ABSTRACT: The present study aimed to evaluate the effects of immunocastration on the animal growth, carcass traits, and meat quality of Nellore cattle receiving or not Ionophore supplementation at pasture or pasture with concentrate (semi-feedlot). The first experiment (Pasture) was carried out during the rainy season, while the second (supplemented = Semi-feedlot) was conducted during the dry season. In each assessment, 60 males were allocated into three treatments, in a completely randomized design: non-castrated, immunocastrated (anti-gonadotropin-releasing hormone vaccine), and immunocastrated animals receiving ionophore. The highly energetic supplemented diet was prepared using 85 % corn and 10 % soybean meal at 1 % body weight, while the ionophore was provided with salt containing 1,650 mg kg−1 of lasalocid. After slaughter, the carcasses were graded, and Longissimus thoracis et lumborum samples were collected for meat quality analysis. The non-castrated animals exhibited a more significant final body weight and hot carcass weight than those immunocastrated regardless of ionophore supplementation (p < 0.05). The carcasses of non-castrated animals had less fat cover and marbling than castrated animals. A high incidence of dark cutting beef was verified in non-castrated animals. The immunocastrated cattle produced tenderer beef, mainly at pasture rearing. In conclusion, regardless of production system or ionophore supplementation, immunocastration was an adequate choice to generate high-quality meat, since it increased marbling and improved beef tenderness. However, limitations regarding animal growth should be estimated.

Resumo: O objetivo deste trabalho foi avaliar as características do comportamento materno-filial em animais da raça Guzerá (Bos indicus) e a influência desse comportamento nas perdas do rebanho. Utilizaram-se 73 fêmeas (multíparas e primíparas) e seus respectivos bezerros para avaliação das seguintes características comportamentais: tempo de contato entre vaca e bezerro (CPCC), idade da vaca ao parto, características do teto, vigor do bezerro ao nascimento, necessidade de assistência humana (HA) e mortalidade até o desmame. A massa média dos bezerros ao nascimento foi de 29,12 kg. O vigor ao nascimento foi observado em 61,64% dos bezerros; no entanto, 27,4% dos bezerros necessitaram de HA. O vigor dos bezerros foi influenciado pelo CPCC, e bezerros sem vigor necessitaram de maior tempo com suas mães. Bezerros com baixo peso ao nascer precisaram de HA, mas bezerros de vacas com tetas de tamanho intermediário não. A ausência de vigor ao nascimento aumentou a taxa de mortalidade. As características idade da vaca e vigor dos bezerros ao nascimento influenciam tanto a necessidade de assistência humana aos bezerros, nas primeiras horas de vida, como as perdas no rebanho.

Abstract: The objective of this work was to evaluate the characteristics of the maternal-offspring behavior of Guzerat bovines (Bos indicus) and the influence of this behavior on herd losses. A total of 73 gestating cows (multiparous and primiparous) and their respective calves were evaluated for the following behavioral traits: contact period between cow and calf (CPCC), cow age at calving, teat conditions, calf vigor at birth, need for human assistance (HA), and calf mortality until weaning. The mean weight of calves at birth was 29.12 kg. Vigor at birth was observed in 61.64% of calves; however, 27.4% of the calves required human assistance. Calf vigor was influenced by the CPCC, and calves without vigor needed more time with their mothers. Calves with low weight at birth required HA, whereas calves from cows with intermediate-sized teats did not. The absence of vigor at birth increased the mortality rate. The traits age of cows and vigor of calves at birth influence both the need for human assistance to calves in their first hours of life and herd losses.

ABSTRACT The objective of this study was to develop accurate regression equations to predict body composition of Nellore cattle using chemical composition of the 9th, 10th, and 11th ribs and to evaluate the models proposed by analyzing mean and linear bias. Sixty-seven Nellore bulls were slaughtered and slaughter body weight (SBW), hot carcass weight (HCW), and 9th-, 10th-, and 11th-rib-cut weight (RCW) were measured. Empty body composition was obtained after grinding, homogenizing, sampling, chemical analysis, and pooling (blood, skin, head + feet, viscera, and carcass). Chemical components were determined in rib cut, carcass, and empty body: protein (RCP, HCP, and EBP), fat (RCF, HCF, and EBF), ash (RCA, HCA, and EBA), and water (RCWt, HCWt, and EBWt). Stepwise options were used to determine variables to be included and excluded from regressions. Predictive ability of equations was verified using standard error of prediction, coefficient of determination, and Cp statistic. Regression estimates were tested to evaluate the models in a database different from that used for equation development. The best equations found to predict carcass components, in kg, were: HCF = -0.994 + 0.123 × SBW - 9.201 × RCW + 34.249 × RCF (R² = 0.86) and HCWt = 2.733 - 0.172 × SBW + 0.821 × HCW - 23.939 × RCF + 12.186 × RCWt (R² = 0.96). For empty body, the best equations, in kg, were: EBF = -1.4 + 0.166 × SBW - 10.073 × RCW + 40.202 × RCF (R² = 0.90) and EBWt = 3.524 + 0.272 × SBW + 0.373 × HCW - 11.727 × RCW + 31.079 × RCWt (R² = 0.98). Body weight has a high predictive power and should be included in equations to estimate body composition of Nellore cattle. Unbiased models are valid as an indirect method for determining body composition in beef cattle.

