The physiological basis of adaptation in goats to harsh environments

Goat living in harsh environments represents a climax in the capacity of do mestic ruminants to adjust to such areas. This ability is multifactorial: l ow body mass, and low metabolic requirements of goats can be regarded as an important asset to them for it minimise their maintenance and water requir ements, in areas where water sources are widely distributed and food source s are limited by their quantity and quality. An ability to reduce metabolis m allows goats to survive even after prolonged periods of severe limited fo od availability. A skillful grazing behaviour and efficient digestive syste m enable goats to attain maximal food intake and maximal food utilisation i n a given condition. There is a positive interaction between the better rec ycling rate of urea and a better digestion of such food in desert goats. Th e rumen plays an important role in the evolved adaptations by serving as a huge fermentation vat and water reservoir. The water stored in the rumen is utilised during dehydration, and the rumen serves as a container, which ac commodates the ingested water upon rehydration. The rumen, the salivary gla nds and the kidney coordinately function in the regulation of water intake and water distribution following acute dehydration and rapid rehydration. G oats in the tropics, when possible, eat a diet composed of tree-leaves and shrubs (browse), which ensure a reliable and steady supply of food all year around, albeit, from a low to medium quality food. Some of the physiologic al features of ruminants defined as intermediate feeders like large salivar y gland, the large absorptive area of their rumen epithelium, and the capac ity to change rapidly the volume of the foregut in response to environmenta l changes are most likely responsible for the goat's superior digestion cap acity. (C) 2000 Elsevier Science B.V. All rights reserved.