Mechanisms of water economy in lactating Ethiopian Somali goats during repeated cycles of intermittent watering

Abstract

We investigated the physiological and behavioural strategies by which lactating Ethiopian Somali goats endure repeated periods of water deprivation. The experiment lasted for 32 days and was divided into four periods of 8 days each. Measurements were taken during the first 4 days in each period. Seven does (W1) were watered once daily and seven does (W4) were watered once every 4th day. Rectal temperature was taken at 0800 and 1715 h. Blood samples were taken in the evening and milk samples in the morning. The goats were on pasture between 0900 to 1215 h and 1315 to 1630 h with behaviour recorded every 5 min. The does were supplemented with 300 g of concentrates per head per day. Plasma and milk osmolality were determined by freezing point depression. Plasma total protein was measured on a TS refractometer. Plasma vasopressin concentrations were analysed by radio-immunoassay. The mean daily water intake of W1 was 1897 ml compared with the calculated mean of 1075 ml in W4 (P , 0.001). The mean diurnal variation of the rectal temperature was 3.58C in both groups. Afternoon rectal temperature in W4 during period 1 was higher than that in the W1 on the days of water deprivation (P , 0.05). With repeated periods, plasma osmolality in W4 increased less over the days of water deprivation. It was 336, 321, 311 and 306 mosm/l on the 4th day at periods 1, 2, 3 and 4, respectively. The corresponding vasopressin concentrations were 10.0, 9.2, 4.2 and 4.4 pmol/l. Total plasma protein concentration during period 1 on days 3 and 4 were higher in W4 than in W1 (P , 0.01). During the subsequent periods, it did not increase more in W4 compared with W1, but it was lower in W4 on the days after watering. W4 milk production decreased by 22% compared with W1 in all periods. With increasing days of water deprivation, the W4 goats spent less time in the sun, grazed shorter time and frequently ate cactus (Opuntia ficus-indica) as compared with W1. Results suggested that dehydrated lactating Ethiopian Somali goats economised on water by diurnal variations of rectal temperature, storing water in the extracellular fluid, by changing behaviour at grazing and by decreasing milk production.

Physiological and behavioral responses to different watering intervals in lactating camels (Camelus dromedarius)

“…It is possible that lactation in combination with heat stress modified the body's reaction to feedback signals on water content. Observations that heat-stressed lactating Ethiopian Somali goats subjected to a repetitive 4-day water deprivation schedule drank large volumes of water and, at the same time, retained the water more efficiently every new cycle support this suggestion (31). Furthermore, heat-stressed lactating Swedish domestic goats continued to drink despite developing hyponatremia and hypovolemia (32).…”

“…Furthermore, heat-stressed lactating Swedish domestic goats continued to drink despite developing hyponatremia and hypovolemia (32). We could speculate that the hypothalamic sodium-osmoreceptors that normally regulate both water intake and release of vasopressin within narrow limits (6, 17) respond differently in heat-stressed lactating camels and goats (31,32).…”

Effect of water restriction on drinking behaviour and water intake in German black-head mutton sheep and Boer goats

“…This observation may indicate a decrease in endogenous metabolic heat production to reduce water requirements for evaporative cooling (Degen, 1977;Ismail et al, 1996), as it is known that water restriction induces a decrease in the metabolic rate, indicating a water conservation mechanism (Choshniak et al, 1995). However, Mengistu et al (2007) reported higher rectal temperatures in Ethiopian goats that were watered every fourth day. Therefore, it is not clear whether the increase or the decrease of rectal temperature indicates an adaptation towards water metabolism or other metabolic parameters.…”

Melatonin rhythm and other outputs of the master circadian clock in the desert goat (Capra hircus) are entrained by daily cycles of ambient temperature

“…The Ta synchronization of the circadian system described in the camel could be related to this specific thermoregulation process. Recently, such heterothermy has been also shown in other desert ungulates, including oryx and goat . Thus, the raised question is whether the observed entrainment of the circadian clock by Ta cycles is specific to camel or is a mechanism shared by other desert large species.…”