ABSTRACT The objective of this study was to evaluate the associations between feed efficiency and feeding behavior, growth and carcass traits in Senepol cattle. A total of 137 animals were evaluated. Of these animals, 36 males were evaluated in a second test, totaling 173 records (initial age of 466±96 days and initial weight of 426±104 kg). Residual feed intake (RFI) was calculated as the difference between observed and expected dry matter intake, estimated by regression of dry matter intake on average daily gain and metabolic body weight (BW0.75), and the animals were classified as negative (high efficiency) and positive RFI (low efficiency). The mean RFI was -0.838±0.078 and 0.797±0.075 kg DM day-1 for negative and positive RFI animals, respectively, with a difference of 1.63 kg dry matter day-1. The dry matter intake of negative RFI animals, expressed as kg day-1 and percentage of mean body weight, was 11.3% and 13.1% lower than that of positive RFI animals. Negative RFI animals spent less time at the feed bunk and ingested less dry matter per visit than positive RFI animals, but did not differ in terms of chest girth, scrotal circumference, or hip height. However, negative RFI animals had lower rump fat deposition (7.13±0.477 mm) than positive RFI animals (7.83±0.473 mm). The Spearman correlation between RFI estimated in the first and second tests was 0.69, indicating that RFI is consistent when evaluated during two different periods of the life of the animal. Senepol animals with low residual feed intake (high efficiency) deposit less subcutaneous rump fat, but this reduction is not accompanied by a reduction in backfat thickness and longissimus muscle area.

Empty body and carcass chemical composition were determined in 67 Nellore bulls from Selection Nellore (NeS) and Control Nellore (NeC) herds of an animal breeding program for growth, slaughtered at 570 days of average age, after 100 days of feedlot. Selection Nellore animals had, respectively, 360 and 430 kg of initial and slaughter body weight, and NeC animals had 318 and 373 kg for the same traits. Animals were slaughtered and empty body composition was determined by chemical analysis of the components blood, hide, head and feet, viscera and carcass. Tissue deposition rates and gain chemical composition were also determined based on gains estimated by comparative slaughter technique. Significant differences were detected between NeS and NeC animals for slaughter body weight, empty body weight, empty body gain rate, and contents of water, protein, ash and retained energy in empty body, showing that selected animals had greater body sizes and growth rates. There were no significant differences in fat contents in empty body and carcass, suggesting that selected animals had higher growth rates as compared with the control, and were slaughtered with good body and carcass fat contents in the same feedlot time. Control Nellore animals showed a 10% higher gain in fat percentage than NeS in the period. This shows that the growth of bone and muscle ceased earlier and NeC group accumulated more fat. Animals selected for growth have heavier carcasses and greater tissue deposition rates with proportional composition similar to unselected animals.

O temperamento de quatro raças bovinas foi avaliado utilizando-se o teste de velocidade de fuga (FT) e o escore de comportamento (BST). FT foi definida como o tempo necessário para animais percorrerem uma distância de 2 m após a pesagem. BST foi baseada no comportamento dos animais na balança, amostrando-se quatro categorias de comportamento: movimentos, intensidade de respiração, vocalizações e coices. Os coeficientes de herdabilidade de FT e BST foram estimados com uso de um modelo de máxima verossimilhança restrita, considerando meio irmãos paternos. Caracu apresentou menores médias para BST do que as demais raças. Nelore apresentou resultados intermediários, seguida por Guzerat e Gyr com médias mais elevadas (p < 0,05). Resultados similares foram observados para FT, mas as médias de Caracu e Nelore não diferiram entre si. Observou-se baixa associação entre FT e BST (r p= -0,36; p < 0,01). A correlação entre rank de touros ordenados pelos seus valores preditos (p) para FT e BST foi moderada e negativa (r s = -0,63; p < 0,001). A herdabilidade de FT e BST foi de 0,35 e 0,34, respectivamente. A comparação de rebanhos Nelore com diferentes critérios de seleção para peso corporal mostrou que linhas de seleção podem modular positivamente o temperamento de Bos indicus.

