EFFECTS OF FEEDING FODDER BEET AND CONCENTRATES WITH DIFFERENT PROTEIN CONTENTS ON DAIRY-COWS OFFERED SILAGE AD-LIBITUM

In two changeover design experiments, fifteen early- and sixteen late- lactation cows were used to investigate the effects of offering food b eet with ad libitum grass silage and concentrates with different CP co ntent on milk yield and quality. In Experiment 1 (early lactation) cow s were offered no fodder beet (0) or 4 kg DM d-1 (4) in conjunction wi th one of three concentrates containing 159, 191 or 244 g CP kg-1 DM ( L,M,H,). Treatments were therefore IL/0, IL/4, IM/0, IM/4, IH/0 and IH /4. In Experiment 2 (late lactation) cows were offered the same level of fodder beet in conjunction with two concentrates containing 129 and 229 (L,H) g CP kg-1 DM. Treatments were therefore 2L/0, 2L/4, 2H/0 an d 2H/4. In both experiments feeding fodder beet reduced silage DM inta kes (P<0.001) and increased total DM intake (P<0.05 to P<0.001). The s ubstitution rate (r) ranged from 0.46 to 0.59 kg of silage DM (kg-1 fo dder beet DM). In Experiment 1, fodder beet tended to increase milk yi eld, composition and yield of constituents, but the effect was statist ically significant for milk protein content only (P<0.01). In Experime nt 2, milk yields for 2L/0, 2L/4, 2H/0 and 2H/4 were 11.3, 12.1, 11.7 and 12.5 kg d-1 respectively (s.e.d. 0.43, non-significant), fat conte nts were 44.4, 47.3, 44-3 and 46.8 g fat kg-1 respectively (s.e.d. 0.7 3, P<0.001), protein contents were 34.3, 35.6, 35.3 and 36.2 g protein kg-1 respectively (s.e.d. 0.28, P<0.001), fat yields were 494, 574, 5 12 and 579 g fat d-1 respectively (s.e.d. 20, P<0.001) and protein yie lds were 385, 426, 407 and 442 g protein d-1 (s.e.d. 13, P<0.01) respe ctively. Increasing CP in the concentrate significantly increased milk yield in Experiment 1 (23-9, 22-5, 23.5, 23.8, 26.2, 26.5 kg d-1 for 1 L/0, 1 L/4, 1 M/0, IM/4, IH/0 and IH/4 respectively, P<0.05). Higher CP in concentrate also resulted in significantly increased milk prote in yield in early-lactation (P<0.001) and milk protein content in late -lactation (P<0.01) cows. There was a significant interaction between fodder beet and concentrate CP content for milk protein yield (P<0.001 ) in Experiment 1.