In vivo digestibility of a range of silages in cattle compared with sheep

Context Ensuring accuracy of feed testing is becoming increasingly important as livestock industries seek to maximise efficiency of producing animal products to meet world requirements. Aim Twenty-four silages were fed to sheep and cattle to test the validity of using sheep-derived digestibility estimates for cattle. Method The silages tested included temperate and subtropical forages, and differed in level of maturity and weed contamination at harvest: several of the forage crops were grown with irrigation. In vivo comparisons were made for digestibility of dry matter (DMD), organic matter (OMD), and organic matter in the dry matter (DOMD) across two experiments. Intake was restricted to 16.5 g/kg liveweight and those silages with low nitrogen (N) contents were supplemented with urea to meet minimum dietary crude protein requirements. Key results DMD, OMD and DOMD ranged from 0.538 to 0.773, 0.550 to 0.810, 0.505 to 0.762 and 0.551 to 0.749, 0.584 to 0.786, 0.539 to 0.702 for cattle and sheep respectively. DMD, OMD and DOMD determined in sheep explained 88.7, 86.3 and 78.4% of the variation of DMD, OMD and DOMD in cattle respectively. In Experiment 1, DOMD was higher in cattle than sheep but for two silages (Silage 1, Subterranean clover: 0.631 vs 0.589; Silage 5, Annual ryegrass/oats, early cut: 0.761 vs 0.702) whereas in Experiment 2 DOMD was lower for cattle than sheep for one silage (silage 21, maize: 0.645 vs 0.691, s.e.d. = 0.019). Conclusions and Implications Since there was no clear trend for sheep to digest higher quality feeds better than cattle or for cattle to digest lower quality feeds better than sheep, we conclude that, at least for silages made from forage, sheep-derived values for digestibility should, in most instances, be applicable to cattle.