Reproductive traits, lactation and foal growth in mares fed altrenogest.

The research monitored the effects of altrenogest on lactating mares during postpartum estrus. It concluded that altrenogest could effectively delay estrus in these horses without affecting their fertility, milk yield and composition, or the growth of their foals.

Study Design

• The study consisted of two groups: a control group and a group fed with altrenogest. The dosage of altrenogest was .044 mg per kg of body weight daily for 15 days after the mares gave birth.
• The mares fed with altrenogest (n = 6) were inseminated during their first postpartum estrus following the treatment. The control group mares (n = 6) were inseminated on their second postpartum estrus.

Observations

• Results showed that ovulation occurred earlier (26 +/- 1 days after birth) in the mares treated with altrenogest compared to the control group (36 +/- 1 days after birth).
• The fertility rates did not differ between the control group and the altrenogest-treated group. In particular, 67% of the mares in the control group conceived compared to 100% of the altrenogest-treated group.
• There were no noticeable differences in uterine tone and size or ovulatory follicle size between the two groups.
• The research found that bacterial populations and endometrial epithelial cell height, as collected by uterine cultures and biopsies, were similar in both the treated and control groups seven and fifteen days after birth.
• During the study, blood was collected on postpartum days 7, 11, 15, 19, and 23, and its estradiol-17 beta levels were detected through radioimmunoassay. At the end of the research, it was found that altrenogest-treated mares had a higher concentration of estradiol-17 beta in the serum (P<.05) on day 23 postpartum compared to the control group.
• Daily milk yields, milk composition, and foal growth were found to be similar across both the control and altrenogest-treated groups. Milk yields were determined using the weigh-suckle-weigh method.

Conclusion

• The research concludes that altrenogest can be administered to postpartum mares to delay estrus without impacting fertility, milk yield and composition, or foal development. This suggests that altrenogest could become a reliable tool for managing the breeding cycle of mares without negatively affecting their overall health or their offspring’s growth.