Milk Production in the Desert: Lactation and Water Economy in the Black Bedouin Goat

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Abstract
The black Bedouin goats which are herded in the extreme deserts of the Middle East are of small body size (16-26 kg). Even when lactating they drink only once every 2 days and can therefore graze far away from the widely spaced watering points. The water economy of the lactating Bedouin goats was studied under laboratory conditions (30 C, 30% relative humidity). Maximum milk yield was remarkably high (61-87 g kg⁻¹ day⁻¹); the volume of water consumed by lactating goats (158 ml kg⁻¹ day⁻¹) was three times the volume consumed before gestation. The rate of water turnover of the lactating goats (210 ml H₂O kg⁻¹ day⁻¹) was double that found in nonlactating females. The ability of the goats to withstand 2 days of water deprivation without the milk yield being affected is attributed to a very high body water content (HTO space), amounting to 77%-85% of the body weight. Following dehydration, when given free access to water, the goats at once replenish their entire water loss. Blood plasma volume (Evans Blue [EB] space) was 9% of body weight in fully hydrated lactating goats. During dehydration EB space decreased in proportion to the decrease in total body fluids. Repeated periods of water deprivation had no effect on the ability to resume full milk production.