The temperament of four beef cattle breeds were measured using a flight time test (FT) and a behavior score test (BST). FT was defined as the time taken by animals to cross a distance of 2 m after weight scale. The BST used a visual assessment of cattle behavior in which the results of four categories defined the score: movements, breathing intensity, vocalization and kicking. FT and BST coefficients of heritability were estimated using the restricted maximum likelihood, considering half siblings. Caracu presented a lower BST value than the other breeds. Nellore presented intermediate results, followed by Guzerat and Gyr with similar and higher means (p < 0.05). Similar results were observed with FT, but Caracu and Nellore did not differ from each other. A low association between FT and BST was found (r p= -0.36; p < 0.01). The correlation between a sire's ranking, according to the predicted breeding values (p) estimated for FT and BST, was moderate and negative (r s= -0.63; p < 0.001). Heritability estimates for FT and BST were 0.35 and 0.34, respectively. Inside Nellore breed, herds with different selection criteria for weight were compared. Our results show that selection line based on weight might positively modulate temperament of Bos indicus cattle.

The objective of the present study was to evaluate the genetic and non-genetic effects that influence vigor at birth and preweaning mortality in Nellore calves. A total of 11,727 records of births that occurred between 1978 and 2006, offspring of 363 sires, were analyzed. Poor calf vigor at birth (VB) and preweaning mortality divided into stillbirth (SB), early mortality (EM) and total mortality (TM) were analyzed as binary variables. Generalized linear models were used for the evaluation of non-genetic effects and generalized linear mixed models for genetic effects (sire and animal models). The incidences were 4.75% for VB, 2.66% for SB, 5.28% for EM, and 7.99% for TM. Birth weight was the effect that most influenced the traits studied. Calves weighing less than 22 kg (females) and less than 24 kg (males) were at a higher risk of low vigor and preweaning mortality. Preweaning mortality was higher among calves born from cows aged <3 and >11 years at calving compared with cows aged 7 to 10 years. Male calves presented less vigor and higher preweaning mortality than female calves. Selection for postweaning weight did not influence preweaning mortality. The heritability estimates ranged between 0.01 and 0.09 for VB, 0.00 and 0.27 for SB, 0.03 and 0.17 for EM and 0.02 and 0.10 for TM. Stillbirth should be included as a selection criterion in breeding programs of Nellore cattle, alone or as part of a selection index, aiming to reduce preweaning mortality.

O presente estudo foi desenvolvido com o objetivo de estimar herdabilidade e repetibilidade para diferentes medidas de eficiência produtiva de vacas e determinar a melhor maneira de calcular as relações de peso, visando a sua utilização como critério de seleção em rebanhos da raça Nelore. Os dados analisados são de animais da raça Nelore, pertencentes ao Projeto de Seleção das Raças Zebuínas e Caracu do Centro APTA Bovinos de Corte, do Instituto de Zootecnia de Sertãozinho. Os animais são selecionados para maior peso ao sobreano (rebanhos NeS e NeT, analisados como um único rebanho) e para peso ao sobreano próximo da média (NeC) do grupo de contemporâneos, desde 1980. As características utilizadas no estudo foram: 1) RPN = relação de peso ao nascer do bezerro / peso da vaca ao parto; 2) RPN2 = relação do peso ao nascer do bezerro / peso metabólico da vaca ao parto; 3) RPD = relação de peso à desmama do bezerro / peso da vaca à desmama; e 4) RPD2 = relação do peso à desmama do bezerro / peso metabólico da vaca à desmama. Os parâmetros genéticos foram estimados considerando dois arquivos: vacas com bezerros (CB) e vacas com e sem bezerros (SB). A RPN e a RPN2 foram calculadas somente no arquivo CB, enquanto que RPD e RPD2 foram calculadas em ambos os arquivos (CB e SB). Os parâmetros genéticos foram estimados pelo método da máxima verossimilhança restrita. As estimativas de herdabilidade para as características RPN; RPN2; RPD_CB; RPD2_CB; RPD_SB e RPD2_SB foram: 0,17±0,02; 0,16±0,02; 0,22±0,04; 0,19±0,03; 0,20±0,01 e 0,16±0,01, respectivamente. As repetibilidades estimadas variaram de 0,22 a 0,68. A utilização das relações de peso como critério de seleção deve promover, a longo prazo, melhorias na eficiência produtiva das vacas. As relações de peso têm sido consideradas apenas como informações para o descarte de vacas em alguns programas de seleção, mas poderiam ser incluídas em índices de seleção, principalmente quando calculada considerando o peso metabólico da vaca à desmama, incluindo tanto as vacas que desmamaram um bezerro, quanto aquelas que falharam em desmamar.

