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Journal of Dairy Science Vol. 65 No. 9 1776-1781
© 1982 by American Dairy Science Association ®
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Influence of Season on Timed Inseminations of Dairy Heifers Synchronized by Postagladin F2{alpha}1

E. H. Jaster, B. O. Brodie2 and J. R. Lodge

Department of Dairy Science, University of Illinois, Urbana 61801

ABSTRACT

Sixty-six cycling Holstein heifers were given two injections of prostaglandin F2{alpha} (25 mg intramuscular) at an 11-day interval. Average time of first observation of estrus differed little between July (55.7 ± 5.3 h) and December, 1980 (50.6 ± 5.1 h). Heifers were inseminated artifically at either 65 or 80 h following the second injection of prostaglandin. Synchronized heifers inseminated at 65 h had a higher conception rate in July (9/18; 50%) than in December (3/15; 20%). However, heifers inseminated at 80 h had a similar conception rate in July (9/18; 50%) and in December (8/15; 53%).

Progesterone in blood serum was measured prior to the second prostaglandin F2{alpha} injection before insemination and on day 21 postbreeding. Averages of progesterone for the 65-h group were 3.91 ± .48, .39 ± .07, and 3.80 ± .76 ng/ml in July and 4.25 ± .44, .33 ± .08, and 3.91 ± .63 ng/ml in December for the three collections. Averages for the 80-h group were 3.62 ± .28, 1.06 ± .56, and 3.60 ± .65 ng/ml in July and 2.17 ± .35, .22 ± .07, and 2.77 ± .43 ng/ml in December. An influence of season on response to prostaglandin and timed inseminations in dairy heifers may affect estrus behavior and conception rate.

FOOTNOTES

1 Supported by the Illinois Agricultural Experiment Station as part of Regional Research Project NC—119, Improving Large Dairy Herd Management Practices.

2 College of Veterinary Medicine.






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Copyright © 1982 by the American Dairy Science Association ®.