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

A factorial experiment was designed 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), 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$sp{0.75}$) taken in early gestation. Forage intake was measured during gestation (Trial 1) and during lactation (Trial 2) using Yb(NO$sb3)sb3$ 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 (TDMI) intake were enhanced with CP feeding, whereas in the drylot forage and TDMI 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 TDMI in the HP and MP groups in the pasture, but did not change TDMI of the LP pasture ewes or the two higher CP drylot groups. Feeding decreased TDMI 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 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. 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. (Abstract shortened with permission of author.).