Hay intake, milk production and rumen fermentation in British Saanen goats given concentrates varying widely in protein concentration

Abstract

About 8 weeks after parturition six multiparous British Saanen goats with permanent rumen fistulas were allocated to three dietary treatments in a random sequence for three successive 30-day periods. The treatments were perennial ryegrass hay ad libitum with 1000 glday of concentrates containing 112 (low-protein, LP), 182 (high-protein, HP) or 255 (very high protein, VHP) g crude protein (CP) per kg dry matter (DM) daily. The CP concentration was increased by substitution of soya-bean meal for cereals. From day 19 of each period, when measurements were made, concentrate allowance was reduced to 850 glday and hay intake was offered at proportionately 0·10 more than consumption in the previous 6 days. Hay intake and milk yield increased linearly with CP in the concentrates, but differences between HP and VHP were small and non-significant. Milk composition was unaffected by the treatments, so yields of milk solids followed the same trends as yields of milk, but these were only significant for solids-not-fat. The digestibility of neutral-detergent fibre, acid-detergent fibre and nitrogen (N) all increased with increasing CP, but significantly so only for N; the digestibility of DM and organic matter was unaffected.

The digestibility of the hay incubated in the rumen was unaffected by the treatments. With increasing N intake, faecal, urine and milk N increased linearly as did apparently digested N but N retention did not follow a consistent pattern. Rumen volatile fatty acids and pH were unaffected but concentration of rumen ammonia and blood urea increased with increasing CP as did rumen fluid dilution rate. The results suggest that, with lactating goats given diets of moderate quality grass hay and concentrates containing soya-bean meal, responses to concentrations of CP greater than about 180 g/kg DM in the concentrates or 140 g CP per kg DM in the total diet are likely to be small.