Untersuchungen zur verzögerten Ovulation beim Rind
Delayed ovulation in dairy cattle – a field study The aim of the present study was, to analyze the incidence of delayed ovulation in dairy cattle and to evaluate its influence on the conception rate. The examinations were carried out on 304 animals (293 cows and 11 heifers) of the breeds Swiss Brown (65%), Holstein (26%) and Simmental (9%). The animals were kept on 49 different farms in the area of the Artificial Insemination Center Rinderunion Baden-Württemberg e.V. (RBW). After the artificial insemination, the internal and external symptoms of estrus were documented in a protocoll, followed by an ultrasound check of the genital tract. During the check the number of follicles on the ovaries were counted, and after measuring the follicles’ diameter the average diameter was calculated. Twenty-four hours later all animals were checked again by ultrasound and checked for a possible ovulation. If no ovulation was observed, the animals were checked again 7–14 days later for the presence of a corpus luteum. The first check of the group was done on more than half of the animals (53%) after the first artificial insemination. The total percentage of animals with delayed ovulation was 46.1%. The pregnancy rate of the group of animals with spontaneous ovulation was 48.8% versus 34.2% from the group with delayed ovulation (difference p>0,05; Chi-Square analysis). The best pregnancy rate of the group of animals with spontaneous ovulation was achieved during the first and second artificial insemination (50.0% and 53.3%). The intervall in days between the date of the delivery and the date of the first insemination had no significant influence on the incidence of delayed ovulation. Likewise no influence of the number of inseminations (1, 2, 3, etc) could be observed. The percentage of animals with delayed ovulation was lowest in the 3rd lactation (33.3%) and highest in the group with 5 lactations and more (54.0%). 63 About half of the animals (143; 49.6%) were inseminated between 11 and 20 hrs. after observation of the estrus onset. A quarter of the animals were inseminated just 21-30 hrs. after the observation of the estrus and by the analysis of the delayed ovulation it was not possible to find a significant difference between the groups. The intensity of the estrus had no relation to the incidence of delayed ovulation. The conception rate from 161 animals with spontaneous ovulation was not related to the time of insemination. The group that was inseminated in the first 10 hrs. after the observation of estrus had a tendency to show the best results. A second insemination (double insemination) was done on 46 of the animals that showed a delayed ovulation. The pregnancy rate of this group was 37.0% and not significantly different from the group with delayed ovulation and single insemination. The results of this study demonstrate that the delayed ovulation is a frequent phenomenon which cause a decrease in the conception rate.
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