Cattle Today

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SUMMER HEAT CAN BRING MANAGEMENT CHALLENGES

by: Stephen B. Blezinger
Ph.D., PAS

Part 1

Summer is typically a great time of the year. A time for baseball and watermelon, a time for home-made ice cream and fireworks. Many years it's a great time for cattle producers as well. It certainly is if you consider what the markets have been and continue to be. I know a lot of managers that are never as happy as they are when they are cutting, raking or baling hay or putting up silage. Unfortunately over recent years some of this joy has been taken out of the production process. Environmental effects such as “El Nino” have created some interesting climatic effects that have, in many cases, wreaked havoc on hay and forage production in certain parts of the United States, especially in the south. Once again, we are seeing similar patterns, with some areas experiencing drought-like conditions while others are receiving excessive rainfall. Some areas will experience average to above average rainfall and have no difficulty with forage production for hay and grazing with the exception of the weather being dry enough, long enough so hay can be dried sufficiently and baled. In other areas, unfortunately, lack of rainfall will reduce levels of hay production, reduce growth of immediately grazable forages and reduce growth of forages that would be grazed in the fall and early winter. In short, significantly reduce the nutrient source available for these cattle for the coming months.

I have from time to time in the past, been accused of being a control fanatic, i.e. controlling your variables such as feed intake, knowing what your forage nutrient levels are, etc., etc. Unfortunately, there's not really effective recommendation for controlling variable weather patterns. There are steps that can be taken to economically compensate for the effects of these environmental conditions on production of forages and cattle in general. We need to discuss the effect of heat on animal physiology and how to compensate for some of this heat stress. Then we can review ways to supply the roughages and nutrient needs of these cattle when normal production is insufficient to meet these needs. The goal here is to lessen the effects of heat on the animal, maintaining production levels. A second goal is to provide for their nutrient needs, thereby maintaining production, without breaking the bank.

Heat Stress and Related Factors

Heat stress is caused by factors which decrease the heat transfer from an animal to it's environment. Some of these factors include: 1) high air temperature; 2) high air humidity; 3) low air movement and 4) thermal radiation load. As would be expected, high air temperature is usually the primary cause of heat stress although the other factors intensify this effect. The end result is an inability of the animal to effectively cool itself. The cooling process requires more physiological “work.” Another interesting consideration is that heat stress has negative effects on healthy animals. It is reasonable to expect, therefore, that animals suffering from disease or from a parasite load would be affected to an even greater degree. Cattle undergoing heat stress can be expected to experience declining levels of milk production, reduced reproductive efficiency and various metabolic disorders which can become life-threatening. Similarly, growing cattle will experience reduced gains and feed efficiency and if shipped to another location (grazing operation, feedyard, etc.) will compound the transit stress therefore increasing end-point morbidity (sickness) and mortality (death-loss).

Two basic factors must be considered when taking an overall view of this situation:

A)      Cattle exposed to heat stress will increase their energy requirement to reduce heat load. This results in an increase in their maintenance energy requirement. Relative maintenance energy requirement, the energy that a cow requires to maintain herself, is 20 percent higher at 95o F than it is at 68o. Therefore, additional energy or more accurately, additional dry matter intake is required to support this increased requirement. Table 1 illustrates the changes experienced in cattle at differing temperature levels and the effect on energy requirements and dry matter intake.


Temperatures around 68 to 70o F are considered to be “thermal-neutral.” In other words, no added energy is needed to heat or cool the cow's body. When temperatures increase or decrease significantly from these levels, however, added energy is needed to maintain normal physiological processes. If energy intake remains the same, some of this energy is taken away from less vital processes and dedicated to the more important matter of survival. The first physiological area debited in the brood cow is reproduction. In growing cattle it is weight gain. As you can see from the table that at higher temperatures, more dry matter is required to meet this increased energy demand. As you can also see from the table, this is not the cow's normal response. Therefore:

B)      Dry matter intake decreases as heat stress increases.

Cattle producers should take steps to reduce heat load on cows. In most situations this becomes a matter of insuring that adequate shade is available and that air-flow is adequate to dissipate heat. In other words, a shed with three closed sides would not be exceptionally helpful. Dairy producers will typically use movable shade structures, fans and misters or sprinklers. In most situations this is not cost effective for the average beef cattle operation so steps must be taken to insure adequate shade and allow for normal air movement. Under certain hot and dry conditions it may be helpful to utilize sprinklers, especially in dry-lot conditions to help control dust and to reduce respiratory stress and the potential incidence of dust pneumonia, etc.

