Effect of time and amount of protein supplementation on ewe forage intake and ewe and lamb performance in drylot and pasture management systems

Abstract

A factorial experiment with four levels of crude protein [CP; 133 (HP), 100 (MP), 67% (LP) of NRC requirements and a control group which received no supplemental feed], three times of supplement initiation [TIME; mid- (P1) or late (P2) gestation or at parturition (P3)] and two management systems (MGMT; pasture or drylot) was designed to study the effects of CP level, time of supplement initiation and management system on grade Rambouillet ewe and lamb performance. Ewes were fed individually and had access to hay (drylot) or native vegetation (pasture) in common. Allowances were based on reference metabolic weights (kg^0.75) taken in early gestation. Forage intake was measured during gestation (Trial 1) and during lactation (Trial 2) using Yb(NO3)3 as an external marker. Trial 1 was a continuous dose trial and Trial 2 was a pulse dose trial. In Trial 1, pasture forage and total dry matter (TDMl) intake were enhanced with CP feeding, whereas in the drylot forage and TDMl were decreased by feeding. Forage digestible energy (FDEI) and total digestible energy (TDEI) intakes were influenced by MGMT; with increasing levels of CP, pasture ewes had an increasing and drylot ewes a decreasing FDEI and TDEI. In Trial 2, CP decreased forage intake relative to the control groups in both management systems. CP improved TDMl in the HP and MP groups in the pasture, but did not change TDMl of the LP pasture ewes or the two higher CP drylot groups. Feeding decreased TDMl in the LP drylot ewes. Drylot ewes had higher FDEI and TDEI than the pasture ewes, but increasing CP intake improved TDEI in pasture ewes in contrast to no improvement over control ewes or a decrease in TDEI in the low CP drylot ewes. Clean fleece weights were higher in the pasture group and for supplemented as compared to control ewes. The MP and HP groups had heavier fleeces than the LP and control sheep. Fiber diameter was finer in the drylot sheep than in the pasture in all three feed periods. In P2, ewes on feed longer had coarser fleeces than P3 or control ewes. In P3 control ewes had finer wool than supplemented ewes and HP and MP ewes had coarser fiber diameter than LP ewes. Period1 and P2 ewes had coarser fleeces than P3 ewes. Birth weights were higher in lambs from ewes receiving the higher CP supplements during gestation for a longer period of time. Growth rates (ADG, 14 and 28 d adjusted weights) were higher in lambs .from ewes fed the higher protein supplements over a longer period of time.