Effect of forage and energy level of diets on the intake and composition of cow milK
1999
Almeida, M.A. | Silva, F.S. | FerrÆo, L. | Ribeiro, J.M.R. | Nunes, A.F.
Generelly, when dairy cows are fed forage ad libitum, the increase of concentrate leads to a decrease of forage intake and changes in rumen fermentation; these changes may cause variations in the production and composition of milk fat and protein. This was observed in 2 trials (T) of 3 groups of 7 Holstein frisian cows which were fed 3 types of low (a), medium (b) and high (c) concentrate diets (35, 70 and 105 MJ/day). All these diets were supplemented ad libitum with Italian rye- grass in T1 (June to October) and with corn silage in T2 (November to March). No significant differences (P0.05) for silage DM intake (Kg/day) were observed. In T1, diets A1, B1 and C1 presented the following results: 6.2, 6.5 and 6.4 while in T2 cows fed A2, B2 and C2 presented the following results: 10.2, 8.57 and 8.5. However, the DM total intake in T1 (8.78, 11.56 and 14.13) and in T2 (13.69, 12.86 and 16.37) increased (P0.05) with the concentrate level. In T1, the concentrate level did not influence milk production which presented an average of 18.14 ñ 0.95 Kg/day and was composed of 2.47 (g%) ñ 0.02 of protein and 2.69 (g%) ñ 0.04 of fat. On the other hand, in T2 only milk weight increased (P0.05) in c2 (24.1 vr. 16.4 kg); fat and protein values (g%) were 2.9 ñ 0.14 and 3.6 ñ 0.27 and did not show differences comparatively to A2 and B2. On the contrary, fat and casein composition was influenced by the concentrate level. In C2 comparatively to A2, fat has lower values of short chain fatty acids (5.7 vr. 6.3%) and lower values of long chain fatty acids (33.4 uvr. 36.2%) and a increase of the acids C12 to C16. In relation to protein, there is an increase of S1cn (41.8 vr. 35.3) and decrease of ácn (56.1 vr. 62.5) and kcn /1.7 vr. 3.7)
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