When piglets don't get enough milk in the first weeks of life, the chances of them thriving dramatically decline. In the U.S. pork production system, piglets with limited access to their mothers' milk are typically "cross-fostered" with other sows. But in the E.U., a different solution is gaining ground. In certain circumstances, underfed piglets are artificially reared with milk replacer, mimicking feeding setups used in biomedical research.
- Sydney Friedman
A new study at the University of Illinois Urbana-Champaign asks a deceptively simple question: what is the best way to feed artificially reared pigs? The answer has implications not just for agriculture, but for biomedical research where pigs are used to study different aspects of human medicine.
"The main driving factor for this study was to bridge the gap between the agriculture and biomedical worlds," said lead study author Kaitlyn Sommer, a doctoral researcher in the Department of Animal Sciences, part of the College of Agricultural, Consumer and Environmental Sciences at Illinois. By testing different feeding strategies, researchers can better understand how nutrition early in a pig's life can affect their growth, metabolism, behavior, and overall welfare.
In this study, 85 piglets were weaned at two days of age and reared individually with a nutritionally complete milk replacer. Half of the piglets were able to drink milk freely (known as ad libitum or free choice feeding), while the other half received carefully measured doses based on body weight, mimicking the frequency and quantity a piglet would get from a sow. Over the 15-day feeding study, the team tracked everything from the piglets' body weight, insulin concentration, behavior, and even soft tissue composition.
The results were striking. "Ad libitum pigs drank more milk overall and gained more weight," Sommer said. However, there were no significant differences in the soft tissue composition between the two groups at the conclusion of the study. Researchers found that the body fat and muscle protein content were comparable between the ad libitum and "prescribed feeding" piglets. The main distinction was in how quickly they grew.
"When we compare how much milk they consumed relative to their body weight, both the ad libitum and prescribed feeding groups consumed similar amounts," Sommer said. "This suggests that ad libitum pigs are simply growing faster, possibly due to differences in insulin production."
One important measurement during this study was the insulin concentration in the piglets' bloodstream. "Insulin is a big part of directing amino acids, which are the building blocks of protein," said Ryan Dilger, senior study author and professor in animal sciences at Illinois. "Piglets ingest amino acids in the form of protein, and insulin is responsible for directing these amino acids toward building skeletal muscle."
Sommer explained that piglets in the ad libitum group ate larger, less frequent meals. This led to prolonged periods where their insulin levels were above the threshold needed to trigger muscle growth. In contrast, the pigs on the prescribed feeding schedule ate more frequent meals, but they consumed smaller volumes of milk every hour. While this schedule more closely resembles milk letdown from the sow, the insulin concentration in these piglets did not always reach the anabolic threshold, which is where the muscle building takes place.
In addition to muscle growth and insulin concentration, the team also tracked how the pigs moved around their enclosures. Using high-tech cameras and automated tracking systems, researchers were able to analyze the preferred location of the piglets. "The prescribed-feeding pigs spent more time near the milk bowl and showed more feeding-related behaviors," Sommer said. "This suggests that the extra time artificially-reared pigs spend near the feeding bowl, and display behaviors like rooting or nosing, might be driven by their natural instinct to nose and suckle at the sow's teat - an action known to encourage milk production."
And yes, there were toys. In the second trial, piglets were provided enrichment including toys and towels, and they grew particularly attached to them. "They'd snuggle up with them, and get upset when we took them out for cleaning," Sommer said.
While the image of a piglet curled up in a towel may sound adorable, the science is both practical and applicable. In production agriculture, understanding how milk access affects behavior could help reduce piglet crushing risk. Hungrier piglets may stay closer to the sow, increasing their likelihood of getting hurt. In the lab, these findings can help researchers fine-tune artificial feeding protocols for pigs being raised to improve biomedical research. This is increasingly important, as pigs are often used as a model for studying human nutrition and health. Due to their genetic similarities to humans, pigs offer insights that mice and other species cannot. "We particularly use pigs to study parts of the gastrointestinal tract, parts of the immune system, and in our lab specifically, brain function," Dilger said.
"Every study opens the door to new questions. What really stood out in this work is just how much the way we feed pigs can influence everything else we're trying to measure," Dilger said.
The goal is to continue to bridge the gap between the agricultural and biomedical applications of raising piglets. With future studies exploring additional behavioral and physiological outcomes, the team hopes to continue to refine piglet-rearing strategies. "There is still so much to learn," Sommer said. "But, every piece brings us closer to understanding how management practices early in life can help piglets thrive, and get them started in the right direction."
The study, "Feeding style alters the growth and behavior of artificially-reared pigs," is published in the Journal of Animal Science [DOI:10.1093/jas/skaf098]. Authors include Kaitlyn M. Sommer, Loretta Sutkus, Pradeep Senthil, and Ryan N. Dilger.
Dilger is also affiliated with the Division of Nutritional Sciences, the Neuroscience Program, the Beckman Institute for Advanced Science and Technology, the Center for Digital Agriculture, the National Center for Supercomputing Applications (NCSA), the Carl R. Woese Institute for Genomic Biology, the Illinois Institutional Animal Care and Use Committee (IACUC), and the Office of the Vice Chancellor for Research and Innovation.
