THE CASE FOR “PROGRESSIVE” WEANING

A new study from France suggests that abrupt weaning can be so stressful that it alters a young horse’s personality.

Researchers at the French Horse and Riding Institute and the National Institute for Agricultural Research Val de Loire Centre in Nouzilly selected 34 Welsh Pony mares and their foals for the study. The horses lived together in large herds or pairs until the foals were about 8 months old, when weaning commenced.

For the experiment, 16 of the mares and foals underwent a “traditional” weaning process: Without any preparation or trial separations, the mares were simply moved to a different farm on weaning day.

The remaining 18 mares and foals were handled differently: The pairs were separated gradually over a fiveweek period, starting with 15 minutes spent on opposite sides of a steel fence each day. The separation time was increased incrementally--by two minutes per day the first week, five minutes per day the second week, 20 minutes per day the third week and 30 minutes per day the fourth week---until the periods lasted six hours. The mares and foals could see, hear and touch each other through the fence, but the foals could not nurse. On weaning day, the mares were taken to a different farm during the separation period.

To quantify behavioral differences between the

groups, the researchers observed the foals throughout the weaning process and documented vocalizations, social interactions with other foals and stress-related behaviors, such as being extremely alert. The researchers also gave each foal a personality test immediately after weaning and again three months later. The test was designed to measure reactivity to humans, gregariousness, fearfulness, curiosity and activity.

In addition, the researchers checked several physiological parameters to evaluate each foal’s level of stress. These included blood concentration of the stress hormone cortisol, the length of telomeres---the protective “caps” on the ends of DNA strands that can be reduced by stress in early life---and the expression of particular genes. “In a previous experiment, we had already found some differences in the expression of some genes in horses that live alone in individual boxes compared to horses that live in an enriched environment,” says Léa Lansade, PhD.

The data showed that foals who were weaned gradually vocalized and trotted less on the day of separation than did the youngsters removed from their dams abruptly. The progressively weaned foals also had lower cortisol levels, and the personality tests showed that they were more curious, less fearful, less gregarious and less reactive to humans than were their peers who were abruptly weaned.

What’s more, the difference between the two groups of weanlings were still evident at least three months later. Lansade says these personality changes could be long-lasting or even permanent. “It is possible, because sudden weaning is a real trauma occurring during the development of the young when personality is not fixed.

”The gene analysis showed that while fear, reactivity and gregariousness correlated with high cortisol levels, curiosity was associated with an increased telomere length and higher expression of genes involved in mitochondrial functions. “That shows that weaning modifies deeply the physiology of the animal, and that leads to a specific transcriptomic fingerprint,” says Lansade. “These analyses are more accurate to evaluate the impact of chronic stress compared to behavior or cortisol levels. We are lucky to have the opportunity to use these new tools in horses.”

Lansade says the duration of the weaning period is probably less important than how the separation is carried out. “We do not know exactly how long a weaning period should be. But, I think that it is important to habituate the foal to be separated very progressively, only a few minutes at the beginning, to avoid any stress. People have to observe their animals during the progressive separations. In that way, they can adjust the length of the procedure in function of the reactions of the mare and the foals.”

Reference: “Progressive habituation to separation alleviates the negative effects of weaning in the mother and foal,” Psychoneuroendocrinology, November 2018

Foals weaned gradually were less fearful, less gregarious and less reactive to humans than were their peers who were weaned more abruptly.