The objective of this study was to estimate heritability and repeatability for different measures of cows' productive efficiency and determine the best way to calculate the weight ratios, in order to use as selection criteria in Nelore herds. Data of Nelore animals from Centro APTA Bovinos de Corte-Sertãozinho, Instituto de Zootecnia were analyzed. The animals are selected for higher yearling weight (NeS and NeT herds, considered as a single herd in this paper) and, for mean yearling weight (NeC) within contemporary group, since 1980. The traits used in this study were: 1) RPN = ratio of birth weight of the calf / cow weight at calving; 2) RPN2 = ratio of birth weight of the calf / metabolic cow weight at calving; 3) RPD = ratio of weaning weight of the calf / cow weight at weaning and, 4) RPD2 = ratio of weaning weight of calf / metabolic cow weaning weight. For estimate genetic and phenotypic parameters, were considered two files: cows with calves (CB) or with and without calves (SB). The RPN and RPN2 were calculated only on CB file, and RPD and RPD2 were calculated in both files (CB and SB). Genetic parameters were estimated by restricted maximum likelihood. Estimates of heritability for traits RPN; RPN2; RPD_CB; RPD2_CB; RPD_SB and RPD2_SB were: 0.17±0.02, 0.16±0.02, 0.22±0.04, 0.19±0.03, 0.20±0.01 and 0.16±0.01, respectively. The repeatability estimates ranged from 0.22 to 0.68. The use of weight ratios as selection criteria should promote, at long-term, improvements in production efficiency. In some breeding programs, weight ratios have been considered only as information for disposal of cows, but could be included in selection indices, especially if it is calculated considering the metabolic weight of cow at weaning from both cows, that weaned a calf as those that failed to wean.

A seleção para peso pós-desmama tem sido aplicada em um rebanho Gir (80 vacas, seis touros) desde 1976, e um rebanho Nelore Controle, NeC (60 vacas, quatro touros), tem sido mantido para avaliação da mudança ambiental. O critério de seleção dos machos foi o peso aos 378 dias (P378), obtido em prova de ganho de peso, e o das fêmeas, o peso aos 550 dias (P550) em recria a pasto. A média dos diferenciais de seleção efetivos dos pais foi, respectivamente, 19,5 e 1,8 kg para Gir e NeC, correspondendo a 0,72 e 0,07 unidades de desvio-padrão (u.d.p.). A média dos diferenciais de seleção efetivos acumulados dos pais, na progênie de 2001, foi 83,7 e 7,2 kg para Gir e NeC, correspondendo a 3,17 e 0,29 u.d.p. O intervalo de geração médio no rebanho Gir foi 5,65 anos e no NeC 5,0 anos e o coeficiente de geração médio individual na progênie de 2001 atingiu 4,25 (Gir) e 4,65 (NeC) gerações de seleção. As estimativas de tendência genética no rebanho Gir, obtidas por quadrados mínimos, foram PN = 0,16; P210 = 0,81 kg/ano; GPRE = 3,02 g/dia/ano; P378 = 2,88; P550 = 2,80 kg/ano; G112 = 11,2 g/dia/ano, AM = 0,003 e AF = 0,004 m/ano. Com base no modelo misto, as estimativas para essas características foram menores (0,03 e 0,28 kg/ano; 1,15 g/dia/ano; 1,45 e 1,07 kg/ano; 3,73 g/dia/ano; 0,003 e 0,002 m/ano). As estimativas de herdabilidade realizadas para P378 e P550 foram 0,69 e 0,64, respectivamente. Os resultados indicaram que a seleção para peso pós-desmama, com base na informação de desempenho individual, promoveu respostas genéticas significativas tanto nas características sob seleção direta quanto nas respostas correlacionadas em características de crescimento da fase pré e pós-desmama no rebanho Gir.

