Differences in digestive ability of more-selective and less-selective sheep ( Ovis aries L.) : A dissertation submitted in partial fulfilment of the requirements for the Degree of Bachelor of Agricultural Science

Abstract

This study aimed to determine if differences in digestive ability between more and less selective sheep exists. 24 sheep were ranked on their selective ability and divided into two groups, 12 more-selective (mean 9.92% stem consumed in diet) and 12 less-selective (mean 11.8% stem consumed in diet). Ewe hoggets were offered two feed types, one where selective behaviour could be expressed (hay chaff offered ad lib) and one where no selection could take place (lucerne pellets offered at maintenance). Sheep were offered each feed type for two weeks, with total faecal and feed residue collection in the second week. The trial ran for 5 weeks from the 16th June to the 21st July 2009. There was a significant difference in apparent digestibility between the more and less selective sheep on the hay chaff diet. More-selective ewes had 2.8, 3.1, 7.0, 3.9 and 2.9% units higher apparent DM, OM, CP, NDF and ADF digestibility respectively. There was no difference in apparent DM, OM, CP, NDF or ADF digestibility between the two groups on the lucerne pellet diet. On the hay chaff diet there was no significant difference in daily ad lib intake (g/kg of body weight) between the more (15.9 g/kg BW) and less-selective (16.4 g/kg BW) ewe hoggets, but the more-selective hoggets had a lower (P<0.05) mean daily faecal output (g DM/kg BW) than the less-selective ewes, 6.04 vs. 6.64 g DM/kg BW/day respectively. On the lucerne pellet diet there was no difference in intake or faecal output between the more and less-selective groups. From this trial it appears there is little benefit associated with being less-selective. Less selective sheep consume a lower quality diet and have no digestive advantage in doing so. The reason for the digestive advantage of the more-selective hoggets was unclear. In contrast to previous research there was no significant difference in nutrient composition of the feed residues between the more and less-selective groups on the hay chaff diet. The more-selective sheep consumed 1.9% less stem than the less-selective group however, more-selective sheep appeared to be selecting based on some other characteristic of the feed that was allowing them a digestive advantage. A possible explanation could be a slower rate of passage in the more selective hoggets due to a larger rumen allowing greater digestion however further research is required before conclusions can be made.