Animal Adaptation

Adaptation has the potential to reduce some of the damage caused by climate change (Hulme 2005). However, little work has been undertaken to identify strategies which will allow domestic animals to adapt to climate change (King 2004).

How is adaptation in domestic animals defined? Is it simply the ability of the animals to survive, grow, and reproduce? Or, is it maintenance of productive performance at some predetermined level? Numerous terms are used to describe animal responses to adverse environments (Folk 1974; Yousef 1987).

In its broadest form, adaptation is defined as a change which reduces the physiological strain produced by a stressful component of the total environment. The change may occur within the lifetime of an organism (phenotypic) or be the result of genetic selection in a species or subspecies (genotypic) (Bligh and Johnson 1973).

• Genetic or Biological Adaptation: Adaptation is achieved through genetic change over time (generations), which involves evolutionary processes, and also through environmental stimulation and experiences during an animal's lifetime (Hafez 1968; Price 1984 cited by Mignon-Grasteau et al. 2005). This comes about via natural selection, and selection of animals by humans (Hafez 1968). Identification of heat tolerant phenotypes within existing breeds, or infusion of genes for heat tolerance may be a partial solution. The biological properties of animals are a result of interactions between stress intensity, magnitude of environmental fluctuations, and the energy available from resources (Parsons 1994).

• Phenotypic or Physiological Adaptation: Animals have the ability to respond to acute or sudden environmental change (e.g. shivering when exposed to cold) (Folk 1974; Hafez 1968; Langlois 1994), and with longer exposure to climate change (although this may be somewhat limited).

Other terms commonly used to describe an animal's response to climatic variables include acclimation, acclimatization and habituation. These were defined by Folk (1974) as follows:

• Acclimatization - the functional compensation over a period of days to weeks in response to a complex of environmental factors, as in seasonal or climatic change

• Acclimation - the functional compensation over a period of days to weeks in response to a single environmental factor only, as in controlled experiments

• Habituation - (i) Specific - specific to a particular repeated stimulus and specific to the part of the body which has been repeatedly stimulated, and (ii) General - a change in the physiological set of the organism relevant to the repeated stimulus and the conditions incidental to its application

Animals are regularly exposed to climatic stress (Parsons 1994). The extents to which they are able to adapt are limited by physiological (genetic) constraints (Devendra 1987; Parsons 1994). Selection criteria for livestock and poultry (and possibly domestic animals in general) need to be considered in the context of climate change, and whether the location (habitat) is likely to be favorable or unfavorable to the species of concern. There is a necessity to select livestock, and use livestock systems (e.g. pasture management) on the basis of expected climatic conditions.

Animal performance may be limited where there is climatic adversity. Animals that have evolved to survive in adverse conditions generally have the following characteristics: high resistance to stress, low metabolic rate, low fecundity, long lives, behavioral differences, late maturing, smaller mature size, and slow rate of development (Devendra 1987; Parsons 1994; Hansen 2004). This suggests that selection or use of animals (often indigenous breeds) that are adapted to adverse climates will have lower productivity than those selected for less stressful climates. In general this is true; however, these animals survive, grow and continue to provide food, fibre and fuel under conditions where the animals higher production potential may at the worst die or at best produce at levels at or below the indigenous breeds. In many of the developing countries located in the tropics, the poor reproductive performance of cows (both indigenous and imported), for example, results from a combination of genetics, management, and environmental factors (Agyemang et al. 1991). Depending on location, climate change may improve the local environment or have major negative impacts. In order to take advantage of positive changes or reduce the impact of negative changes, farmers will need to adapt. Improved genetics (including suitability to the environment) and improved management may go a long way to take advantage of changes or minimize the impact. The use of housing, microclimate modification (e.g. shade, sprinklers), improved nutritional management, disease control, and new reproductive technologies are usually needed if animals are to meet their genetic potential (Champak Bhakat et al. 2004; Voh et al. 2004; Magana et al. 2006). However, the cost of implementation of these processes may be too high to be economically viable, especially in developing countries.

