Risk factors for postpartum ovarian cysts and their spontaneous recovery or persistence in lactating dairy cows

Cystic ovarian disease is a major cause of reproductive failure and economic loss for the dairy industry. Many cysts that develop during the early postpartum period regress spontaneously. However, it is difficult to decide at what point it would be more cost effective to treat ovarian cysts than to wait for spontaneous recovery. The objective of this study was to analyze risk factors for the development of the ovarian cystic condition during early and late postpartum, and for its persistence or recovery during the pre-service period in lactating dairy cows. Using multiple logistic regression, we analyzed data derived from 873 lactating dairy cows from a single herd. An ovarian cyst was diagnosed if it was possible to observe a single follicular structure with an antrum diameter greater than or equal to 25 mm in the absence of a corpus luteum in three sonograms performed at 7-day intervals. The cystic condition was denoted as early if the cyst was diagnosed 43-49 days postpartum, and late if detected 57-63-day postpartum. Spontaneous cyst regression before 60-day postpartum was regarded as early cystic recovery. For the early cystic group, there were no significant effects of lactation number, body condition score on prepartum Day 60, at parturition or on postpartum Day 30, or of body condition loss from parturition to 30-day postpartum. Cows calving in summer were 2.6 times more likely to develop ovarian cysts than those giving birth in winter. The risk of having a cyst was 1.9 times higher in cows with an abnormal puerperium. A 1-kg increase in milk yield raised the risk of cysts by a factor of 1.05. A 1-unit increase in body condition score (scale from 1 to 5) from prepartum Day 60 to parturition increased the risk of cyst development 8.4 times. Milk production and lactation number were negatively correlated with spontaneous early cyst recovery. A 1-kg decrease in milk production increased the probability of cyst recovery by a factor of 1.06, and a 1-unit drop in lactation number was associated with a 1.4-fold increased probability of cyst recovery. For the late cystic group, there were no significant effects of abnormal puerperium and body score data, except for a prepartum change in body score. Calving season (Odds ratio: 2.3), lactation number (Odds ratio: 1.36), increased milk production (Odds ratio: 1.05) and increased body condition score during the prepartum period (Odds ratio: 4.3) were all related to an increased risk of ovarian cysts. The probability of having a late cyst was 36.6 times greater in cows with early cysts. These findings suggest that it would be profitable to treat multiparous cows having cysts very early in the postpartum period, while treatment of primiparous cows should be delayed, at least until the end of the pre-service period, to provide the opportunity for spontaneous recovery.