The effect of pre-partum feeding of heifers on milk composition

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Abstract
Summary: The effect of the level of pre-partum feeding of Friesian heifers on the yields and composition of the milk in the subsequent lactation has been investigated using 23 heifers on each of 2 treatments. For 1 treatment, over a period of 6 weeks before calving, generous grazing on good pasture was supplemented with 8 lb/cow daily of concentrates, and for the other only restricted grazing of an already sparse sward was allowed.For the period 3—8 weeks from calving the heifers fed at the high plane pre-partum produced significantly more milk than those fed at the low plane (36·8 compared with 31·9 lb/cow daily). The solids-not-fat (S.N.F.) and fat contents of their milk were also significantly higher (8·71 compared with 8·47%, and 3·72 compared with 3·38%, respectively). For the period 3—14 weeks from calving the effect of milk yield was slightly greater but the effect on composition was less. For the period 3—30 weeks from calving the difference in milk yield remained significant (31·3 compared with 26·1 lb/cow daily), but the average differences in S.N.F. and fat contents over this period (8·63 compared with 8·51%, and 3·75 compared with 3·59%, respectively) were not significant.The heifers fed at the higher plane increased in liveweight before calving at a rate which was highly significantly greater than that of the heifers fed at the low plane. After calving, the heifers which had been on the higher plane remained almost constant in weight during the first 12 weeks whilst the others regained some of their losses, a difference which was highly significant. This recovery was apparently made at the expense of milk yield and composition.