Effects of age and liveweight of dairy heifers at first calving on multiple lactation production
R. C. Dobos A E , K. S. Nandra B , K. Riley B , W. J. Fulkerson C , A. Alford A and I. J. Lean DA NSW Department of Primary Industries Beef Industry Centre, Armidale, NSW 2351, Australia.
B NSW Department of Primary Industries, Elizabeth Macarthur Agricultural Institute, Camden, NSW 2570, Australia.
C M. C. Franklin Laboratory, University of Sydney, Camden, NSW 2570, Australia.
D Bovine Research Australasia, Camden, NSW 2570, Australia.
E Corresponding author. Email: robin.dobos@agric.nsw.gov.au
Australian Journal of Experimental Agriculture 44(10) 969-974 https://doi.org/10.1071/EA03077
Submitted: 27 March 2003 Accepted: 20 November 2003 Published: 25 November 2004
Abstract
This paper reports on both the individual and combined effects of age and liveweight at first calving (AFC and LWFC, respectively) for Australian Holstein–Friesian heifers on multiple lactation production. One hundred and thirty-five heifers were allocated to 1 of 3 AFC treatments. Within each AFC treatment, heifers were randomly assigned to 1 of 3 LWFC treatments. From 16 weeks of age until first calving, heifers in all groups grazed pasture and were provided with supplementary feed when the quantity and quality of pasture was inadequate to meet growth requirements. Mean AFC and LWFC achieved were 25.1 ± 0.121, 29.9 ± 0.11 and 33.9 ± 0.09 months and 498 ± 4.09, 549 ± 5.40 and 595 ± 5.09 kg, respectively. As AFC increased, total production over the first 3 lactations increased. For each month's delay in AFC an extra 56.7 L milk, 1.78 kg milk fat, 1.45 kg milk protein and 3.23 kg fat + protein over the first 3 lactations was produced but by the third lactation the response was minimal. By end of third lactation the remaining heifers that calved at 25.1 months AFC were producing similar amounts to those that calved at the older AFC. As LWFC increased from 498 to 595 kg, production over the first 3 lactations increased. The response to an extra kilogram increase in LWFC was 4.82 L milk, 0.20 kg milk fat, 0.18 kg milk protein and 0.38 kg fat + protein over the first 3 lactations. The greatest benefit was when LWFC increased from 498 to 549 kg. Increasing LWFC from 549 to 595 kg did not significantly increase milk, milk fat and milk protein yields from the second to third lactation. The combined effects of AFC and LWFC indicated that to reduce the negative effects on production due to decreasing AFC, LWFC would have to increase by 7.2, 2.9 and 2.2 kg for each month decrease in AFC (for milk, fat and protein production, respectively). By the end of the third lactation, only 58 heifers remained in the herd. The number of heifers remaining within the 9 groups ranged from 4 to 10. Increasing LWFC while decreasing AFC reduced the chances of a heifer remaining in the herd but this may have been biased by the feeding regime imposed during lactation. Responses to increasing AFC decreased as the number of lactations increased, indicating that heifers calving at younger AFC produce similar amounts to their older herd-mates by the end of third lactation. Increasing LWFC from 498 to 549 kg had the greatest benefits for yield, indicating a possible maximum LWFC of 549 kg for our study. Therefore, the negative effects due to decreasing AFC can be offset in part, by increasing LWFC. However, on-farm resources and ultimately milk price will determine the choice of combination of AFC and LWFC.
Acknowledgments
The authors acknowledge the financial support of NSW Agriculture, the University of Sydney, the NSW Dairy Corporation, the NSW Dairy Farmers Association, Dairy Farmers Ltd, Elanco Animal Health, DEETYA, Semex Australia Pty Ltd, Herd Improvers Australia Pty Ltd, and Wrightsons Seeds Pty Ltd. We also acknowledge the assistance of Dr R. Kellaway, Mr B. Rhees, Ms Y. Lieschke-Mercer, Ms S. Plowman, Mr T. Osborne and EMAI dairy staff.
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