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Stage of Estrous Cycle, Time of Insemination, and Seasonal Effects on Estrus and Fertility of Holstein Heifers after Prostaglandin F₂¹

Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506

ABSTRACT

Stage of estrous cycle, time of insemination, and season of the year were examined for their influence on estrus and fertility of 223 Holstein heifers after prostaglandin F₂ (treatment). Heifers treated during early stages (days 5 to 8) of the estrous cycle had shorter (by 11 h) and less variable intervals to estrus compared with treatment of heifers during late stages (days 14 to 16) of the estrous cycle. A greater proportion of heifers in the early cycle treatment (79/81, 97%) were in synchronous estrus (20-h period) after treatment compared with the late cycle treatment (71/86, 83%). Conception rates were lower when early cycle heifers were inseminated at 80 h after prostaglandin F₂ than when inseminated according to estrous detection and also lower as compared with late cycle heifers inseminated at 80 h. No differences in fertility were observed for late cycle heifers inseminated at 80 h compared with those inseminated according to estrous detection. Season of the year had no influence on intervals to estrus or on proportion of heifers expressing estrus after prostaglandin F₂, regardless of stage of estrous cycle. Conception rate during winter, however, was higher in early but not late cycle heifers inseminated after prostaglandin F², as compared with fall or spring. Variability of interval to estrus and of fertility after inseminations by appointment at 80 h appears to be due to stage of estrous cycle at time of prostaglandin F₂ treatment rather than season of the year.

¹ Contribution No. 84-127-J, Kansas Agricultural Experiment Station, Manhattan, KS 66506.

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