Intake and digestion of mature Flinders grass (Iseilema spp.) by sheep and their response to the addition of urea and minerals

Abstract

Studies were conducted of the voluntary feed consumption (VFC) and digestion by sheep offered mature Flinders grass hay containing, on a dry matter basis, 4.2% crude protein (CP), 71.8% cell wall constituents (CWC) and 12.6% total ash. The nutritive value of the hay was low, as indicated by the relatively low values for organic matter (OM) digestibility (40.9%), VFC (879 g OM/day) and CP digested in the intestines (5.8 g CP/100g feed OM intake). Digesta flows from the rumen and abomasum per unit OM intake, rumen and abomasal digesta pH, ammonia concentration in rumen liqour, and CP reaching the intestines relative to CP and digestible OM intakes were similar to values previously obtained with temperate grasses. Supplementation of the hay with urea increased VFC by 16%, and minerals in addition to the urea enhanced it by a further 6%. The supplements substantially increased OM and CWC digestibilities (by 16-17%) and CP digested in the intestines (DCPi) per unit hay intake (by 10%); these improvements could be attributed to changes in ruminal digestion. The higher levels of intake and digestion with the supplements were accompanied by increased concentrations of volatile fatty acids (VFA) in the rumen. It was calculated, by using the ad libitum feeding results, that the supplements of urea and minerals would have increased the intakes of digestible OM and DCPi by 44 and 36% respectively. However, with the supplements, DCPi per kg digestible OM remained low at 13.3 g. The data facilitate interpretation of previous animal production studies with Flinders grass hay and indicate that production may be limited by inadequate amino acids in the supplemented diet.