Abstract The aim of the present study was to assess the carcass and meat characteristics of feedlot steers in Brazil according to genetic group through a systematic review and meta-analysis. An electronic article search was conducted at the Scielo and Google Scholar databases and data were grouped according to genetic predominance. The results were tested for heterogeneity and submitted to a normality test and F test and the means were compared by the Tukey test. Predominantly British steers were finished at a younger age, required longer confinement times and displayed lower hot carcass weights and smaller loin eye areas at slaughter. Muscle carcass percentages were higher in Continental and Synthetic steers compared to British and Zebu steers, while fat percentages were higher in British and Zebu steers compared to continental and synthetic breeds. Meat marbling was higher in British, continental and crossbreed steers compared to synthetic and zebu steers. A British steer origin allows for decreased slaughter age, although leading to reduced hot carcass weight, while a genetic Zebu predominance can produce high fat percentage carcasses. metaanalysis. metaanalysis meta analysis. analysis meta-analysis age breeds weight carcasses

Resumo O objetivo do presente estudo foi avaliar as características da carcaça e da carne de novilhos confinados no Brasil de acordo com o grupo genético por meio de uma revisão sistemática e meta-análise. Foi realizada busca eletrônica de artigos nas bases de dados Scielo e Google Acadêmico e os dados foram agrupados de acordo com a predominância genética. Os resultados foram testados quanto à heterogeneidade e submetidos ao teste de normalidade e teste F e as médias comparadas pelo teste de Tukey. Novilhos predominantemente britânicos foram terminados em idade mais jovem, necessitaram de tempos de confinamento mais longos e apresentaram menores pesos de carcaça quente e menores áreas de olho de lombo no abate. Os percentuais de carcaça muscular foram maiores nos novilhos Continentais e Sintéticos em relação aos Britânicos e Zebu, enquanto os percentuais de gordura foram maiores nos Britânicos e Zebu em comparação aos continentais e sintéticos. O marmoreio da carne foi maior nos novilhos britânicos, continentais e mestiços em relação aos novilhos sintéticos e zebuínos. A origem do novilho britânico permite menor idade de abate, embora leve à redução do peso da carcaça quente, enquanto a predominância genética do zebu pode produzir carcaças com alto percentual de gordura. metaanálise. metaanálise meta análise. análise meta-análise Tukey jovem abate zebuínos

ABSTRACT Determining what and how much each environmental factor affects pregnancy is crucial to the sustainability and management of beef cow herds. The study evaluated through logistic regression the effect of environmental variables on the increase or reduction in the pregnancy rate of beef cows. The average pregnancy rate in the cows was 73 %, with an average age for the herd of 3.7 years. An increase in age of one year represented a 30 % increase in pregnancy, while a reduction of one year reduced the odds of pregnancy in the cows by 23 %. During the lactation period, an extra seven days’ lactation reduced the odds of pregnancy by 12 %. For every seven days that weaning was brought forward, the cows’ pregnancy odds increased by 14 %. An increase of 0.1 kg in average daily gain represented an increase of 17 % and 15 % in the odds of pregnancy during the first 60 days post-partum and 60 days to the end of the reproductive period. On the other hand, the loss of 0.1 kg in average daily gain resulted in a 14 % and 13 % reduction in the cows’ pregnancy odds, respectively. Factors such as age, the precocity of calving in the calving season, the time the calf remains with the cow and better performance in cows between calving and the end of the mating are strategies that increase the chances of pregnancy in beef cows. herds 7 37 3 3. years 2 period 1 forward 01 0 0. 6 postpartum post partum hand respectively season

