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Mares Show Changes in Dry Matter Intake in Late GestationBy Kentucky Equine Research Staff · July 28, 2014

Late in gestation, mares have a high demand for energy to support the growing fetus. There is some speculation that the physical presence of the maturing fetus decreases the volume of the intestinal tract, potentially decreasing overall dry matter intake. Other studies refute that theory and suggest dry matter intake is related to energy needs rather than the volume of the gastrointestinal tract.

Thus, it remains unclear whether there is a need to supplement concentrates late in gestation to compensate for the potential decrease in dry matter intake. American researchers* measured body weight, body condition score, and rump fat in mares that were fed hay only or both hay and concentrates.

The study authors identified a number of interesting findings:

  1. Mares supplemented with grain had significantly higher body weight and body condition scores compared with mares fed only hay, but all mares maintained a body condition score of greater than 6, which is appropriate for pregnant mares;
  2. Mares fed hay only lost 1.3% of their body weight, which was unexpected because fetal growth is greatest in the last 60 days of gestation. Thus, a loss in body weight suggests that mares fed hay only did indeed have insufficient energy consumption;
  3. All mares included in the study, regardless of diet, consumed more during the tenth month of gestation than the eleventh month, and;
  4. Regardless of diet, there was no difference in either mare body weight or foal body weight in mares fed only hay or concentrates 12 hours following parturition.

All included mares exceeded the currently recommended energy requirements outlined by the Nutrient Research Council (NRC). The lack of agreement between mare body weight and NRC guidelines supports the need for additional research in gestating mares.

In the meantime, critically analyze your pregnant mare’s actual intake of hay and/or concentrates together with her body condition score both pre- and postpartum to maximize the health of both mare and foal. 

*Winsco, K.N., J.A. Coverdale, T.A. Wickersham, et al. 2013. Influence of maternal plane of nutrition on mares and their foals: Determination of mare performance and voluntary dry matter intake during late pregnancy using a dual-marker system. Journal of Animal Science 91(9):4208-4215.