EN
The aim of the studies was to evaluate an „ex juvantibus” intensity in the rate of a retarded ovulation and possibility to control the retardation using GnRH (Receptal, Dirigestran). The examinations were done in two cowsheds differing by breeding conditions and milk yield. In the cowshed A (good conditions) in which cows received at the day of insemination Receptal or Dirigestran, a percentage of pregnancies icreased by 12% and 9,5%, respectively comparing to control animals. In the cowshed В a significant differences between treated animals and control ones were not found. Receptal or Dirigestran applied at the day of the first insemination after calving increased a percentage of pregnant cows by 17.7% and 15%, respectively (cowshed A) and by about 11% in the cowshed B. Somewhat inferior results were obtained after the use of the drug containing GnRH at 2—4 insemination. In winter in the cowshed A a higher percent of pregnant cows was noted by 17.6% (Receptal) and by 7.7% (Dirigestran) whereas in summer fertility increased after the use of these drugs by 10%. In the cowshed В in winter fertility increased by 6.6% (Receptal) and by 8.3% (Dirigestran). In summer differences in fertility between control and treated groups were not observed. The therapy of non-symptomatic sterility with hormones may give a positive results in cowsheds in which zoohygienic condition and nutrition of animals is improved.