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

The digestibility of concentrate feeds has been determined by difference us ing hay as a basal forage in many institutions. The objective of this exper iment was to examine the effect of hay intake level and dietary crude prote in (CP) content on hay digestibility. Groups of wether lambs (1 year old) w ere fed three levels (600, 700 and 800 g/day) of hay each at two CP content s (103 and 182 g CP/kg DM), achieved by using a urea solution. An extra gro up of lambs were fed hay unsupplemented with urea (42 g CP/kg DM) at a leve l of 800 g/day. The true organic matter digestibility (True OMDI calculated using two methods: True OMD 1 and 2) and apparent OMD of all treatments fe d the 181 g CP/kg DM diets were significantly higher (P < 0.05) than treatm ents 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 tr ue digestibility also increased as hay allowance increased and a significan t 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 occur red between the 182 and the 42 g CP/kg DM diets (with the exception of CP d igestibility). Although the effect of CP content was significant in some ca ses, the magnitude of the observed digestibility response is of little cons equence for concentrate feed evaluation. (C) 2001 Elsevier Science B.V. All rights reserved.