FERTILITY OF ESTRUS SYNCHRONIZED DAIRY HEIFERS TREATED WITH CAP ALONE OR IN COMBINATION WITH ESTRADIOL BENZOATE . HCG OR GnRH

In 1970 , 1971 and 1973 in a single dairy farm a total of 20 6 German red pied heifers were subjected to synchronization treatment. Treatment schedules consisted of chlormadinone acetate (CAP) given orally daily for i8 days io mg/day). Half of the animals were used to measure the effect of additional hormones on conception rate. 3r heifers received 5 mg of estradiol benzoate, 35 animals, i,ooo IU of HCG and 30 heifers 1.5 mg of GnRH 2j , 6 and hours before the first insemination, respectively. Estrogen treatment had no-effect on the pregnancy rate (30 .8 p. 100 vs. 33 . p. ioo), treatment with i,ooo IU of HCG decreased the conception rate after insemination in the first post-treatment estrus (j 3 p. 100 vs. 3i.! p. 100 ; P < 0.5 ). An improvement of the pregnancy rate was obtained after injection of 1.5 mg of GnRH (36.! p. 100 vs. 63. p. 100 , I’ < 0.5 ). In heifers treated only with CAP it seems that the occurrence of marked estrous symptoms and the time of ovulation is related with the pregnancy rate. Post-estrual bleeding had no detrimental effect on conception rate. About 80 p. IOO of all experimental heifers, which failed to conceive in the first post-treatment estrus, showed a regular estrous cycle (r 9-2 days). There was no difference in the average length between the first and second post-treatment earous cycles.