EFFECT OF LEVEL OF MEAT-AND-BONE MEAL AND PASTURE TYPE ON MILK-YIELD AND COMPOSITION OF COWS GRAZING TROPICAL PASTURES

An experiment was conducted with Holstein-Friesian cows to determine the effect on milk yield and composition of feeding different amounts of meat-and-bone meal (MBM). Thirty-two cows grazed either tropical grass pastures fertilised with nitrogen (GN) or tropical grass-legume pasture (GL). Cows were offered 2.5 kg DM/day of a molasses supplement incorporating 1 of 4 levels of MBM: 0, 250, 500 or 750 g DM/day. The experiment was conducted over the first 160 days of lactation. With GN pastures, fat-corrected milk (FCM) yield (kg/cow.day) for days 1-160 of lactation was linearly related to the intake of MBM (kg DM/cow.day) and was described by the equation FCM = 14.0 + 1.84 MBM (P < 0.01, R2 = 0.95). Most of this response occurred in the first 100 days of lactation, when significant (P < 0.05) relationships between milk yield, FCM yield and intake of MBM were found. Milk yield and FCM yield of cows grazing grass-legume pastures were increased by feeding MBM, but the FCM response was a mean of 32% less than with the nitrogen-fertilised pasture and non-significant at the 5% confidence level. The following mean values over 160 days were recorded for cows on GN and GL pastures, respectively: milk yield, 15.8 and 17.4 kg/day; FCM yield, 14.6 and 16.7 kg/day; butterfat, 3.54 and 3.69%; solids-not-fat, 8.40 and 8.59%; lactose, 4.91 and 4.95%. It was concluded that a MBM supplement will increase the milk yield for cows grazing nitrogen-fertilised pastures, but only during early lactation.