Date Full Report Received


Date Abstract Report Received



Primary Investigator:

This experiment evaluated the effects of heat stress across multiple generations. In a previous experiment, pregnant gilts were housed in either heat stress or thermoneutral (control) conditions for the entirety of gestation. Female offspring from those pregnancies (F1 generation) were retained, grown to breeding age and then inseminated. The data collection phase for the current experiment began at farrowing and specifically included: 1) post-farrowing lactational measurements, and 2) measurements of growth and carcass quality of offspring (F2 generation). The weigh-suckle-weigh method was used to evaluate the milk production of the F1 generation approximately 19 days after their first farrowing. The results of the weigh-suckle-weigh procedure indicated that milk production did not differ between dams based upon exposure to heat stress in utero. Some aspects of the milk nutrient composition were affected by in utero treatment. Protein content tended to be higher in milk from dams that were heat stressed in utero. Conversely, lactose content was lower in milk from dams that were heat stressed in utero. Milk fat, solids non-fat and somatic cell count did not differ based upon in utero treatment. At the time of weaning, a subset of offspring (male and female) from these litters were retained and grown to slaughter weight in mixed pens under identical management and environmental conditions. Thus, these pigs were the offspring of gestationally heat stressed dams (OgHS) or the offspring of gestationally thermoneutral dams (OgTN). The environment which the dams were exposed to while they were developing in utero did not impact growth of their offspring to market weight. Days of age and live weight at the time of slaughter did not differ between treatment groups, indicating that the number of days needed to reach a similar market weight was not affected by treatment. Interestingly, carcass analysis after 24 hrs post-mortem showed that the OgHS tended to have greater backfat and dressing percentage. There were no detectable differences in loin eye area or lean percentage. The tendency for greater adiposity as indicated by increased backfat thickness indicates that transgenerational effects of in utero heat stress may be diluted, but still evident. These findings suggest that the effects of heat stress on production go beyond the immediate impacts that can be easily measured, indicating that the financial losses associated with heat stress are generally underestimated.

Key Points:
• Exposure of piglets to heat stress while in utero has long-lasting effects. For females, this in utero insult results in altered milk composition after first farrowing.
• Milk production as assessed by weigh-suckle-weigh did not differ between females exposed to heat stress in utero versus those that were not.
• Offspring of dams that were heat stressed in utero tended to have greater backfat and dressing percentage at slaughter. These results are the first to indicate that heat stress experienced during gestation can affect multiple generations of swine (may be direct effect or a consequence of altered milk composition).
• In utero heat stress of dams did not affect market weight, days to market weight, loin eye area or lean percentage of offspring at slaughter.

Contact Information:
Michelle Rhoads, Ph.D.
Department of Animal & Poultry Sciences
Virginia Polytechnic Institute & State University
3450 Litton-Reaves Hall (0306)
Blacksburg, VA 24061
Phone: 540-231-4740