Modelos para avaliação genética da produção de leite no dia do controle nas três primeiras lactações / Models for genetic evaluation of milk yield on the day of control in the three first lactations

Objetivou-se verificar se a utilização do modelo autorregressivo (MAR) é adequada para obtenção de parâmetros genéticos para produção de leite no dia do controle (PLDC) de bovinos leiteiros da raça Gir. Foram analisados 125.191 registros de produções diárias, nas três primeiras lactações, por meio dos modelos de repetibilidade (MREP) e MAR. No MREP, foi considerado o efeito de ambiente de curto prazo; no MAR, foi considerado, também, o efeito de ambiente de longo prazo. Os modelos foram comparados por meio do logaritmo da função de máxima verossimilhança (−2logL) . A herdabilidade estimada pelo MREP foi 0,18; no caso do MAR, as estimativas para primeira, segunda e terceira lactações foram 0,32, 0,28 e 0,26, respectivamente. A estimativa de autocorrelação dos componentes de variância de longo prazo foi próxima de zero, e as de curto prazo foram de alta magnitude para primeira (0,79), segunda (0,79) e terceira (0,81) lactações. Logo, a influência do ambiente de curto prazo dentro de cada lactação não é a mesma. O valor de −2logL mais próximo de zero foi obtido para o MAR (-294.884,7778) em relação ao MREP (-329.266,4810). Assim, o MAR é adequado para obtenção de estimativas de parâmetros genéticos para PLDC nas três primeiras lactações de bovinos leiteiros.(AU)

Aimed to verify if the autoregressive model (MAR) is adequate to obtain genetic parameters for Gyr dairy cattle milk yield on the test day in the three first lactations. Analysis was performed on 125,191 records of daily production of 9,242 cows using repeatability model (MREP) and MAR. On MREP, a long-term environment was considered, on MAR, the short-term environment was also taken into consideration. The models were compared by logarithm of the maximum likelihood function (−2logL) . The heritability estimated using the MREP model was 0.18, while the heritability estimated by MAR for first, second, and third lactations were 0.32, 0.28 and 0.26, respectively. The autocorrelation estimates of the components of long-term variance were close to zero, and those of the short-term were of high magnitude for first (0.79), second (0.79) and third (0.81) lactations. Therefore, the influence of the short-term environment within each lactation is not the same. The value of −2logL closer to zero was obtained for MAR (-294,884.7778) in relation to MREP (-329,266.4810). Thus, MAR is suitable for obtaining genetic parameters estimates for PLDC in the first three lactations of dairy cattle.(AU)

Accuracy of genomic predictions in Gyr (Bos indicus) dairy cattle.

Genomic selection may accelerate genetic progress in breeding programs of indicine breeds when compared with traditional selection methods. We present results of genomic predictions in Gyr (Bos indicus) dairy cattle of Brazil for milk yield (MY), fat yield (FY), protein yield (PY), and age at first calving using information from bulls and cows. Four different single nucleotide polymorphism (SNP) chips were studied. Additionally, the effect of the use of imputed data on genomic prediction accuracy was studied. A total of 474 bulls and 1,688 cows were genotyped with the Illumina BovineHD (HD; San Diego, CA) and BovineSNP50 (50K) chip, respectively. Genotypes of cows were imputed to HD using FImpute v2.2. After quality check of data, 496,606 markers remained. The HD markers present on the GeneSeek SGGP-20Ki (15,727; Lincoln, NE), 50K (22,152), and GeneSeek GGP-75Ki (65,018) were subset and used to assess the effect of lower SNP density on accuracy of prediction. Deregressed breeding values were used as pseudophenotypes for model training. Data were split into reference and validation to mimic a forward prediction scheme. The reference population consisted of animals whose birth year was ≤2004 and consisted of either only bulls (TR1) or a combination of bulls and dams (TR2), whereas the validation set consisted of younger bulls (born after 2004). Genomic BLUP was used to estimate genomic breeding values (GEBV) and reliability of GEBV (R2PEV) was based on the prediction error variance approach. Reliability of GEBV ranged from ∼0.46 (FY and PY) to 0.56 (MY) with TR1 and from 0.51 (PY) to 0.65 (MY) with TR2. When averaged across all traits, R2PEV were substantially higher (R2PEV of TR1 = 0.50 and TR2 = 0.57) compared with reliabilities of parent averages (0.35) computed from pedigree data and based on diagonals of the coefficient matrix (prediction error variance approach). Reliability was similar for all the 4 marker panels using either TR1 or TR2, except that imputed HD cow data set led to an inflation of reliability. Reliability of GEBV could be increased by enlarging the limited bull reference population with cow information. A reduced panel of ∼15K markers resulted in reliabilities similar to using HD markers. Reliability of GEBV could be increased by enlarging the limited bull reference population with cow information.

