Genetic parameters, genetic trends and correlated responses of growth traits considering maternal ability in Nelore cattle.

The growth of Nelore cattle was analysed considering the following performance parameters; the effect of the calving order of cows on the phenotypic expression of birth weight (BW), average daily gain from birth to weaning (BWG), and weaning weight (WW), the estimated genetic parameters for the traits, including the covariance components between direct and maternal genetic effects. Genetic trends and correlated responses were also obtained for the studied traits. The calving order of cows, as well as other fixed effects used to obtain the adjusted phenotypic means, were statistically significant (p < 0.001) for studied traits. Direct heritability was estimated at 0.24 ± 0.01 (BW), 0.15 ± 0.01 (BWG), and 0.18 ± 0.01 (WW), while maternal heritability was 0.06 ± 0.01 (BW), 0.12 ± 0.01 (BWG), and 0.11 ± 0.01 (WW). The correlations between direct and maternal effects within the same trait were negligible. Moderate to higher direct genetic correlations (ranging from 0.54 ± 0.04 to 0.98 ± 0.01) and maternal genetic correlations (ranging from 0.34 ± 0.09 to 0.99 ± 0.002) were estimated between the studied traits. Unlike direct genetic effects, there was no significant change in maternal genetic effects over time (p > 0.05). These results indicated the need for revising selection indexes for enhancing maternal ability. Correlated responses were generally lower compared to direct responses, except for BWG. The selection for BWG, considering the maternal genetic effect, would be more efficient to improve maternal ability of the cows for pre-weaning growth in relation to selection for WW. Our results found that direct genetic merit improves pre-weaning weight and this trait can be incorporated into the breeding goal as reflected in the WW.

Effects of monensin in supplements for beef cattle in tropical grazing systems during the rainy season.

Two experiments were carried out to evaluate the effect of monensin in supplements for grazing heifers. In experiment I, treatments consisted of protein supplements (low intake - 0.5 kg/animal/day and high intake - 1.0 kg/animal/day) associated or not with monensin. Animal performance, nutrient intake, and digestibility were evaluated. Forty crossbred heifers with an initial body weight (BW) of 213.8 ± 4.5 kg were used. There was no difference in average daily gain between treatments (average of 0.588 kg/animal/day). There was no interaction between monensin and supplements for intake parameters and digestibility. Dry matter (DM) intake was equal between treatments (~ 2% of BW). However, there was a reduction in pasture intake with the high-intake supplement. In experiment II, treatments consisted of two types of supplements (protein or mineral) associated or not with monensin. The variables analyzed were productive performance, ingestive behavior, and thermal comfort, evaluated through the index of thermal stress for cows (ITSC). Forty crossbred heifers with a BW of 159.2 ± 1.3 kg were used. The type of supplement did not influence the performance of the animals. However, monensin promoted greater weight gain in the animals (110 g/animal/day). There was an interaction effect between supplementation and monensin addition on behavioral activities, except for idle time. The inclusion of monensin in the protein supplement reduced the grazing time. The ITSC value influenced the activities of ingestive behavior, and the increase of this index reduced the grazing time in all treatments. Forage quality influences the response to monensin use, and the addition of monensin in supplements for grazing cattle during the rainy season is recommended for forages with high CP content.

Hypoglycemic and Antihyperlipidemic effects of Syzygium cumini (Lamarck) Skeels and Syzygiumpaniculatum (Gaertn.)

SUMMARY Introduction: there is a recent increase in interest in the use of medicinal and phytotherapeutic plants. Objective: to verify the effect of ethanolic extracts from different parts of fruits of two species of the genus Syzygium, on glucose and lipid levels in the blood, using animal models. Results: the bark extract of the seeds of S. cumini (Lamarck) Skeels proved to be effective in reducing blood glucose levels. This same extract was also effective in lowering blood cholesterol levels. The extract from the seed nuclei of S. cumini (Lamarck) Skeels and S. paniculatum (Gaertn) were effective in reducing blood triglyceride levels. Extracts from all parts of the fruits of S. cumini (Lamarck) Skeels and of the seed nuclei of S. panic-ulatum (Gaertn) prevented weight gain in the animals. Conclusión: in general, the seed extract of both species showed a direct influence on the parameters and characteristics under study.

Introducción: hay un reciente aumento del interés en el uso de plantas medicinales y fitoterapéuticas. Objetivo: verificar el efecto de los extractos etanólicos de diferentes partes de frutos de dos especies del género Syzygium, sobre los niveles de glucosa y lípidos en la sangre, utilizando modelos animales. Resultados: el extracto de corteza de las semillas de S. cumini (Lamarck) Skeels demostró ser eficaz para reducir los niveles de glucosa en la sangre. Este mismo extracto también fue eficaz para reducir los niveles de colesterol en la sangre. El extracto de los núcleos de semillas de S. cumini (Lamarck) Skeels y S. paniculatum (Gaertn) fueron eficaces para reducir los niveles de triglicéridos en la sangre. Los extractos de todas las partes de los frutos de S. cumini (Lamarck) Skeels y de los núcleos de semillas de S. paniculatum (Gaertn) impidieron el aumento de peso en los animales. Conclusión: en general, el extracto de semillas de ambas especies mostró una influencia directa sobre los parámetros y características en estudio.

