Thermal Stress Indices in Young Nellore Bulls Raised in Tropical Environments

Background: Thermal stress indices are important in predicting and choosing means for mitigating heat stress and defining critical environmental conditions for animal welfare and performance. The aim of this study was to determine the association between 16 thermal stress indices and thermophysiological variables in young Nellore bulls raised in a tropical pasture to determine the most effective parameter of heat stress to assist in the management of the thermal environment and animal welfare.Materials, Methods & Results: Seventy-eight young Nellore bulls (Bos taurus indicus), with a mean age of 10.5 months and mean body weight of 242.09 ± 32.17 kg at first collection, and 17.92 months and body weight 335.80 ± 39.02 kg at last collection, were used. During the experimental period, rectal temperature (RT) and surface temperature at the forehead, scapula, and groin, from which the average surface temperature (AST) was calculated, were measured. The difference between the AST and air temperature (i.e., AST – AT) and between the RT and AST (i.e., RT – AST) defined the thermal gradient. For the evaluation of thermal environment, the dry bulb, wet bulb, and globe temperatures, and wind speed were measured. Relative humidity, mean radiant temperature, solar radiation, temperature humidity index (THI), black global temperature humidity index (BGHI), equivalent temperature index (ETI), environmental stress index (ESI), respiratory rate predictor (PRR), heat load index (HLI), comprehensive climate index (CCI), and index of thermal stress for cows (ITSC) were calculated. The average and maximum air temperatures were above thermal comfort levels, while the average relative humidity was within the ideal limit for cattle. The average globe temperature was higher than the air temperature. Solar radiation presented very high values and wind speeds were very low. RT indicated normothermia in the cattle, and AST and thermal gradient (i.e., AST – AT) indicated thermal comfort. The 16 thermal stress indices demonstrated a significant positive and moderate correlation with AST, but were not significantly correlated with RT.Discussion: The average (28.14°C) and maximum (31.90°C) air temperatures indicated discomfort, since the ideal temperature for cattle is ≤ 27°C. The high thermal load of this region can contribute to poor animal welfare, thus requiring the provision of natural or artificial shade for pasture farming. The cattle in this study were in thermal equilibrium given that they maintained RT within the normal range, and the maximum limit was higher. If RT is maintained within physiological limits, the mechanisms of thermoregulation are able to eliminate excess heat (i.e., thermolysis is equivalent to thermogenesis). The AST was 5.4°C below the RT. It is important to note that deep body temperature (i.e., RT) is more stable than the surface body temperature, which is influenced by ambient temperature. Considering that there was no correlation between thermal stress indices and RT, and that the cattle were able to maintain RT within physiological limits, the Nellore bulls in this study were adapted to the environment. The thermal stress indices evaluated in this study adequately reflected heat stress in young Nellore bulls raised in pastures in a tropical environment. Surface temperature was the physiological parameter that responded most significantly to environmental conditions

INFERÊNCIA BAYESIANA E SUA APLICAÇÃO NA AVALIAÇÃO GENÉTICA DE BOVINOS DA RAÇA NELORE: REVISÃO BIBLIOGRÁFICA

O método da máxima verossimilhança restrita tem sido o escolhido pelos programas de melhoramento genético para estimação dos componentes de variância e predição dos valores genéticos. No entanto, a inferência bayesiana aparece como uma alternativa de grande flexibilidade, tanto em relação aos modelos que podem ser utilizados nas análises quanto em relação às inferências que podem ser realizadas a partir dos resultados. A sua aplicação em análises genéticas permite a obtenção de densidades posteriores das variáveis estudadas e pode ser utilizada tanto em pequenos ou grandes conjuntos de dados, não sendo necessário o conhecimento da distribuição inicial do parâmetro que se deseja estimar. No Brasil, o método da Amostragem de Gibbs, que permite uma inferência bayesiana, tem sido aplicado com êxito em diversos estudos envolvendo dados de campo de bovinos da raça Nelore. PALAVRAS-CHAVE: Amostragem de Gibbs, modelos lineares, parâmetros genéticos

Consumption of dry matter observed and predicted by the nutritional systems in senepol bulls kept in confinement

