by R.H. Ansell
In recent times considerable numbers of Bos taurus dairy cattle have been introduced into many countries in the Near East where the prevailing species is Bos indicus. Since the climate in this region differs markedly from that in the natural habitat of the European breeds, the question has frequently been raised as to whether climatic factors have been responsible for the often disappointing results obtained from Bos taurus cattle. Alternatively, are these poor results due to inadequate management and feeding and lack of knowledge of the requirements of exotic cattle?
This article reviews the results of a three-and-a-half-year study (Ansell, 1974) conducted in the United Arab Emirates, where the summer climate is extremely inimical to dairy production. The study was made on British Friesian cattle, which are not noted for their heat tolerance.
In view of the relative success achieved in maintaining high production under such harsh climatic conditions, this article has been written for the benefit of those who plan to introduce high-yielding European cattle into other parts of the Near East or to countries with similar climates. It describes some of the problems likely to be encountered and the steps that can be taken to alleviate the stresses imposed on the cattle.
R.H. Ansell is Livestock and Range Management Adviser in the FAO/ UNDP project in Juba, Sudan. The work reported in this article was undertaken when he served as Regional Veterinary Officer, Ministry of Agriculture, United Arab Emirates.
Body heat in cattle is largely the product of the exothermic physical and chemical reactions within the animal and the absorption of heat by radiation and conduction from the environment. The dissipation of body heat is achieved by radiation, conduction and evaporation of moisture. Other minor methods of acquiring and dissipating heat are the voidance of faces and urine, raising ingesta to body temperature, and endothermic reactions. But these can be ignored in the context of animal management, with one exception: the ingestion of cold water, which could be of some significance.
Evaporation of moisture, whether from the skin or lungs, is a major factor in heat dissipation, and it is unfortunate that cattle, in particular the European breeds, are less well endowed with sweat glands than heattolerant mammals such as man.
Evaporation is one of course dependent on the humidity of the air and the wind velocity over the evaporating surface. Although this is a controversial subject and involves complex physical concepts, it can be safely assumed that relative humidity readings as taken from a wet and dry bulb thermometer can be used as a guide to the evaporative capacity of the air. It is this major dependence on evaporation for heat dissipation which makes high relative humidities — in association with high temperatures—so critical in producing heat stress. Various formulae have been devised combining humidity and temperature to produce a “heat index”. Perhaps the most promising of these is that of Bianca (1962): heat index = dry bulb °C × 0.35 + wet bulb °C × 0.65. But neither this nor other formulae have been fully confirmed experimentally, although they to provide a crude assessment of comparative climatic severity when the introduction of exotic stock to unfavourable climates is being considered.
Friesian bull in fine condition after a severe summer in the United Arab Emirates
Conduction and radiation are simpler concepts of heat dissipation than evaporation. They are dependent on environmental temperatures and on the surface area/body weight ratio of the animal, i.e. an animal with a large surface area in relation to its bulk (e.g. a bat) can dissipate heat by these means more easily than one with a low surface area to body weight ratio. It has often been assumed in this connexion that the large dewlap, pendulous sheath, large ears and hump of Asiatic cattle which contribute to their increased surface area also contribute to heat tolerance. However, this is not necessarily the case, since experimental surgical excision of these organs has shown that the heat tolerance of the animals so treated is unaffected. This observation may be of some consequence in that it would be useless to select smaller animals from within a breed for introduction into hot climates solely in the belief that their surface area/body weight ratio would result in increased heat tolerance. The effect of such selection, if any, might be insignificant in relation to that of other factors.
An important aspect of heat dissipation is the diurnal variation in dry bulb temperature. Cattle can build up heat within their bodies to a considerable degree during the day without adverse effects if the night temperatures are sufficiently low to allow for its dissipation. But high sustained body temperatures are destructive.
A detailed knowledge of the climate of the area in question is therefore essential for assessing the heat stress likely to be encountered by animals. Monthly means of maximum and minimum temperatures are of little use; diurnal variations of temperature and humidity and their duration are of much greater significance. The results obtained in the United Arab Emirates suggest that on grounds of climatic factors alone, there are likely to be very few areas in the Near East where European breeds cannot be maintained successfully.
Figures 1 and 2 illustrate the severity of the climatic conditions experienced in the United Arab Emirates; they are near the upper limit of tolerance of Friesian cows in milk. It should be noted that the temperatures were recorded in well-shaded sites; they should not be equated with temperatures recorded in the standard “Stevenson screen” type meteorological box which, during the hours of sunlight, gives much higher readings.
Figure 1. Method of depicting climatic stress in British Friesian cattle in the United Arab Emirates, June 19721
SOURCE: Work done by the author at Digdaga, Ras Al Khaimah, United Arab Emirates in June 1972.
