There is no information available about the incidence of anestrus and its clinical forms after service in dairy cows in Poland. Thus, the aim of this study was to investigate the incidence of clinical forms of anoestrus after unsuccessful artificial insemination in dairy cows based on ultrasound examination. The study was carried out on 1543 Polish Holstein-Friesian cows in 8 dairy herds in north-east Poland over a three-year period. Cows were examined for pregnancy on day 35 after AI using a Honda 1500 portable ultrasound scanner equipped with a 5 MHz linear-array transducer. Cows diagnosed as pregnant were re-examined on day 45. Of the 1543 inseminated cows, 408 (26.4%) showed no estrus signs and were diagnosed not-pregnant by ultrasonography, 328 (21.3%) returned to estrus within 35 days, and 807 (52.3%) were pregnant via artificial insemination. The incidence of anestrus after service in non-pregnant cows varied among herds from 10.3% to 32.9% of cows (p<0.05). Based on ultrasound examination silent heat was diagnosed in 324 (79.4%), corpus luteum pseudograviditatis in 36 (8.8%), ovarian cysts in 26 (6.4%), and ovarian afunction in 22 (5.4%) of 408 anestrous, non-pregnant cows. The results of this study showed that the incidence of anestrus after service in dairy herds in North-East Poland was high. The most prevalent clinical form of post-service anestrus was silent heat.

Previous studies have compared the effectiveness of dinoprost and cloprostenol in cows yielding conflicting results. The aim of our study was to evaluate the efficacy of single treatment with cloprostenol or dinoprost on estrus and reproductive performance in cows with unobserved estrus after service. The study was conducted over four years in two dairy herds of Polish Holstein Frisian cows under a herd health program with an average milk yield per cow over 9000 L. Cows (n=523) diagnosed ultrasonographically as non-pregnant and with a corpus luteum were randomly assigned to be treated with either cloprostenol (n=261) or dinoprost (n=262). The estrus detection rates after administration of cloprostenol or dinoprost were 59.4%, and 57.6%, respectively. The difference between both groups was not statistically significant (p>0.05). Distribution of observed estrus did not differ between cloprostenol and dinoprost. There were no differences (p>0.05) between cloprostenol and dinoprost in conception rate (65.2% vs. 66.2%, respectively) and pregnancy rate (57.5% vs. 54.9%, respectively). Mean days open were similar in cows of both treatments (177.5 ± 74.6 days vs. 175.8 ± 62.6 days, respectively; p>0.05). In conclusion, data from this study showed no significant differences in estrus detection rates and fertility between cows with unobserved estrus after service treated with cloprostenol or dinoprost. Both products are equally useful for the treatment of non-pregnant dairy cows with anestrus after service within a reproductive herd health program.