The effect of plane of nutrition during rearing on growth, production, reproduction and health of dairy cattle. III. Milk production during the first three lactations

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Abstract
1. The fat-corrected milk yields and butterfat and solids-not-fat percentages of the milk of heifers reared on the four planes of nutrition described in part 1 of this series are compared, i.e. high high (HH), high low (HL), low low (LL), low high (LH). 2. The most significant feature of the F.C.M. yields was the poor performance of the HL group in each lactation. When variability due to differences in lactation length had been eliminated the yields of the HL group in the first and second lactations were found to be significantly lower than those of the other treatment groups. 3. In the first lactation the mean B.F. percentages of HH, LH, HL and IX animals were respectively 3·92, 3·85, 3·81 and 3·74. These differences were significant at the 5% level. When the weekly yields and percentages of the HH and LL groups were compared it was found that the difference was almost entirely confined to the first 6 weeks of lactation. In the second and third lactations the mean B.F. percentages of all groups were similar. 4. Only in the second lactation were the S.N.F. percentages significantly different between groups. No explanation can be offered. 5. A comparison of the live-weight changes of HH and LL animals following successive calvings showed that recovery by the LL animals was most rapid immediately following first parturition and also during the first and second dry periods. 6. The plane of nutrition during rearing had no apparent effect on the pattern of change in milk yield and composition between first and third lactations, except that HH animals showed a more uniform rate of fall in S.N.F.% between one lactation and the next compared with the other three groups. Heifer lactations were longer and the milk had higher contents of B.F. and S.N.F. than later lactations. 7. The estimated feed costs of the rearing from birth to first calving of the HH, LH, HL and LL animals were markedly different. 8. The results are discussed in relation to practice.