Effect of a single dose of long acting eprinomectin on bull reproductive performance

The objective was to examine the effects of a single injection of long-acting eprinomectin on performance parameters and semen quality of reproductively-active bulls. To study these effects, 11 bulls were allocated by breeding group and assigned to one of two treatments; injectable doramectin (DOR; Dectomax™, Zoetis, Animal Health, Parsippany, NJ; n = 6; BW = 833 ± 60 kg) or injectable eprinomection (EPR; Longrange™, Merial, Duluth, GA; n = 5; BW = 783 ± 73 kg) at a dosage rate of 1 mL/50 kg of BW. At time of treatment, initial BW, BCS, and fecal samples were taken and a breeding soundness exam (BSE) was conducted. The BSE included a general health and locomotion evaluation, assessment of scrotal tone (ST), scrotal circumference (SC), external palpation of sex organs (scrotum, testes, and epididymis), internal palpation of accessory sex glands, visual assessment of penis and prepuce, and collection of a semen sample via electroejaculation. A drop of ejaculate was placed on two warmed slides, one of which received a cover slip in order to assess progressive motility and the other being stained with Eosin-Nigrosin for assessment of morphology. Morphological abnormalities were classified as primary or secondary and broken down by head, proximal droplet, distal droplet, and tail defects. Following a 46 d breeding season, final BW, BCS, and fecal samples were taken and BSE were again conducted. Results were analyzed using PROC MIXED of SAS. Initial and final BW and BCS did not differ between treatments (P > 0.18). Change in BW, BCS, and ADG during treatment period were also not different between groups (P > 0.32). No differences (P > 0.18) in motility, ST, or SC were noted between treatments. No differences in sperm morphology were noted between treatments. While there was a tendency (P = 0.07) for EPR bulls to have a greater reduction in fecal egg count over the course of the treatment period, this is mostly a function of EPR bulls tending (P = 0.06) to have a greater internal parasite load at treatment administration (DOR = 2.72; EPR = 19.72 eggs/g). Overall, use of long acting eprinomectin for internal parasite control did not have a negative impact on sperm quality and bull fertility over the course of the breeding season. While limitations in observational units are acknowledged, data from this study suggest that a single injection of long acting eprinomectin is not detrimental to bull reproductive function.