Interpretive Summary: Influence of litter size on insulin sensitivity in multiparous sows
By: Dr. Caitlin Vonderohe
Pregnant females undergo multiple, dramatic physiologic changes to meet the nutritional demands of a growing fetus. Uterine blood flow increases throughout pregnancy in ewes, cows, goats, rabbits and sows to increase delivery of nutrients. A reversible, but progressive physiologic insulin resistance also occurs in the last trimester of pregnancy of rats, ewes, humans and rabbits to divert a maximal amount of glucose from maternal tissues to be available for fetal use. A similar phenomenon was previously found in the sow, but to a lesser degree. A study recently published by Pére and Etienne in the Journal of Animal Science entitled “Influence of litter size on insulin sensitivity in multiparous sows” hypothesized that uterine blood flow and insulin resistance increases with litter size in sows.
Seventeen multiparous, commercially bred sows were allocated to one of two treatments. The control sows had twice the number of piglets as the LIG group. LIG sows underwent surgery to ligate the left oviduct prior to breeding. All sows were estrous synchronized and bred to Pietrain boars via artificial insemination. All sows underwent surgery on day 68 of pregnancy to implant multiple catheters for uterine glucose measurement and a blood flow probe in the middle uterine artery. The number of fetuses in each uterine horn was also determined at this time.
A meal test was performed wherein blood was simultaneously sampled from the uterine and carotid catheters before, and at 15-minute intervals after a meal. A glucose tolerance test was then performed by infusing a 1.665 M glucose solution through a jugular catheter and subsequently drawing blood samples from the carotid and uterine artery. Finally, a euglycemic hyperinsulinemic clamp was also performed to assess glucose and insulin mechanics. Blood glucose, insulin, and non-esterified fatty acids were measured in plasma samples.
There were more piglets born control sows, compared to sows on the LIG treatment. Uterine blood flow did not differ between treatments, therefore there was greater blood flow distributed per fetus in the LIG sows because of the smaller litter size. The greater blood flow per fetus resulted in larger piglets at birth from LIG sows. The three tests of insulin sensitivity (meal test, euglycemic, hyperinsulinemic clamp, and glucose tolerance test) concluded that the LIG sows were more insulin resistant than control sows. The authors hypothesize that the increased insulin resistance observed in the sows with smaller litter sizes is due to the faster growth rate of the fetuses. Sows likely metabolically adapt to the nutrient demands of large litters to maintain a balance in late pregnancy.
To view the full article, visit the Journal of Animal Science.