Mechanisms of animal adaptation have been defined by Devendra (1987) as: anatomical, morphological, physiological, feeding behavior, metabolism, and performance. Physiological and behavioral adaptations are employed first in response to environmental changes. Animals employ multiple strategies in order to adapt to the environment. For example, Sudanese Desert goats tolerate thermal stress and nutritional shortage (food and water) by their capacity to lose heat via panting and cutaneous evaporation, as well as their ability to concentrate urine to levels above 3,200 mosmols/kg (Ahmed and Elkheir 2004). Additional characteristics of adaptation by goats under different climates are presented in Table 7.2. Camels also use multiple strategies to cope with thermal stress and nutritional shortages. They use sweating to control body temperature in an environment where water loss needs to be minimized. However, they have the ability to increase body temperature during the day (up to 41°C) and then dissipate the heat during the night when desert temperatures may approach or fall below 0°C. Storing heat during the day and dissipating the heat at night is a method of conserving energy and water loss. Camels have an ability to consume large amounts of water when dehydrated. Guerouali and Filali (1995) reported that the water intake of hydrated camels averaged 1.33% of body weight. The camels were then exposed to a 27 day dehydration period. When re-hydrated, water intake increased to 19.12% of body weight within a couple of minutes. Water intakes of up to one third of body weight have been reported. Large water intakes

Table 7.2 Adaptive properties of goats

Climate

Anatomical

Morphological

Physiological

Metabolism

Feeding3

Performance

Arid/semi-arid

Large size

White, black

Panting.

Increased

Browse over long distances.

Meat/milk/fiber

(30-50kg),

or brown

sweating

mobilization

resistance to dehydration.

long legs

coat color.

of fat during

dessication of feces, increased

and ears.

shiny surface.

periods of

concentration and reduced urine

scrotum

white colored

feed shortage.

volume, rumen acts as water

shows two

goats absorb

low water

reservoir, high digestive

distinct sacs

less solar radiation

turnover rate

efficiency of coarse roughages, efficient utilization and retention of nitrogen

Sub-tropical

Intermediate

White, black or

Panting.

Lower water

Intermediate

Meat/milk/fiber

size

brown coat.

sweating

turnover rate

(25-30kg)

less shiny coat

Humid/sub-humid

Small size

Mainly black or

Reduced

Low metabolic

Reduced walking due to increased

Meat

(10-25kg),

brown coat

panting.

rate

availability of forages and crop

short legs.

color, shiny

more access

residues

small ears

coat

to shade

"Feeding behaviour and feed utilization.

"Feeding behaviour and feed utilization.

may lead to osmotic shock. However, camels are able to store large amounts of water in the stomach. The camel can also dehydrate without affecting blood viscosity and composition. This may be due in part to the shape of camel erythrocytes, which are oval rather than bi-concave as seen in most mammals (Fowler 1999).

Cattle of Indian origin (Bos indicus) and those from Europe and parts of Africa (Bos taurus) have undergone a separate evolution for several hundred thousand years (Hansen 2004). The Indian or Zebu cattle have during their genetic adaptation acquired genes for thermotolerance (Hansen 2004), and therefore have a higher degree of heat tolerance compared to Bos taurus cattle (Allen 1962; Finch 1986;

Hours after entering chambers
Evolution Ofcamel

Hours after entering chambers

Fig. 7.2 Differences between Hereford (closed circles) and Brahman (open squares) for respiration rate and rectal temperature over 10 h in an environmental chamber when THI > 90 (Adapted from Gaughan et al. 1999)

Hours after entering chambers

Fig. 7.2 Differences between Hereford (closed circles) and Brahman (open squares) for respiration rate and rectal temperature over 10 h in an environmental chamber when THI > 90 (Adapted from Gaughan et al. 1999)

Spiers et al. 1994; Hammond et al. 1996, 1998; Gaughan et al. 1999; Burrows and Prayaga 2004). However, some Bos taurus African breeds such as Tuli, and D'Nama have developed heat tolerance, and appear to be as good as Bos indicus cattle in this regard. Under hot climatic conditions, the genetic adaptation of Bos indicus cattle allows them to have a lower respiration rate and rectal temperature than Bos taurus cattle (Fig. 7.2). An excellent review on the adaptation of zebu cattle to thermal stress was undertaken by Hansen (2004). Adaptation to hot conditions has resulted in animal acquiring specific genes, some of which have been identified (see discussion below).

