Utilization of clover diets by sheep. 2. Intake, digestion and utilization of nitrogen and sulfur

Abstract

Nine mature Merino wethers were fed three clover diets at 95% of previously measured intake under steady state conditions. The diets were mature subterranean clover (MSC), green subterranean clover (GSC) and persian clover (PC). The utilization of dietary N and S was studied for each feed.The ratios of digestible organic matter (DOM) to crude protein (CP) in the diets ranged from 3.9 to 5.5 : 1. The flow of microbial crude protein (MCP) from the abomasum was only 34 g day-1 in sheep given MSC compared to 77 g day-1 for GSC and 85 g day-1 for PC. However, the calculated efficiencies of MCP synthesis were 230-250 g MCP per kg OM apparently digested in the rumen for the three clovers. Despite the similar efficiencies of MCP synthesis, the ammonia-N (30 mg l-1) and sulfide-S (220 8g l-1) concentrations in the rumen of sheep fed MSC were low. The concentrations for the the other clovers were ammonia-N 90-110 mg l-1 and sulfide-S 730-1770 8g l-1. The amount of CP apparently digested in the intestines (DCPi) was only 31 g day-1 in sheep given MSC compared to 100 g day-1 and 81 g-1 in those fed GSC and PC, respectively. While this indicates that protein insufficiency in the tissues may have limited the intake of MSC, the DCPi values per unit of DOM intake were 150,210 and 150 g kg DOM-1 for MSC, GSC and PC, respectively. Sheep excreted more N and S (% of intake) in faeces when given MSC compared to GSC or PC.The sheep were in positive apparent balance for N and S when fed GSC or PC, but were mobilizing these nutrients from tissues at the low intakes of DOM, N and S with MSC. The wool growth rates and amounts of N and S incorporated into wool when MSC was fed were about half the other two feeds.These results are discussed in relation to other work on the utilization of N and S by sheep and likely effects of this on the intake of the feeds.