The objective was to compare the dry matter consumption (CMS) observed, through the use of the GrowSafe® electronic system, with that predicted by the BR-Corte (2010 and 2016) and NRC (2000) nutritional systems in confined Senepol bulls. To this end, 24 Senepol Bulls were used in a completely randomized design, uncastrated with an average initial weight of 368 kg and 16 months of age. The evaluation of the accuracy and approximation of the CMS estimates by the nutritional systems was adjusted by the simple linear regression model and the decomposition of the mean square of the prediction error (QMEP). The mean CMS observed was 10.33 kg.day-1, higher than the values predicted by the nutritional systems, in which the values predicted by the NRC (2000) and BR-Corte 2010 and 2016 underestimated the CMS by 29.62, 6.19 and 2.03%, respectively. The verification of QMEP and its decomposition made it possible to infer the proximity of the values predicted by the BR-Corte 2010 and 2016 models and the values observed, which presented a better adjustment in relation to the NRC. Surprisingly the values predicted by the NRC, created from a database with Bos taurus animals, showed greater distance from the values predicted and observed, and it was expected greater accuracy of the NRC models for this category and animal breed. It is concluded that the BR-Corte 2016 was the most appropriate model to estimate the CMS of confined Senepol bulls

Genetic analysis for visual scores of bovines with the linear and threshold bayesian models

O objetivo deste trabalho foi comparar as estimativas de parâmetros genéticos obtidas em análises bayesianas uni-característica e bi-característica, em modelo animal linear e de limiar, considerando-se as características categóricas morfológicas de bovinos da raça Nelore. Os dados de musculosidade, estrutura física e conformação foram obtidos entre 2000 e 2005, em 3.864 animais de 13 fazendas participantes do Programa Nelore Brasil. Foram realizadas análises bayesianas uni e bi-características, em modelos de limiar e linear. De modo geral, os modelos de limiar e linear foram eficientes na estimação dos parâmetros genéticos para escores visuais em análises bayesianas uni-características. Nas análises bi-características, observou-se que: com utilização de dados contínuos e categóricos, o modelo de limiar proporcionou estimativas de correlação genética de maior magnitude do que aquelas do modelo linear; e com o uso de dados categóricos, as estimativas de herdabilidade foram semelhantes. A vantagem do modelo linear foi o menor tempo gasto no processamento das análises. Na avaliação genética de animais para escores visuais, o uso do modelo de limiar ou linear não influenciou a classificação dos animais, quanto aos valores genéticos preditos, o que indica que ambos os modelos podem ser utilizados em programas de melhoramento genético.The objective of this work was to compare the estimates of genetic parameters obtained in single-trait and two-trait bayesian analyses, under linear and threshold animal models, considering categorical morphological traits of bovines of the Nelore breed. Data of musculature, physical structure and conformation were obtained between years 2000 and 2005, from 3,864 bovines of the Nelore breed from 13 participant farms of the Nelore Brazil Program. Single-trait and two-trait bayesian analyses were performed under linear and threshold animal models. In general, the linear and threshold models were efficient in estimating genetic parameters for visual scores under single-trait bayesian analyses. In the two-trait analyses, it was observed that: using continuous and categorical data, the threshold model provided greater estimates of genetic correlation than those of the linear model; with categorical data, the heritability estimates were similar. One major advantage of the linear models was its smaller requirements in the analyses processing time. In the genetic evaluation of animals for visual scores, the use of the linear or threshold model did not influence the classification of the animals, based on their predicted breeding values, which suggests that both models can be used in genetic improvement programs

Bayesian inference in genetic parameter estimation of visual scores in Nellore beef-cattle

The aim of this study was to estimate the components of variance and genetic parameters for the visual scores which constitute the Morphological Evaluation System (MES), such as body structure (S), precocity (P) and musculature (M) in Nellore beef-cattle at the weaning and yearling stages, by using threshold Bayesian models. The information used for this was gleaned from visual scores of 5,407 animals evaluated at the weaning and 2,649 at the yearling stages. The genetic parameters for visual score traits were estimated through two-trait analysis, using the threshold animal model, with Bayesian statistics methodology and MTGSAM (Multiple Trait Gibbs Sampler for Animal Models) threshold software. Heritability estimates for S, P and M were 0.68, 0.65 and 0.62 (at weaning) and 0.44, 0.38 and 0.32 (at the yearling stage), respectively. Heritability estimates for S, P and M were found to be high, and so it is expected that these traits should respond favorably to direct selection. The visual scores evaluated at the weaning and yearling stages might be used in the composition of new selection indexes, as they presented sufficient genetic variability to promote genetic progress in such morphological traits

