Effects of stocking rate on pasture production, milk production and reproduction of supplemented crossbred Holstein–Jersey dairy cows grazing lucerne pasture

Abstract

Effects of stocking rates of 1.6, 2.1 and 2.6 cows/ha on farm efficiency were evaluated using 92 crossbred Holstein–Jersey cows in a completely randomised design for 2 yr in Argentina. A 44.1 ha farm was divided into three farmlets and one spring calving herd was allocated to each. Cows grazed on lucerne based pastures ( Medicago sativa L.) and were supplemented with high tannin sorghum silage ( Sorghum bicolor) produced on farm plus imported concentrates (1.8 t dry matter (DM) concentrate/cow/yr in all treatments). Stocking rate (SR) had no effect on pasture production, quality, persistence or botanical composition. Efficiency of grazing (herbage consumed/herbage allowance × 1000; g/kg DM) increased with increasing SR (P<0.05), being 143 g/kg DM higher for high SR (2.6 cows/ha) than for low SR (1.6 cows/ha). Herbage DM intake and total DM intake/cow decreased as SR increased (P<0.05), but only in mid lactation. Yields of milk and fat/cow/lactation did not differ between treatments, however milk protein yield/cow was lower for medium SR cows (P<0.05) and a tendency (P=0.063) for a decline in milk production/cow at higher SRs occurred. Live weight and body condition score were not affected by SR. As SR increased from 1.6 to 2.6 cows/ha, herbage DM consumed increased by 2.4 t DM/ha/yr (P<0.05), milk yield increased by 5840 kg/ha/yr (P<0.05) and milk solids yield ( i.e., fat plus protein) increased by 443 kg/ha/yr (P<0.05) with no serious animal health or reproductive issues from year round grazing of legume pastures. Results show that the theoretical reductions in milk yield/cow expected at higher SR compared to lower SR were prevented by using supplemental feeds, mainly in early lactation.