An e-publication by the World Agroforestry Centre
METEOROLOGY AND AGROFORESTRY
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An e-publication by the World Agroforestry Centre |
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METEOROLOGY AND AGROFORESTRY |
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section 6: agroforestry and animals Climate, animal and agroforestry M. Djimde and F. Torres
International Council for Research in Agroforestry (ICRAF) W. Migongo-Bake
Semi-Arid Food Grain Research and Development (SAFGRAD) Abstract Climate affects domestic animals both directly and indirectly. Direct influences are on thermoregulation, feed and water intake and utilization, animal growth, milk production and reproductive performance. Major indirect effect of climate is on quantity and quality of feed supply. The second most important indirect effect of climate is its influence on the distribution of pests and diseases. There appears to be a great scope for agroforestry to alleviate adverse climatic effects on livestock through provision of shelter for animals and pasture. Tree shade, windbreaks, shelterbelts, trees in pasture have agroforestry potentials in alleviating climatic stress on animals and increasing pasture production.
Environmental conditions under which livestock are produced vary greatly. They include the temperate zones; semi-arid areas; low wet tropics; and high-altitude areas. These environmental conditions i.e., climatic factors, influence animal husbandry and, in particular, animal reproduction and productivity. Livestock production is influenced by climate both directly and indirectly, affecting health, reproductive efficiency, productive conversion of feed and, indeed the very survival of the animal - particularly at critical stages of its life cycle. Direct influences affect in particular the heat balance of the animal whereas indirect influences affect land use and management, feed production and conservation, disease and parasites (Starr 1986). Therefore the provision of favourable microclimates represents an important management aspect in livestock production. In this framework we attempt in this paper to present climate-livestock relationships and the possible role of agroforestry in alleviating adverse effects of climate. Although the animal component in agroforestry includes a wider range of fauna (e.g., bees, worms, fish etc.), we concern ourselves with conventional domestic livestock (e.g., ruminants, pigs, poultry).
Thermoregulation All domestic livestock are homeotherms. That means, they attempt to maintain their body temperatures within a range most suitable for optimal biological activity. In order to maintain their body temperature animals must cope with the climate. Domestic livestock must preserve a thermal balance between their heat production or gain from the environment and their heat loss to the environment. The thermal balance can be expressed by the equation M-E±F±Cd±Cv±R = O where M is metabolic heat production; E, heat loss from skin and respiratory passages by evaporation; F, heat lost or gained bringing ingested food or water to body temperature; Cd, heat lost or gained by direct contacts between the body and surrounding surfaces; Cv, heat lost or gained by convection due to contact between the air and skin and/or linings of the respiratory passages; and R, heat lost or gained by radiation (Williamson and Payne 1984). Of the various ways that domestic livestock lose heat, evaporative loss is potentially the most important under normal circumstances. It depends on the ambient air temperature, the amount of available moisture, the area of evaporating surface, the absolute humidity of the air surrounding the animal and the degree of air movement. The ability of livestock to lose heat through conduction (Cd) is very limited. Convection (Cv) heat loss is of course increased when cool breezes blow on the animal, and increased air movement may also increase evaporative heat loss. Consequently livestock accommodations in the tropics should always be built in such a way as to encourage maximal air movement on and around the animals. Solar radiation may not only increase the heat load on the animal but also directly affect the skin, causing skin cancers and other photosensitive disorders.
The effect of climate on livestock is manifested in their grazing behaviour. Cattle in the tropics if not yarded make use of any natural shade available rather than grazing in the middle of the day, to avoid the climatic stress due to high insolation and air temperatures. The reduction of night grazing practised in the tropics because of predators leads to significant decline in liveweight gain.
Feed intake High ambient temperatures depress the feed intake of all cattle. Increasing humidity combined with high ambient temperature also depresses the feed intake of all cattle.
