Protein supplementation and herbage allowance for pregnant ewes grazing low-quality pasture

Abstract Text: Protein supplements mixed with mineral salt have been widely used in beef production in tropical countries, but few studies have been carried out to test their use with sheep or pregnant animals. This study assessed the effect of protein supplementation under two herbage allowances aiming at overcoming ewe undernutrition during gestation and lactation in low-quality pastures during winter. At approximately fifty days of gestation, 36 ewes carrying singletons and of similar stage of pregnancy were chosen from a group of 50 using an ultrasound technique. Ewes were allocated into four treatments in a randomized block design with three replications, where each paddock with 3 ewes was considered the experimental unit. The treatments were arranged in 2x2 factorial design of two herbage allowances: 1) low (LH) - 10 kg^-1 dry matter (DM) per 100 kg liveweight (LW) and 2) high (HH) 20 day^-1 DM per 100 LW; and two supplements: 1) protein plus a mineral salt mix (PS) and 2) mineral salt alone (S). Both supplements were offered in ad libitun amounts.  Due to differences in daily nutrients requirements and pasture quality, the trial was divided into two periods: pregnancy and lactation. Animals grazed a low-quality Brachiaria arrecta cv Napier (crude protein: 67 g kg^-1, neutral detergent fiber: 710 g kg^-1) pasture. Animal performance was assessed every 21 days. Other variables such as herbage structure and composition, lamb birth weight, daily supplement intake and placenta weight were also measured. There was no effect (P≥0.05) of PS on ewe average daily gain (ADG), placenta weight, lamb birth weight or lamb ADG. Protein supplement intake was greater (P≤0.05) than mineral salt intake in both reproductive stages, being greater during lactation, but it was not enough to increase the productive performance of ewes during the last third of pregnancy or during lactation. In conclusion, regardless of herbage allowance, the use of protein supplements on low-quality pastures does not improve the nutritional status of ewes or lambs before weaning. Keywords: fetal development, maternal nutrition, sheep