Red Sindhi cattle in Brazil: population structure and distribution.

The Red Sindhi cattle breed was imported to Brazil in small numbers. Nowadays, the herds of this breed are distributed in the Northeast, Southeast and Midwest regions of the country. In this study, DNA samples of animals originating from 15 herds in the Northeast and Southeast regions have been analyzed to obtain the ancestry proportions, and to gain a better understanding of the current population structure of this breed in Brazil. Samples were genotyped using three different single nucleotide polymorphism (SNP) marker panels. Those markers have been used with the approach of unsupervised hierarchical clustering of individuals, and consequently, the ancestry of the population was divided into six different subpopulations. Three of those ancestry subpopulations were identified to be present in various different herds, while the other three were restricted to only one or two herds each. One of those herds has been kept isolated for more than 30 years, and it was identified to contain two almost exclusive subpopulations. To avoid important losses in the genetic diversity within the Red Sindhi breed in Brazil, we recommend the identification of superior sires from every subpopulation in the establishment of a breeding program for this breed.

Genetic parameters for milk production traits and breeding goals for Gir dairy cattle in Brazil.

To implement an animal breeding program, it is important to define the production circumstances of the animals of interest to determine which traits of economic interest will be selected for the breeding goal. The present study defined breeding goals and proposed selection indices for milk production and quality traits of Gir dairy cattle. First, a bioeconomic model was developed to calculate economic values. The genetic and phenotypic parameters were estimated based on records from 22,468 first-lactation Gir dairy cows and their crosses for which calving occurred between 1970 and 2011. Statistical analyses were carried out for the animal model, with multitrait analyses using the restricted maximum likelihood method. Two situations were created in the present study to define the breeding goals: 1) including only milk yield in the breeding goal (HGL1) and 2) including fat and protein in addition to the milk yield (HGL2). The heritability estimates for milk, protein, and fat production were 0.33 ± 0.02, 0.26 ± 0.02, and 0.24 ± 0.02, respectively. All phenotypic and genetic correlations were highly positive. The economic values for milk, fat, and protein were US$0.18, US$0.27, and US$7.04, respectively. The expected economic responses for HGL2 and for HGL1 were US$126.30 and US$79.82, respectively. These results indicate that milk component traits should be included in a selection index to rank animals evaluated in the National Gir Dairy Breeding Program developed in Brazil.

Expression of immune response genes in peripheral blood of cattle infested with Rhipicephalus microplus.

The bovine tick Rhipicephalus microplus is responsible for severe economic losses in tropical cattle production. Bos indicus breeds are more resistant to tick infestations than are Bos taurus breeds, and the understanding of the physiological mechanisms involved in this difference is important for the development of new methods of parasite control. We evaluated differences in the transcript expression of genes related to the immune response in the peripheral blood of cattle previously characterized as resistant or susceptible to tick infestation. Crossbreed F2 Gir x Holstein animals (resistant, N = 6; susceptible, N = 6) were artificially submitted to tick infestation. Blood samples were collected at 0, 24, and 48 h after tick infestation and evaluated for transcript expression of the CD25, CXCL8, CXCL10, FoxP3, interleukin (IL)-10, and tumor necrosis factor alpha (TNFα) genes. Gene expression of CD25 (6.00, P < 0.01), IL-10 (31.62, P < 0.01), FoxP3 (35.48, P < 0.01), and CXCL10 (3.38, P < 0.05) was altered in the resistant group at 48 h compared with samples collected before infestation. In the susceptible group, CXCL8 (-2.02, P < 0.05) and CXCL10 (2.20, P < 0.05) showed altered expression 24 h after infestation. CXCL8 (-5.78, P < 0.05) also showed altered expression at 48 h after infestation when compared with samples collected before infestation. We detected a correlation between T γδ cell activity and the immunological mechanisms that result in a higher resistance to R. microplus in cattle.