Abstract Potential variables for the reproductive success of beef cows were evaluated. Included in the model were the age of the cow at calving; the interval between the Julian calving date and the end of the breeding season; the body weight and conditions at calving, at 75 days post-partum and at the end of the breeding season; and the mean daily variation in weight between these dates. Logistic regression was used in the analysis, with the parameters evaluated using the odds ratio statistic, estimating the chance of pregnancy. The mean rate of pregnancy was 84% and 55% for early and late-weaned cows, respectively. For early weaned cows, the regression variables were the Julian calving date, age of the cow, weight gain from calving to 75 days post-partum, and from 75 days post-partum to the end of the reproductive period. For late-weaned cows, there were only two regression variables, weight at calving and weight gain from calving to the end of the reproductive period. For every year above the average age of the herd, early weaned cows have an 80.9% greater chance of pregnancy, while a reduction of one year reduces the chance of pregnancy by 44.7%. In early weaned cows, every seven days after the mean Julian calving date reduces the chances of pregnancy by 22.6%, whereas every seven days before the mean calving date increases pregnancy by 29.2%. Greater gains in cow body weight, from calving to the end of the reproductive period, determine a greater probability of pregnancy. season 7 postpartum post partum dates analysis statistic 84 55 lateweaned late respectively postpartum, partum, period herd 809 80 9 80.9 447 44 44.7% 226 22 6 22.6% 292 29 2 29.2% 8 5 80. 4 44.7 22.6 29.2 44. 22. 29.

Abstract The objective of this work was to evaluate, through meta-analysis, the impact of subcutaneous fat thickness on beef qualitative traits. Combined data from 13 studies were used, comprising 245 carcasses of male bovines slaughtered in Brazil. Effect size for all parameters was calculated as mean difference or standardized mean difference, at 95% probability. The meta-analysis of random and fixed effects was carried out when I2>50% and I2<50%, respectively, for each indicator separately, with means for fat thickness, classified in the “control” (3–6 mm), “low” (<3 mm), and “high” (>6 mm) groups. Carcasses in the “high” group showed greater intramuscular fat deposition, whereas those in the “low” group presented an intramuscular fat deposition similar to that of the control. When the fat thickness was below the recommended threshold of 3 mm, shear force increased. Subcutaneous fat thickness values greater than 6 mm induced a positive change in the perception of tenderness by the panel of evaluators. Beef carcasses with a subcutaneous fat thickness over 6 mm tend to accumulate more intramuscular fat content and are tenderer for consumers’ acceptance. Carcasses with a fat thickness less than 3 mm produce tougher meat. evaluate metaanalysis, metaanalysis meta analysis, analysis traits 1 used 24 Brazil 95 probability I250 I I2 50 I2>50 I2<50% respectively separately control “control 3–6 36 (3– , low “low <3 (< high “high >6 (> groups increased evaluators consumers acceptance meat 2 9 I25 5 I2>5 I2<50 3– (3 < ( > I2> I2<5 I2<

Resumo O objetivo deste trabalho foi avaliar, por meio de meta-análise, o impacto da espessura de gordura subcutânea nas características qualitativas de carne bovina. Foram utilizados dados combinados de 13 estudos, compreendendo 245 carcaças de bovinos machos abatidos no Brasil. O tamanho do efeito para todos os parâmetros foi calculado como diferença média ou diferença média padronizada, a 95% de probabilidade. A meta-análise de efeitos aleatórios e fixos foi realizada quando I2>50% e I2<50%, respectivamente, para cada indicador separadamente, com as médias para espessura de gordura classificadas nos grupos “controle” (3–6 mm), “baixo” (<3 mm) e “alto” (>6 mm). As carcaças do grupo “alto” apresentaram maior deposição de gordura intramuscular, enquanto as do grupo “baixo” apresentaram deposição de gordura intramuscular semelhante à do controle. Quando a espessura da gordura estava abaixo do limite recomendado de 3 mm, a força de cisalhamento aumentou. Valores de espessura de gordura subcutânea maiores que 6 mm induziram mudança positiva na percepção de maciez pelo painel de avaliadores. As carcaças bovinas com espessura de gordura subcutânea superior a 6 mm tendem a acumular maior teor de gordura intramuscular e são mais macias para aceitação do consumidor. As carcaças com espessura de gordura inferior a 3 mm produzem carne mais dura. avaliar metaanálise, metaanálise meta análise, análise bovina 1 estudos 24 Brasil padronizada 95 probabilidade I250 I I2 50 I2>50 I2<50% respectivamente separadamente controle “controle 3–6 36 (3– , baixo “baixo <3 (< alto “alto >6 (> mm. . aumentou avaliadores consumidor dura 2 9 I25 5 I2>5 I2<50 3– (3 < ( > I2> I2<5 I2<

