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:
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.
6) Strategy: If intake of supplemental products (minerals, proteins, liquid feed tanks) 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.