The effects of Acacia aneura feeding on abomasal and intestinal structure and function in sheep

Sheep were pair-fed rations comprising chopped Acacia aneura (mulga) leaf and mulga plus polyethylene glycol (PEG) 4000 on the basis of intake of oaten hay chaff (OHC) and oaten hay chaff plus polyethylene glycol, respectively, and to an ad libitum fed control group. Feed intake and liveweight gain were recorded for a period of 32 days after which abomasal and intestinal samples were obtained for histological and biochemical analyses. Mucosal and muscle layer depths were measured for all samples. In sheep fed a mulga diet, voluntary feed intake and liveweight were reduced, but no diet effect was observed on intestinal morphometry. However, striking histological differences were observed. A marked increase in villous height and crypt depth were recorded for abomasal and intestinal samples from sheep fed mulga compared with PEG controls. Long, thin gastric pits, closed to the surface, were a feature of mulga-fed sheep, contrasting with deep, wide gastric pits open to the luminal surface in OHC-fed animals. Abomasal epithelia from mulga and mulga + PEG fed sheep showed discrete areas of tissue fragility compared with OHC-fed animals. Intestinal alkaline phosphatase, aminopeptidase-N and dipeptidylpeptidase IV activities were reduced in mulga-fed sheep and this was largely alleviated by including PEG in the diet. These results therefore demonstrate that anti-nutritive factors in mulga have significant and striking effects on intestinal structure and function in vivo, and this effect can at least partly be alleviated by incorporation of PEG in the diet.