ABSTRACT: Heterosis plays an important role on yield and profitability of beef production systems. This study evaluates the morphometrics of purebred Nellore (N) and Charolais (C) animals and of the second (G2) and third (G3) generations of their alternating crosses, regarding the effects of genetic group and heterosis from birth to 365 days of age. The experiment comprised 159 calves (C = 29, N = 22, G2 - 3/4C 1/4N = 21, 3/4N 1/4C = 9, G3-5/8C 3/8N = 44 and 5/8N 3/8C = 34). The foreshank girth (FG), thoracic girth (TG), body length (BL), and hip height (HH) were measured after birth, and at 63, 210, and 365 days of age, and the total increases were calculated. The Charolais animals had greater FG, TG, and BL values than Nellore, while the latter had greater HH. For the offspring generations, the predominance of Charolais genes in the genotypes resulted in greater measurements for FG and TG in G2, whereas the predominance of Nellore genes resulted in higher HH values in both generations. The crossbred animals had greater values for all measurements than the purebreds, with more significant differences in FG, TG, and BL compared to Nellore purebreds and in HH compared to Charolais. Charolais animals show higher values for muscularity; while, Nellore animals are taller. Crossbred animals show greater development compared to purebreds, indicating a significant effect of heterosis.

Resumo O objetivo deste trabalho foi analisar a agregação e a desagregação de valores dos animais comercializados em busca das bonificações do programa Carne Angus no estado do Rio Grande do Sul, Brasil. Foram analisados os dados de 40.698 carcaças de bovinos abatidos em uma indústria frigorífica que realiza a certificação para o programa Carne Angus, durante o ano de 2014. A agregação de valor foi calculada pela diferença entre o preço base negociado para o lote e o preço final obtido pelo animal depois do processo de certificação. A desagregação foi calculada em função dos fatores que impediram os animais de serem enquadrados no programa de certificação. Os resultados mostram que o maior motivo para a desclassificação de animais com o padrão racial foi a dentição e o acabamento, os quais desclassificam, respectivamente, 34,3 e 12,7% dos animais com padrão racial. A desagregação de valor resultante de 7.177 animas que foram desclassificados por falta de acabamento ou por dentição avançada atingiu um valor de R$ 1.213.528,00, ou US$ 369.077,86 (US$ 51,43 por cabeça), quantia esta que deixou de ser repassada da indústria aos produtores rurais.

Abstract The objective of this work was to analyze price aggregation and disaggregation in commercialized animals searching for “Programa Carne Angus” benefits in the state of Rio Grande do Sul, Brazil. Data from 40,698 carcasses with Angus cattle racial pattern, slaughtered in a meat industry that performs the “Programa Carne Angus ”certification, during the 2014 year were analyzed. The aggregated value was calculated by the difference between the negotiated base price for the lot and the final price obtained by animal after the certification process. The disaggregation was calculated based on the factors preventing the animals from being included in the certification program. The results show that the major disqualifying factor in males with the racial pattern was carcass fatness, and for females was the dentition, which disqualified 34.3 and 12.7% respectively. Value breakdown from 7,177 disqualified animals due to lack of finishing, or advanced dentition, reached R$ 1,213,528.00, or US$ 369,077.86 (US$ 51.43 per head), an amount that is no paid on from the industry to rural producers.

Resumo: O objetivo deste trabalho foi avaliar a influência de diferentes tempos de descanso pré-abate no temperamento, nos indicadores fisiológicos de estresse e na qualidade da carne de bovinos de corte. Trinta e dois novilhos mestiços Aberdeen Angus x Nelore castrados foram distribuídos em quatro tempos de descanso pré-abate: 12, 18, 24 e 48 horas. Foram avaliados as seguintes variáveis: níveis séricos dos indicadores fisiológicos de estresse glicose e cortisol (na chegada dos animais ao matadouro, após o período de descanso e no sangramento), temperamento animal (movimentação, resistência à aproximação e agressividade) e qualidade da carne (valor final para pH, capacidade de retenção de água, parâmetros de coloração e maciez). Com um maior período de descanso pré-abate, a pontuação de temperamento foi mais alta, o que indica que os animais estavam mais agitados e resistentes à aproximação de humanos. Os níveis séricos de cortisol e glicose correlacionam-se positivamente com o temperamento animal e negativamente com a qualidade da carne. No sangramento, observou-se aumento nos níveis de glicose e de cortisol, respectivamente, no tempo de descanso de mais de 24 horas e no de 12 horas. O tempo de descanso de 48 horas reduz a maciez da carne e sua capacidade de retenção de água.