CORRELAÇÕES FENOTÍPICAS ENTRE CARACTERÍSTICAS PRODUTIVAS DE TOUROS JOVENS DA RAÇA NELORE AVALIADOS EM PROVAS ZOOTÉCNICAS

This study aimed to estimate the phenotypic correlations between such characteristics as growth, scrotal circumference, carcass evaluated by ultrasound, and the morphological characteristics assessed by visual scores of young Nellore bulls evaluated in individual performance tests. The data obtained from 110 young Nellore bulls, participants in the 1st and 2nd Test of Individual Performance of Bulls, at the Federal University of Uberlândia were used in this study. The contemplated characteristics were daily weight gain (kg/day), initial weight (kg), final weight (kg), initial scrotal circumference (cm), final scrotal circumference (cm), area of Longissimus muscle (cm²), carcass finish (mm), fat thickness (mm), thickness of rump fat (mm), and the morphological characteristics assessed by visual scores such as body structure, early maturity and muscle. There were positive associations of low to medium intensity between all traits evaluated, except among weight characteristics at the beginning and end of the performance tests, and among the fat thickness and thickness of rump fat characteristics with carcass finish. Traits evaluated showed no negative correlations, indicating that these may be placed together in selection indices

INFERÊNCIA BAYESIANA E SUA APLICAÇÃO NA AVALIAÇÃO GENÉTICA DE BOVINOS DA RAÇA NELORE: REVISÃO BIBLIOGRÁFICA BAYESIAN INFERENCE AND ITS APPLICATION IN THE GENETIC EVALUATION OF THE NELLORE CATTLE: BIBLIOGRAPHIC REVIEW

O método da máxima verossimilhança restrita tem sido o escolhido pelos programas de melhoramento genético para estimação dos componentes de variância e predição dos valores genéticos. No entanto, a inferência bayesiana aparece como uma alternativa de grande flexibilidade, tanto em relação aos modelos que podem ser utilizados nas análises quanto em relação às inferências que podem ser realizadas a partir dos resultados. A sua aplicação em análises genéticas permite a obtenção de densidades posteriores das variáveis estudadas e pode ser utilizada tanto em pequenos ou grandes conjuntos de dados, não sendo necessário o conhecimento da distribuição inicial do parâmetro que se deseja estimar. No Brasil, o método da Amostragem de Gibbs, que permite uma inferência bayesiana, tem sido aplicado com êxito em diversos estudos envolvendo dados de campo de bovinos da raça Nelore.
 PALAVRAS-CHAVE: Amostragem de Gibbs, modelos lineares, parâmetros genéticos. Restricted Maximum Likelihood method has been the choice method of the genetic improvement programs to estimate variance components the breeding values. However, the bayesian inference appears as an alternative of the great flexibility, as much in relation the models that can be used in the analyses, how in relation the inferences that can be carried from the results. Its application in genetic analyses allows obtaining the posteriors densities of the variables and can be used in small or great data sets, not being necessary the knowledge initial distribution of the parameter. In Brazil, Gibbs sampling method, that allows a bayesian inference, has been used with success in diverse studies involving field data of Nellore cattle.
 KEY WORDS: Genetics parameters, Gibbs sampling, linear models

Quantitative genetic analysis for meat tenderness trait in Polled Nellore cattle

The aim of the present study was to analyze the interrelationships among the variables and also estimate the genetic correlations between tenderness (WBSF), growth (ILW, FLW and ADG) and carcass (BF, RF and LMA) features. Other purpose was to identify individuals who were more likely to be carriers of favorable genes for tenderness. Growth, carcass and tenderness data from 415 Polled Nellore animals was analyzed. Factor analysis and canonical correlations were used to analyze the phenotypic relationships. The covariance components and genetic parameters were estimated using Gibbs Sampling method. Lack of phenotypical correlations between the WBSF and the other traits were observed. The genetic correlations between WBSF and the other evaluated traits were of a low magnitude, with values of -0.15; -0.18; -0.13; 0.10; -0.12 and 0.18, between WBSF and ILW, FLW, ADG, BF, RF and LMA, respectively. The results support the conclusion that tenderness selection will not affect the selection of other economic traits and vice-versa, but for a better knowledge of the genetic relationships between meat tenderness and other traits for Polled Nellore more studies are required. The heritability estimated for WBSF was of a low magnitude (0.11 ± 0.022). Based on the principle of probability of identical genes by ancestry individuals who were more likely to be carriers of favorable genes for tenderness were identified. Further work will include creation of a segregating population that will serve as experimental material for future gene prospecting and identification research