1 The curves represent the arithmetic mean of once weekly readings taken at hourly intervals. The length of the vertical bars gives the range of the readings.
Effect of diet
The results of climatic chamber experiments conducted at the University of Missouri in the United States, and elsewhere, suggested that depression of appetite is a significant factor in reducing the milk yields of animals subjected to high environmental temperatures. These results were not corroborated in the United Arab Emirates study, since it was possible to maintain the animals on a constant diet throughout winter and summer with a ration that maintained both yield and body condition. This diet consisted of: a maintenance ration of 20.5 kg freshly cut alfalfa, 32 kg compounded dairy nuts, 1.8 kg bran, 14 g mineral and vitamin supplement and 57 g dicalcium phosphate; and a production ration of 1.8 kg of compounded dairy nuts per 4.5 kg of milk.
Figure 2. Methods of depicting climatic stress in British Friesian cattle in the United Arab Emirates, 22 June 1972 1
SOURCE: Work done by the author at Digdaga, Ras Al Khaimah, United Arab Emirates in June 1972.
1 The curve represents hourly readings of relative humidity and ambient temperature taken on one day and converted according to the formula of Bianca (1962). It depicts a pattern that approaches the upper limit of tolerance of fully acclimatized Friesian cows in milk.
No grazing was available to the animals, and salt was not included in the ration since the salinity of the drinking water was very high and salt was in any case refused when offered.
This diet proved very satisfactory and resulted in a Compton metabolic profile well within standard limits. It is possible that the severe depression of appetite reported in the climatic chamber studies (which was not encountered to any great degree in the study) may have been a psychosomatic effect on the animals resulting from the close confinement inherent in chamber experiments. However, it was observed that the animals in the study took considerably longer to consume the ration in the summer months when conditions became extreme.
The suppression of spermatogenesis and early foetal reabsorption (Stott and Williams, 1962) are well documented under high temperature regimes. These phenomena were amply demonstrated in the first year of the United Arab Emirates study in that no successful conceptions took place between the months of June and October, although libido and manifestations of heat were not seriously affected. Two points are worthy of note in this connexion: spermatogenesis can be impaired for as long as nine weeks after exposure to heat (Johnston, Naelapaa and Frye, 1963); and oestrous periods tend to be “quiet” and short, thus making heat detection difficult if Al is to be practised.
It was also found that calving in the hot season subjected the animals to unacceptable stress conditions. Gestation periods were shorter by approximately 10 to 14 days for summer calvings, birth weights of calves were significantly reduced, and calves born during the height of the summer were found to be as much as 56 days premature in some cases. The shortened gestation periods adversely affected the dry periods prior to parturition. A high proportion of primary inertia was also encountered in the herd studied, but its relation to season of calving could not be demonstrated. It does not necessarily follow that all of these manifestations will occur in more moderate temperatures, but the possibility nevertheless remains.
Palm leaf shades are simple and cheap to construct
Thus seasonal calving and close supervision of parturition are essential under climatic conditions as extreme as those encountered in the United Arab Emirates. Under such conditions, services should be limited to the months of February, March and April if neither conception nor parturition are to occur during the summer months.
Great care must be taken during the first 10 days of life of the calf because its thermoregulatory mechanism appears to be defective during this period, and it may develop extreme hyperthermia and die if artificial cooling is not provided.
For premature calves, this critical phase extends over a longer period. But once the calves have passed it, they tolerate heat stress well and pose few problems. Of 94 calves born during the period of the current study, none died after the first five days of life from any cause, and no cases of calf scours occurred.
Research workers have used a number of methods to attempt to estimate variations in milk yield attributable to different factors. Each has its limitations, and the best that can be said of any of them is that they only indicate approximate trends. In the United Arab Emirates study the depression of milk yield attributable to the climate was estimated by reference to the standard lactation curve constructed on the basis of the formula devised in the United Kingdom by the Milk Marketing Board (1969/ 70). On this basis it was found that the depression of yield attributable to the hot season amounted to the surprisingly low figure of 2.7 percent of the theoretical 305-day lactation, but this was almost entirely offset by the hitherto unsuspected “post-stress rebound”.
The average yield of the 19 heifers having a 305-day lactation period in the present study was 3 253 kg. This compares favourably with the yield of 3 842 kg quoted as the average yield of 859 British Friesians used by the Milk Marketing Board to compile the standard lactation curve. A surprising factor was that the early summer months showed no reduction in yield; sometimes the reverse occurred. But toward the end of summer “fatigue” seemed to set in, and most of the reduction occurred at that time.
Health and disease
Problems were experienced with hoof necrosis attributable to the animals standing for long periods on sawdust moistened with urine and dung. This is of relevance to areas where bedding is in short supply and where. animals must be confined on hard standings for long periods. It appears that most bedding at temperatures approaching bacterial incubation levels can be destructive to hoof tissues.
