New Zealand Journal of Agricultural Research abstracts
Predicting calving curves for herds using controlled breeding programs
K. L. Davis
Dexcel Limited
Private Bag 3221
Hamilton, New Zealand
G. A. Anderson
K. L. Macmillan
Department of Veterinary Science
University of Melbourne
250 Princes Highway, Werribee
Vic 3030, Australia
Abstract A database of gestation lengths (GLs) was generated
over 2 years in three large dairy herds which had used controlled breeding
programs (CBPs). This was compared with a database comprising a single calving
season of 124 seasonally calving dairy herds using conventional artificial
insemination programs (CAIs). Multiphase regression was used to derive two
corrected databases by excluding outlying values of gestation length. The
mean gestation length derived from the CBP database was slightly shorter
than that of the CAI database (280.80 days, n = 775 versus 281.87
days, n = 1986; P < 0.001), but the two databases had similar
variances (SD = 4.21 and 4.12 days, for CBP and CAI respectively; P
= 0.36). The results from the multilevel analysis showed a mean difference
in gestation length of 0.94 (SE 0.50) days; (P = 0.06) between CAI
and CBP. The mean gestation length and its SD from the CBP data were used
to predict calving curves in herds using CBPs which could be compared with
observed calving data. The observed and predicted calving patterns generated
for two farms were not significantly different (P = 0.37 and 0.31).
The accuracy of the predictions was critically dependent on the completeness
and accuracy of conception data and details for cows induced to calve prematurely.
Keywords gestation length; controlled breeding programs;
dairy; predicted calving patterns
A02035 Received 20 June 2002; accepted 3 March 2003; published 30 June
2003
New Zealand Journal of Agricultural Research, 2003, Vol. 46: 97-104
0028-8233/03/4602-0097 $7.00/0 © The Royal Society of New Zealand
2003Predicting calving curves for herds using controlled breeding programs
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