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.
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