The effect of dietary protein content and hay intake level on the true and apparent digestibility of hay

Abstract

The digestibility of concentrate feeds has been determined by difference using hay as a basal forage in many institutions. The objective of this experiment was to examine the effect of hay intake level and dietary crude protein (CP) content on hay digestibility. Groups of wether lambs (1 year old) were fed three levels (600, 700 and 800 g/day) of hay each at two CP contents (103 and 182 g CP/kg DM), achieved by using a urea solution. An extra group of lambs were fed hay unsupplemented with urea (42 g CP/kg DM) at a level of 800 g/day. The true organic matter digestibility (True OMD, calculated using two methods: True OMD 1 and 2) and apparent OMD of all treatments fed the 182 g CP/kg DM diets were significantly higher ( P<0.05) than treatments fed the 103 g CP/kg DM diet (OMD: 632.8 g/kg vs. 604.2 g/kg; True OMD 1: 720.6 vs. 694.1 g/kg; True OMD 2: 711.8 vs. 681.0 g/kg). Apparent and true digestibility also increased as hay allowance increased and a significant linear effect was observed for GED. For the three groups fed 800 g/day of hay, significant differences in digestibility due to CP content only occurred between the 182 and the 42 g CP/kg DM diets (with the exception of CP digestibility). Although the effect of CP content was significant in some cases, the magnitude of the observed digestibility response is of little consequence for concentrate feed evaluation.