Effects of metabolizable protein supplementation to ewes during late gestation on wether lamb feedlot performance, carcass characteristics, and nitrogen balance

The objective of the current study was to determine the effects of maternal MP restriction or supplementation during late gestation on male offspring feedlot performance, carcass characteristics, and nitrogen retention. In yr 1, maternal dietary treatments were applied at d 100 of gestation, were similar in total energy, and contained: 60MP1: 60% of MP requirements; 80MP1: 80% of MP requirements; and 100MP1: 100% of the MP requirements on a DM basis during late gestation. In yr 2, maternal dietary treatments were similar in total energy and contained: 60MP2: 60% of MP requirements; 100MP2: 100% of the MP requirements; and 140MP2: 140% of MP requirements on a DM basis during late gestation. In yr 1, there was no effect (P ≥ 0.14) of maternal dietary treatment on initial BW, final BW, ADG, G:F, or morbidity. There was a quadratic effect (P = 0.04) for days on feed, with the 80MP1 lambs being on feed longer than the 60MP1 and 100MP1 lambs. A quadratic effect (P = 0.05) was also observed for DMI, with the 80MP1 wethers consuming less feed than the 60MP1 and 100MP1 wethers. There was no effect (P ≥ 0.06) of maternal MP intake during late gestation on the carcass characteristics or the majority of N balance parameters of initial BW, DM, NDF, ADF, or N digestibility, daily fecal N excretion, or daily N balance of wethers in yr 1. However, daily urinary N excretion per unit of initial BW was linearly reduced (P = 0.02) as MP intake increased and daily digested N retained increased linearly (P = 0.04) as maternal MP increased. There was a treatment × day interaction (P = 0.004) for serum urea N concentrations. The 60MP1 wethers had greater serum urea N concentrations on d 16, 18, 19, and 20 (P ≤ 0.04) than 80MP1 and 100MP1 wethers; and on d 17 (P = 0.05) compared with 80MP1 wethers. In yr 2, there was no effect (P ≥ 0.18) of maternal dietary treatment on initial BW, final BW, ADG, G:F, or morbidity. There was a linear increase (P = 0.04) in DMI as maternal MP increased from 60 to 140% of MP requirements. Carcass characteristics (P ≥ 0.29) and N balance parameters (P ≥ 0.24) in yr 2 were not affected by ewe MP intake during late gestation. These results suggest that maternal MP intake above or below requirements during late gestation may not affect wether feedlot performance or carcass characteristics.