title: Influence of season on timed inseminations of dairy heifers synchronized by prostaglandin F2 alpha.
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 artificially 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.
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D004973:Estrus Synchronization / Q000187:drug effects*; D005260:Female; D005298:Fertility; D007315:Insemination, Artificial / Q000662:veterinary*; D011247:Pregnancy; D011374:Progesterone / Q000097:blood; D011461:Prostaglandins F, Synthetic / Q000494:pharmacology*; D012621:Seasons; D013997:Time Factors
chemical_list: D011461:Prostaglandins F, Synthetic; D011374:Progesterone