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Journal of Dairy Science Vol. 53 No. 6 752-756
© 1970 by American Dairy Science Association ®
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Changes in Reproductive Performance in Dairy Herds Using the Herd Reproductive Status System1

J. H. Britt and L. C. Ulberg

Department of Animal Science, North Carolina State University, Raleigh 27607

ABSTRACT

Analysis of data for 66,492 cow-months from 1959 through 1967 revealed certain changes in reproductive performance for the North Carolina Institutional Breeding Association herds using the Herd Reproductive Status system. The average days open for cows conceiving and average monthly per cent of the herd open over 100 days (problem cows) decreased from 125 to 105 days and 13 to 8 per cent, respectively. The average Herd Reproductive Status increased from 58 in 1959 to 74 in 1967. Services per conception, average days open for problem cows and average days open for reproductive culls did not change significantly. Individual herd changes in reproductive performance differed. Seasonal changes in Herd Reproductive Status for the 9 years showed an average high of 77 ± 1 (Mean ± SE) in April contrasted to a low of 65 ± 2 for both August and September. Per cent of the herd conceiving each month showed a similar seasonal fluctuation with an average high of 11% in March and low of 4% in August. Simultaneous increases in production per cow per day occurred with decreases in average days open for cows conceiving and increases in Herd Reproductive Status. These improvements in reproductive performance are attributed primarily to changes in managemental rather than physiological factors.

FOOTNOTES

1 Paper no. 3021 of the Journal Series of the North Carolina State University Agriculture Experiment Station, Raleigh.






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Copyright © 1970 by the American Dairy Science Association ®.