Effects of a Streptococcus equi infection–mediated nutritional insult during mid-gestation in primiparous Thoroughbred fillies. Part 1: placental and fetal development.

This study examines how changes in nutrition during pregnancy, especially an unexpected infection causing a significant drop in food intake, can impact the development of the placenta and fetus in the mare. The findings suggest that a sudden change in weight during the middle of gestation can negatively affect both placental and fetal development.

Objective and Methods

• The main objective of this study was to investigate how two different nutritional levels, along with an unexpected infection-induced nutritional disturbance, could impact the development of the placenta and fetus in mares.
• The researchers enlisted twenty maiden Thoroughbred fillies, all either three or four years old and impregnated by the same Thoroughbred stallion. These fillies were then maintained on either a high or moderate food intake throughout their pregnancies.
• During mid-gestation, all the mares unexpectedly contracted a Streptococcus equi infection, which resulted in varying degrees of weight loss.
• The researchers then made various gross and stereological measurements of the placenta, and also measured the birth weight, crown-rump length, ponderal index and plasma IGF-1 concentration of the foals at term.

Results

• The results indicated that weight gains during gestation were significantly higher among the mares maintained on high nutrition versus those on a moderate food intake.
• Despite this, the researchers found that the growth parameters of the placenta and fetus did not seem to be influenced by the level of nutritional intake.
• However, a transient weight loss in mid-gestation (caused by reduced food intake due to the infection) led to morphological changes in the allantochorion (part of the placenta) and a decrease in foal birth weight.

Conclusions

• The study concluded that excessive weight gain during gestation in maiden Thoroughbred fillies does not result in nutrient distribution to the mare at the expense of the fetus. Meaning, the nutritional intake does not disadvantage the fetus, despite the mother’s significant weight gain.
• The sudden weight loss experienced in mid-gestation, on the other hand, has detrimental effects on the development of the placenta, which in turn affects the growth of the fetus.
• Consequently, clinicians should be aware of the potential effects of maternal infection and the resulting weight loss on the outcomes of pregnancy.