THE INFLUENCE OF THE FAT CONCENTRATION OF THE DIET ON THE RESPONSE BY DAIRY-COWS TO BODY CONDITION AT CALVING

Twenty-four Friesian dairy cows were divided into two groups of 12 between 12 and 18 weeks prior to calving and fed to achieve condition scores at calving of 3.2 (F) or 2.3 (T). For the first 11 weeks of lactation, six cows from each group (H) were given daily 9 kg of a high-fat compound (acid ether extract (AEE) 96 g/kg dry matter (DM)), 3 kg molassed sugar-beet pulp and hay ad libitum. The other six cows in each group (L) were given 10 kg of a low-fat compound (AEE 29 g/kg DM), 2 kg sugar-beet pulp and hay ad libitum. Allowances of compound and sugar-beet pulp were designed to provide equal amounts of energy, neutral-detergent fibre and protein. The fat source used in compound H was a calcium salt of palm acid oil (Megalac(R)). DM intake was not affected by treatment but fat intake was significantly higher on diet H (P < 0.001). Group TH had higher intakes of digestible energy (DE) than group FH (249 v. 229 MJ/day; P < 0.05), but condition at calving did not affect DE intake with diet L (FL = 230, TL = 233 MJ/day). Milk yield was not significantly affected by treatment, although cows in group TL tended to yield less milk than other groups (28.3, 27.3, 28.0 and 24.3 kg/day for FH, FL, TH and TL respectively). The concentration of milk fat was higher and of milk protein lower with diet H compared with diet L (milk fat 48.1, 42.2, 42.9 and 39.6; milk protein 28.0, 31.0, 28.4 and 30.5g/kg for FH, FL, TH and TL respectively). Loss of condition score was greater for cows in group F (0.65 units) than for those in group T (0.04 units). Within group F, loss of condition tended to be greater with diet L. It is concluded that the increased intake of fat with diet H tended to decrease loss of condition in cows that were fat at calving but increase milk yield in cows that were thin at calving. It also tended to increase milk fat concentration but decreased milk protein concentration.