Abstract: The objective of this work was to evaluate the influence of lairage periods on the temperament, physiological indicators of stress, and meat quality of beef cattle. Thirty-two castrated Aberdeen Angus x Nellore crossbred steers were distributed into four lairage periods: 12, 18, 24, and 48 hours. The following variables were evaluated: serum levels of the physiological indicators of stress glucose and cortisol (upon arrival at the slaughterhouse, after the lairage period, and at bleeding), animal temperament (movement, resistance to approach, and aggressiveness), and meat quality (final pH, water-holding capacity, color parameters, and tenderness). With a longer lairage period, the temperament score was higher, indicating that the animals were more agitated and resistant to human approach. Serum cortisol and glucose levels correlate positively with animal temperament and negatively with meat quality. At bleeding, an increase was observed in glucose and cortisol levels, respectively, for lairage periods longer than 24 hours and of 12 hours. The lairage of 48 hours reduces meat tenderness and water-holding capacity.

Resumo: O objetivo deste trabalho foi avaliar o efeito do grupo genético e da heterose na relação entre peso corporal e medidas morfométricas, em bezerros puros e mestiços das raças Nelore e Charolesa de segunda (G2) e terceira (G3) gerações. Peso corporal (PC), ganho de peso médio diário (GMD), circunferência da perna dianteira (CPD), circunferência torácica (CT), comprimento corporal (CC) e altura da garupa (AG) foram medidos ao nascimento e aos 63, 210 e 365 dias de idade, nos animais de G2 e G3. Os animais da raça Charolesa foram superiores aos da Nelore quanto aos ganhos de PC, GMD, CC e CT, e para a razão entre o ganho de PC e o de AG; os animais Nelore foram superiores quanto aos ganhos de AG. Animais mestiços de ambas as gerações foram superiores aos animais puros quanto aos ganhos de PC, CC e AG. Na G2, a predominância dos genes da raça Charolesa resultou em maiores ganhos de PC, GMD, CPD e CT. Os animais da G3 foram superiores aos puros quanto a GMD, CPD e CT. Não se encontraram diferenças na proporção entre os ganhos nas medidas de peso e morfometria. Heterose e complementaridade são aparentes para as medidas de peso e corporais de bezerros mestiços de cruzamentos rotacionais.

Abstract: The objective of this work was to assess the effect of genetic group and heterosis on the relationship between body weight and morphometric measurements, in purebred and crossbred animals from the second (G2) and third (G3) generations of Nellore and Charolais calves. Body weight (BW), average daily weight gain (ADG), foreleg circumference (FC), thoracic girth (TG), body length (BL), and croup height (CH) were measured at birth and at 63, 210, and 365 days of age in animals from G2 and G3. Charolais animals were superior to Nellore ones for gains BW, ADG, BL, and TG, as well as for the ratio between BW gain and CH gain; Nellore animals were superior for CH gains. Crossbred animals of both generations were superior to the purebred animals for gains of BW, BL, and CH. In G2, the predominance of Charolais genes resulted in greater gains of BW, ADG, FC, and TG. The G3 animals were superior to the purebred animals for ADG, FC, and TG. No differences were found for the ratio between gains of weight and morphometric measurements. Heterosis and complementarity are apparent for weight and body measurements of crossbred calves from rotational crossings.

