It’s no secret: Equine obesity levels are on the rise. While all overweight horses need to drop a few pounds, you might want to pay special attention to the particularly chubby broodmares gobbling up grass in your pastures—especially if you’re hoping for a foal this spring. Researchers have confirmed that obesity appears to have negative effects on mares’ follicles and oocytes.

Dawn Sessions-Bresnahan, MS, PhD, an assistant professor in the Berry College Department of Animal Science, in Mount Berry, Georgia, worked with colleagues at Colorado State University, in Fort Collins, to determine if increased body weight affected reproduction.

The researchers used 16 nonlactating mature mares with body conditions of either 5.1 (10.5% body fat) or 7.9 (16.2% body fat) on the 1 to 9 scale. The former mares were considered controls and the latter ones were classified as obese. When the researchers detected a follicle greater than 35 millimeters with uterine edema (fluid swelling indicative of impending ovulation), they administered a gonadotropin-releasing hormone analog to help the follicle mature.

Approximately 22 to 24 hours after administration, the team collected the oocytes (immature egg cells), granulosa cells (which surround developing ovarian follicles), and follicular fluid (which is released during ovulation) from each follicle. On the same day, the team collected blood samples prior to morning feeding to evaluate mares’ levels of glucose, insulin, leptin, adiponectin, and other metabolites