Effect of refeeding on growth performance, blood metabolites and physiological parameters of Dorper x Santa Ines lambs previously subjected to feed restriction

Context. Weaned lambs raised on pasture-based systems in Brazil are often subjected to periods of forage shortage, limiting their nutrient and energy intake and, hence, their growth. Fast recovery of lamb body weight is important to the efficiency, sustainability and profitability of these sheep production systems. Aim. We evaluated the effects of refeeding on growth performance, blood metabolites and physiological parameters of Dorper x Santa Ines lambs after low and moderate feed restriction, to determine whether there was a compensatory growth response.Methods. Twenty-four non-castrated male lambs were assigned to a completely randomised design with three treatments and eight replicates. The trial was conducted in a feedlot and divided into two phases: (I) feed restriction for 64 days, and (2) refeeding for 42 days. In Phase I, the respective treatments provided energy supplies of 0.481, 0.841 and 1.205 MJ metabolisable energy per kg metabolic weight daily, corresponding to 60% (PR60, moderate) and 30% (PR30, low) feed restriction levels and ad libitum intake. In Phase 2, the lambs in PR60 and PR30 treatments were refed ad libitum. Performance and blood measurements were taken in Phase 1 for the ad libitum treatment, and Phase 2 for PR60 and PR30 treatments. Key results. Highest initial and final bodyweights of 32.7 and 41.2 kg were recorded in the PR30 treatment during Phase 2, compared with 23.0 and 36.7 kg averaged over PR60 and ad libitum treatments. Average daily gain did not differ among treatments (276 g/day, on average). Dry matter intake was significantly higher in PR30 than the ad libitum treatment (1406 vs 1158 g/day), with PR60 intermediate (1267 g/day). Serum levels of albumin, urea and creatinine indicated that protein metabolism was strongly affected by the PR60 treatment. High metabolic rate and subsequent rapid growth determined high respiratory rate and rectal temperature in the lambs from PR60 and PR30 treatments. Conclusions. Moderate feed restriction relative to maintenance level followed by an ad libitum refeeding period in the feedlot leads to a strong compensatory growth response in Dorper x Santa Ines lambs.