What is Stress?

Stress is defined by Mr. Webster as �the physical pressure, pull, or other force exerted on one thing by another; strain,� or �a specific response by the body to stimulus, such as fear or pain, that disturbs or interferes normal body physiological equilibrium.� The first part of the definition is related more to the physical world while the second applies more directly to the biological. Both are applicable however. Stress can be considered anything that is applied to an animal from an outside source that has an effect on that animal's �normal� physiological activity. A lot of this may be psychological. Whether something is stressful or not may be related to how we view or perceive certain activities or occurrences. This is also true of cattle as well. It can also be related to the activities or occurrences we may or may not be accustomed to. For instance, some people enjoy running as a form of exercise and relaxation (i.e. reduces stress). I only run when being chased by a man with a gun or a large animal who wants to crawl in my back pocket (i.e. increases stress). While we consider some forms of stress beneficial (i.e. processing cattle to provide vaccinations, dewormers, etc.), in general we normally consider stress to be counter productive. This counter productive stress is where our emphasis lies in this context.

The results of stress are many-fold, some obvious and some not so obvious. In many cases stress from handling or improper handling can have longer-term behavioral effects on the animal. In other words, if a cow has a bad experience in the corrals and processing area, she will remember that event and will react negatively the next time she is forced into the situation. This can increase stress levels at subsequent processing periods. This can lead to reduced performance as well as injury to the animal or even the producer.

Even an activity as simple as walking or driving through the herd out on pasture can produce evidence of stress related responses. Have you ever noticed that as you walk upon a group of cows that are at rest, in many cases they will begin to get up and move away. In the process they will immediately increase urine and feces output. This is a physiological response to the �fight or flight� process most living animals have in-bred. The body is preparing itself for defense or to get the heck out of Dodge.

Less obvious are the biological changes we can measure in the animal after a period of stress. By measuring blood metabolites we can observe changes to many of the compounds (hormones, enzymes, nutrients) as a result of stress. While this is a normal response to stressful stimuli and is beneficial in the short term, longer term effects can be detrimental. For instance, we have seen that in cattle being weaned and transported through normal marketing channels and onto a new location that there is a significant reduction in Zinc levels in the body. In other words, through the handling and transportation stress zinc tends to be removed from liver and blood stores through increased excretion. Zinc is a required compound in numerous enzymes and other systems that allow the immune system to perform normally. If zinc levels are low this creates a situation where the immune system will not perform at the level it should and the animal will not be able to �fight off� the various infectious agents it comes in contact with as effectively. This, therefore, increases the incidence of sickness in recently transported cattle. Now consider that this is only one of a multitude of blood metabolite levels that changes and you can see the profound effect that stress can have on the animal.

Types of Stress

In a typical cattle operation we see various stressful stimuli that affect the animals we produce. By and large we want to reduce these stresses as much as possible. Some of the stressful stimuli we see include:

�Environmental Stress

�Nutritional Stress

�Handling Stress

�Transportation or Marketing Stress (could fall under handling but we'll separate it for this discussion).

Let's take a look at each of these.

Environmental Stress

Environmental stress can take a number of forms. One of the most common we see at this time of the year is heat stress. A cow has a �thermalneutral zone� ranging from around 50o to 70o Fahrenheit. Within this range, no additional energy is needed to heat or cool the body. During the summer months, obviously temperatures go well above the upper range on this scale. The animal's body has to make the necessary adjustments to cool itself in some way. Physiologically we see the animal's heart rate and respiration increase in an attempt to move excess heat out of the body. This requires additional energy (i.e. calories from nutrient intake). The problem we encounter here is that during the summer months we see lower nutrient intakes simply because the cattle do not wish to venture out into the heat to graze as they normally would. It's very important to provide adequate shade and plenty of water during the hot times of the year. Hopefully water and shade are not located too far apart. Also, it becomes more important to provide some supplemental feeding to offset the reduction in normal nutrient intake as mentioned. Ideally, more shade than absolutely necessary should be provided to allow cows to spread out and provide for improved air circulation. Finally, one last way to help reduce heat stress is to make sure that the quality of the forages provided is good. In any situation when a cow consumes forage or feed and the rumen is stimulated during the normal digestive process, it generates heat. Consumption of poorer forages requires increased activity and subsequently increased heat is generated. Better quality forages can help reduce this added heat production.

As with humans, cattle are also subject to the effects of humidity. On high heat index days, they can be as uncomfortable as we are. It's important to remember this and if handling or processing is necessary, do so early in the morning while temperatures are still cool and finish or stop by mid to late morning to reduce heat stress.

Similarly, in winter, protection from the cold weather is as important as protection from the heat in summer. Once again, when the temperature falls below the lower end of the range given above, cattle are required to utilize more energy to maintain body temperatures. The one benefit in cold weather is that research has shown that cattle will voluntarily increase forage and feed intake levels to compensate for this additional need up to a point. When it becomes excessively cold we see intakes begin to drop off again. Here again, we see the importance of keeping forage and supplemental feed sources near areas of shelter so adequate intake is more likely. A situation that is converse to hot weather is that shelter needs to be provided that can restrict air-flow (wind) to some degree to lessen the effects of wind-chill. Moisture and humidity has an effect on the animal during cold weather as well. If precipitation is significant and the animal is wet the physiological response we see by the animal is the same as if it were as much as 10o colder. In other words, if the temperature is 35o and the cow is wet, she has to use approximately the same amount of energy to maintain body temperatures as if it were 25o and she was dry.

In cold temperature situations there is an advantage to feeding the coarser quality forages we discussed above. This helps the cow to generate more heat in the rumen and increases her ability to stay warm.

Other environmental stresses include those from excessive or lacking rainfall (drought). During periods of excessive rainfall, mud accumulation can become a problem, especially in high traffic areas. Travel through muddy areas increases the amount of energy expended for this added physical activity. It is a good idea to allow the cattle as much space as possible to reduce crowding and over traveled areas as much as possible.

Dry or drought conditions, which many of us have become very familiar with, create a whole host of problems. One obvious effect is a reduction in the availability of forages creating nutritional stress which we'll discuss more later. Other stresses include increased dust production, this creates an irritation to respiratory systems and can increase the incidence of sickness due to irritation of the lining of the lungs. Once again, try to reduce congregation of the cattle as much as possible, primarily by providing more than adequate amounts of shade. Pens and corrals should be wetted down to reduce dust as well before working cattle.

Nutritional Stress

A certain degree of nutritional stress can be produced any time less than adequate nutrients are provided to meet the animal's needs. This can include dry matter intake in general, protein, energy, mineral, vitamin or even water intake. Fortunately the only remaining critical nutrient is air and typically we don't run into a shortage of that unless your running your herd in downtown Dallas or Atlanta.

As mentioned, in drought situations we can run into a lack of necessary forage availability to provide the needed dry matter intake and subsequent overall nutrients the animal needs. In these situations it becomes necessary to provide a supplemental forage source to meet this need. In many cases, these forages are substandard so additional supplementation may be needed as well to maintain a base-line production level.

Providing inadequate levels of protein and energy always reduces performance in some manner and is stressful to the animal. Anytime we short the cow it is like running your car with a lower than optimal level of oil, coolant or gas. At some point she is going to shut down one or more of her physiological processes and as we've discussed before, in many cases this is the reproductive system.

Monitoring nutrient intake year-round and comparing it to forage conditions and where the cow is in her production cycle helps insure that the appropriate nutrients are provided at the appropriate time. This can significantly reduce nutritional stress.

In the upcoming issue we'll continue this discussion and cover handling and transportation stress. These areas tend to be major factors in the stresses of cattle production.