Selection for yearling weight has been applied in a herd of Gir breed (80 cows, 6 sires) since 1976 and a Nelore Control herd (60 cows, 4 sires) has been used to evaluate the environmental change. Selection criteria were bull weight at 378 days (P378) in a performance test and heifer weight at 550 days (P550), under grazing conditions. The effective midparent selection differentials for P378 and P550 were 19.5 and 1.8 kg respectively for Gir and NeC, corresponding to 0.72 and 0.07 standard deviation units (s.d.u). The midparent cumulative effective selection differentials for the 2001 offspring were respectively 83.7 and 7.2 kg for Gir and NeC, corresponding to 3.17 and 0.29 s.d.u. The average generation intervals were 5.65 and 5.0 years respectively for the Gir and NeC herds. The individual generation coefficient for the 2001 offspring attained the values of 4.25 (Gir) and 4.65 (NeC). Annual genetic trends estimated by least square methodology in the Gir herd were - PN: 0.16; P210: 0.81 kg/year; GPRE: 3.02 g/day/year; P378: 2.88; P550: 2.80 kg/year; G112: 11.2 g/day/year; AM: 0.003 and AF: 0.004 m/year. Using the mixed model methodology, the estimates for these traits were lower, 0.03, and 0.28 kg/year; 1.15 g/day/year; 1.45 and 1.07 kg/year; 3.73 g/day/year; 0.003 and 0.002 m/year. The realized heritability was 0.69 and 0.64 for P378 and P550, respectively. The results indicated significant genetic response from direct selection based on individual performance information for postweaning weight as well as correlated response in pre and postweaning growth traits in a Gir herd.

Componentes de variância e parâmetros genéticos para características de crescimento foram estimados usando diferentes modelos em um rebanho da raça Gir. Utilizou-se o método da máxima verossimilhança restrita sob modelo animal univariado. Os modelos de análise incluíram os efeitos fixos de mês de nascimento, grupo contemporâneo e idade da vaca. Cinco modelos diferindo quanto aos efeitos aleatórios foram testados. Para todas as características da fase pré-desmama, o teste de razão de verossimilhança (LRT) indicou o modelo com efeito genético aditivo direto e efeitos maternos (genético e de ambiente permanente) como o de melhor ajuste. As estimativas de herdabilidade direta para peso ao nascer (PN), peso aos quatro meses corrigido para 120 dias (P120), peso à desmama corrigido para 210 dias (P210) e ganho diário na fase pré-desmama (GPRE) foram, respectivamente, 0,31± 0,07; 0,14 ± 0,06; 0,23 ± 0,07 e 0,22 ± 0,07. Para as características da fase pós-desmama, o modelo que forneceu o melhor ajuste aos dados incluiu apenas o efeito genético aditivo direto. As estimativas de herdabilidade direta para peso de machos ao final da prova de ganho de peso (P378), peso de fêmeas corrigido para 550 dias (P550), ganho diário na prova de ganho de peso (G112), altura aos 378 dias em machos (AM) e altura aos 550 dias, em fêmeas (AF) foram, respectivamente: 0,45 ± 0,11; 0,29 ± 0,11; 0,37 ± 0,11; 0,79 ± 0,13 e 0,36 ± 0,0. Os efeitos maternos, tanto o genético quanto o de ambiente permanente, foram fontes de variação importantes para as características da fase pré-desmama, não sendo verificada influência desses efeitos sobre as características da fase pós-desmama.

Variance components and genetic parameters for growth traits of Gyr breed were estimated using univariate analyses by restricted maximum likelihood. Five models differing in the random effects were evaluated. The models included the fixed effects of month of birth, contemporary group and age of cow. According to the likelihood ratio test (LRT) the best fit for all traits measured in the pre-weaning period was obtained by the model including the direct and maternal effects (genetic and environment). Heritability estimates for birth weight (PN), weight adjusted to 120 days (P120), weaning weight adjusted to 210 days (P210) and daily weight gain in pre-weaning period (P210) were respectively, 0.31 ± 0.07, 0.14 ± 0.06, 0.23 ± 0.07, and 0.22 ± 0.07. For the post-weaning traits, the best fitting model was the one which included only the direct genetic effect. Heritability estimates for male performance test weight at 378 days (P378), heifer weight at 550 days (P550), daily weight gain during the performance test (G112), male height at 378 days (AM) and heifer's height at 550 days (AF) were respectively, 0.45 ± 0.11, 0.29 ± 0.11, 0.37 ± 0.11, 0.79 ± 0,13, and 0.36 ± 0.0. The maternal genetic and permanent environmental effects were important sources of variation only for the traits measured in the pre-weaning period.

The objective of this study was to evaluate environmental factors that affect infestation of Caracu cattle breed by horn fly (Haematobia irritans) and to estimate genetic parameters for level of infestation. Infestation was evaluated on females from two herds in two consecutive years. Total number of flies on animals (FC) was counted, an infestation score (FS: 1 to 5) was recorded according to the estimated number of flies on animals, and number of parasites in photographs (FF) taken when the animals were evaluated was also counted. On each animal from one to eight observations were taken. A total of 3,836, 2,751 and 3,754 records from 718 animals were obtained for FC, FF and FS, respectively. The incidence of flies was lower during winter and higher during summer, and the thicker the hair coat of the animal the greater the infestation. Heritabilities and repeatabilities were equal to 0.10 and 0.10, 0.08 and 0.12, and 0.06 and 0.08, for FC, FF and FS, respectively. Findings indicate that selection for FC will result in low genetic progress and that animals should be evaluated more than once for selection purposes.

