Foal Stress Levels Stay Increased Weeks After Weaning

Researchers say that even three weeks after weaning foals still experience increased stress levels.

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Weanlings in front of pond
Researchers found that weanlings spend more time standing after weaning than before. | Anne M. Eberhardt/The Horse
Weaning can be very stressful for foals. In fact, researchers on a new study have said breeders should expect a transition time of several weeks before weanlings start to “get back to normal.”

Recently weaned foals tend to spend considerably more time standing still or lying sternal (upright, with the chest against the ground) in the daytime for more than three weeks, compared to their more active behavior just before weaning. This suggests a normal adaptive behavior time frame as the animals adjust to their new social and nutritional situations, said Kristin Delank, PhD candidate in Ludwig Maximilian University of Munich’s Department of Veterinary Science, in Germany.

The study findings “provide a basis for foal keepers to have a pitch on when the stress of a foal might be more than usual after weaning,” she explained.

“For example, if the foal still shows signs of high stress after three weeks after weaning, there might be an additional stressor, and it is time to provide extra care,” said Delank, who works in the department’s Animal Welfare, Behavioral Studies, Animal Hygiene, and Animal Husbandry division. “And also, the other way around, if someone is concerned about a foal still seeming stressed in the second week after weaning, it might just need some more time.”

Investigating the Longer-Term Stress of Weaning

Historically, researchers studying weaning stress have focused primarily on short-term reactions or, at most, stress responses over the first week after weaning, said Delank. “I wanted to get more in detail into the behavioral changes, and I wanted to determine how long the transition phase is for a foal to acclimate within the new situation,” she said.

“Our thesis was that foals would have adapted within three weeks, but the results have shown that a time frame of four weeks would probably have been better,” she added.

Delank and her fellow researchers observed the behavior of four fillies and six colts at the state stud farm of Baden-Wurttemberg, in Germany, from 7 a.m. to 5 p.m. on the day before and the day after foals were removed from their dams and on three more days over the next three weeks. The researchers recorded each foal’s activity every five minutes during the observation time. They also collected the animals’ feces on the day before and after weaning as well as on four more days over the next three weeks.

The foals were all pureblood Arabians, except for one Warmblood filly, said Delank. They lived in groups with their dams until they underwent abrupt weaning, after which they lived in groups with other foals of the same age.

Post-Weaning: More Idle Time, Higher Stress Hormone Levels

The researchers saw the foals spend much more time standing still after weaning than before, Delank said. They were also less active generally and spent more time resting, but they spent far less resting time lying down than they did prior to weaning. When they did lie down after weaning, they were usually in a sternal position rather than flat, she added. And they spent more time lying down in the daytime than at night—possibly because they felt safer in the light, she said.

“We hope to determine the lying behavior during night and day through future research, to hopefully find a checkable indicator for foal welfare,” Delank said.

Cortisol concentrations in the fecal samples—which revealed stress levels from 24 hours earlier—showed the foals had a marked stress response to the weaning, she said. On weaning day, their cortisol concentrations were about twice as high as they were two days before weaning. The levels continued to increase in the first week and then slowly declined over the study period. Most of the foals never returned to their pre-weaning cortisol levels within the first three weeks after weaning, she added.

Three weeks after weaning, the foals had still not returned to their previous, pre-weaning state of activity as well, Delank said.

One foal—the Warmblood—seemed to have a particularly difficult time adjusting, she added. The filly showed stronger behavioral stress responses and higher cortisol levels throughout the study, especially when new stressors—such as farrier care—were introduced.

In PLOS ONE the researchers noted “this particular foal refusing concentrated feed and overall seeming more depressed than its companion animals.”

Aiming for Controlled Weaning-Related Stress

Weaning creates a multifaceted stressful experience due to how it affects many aspects of the foal’s life, said Delank and her co-authors. “In addition to separation from the mare, there is a change of diet, integration into a new social group, change of location, or a change of management procedures,” they said.

“It is not possible to accomplish weaning without producing stress in the foal,” they added. “The goal must be to determine the process that provides the best long-term welfare for the foal.”

Breeders interested in monitoring their weanlings’ welfare can refer to the signs of stress the team provided in their paper (Figure 4), Delank told The Horse. While her findings weren’t statistically significant, she said spotting those behaviors in weaned foals could indicate you need to make adjustments to reduce stress.

For instance, weaning foals in groups rather than alone or in pairs might be beneficial for their welfare, based on anecdotal observations, she added, but further research is necessary.


Written by:

Passionate about horses and science from the time she was riding her first Shetland Pony in Texas, Christa Lesté-Lasserre writes about scientific research that contributes to a better understanding of all equids. After undergrad studies in science, journalism, and literature, she received a master’s degree in creative writing. Now based in France, she aims to present the most fascinating aspect of equine science: the story it creates. Follow Lesté-Lasserre on Twitter @christalestelas.

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