@conference {40316,
	title = {Plasma hormone concentrations in pasture-fed Friesian cows treated with recombinantly-derived bovine somatotropin (bST)},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {51},
	year = {1991},
	month = {Jan},
	pages = {235-238},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	abstract = {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.  },
	issn = {1176-5283},
	author = {McCutcheon SN and Hoogendoorn CJ and Lynch GA and Wickham BW and Breier BH and Gluckman PD}
}