Parâmetros genéticos para pesos (17.942 observações), obtidos em intervalos de 60 dias, do nascimento ao momento da seleção (378 dias de idade), de 2.582 animais machos da raça Nelore, foram estimados em análises univariadas pelo método da máxima verossimilhança restrita. Os modelos de análise incluíram os efeitos fixos de grupo de contemporâneos, mês de nascimento, idade da mãe e idade na pesagem como covariável. Três modelos diferindo nos efeitos aleatórios foram testados: o modelo1 (M1) ajustou para os efeitos genéticos aditivos direto e materno e de ambiente permanente materno; no modelo 2 (M2), excluiu-se o efeito genético materno; e o modelo 3 (M3) ajustou somente para o efeito genético aditivo direto. O teste de razão de verossimilhança (LRT) detectou diferenças significativas para todas as idades, de M2 e M1 com o modelo simples (M3), evidenciando a importância dos efeitos maternos. Com exceção do peso ao nascer (0,40), valores baixos (0,05 a 0,12) de h² foram estimados em M1 e M2 para os pesos até os 8 meses de idade. Após esse período a herdabilidade foi maior, chegando a 0,28 aos 13 meses de idade. As estimativas da fração da variância total, em decorrência do efeito de ambiente permanente materno, foram altas e permaneceram praticamente inalteradas nos modelos 1 e 2. Efeitos maternos, não necessariamente decompostos (em genético aditivo e ambiente permanente), influenciaram o crescimento de animais machos da raça Nelore. Modelos nos quais foram incluídos efeitos maternos, além do genético aditivo direto, foram mais adequados para descrever a trajetória das variâncias ao longo das fases iniciais de crescimento de machos Nelore.

Genetic parameters for weights (17, 942 records), obtained in intervals of 60 days, from the birth to selection (378 days of age), of 2,582 males of the Nellore breed was estimated in univariate analyses by the Maximum Restricted Likelihood method. The models of analysis models included the fixed effects of contemporary groups, month of birth, mother age and age when the weights were collected as covariate. Three models differing in random effects were tested: the model 1 (M1) was adjusted for the direct and maternal addictive genetic effects and maternal permanent environment; in model 2 (M2) the maternal genetic effect was excluded; and the model 3 (M3) was only adjusted for the direct addictive genetic effect. The test of likelihood (LRT) detected significant differences, for all the ages, of M2 and M1 in relation to the simple model (M3), evidencing the importance of the maternal effects. Except for the birth weight (0.40), low values (0.05 to 0.12) of h² were found for M1 and M2 until 8 months of age and, after this period, reasonable increase could be observed, reaching 0.28 until 13 months of age. The estimates of the total variance fraction, due to the effect of maternal permanent environment, were high and practically became unaffected between the models 1 and 2. Maternal effects, not necessarily decomposed (in genetic addictive and permanent environment), affected the Nellore males growth. Models that contemplate maternal effects, besides the genetic addictive direct effects, are more realistic to describe the trajectory of the variances in the initial phases of growth of Nelore male calves.

Parâmetros genéticos foram estimados para peso na entrada da monta (PEM), considerado como indicativo do peso adulto de vacas Nelore. O arquivo de dados continha 7.902 registros de 1.556 vacas pertencentes a um experimento de seleção conduzido na Estação Experimental de Zootecnia de Sertãozinho, SP, Brasil. O PEM foi analisado como o último peso disponível para cada vaca no arquivo (PEM_U) ou como registros repetidos, incluindo todos os pesos (PEM_R). As análises foram feitas também em dois outros arquivos excluindo os registros das vacas descartadas antes de chegar aos 4 anos de idade, para o último peso registrado (PEM_U2) e para os registros repetidos (PEM_R2). Os componentes de variância foram estimados por máxima verossimilhança restrita, ajustando modelo animal uni e multivariado. O modelo multivariado incluiu pesos à seleção ajustados para 378 (somente machos) e 550 (somente fêmeas) dias de idade. As estimativas de herdabilidade obtidas nas análises univariadas foram 0,30±0,05; 0,37±0,06; 0,35±0,04; e 0,42±0,05, para PEM_U, PEM_U2, PEM_R e PEM_R2, respectivamente. Os valores correspondentes para as análises multivariadas foram 0,34; 0,42; 0,56; e 0,57. As estimativas de repetibilidade de PEM_R e PEM_R2 foram 0,58±0,01 e 0,69±0,01 nas análises univariadas e 0,61 e 0,72 nas análises multivariadas. As estimativas da mudança genética em PEM foram positivas e significativas, iguais a 0,40±0,08 e 0,35±0,07 por cento da média ao ano, para os dois rebanhos selecionados do experimento. Há evidências de que o emprego de modelos multivariados incluindo registros repetidos e os pesos à seleção de machos e fêmeas seja mais apropriado que a utilização de apenas o último PEM como indicativo do peso adulto. O PEM poderia ser incluído em um programa de seleção visando mudanças (aumento ou diminuição) ou monitoração, para manter o peso adulto desejável.