The direct effect of climate on the water intake of livestock is very complex, as water is required by the animal for at least two different purposes: first as an essential nutrient and component of the body, and secondly to assist the animal lose heat by evaporative cooling. In general, the water intake of livestock increases with increasing ambient temperature. Humidity also affects water intake. Increasing humidity combined with high ambient temperatures decreases water consumption and increases the frequency of drinking. Increased radiation load on livestock increases water consumption which is used for evaporative cooling (Williamson and Payne 1984).
Increasing ambient temperature may decrease the efficiency of feed utilization.
Growth is a complex set of metabolic events which are environmentally and genetically controlled. Among the climatic conditions that may impose stress on the rate of prenatal, preweaning and postweaning growth are temperature, humidity, air movement and radiation (Hafez 1968). Reduced feed intake and grazing time is likely to affect animal growth (Webster and Wilson 1980; Williamson and Payne 1984).
The environmental temperature is perhaps the most important climatic component affecting prenatal growth. Miniature calves are often born to unadapted exotic breeds of livestock following summer pregnancy in the tropics. Pregnant ewes (breed dependent) exposed to high experimental temperatures bore miniature lambs, the reduction in weight being proportional to the length of exposure. This dwarfing is, according to Yeates (1958), a specific effect of temperature and not an effect of reduced feed intake.
Growth of the suckling offspring will depend upon both its own environmental surroundings and the environmental factors imposed upon its mother and her milk supply.
Climate and milk production Milk production is reduced during exposure to heat, or during the summer. This cannot be attributed solely to a fall in feed intake or forage quality. The effect of heat on physiological mechanisms related to lactation is also of importance, mainly the low level of thyroxine during the summer. Similarly milk constituents undergo changes due to high environmental temperature. Most of the available experimental evidence indicates that, for example, butter-fat and non-fat solids production is depressed by high ambient temperature.
The major climatic factors affecting reproduction are ambient temperature, humidity and length of daylight (Williamson and Payne 1984). Hypofunction of the anterior pituitary may be a major result of high temperature leading to an insufficient production of sexual hormones, which in turn results in reproductive failure (Hafez 1968). Sudden violent fluctuations in ambient temperature, such as occur in the sub-tropics, can directly affect the reproductive performance of cattle. High humidities reinforce these effects. There is evidence from field observations that both embryonic death and foetal dwarfing of sheep occur in hot environments. High ambient temperatures also appear to affect embryo survival in sows and may have some effect on oestrus. Constant high ambient temperatures reduce the rate of laying of eggs and the total number laid as well as a diminution in egg weight and shell thickness. In all male domestic livestock there is evidence that spermatogenesis is adversely affected by high ambient temperatures.
The major indirect effect of climate on livestock is on the quality and quantity of the feed available to them. Other indirect effects are on the incidence of disease and parasites and on the storage and handling of animal products.
The quantity and quality of feed available to tropical livestock are primarily dependent upon the climatic factors influencing plant growth (Webster and Wilson 1980). The most important climatic factors that limit plant growth, and hence the quantity of the feed available, are ambient temperature, effective rainfall, length of daylight and the intensity of solar radiation. The quality of feed depends mainly on effective rainfall and on the intensity of solar radiation (Williamson and Payne 1984).
Another indirect effect of climate on farm animals is its influence on the distribution of the major pests and diseases and on the arthropod vectors that are responsible for their spread. High ambient temperatures and humidities provide a favourable breeding environment for internal and external parasites, fungi and disease vectors.
Tropical climate, humid or arid, favours the rapid deterioration of stored animal products, thus increasing processing and handling costs. This indirectly affects animal production since increased processing, handling and storage charges may make increased production uneconomic in certain marginal areas that are otherwise suitable for the development of a livestock industry (Williamson and Payne 1984).
Agroforestry can alleviate adverse climatic effects on livestock by providing shelter for animals and increasing pasture productivity. Shelter effect on livestock production can be direct or indirect; direct through shade trees and windbreaks; indirect through an increase of pasture productivity by utilizing trees, windbreaks and shelterbelts to improve microclimate.