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

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

Resumo O objetivo deste estudo foi analisar o comportamento da precocidade ao longo de nove anos de novilhos da raça Hereford e suas cruzas abatidas com dentição de leite até seis dentes. Foram analisadas aproximadamente 144 mil carcaças certificadas no programa Carne Pampa, entre os anos 2010 e 2018. Avaliou-se o incremento no peso de carcaça fria por ano em três épocas do ano: a estação quente foi definida de 26 de dezembro a 25 de maio, o vazio de outono foi definido entre 26 de maio a 25 de julho e a estação fria de 26 de julho a 25 de dezembro. Para avaliar o comportamento dos pesos de carcaça fria ao longo dos anos por estação, os dados foram submetidos à análise de regressão linear simples. Os pesos médios por estação foram comparados por teste de comparação de médias. A época que apresentou maior peso médio de carcaça foi a estação fria, com 239,1 kg, que mostrou um incremento anual de 6,45 kg. Analisando o comportamento do peso médio de carcaça por dentição na estação fria, animais com dentição de leite apresentaram maior incremento de peso ao longo dos anos, na estação quente, animais abatidos com dois dentes apresentaram maior incremento de peso, assim como na estação vazio de outono. A categoria que apresentou menor incremento de peso nas três estações foram os animais abatidos com seis dentes. Concluiu-se que, ao longo dos nove anos, houve aumento na precocidade de abate em bovinos machos certificados no programa Carne Pampa.

Abstract The aim of this study was to analyse precocity behaviour over nine years in Hereford steers and their crosses, slaughtered with from zero to six teeth. Approximately 144,000 certified carcases in the Carne Pampa programme were analysed between 2010 and 2018. The increase in cold carcase weight per year was evaluated for three periods of the year: the hot season was defined as 26 December to 25 May, the autumn void was defined as 26 May to 25 July, and the cold season from 26 July to 25 December. To assess the behaviour of cold carcase weight over the years per season, the data were submitted to simple linear regression analysis. The average weights per season were compared by the mean value comparison test. The cold season had the highest mean carcase weight, with 239.1 kg, showing an annual increase of 6.45 kg. Analysing the behaviour of mean carcase weight by dentition, animals with zero teeth showed a greater weight increase over the years during the cold season as well as during the autumn void; during the hot season, animals slaughtered with two teeth showed the greater increase in weight. The category that showed the least increase in weight for all three seasons were animals slaughtered with six teeth. It was concluded that over the nine years, there was an increase in slaughter precocity in male cattle certified in the Carne Pampa programme.

Resumo: O objetivo deste trabalho foi identificar relações do índice de massa corporal (IMC) com as reservas energéticas corporais e a composição tecidual de cortes da paleta e do pernil de cordeiros Corriedale. Vinte e dois cordeiros com idade média de 18 meses foram utilizados. Regressões lineares foram determinadas entre as características estudadas. A massa corporal média, o escore de condição corporal (ECC) e o IMC foram 49,09±7,8 kg, 2,69±0,81 e 10,66±0,99, respectivamente. O IMC correlacionou-se ao ECC (r = 0,51) e à gordura interna total (r = 0,81). Equações lineares múltiplas que envolveram o IMC e o ECC forneceram coeficientes de correlação entre 0,50 e 0,76, com valores significativos para todas as características estudadas. O índice de massa corporal permite estimar as reservas de energia corporal de ovinos Corriedale.

Abstract: The objective of this work was to identify relationships of the body mass index (BMI) with the body energy reserves and tissue composition of shoulder and leg cuts of Corriedale lambs. Twenty-two sheep with average age of 18 months were used. Linear regressions were determined between the studied characteristics. The mean body mass, body condition score (BCS), and BMI were 49.09±7.8 kg, 2.69±0.81, and 10.66±0.99, respectively. The BMI was correlated with the BCS (r = 0.51) and internal fat (r = 0.81). Multiple linear equations, involving BMI and BCS, yielded correlation coefficients between 0.50 and 0.76, with significant values for all studied characteristics. The body mass index allows estimating the body energy reserves of Corriedale sheep.