This situation creates several nutritional challenges and factors that affect the overall nutritional program.

1) As noted in Table 1 above, forage and feed intake can decline significantly as temperatures increase. Strategy: use “tricks of the trade” to encourage intake. One is an inclusion of a yeast culture in supplements. Yeast can be added to free-choice minerals or other supplements and will stimulate the ruminal and digestive environment in a manner which increases dry matter intake.

2) Blood flow is reduced to the digestive tract as cows attempt to dissipate heat. Blood flow to skin and extremities is increased at this time. Strategy: Provide better quality pastures and/or hays at this time in addition to good quality, properly balanced supplements to improve overall improved digestibility of forages and feeds.

3) When forages and feed are digested, heat increment (heat production) is increased which increases additional heat the cow must dissipate. Strategy: Once again: if possible, allow access to better quality pastures or forages and more digestible energy sources. Supplemental fat can be added in supplements to provide energy which is not associated with digestion. However, fat needs to be added carefully, especially from oilseeds such as whole cottonseed. Excessive use of whole cottonseed can boost the amount of unsaturated fatty acids which reduces fiber digestibility.

4) Cattle will graze/eat during cooler times of the day. This primarily results in more night and early morning grazing. Strategy: put out supplements (minerals, meals, etc.) later in the evening or early in the morning to stimulate consumption.

5) Locate feeders and water sources (if possible) closer to shaded areas. Strategy: If intake of supplemental products is lower than desired, move feeders closer to shaded or loafing areas so cattle do not have to venture out as far or for as long into the heat to eat.

Providing a high quality mineral is always important to performance. Research has shown that the appropriate feeding of certain minerals helps to alleviate heat stress. Table 2 illustrates the improved response to feeding certain minerals in dairy cattle. Similar results can be expected in beef cattle as well.

Higher levels of sodium (from .18 to .5 percent) of total ration dry matter are beneficial under heat stress. This is equal to 50 to 140 grams (1.6 to 5 ounces) of salt fed daily. Sodium is excreted in urine while potassium losses occur through sweating. Maintaining a ration of 3 parts potassium to 1 part sodium is desirable. Magnesium should also be boosted from .2 to .3 percent in overall dry matter when potassium levels are elevated.

Other mineral levels such as copper, zinc, etc. should also be increased in supplements. As with sodium, during stress, significant amounts of many of the trace elements are lost through urination and must be replaced to maintain normal levels. Since intake levels are not optimal as indicated above use of organic or chelated mineral sources is often warranted due to higher bioavailabilities of these elements and improved efficiency of absorption.

While we commonly hear of management of heat stress in the dairy industry, heat stress is equally detrimental to the performance of beef cattle. Heat stress is something you must manage. Hoping that the summer will get cooler or that it's bound to rain sooner or later is simply not enough. Gain, breeding and milking performance suffers greatly at this time and can become very costly if ignored. Management is not expensive but does require attention to detail. Even small details can have a profound effect.

We know that inability to cool an animal's body creates stress and stress reduces performance. People have the luxury of going inside, into the air conditioning or removing some clothing (up to a point). A good friend of mine from Wisconsin and I were debating which was worse, their extreme cold or our extreme heat. My argument to him was that you can always put on more clothes but you can only take off so much in public and not get arrested. While cattle do have the luxury of walking around naked most of the time, they are not quite as fortunate when it comes to the availability of air conditioning.

Secondly, the high temperatures are often accompanied by dry weather as is the case this year through much of the South. In some parts of the Southern United States, rainfall has been all but non-existent in addition to being exceptionally hot. This has created significant concern over availability of forages for grazing as well as that to be harvested for feeding this fall and winter.

In the next issue we'll review a few strategies to aid in managing this stressful period.

Dr. Steve Blezinger is a nutritional and management consultant with an office in Sulphur Springs, TX. He can be reached at 667 CR 4711 Sulphur Springs, TX 75482, by phone at (903) 885-7992 or by e-mail at sblez@peoplescom.net.

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