Genetic parameters were estimated for weight at the beginning of breeding season (PEM), considered as an indicative of mature weight of Nelore cows. Data file comprised 7,902 records from 1,556 cows from to a selection experiment conducted at the Estação Experimental de Zootecnia de Sertãozinho, SP, Brazil. PEM were analyzed either as the last weight available for each cow in the data file (PEM_U) or as repeated records, including all weights (PEM_R). The analyses were also performed excluding the records of cows culled before reaching 4 years of age, and for both the last (PEM_U2) and the repeated (PEM_R2) records. Variance components were estimated by restricted maximum likelihood, fitting single and multiple trait animal models. The multiple trait models included the selection weights adjusted for 378 (males only) and 550 (females only) days of age. Heritability estimates obtained from the single trait analyses were 0.30±0.05, 0.37±0.06, 0.35±0.04 and 0.42±0.05, for PEM_U, PEM_U2, PEM_R and PEM_R2, respectively. Corresponding values for the multiple trait analyses were 0.34, 0.42, 0.56, and 0.57. Repeatability estimates for PEM_R and PEM_R2 were 0.58±0.01 and 0.69±0.01 for the single, and 0.61 and 0.72 for the multiple trait analyses, respectively. Estimates of genetic changes were significantly positive and equal to 0.40±0.08 and 0.35±0.07 percent of the mean per year, for the two selected lines in the experiment. The results obtained in the present study indicated the multiple trait repeated records models as the most appropriate for analyzing the PEM as an indicative of mature weight. The PEM could be included in a selection program aiming at monitoring a desirable mature weight.

Registros de 1021 vacas Nelore foram analisados com o objetivo de estudar o efeito da seleção para crescimento na permanência de fêmeas no rebanho até cinco anos de idade, considerando-se que ela foi selecionada (P5|S). A variável, codificada como 0=descartada ou 1=não descartada, foi analisada com modelo de limiar. As vacas, nascidas de 1981 a 1997, foram provenientes dos rebanhos selecionados (NeS e NeT) e controle (NeC) da Estação Experimental de Zootecnia de Sertãozinho. Nos rebanhos NeS e NeT, foram selecionados animais com diferenciais de seleção máximos, dentro de rebanho e ano, e em NeC aqueles com diferenciais de seleção nulos, para peso ao sobreano. Após 3,5 gerações de seleção, o peso à seleção das fêmeas dos rebanhos NeS e NeT foi 22% maior que das fêmeas do NeC. A média observada de P5|S foi 68%. Os efeitos de rebanho e peso à seleção foram não significativos. O efeito da geração ao qual a fêmea pertence foi significativo, com tendência, similar nos três rebanhos, de diminuição da P5|S ao longo dos anos, refletindo as mudanças de manejo de novilhas à primeira monta, e não o efeito da seleção para crescimento. As variâncias de origem genética aditiva, estimadas por modelo animal, modelo touro e modelo touro avô-materno, foram 0,06; 0,16 e 0,17, proporcionalmente à sigma²e fixa em uma unidade da medida, e as herdabilidades iguais a 0,06±0,06; 0,15±0,13 e 0,16±13, respectivamente. As médias dos valores genéticos dos touros, por ano de nascimento, mostraram variação, sem tendência de alteração e de diferenciação entre os rebanhos no decorrer dos anos. A seleção para peso ao sobreano dentro de rebanho, por 3,5 gerações de seleção, não afetou a permanência das vacas no rebanho até cinco anos de idade. O modelo touro de limiar foi capaz de separar a mudança genética da mudança ambiental.

