Newsdate: Mon 04 April 2016 – 06:30 am
Location: SACRAMENTO, California

In her latest spring blog post, Dr. Clair Thunes of Summit Equine Nutrition addresses the importance of nutrition during the third trimester of a mare's pregnancy. Since the health of the mare and the foal plus that of future foals are contingent on making sure the pregnant mare consumes enough nutrients to maintain body weight and support the needs of the fetus, the issue of nutrition becomes paramount during the last three months as the mare's pregnancy approaches parturition.

A pregnant mare getting exercise

According to Dr. Thunes, 'pregnant mares must consume enough nutrients to both maintain their own body weight throughout the pregnancy and also to create new tissues, those of the fetus and those that support the pregnancy such as the placenta.

According to Dr. Thunes, "pregnant mares must consume enough nutrients to both maintain their own body weight throughout the pregnancy and also to create new tissues, those of the fetus and those that support the pregnancy such as the placenta. Due to the very small amount of tissue deposition in the first months of pregnancy, providing the mare is in good weight and not working, she can be fed as a horse at maintenance for the first 4 months.However, due to the development of the tissues supporting the pregnancy, starting in month 5 her nutrient requirements change."

Energy to sustain fetal growth

"Fetal growth is greatest during the last 60 days of gestation and therefore traditionally it was not felt necessary to increase energy intake until the 3^rd trimester. However, while fetal growth is greatest in the last trimester, more recent research (Reynolds et al., 1986 and Fowden et al., 2000) has shown that during the 2^nd trimester there is an increased energy requirement for development of placental tissues. Therefore, the guidelines laid out in the 2007 National Research Council’s (NRC) Nutrient Requirements of Horses recommends that energy in the diet be gradually increased starting at the 5^th month of gestation with a greater rate of increase in the last 3 months

Mares who do not gain weight during the last trimester will be utilizing their own body energy stores to support fetal growth. This puts the mare at a disadvantage after foaling when she will need those body energy stores for milk production. Mares who do not receive the necessary energy during this time may foal late in an attempt to have their foals be at the correct weight at foaling. If the mare did not enter gestation with a body condition score (BCS) of 5 or above these energy intakes would need to be increased further in order for her to gain weight and have a BCS of 5 by the 9^th month. The best starting source for the extra energy requirement is from hay, however as the fetus grows the amount of space within the body cavity for the digestive tract becomes proportionally less. Your broodmare may not be physically able to eat the amount of hay that would be required to meet her energy requirement. This is especially true if you are feeding a lower quality hay with a higher proportion of non-fermentable fiber.

If your mare will not physically eat enough hay to meet her increasing energy needs then you will need to turn to other more energy dense feeds such as grains or commercially compounded feeds. The benefit of starting this before foaling is that the mare will have adjusted to this type of diet before reaching the very demanding metabolic state of lactation."

 Protein needs of mare and fetus

"Protein is needed to increase lean body mass so it comes as no surprise that the mare’s protein requirement increases during the last trimester. Interestingly there have been studies (van Niekerk and van Niekerk 1997a) showing that feeding diets deficient in protein may lead to a slower return to ovulation possibly due to lower progesterone concentrations post foaling. This is an important consideration if you are planning on re-breeding your mare. In early pregnancy low protein levels have been linked to lost weight and early fetal loss."

For further information, read Dr. Thunes complete article Feeding the 3rd Trimester Mare, Part I. on her website and learn more about Dr. Thunes's contributions to better horse nutrition.