Effects of Herbage Allowance on Dry Matter Intake, Efficiency of Grazing,Milk Yield and Grazing Behaviour of Crossbred Holstein-Jersey Dairy Cows Grazing Alfalfa Pastures
The objectives of this study were to research the effects of herbage allowance (HA) on dry matter (DM) intake, milk yield, grazing efficiency and grazing behaviour of dairy cows grazing alfalfa (Medicago sativa L.) pastures, and to compare the estimates of herbage DM intake using either an external intake marker developed from a purified enriched lignin (LIPE®) or the animal performance method, the latter based on calculations of energy requirements.Twenty six spring calving crossbred Holstein-Jersey dairy cows (84 days in milk) were balanced and assigned to either the low HA (Lo-HA; 10.0 kg DM/cow/day) or the high HA treatment (Hi-HA; 14.5 kg DM/cow/day). Cows were offered alfalfa (Medicago sativa L.) pastures at grazing, Sorghum (Sorghum bicolor) silage (3.7 kg DM/cow/day) and concentrates (5.6 kg DM/cow/day). Herbage DM intake was estimated using the sward cutting method, the animal performance method and an indigestible intake marker (LIPE®). Decreasing herbage allowance (HA) decreased
herbage DM intake by 1.1 kg cow/day (P < 0.05), increased the efficiency of grazing by 210 g/kg (P <0.01), increased silage DM intake by 0.3 kg cow/day (P < 0.05), decreased total metabolisable energy intake by 12 MJ ME cow/day (P <0.05), but did not affect total DM intake (P > 0.05). The cows on the Lo-HA treatment produced less milk (-4.1 kg cow/day (P <0.05) and grazed 26 min/day longer (P < 0.05) than cows at the Hi-HA. Herbage DM intake measured with LIPE® was positively correlated with estimates of herbage DM intake from the animal performance method (R= 0.65, P < 0.01).This study showed that cows at the Hi-HA treatment had greater herbage DM intake and milk yield, but had an efficiency of grazing 210 g/kg lower than cows at the Lo-HA in early lactation.