No statistically significant difference was detected between the incidence of mastitis in summer and winter; the level of incidence was within reasonable limits.
An important health hazard was the pathogenicity of Theileria annulata, which is endemic throughout most of the Near East. Whereas mortality from this cause is comparatively low among indigenous cattle, it is very high among Bos taurus breeds. Tick control must therefore be complete and provision must be made for dipping or power spraying; hand spraying is usually inadequate.
No other special disease problems attributable to the unfavourable climate were encountered during the three and a half years covered by the study. It may therefore be concluded that if normal prophylactic medicine is practised, the incidence of infectious diseases should pose no difficulty. Nevertheless, it would be highly desirable to monitor the health of the herd by taking rectal temperatures daily. Since high body temperatures are to be expected under conditions of heat stress, it is imperative that a continuous record be kept to differentiate between the high temperatures caused by climate and those due to pathological conditions. In addition, care should be exercised in taking thermometer readings when ambient temperatures are higher than body temperatures, so that the mercury level does not rise in the thermometer after its removal from the rectum. A cotton swab soaked in alcohol is useful under these conditions.
Signs of heat stress
When the upper limit of heat tolerance is approached, cattle show some unmistakable and often alarming stress symptoms:
Open mouth breathing. This is indicative of very advanced stress; the head is extended, the mouth held open, and profuse salivation takes place.
High respiratory rates. These may be in the 100 to 120 range, but surprisingly they can be tolerated daily for long periods without causing any apparent symptoms of respiratory alkalosis.
Second phase breathing. This is a phenomenon first recorded by Beakley and Findlay (1955). At rectal temperatures of approximately 41.8°C there is a sudden drop in respiratory rate with a concurrent increase in tidal volume. This phase is also a symptom of advanced stress and should not be allowed to continue.
Body splashing. Strenuous efforts may be made by animals to paw water back onto their bodies from water troughs or to beat the water with their heads.
Refusal to lie down. This is a common phenomenon. Usually all the animals in the herd will stand for long periods when they would normally be expected to lie down; ablation of the “elbows” is often associated with this stage.
Huddling. Contrary to expectation, cattle subjected to heat stress will huddle together and will disperse as soon as the temperature drops to a moderate level.
High rectal temperatures. Afternoon temperatures of 40.5°C are not uncommon and can be tolerated for long periods providing that nightly remissions take place. However, if the rectal temperature exceeds 41°C, steps should be taken to reduce it.
Most of the above symptoms are valuable clinical indications of the degree of stress being experienced by cattle, and could serve as a guide to the time when steps to alleviate the stress must be taken. It may be noted in this connexion that lactating and heavily pregnant animals have a lower degree of heat tolerance than non-lactating animals. One Bos indicus animal in the study demonstrated its superior heat tolerance by lying happily in the sun with a barely perceptible respiratory rate of 8 to 10, when respiratory rates among Bos taurus cattle were in the region of 120. However, its growth curve was markedly depressed, and it could best be described as being almost in a state of aestivation.
Amelioration of climate
Although the foregoing may appear to be a formidable list of woes likely to be encountered by cattle under adverse climatic conditions, in practice most of them were encountered only when deliberate efforts were made to refrain from taking steps to mitigate climatic stress. When such steps were taken, the herd remained remarkably trouble-free and tolerated the conditions of the Persian Gulf littoral very well. The more important methods adopted are listed below.
Showering. A variety of methods for cooling dairy cattle were tried:
However, probably the most costeffective method consists of providing the animals with an artificial sweating mechanism to equate them with the freely sweating, heat-tolerant mammals. This can be done in a number of ways: the easiest is to invert a revolving domestic garden sprinkler on to the ceiling of a concrete-floored cattle shed. It was found that the cattle then formed an outward-facing circle at the periphery of the spray, and that a few hours free access to this in the afternoons reduced otherwise elevated body temperatures to normal limits, even in the relatively high humidities of the Gulf. The temperature of the water is to all intents and purposes immaterial since the latent heat of evaporation is utilized. The effectiveness of this method is amply demonstrated in Figure 3, which shows the mean rectal temperature of 21 cows with and without access to showering. The advantage of this method is that energy is not expended in lowering the temperature of large masses of air (as in desert coolers or air conditioners) which may not come into contact with the animal. However, a reasonable supply of water is necessary, but no more than is usually required if dairying is to be practised. Similarly, the temperature of an individual animal may be reduced dramatically by soaking it with water. It is not necessary to play a continuous stream of water over the animal, although if one wetting of the coat is insufficient, the coat may be re-wetted when dry. This effect is shown in Figure 4.
