Effect of grass species and cutting time on in vivo digestibility of silage by horses and sheep

Two simultaneous digestibility trials using total faecal collection were conducted to compare the digestibility of six silages by sheep and by horses. Timothy/meadow fescue (Phleum pratense L./Festuca pratensis Huds., TMF) and tall fescue (Festuca arundinacea Schreb., TF) silages harvested at three different cutting times (19 June, 26 June, and 2 July) in round bales were fed to six rams and six mares according to an unbalanced 6×4 Latin square design with 3-week experimental periods. A 5-day faecal collection period was used for horses and a 7-day collection period for sheep. During the collection periods the sheep and horses were fed at their maintenance levels [42 and 62g dry matter (DM)/kgW⁰.⁷⁵/day, respectively]. The silages were of good fermentation quality as judged from pH, low concentration of butyric acid and ammonia N. When the silages were fed ad libitum, the sheep preferred the TMF silage to the TF silage (P<0.01) and their DM intake decreased with a delay in harvest (P<0.01). The horses avoided eating the thick stems in late cut TF silage. No digestive or behavioural problems occurred in either the sheep or horses during the study. Postponing the harvest decreased the digestibility of both grass species. The digestibility of the TMF silage was significantly higher than that of TF silage cut on the same date. The digestibility values obtained by sheep were higher than those obtained by horses. The organic matter digestibility (OMD) of the early, mid and late cut TMF silages was 673, 567 and 517g/kg DM and 757, 680 and 634g/kg DM in horses and sheep, respectively. The respective OMD of TF silages in horses was 609, 527 and 457g/kg DM and in sheep 740, 669 and 592g/kg DM. Using the digestibility determined by sheep led to overestimation of the energy value of forages in horse feeding. However, since the relationship between these two animals was fairly linear, sheep can be used to determine the energy value of forages for horses. Based on, the level difference in digestibilities, higher nutrient recommendations for horses have been used in some feed evaluation systems. Tall fescue silage seemed to be a suitable feed for both sheep and horses.