-The objective of this study was to estimate the heritability of probability of early pregnancy (PEP) and scrotal circumference (SC) and the genetic correlation between these traits in Nellore cattle. PEP records from 11,696Nellore females born between 1983 and 2001 were analyzed. PEP was assumed to be one for females that effectively bred in the herd (19.84%) and zero for those discarded before first calving (80.16%). The model used to study PEP included the effects of contemporary group, age of dam at calving and heifer weaning age, direct additive genetic effects, and residual effects. For SC, 9335 records were analyzed considering the effect of contemporary group, direct additive genetic effects and residual effects. Covariance components were estimated by Gibbs sampling applied to a two-trait sire model, using a threshold model for PEP and a linear model for SC. Estimated mean heritability was 0.47 ± 0.05 for PEP and 0.27 ± 0.03 for SC, and the genetic correlation between traits was 0.12 ± 0.20. These results indicated the existence of additive genetic variation for PEP and this trait should therefore respond to selection. The estimated genetic correlation between PEP and SC indicated a low, but favorable, association. Thus, SC might be used together with PEP in genetic evaluations of sexual precocity. This procedure would increase the accuracy of predicting expected progeny differences for PEP. Foram analisadas 9.335 informações de perímetro escrotal, considerando os efeitos de grupo de contemporâneos, genético aditivo direto e residual. Os componentes de covariância foram estimados usando amostragem de Gibbs, em análise bicaracterística, utilizando-se modelo touro; a PPP, por modelo de limiar; e o perímetro escrotal, por modelo linear. As análises forneceram estimativas médias de herdabilidade iguais a 0,47 ± 0,05 e 0,27 ± 0,03 para PPP e PE, respectivamente, e de 0,12 ± 0,20 para a correlação genética entre essas características. Esses resultados indicam que existe variação genética aditiva para PPP e, portanto, essa característica deve responder à seleção. A correlação genética estimada entre PPP e PE indica associação baixa entre essas características, porém favorável. Assim, pode-se utilizar o perímetro escrotal juntamente com a PPP nas avaliações genéticas da precocidade sexual, um procedimento aumentaria a acurácia da predição da DEP

RESUMO -Foram estudados a produção de leite de vacas Nelore e o comportamento de amamentação em diferentes sistemas de produção: NR-Nelore Referência, sob manejo extensivo (manejo tradicional); NI-Nelore, sob manejo intensivo; e três cruzamentos CNCanchim x Nelore, AN-Angus x Nelore e SN-Simental x Nelore, sob manejo intensivo. Em três momentos da lactação (60, 120 e 180 dias após o parto), foram medidos, nos bezerros, o número e a duração das mamadas, o ganho diário de peso (kg/dia) e o peso à desmama. O momento da lactação e a interação sistema de produção x momento da lactação apresentaram efeito significativo sobre a produção de leite. A produção de leite não apresentou corrrelação com o comportamento de amamentação nem com o ganho de peso dos bezerros dos diferentes sistemas de produção. Condições deficientes de alimentação não resultaram em menores produções de leite de vacas Nelore, mas sim em acentuadas perdas de peso (80 kg) durante a estação de monta no sistema NR. O tempo diário de amamentação apresentou diminuições significativas no sistema extensivo com o decorrer da lactação, enquanto os sistemas intensivos não mudaram ou aumentaram os minutos de amamentação por dia. Para as condições nas quais o experimento foi desenvolvido, os bezerros cruzados apresentaram os melhores desempenhos durante a fase pré-desmama, em comparação com os bezerros Nelore.Palavras-chave: comportamento de amamentação, gado de corte, produção de leite Milk Yield and Suckling Behavior in Five Beef Cattle Production SystemABSTRACT -Milk yield in Nellore cows and suckling behavior of their calves of different production systems: NR-Extensive Nellore, NI-Intensive Nellore; and three crossbreeding systems (CN-Canchim-Nellore, AN-Angus-Nellore and SN-Simmental-Nellore in intensive management), were studied. Milk production of cows and number and length of suckles, and daily gain (kg/day) of calves were obtained in three moments of lactation (60, 120 and 180 days after calving). Moment of lactation and production system by lactation moment interaction had a significant effect in milk yield. Milk yield did not show any relationship with suckling behavior or daily gain in calves. Extensive grazing condition did not reduce milk yield of Nellore cows although it determined significant cow weight losses (80 kg) during the breeding season in the NR system. Daily length of suckling decreased in the NR system as lactation progressed, and was sustained or increased in the intensive systems. Crossbred calves showed higher daily gain and weaning weight than purebred.

