Reasons for performing study: There is a paucity of information on factors that influence placental development in the horse.
Hypothesis: Changes in nutrition, particularly around the time of proliferative placental growth, can affect development of the placenta and fetal growth.
Objective: To investigate the effects of 2 planes of nutrition and an unforeseen infection-mediated nutritional insult on placental and fetal development in the mare.
Methods: Twenty maiden Thoroughbred fillies, age 3 or 4 years, mated to one Thoroughbred stallion, were maintained on either High or Moderate food intake throughout pregnancy. In mid-gestation all the mares unexpectedly became infected with Streptococcus equi and suffered varying degrees of weight loss as a consequence. Gross and stereological measurements of the placenta and measurements of foal birthweight, crown–rump length, ponderal index and plasma IGF-1 concentration were made at term.
Results: Gains in bodyweight during gestation were significantly higher in the High vs. the Moderate nutrition groups. Placental and fetal growth parameters were not influenced by the plane of nutrition. However, transient weight loss in mid-gestation from acutely reduced food intake resulted in morphological changes to the allantochorion and decreased foal birthweight.
Conclusions: Excessive weight gain during gestation in maiden Thoroughbred fillies does not result in nutrient partitioning to the dam at the expense of the fetus. However, sudden weight loss in mid-gestation has detrimental effects on placental development which results in reduced fetal growth.
Potential relevance: Clinicians should appreciate the likely effects of maternal infection and resulting weight loss on pregnancy outcome.