Viable offspring after successful non-surgical embryo transfer in goats / Nascimento de fetos viáveis após transferência de embriões não-cirúrgica em caprinos

O objetivo do presente estudo foi avaliar a viabilidade da técnica de transferência não cirúrgica em cabras. Quatro cabras não-lactantes pluríparas da raça Toggenburg foram utilizadas como receptoras de embriões, sendo que duas receberam um embriões e duas receberam dois embriões coletados não cirurgicamente cabras doadoras. Os corpos lúteos das receptoras foram detectados um dia antes da transferência de embriões por ultrassonografia transretal. Uma seringa de 5mL contendo 2mL de meio holding foi acoplada em um cateter tomcat, no qual os embriões foram aspirados em uma coluna central a duas outras colunas. Um espéculo Colin número 2 foi inserido na vulva e na vagina, e com o uso de uma fonte de luz, a cerviz foi localizada e imobilizada com uma pinça de Allis. Um cateter uretral número seis acoplado a um mandril e lubrificado com meio PBS foi inserido na cérvix, e assim os aneis cervicais foram gradualmente transpostos. Após perder a resistência, o cateter uretral foi movido lateralmente para o corno uterino desejado. O mandril e a pinça de Allis foram retirados e o conjunto seringa e tomcat foi acoplado ao cateter uretral e o conteúdo injetado no corno uterino ipsilateral ao corpo lúteo com posterior retirada do cateter. Cabras que ovularam em apenas um ovário foram usadas para testar a eficiência da deposição do embrião. O tempo gasto entre a inserção do espéculo e a sua remoção foi inferior a três minutos. O tempo para transpor a cérvix foi inferior a um minuto. A ultrassonografia revelou a deposição de líquido no corno desejado. Receptoras que receberam dois embriões tornaram-se gestantes e pariram três crias. Estes primeiros resultados encorajam a técnica e demonstram que a transferência de embriões em caprinos pode ser feita totalmente por procedimentos não cirúrgicos...

Comparison of factor-analytic and reduced rank models for test-day milk yield in Gyr dairy cattle (Bos indicus).

We analyzed 46,161 monthly test-day records of milk production from 7453 first lactations of crossbred dairy Gyr (Bos indicus) x Holstein cows. The following seven models were compared: standard multivariate model (M10), three reduced rank models fitting the first 2, 3, or 4 genetic principal components, and three models considering a 2-, 3-, or 4-factor structure for the genetic covariance matrix. Full rank residual covariance matrices were considered for all models. The model fitting the first two principal components (PC2) was the best according to the model selection criteria. Similar phenotypic, genetic, and residual variances were obtained with models M10 and PC2. The heritability estimates ranged from 0.14 to 0.21 and from 0.13 to 0.21 for models M10 and PC2, respectively. The genetic correlations obtained with model PC2 were slightly higher than those estimated with model M10. PC2 markedly reduced the number of parameters estimated and the time spent to reach convergence. We concluded that two principal components are sufficient to model the structure of genetic covariances between test-day milk yields.

Comparação dos índices de eficiência reprodutiva por diferentes métodos em rebanhos bovinos leiteiros / Comparison of reproductive efficiency indexes by different methods in dairy cattle herds

O presente estudo teve como objetivo promover o levantamento de índices zootécnicos para calcular e comparar a eficiência reprodutiva de rebanhos bovinos leiteiros por diferentes métodos. O intervalo de partos dos rebanhos estudados apresentou uma variação de 13,3 a 15,2 meses por meio dos diferentes métodos utilizados para sua obtenção, não se observando diferença significativa (P>0,05) entre eles. As avaliações pelos métodos de Johnson et al. (1964) e Butendieck et al. (1972) mostraram, respectivamente, eficiência reprodutiva de 79,5 e 77,8%. Embora considerados métodos mais eficientes que o de Willcox et al. (1957), cuja média encontrada para os mesmos rebanhos foi de 90,2%, não se observou diferença significativa entre os resultados obtidos pelos três métodos.

