Dietary nutrient restrictions in the post-weaning period change feed efficiency and productivity of Santa Inês ewe lambs

Context Interest in sheep production has grown considerably, mainly in the meat market segment in large urban centres. This growth is due to improved efficiencyand quality products, which makes the segment attractive for production. Aims Our objective was to evaluate the effects of dietary nutrient restrictions on the feed efficiency and productivity of Santa Inês ewe lambs. Methods Twenty Santa Inês ewe lambs were weaned at an average weight of 15.09 ± 2.63 kg and were randomly assigned in a 2 × 2 factorial design to nutritional plans for carcass finishing (early and late maturity) and levels of nutrient restriction (0% and 15% reduction of both crude protein (CP) and total digestible nutrients (TDN) relative to requirements) with five replications per treatment. The trial was divided into two phases: lambs aged 4–8 months (<8 months) and lambs >8 months old. Key results There were no differences (P > 0.05) between diets for average daily gain (ADG), dry matter intake (DMI), feed efficiency and residual feed intake. Ratios of ADG : DMI (% of liveweight (LW) and LW0.75) were affected (P ≤ 0.05) by restriction in ewe lambs >8 months old. Restriction model tests (ω1, ω2, ω3 and ω4) did not differ (P > 0.05) from complete models for diets formulated for early maturity; therefore, a single standard growth curve fitted this nutritional plan. On the other hand, the restriction model responses for diets formulated to late maturity differed (P ≤ 0.05) from the complete model, generating different standard growth curves according to the applied restriction. Feeding Santa Inês ewe lambs a restricted diet (by 15% CP and TDN) in an early-maturity nutritional plan will allow lambs to reach slaughter LW earlier than those fed unrestricted diets. Conclusions and implications When the objective is to terminate animals at a later age (>8 months), unrestricted diet formulated to a late-maturity nutritional plan will produce higher LW and subsequent reproductive efficiency. By contrast, reducing CP and TDN by 15% for ewe lambs >8 months of age may reduce growth rates at an initial phase.