A comparison of supplementary sources of nitrogen and energy for increasing the voluntary intake and utilization of barley straw by sheep

Abstract

SUMMARYChopped barley straw was fed ad libitum to penned Romney wether sheep. Supplements of urea, ground wheat grain + urea, lucerne hay and autumn saved pasture (ASP) were given for five periods each of 3 weeks using a 5 × 5 Latin square design. The latter three supplements supplied similar amounts of nitrogen and approximately 20% of the energy required for maintenance.The concentration of ammonia in the rumen fluid of sheep fed the basal straw diet was low and was increased by all the supplements. The concentration of total volatile fatty acids (VFA) in rumen fluid was unaffected by supplementation with urea, but was increased by the three supplements of nitrogen and energy. Differences in VFA molar proportions between treatments were small.Sheep offered straw alone had a digestible energy (DE) intake of 69% of maintenance and showed a weight loss of 121 g/day. Supplementation with urea had no effect upon apparent energy digestibility (42%) or voluntary intake, but significantly reduced the rate of live-weight loss. The lucerne hay and ASP supplements also had no effect upon straw consumption, but increased total DE intake to 87% of maintenance due to the additional energy provided by the supplements, and reduced live-weight loss. Supplementation with wheat + urea increased the estimated amount of digestible organic matter derived from straw by 8·5%, increasing DE intake to 94% of maintenance and reducing live-weight loss to 18 g/day.Averaged over all five groups of animals, straw intake increased by 9% in the second period of feeding and then gradually decreased with time, reaching a value in period 5 which was similar to period 1.