Literature on the specific effects of shade trees or tree windbreaks is very scarce. A thesis by Goldson (1973) on dairy production in a cashew-pasture combination in coastal Kenya indicates that the biggest contribution of the trees to the animal was the reduction of solar radiation as manifested in animal behaviour. However, there was no difference between the milk yields of animals in four treatments with and without shade during the wet and dry season. According to Robinson (1982) the effects of heat stress reduction by shade trees on animal production are numerous and the extent of the effects depends on the climate and the animal breed. He postulated some of the effects as follows:
Norman and Ernest (1986) reported shade to be beneficial to livestock in a high temperature environment and suggested that tree plantings can be designed with the primary function of providing shade for livestock and helping to distribute grazing uniformly in a pasture. Whereas provision of shade to animals is crucial in hot environments, windbreaks become important management tools at low temperatures. With the cold windy weather of New South Wales, sheltering lambing ewes from the wind by using a tall unpalatable phalaris reduced mortality of single lambs from 18 to 9%, and that of multiple births from 51 to 36% (Alexander et al. 1980). McLaughlin (1970) compared the survival of new born lambs in south-western Victoria, Australia, in 3 lambing systems: a) exposed paddocks; b) paddocks surrounded by Cyprus (Cupressus macrocarpa) hedges 5.8 m high; and c) individual pen lambing in a shed. In the first year, the two last systems increased the survival of single and twin lambs in the period between birth and 48 hours of age. In the second year, the third system increased the survival of single lambs, but no other differences were significant. They concluded that the second system offers an alternative to individual pen lambing as method of improving lamb survival. j The value of tree windbreaks for reducing lamb mortality on sheep properties in south-eastern Australia has been discussed by Ive (1986). He used 22 years of daily meteorological data from Ginninderra Experiment Station (New South Wales) to calculate the relationship between lamb mortality and wind velocity, and found that major reduction in lamb mortality does not occur until wind velocity is reduced to near zero. Ive concluded that tree windbreaks (which cannot be expected to reduce wind velocity to near zero, at least for any substantial distance from the windbreak) should be seen as only one farming practice in a management program to reduce lamb mortality.
In environments where water stress prevails some evidence suggests that pasture can grow earlier in the understorey of trees due to better moisture conditions. Furthermore pasture growth can continue considerably longer into the dry season, owing mainly to a suitable moisture regime being maintained for longer (Robinson 1982). The effect of shelter on the productivity of grasslands, was reviewed by Marshall (1967). The effect of artificial windbreaks (sheet iron fences ) on behaviour and production of sheep in adjoining paddocks was studied by Lynch and Marshall (1969). They compared body weight after a 21- month drought period with a 23-month non-drought period at three stocking rates (15, 30 and 38 ewes per hectare in a Phalaris tuberosal Trifolium repens pasture) at Armidale, Australia. During the drought period, sheep body weight increased more in the sheltered than unsheltered paddocks, ranging from 7% to 22% at the low and medium stocking rates. Pasture productivity in the sheltered paddocks was about double that of the unsheltered ones at all stocking rates. Increases in body weight during the rainy period was approximately 20%, but only for the medium and high stocking rates. Sheep at the lowest stocking rate had abundant feed in the wet period in both the sheltered and unsheltered paddocks, and little difference in sheep live weight between these treatments was found. They concluded that variation in animal productivity was largely due to differences in pasture availability rather than to the direct effect of shelter because: a) the sheep were in full wool through mid-winter and were consequently well insulated against cold; b) the threshold wind speeds above which most sheep move to shelter are encountered infrequently at Armidale and consequently the opportunity to benefit from shelter in windy weather was slight; and c) the shading effect of the fences from direct sun is minimal in mid-summer at the latitude of Armidale. According to the authors, moisture conserved by the shelter was probably the main factor to which the pasture responded in the experiment, a conclusion which is supported by the fact that the sheltered pasture invariably remained green for longer than the unsheltered pasture with the onset of dry spells. Wind may also affect pasture growth directly. In experiments where Festuca arundinacea and Lolium perenne grasses were exposed to constant windspeeds of 1.1, 4.0,7.4 and 10.0 m s-1 in a wind tunnel for 14 days, Russel and Grace (1978a; 1978b) found that increasing windspeed reduced rate of leaf extension, relative growth rate and leaf area ratio. They concluded that mechanical stimulus itself may have caused the reduction in leaf growth rates since no water stress and no change in rate of photosynthesis were observed. It has been shown that shading may have an adverse effect upon both growth and chemical composition of pasture species, at least under temperate conditions. However the known negative effect of temperature upon quality of forage grasses (Deinum 1966) may lead to a beneficial effect of shading under tropical conditions (Norman and Ernest 1986).