The study aimed to promote the lifting of indexes to calculate and compare the reproductive efficiency of dairy cattle herds by different methods. The parturition interval studied showed a variation from 13.3 to 15.2 months by means of different methods for obtaining it are not observing a significant difference (P> 0.05) between them. Evaluations by the methods of Johnson et al (1964) and Butendieck et al. (1972) showed, respectively, reproductive efficiency of 79.5 and 77.8%. Although regarded as the most efficient methods of Willcox et al. (1957), whose average found in the same herd was 90.2%, there was no significant difference between the results obtained by three methods.

Comparison of random regression models to estimate genetic parameters for milk production in Guzerat (Bos indicus) cows.

Random regression models have been widely used to estimate genetic parameters that influence milk production in Bos taurus breeds, and more recently in B. indicus breeds. With the aim of finding appropriate random regression model to analyze milk yield, different parametric functions were compared, applied to 20,524 test-day milk yield records of 2816 first-lactation Guzerat (B. indicus) cows in Brazilian herds. The records were analyzed by random regression models whose random effects were additive genetic, permanent environmental and residual, and whose fixed effects were contemporary group, the covariable cow age at calving (linear and quadratic effects), and the herd lactation curve. The additive genetic and permanent environmental effects were modeled by the Wilmink function, a modified Wilmink function (with the second term divided by 100), a function that combined third-order Legendre polynomials with the last term of the Wilmink function, and the Ali and Schaeffer function. The residual variances were modeled by means of 1, 4, 6, or 10 heterogeneous classes, with the exception of the last term of the Wilmink function, for which there were 1, 3, 6, or 10 classes. The models gave similar hereditability estimates, ranging from 0.20 to 0.33. Genetic correlations between adjacent records were high values (0.83-0.99), but they declined when the interval between the test-day records increased, and were negative between the first and last records. The model employing the Ali and Schaeffer function with six residual variance classes was the most suitable for fitting the data.

A new tetra-primer ARMS-PCR for genotyping bovine kappa-casein polymorphisms.

Kappa-casein (κ-casein) is one of the most abundant milk proteins. Its main function is to avoid the aggregation of casein micelles, keeping them, and therefore calcium phosphate, in pockets in solution. In bovines, a κ-casein functional polymorphism has been associated with fat, calcium, and protein milk contents and faster curd contraction in cheese production. Quicker curd contraction reduces the loss of milk solids, enhancing cheese yield. This polymorphism induces a double amino acid substitution (Thr136Ile and Ala148Asp). The polymorphism is normally detected by PCR-RFLP, which is a laborious method. An interesting methodological alternative is the tetra-primer amplification refractory mutation system PCR (tetra-primer ARMS-PCR). A tetra-primer ARMS-PCR for the detection of this κ-casein polymorphism has been described. However, specificity was not achieved, probably due to problems with primer design. We developed a new tetra-primer ARMS-PCR for the detection of the κ-casein polymorphism. This new method was validated in a double-blind test, by comparison with the results obtained for 50 Guzerá bulls formerly genotyped by PCR-RFLP. This new method achieved 100% sensitivity and specificity. We conclude that this method is a useful, cost-efficient alternative for the detection of functional κ-casein polymorphisms.

Random regression models using Legendre polynomials or linear splines for test-day milk yield of dairy Gyr (Bos indicus) cattle.

Studies investigating the use of random regression models for genetic evaluation of milk production in Zebu cattle are scarce. In this study, 59,744 test-day milk yield records from 7,810 first lactations of purebred dairy Gyr (Bos indicus) and crossbred (dairy Gyr × Holstein) cows were used to compare random regression models in which additive genetic and permanent environmental effects were modeled using orthogonal Legendre polynomials or linear spline functions. Residual variances were modeled considering 1, 5, or 10 classes of days in milk. Five classes fitted the changes in residual variances over the lactation adequately and were used for model comparison. The model that fitted linear spline functions with 6 knots provided the lowest sum of residual variances across lactation. On the other hand, according to the deviance information criterion (DIC) and bayesian information criterion (BIC), a model using third-order and fourth-order Legendre polynomials for additive genetic and permanent environmental effects, respectively, provided the best fit. However, the high rank correlation (0.998) between this model and that applying third-order Legendre polynomials for additive genetic and permanent environmental effects, indicates that, in practice, the same bulls would be selected by both models. The last model, which is less parameterized, is a parsimonious option for fitting dairy Gyr breed test-day milk yield records.

Milk yield persistency in Brazilian Gyr cattle based on a random regression model.

