Effects of prompt versus stepwise relocation to a novel environment on foals' responses to weaning in domestic horses (Equus caballus)

Abstract

a b s t r a c tArtificial weaning is often highly stressful for both mother and offspring. We investigated the effect of 2 different weaning and relocation schedules on growth rate and saliva cortisol concentrations in a group of loose-housed domestic horses. We predicted higher acute stress (cortisol concentrations), but a lower long-term effect on weight gain, which would indicate lower chronic stress in foals, if the foals were moved to the new environment immediately after separation from the mothers ("prompt relocation" [PR]) compared with relocation that was adjourned for a week ("stepwise relocation" [SWR]). Within 2 seasons, 56 foals weaned at age of 165-250 days were regularly weighed up to 140 days after weaning. Growth rate significantly differed between SWR and PR foals. The PR weanlings revealed relatively stable increase in their weights, whereas SWR foals experienced a significant drop in growth during the first 3 weeks after weaning. The weight differences were still apparent 5 months after weaning (predicted weight, least squares means AE standard error: 374.40 AE 1.75 kg in PR vs. 362.71 AE 1.66 kg in SWR foals). Cortisol concentrations changed significantly between and within different weaning procedures and were highest in PR foals after weaning and relocation. Compared with pre-weaning values, cortisol levels increased in PR but not in SWR foals, either after weaning or deferred moving. We found large individual variability in foals' growth and in cortisol concentrations for both weaning procedures. There was also a year effect in SWR foals. Stepwise changes of the physical and social environment (deferred removal to the remote facility) within a short period after abrupt weaning resulted in lower acute stress but induced long-term negative effects on foals' growth rate compared with joint weaning and relocation. Our results support rather prompt moving of the weanlings to the new facility, rather than to a stepwise location on horse breeding farms.

Behavioral and hormonal assessment of stress in foals (Equus caballus) throughout the weaning process

“…Furthermore, due to the 24-hour delay of cortisol metabolite expression in the feces, the stress hormone level displays a rather normal day within the foal's life without being influenced by the presence of the observer. Agreeing with other studies using the same or salivary cortisol metabolite measurement [4,9,14,15,28], all foals displayed a distinct direct hormonal stress response to the weaning process through increased cortisol metabolite levels. The average measured cortisol metabolite levels of the foals before weaning were 2.82 ng/g in this study.…”

“…The slow weaning process is described as the more natural way because under natural conditions the offspring decreases the contact to its mother gradually [1,2]. The natural weaning is also encouraged by the mare in preparation for the new foal [4,10,15]. In terms of behavioral changes, foals seem to adapt better to gradual weaning than to abrupt weaning [6,8,9].…”

“…Transportation causes stress in horses, as well as the adaptation to a new environment [16][17][18]. For example, Dubcova ´et al [15] studied the long-term effect of relocating foals to a rearing farm sometime after weaning had occurred. They found that concerning the long-term effects on the foals, separating both events in time has a more negative effect than simultaneously segregating and relocating the weanlings.…”

“…The two methods most validated for horses are the detection of cortisol metabolites in saliva [26] and in the feces [27]. Both methods have been used successfully to detect the stress level of foals during weaning [4,7,9,14,15,28]. Because detecting the cortisol metabolites in feces involves no force on the horse through sampling, we chose this method over the saliva glucocorticoid detection.…”

Same or different? Why establishing the range of behavioral variability matters

“…Dubcová et al (2015) asked whether gradual or abrupt weaning was less stressful for foals in a group of domestic horses. The experimental design involved a group of foals that was promptly weaned v. one that was weaned stepwise, with the prediction that the former group would experience acute stress but smoother long-term accommodation.…”