Weather and climate are environmental factors affecting domestic animals both directly and indirectly. Any improvement in animal health and production necessitates managerial measures to alleviate adverse climatic effects. There appears to be a great scope for agroforestry to counter these climatic disturbances on livestock production by providing shelter to the animals and creating favourable microclimates for an increase in pasture production (shade, windbreaks, trees in pasture, shelterbelts).
Alexander, G., J J. Lynch, B.E. Mottershead and J.B. Dondly. 1980. Reduction in lamb mortality by means of grass windbreaks: results of a five year study. Proc. Aust. Soc. Anim. Prod. 113: 329-332. Deinum, B. 1966. Influence of some climatological factors on the chemical composition and feeding value of herbage. Proc. X Int. Grassl. Congr.. Finland. Sect 2: 415-418. Goldson, J.R. 1973. The effect and contribution of the cashew tree (Anacardum occidentalis) in a cashew-pasture-dairy cattle association in the Kenya Coast. An unpublished PhD thesis. University of Reading. Hafez, E.S.E. (ed.). 1968. Adaptation of domestic animals. Philadelphia: Lea & Febiger. Lynch, J.J. and J.K. Marshall. 1969. Shelter: a factor increasing pasture and sheep production. Aust. J. Sci. 32(1): 22-23. Ive, J.R. 1986. The value of tree windbreaks for reducing lamb mortality on sheep properties in South-Eastern Australia. Proc. Int. Symp. Windbreak Technol.: 155-157. Marshall, J.K. 1967. The effect of shelter on the productivity of grasslands and field crops. Field Crop Abstr. 20(1): 1-14. McLaughlin, J.W. 1970. The effect upon neonatal lamb mortality of lambing systems incorporating the use of partial and complete shelter. Proc. Aust. Soc. Anim. Prod. Vol. 8. Norman, E.S. and C.S. Ernest. 1986. Planting trees for livestock shade. Proc. Int. Symp. Windbreak Technol.:243. Robinson, P. 1982. The role of silvopastoralism in small farming systems. Proc. ICRAF/BAT Workshop (Nairobi, Kenya): 147-169. Russel, G. and J. Grace. 1978a.The effect of wind on grasses. V. Leaf extension, diffusive conductance and photosynthesis in the wind tunnel. J. Exp. Bot. 29(12): 1249-1258. Russel, G. and J. Grace. 1978b. The effect of windspeed on the growth of grasses. J. Appl. Ecol. 16: 507-514. Starr, J.R. 1986. Weather and climate and animal performance. Geneva: Comm. Agr. Met., World Meteorological Organization. Webster, C.C. and P.N. Wilson. 1980. Agriculture in the tropics. London: Longman. Williamson, G. and WJA. Payne. 1984. An introduction to animal husbandry in the tropics. 3d ed. London and New York: Longman. Yeates, N.T.M. 1958. Foetal dwarfism in sheep — an effect of high atmospheric temperature during gestation. J Agric. Sci. 51: 84- 89. |