15 Effects of Timed Artificial Insemination Protocol Using Prostglandin F_2α and Estradiol Benzoate on Conception Rate in High-Producing Dairy Cows

Abstract

For several years, milk production per Holstein cow has been increasing while reproductive performance has declined worldwide. Timed AI (TAI) protocols with synchronization of oestrus and ovulation are tools for the improvement of reproductive performance in high producing dairy herds. In protocols for synchronization of oestrus and ovulation, oestradiol benzoate (EB) has been used to increase the number of animals that show oestrous behaviour, synchronize ovulation, and improve conception rate (CR). The objective of this study was to compare a simple oestrus synchronization and TAI protocol using prostaglandin F_2α (PG) and EB with a more complicated TAI protocol or oestrus detection and AI on CR in high-producing Holstein cows. The study was conducted from 2014 to 2016, using 1,036 Holstein cows from 3 commercial dairy herds in central Hokkaido, Japan. The average parity number was 2.6 ± 1.5, and days open averaged 152.2 ± 82.0 days. The average milk yield (305 days) was 11,348 ± 1,619 kg. Oestrus synchronization of cows was achieved using PG followed by EB and TAI (PG was given to cows with a cutoff for CL diameter of >20 mm by ultrasonography; EB (1 mg) was administered 24 h later and AI was carried out 24 to 48 h after EB injection), or by Heatsynch + CIDR [gonadotropin-releasing hormone (GnRH) injection and CIDR insertion at random stages of the oestrous cycle, CIDR removal, and PG injection 7 days later, EB injected 24 h after CIDR removal, and TAI 24 to 32 h after EB injection]. Cows observed in natural oestrus were used as controls. All cows were inseminated after the onset of standing heat or removal of the tail chalk (Paintstik®, LA-CO Industries, Elk Grove Village, IL, USA). Pregnancy diagnoses were performed using ultrasonography between 30 and 45 days after AI. The CR were compared using chi-square test. The CR (no. of pregnant cows/no. of total cows in the treatment group) of the natural oestrus group, PG + EB, and Heatsynch + CIDR cows were 39.2% (302/771), 38.7% (48/124), and 31.2% (44/141), respectively. Overall CR for the 3 groups was 38.0%. There were no significant differences in CR among the 2 groups (P > 0.07). These results show that a simple oestrus synchronization protocol with injection of PG followed by EB can be used effectively for high-producing dairy herds, yielding a satisfactory CR similar to that obtained with the Heatsynch + CIDR protocol or natural oestrus.