by Sally Colby
Stress studies in humans clearly show social environment stressors are among the most serious stressors we face. Factors such as a low socio-economic status or not having a good social support network can have a major impact on our health, and caregivers often experience social stress. Many aspects of what has been learned about human stress can be applied to livestock.
Dr. Katy Proudfoot, veterinarian and associate professor and director of the animal welfare center at the Sir James Dunn Animal Welfare Centre at the Atlantic Veterinary College in Prince Edward Island, studies the effects of stress during the periparturient period – the time immediately prior to and following calving.
“Social stress is a stress response arising from an animal’s social environment,” said Proudfoot. “Sources of social stress for cows include crowding, social defeat, social instability, low herd status and social isolation.”
For most people, crowds are not a positive experience, and overcrowding often leads to stress. “Social instability is a change in the social environment – meeting unfamiliar individuals,” said Proudfoot, “which can be particularly stressful for those who don’t like meeting unknown individuals.” Social instability also occurs in dairy cows, and the reasons are often complicated.
Stress due to overcrowding in dairy cattle is the result of high stocking density. The situation might be too many cows for stall space, or too many cows for linear space or headlocks. “Cows have to compete for access to something they really want,” said Proudfoot. “If she has to fight her way through to get to the feed bunk, that can be a stressor for her.”
Every observant dairy manager has seen displacement at the feed bunk, where one cow pushes other cows out of her way to get to where she wants to be. Proudfoot explained any behavior related to fighting as agonistic behavior. “That could be outward aggression or retreat,” she said. “Feed bunk displacement is a common place to measure overstocking and other stressors.”
Social instability for cows can result from pen moves, which may happen frequently during the transition period. “Cows might go from a far-off pen to a close-up pen to a close-fresh pen to a high-lactating pen within a period of several months,” said Proudfoot. “That can be stressful, particularly if the cow is moved to a group of unfamiliar animals. Cows know each other, and if a cow is moved to a pen of cow she’s never met, she has to work out her social relationship with all the cows in that pen.”
A cow entering a new pen may be consistently knocked back from feed, and it takes about three days before the pen stabilizes. “That’s just one cow being moved to one pen,” said Proudfoot. “If that happens daily, there’s a lot of social disturbance in that pen. Stressors not only impact social behavior, they also impact feeding behavior and milk production.” Regrouping pre-fresh cows also results in lower feed intake and rumination time.
Another reason to pay attention to social stress is from an animal welfare standpoint. Proudfoot said some stress is tolerable, but long-term, chronic stress impacts health, the animal’s mental state and her ability to perform natural behaviors. “We care about the fact that social stress is going to impact disease,” she said, “and we care that it can also impact other aspects of animal welfare.”
Proudfoot said the benefit of studying study social stress, particularly in transition cows, is to determine how pre and post calving practices such as overstocking and regrouping are related to post-calving illnesses such as ketosis, metritis and hypocalcemia. “We really don’t understand how the social environment and the impact of management can impact disease risk in the transition period,” she said. “We haven’t gotten a handle on why some cows get sick and other stay healthy after calving, but transition disease is a major challenge in the dairy industry.”
Proudfoot said an all-in, all-out policy for groups results in more stable social groups. However, the farm must be of sufficient size to make this practical. “This creates a stable social group that eliminates pen moves with cows going in and out,” she said. “When cows are moved out, no new cows are moved in.”
Research aimed at all-in, all-out management showed reduced displacement at the feed bunk, but compared to regrouping once weekly, there were no effects on immunity, overall health or reproduction. Proudfoot said controlling the number of pen moves by moving a group of cows once a week is a good management strategy and helps limit instability in the group.
One controversial topic in the dairy industry is separating calves after calving. “Ask a dairy producer about this and it’ll get heated,” said Proudfoot. “Ask someone in the public about it and it will also get heated. We should forget the controversy and think about the impact of social stress from the cow’s perspective.”
While some cows may seem indifferent when their calf is removed from the pen, others can become quite stressed. These cows show stress by vocalizing, pacing and trying to follow the calf.
Earlier research indicates there’s more stress at separation when the cow and calf are kept together longer; likely the result of ample bonding time. More recent research shows that even though the acute stress response that occurs at separation may be worse, there are benefits to the period of contact for both the cow and the calf.
“A lot of this research is happening in Europe, and it’s something we should pay attention to,” said Proudfoot. “Typically when something happens in Europe, it happens here about 10 years later. I would not be surprised if we’re talking about keeping cows and calves together in some way in the next five to 10 years.” Proudfoot added that cow/calf management is an area that requires more research to avoid adding more stress through changed management practices.
Proudfoot said it’s important to realize that real-world social stressors don’t occur just one factor at a time, and multiple stressors on the farm result in the cumulative effects of stress. “We don’t understand that well in transition cows,” she said, “particularly in a time when a lot of things are going on for the cow.”
Research has shown that management and social environment factors influence cows before and after calving. The people who handle cows are part of the herd’s environment and can also be a significant source of stress for cows. “Stress and disease vulnerability may vary by parity, social status or other individual cow differences,” said Proudfoot. “But we’re just scratching the surface – we need more research to understand better.”