Behavioral and hormonal effects of two weaning situations in trotter foals

Weaning is recognized as being a stressful event for foals. The outcome of this weaning stress can depend upon the procedure that was used. The aim of the present study was to investigate the behavioral and hormonal effects of two different weaning situations in Standardbred trotter foals born in Italy. In situation 1 (10 foals), weaning was performed at around 5 months of age, two foals/week, and foals were handled regularly after weaning in stud 1 (S1). In situation 2 (12 foals) weaning was performed at around 7 months of age, all foals on the same day, and there was little handling after weaning in Stud 2 (S2). Behavioral observations and saliva and hair sampling for RIA cortisol levels assessment were done on day -7, day 0 (weaning day), day 7 and day 30. Behavioral data were analyzed using Generalized Linear Mixed Models, Friedman ANOVAs, U-Mann Whitney tests. Cortisol data were analyzed using repeated measure ANOVAs. Spearman correlations were used to assess correlations. Foals in both studs vocalized (all Bonferroni adjusted P < 0.05) significantly more on the day they had been weaned than on any other day. They also showed a decrease in time spent eating on D0 supporting that weaning was a stressful event for them. The decrease in eating behavior was present also on D7 for S1, but not for S2 foals (S1: Bonferroni adjusted P < 0.05 for contrasts between D0 and D-7/D30; S2: Bonferroni adjusted P < 0.05 for all contrasts between days). Saliva cortisol concentrations differed significantly only depending on “age at the beginning of the experiment” (AB) and sex of the foal, whereas hair cortisol varied depending the day and the interaction day*AB and day*stud (all P < 0.01), with S1 foals having higher hair concentrations than S2 foals on the seventh day after weaning. Results suggest that the weaning situation in stud 1 (which included being weaned two at a time at 5 months of age) could be more stressful for foals than that experienced in stud 2 (which included being weaned all together at 7 months of age). As the weaning situations evaluated in the present experiment were compound stimuli, it would be interesting to confirm them in an experiment in which all features of the compound situation are teased apart (including possible confounding variables, such as stud) and foals are randomly allocated into experimental groups.