Sheep and goats are thought to be less susceptible to environmental stress than other domesticated ruminant species (Khalifa et al. 2005). They are widely distributed in regions with diverse climatic conditions and possess unique characteristics such as water conservation capability, higher sweating rate, lower basal heat metabolism, higher respiration rate, higher skin temperature, constant heart rate and constant cardiac output (Borut et al. 1979; D'miel et al. 1979; Shkolnik et al. 1980; Feistkorn et al. 1981).

Differences in physiological responses of sheep adapted to hot conditions (Omani - indigenous breed of Oman) and non-adapted to hot conditions (Merino -Australian) were reported by Srikandakumar et al. (2003). When exposed to hot conditions, the Omani sheep had lower respiration rate than the Merino (65 vs. 128 breaths/min, respectively) (Fig. 7.3). There were no differences in rectal temperature during exposure to hot conditions, but the rectal temperature of the Omani sheep was significantly lower during exposure to cool conditions. The rectal temperature

c 120

cc 80 EC

I 60

RR-hot

Fig. 7.3 Differences in respiration rate (RR) between Australian merino and Omani sheep when exposed to cool and hot conditions (Adapted from Srikandakumar et al. 2003)

RR-cool

RR-hot

Fig. 7.3 Differences in respiration rate (RR) between Australian merino and Omani sheep when exposed to cool and hot conditions (Adapted from Srikandakumar et al. 2003)

39.8

39.6

39.4

38.8

RT-cool

RT-hot

Fig. 7.4 Differences in rectal temperature (RT) between Australian merino and Omani sheep when exposed to cool and hot conditions (Adapted from Srikandakumar et al. 2003)

of the Omani sheep increased by 0.7°C during hot conditions compared to 0.3°C in the Merino sheep (Fig. 7.4).

Goats are a very good example of a domestic animal that is highly adapted to harsh conditions. Silanikove (2000) postulated that goats living in harsh environments represent a climax in the capacity of domestic ruminants to adjust to such areas. Again this ability is multifactorial. While performance in terms of growth rate is greatly reduced, low body mass and low metabolic requirements of goats can be regarded as important assets in minimising their maintenance and water requirements in areas where water sources are widely distributed and food sources are limited by their quantity and quality. An ability to reduce metabolism allows goats to survive even after prolonged periods of severely limited food availability. A skillful grazing behaviour and efficient digestive system enable goats to attain maximal food intake and maximal food utilization in a given condition. There is a positive interaction between the recycling rate of urea and a better digestive capacity of desert goats. The rumen plays an important role in the evolved adaptations by serving as a relatively large fermentation vat and water reservoir. The water stored in the rumen is utilized during dehydration, and the rumen serves as a container which accommodates the ingested water upon re-hydration. The rumen, salivary glands, and kidney coordinate functions in the regulation of water intake and water distribution following acute dehydration and rapid re-hydration.

Animals that have been exposed to non-lethal thermal stress will usually adapt to the conditions. The adaptation may be of short duration (e.g. reduction in feed intake; Mader et al. 2002) or long-term (e.g. reproductive failure). Long-term adaptation has been shown in chickens that were exposed to hot conditions at 4-7 days of age. The exposure reduced the effects (reduced heat production, lower mortality) of heat stress at a later age (May et al. 1987; Wiernusz and Teeter 1996; Yahav and Plavnik 1999; Yalchin et al. 2001).

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