Estimates of nutritional requirements and use of Small Ruminant Nutrition System model for hair sheep in semiarid conditions

The objective was to determine the efficiency of utilization of metabolizable energy for maintenance (km) and weight gain (kf), the dietary requirements of total digestible nutrients (TDN) and metabolizable protein (MP), as well as, evaluate the Small Ruminant Nutrition System (SRNS) model to predict the dry matter intake (DMI) and the average daily gain (ADG) of Santa Ines lambs, fed diets containing different levels of metabolizable energy (ME). Thirty five lambs, non-castrated, with initial body weight (BW) of 14.77 ± 1.26 kg at approximate two months old, were used. At the beginning of the experiment, five animals were slaughtered to serve as reference for the estimative of empty body weight (EBW) and initial body composition of the 30 remaining animals, which were distributed in randomized block design with five treatments (1.13; 1.40; 1.73; 2.22 and 2.60 Mcal/kg DM), and six repetitions. The requirement of metabolizable energy for maintenance was 78.53 kcal/kg EBW0,75/day, with a utilization efficiency of 66%. The average value of efficiency of metabolizable energy utilization for weight gain was 48%. The dietary requirements of TDN and MP increased with the increase in BW and ADG of the animals. The SRNS model underestimated the DMI and ADG of the animals in 6.2% and 24.6%, respectively. Concludes that the values of km and kf are consistent with those observed in several studies with lambs created in the tropics. The dietary requirements of TDN and MP of Santa Ines lambs for different BW and ADG are, approximately, 42% and 24%, respectively, lower than those suggested by the american system of evaluation of food and nutrient requirements of small ruminants. The SRNS model was sensitive to predict the DMI in Santa Ines lambs, however, for variable ADG, more studies are needed, since the model underestimated the response of the animals of this study.