Overstocking is a commonly used management practice on many dairy farms across the country. While not all animals in these situations are affected, the subdominant cows are likely to experience typical behavioral changes such as reduced lying time, increased eating rate, and displacements from the feed-bunk or the free-stall. Furthermore, alterations in these behaviors may impact overall production, efficiency, and health. However, these responses are not always seen in research trials or in commercial settings. So what kind of stress does higher stocking density place on these cows? The most likely answer: Chronic Intermittent Sub-Clinical Stress. Sounds like a mouthful, but understanding the type of stress our cows are experiencing can help us identify solutions to reduce stress and improve well-being for these animals.
Stocking density often results in stress that is chronic and intermittent in nature for subdominant cows. Because this results in cows competing for resources or space, affected animals consistently experience this stress, placing them in a chronic state. They will experience this until their environment is changed; either enough resources for all animals to minimize competition is achieved or they alter their position within the herd hierarchy. The latter usually is harder to accomplish unless the animal is moved to a less competitive environment. These cows also experience this stress intermittently. Sources of competition are scattered throughout their day such as space at the feed-bunk or water trough, free-stall access and order heading into a milking parlor or footbath. Therefore, we can see how hard it may be for these animals to be relieved of this stress in their typical environments. But what kind of stress are we dealing with?
Subclinical stress doesn’t shift enough biological resources to cause changes in biological function, thus very little to no clinical signs are seen. Therefore, it’s reasonable to see how subdominant cows may have changes in behaviors but we don’t always see clinical outcomes such as lower milk production or altered health status. So if we don’t see many production affects from stocking density, should we still be concerned? Yes! Although subclinical stress may not always result in visible signs, this stress is still reducing biological reserves in the cow. In other words, her “cushion factor” against disease or other stressful events becomes reduced. Thus, it’s easy to see that when combined with other stressful situations, stocking density may limit the cow’s ability to withstand a second stressor, entering a state of distress. This is often associated with visible changes in biological function (production, health, reproduction) and can be greater when stressors are combined. Interactions among stressors and stocking density are hot-topic issues among production animals, and research is currently ongoing within this field.
Using our understanding of the type of stress cows are experiencing, we can start to explore solutions to minimize this stress and better manage them. Due to the chronic and intermittent state, several options can mitigate these consistent stress conditions: remove aggressively low-producers from the herd, separate multiparous and primiparous cows, move more timid multiparous cows to a primiparous pen, and reduce to overall length in which the pens are overstocked. Furthermore, minimize external sources of stress to overstocked cows to prevent them from entering clinical stages of distress. Reducing the stress load on sub-dominant cows now will pay dividends down the road in terms of production, health, and overall well-being of your herd.