Abstract
The objectives of current study were to assess the prevalence and risk factors associated with postpartum anestrus in lactating dairy cows in Sylhet region, Bangladesh. A total of 420 postpartum cows of different breed and age were selected randomly from different dairy farms in studied area. Structured questionnaire was used to collect data from farm owner on prevalence and risk factors for postpartum anestrus. Observed heat within 60 days after parturition was considered as normal cyclic cows and others were considered as postpartum anestrus. The prevalence of postpartum anestrus was 36.20%. The study shows that older cows take relatively more time for ovarian resumption. Cow’s having first parity shows cyclicity within 60 days of parturition, and postpartum anestrus increases significantly with the advancement of parity. Postpartum anestrus was significantly higher (P< 0.001) in cows with poor (≤1.0) and excessive (>3) body condition scores (BCS), respectively, compared to those with moderate/optimal BCS (2–3). The postpartum cyclicity in cows within 60 days with a history of normal placental expulsion was significantly higher than in the cows with RFM. Ovarian cyclicity was highest (75.92%) among the cows that were maintained in adequate hygienic conditions and lowest (43.51%) in a poor environment. The highest percentage (88.10%) of cows showed postpartum cyclicity with a history of short lactation length (0-150 days) and resumption of postpartum estrous cycle increases significantly with lactation length. Resumption of postpartum estrus cycles in cows takes more time with a history of minimal (<15 liters) daily milk production than the cow with medium (>15-25 liters) daily milk production. Cows get an adequate feed supply (both concentrate and green grass), which shows a positive effect on postpartum cyclicity. Pre and postpartum complications have a significant (p<0.001) effect on the postpartum cyclicity of cows. Endometritis (81.25%) followed by pyometra (75.76%) were recorded as major reproductive obstacles in ovarian resumption, whereas uterine prolapse (70.59%) followed by abortion (61.54%), milk fever (58.33%), stillbirth (58.33%) and dystocia (57.63%) were the major recorded complications in post-partum phase. The study also revealed that the non-restricted suckling period has a significant (p<0.001) negative effect on ovarian resumption. The risk factors including parity, BCS, placental expulsion, hygienic condition, lactation length, daily milk production and management system were significantly (P<0.01) influenced the postpartum cyclicity. Maintaining optimal BCS of cows, proper hygienic and good management practice, and farmer's training on management of cattle reproduction would improve the number of cows for breeding by 60 days postpartum.

Key words: Cyclicity, Postpartum anestrus, Prevalence, risk factors, crossbred cows.