Feeding behaviour, food intake and milk production responses of lactating dairy cows to diets based on grass silage of high or low dry-matter content, supplemented with quickly and slowly fermentable energy sources

Abstract

AbstractTwelve dairy cows in early lactation were offered low (L; 215 g/kg) or high (H; 449 g/kg) dry matter(DM) content silages, prepared using material from the same sward. In addition, all animals received 9 kg/day, of supplements based on barley (B), sugar-beet pulp (SB) or a 50: 50 mixture of the two (B: SB), in two equal portions at 07:30 and 14:30 h. The six treatments were offered in an incomplete Latin square design. Mean intakes of H (14·4 kg DM per day) were significantly higher than intakes observed for L (10·0 kg DM per day) (P < 0·001). Within silage type, highest intakes were observed for cows receiving the SB supplement (P < 0·01). Higher intakes of H were reflected in higher total milk yield (P < 0·05) as well as fat (P < 0·05) and protein (P < 0·01) yield. Milk protein concentration was greater for animals receiving silage H (P < 0·001), with lower values being observed for animals consuming SB (P < 0·05), within silage type. Time spent eating, duration and number of meals were similar for either silage and the higher intakes of H silage reflected greater intake rates (g DM per min) (P < 0·001) resulting in larger meal sizes (P < 0·001). All chewing indices (time spent eating silage, ruminating and total time chewing per kg DM ingested) were greater for the L silage (P < 0·001). It is concluded that the benefits in forage intake with higher DM grass silages, for high yielding dairy cows, are associated with consequential benefits in milk yield and milk protein content. The most likely explanation for the greater intakes is a faster particle breakdown in the rumen allowing larger meal sizes before animals became constrained. The higher intakes of silage when animals consumed the SB supplement may be due to a slower rate of fermentation of the supplement, which was more closely matched to that of silage. Although not significant there was a tendency for differences in silage intake between animals receiving B compared with SB supplements to be greater for animals receiving the H silage suggesting that supplementation strategies to ensure optimal forage utilization may differ for silages of differing DM content.