Características metabólicas do período de transição e eficiência produtiva de vacas de corte de diferentes genótipos criadas no sul do Brasil.

Abstract

The aim of this study was to determine metabolic traits of the transitional period and their relationship with maternal ability and reproductive performance of beef cows of different genotypes raised in Southern Brazil. Cows of seven breed compositions: Angus (ANAN), Hereford (HHHH), Angus x Caracu (ANCR), Angus x Hereford (ANHH), Angus x Nellore (ANNE), Nellore x Angus (NEAN) and Nellore (NENE), held in extensive breeding conditions in the city of Bagé, Southern Brazil, were used in this study. Blood samples were collected around 30 days before parturition (day -30), and every seven days from calving (day 0) to six weeks postpartum (day 42), for determination of serum albumin, glucose, non-esterified fatty acids (NEFA), beta-hydroxybutyrate (BHB), urea, insulin and IGF-I. In these dates cows weighing and determination of body condition scores (ECC) were also performed. Milk yield was obtained by mechanical milking on three occasions, beginning, middle and end of lactation. On the day of calving the calves were weighed, repeating this procedure at weaning, when cows’ weight were also obtained to determine individual efficiency (EI), actual fertility (FR), calving interval (IP) and calf weight adjusted for 205 days (P205). There was a significant decrease in weight and BCS of cows on day 7. Cows of ANNE composition had higher average ECC than ANAN and HHHH cows. We verified low concentrations of IGF-I in early postpartum and gradual elevation to the last collection (day 42), low concentrations of insulin in the early weeks postpartum (day 14), elevated NEFA concentrations on day 7, followed by increased concentrations of BHB on collection day 21. Cows ANNE and NEAN showed higher concentrations of IGF-I that cows ANAN, HHHH and ANHH. Significant correlations were found between IGF-I and insulin, glucose and albumin in the end of the sampling period (day 42). Cows of ANCR genotype had the highest milk production at peak lactation, differing significantly from HHHH and NENE cows. Cows ANCR also had the highest total milk production, differing significantly from NENE cows. Cows ANNE had the lowest IP, differing significantly from cows NENE. Serum levels of hormones and metabolites found in this study characterize severe negative energy balance in the transition period of beef cows raised on native pasture in Southern Brazil. Crossbred cows of the ANNE, NEAN and ANCR composition showed better adaptation than the other genotypes, demonstrating the metabolic profile, less intense negative energy balance in early postpartum, which was reflected in superior performance on the maternal ability and reproductive efficiency.