Investigating the length of postpartum anestrous and the causes of it's prolongation in Sistani cattle

The aim of present study was to evaluate the length of post-partum anestrus in Sistani cows of Zahak research station and also to investigate the causes of prolongation of post-partum anestrus in this breed. The data included the date of 1188 calvings and the first post-calving estrus were extracted from the farm archive. The average calving-first estrus interval was calculated in Excel and considered as the length of post-partum anestrus. Comparison of average length of post-partum anestrus in different decades was done using One-way ANOVA test in SPSS software. To determine the causes of prolongation of post-partum anestrus, all cows that did not show estrus more than 2 months after calving at the period of the study (N: 33) were evaluated in two stages of rectal ultrasound, 12 days apart. The average length of post-partum anestrus for 1188 calvings was 126.5 ± 90.1 days. Among the anestrus cows examined ultrasonographically, 75% did not have corpora lutea in both examinations and had inactive ovaries, and 25% had corpora lutea in one or both stages, and silent estrus was considered the cause of anestrus. None of the anestrous Sistani cows had ovarian cyst or pyometra. According to the results of the present study, the period of post-partum anestrus in Sistani cows of Zahak research farm is long and the main cause for this prolongation is the delay of the ovary in returning to cyclic activity, In addition, silent estrus is the cause of some cases of anestrus.