With the objective of evaluating measures of milk yield persistency, 27,000 test-day milk yield records from 3362 first lactations of Brazilian Gyr cows that calved between 1990 and 2007 were analyzed with a random regression model. Random, additive genetic and permanent environmental effects were modeled using Legendre polynomials of order 4 and 5, respectively. Residual variance was modeled using five classes. The average lactation curve was modeled using a fourth-order Legendre polynomial. Heritability estimates for measures of persistency ranged from 0.10 to 0.25. Genetic correlations between measures of persistency and 305-day milk yield (Y305) ranged from -0.52 to 0.03. At high selection intensities for persistency measures and Y305, few animals were selected in common. As the selection intensity for the two traits decreased, a higher percentage of animals were selected in common. The average predicted breeding values for Y305 according to year of birth of the cows had a substantial annual genetic gain. In contrast, no improvement in the average persistency breeding value was observed. We conclude that selection for total milk yield during lactation does not identify bulls or cows that are genetically superior in terms of milk yield persistency. A measure of persistency represented by the sum of deviations of estimated breeding value for days 31 to 280 in relation to estimated breeding value for day 30 should be preferred in genetic evaluations of this trait in the Gyr breed, since this measure showed a medium heritability and a genetic correlation with 305-day milk yield close to zero. In addition, this measure is more adequate at the time of peak lactation, which occurs between days 25 and 30 after calving in this breed.

Quantitative trait loci affecting lactose and total solids on chromosome 6 in Brazilian Gir dairy cattle.

Fourteen Brazilian Gir sire families with 657 daughters were analyzed for quantitative trait loci (QTL) on chromosome 6 affecting lactose and total solids. Cows and sires were genotyped with 27 microsatellites with a mean spacing between markers of 4.9 cM. We used a 1% chromosome-wide threshold for QTL qualification. A QTL for lactose yield was found close to marker MNB66 in three families. A QTL for total solid yield was identified close to marker BMS2508 in three families. A QTL for lactose percentage, close to marker DIK1182, was identified in two families. A QTL for total solid percentage, close to marker MNB208, was identified in four families. These QTLs could be used for selection of animals in dairy production systems.

Expressed sequenced tags profiling of resistant and susceptible Gyr x Holstein cattle infested with the tick Rhipicephalus (Boophilus) microplus.

Tick resistance in cattle is mainly found in zebu (Bos indicus) animals, although it is also present in some taurine (B. taurus) breeds. In order to characterize functional genes involved in tick resistance/susceptibility in cattle, two cDNA libraries were generated using skin tissues of selected Holstein x Gyr animals. A total of 2700 high-quality reads from both resistant and susceptible cDNA were assembled into 458 sequences (contigs) and 834 singletons, with a mean size of 447.7 nucleotides. Assignment of homologous proteins by BLASTX revealed 790 (61.1%) and 300 (23.2%) hits in resistant and susceptible cDNA, respectively; 121 of these hits matched bovine proteins. A total of 502 (38.9%) unique sequences were found to have no significant homology with known sequences and were classified as novel sequences. In general, the most abundant sequences consisted of those coding for hypothetical proteins whose function had not yet been determined, in addition to ribosomal proteins, binding proteins and structural proteins, such as keratin and collagen. The most abundant protein found was collagen type III alpha, although ribosomal proteins accounted for half of the 40 most frequent hits. In addition, five matches within the top 40 best hits corresponded to immune response proteins. These sequences could be used for future studies on functional genomics of cattle tick resistance as well as for genomic sequencing projects.

Effect of pregnancy on the genetic evaluation of dairy cattle.

We investigated the effect of stage of pregnancy on estimates of breeding values for milk yield and milk persistency in Gyr and Holstein dairy cattle in Brazil. Test-day milk yield records were analyzed using random regression models with or without the effect of pregnancy. Models were compared using residual variances, heritabilities, rank correlations of estimated breeding values of bulls and cows, and number of nonpregnant cows in the top 200 for milk yield and milk persistency. The estimates of residual variance and heritabilities obtained with the models with or without the effect of pregnancy were similar for the two breeds. Inclusion of the effect of pregnancy in genetic evaluation models for these populations did not affect the ranking of cows and sires based on their predicted breeding values for 305-day cumulative milk yield. In contrast, when we examined persistency of milk yield, lack of adjustment for the effect of pregnancy overestimated breeding values of nonpregnant cows and cows with a long days open period and underestimated breeding values of cows with a short days open period. We recommend that models include the effect of days of pregnancy for estimation of adjustment factors for the effect of pregnancy in genetic evaluations of Dairy Gyr and Holstein cattle.

