155 Fertility of sexed semen in Holstein heifers and cows

Abstract

Compared with conventional semen, use of sexed semen decreases the conception rate (CR); therefore, it is important to address the factors that lead to sperm damage. Recently, a novel sexed semen technology was developed for improving dairy cattle fertility (Betthauser et al. 2016 J. Dairy Sci. 99 (E-Suppl. 1), 534). However, there are few reports about the fertility of this novel sexed semen in dairy cattle in Japan. The objective of this study was to compare the CR of traditional sorting semen (S1: flow cytometry/cell sorting) and the novel sexed semen (S2: Sexcel^TM, ABS Global Inc.) in Holstein heifers and cows in Japan. The CR for the first insemination was obtained from 391 Holstein cows and 148 heifers (10.7-17.8 months old) from 14 dairy farms in Hokkaido from June 2017 to April 2019. Semen used for AI was collected from six bulls and packaged into 0.25-mL straws and frozen. Cows inseminated with conventional frozen semen (S3: unsexed semen in 0.5-mL straws) were used as controls. Calving data were collected from 123 cows and 69 heifers that had calved between January 2018 and May 2019. The diagnosis of pregnancy was confirmed using ultrasonography between 30 and 45 days after insemination. The CR and sex ratio were analysed using chi-square test. The average parity number was 1.9 ± 1.1, and average days open was 84.9 ± 20.4 days. The average interval between calving and the first service was 86.2 ± 20.3 days. The average milk yield (at 305 days) was 12 195 ± 1595 kg. All of the animals were inseminated after the onset of standing heat or removal of the tail chalk of natural heats and oestrus and ovulation synchronisation programmes on the farm. Conception rates of heifers of the first service of S1 (n = 54) and S2 (n = 94) were 68.5 and 70.2%, respectively. Conception rates of cows of the first service of S1 (n = 32), S2 (n = 173), and S3 (n = 186) were 56.3, 57.8, and 53.8%, respectively. There were no significant differences in CR between these groups (P > 0.4). The proportion of female calves produced using S1 (n = 61) and S2 (n = 57) was 91.8 and 93.0%, respectively, which was significantly more (P < 0.01) compared with the 50.0% produced using S3 (n = 74). There were no significant differences between S1 and S2 (P > 0.8) in terms of the proportion of calves produced. The results of this study demonstrated that the traditional sorting and novel sexed semen (S1 and S2, respectively) did not differ in terms of the first-service CR and produced considerably more female calves than when the conventional semen (S3) was used. Furthermore, these findings indicate that the use of this novel sexed semen could achieve a sex ratio close to 90% female offspring.