Key points are not available for this paper at this time.
Forty-eight Holstein and Guernsey cows were assigned according to age and breed to one of seven groups based on days following parturition. Cows in Groups II to VII received an intramuscular injection of 100 /μg gonadotropin releasing hormone (GnRH) on either 1 or 2, 3 or 4, 5 or 6, 7 or 8, 12 or 13, or 18 or 19 days postpartum, respectively (six cows per group). An injection of the carrier vehicle for GnRH was given to cows in Group I (controls), which included two cows per each postpartum treatment period (12 cows). Prior to treatment, plasma LH increased (P.05) for cows in Groups I, II, III and IV but was significantly increased in cows of Groups V, VI and VII (P.10). The inclusion of both days postpartum and preinjection estradiol-17ß in step-up multiple regression significantly improved the coefficient of determination (R2 = .59) in comparison to either variable alone. Preinjection LH and progesterone, however, did not significantly improve the model.
Kesler et al. (Sat,) studied this question.