Dairy farmers often debate the importance of liveweight of rising 2 year old heifers and the value of various heifer wintering systems on subsequent production. Lifetime performance of all dairy cows born on the Taranaki Agricultural Research Station have been recorded since 1978 on a computerised data base. This data base was utilised to determine the liveweight gain of heifers and cows over winter and the effects of this on production in the following season. Initial analysis of the data showed a significant (P<0.01) age effect on winter liveweight gain within a mixed age herd of cows. The average liveweight gain over eight years of the older cows (4 yr +) was 3 times that of the rising 2 year olds. Further analysis showed a significant (P<0.05) age effect on the relationship between liveweight at calving and production of milkfat in the following season. Higher liveweight at calving resulted in a greater increase in production for 2 year olds than for older cattle. The conclusion to be drawn from this is that wintering rising 2 yea old heifers separately from older cows to achieve higher liveweight may have beneficial effects on the following seasons production. A field trial in winter 1990 to test this assumption showed the winter liveweight gain of rising 2 year old heifers and mature cows, offered the same herbage allowance, was significantly (P<0.01) higher when wintered separately than wintered as a mixed age herd. Subsequent milk solids production from the two-wintering systems was the same despite different liveweight at calving. Aspects of herd behaviour were suggested as the cause of the nil response.
Proceedings of the New Zealand Society of Animal Production, Volume 51, , 235-238, 1991
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