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Page 26 3 Water Sheep obtain water from snow and dew and by drinking; metabolic water is obtained from oxidation of nutrients in feed. The exact amount of water required by sheep is not known and varies considerably depending on body metabolism, ambient temperature, stage of production, size, wool covering, amount of feed consumed, and feed composition (Forbes, 1968). Voluntary water consumption is two or three times dry matter consumption and increases with high-protein and salt-containing diets. Available snow, high-moisture feeds, and infrequent watering tend to reduce daily water consumption. Forbes (1968) has confirmed that there is a significant relationship between total water intake (TWI) and dry matter intake (DMI) that can be represented by the formula Producers feeding pelleted rations note the obvious increase in water intake accompanied by increased urine output as a result of increased DMI. Conversely, sheep denied water for more than 24 hours ate little or no dry feed containing 15 percent protein, but intake was little affected when fed 2 percent protein hay (Forbes, 1968). The relationship between water intake and mean temperature over 1°C also is significant (Forbes, 1968): where TWI/DMI is the average total water intake per unit of dry matter intake (kg/kg) and T is the average temperature in °C for each week. Pregnancy and lactation also increase water intake. Water intake increases by the third month of gestation, is doubled by the fifth month, and is greater for twinbearing ewes than for ewes carrying a single fetus. A lack of water accompanied by a severe depression in feed intake predisposes ewes to pregnancy toxemia. Forbes (1968) noted that water intake during early lactation is greater than the sum of water intake for nonpregnant ewes and the water in the milk, due to a higher metabolic rate and greater excretion. It is estimated that lactating ewes require 100 percent more water than nonlactating ewes. Sheep may consume 12 times more water in summer than in winter; subsist on once-a-day watering when temperatures are below 40°C; and suffer no reduction in weight gains, feed intake, or digestibility of dry matter when snow is available and the temperature ranges between 0° and 21°C (Butcher, 1970). Lactating ewes would likely be stressed under a similar regime. Adequate intake of good-quality water is essential for sheep to excrete excess toxic substances such as oxalates, ammonia, and mineral salts (phosphates that cause urinary calculi). The effect of water temperature on rumen temperature, digestion, and rumen fermentation in sheep was studied by Brod et al. (1982), who reported that rumen temperatures were affected by temperature of water consumed, with 0°C water depressing rumen temperature more than 10°, 20°, or 30°C water. It required 108, 96, 96, and 72 minutes at water temperatures of 0°, 10°, 20°, and 30°C, respectively, to regain initial rumen temperature. Water temperature had no significant effect on nitrogen balance or on DM, protein, or crude fiber digestibility, although digestion coefficients tended to be lower with 0°C water. Water temperature had no significant effect on rumen pH, but water at all temperatures depressed rumen pH 2 to 4 hours postfeeding. Volatile fatty acids (VFA) and ammonia-nitrogen concentrations increased 1 to 4 hours postfeeding. Brod et al. concluded that 0°C water suppresses rumen microbial activity as evidenced by (1) elevated pH at 4 hours postfeeding for 0°C water compared with pH values for 10°, 20°, and 30°C water and (2) by depressed concentrations of VFA and ammonia-nitrogen and lower digestibility values compared with the other water-temperature treatments.
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