Reproductive Responses of Lactating Dairy Cows According to Estrus Behavior and CIDR Uses in a Heatsynch Protocol.

Background: The timed artificial insemination (TAI) protocols have been used worldwide as a first service artificial insemination (AI) breed system as well as to resynchronize cows diagnosed as not pregnant. The benefits associated to Heatsynch are the lower cost of the protocol and the increase in the number of cows detected in estrus. Furthermore, it has been suggested that protocols combining AI after estrus detection followed by TAI could increase overall conception rates, as well as increased AI submission rates. The aim of this study was evaluate reproductive responses of dairy cows submitted to a Heatsynch protocol according the estrus behavior and controlled internal device release (CIDR) uses. Material, Methods & Results: Holstein lactating cows (n = 562) were enrolled in protocol using (CIDR) (1.9 g of progesterone) insertion at (day 0) D0 either a new one, a previous used once (7 days - second use) or twice used (14 days - third use). Based on the detection of estrus and the moment of AI after the CIDR removal, cows were divided into 3 groups: cows showing signs of estrus and therefore AI 36 to 60 h after CIDR removal (EPTAI group; n = 241); cows showing estrus and AI 72 h after CIDR removal (ETAI group; n = 207); and cows that did not show any sign of estrus after CIDR removal and were TAI 72 h later (NoETAI group; n = 335). Previous to the first postpartum insemination (47.01 ± 5.43 days in milk) cows were pre-synchronized using one dose of PGF2α (Lutalyse, Pfizer Saúde Animal, Brazil). At 60 ± 3.52 days in milk (DIM), day 0 of the Heatsynch protocol, cows were subjected to gynecological examination by a Veterinarian, where only those animals considered as healthy cows with no signs of uterine disease were kept in the study. In a subset of animals (105/783; 13.4%) an ovary evaluation was performed by ultrasonography (WED-3000, B-mode, linear array, ultrasound scanner equipped with a 5.0-MHz transducer, Welld, Shenzhen, China) at the beginning of synchronization protocol aiming to check the presence of a corpus luteum (CL) and classify the cows as cycling or not cycling. Ovarian structures were examinated aiming to check the CL presence on day zero of the program in a subset of the cows and pregnancy status was also determined by ultrasonography. Higher conception rates were found in EPTAI and ETAI groups than NoETAI, respectivaly 44.8%, 38.2% and 24.8%. Pregnancy losses were calculating considering cows that were not pregnant at 60-65 days re-check and those that showed signs of estrus before the first pregnancy determination. The CIDR reutilization did not affect the estrus behavior, conception rate or pregnancy losses. In conclusion, reproductive responses in dairy cows during a Heatsynch protocol are not affected by CIDR reutilization and are improved in cows showing estrus signs. Discussion: Cows submitted to Heatsynch protocols that demonstrate estrus signs have increased pregnancy rates and lower pregnancy losses. In addition to that, cows exposed to low estradiol concentrations were more likely to experience subsequent premature luteolysis. Thus, coupled with the estradiol cypionate (ECP) action, it can be postulated that cows showing estrus signs during a timed AI protocol could have a higher ovulation rate. This can assume great importance in high producing dairy herds, since in response to ECP becomes possible to overcome the lower concentrations of estradiol due to high hepatic clearance and catabolism o esteroid hormones. [ABSTRACT FROM AUTHOR]