Introdução: há um aumento recente do interesse pelo uso de plantas medicinais e fitoterápicas. Objetivo: verificar o efeito de extratos etanólicos de diferentes partes de frutos de duas espécies do gênero Syzygium, sobre os níveis de glicose e lipídios no sangue, por meio de modelos animais. Resultados: o extrato da casca das sementes de S. cumini (Lamarck) Skeels mostrou-se eficaz na redução da glicemia. Este mesmo extrato também foi eficaz na redução dos níveis de colesterol no sangue. Os extratos dos núcleos das sementes de S. cumini (Lamarck) Skeels e S. paniculatum (Gaertn) foram eficazes na redução dos níveis de triglicerídeos no sangue. Extratos de todas as partes dos frutos de S. cumini (Lamarck) Skeels e dos núcleos das sementes de S. pani-culatum (Gaertn) impediram o ganho de peso nos animais. Conclusão: em geral, o extrato de sementes de ambas as espécies apresentou influência direta nos parâmetros e características em estudo.

Random regression models to account for the effect of genotype by environment interaction due to heat stress on the milk yield of Holstein cows under tropical conditions.

The present study had the following objectives: to compare random regression models (RRM) considering the time-dependent (days in milk, DIM) and/or temperature × humidity-dependent (THI) covariate for genetic evaluation; to identify the effect of genotype by environment interaction (G×E) due to heat stress on milk yield; and to quantify the loss of milk yield due to heat stress across lactation of cows under tropical conditions. A total of 937,771 test-day records from 3603 first lactations of Brazilian Holstein cows obtained between 2007 and 2013 were analyzed. An important reduction in milk yield due to heat stress was observed for THI values above 66 (-0.23 kg/day/THI). Three phases of milk yield loss were identified during lactation, the most damaging one at the end of lactation (-0.27 kg/day/THI). Using the most complex RRM, the additive genetic variance could be altered simultaneously as a function of both DIM and THI values. This model could be recommended for the genetic evaluation taking into account the effect of G×E. The response to selection in the comfort zone (THI ≤ 66) is expected to be higher than that obtained in the heat stress zone (THI > 66) of the animals. The genetic correlations between milk yield in the comfort and heat stress zones were less than unity at opposite extremes of the environmental gradient. Thus, the best animals for milk yield in the comfort zone are not necessarily the best in the zone of heat stress and, therefore, G×E due to heat stress should not be neglected in the genetic evaluation.

A new way to measure milk yield persistency: a genetic point of view with application to Gyr (Bos indicus) cattle.

The objective of this work was to estimate genetic parameters for a measure of persistency of milk yield and to evaluate its association with 305-d cumulative milk yield and lactation length. 12 346 records from 8202 dairy Gyr cows including lactations up to fifth calving were used. The measure of persistency was obtained from one of the parameters of a quadratic model that describes the cumulative yield across lactation as a function of days in milk. A three-trait multivariate analysis was done. Heritability and repeatability for persistency were 0.08 and 0.21, respectively. Deviance Information Criterion provided evidence that the additive genetic covariance between the measure of persistency studied and 305-d cumulative yield is zero. Genetic correlations between persistency and lactation length were 0.50 and 0.27 for first or all lactations, respectively. Milk yield persistency as measured in this study has low heritability. Selection for persistency can increase lactation length. The measure of milk yield persistency studied here is genetically independent of total milk yield and can be included in routine genetic evaluations of dairy cattle.

Reaction norm model to describe environmental sensitivity across first lactation in dairy cattle under tropical conditions.

Reaction norm models have been widely used to study genotype by environment interaction (G × E) in animal breeding. The objective of this study was to describe environmental sensitivity across first lactation in Brazilian Holstein cows using a reaction norm approach. A total of 50,168 individual monthly test day (TD) milk yields (10 test days) from 7476 complete first lactations of Holstein cattle were analyzed. The statistical models for all traits (10 TDs and for 305-day milk yield) included the fixed effects of contemporary group, age of cow (linear and quadratic effects), and days in milk (linear effect), except for 305-day milk yield. A hierarchical reaction norm model (HRNM) based on the unknown covariate was used. The present study showed the presence of G × E in milk yield across first lactation of Holstein cows. The variation in the heritability estimates implies differences in the response to selection depending on the environment where the animals of this population are evaluated. In the average environment, the heritabilities for all traits were rather similar, in range from 0.02 to 0.63. The scaling effect of G × E predominated throughout most of lactation. Particularly during the first 2 months of lactation, G × E caused reranking of breeding values. It is therefore important to include the environmental sensitivity of animals according to the phase of lactation in the genetic evaluations of Holstein cattle in tropical environments.