Foals take at least three weeks to adjust to weaning according to recent research.
A study in Germany followed a group of foals from the day before weaning for the following three weeks. Kristin Delank and colleagues at the Ludwig-Maximilian-University of Munich aimed to demonstrate the medium-term effects of weaning on foals’ welfare.
To achieve this, they monitored the behaviour of a group of foals’ behaviour, and assessed levels of cortisol metabolites in their faeces, over a three-week period beginning the day before weaning. The group consisted of nine Arabian foals (six colts and three fillies), and one warmblood filly.
Observations took place at the state stud farm of Baden-Wuerttemberg in Germany. A full report is published by PLoS ONE.
“Until weaning, all foals were raised in a group with other dams and their foals, and the housing method was an open stabling with daily pasture time depending on weather conditions” the researchers explain.
“The feeding consisted of grass on the pasture, hay ad libitum renewed three times a day, and for the dams concentrated feed twice a day in the stable. The foals also had access to the concentrated feed of their mothers.”
The foals were not all weaned at the same time, but in batches following the stud’s usual routine. Weaning was divided into three blocks, depending on the age and maturity of the foals - the first being in September, the second in October, and the last in November.
“On the day of weaning, a veterinarian sedated the foals before they were transported to a breeding station 18 kilometers from the stud farm.”
Behavioural observations were carried out the day before, and the first full day after, weaning, and then at intervals over the following three weeks. An observer recorded the behaviour shown by the foals every five minutes throughout the eight-hour observation session (from 7am to 5pm.)
The researchers report that, before weaning, foals spent most of the time moving. After weaning this changed, and they spent more time standing and resting. Weaned foals showed a significant increase in resting while standing. They also spent more time resting in a lying position during the day for the first eight days.
Four behaviours, (“aggressive behaviour,” “passive reaction,” “anxious behaviour,” and “vocalizing”) that were only seen after weaning, not before, were examples of stress-induced behaviours. (See figure) (The researchers suggest that a possible explanation for the increase in stress related behaviour on day 20 was that it coincided with a visit from the farrier.)
This graphic displays the total count of the shown behaviour for each day. All 10 foals are included. Note that observation day 1 is one day before weaning and observation day 3 one day after weaning.
To gauge the stress experienced by the foal, the researchers measured the levels of a cortisol metabolite, 11,17-dioxoandrostane, in the faeces. This allowed them to get an indication of plasma cortisol levels without having to collect blood samples and disturb the foals further.
They found that all foals had a distinct hormonal stress response to the weaning process, as shown by a significant increase in faecal cortisol metabolite levels. The average cortisol metabolite level the day before weaning was 2.82 ng/g. this rose to 5.56 ng/g on the day of weaning, indicating stress experienced during the weaning process.
They report “The stress hormone levels increased until day 5 (i.e., three days after weaning), from day 9 the cortisol metabolite concentration shows a decrease while still being significantly higher (p = 0.001) than on day 0.”
Stress hormone levels were checked in six foals 17 days after weaning, when they were still higher than before weaning. Finally, at 19 days after weaning, three foals were tested, and were found to have faecal cortisol metabolite levels similar to the whole group of foals on the day before weaning.
The researchers conclude “the foals showed an expected behavioural development and an expected curve of cortisol metabolite values throughout the study. However, it seemed that the changes had not returned “back to normal” at three weeks after weaning. Therefore, we suggest that weaned foals need a minimum of three weeks to acclimate to the new situation.”
“It is not possible to accomplish weaning without producing stress in the foal. The goal must be to determine the process that provides the best long-term welfare for the foal.”
For more details, see:
Behavioral and hormonal assessment of stress in foals (Equus caballus) throughout the weaning process.
K Delank, S Reese, M Erhard, A-C Wöhr (2023)
PLoS ONE 18(1): e0280078.
(Open access article published under a Creative Commons licence)