Effect of supplementation and stage of lactation on performance of grazing ewes.

This study evaluated the effects of stage of lactation and supplementation on lactation performance of 95 dairy ewes grazing kura cloverorchardgrass pastures. Ewes lambed in January or April and consumed 0 or 0.82 kg/d of supplement (16% CP mixture of corn and high protein pellet) in a 2 x 2 factorial arrangement of treatments. The trial began when ewes went to pasture on May 25 and continued for 82 days. Unsupplemented ewes in both lambing groups showed a greater range in their daily milk yields than supplemented ewes throughout the trial, probably in direct response to variations in pasture quality during the grazing season. The January lambing ewes compared to the April lambing ewes produced less (P < .001) milk (91.1 vs. 136.8 kg, respectively), milk fat (5.6 vs. 7.8 kg, respectively), and milk protein (4.7 vs. 6.3 kg, respectively) during the trial. The supplemented ewes compared to the unsupplemented ewes produced more (P < .01) milk (123.2 vs. 104.2 kg, respectively), milk fat (7.2 vs. 6.2 kg, respectively), and milk protein (5.9 vs. 5.0 kg, respectively). Supplementation had a similar positive effect on milk, milk fat, and milk protein yield in both lambing groups. Milk urea nitrogen (MUN) can be used as an indicator of the efficiency of protein utilization in sheep. Trial MUN levels across treatments tended to be higher (18 to 34 mg/dL) than recommended levels for sheep (14 to 22 mg/dL), indicating an excess of protein intake. This can be explained by the high quality pastures, which ranged in crude protein from 16 to 30%. Across all treatments, the correlation between pasture crude protein and MUN was .65. Within the supplementation treatment, the correlation was numerically higher but not significantly different than the correlation within the unsupplemented treatment (r = .78 and .52, respectively). [ABSTRACT FROM AUTHOR]