Abstract/Summary

This study investigated whether simple, cheap enrichments – ‘get-away bunks’ (a wire mesh semi-cylinder attached to the cage ceiling) and small manipulable objects (balls and suspended chewing items) – could improve welfare and productivity in nursing mink dams (Neovison vison) in commercial farm conditions in southern Ontario (Canada). Experiment 1 replicated a study conducted the previous whelping season on the same farm. It evaluated whether providing bunks to multiparous dams (n = 164) could decrease their morbidity and mortality or boost kit weaning weight, and assessed dams’ overnight use of these structures to compare day and night utilization. Overnight bunk-use proved to be no different from daytime use, and night- and day-use co-varied; bunk use recorded in daylight is thus a good proxy for overall use. Bunk use did not, however, influence kit weights at weaning, nor reduce dam deaths from nursing sickness (replicating the previous year's findings), nor significantly improve subjectively scored teat health (unlike the previous year's findings). Experiment 2 reassessed bunk effects using larger sample sizes, and investigated their interaction with enrichment objects. Focusing on primiparous dams (n = 318), it evaluated whether providing balls and items to chew, along with bunks in a cross-factored design, could decrease stereotypic behaviour, glucocorticoid output (assessed via faecal cortisol metabolites: FCM), kit losses, and, again dam mortality. Objects were provided c. 10 months earlier (since the previous July) for approximately 60% of the object-enriched dams, and c. 5 months earlier (since January) for the remaining 40%. Analyses showed that effects of bunks and enrichment-objects did not significantly interact for any variable. Bunks significantly reduced kit mortality: kit losses/litter were reduced by c. 0.3 infants, resulting in negligible levels of mortality, and bunks tended to reduce dam stereotypy levels by about half (from approximately 12.5% to 6% of time spent active). However, bunks had no significant effects on FCM or dam mortality rates. Bunk-use also significantly co-varied with litter size, being greatest in dams with bigger litters. Enrichment objects tended to increase weaning litter size, an effect caused by dams provided with these objects for 5 months weaning 0.9 more kits per litter than females without these items. However, this type of enrichment again had no significant effects on FCM or dam mortality. Instead, which farm animals lived on appeared to be the major determinant of FCM and dam mortality: both significantly varied between farms, with one farm showing notably higher levels of both. Also, even controlling for farm, females who died tended to have had elevated glucocorticoids when sampled 2–3 weeks prior to death. In conclusion, bunks and manipulable enrichment objects seem ineffective against nursing sickness, but had independent, additive effects on the productivity of young adult females, possibly acting by improving primiparous dams’ welfare.