Post-peak supplementation of pasture fed dairy cows with sulla and maize silages

Abstract

A trial was carried out at Dexcel in Hamilton to investigate the effects of silage supplementation of grazing dairy cows post-peak lactation. Forage mixtures used in the four week trial were based on previous trial results and information from in vitro and in sacco incubations. Sulla and maize silages were used to supplement pasture and to meet minimum requirements for protein. Five groups of ten cows were grazed on a restricted daily allowance of 18 kg dry matter (DM) pasture/cow to simulate a summer pasture deficit, and four groups received sulla silage (S) or maize silage (M) alone or in mixtures of 25M:15S or 15M:25S to make up 40% of total DM intake. A sixth group was given an unrestricted (38 kg DM/cow/day) pasture allowance. The pasture was of high nutritive value and not typical of usual summer conditions, which limited the effects of supplementation in the trial. The restricted pasture allowance resulted in a low level of substitution (0.29) when the silages were fed and substantially increased feed intakes. Although differences in cow responses to the silage mixtures were minor, liveweight and milk production were improved relative to restricted pasture allowance but not for cows given 38 kg pasture DM/ day. The low level of substitution demonstrated the impact of the restricted pasture allowance on cow performance. In sacco data show highest DM degradation rate (k, h-1) when cows were fed pasture with sulla silage (0.08); diets with a high proportion of maize silage were degraded slowly (P<0.01). Supplementation with sulla may increase digestion rate and rumen clearance and reduce the effect of fibre in ryegrass diets. Keywords: dairy cows, maize, pasture, silage, sulla