Needle-free injection device for administration of cloprostenol to induce luteolysis in lactating dairy cows

The objective of this study was to evaluate the effectiveness of using a needle-free injection system for the intramuscular delivery of cloprostenol in lactating dairy cows. Twenty-six lactating Holstein dairy cows were randomly assigned to 1 of 3 treatments: (1) a single needle-free injection of 2 mL (0.5 mg) cloprostenol i.m. (NFI-PG; n = 10); (2) a single conventional needle injection of 2 mL (0.5 mg) cloprostenol i.m. (NDL-PG; n = 10); or (3) a needle-free injection of 2 mL physiological saline i.m. (CNTL, n = 6). Outcome measurements included corpus luteum (CL) size and blood flow via ovarian ultrasound, as well as progesterone (P4) and plasma cortisol (CORT) concentrations, all assessed at predetermined time points. Data were analyzed using a mixed model with the cow as the experimental unit, and fixed effects of group, day, and the group-by-day interaction. No significant differences were observed in P4 and CL outcome measures between the NFI-PG and NDL-PG groups. Both NFI-PG and NDL-PG cows exhibited similar decreases in P4 across all time points. In contrast, no significant changes in P4 concentrations and CL measures were observed in the CNTL group. Thus, the CNTL cows exhibited significantly higher P4 concentrations from 8 to 92 h compared with the NFI-PG and NDL-PG groups. Regression of CL, as indicated by a decrease in CL volume, blood flow, and P4 concentrations, was observed following both NDL-PG and NFI-PG injections, but not in the CNTL group. The NFI-PG cows had significantly lower CORT levels throughout the entire time period compared with both CNTL and NDL-PG cows. In conclusion, the use of a needle-free injection system for cloprostenol delivery resulted in similar outcomes to conventional needle injections, with comparable decreases in P4 and CL measures in lactating dairy cows and lower CORT concentrations.