Besides heat stress, which is the most recognizable environmental stress, cattle are susceptible to a variety of psychological stress factors caused by rough handling, poorly designed and followed routines, stall availability, overcrowding, regrouping, bully cows, transporting, waste disposal and cleanliness issues. All of these factors can have negative effects, including an apprehension of people, a likelihood of injury and a susceptibility to disease due to a depressed immune condition.
When faced with potential stress, a cow will naturally trigger a fight-or-flight mechanism to aid in their preparation for danger, allowing the release of hormones such as cortisol and adrenaline. The release of these hormones will negatively impact milk yield, precipitate incomplete letdown, increase residual milk buildup, and depress immune and reproductive systems. This suppression of the immune system can lead to a greater risk of mastitis and higher somatic cell counts.
Chronically stressed cows are prone to infections leading to higher numbers of white blood cells in their milk. Yields can be reduced overall by as much as 30% in highly stressed cows, along with significant reductions in fats and proteins. When stressed by feed availability and overcrowding, stronger and more aggressive cows sorting through the feed can change and affect the composition of the diet for the weaker, more passive cows. Foot problems are common for cows forced to stand in a slurry of manure on concrete floors for longer periods of time by softening the hoof, leading to a larger incidence of lameness.
Research done in 2005 by noted expert in the field, Professor L. Munksgaard of Denmark’s Aarhus University, studied the effects of limited feeding time on dairy cows, concluding that cows adapted to the loss of eating time available by increasing the rate of intake, or eating faster. The reduction in feed intake turned out to be less than the actual time lost to eating. When faced with the choice of either eating or lying down, they were willing to relinquish feeding to maintain rest time.
Another study done by Munksgaard in 1996 demonstrated cows deprived of adequate lying time generated increased amounts of cortisol, which was directly linked to the suppression of their immune functions. University of Wisconsin research completed in 1999 focused primarily on heat stress, but since it is generally accepted the results of different stressors are similar, their findings can be loosely related to psychological stresses. They concluded conception rates among dairy cows fell steadily from 40% down to 15% at the highest-stress conditions and slowly returned to normal when heat stresses were reduced and removed.
The most natural and basic behaviors related to the health, welfare and productivity of cows are rest, feeding and rumination, with the average dairy cow requiring 10 to 14 hours of lying down or rest time and three to five hours of feeding time during a 24-hour period. The remaining few hours are necessary for actual milking periods and moving to and from the milking parlor. Numbers that do not fall within these parameters demonstrate a likely increase in the levels of stressors faced.
There are many practical ways to improve the well-being of dairy cows. Craft and follow an efficient routine, handling cows in a calm and consistent manner. Practice proper waste and sanitation management, plus design or modify facilities and infrastructure to allow for sufficient ventilation and heat dispersal. Ensure adequate space per animal as well as unimpeded access to feed and water amenities.
Managing the stress of dairy cows will result in more productive animals. Although producers have less control over some stressors like calving and dry-off periods, many psychological and physical stressors can be reduced or virtually eliminated. By decreasing their effect on immune functions, production can be increased significantly. Assess the stress conditions on your farm that can be controlled, reduced or eliminated to allow for an economic payoff, along with building a happier and healthier cow herd. 
Bruce Derksen is a freelance writer based in Lacombe, Alberta, Canada.
