Supplementation of Dairy Cows Grazing Intensively Managed Tropical Grass Pastures at Two Stocking Rates

Abstract

The effects of stocking rate and level of supplementation with concentrate on cows grazing intensively managed tropical pastures were measured with four treatments: grazing alone at 2.5 head per ha per year (T1); grazing plus concentrate at the rate of 1 kg per 2 kg of milk irrespective of daily yield (T2); grazing plus concentrates at the rate of 1 kg per 2 kg above 10 kg daily (T3); and grazing at 5 head per ha plus concentrates at the same level as cows in T2 (T4). All three supplemented groups (T2, T3 and T4) produced significantly greater yields of milk and fat. Average milk yields (kg, M.E. basis) were 3450, 5568, 4709 and 5462 for cows on T1, T2, T3 and T4, respectively. Cows on the higher level of supplement (T2 and T4) gained significantly more weight over the lactation period than cows on T1 and T3. The effect of the supplement appears to be greatest during the early part of lactation when physiological limitations on the consumption of pasture prevent sufficient nutrient intake to supply demand. Cows on T2 produced only 105 kg more milk than cows on T4, while the expected difference, based on increased pasture availability, was over 455 kg. The reduced difference in level of production is postulated as an effect of excessive pasture growth on both intake and diet selection. While milk production was highest for cows receiving the high levels of supplement (T2 and T4), expected return per lactation in income over the cost of supplements, lime and fertilizer were greatest for T3 (medium supplement). Expected returns on a per ha basis were greatest for T4 with 5 cows per ha. Results indicate that where land costs are high, most efficient use of pasture and concentrate resources may be reached by grazing at the rate of 5 head per ha and supplementing with concentrate at 1 kg per 2 kg of milk.