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Abstract
A similar proportion of herds in the Wellington-Hawke's Bay (W.H.B.) and the Taranaki (Tar.) Herd Improvement Associations (H.I.A.) used A.B. in the 1971 season (53% v. 50%). In both Associations the proportion of herds which used A.B. increased with increasing herd size. A higher proportion of cows in these herds were reported in calf to A.B. in the W.H.B.H.I.A. (63% v. 52%) because herd owners submitted a higher proportion of their herd for insemination (78% v. 68%) and used A.B. for a longer period (51 days v. 36 days). In the Tar. H.I.A. 29.3% of the A.B. users with 100 to 149 cows used the service for only 4 weeks or less, whereas the comparable figure in the W.H.B.H.I.A. was 4.1%. The effects of these two differences were slightly offset by a lower conception rate (C.R.) in the W.H.B.H.I.A. (62.4% v. 68.3%), but this lower C.R. was partly due to the negative correlations found between C.R. and the proportion of the herd submitted for insemination and between C.R. and the period of A.B. usage. These effects may be due to a higher incidence of incomplete records inflating the apparent C.R. in the Tar. H.L.A.
If other Associations had been as effective as the W.H.B.H.I.A. in encouraging A.B. users to use A.B. intensively, the numbers of cows inseminated would have increased by 9% and the numbers of cows reported in calf to A.B. by 8%. All Associations had considerable potential to increase sales by encouraging herd owners to use A.B. intensively. The marked differences in A.B. usage between Associations suggest that mating management, education, and methods of charging should all be investigated as avenues for increasing the effectiveness of the A.B. service as a method of achieving efficient herd improvement through breeding.