Quantitative trait loci affecting milk production traits on bovine chromosome 6 in zebuine Gyr breed.

Fourteen Brazilian dairy Gyr sire families with 657 daughters were analyzed for quantitative trait loci (QTL) on chromosome 6 by using a daughter design for 5 economic traits: milk, fat, and protein production, fat and protein percentage. The cows and sires were genotyped for 27 microsatellites with average spacing between markers of 4.9 cM. In the analyses across 14 families, for the largest significant families, and within family, a QTL was located for milk yield and fat yield close to marker BMS2508 at the 5% chromosome-wide significance level across families and 1% chromosome-wide within families. For fat percentage, a QTL near DIK4482 was identified at the 5% chromosome-wide significance level when all families were analyzed together and at the 1% chromosome-wide significance level within the largest significant families. The different analyses yielded results that were generally consistent for milk yield, fat yield, and fat percentage. The order of the markers in the derived map was consistent with that in the consensus map. Some QTL and candidate genes in dairy cattle for milk production traits are probably preserved in Bos taurus and Bos indicus.

Differential expression of genes in resistant versus susceptible Gyr x Holstein cattle challenged with the tick Rhipicephalus (Boophilus) microplus.

The bovine tick Rhipicephalus (Boophilus) microplus causes major losses in cattle production systems in tropical regions. Bos indicus breeds are more resistant to ticks than B. taurus breeds. Resistance genes could be an alternative to control this parasite. We examined the pattern of gene expression of three calcium-binding-protein genes: translationally controlled tumor protein 1 (TPT1), allergen Bos d3 (S100A7), calcium channel protein transient receptor potential vanilloid 6 (TRPV6), and the cysteine proteinase inhibitor gene (CST6). These genes were selected from cDNA libraries prepared from skin biopsies taken from resistant and susceptible Gyr x Holstein F2 animals. These biopsies were also used to study the expression level of these genes through real-time PCR analysis. The relative expression levels of the S100A7, TPT1, TRPV6, and CST6 genes were 2.01 ± 0.6, 1.32 ± 0.9, 1.53 ± 1.2, and 2.03 ± 0.7 times higher in the susceptible group, respectively. Skin lesion tissue from the susceptible animals showed significantly more mRNA transcripts of these genes in comparison with the resistant animals (P = 0.001). However, this hypersensitivity does not seem to protect the susceptible animals against tick infestation.

Digestibilidade da matéria seca de silagens de milho e de suplementos concentrados determinada por procedimentos in vitro / Dry matter digestibility of corn silages and concentrates determined by in vitro procedures

Compararam-se os valores de digestibilidade in vitro da matéria seca (DIVMS) de quatro silagens de milho e de seis concentrados (três proteicos e três energéticos), determinados pelo método de dois estádios realizados em tubos individuais ou em equipamento automatizado de fermentação, e avaliou-se a ocorrência de efeito associativo na digestão de alimentos destas três classes incubadas em um mesmo jarro de fermentação da incubadora in vitro, ou em jarros diferentes contendo a mesma classe de alimentos. Utilizou-se delineamento inteiramente ao acaso, em esquema fatorial 3 x 3 (procedimentos in vitro x classes de alimentos). Os valores de DIVMS determinados pelo método dos tubos foram mais próximos dos relatados na literatura e menores (P<0,02) que os obtidos pelos procedimentos automatizados. Não houve diferença (P>0,05) nos valores de DIVMS dos concentrados e das silagens de milho incubados no mesmo jarro de fermentação da incubadora ou, separadamente por alimento, em jarros diferentes.

