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.

Dos sistemas para la alimentación de vacas lecheras pastoreando gramíneas fertilizadas intensivamente

“…The results in this study differ from those of Yazman et al (1979;1982), who reported that supplementation of concentrate, at the rate of 1 kg per 2 kg of milk, increased production over that obtained with supplementation after the 10 th kg of milk. Caro-Costas and Vicente-Chandler (1969) studied effects of concentrate supplementation at the rates of 1 kg per 2.15, 4.30, 6.45 and 8.60 kg of milk produced, using a stocking rate of 2.5 cows per hectare of pasture fertilized with 2,270 kg of 15-5-10/ha/yr.…”

“…These results must be evaluated within the context of the small number of observations involved. However, the results from other studies (Caro-Costas et ah, 1972;McDowell et al, 1975;Yazman et al, 1979;1982) have also suggested that cows grazed at high stocking rates and heavily supplemented with concentrates under similar management conditions, required more services per conception, remained open longer and had longer calving intervals than cows grazed at low stocking rates and fed lower amounts of concentrates.…”

“…Milk production peaked after a mean postpartum interval of 30 days in both treatments. Later peaks, between 30 and 50 days postpartum, were observed by Yazman et al (1979;1982). 'Camoens et al, 1976.…”

“…Under optimal climatic and nutritional conditions immature tropical forages can, in fact, achieve good digestibility. However, a pasture diet will require supplemental energy and in some cases crude protein (CP) to allow for maximum milk production (Caro-Costas et al, 1972;McDowell et al, 1975;Yazman et al, 1979;1982). These additional nutrients can be provided by supplementing with low to moderate levels of dairy concentrates.…”

Revisión histórica y científica sobre el desarrollo de la ganadería de leche en Puerto Rico con énfasis en el ganado pelón

“…El ensilaje de maíz y el heno de alfalfa son altamente utilizados en la industria lechera de EEUU, aportando un alto contenido de energía y proteína de calidad a la dieta de las vacas lactantes (Kezar, 2001;Knowlton y Nelson, 2003;Knowlton y Nelson, 2010). Desafortunadamente, los pastos tropicales maduran rápidamente, reduciendo así su potencial nutricional para producir leche (Yazman et al, 1979). En PR se ha tratado de compensar esta situación mediante el alto uso de alimento concentrado en la dieta de la vaca lechera (Ruiz y Cancel-Medina, 2006).…”