Incidência da retenção de placenta e as consequências na produção de leite e na eficiência reprodutiva de vacas holandesas / Incidence of Retained Placenta and the Consequences on Milk Production and Reproductive Efficiency of Holstein Cows

ABSTRACT

Background: Retained placenta (RP) is failure on fetal membranes expulsion in first 12 h postpartum. RP promotes delay in uterine involution and resumption of ovarian postpartum activity, besides increasing risk of uterine infections, being the major reason for low fertility of dairy cows. There are many treatments for RP however there are controversies about the efficacy of these methods, thus limited treatments effectiveness emphasize the importance of RP prevention. This study aimed to evaluate the effects of parity and calving season in RP incidence, in milk production and in calving to conception interval (CCI), as well as RP effects on these variables. Materials, Methods & Results: Data were collected at a farm located in Rio Paranaíba city, Minas Gerais state, Brazil during 2012, whose herd was composed by 700 Holstein dairy cows producing 32 kg of milk production per day. Calving of 291 cows was registered during the experiment period. To diagnose RP occurrence, cows were observed immediately after calving, and when was possible also during calving, and those cows that had not eliminated all of placenta until 12 h after fetal expulsion was considered with RP. The effects of parity and calving season on RP incidence were analyzed by logistic regression, and the effects of parity, calving season and RP occurrence on milk production and on CCI duration were evaluated by analysis of variance, both using SAS program. The incidence of RP in herd was 13.75% (40/291). The RP incidence was not affected by parity and calving season, however there was a tendency (P = 0.066) of lowest incidence of RP for calvings that had occurred during winter. The effects of parity, calving season and RP occurrence on milk production adjusted to 305 days of lactation were not verifi ed (P > 0.05). CCI duration was infl uenced (P = 0.007) by parity, cows with three or more lactations had higher interval from parturition to conception. The effects of calving season (P = 0.001) and RP occurrence (P = 0.043) were also detected on CCI duration. Calvings that had occurred during summer resulted in signifi cant increase on CCI. Cows that developed RP had an interval from parturition to conception around 27 days longer than cows without RP. Discussion: Results of present study shows the negative effect of RP on reproductive efficiency of dairy cows, without compromise milk production. The increase on parity tends to increase the probability of RP development, these can be assigned by the fact that multiparous could have less efficient immune system when compared to primiparous, although this was not confirmed by the present study. The effect of calving season on CCI evidence that heat stress can damage cows postpartum recovery and, consequently delay conception, fact associated with higher CCI found for cows that had calving during summer. The incidence of RP and milk production was not affected by calving season, however heat stress in hot seasons of the year can be involve in another reproductive process, like oocyte, early embryonic and of corpus luteum developments, as well as endometrium and hypothalamic-pituitary axis that are sensitive to hyperthermia caused by heat stress. Environmental temperature control, using ventilation and automatic water sprinkling when temperature goes up to 18°C, and efficacy of RP treatment implemented by the farm could justify the absence of detectable effects of parity, calving season and RP occurrence on milk production, however they were not enough to overcome the negative effects of RP on Holstein cows fertility.