polinomiais de diferentes ordens e números de segmentos foram avaliadas na modelagem dos efeitos associados à curva de crescimento de bovinos da raça Nelore Mocho. Foram utilizados 15.148 registros de peso de 3.115 animais com idade entre 1 e 660 dias, criados na região norte do Brasil e nascidos entre 1995 e 2010. Os efeitos aleatórios foram modelados usando polinômios do tipo B-splines. Como efeitos aleatórios, foram considerados os efeitos genéticos aditivo direto e materno e os efeitos de ambientes permanentes direto e materno. Foram considerados como efeitos fixos, os grupos de contemporâneos, a idade da vaca ao parto (efeito linear e quadrático) e os polinômios de Legendre de quarta ordem, representando a curva média de crescimento. O resíduo foi modelado por meio de sete classes distribuídas segundo a idade. O modelo que considerou funções B-splines cúbicas com quatro nós para o efeito genético aditivo direto e três nós para os efeitos genético materno, ambiente permanente animal e ambiente permanente materno (C6555) foi o mais adequado. Concluiu-se que funções de covariâncias sob polinômios B-splines são eficientes e podem ser utilizados como alternativas para modelar a curva de crescimento de bovinos da raça Nelore Mocho do nascimento até 660 dias de idade.(AU)

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The aim of the study was to tested hypotheses that the primiparous cow’s behaviour is impacted by the method of rearing from the second day of life to weaning. 53 Holstein primiparous cows were used. They were reared in different ways during milk nutrition. Calf-heifers were assigned to one of five rearing groups on the second day after having nursed their mothers for 24 hours: H) hutch; HA) hutch, from 7 days pen with an automated drinking machine (ADM); MA) with mother, from 7 days pen with an ADM; MH) with mother, from 7 days hutch; MN) with mother, from 4 days with nursing cows. After weaning (56 days), all heifers were kept in group pens, after calving in free-stall housing. Maze learning ability was tested in the third month of lactation. In the 5th month, cows were observed in the open-field, in the seventh month they were subjected to an aversion test (AT). Group MN was the slowest in solving all tasks and HA the fastest. Differences were recorded among groups in the first-day evaluation (P < 0.01). No differences in open field tests were found. In the AT traversing, the slowest were groups H and HA, the fastest MH and MA (P < 0.01). The time of the first return was different (P < 0.001). On the first day, the most vocalized cows of the MN group (P < 0.05). The results show that the method used to rear heifers may have a significant impact on their maze and aversive behaviour.

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O sistema de cria é um dos principais setores da bovinocultura de corte, com impactos diretos na ocupação da terra (70% das pastagens são ocupadas pela cria) e na produtividade da cadeia da carne. O número e o peso dos bezerros produzidos por matriz e a idade das novilhas ao primeiro parto influenciam diretamente a eficiência do setor. As biotecnologias da reprodução, com destaque para a inseminação artificial em tempo fixo (IATF), têm colaborado significativamente para o desenvolvimento de um sistema de produção cada vez mais eficiente e sustentável. Em 2020 foram comercializadas no Brasil 23,7 milhões de doses de sêmen e 21,3 milhões de protocolos de IATF (90% das inseminações foram realizadas por IATF). Em 2002 eram utilizados apenas 100 mil procedimentos de IATF, que representavam somente 1% das inseminações realizadas. Nesse mesmo período (2002 a 2020), o percentual de matrizes inseminadas passou de 5% para 20% (acréscimo de 400%), com aumento de 213 vezes no empego da IATF. Os programas de IATF oferecem uma abordagem organizada e prática para o uso da IA, além de melhorarem a eficiência reprodutiva, genética e produtiva dos rebanhos. O uso da IATF antecipa a prenhez na estação de monta e a idade a primeira concepção das novilhas, aumentando significativamente a eficiência reprodutiva, produtiva e o retorno econômico do setor. Recentes estudos evidenciaram que os sistemas de cria que utilizam a IATF apresentam redução de 37,7% na emissão de CO2 equivalentes (produz mais bezerros de qualidade genética com menos matrizes que a monta natural), colaborando com a sustentabilidade da pecuária. Evidencia-se, também, que a nutrição, além de outros fatores, exerce papel importante na reprodução e afeta diretamente o desempenho da IATF. Entretanto, ainda existem mitos e realidades sobre os fatores que podem afetar o sucesso desta biotecnologia. O objetivo dessa revisão é apresentar e discutir os principais temas que impactam a eficiência da IATF em rebanhos de corte.

