Physiological and nutritional adaptation of broodmares during the transition from late pregnancy to early lactation: Digestibility changes and the role of uNDF as an internal marker.

Nutritional management of broodmares during late pregnancy and early lactation is essential for maternal health and foal well-being. This study evaluated a targeted dietary adaptation during the transition from late gestation to early lactation, monitored nutrient digestibility, and applied undigested neutral detergent fiber (uNDF) as an intrinsic digestibility marker. A prospective nutritional study was conducted on 11 clinically healthy Trotter broodmares (3 primiparous, 8 multiparous) monitored under standardized conditions. Mares received a forage-based diet with controlled starch intake and a concentrate adjusted to the physiological stage. Feed and fecal samples were collected to determine nutrient digestibility using uNDF. The dietary protocol was effective, with no evidence of impaired intestinal fermentation. Digestibility values remained within ranges reported for healthy horses (organic matter 56–63%, crude protein 69–80%, starch 79–86%, neutral detergent fiber 39–42%), suggesting no marked impairment of nutrient utilization. Based on fecal analysis, peripartum changes in fermentation were observed, particularly on the day of parturition, but remained within physiological limits. A slight, but significant, increase in fecal dry matter (+ 3%) suggested a predisposition to postpartum constipation. Starch digestibility increased during parturition (up to 87%), possibly associated with a transient reduction in gastrointestinal transit rate, while fiber digestibility remained stable. Digestibility estimates obtained using uNDF were consistent with values reported using total fecal collection, supporting its applicability as a non-invasive marker. These findings support gradual dietary transitions in broodmares and show that uNDF was successfully applied as an internal marker to verify the changes in nutrient digestibility observed during the study.