Fluid Balance in Ruminants: Adaptation to External and Internal Challenges

Abstract

Ruminants are widespread in hot, arid regions. This demands adaptation to large circadian temperature fluctuations and recurrent periods of food and water shortage. Pregnancy and lactation add to the demands on the adaptive mechanisms due to the greater need for food, water, and electrolytes. The blood volume increases to meet the requirements of the fetoplacental unit and the mammary glands. Unlike urine, the milk cannot be concentrated by antidiuretic hormone (vasopressin). During water deprivation, lactating animals therefore become dehydrated more rapidly than nonlactating animals. Nevertheless, desert-adapted lactating ruminants endure frequent periods of water deprivation without incurring bad health. For the offspring living in hot and dry conditions, it is an advantage that the milk is not concentrated, even if the mother has a high antidiuretic hormone concentration to enable her to concentrate the urine. Since ruminants are prey, they need to drink rapidly when they get access to water. The forestomach allows the animals to store water in the reticulorumen. There is no danger of water intoxication even if they drink to satisfaction in a couple of minutes after having lost as much as 30% of their body weight.

Evaluation of physiological and blood serum differences in heat-tolerant (Romosinuano) and heat-susceptible (Angus) Bos taurus cattle during controlled heat challenge1

“…However, it has been shown that hematocrit is not a reliable indicator of dehydration because it is highly variable (Parker et al, 2004;Scharf et al, 2008b). One rapid response to dehydration is a significant reduction in feed intake (Bianca et al, 1965;Olsson, 2005;Scharf et al, 2008b). Even though animals in the current study were limit-fed, dehydration should have resulted in some reduction in feed consumption.…”

Water Stress in Small Ruminants

“…This explains why dehydrated goats and sheep decrease their urine volume while the osmolality and vasopressin levels augment. Olsson (2005) [113] noted that thermoregulation and fluid balance, as regulated by thirst control, vasopressin secretion, sodium balance and other osmotic and cardiovascular signals, seem to be centrally regulated at the hypothalamic level, particularly the preoptic and anterior hypothalamic neurons. Silanikove (1994) [15] presents a detailed account of the dynamics of major electrolytes under dehydration in connection with water conservation and homeostatic mechanisms in ruminants.…”

Dehydration enhances multiple physiological defense mechanisms in a desert lizard, Heloderma suspectum

“…Dehydration reduces productivity (e.g. in plants; Farooq et al, 2009), alters blood chemistry (Hamadeh et al, 2006) and causes other alterations in physiology or behavior (Olsson, 2005;Dupoué et al, 2014). Furthermore, as both survival and reproduction rely on the availability of sufficient water resources, water imbalance can reduce animal fitness.…”