Feeding yard constructed of pipe and galvanized sheeting. Note venturi arrangement at apex of roof
Shelter engineering. The provision of properly constructed shade is essential in tropical latitudes. A Friesian cow confined without shade in the temperatures and humidities of the Persian Gulf will reach a stage of lethal hyperthermia within a few hours.
Ideally, shelters should have high insulating properties and should be extensive enough to eliminate much of the radiation from the sky. They should have a low radiation coefficient, and as a general rule should be at least 3 metres high. A large, leafy, non-deciduous tree approaches the ideal. Thatch from palm leaf, straw or grass is a very satisfactory material. Asbestos cement, galvanized iron or aluminium are less satisfactory but are usually the most commonly available materials. Their defects may be offset to a certain extent by making their surfaces reflecting (with silver or white paint), and by constructing the shelters properly. A highly effective but costly method of construction with these materials is to have a two-skin roof with an air gap of not less than 12 cm between the two skins. This air gap should have free access to the outside at the apex. If only a single skin of these materials can be afforded, the pitch of the roof should be made reasonably steep (not less than 20°); this will accelerate the upward movement of hot air layers adjacent to the undersurface. In addition, it should be as high as can be conveniently constructed, recognizing however that the extent to which a shadow moves is in direct proportion to the height of the shade. Thus when high shelters are designed, care must be exercised to ensure that the shadow is not cast outside the animals' quarters. Air gaps at the apexes of buildings for the exhaustion of hot air can be enhanced by constructing a flat or curved “lid” over the gap in order to produce a venturi effect.
Figure 3. Mean rectal temperature of 21 cows with and without access to showering, United Arab Emirates, August 19721
SOURCE: Work done by the author at Digdaga, Ras Al Khaimah, United Arab Emirates in August 1972.
1 Reading were taken from cows with access to an overhead sprinkling system between 12.00 and 16.00 hrs in a climate similar to that depicted in Figure 1.
In most areas of the Near East low wind velocities are a problem. But where high hot winds do occur, slatted walls or fences reduce the velocities considerably and interfere little with normal ventilation. The width between slats may be varied to suit prevailling wind speeds, but equal spacings are often a satisfactory compromise.
Feeding. Since a specific heat increment is associated with feeding, it is necessary to arrange feeding schedules to correspond with the cooler periods of the day — usually at night and in the early morning. Milking times should be organized in a similar fashion, since concentrates are normally offered at these times. The interval between milkings should be as wide as can be consistent with these factors.
Zero grazing systems in extreme climatic conditions have a decided advantage in that energy expenditure and heat production due to walking are kept to a minimum. However, if grazing is practised, the distance walked should be kept to a minimum and the grazing confined to the hours of darkness.
Local conditions will of course dictate what diets are available, but experimental work has confirmed that more heat is produced from roughages for a given nutrient intake than from concentrates, and that succulent herbage is more readi'y ingested under high ambient temperatures than dry ligneous material.
Water. Water should, of course, be available at all times. The consumption of water by European cattle under heat stress may be more than twice that in their natural habitat.
Chilled drinking water is welcomed by stock. It undoubtedly reduces the heat load of the animals considerably, but the medium-and long-term effects of this practice on ruminant digestion have not been fully explored. This method of climatic alleviation must therefore be approached with caution.
Figure 4 Effect of wetting on the respiratory and rectal temperature of a six-day-old calf, 26 August 19711
SOURCE: Work done by the author at Digdaga. Ras Al Khaimah, United Arab Emirates in August 1972
1 Intermittent hosing begins at Point A. Point B represents one soaking only. At Point C, the respiratory rate has dropped with increased rectal temperature (second phase breathing).
The principal conclusion of this study is that if appropriate steps are taken to mitigate the effects of climate and a high level of management practices is maintained, there appears to be no reason why high ambient temperatures and humidities should be inimical to successful dairy development with European breeds in the Near East.
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Beakley, W.R. & Findlay, J.D. 1955. The effect of environmental temperature and humidity on the respiration rate of Ayrshire calves. J. agric. Sci., Camb., 45: 452–460.
Binaca, W. 1962. Relative importance of dry and wet bulb temperature in causing heat stress in cattle. Nature, 195 (4838): 251–252.
Johnston, J.E., Naelapaa, H. & Frye, J.B., JR. 1963. Physiological responses of Holstein, Brown Swiss and Red Sindhi crossbred bulls exposed to high temperatures and humidities. J. Anim. Sci., 22: 432–436.
Milk Marketing Board. Production Division. 1969/70. Studies of the lactation curve. Thames Ditton.
Stott, G.H. & Williams, R.J. 1962. Causes of low breeding efficiency in dairy cattle associated with seasonal high temperatures. J. Dairy Sci., 45: 1369–1375.