RESUMO A incidência de contusões nas carcaças bovinas é consequência de distintos fatores potencialmente estressantes e agressivos a que são submetidos os animais durante o manejo pré-abate. Este estudo teve como objetivo identificar os fatores pré-abate associados a lesões de contusões severas observadas em diferentes regiões da carcaça dos bovinos. Foram avaliados 5.028 lotes de bovinos abatidos referentes a 154.100 animais. As carcaças foram analisadas quanto a: sexo, manejo na fazenda, condição da infraestrutura da fazenda, tipos de caminhão, distâncias e tempo de transporte da fazenda ao abatedouro, densidade da carga e estações do ano em que ocorreu o abate dos animais. Os resultados demostraram que a região da ponta de agulha e do dianteiro são as zonas mais afetadas com a incidência de contusões sendo as fêmeas as mais vulneráveis. Densidades de cargas acima de 401 kg m-2 ocasionam incremento no número de contusões. A utilização de veículos de maior tamanho promove o acréscimo de contusões, assim como a utilização de instalações da fazenda precárias. Em tempos de transportes superiores a três horas foi observado um decréscimo no número de contusões. Todas as variáveis avaliadas são potenciais causadoras de lesões nas carcaças bovinas. Deste modo, melhorar as condições de manejo e instalações nos carregamentos dos bovinos bem como diminuir o estresse de transporte são fatores determinantes de menores números de contusões em carcaças bovinas.

ABSTRACT The incidence of bruising in bovine carcases is a consequence of several potentially stressful and aggressive factors to which the animals are subjected during pre-slaughter handling. The aim of this study was to identify pre-slaughter factors associated with the severe bruising in different regions of the bovine carcass. The study evaluated 5,028 batches of slaughtered cattle from 154,100 animals. The carcases were analysed for gender, handling on the farm, condition of farm infrastructure, type of truck, distance and journey time from the farm to the slaughterhouse, loading density and time of year in which the animals were slaughtered. The results showed that the sidecut and forequarter are the areas most affected by bruising, with females being the most vulnerable. Loading densities above excess of 401 kg m-2 cause an increase in the number of bruises. The use of larger vehicles results in an increase in bruising, as does the use of poor farming facilities. A decrease in the number of bruises was seen for journey times of more than three hours. All the variables under evaluation are potential causes of injury to bovine carcases. As such, improving the handling conditions and facilities for loading cattle, as well as reducing the stress of transport, are factors which determine a smaller number of bruises in bovine carcases.

ABSTRACT Body development and reproductive performance of a hundred forty-two 14 to 15-month-old heifers, classified at weaning according to frame size as small, medium, and large, were evaluated. The parameters evaluated were: body weight, hip height, body condition score, weight gain, ovarian activity, and pregnancy rate. At weaning, body weight and hip height were significantly different among frame scores, (small – 133.0 kg, 92.2 cm; medium – 158.5 kg, 96.6 cm; and large – 185.2 kg; 100.2 cm). After weaning, heifers grazed together on natural pastures during the autumn and on ryegrass (Lolium multiflorum La.) during the winter and spring. Frame score differences remained until the beginning of the breeding season (BS), starting on average at 14 months of age. Weight gain between weaning and the beginning of BS was not different among frame scores (0.740 kg/day, on average). Body weights at the beginning of the BS were significantly different, of 255.7 kg (53.3% of the mature weight) for small heifers, 285.0 kg (59.4%) for medium heifers, and 307.6 kg (64.1%) for large heifers. Ovarian activity at the beginning of the BS was not different among the three groups. The average weight gain values during the BS of 0.492, 0.472, and 0.421 kg/day for small, medium, and large heifers, respectively, were significantly different. Pregnancy rates were not different among groups (small, 71.4%; medium, 76.4%; and large, 76.5%). Frame score did not influence the reproductive performance of heifers, but the small and medium heifers conceived 29 and 20 days earlier, respectively, than the large heifers.

Resumo Objetivou-se verificar o efeito de dois períodos de parto, na estação de parição (precoces: setembro; e tardios: outubro), sobre a eficiência de 54 vacas Red Angus primíparas aos 24 meses de idade. As vacas foram mantidas em pastagem natural e cultivadas de Lotus corniculatus e Lolium multiflorum nos períodos pré e pós-parto, respectivamente. Utilizou-se inseminação artificial em tempo fixo, com dois protocolos, em intervalo de 30 dias. Realizaram-se diagnósticos de gestação 30 dias após cada protocolo. Bezerros de vacas paridas precocemente ganharam mais peso durante o aleitamento, sendo mais pesados ao desmame, quando comparados aos de vacas tardias, perfazendo maiores ganhos do conjunto vaca-bezerro durante a lactação (0,721±0,030 e 0,699±0,032 kg). O desempenho reprodutivo foi superior paras as vacas paridas precocemente nas duas sincronizações e no índice de prenhez total (86,2 e 52%). Vacas precoces na parição obtiveram maiores índices de produção de bezerros (161,5±3,2 e 92,5±3,5 kg), produção de bezerros/kg de vaca ao desmame (40,9±0,97 e 23,7±1,04 kg) e eficiência produtiva ao parto (34,3±1,25 e 20,8±1,35 kg). Vacas paridas precocemente são mais eficientes na produção de kg de bezerros/kg de vaca ao parto e ao desmame e, associando-se kg produzidos e prenhez subsequente, apresentam maior índice de produção de bezerros.

