Effects of gestational heat stress linger for generations

Heat stress suffered while gilts are in gestation has long-lasting effects on the performance of the gilts themselves, but also the performance of their offspring, and even further down in the gilts’ lineage.

Shelly Rhoads, a Virginia Tech assistant professor in Animal and Poultry Sciences, worked on research funded by the Pork Checkoff to determine whether in utero heat stress does in fact have lingering ramifications.

Rhoads presented the research findings in the Aug. 18 National Pork Board webinar, “Impact of in utero heat stress on subsequent lactational performance and performance of offspring.”

Gilts for this research (F0) were exposed to heat stress during their gestation periods while at the University of Missouri. At puberty the offspring of those gilts (F1) were then transported to Virginia Tech, inseminated and allowed to farrow.

Milk quality, not quantity

Once the F1 gilts farrowed, milk samples were collected on day zero, 7, 14 and 21 for analyses of fat, protein, lactose and solids nonfat content. Milk production was also measured. Rhoads’ research found no difference in milk production between the gilts that were in utero heat stressed and those that were in thermoneutral conditions in utero.

Variances did arise when the composition of the milk evaluated. Milk from the in utero TN females contained more lactose, but tended to contain less protein and solids nonfat than milk from the in utero HS females. Lactose content “has been pretty well linked to piglet survival and growth rate in the piglets, so it’s pretty important,” Rhoads says. That importance showed up as the offspring were followed through to the slaughter and carcass characteristics were recorded, and the differences between the TN and HS offspring can partially be attributed to the lactose composition.

Rhoads was quick to point out that this research has left her with more questions than answers, and is looking toward further research.

Gender growth rate

Four “grand piglets” of the F0 gilts were chosen from each litter (average piglets, two male, two female) and followed through to slaughter. Heat stress variances showed up within the genders, but not between the two genders of piglets. Rhoads says results showed no growth rate difference between the barrows of TN or HS legacy.

Growth rate variance was seen in the females with the offspring of the gestational thermoneutral outperforming the offspring of the gestational heat stressed gilts. That OgTN advantage became more apparent in the late-finish stage (21, 23 and 25 weeks of age). “This is pretty interesting to see this heat stress impact on the grand piglets of the F0 gilts,” Rhoads says.

Another interesting finding was that the backfat thickness was higher in the OgHS than in the OgTN. “We would expect that in the F1, but to see that in the F2 generation is pretty amazing,” she says.

Seeing the effects go beyond the F1 generation, leads Rhoads to suggest that the industry look long and hard at the females that are being kept for multiple generations. “Do we need to be looking at targeted breeding programs,” she questions, “or looking at maternal lines that maybe aren’t so susceptible” to heat stress.

Since this research left Rhoads asking more questions, she realizes more work needs to be done, which she outlined as:

  • Lactation/piglet immune response
  • Relative contribution of milk composition to observed carcass differences
  • Primiparous versus multiparous dams
  • Metabolism
  • Reproduction
  • Epigenetic impact

One more webinar in the NPB’s “Assessing and Understanding the Impact of Seasonal Loss of Productivity” series will be at noon Aug. 25 with Jason Ross presenting “Understanding the biology of seasonal infertility to develop mitigation strategies for swine.” Ross is an associate professor of Animal Science, Lloyd Anderson Endowed Professor in Physiology at Iowa State University.

There is no cost, but participants must register in advance. To register, go to www.pork.org/production-topics/animal-science.

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