Our objective was to evaluate the metabolic, endocrine and hepatic mRNA profiles through the gestation-lactation cycle in purebred (PU: Angus and Hereford) and crossbred (CR: reciprocal F1 crosses) mutliparous beef cows (n = 32), grazing on two herbage allowances of native pastures (2.5 v. 4 kg dry matter/kg BW; LO v. HI) and their associations with cow's productive performance (calf birth weight, milk production and commencement of luteal activity). Cow BW, body condition score (BCS) and blood samples were collected monthly, starting at − 165 days relative to calving (days), and every 2 weeks after calving until +60 days of lactation. Liver biopsies were collected at − 165, − 75, − 45, − 15 ± 10, and +15 and +60 ± 3 days. Metabolic, endocrine and hepatic gene expression profiles, and calf birth weight, milk yield and postpartum commencement of luteal activity were evaluated. Overall, the most pronounced changes in metabolic, endocrine and hepatic gene expression occurred during winter gestation (−165 to − 45 days), when all cows experienced the onset of a negative energy balance (decreased BCS, glucose and insulin, and increased non-esterified fatty acid concentrations, P < 0.008). Concentrations of insulin and IGF-I were greater (P < 0.037) in HI than in LO cows. However, serum IGF-I concentrations and hepatic growth hormone receptor (GHR) and IGF1 mRNA decreased (P < 0.05) during the winter gestation period only in HI cows. Although IGF-I concentrations decreased (P < 0.05) during the early postpartum (−15 v. + 15 days) for all cows, the typical molecular mechanism that control the uncoupling of the growth hormone-IGF1 axis during the transition period of the dairy cattle (reduced hepatic GHR1A and IGF-I mRNA) was not observed in this study. The hepatic mRNA expression of key transcripts involved in gluconeogenesis and fatty-acid oxidation were upregulated (P < 0.05) during winter gestation (from − 165 to − 45, − 15 or +15 days, depending on the cow groups). Particularly, acyl-CoA oxidase-1 mRNA was greater for CR than for PU cows during winter gestation (−75 and − 45 days), and fibroblast growth factor-21 mRNA was downregulated (P < 0.01) only for HI cows during the transition (−15 v. 15 days) and lactation period (+15 to +60 days, P < 0.01). These results, together with the greater BCS, estimated energy intake, increased milk yield and shorter commencement of luteal activity in HI than in LO, and in CR than in PU cows (P < 0.018), would indicate that HI and CR cows were able to adapt more efficiently to changes in nutrient and energy supply through the gestation-lactation cycle.

-The objective of this study was to evaluate the effect of a short-term supplementation with rice bran (2 kg/cows/day) on the endocrine and metabolic profiles and hepatic gene expression, associated with the reproductive response in beef cows in grazing conditions. Thirty-eight primiparous beef cows (Hereford, Angus and Hereford × Angus) were used in a randomized block design according to genotype, calving date and body condition score at calving (BCS). At 64±14 days postpartum (day 0 of the experiment), cows were assigned to two nutritional treatments: i) control, grazing native pastures (CON, n=19) and ii) supplemented (SUP, n = 19) for 21 days (days 1 to 21 of the experiment). Blood samples were collected at 0, 7 and 22 days and liver biopsies were obtained at day 22 to determine the abundance of mRNA of growth hormone receptor (GHR), insulin-like growth factor -I (IGF1), and its binding proteins -2 and -3 (IGFBP2 and IGFBP3), and insulin receptor (INSR) using SYBR-Green real-time RT-PCR with hypoxanthine phosphoribosyltransferase as endogenous control. Short-term supplementation with rice bran did not modify either cow BCS or BW, or calf BW or average daily gain. However, it decreased by 11 days the length of postpartum anestrus of primiparous cows in grazing conditions, associated with increased concentrations of glucose and insulin, and reduced hepatic expression of IGFBP2 mRNA at the end of the experimental period.