Digestibility and plasma glucose and insulin concentrations in athletic horses after abrupt feed changes between grass silage and hay

Abstract

The aim of the study was to investigate effects on digestibility, faecal dry matter (DM) and plasma glucose and insulin levels in standarbred horses in training following abrupt feed changes between grass silage and hay. Five geldings, in race condition, were used. A silage (45% DM) and hay-only diet (82% DM) were fed (11.6 MJ ME/kg DM, 2 kg DM/100 kg BW and day) in a cross-over design. Horses were randomised on diets and the silage and hay was fed in a 9 days pre-period before the start of the experiment. Each experimental period started with an abrupt change of diet. The grass forages (timothy, meadow fescue) were a first cut harvested in the same field on the same day. Total faecal collection was performed the first 48 hours after the feed change. Blood was drawn before and 24 hours after feed change (before the morning feeding). Analysis of variance was performed. The DM digestibility was higher on the silage than on the hay diet (69.5 vs. 65.4 %, SEM 0.9, P<0.01). The plasma insulin concentration increased when horses were shifted to the silage (P<0.01). The 24 h plasma glucose concentration tended to be higher (P=0.09) on the silage compared to the hay diet. In conclusion, within 48 hours after a change between silage or hay diets DM digestibility and glucose metabolism was altered in athletic horses. The suggested alterations in the metabolism need further investigations.