Abstract The aim was to evaluate the effects of two calving periods, during the calving season (early: September; and late: October), in the efficiency of 54 Red Angus primiparous cows at 24 months of age. Over the pre-parturition and parturition periods, the cows were kept in natural and cultivated pastures of Lotus corniculatus and Lolium multiflorum, respectively. Fixed-time artificial insemination was used, with two protocols in a interval of 30-day. Pregnancy diagnosis was performed 30 days after each protocol. Calves from early calving cows presented larger weight daily gain, and were heavier at weaning when compared to later calving cows, resulting in higher cow-calf gains during the lactation (0.721±0.030 e 0.699±0.032 kg). The reproductive performance was higher for the early calving cows in both synchronizations, and in the total pregnancy rate (86.2 and 52%). Early calving cows had a higher calf production rate (161.5±3.2 e 92.5±3.5 kg), calf/kg of cow at weaning (40.9±0.97 e 23.7±1.04 kg), and productive efficiency in the calving (34.3±1.25 e 20.8±1.35 kg). Early calving cows are more efficient in production of calves kg/cows kg in the calving and in the weaning, and when associated the kg produced and the subsequent pregnancy, presented a higher calf production rate.

RESUMO. O estudo objetivou avaliar a eficiência produtiva durante a lactação de vacas com predominância Nelore de diferentes tamanhos corporais no sul do Brasil. Foram formados três grupos de vacas a partir do peso vivo: leves (≤ 316 kg), moderadas (≥ 317 e ≤ 400 kg) ou pesadas (≥ 401 kg). A variação de peso corporal e o ganho total do nascimento aos 210 dias dos bezerros de vacas pesadas (0,155±0,03 e 111,6±5,1 kg) foram superiores aos filhos de vacas leves (0,064±0,03 e 91,0±4,3 kg) e moderadas (0,144±0,03 e 97,7±4,0 kg). O índice de produção de bezerros apresentou diferença (p < 0,05) com o rebanho de vacas pesadas (93,5±3,2 kg) produzindo 57,4 e 19,7% mais quilogramas de bezerro que as leves (59,4±2,7 kg) e moderadas (78,1±2,4 kg), respectivamente. Vacas Nelores pesadas produzem bezerros mais pesados ao nascimento e possuem melhor desempenho reprodutivo, determinando o melhor índice de produção de bezerro; porém, as mesmas necessitam de maior área para a mesma oferta de forragem. Bezerros filhos de vacas Nelore com maior peso corporal possuem maior ganho de peso do nascimento aos 210 dias e são mais pesados aos 210 e 270 dias de idade.

ABSTRACT. This study was developed to evaluate productive efficiency during the lactation period of cows with predominant Nellore genetic composition based on their body size. Cows were divided into the following categories: light (≤ 316 kg), moderate (≥ 317 and ≤ 400 kg), or heavy (≥ 401 kg). Body weight change and total gain from birth to 210 days of age of calves born from heavy cows (0.155±0.03 and 111.6±5.1 kg) were higher than those of calves born from light (0.064±0.03 and 91.0±4.3 kg) and moderate (0.144±0.03 and 97.7±4.0 kg) cows. Calf production index differed (p < 0.05) with the herd of heavy cows (93.5±3.2 kg), producing 57.4 and 19.7% more kilograms of calf than light (59.4±2.7 kg) and moderate (78.1±2.4 kg) cows, respectively. Heavy Nellore cows produce heavier calves and have a better reproductive performance, which lead to a better calf production index. However, they require a larger area for the same herbage allowance. Calves born from heavier Nellore cows gain more weight from birth to 210 days of age and are heavier from 210 to 270 days of age.