The cow-calf operation system is one is one of the main sectors of beef production, with direct impacts on land occupation (70% of pastures are occupied by the cow-calf operation system) and on the productivity of the meat chain. The number and the weight of calves produced per cow and the age of the heifer at first calving directly impact the efficiency of the sector. Reproductive biotechnologies, with emphasis on fixed-time artificial insemination (FTAI), have significantly contributed to the development of an efficient and sustainable production system. In 2020, 23.7 million doses of semen and 21.3 million FTAI protocols were marketed in Brazil (90% of inseminations were performed by FTAI). In 2002, only 100,000 FTAI procedures were used (a 213-fold increase in 19 years), which represented only 1% of the inseminations performed. During this same period (2002 to 2020), Brazil went from 5% to 20% of inseminated cow and heifers (increase of 400%). FTAI programs provide an organized and practical approach to the use of AI, as well as improve the reproductive, genetic and productive efficiency of the herds. The use of the FTAI anticipates the conception of cows in the breeding season and the age of the first conception of heifers, significantly increasing the reproductive and productive efficiency and the economic return of livestock. Recent studies have shown that breeding systems that use FTAI present a reduction of 37.7% in the emission of CO2 equivalents (it produces more calves of genetic quality with fewer dams than natural service), collaborating and with the sustainability of livestock. It is also evident that nutrition plays an important role in reproduction and directly affects the FTAI performance. However, there are still myths and realities about the factors that can affect the success of this biotechnology. The aim of this review is to present and discuss the main topics that impact the efficiency of FTAI in beef herds.

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The objective was to evaluate factors that influence calving probability in the first and second reproductive years of beef heifers that reached the minimum recommended body weight (BW) in the first breeding season. Two hundred twenty-seven 24-month-old Charolais × Nellore heifers that mated between 2003 and 2012 were analyzed. The parameters evaluated were: year effect; individual and maternal heterozygosis; percentage of Charolais genotype; average daily gain (ADG) from weaning to the end of the first breeding season; BW at 18 and 24 months of age, end of breeding season, parturition, and weaning; Julian date of calving; and adjusted calf weight at weaning. These variables were subjected to logistic regression. Calving rates in the first and second reproductive years were 58.1 and 49.5%, respectively. Performance until the end of the first breeding season, BW before the first breeding season, and individual heterozygosis affected the calving probability in the first breeding season. In the second breeding season, BW variation from the first breeding season and calving, Julian date of calving, and BW at the end of the second breeding season influenced calving probability. Until the end of the first breeding season, ADG of beef heifers responded positively to the calving probability, even after reaching the usually recommended BW for the first breeding season. Primiparous cows calving at the beginning of the breeding season and gaining more BW between the first and second breeding season are more likely to give birth in the second breeding season.(AU)

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The calving period influences productivity and reproductive efficiency the herds. The objective of this study was to evaluate two calving months (October and November) and their effect on the efficiency of a breeding herd for three consecutive years. A total of 298 Braford cows were evaluated at three, four, and five years of age, with their calves early-weaned at 148 days of age. The performance characteristics of the cow/calf pairs were evaluated with the calving month and calf sex as the independent variables. The animals were kept as a single group for the three years of observation. Cows calving in November were heavier and had a higher body condition score at calving. Cows calving in October were heavier and produced heavier calves at weaning. Male calves were heavier at birth and weaning than females (30.8 vs 28.6 kg and 118.9 vs 114.7 kg, respectively). The pregnancy rate was 82.35 and 69.23% for cows calving in October and November, respectively. Calving intervals were shorter in cows calving in November. Cows calving in October were more efficient compared with those calving in November, with a higher actual fertility rate. The production of kilograms of the calf/cow pair was higher for cows calving in October.

O período do parto influencia a produtividade e a eficiência reprodutiva dos rebanhos. O objetivo deste estudo foi avaliar dois meses de parto (outubro e novembro) e seus efeitos sobre a eficiência de um rebanho de cria por três anos consecutivos. Foram realizadas 298 avaliações de vacas Braford aos três, quatro e cinco anos de idade, com seus bezerros desmamados aos 148 dias de idade. As características de desempenho dos pares vaca / bezerro foram avaliadas com o mês e o sexo do bezerro como variáveis independentes. Os animais foram mantidos em um único grupo nos três anos de observação. As vacas que pariram em novembro foram mais pesadas e tiveram maior escore de condição corporal no parto. As vacas que pariram em outubro foram mais pesadas e produziram bezerros mais pesados no desmame. Os bezerros machos foram mais pesados ao nascer e ao desmame do que as fêmeas (30,8 vs 28,6 kg e 118,9 vs 114,7 kg, respectivamente). A taxa de prenhez foi de 82,35 e 69,23% para as vacas que pariram em outubro e novembro, respectivamente. Os intervalos de partos foram mais curtos nas vacas paridas em novembro. As vacas que pariram em outubro foram mais eficientes quando comparadas com as que pariram em novembro, com maior taxa de fertilidade real. A produção de quilogramas do par bezerro / vaca foi maior em vacas que pariram em outubro.