Records of 1021 Nelore cows were analyzed in order to evaluate the effect of selection for growth on their stayability in the herd up to five years, considering that they were selected (P5|S). The coded variable (0=culled and 1=not culled) was analyzed with a threshold model. The Nelore cows were born from 1981 to 1997 within the selected (NeS and NeT) and control (NeC) lines of the Experimental Station of Sertãozinho (SP-Brazil). In NeS and NeT the selected (replacement) animals were those with high selection differentials, within line and year, and in NeC those with null selection differentials for yearling weight. After 3.5 generations of selection, the NeS and NeT selection weight was 22% higher compared to NeC. The observed P5|S mean was 68%. Line and selection weight effects were not significant for P5|S. The generation effect was significant, showing a decreasing trend of P5|S along the years in a similar fashion for all the three lines. This tendency could be explained mainly to environmental effects, like increasing replacement rates of heifers, and not to selection for weight. The additive genetic variance, estimated by animal model, sire model and sire and maternal grandsire model were 0.06, 0.16, e, 0.17, proportionally to sigma²e constrained to one, and the heritabilities were 0.06±0.06, 0.15±0.13 and 0.16±0.13, respectively. The annual average breeding values of sires showed variation, without a regular trend along the years, similarly for the three lines. The selection for yearling weight within-herd, after 3.5 generations, did not cause any change in cow stayability up to five years of age. The threshold sire model was able to separate the genetic from the environmental trend.

Este trabalho foi conduzido com o objetivo de avaliar o efeito de fatores de meio sobre a infestação de bovinos Caracu pelo carrapato Boophilus microplus (Canestrini, 1887) e estimar parâmetros genéticos do grau de infestação por esse ectoparasita. Foram realizadas contagens em fêmeas de dois rebanhos, nas quatro estações, por dois anos consecutivos (setembro/1998 a julho/2000). Contou-se o número de carrapatos (NC) em um dos lados do animal e atribuiu-se escore visual (EC) de acordo com a quantidade de carrapatos no animal. Foram feitas de uma a oito avaliações, totalizando-se 4.079 e 3.994 observações de NC e EC, respectivamente, em 718 animais. Os dados foram analisados pelo método dos quadrados mínimos com um modelo que incluiu efeitos de rebanho (R), cor do animal (C), R x C, animal dentro de R x C como erro a, ano e estação da avaliação, espessura de pelame e idade do animal como covariável. As estimativas dos componentes de variância foram obtidas pelo método da máxima verossimilhança restrita livre de derivadas, utilizando-se um modelo que incluiu os efeitos fixos de grupo de contemporâneos (fazenda-ano-época), espessura do pelame e idade do animal como covariável e os efeitos aleatórios aditivos diretos e de ambiente permanente. Antes das análises, a variável NC foi transformada para log10 (n + 1) e EC para (x + 0,5)½, em que n é o número de carrapatos contados no animal e x, o escore (0 a 4). A incidência de carrapatos foi maior no verão e, quanto maior a espessura do pelame, maior o nível de infestação. As estimativas de herdabilidade e repetibilidade foram, respectivamente, 0,22 e 0,29 para NC e 0,15 e 0,21 para EC; a correlação genética entre NC e EC foi igual a 1,00. Os resultados sugerem que é possível obter progresso genético para resistência a carrapato pela seleção.

The objective of this study was to evaluate environmental aspects that affect the infestation of the Caracu cattle breed by the cattle tick Boophilus microplus (Canestrini, 1887) and to estimate genetic parameters for the level of this infestation. Countings of the parasite were done on female cattle from two herds, during all four seasons of the year, in two consecutive years (from September 1998 through July 2000). The number of ticks (NC) on one side of the animal was counted, and the infestations were also evaluated by scores (EC), according to the estimated number of parasites on the animal. Each animal had from one to eight observations. A total of 4,079 and 3,994 observations were obtained for NC and EC, respectively. The data were analyzed by the least squares method with a model that included the effects of herd (H), color of the animal (C), H x C, animal within H x C as error a, year, season, thickness of the hair, and age of animal as a covariable (linear and quadratic effects). The variance and covariance components were estimated by the restricted maximum likelihood derivative free method, using a model that included the effects of contemporary group (herd - year - season), hair thickness and age of the animal as a covariable (linear and quadratic effects), and the random additive direct and permanent environmental effects. Before the analyses, NC was transformed to log10 (n + 1) and EC was transformed to (x + 0.5) ½, where n is the number of ticks counted on the animal and x is the score for EC (0 to 4). The incidence of ticks was higher during the summer, and the ticker the hair the higher the infestation. The heritability and repeatability estimates were equal to 0.22 and 0.29, and 0.15 and 0.21 for NC and EC, respectively, and the genetic correlation between NC and EC was 1.00. The results indicate that there is enough additive genetic variation on tick numbers to support a selection program to increase resistance.