The values of in vitro dry matter digestibility (IVDMD) of four corn silages and six concentrates (three proteic and three energetics) were determined by the two-stage technique that utilizes individual digestion tubes and by an automatic equipment of fermentation (filter bag technique). It was also evaluated the associative effect on digestion of these three food classes when incubated in the same fermentation jar of the "in vitro incubator" and when in different vessels containing the same class of foods. The experimental design was completely randomized in a 3 x 3 factorial arrangement (in vitro procedures x food classes). The IVDMD values determined in tubes were closer to those found in the literature and lower (P<0.02) than those obtained by the automatic procedure. No differences were found (P>0.05) in IVDMD of concentrates and silages when incubated together in the same fermentation jar or separated by food classes in separated jars.

Avaliação da persistência na lactação da raça Guzerá, utilizando modelos de regressão aleatória / Evaluation of lactation persistency of Guzerat cows using random regression models

Estimaram-se a herdabilidade e as correlações genéticas e de ambiente permanente entre seis medidas de persistência da lactação de vacas da raça Guzerá, utilizando modelo de regressão aleatória. Foram considerados 8276 registros de produção de leite no dia do controle, na primeira lactação, de 1021 vacas. A regressão aleatória foi calculada pela função logarítmica de Ali e Schaeffer e pelo polinômio de Legendre, obtendo-se os coeficientes para os efeitos fixos, genético aditivo e de ambiente permanente. A função que mais se adequou aos dados foi a de Ali e Schaeffer, mas apresentou problemas de convergência. Os resultados evidenciaram que a persistência é uma característica com herdabilidade de valor moderado e de baixa correlação com o valor genético para produção de leite aos 305 dias, indicando a possibilidade de se obter resposta à seleção para mudança na curva de lactação sem afetar negativamente a produção total de leite na lactação. A medida de persistência que calcula a diferença de produção de leite entre as fases intermediária e inicial da lactação apresentou alta correlação com a produção aos 305 dias.

The heritability and the genetic and permanent environment correlations were estimated among six different measures of persistency in the lactation of Guzerat cow, using the Random Regression Model. A total of 8,403 records from 1,034 first lactation cows were evaluated. The Random Regression Model was calculated by the logarithmic function of Ali and Schaeffer and Legendre polynomials to get coefficients for fixed, additive genetic and permanent environment effects. Ali and Schaeffer was the function that better fit to the data, but it had convergence problems. The results showed that persistence is a trait with moderate heritability, and low correlation with genetic value for 305-d milk production which allows to select animals in order to alter the format of the curve of production without affecting the total productivity. The measure of persistence that calculates the difference of milk production between the medium and initial phases was highly correlated with 305-d milk production.

Taxa de sudação e parâmetros histológicos de bovinos submetidos ao estresse calórico / Sweat rate and histological parameters of cattle submitted to heat stress

Caracterizaram-se o pelame, a taxa de sudação e os parâmetros histológicos de 71 bovinos F2 (½ Gir x ½ Holandês), 39 machos e 32 fêmeas, entre 14 e 20 meses de idade, submetidos a condições de termoneutralidade (22ºC e 70 por cento de umidade relativa - UR) e ao estresse calórico (42ºC e 60 por cento UR). Os tratamentos foram realizados nas estações de verão e inverno em câmara bioclimática. O comprimento dos pelos e a espessura da capa foram maiores no inverno que no verão, sendo de 1,58 e 1,04cm e 5,31 e 3,91mm, respectivamente (P<0,05). A histologia da pele mostrou que, no verão, a área da glândula sudorípara e a distância da glândula ao epitélio foram menores que no inverno, sendo de 2589 e 4051µm e 294 e 344µm, respectivamente (P<0,05). Concluiu-se que a estação do ano influencia as características de pelame, o posicionamento e a atividade das glândulas sudoríparas de forma a maximizar o controle da homeostase térmica.

Coat thickness, sweat rate, and histological parameters were characterized in 39 males and 32 females crossbred cattle (½ Holstein x ½ Gir), averaging 14 to 20 months of age, submitted to thermoneutrality (22ºC and 70 percent of relative humidity - RH) and heat stress (42ºC and 60 percent RH) in summer and winter in a climatic chamber. Fur length and coat thickness were significantly higher in summer than winter, 1.58 and 1.04cm and 5.31 and 3.91mm, respectively (P<0.05). Skin histology showed that sweat gland area and distance of gland to epithelium was shorter in summer than in winter, 2,589 and 4,051µm and 294 and 344µm, respectively (P<0.05). It was concluded that the season influenced the coat thickness, the sweat glands disposal and activity to maximize thermic homeostasis control.