describe the importance of water to life
life could not be sustained without water – the absences of water could cause death faster than absences of any other nutrient
what portion of the body mass is water? molecules?
1/2 to 2/3 of body mass in adult animals is water & up to 90% in newborn animals
99% of the body is molecules
what are the 2 basic functions of water in the body?
- aids in body metabolism
- temperature regulation
what are the 4 important overall functions of water in body metabolism? explain.
- water is a solvent: most cellular protoplasms/cytoplasms is a mixture of colloids & crystalloids in water
- water is a transport medium: medium for transportation of semisolid digesta in the GI tract, blood, tissue fluids, cells & secretions & in urine & sweat
- water is a dilutent: provides dilution of cell contents & body fluids so free chemical movement can occur w/in cells & in fluids & GI tract
- water fxns in hydrolysis & oxidation: in hydrolysis, water is a substrate in the reaction & in oxidation it is a product
what is metabolic water?
metabolic water is water of oxidation
what chemical component yields the most metabolic water upon hydrolysis?
the metabolic water/gram is higher in fat
which nutrient compound supplies the most net metabolic water?
why don’t hibernating animals need to drink water?
the metabolic & preformed water metabolized is enough to sustain normal functions
what are the 3 properties of water that allow it to have a marked effect on temperature regulation?
- high specific heat index
- high thermal conductivity
- high latent heat of vaporization
how can an animal increase heat loss through its lungs?
the lungs have a large evaporative surface area.
can you think of an environmental situation in which evaporative cooling would not be very efficient & one where it would be highly efficient?
evaporative cooling would be less efficient in humid environments & dry environments it would be very efficient.
how many calories are lost from the body by evaporating 5 grams of water?
1 gram of water requires 580 calories of heat so…
580 (5 grams) = 2900 calories
how does the body prevent itself from having large changes in temperature?
the body has a great capacity to store heat — this prevents sudden temperature changes
how is water’s thermal conductivity useful in dissipating body heat?
evaporation of body water
where is water absorbed in the digestive tract?
most sections of the GI tract:
- ruminants: rumen & omasum
what are 5 sources of water to an animal?
- drinking water
- water in or on feed
- metabolic water
- water liberated from metabolic reactions
- preforms of water associated w/ body tissues (catabolized during a negative energy state)
what types of factors determine the relative importance of these to a specific animal?
diet, habitat & the ability to conserve body water
compare the water needs of a desert rat to that of a producing livestock.
desert rat: will not require drinking water except in rare occasions
livestock: require copious amounts of drinking water when producing at a high level, especially when heat stressed
why do you think dairy cows drink so much more water than beef cows?
they are constantly lactating (producing milk) & milk is made mostly of water
is the water in feed an important contributor to livestock water needs? if so, how important?
forage = 5-7% water
hay = 90% water
young lush vegetation = 90% water
the precipitation & dew on ingested feed may account for a very substantial amount of water consumption
describe one (or more) situations where a perfectly normal animal might not need to drink water
- hibernating animals
- foraging animals
- desert animals
- less active animals
describe the methods of water loss from the body in detail, but no great detail than the course guide.
- expired water from lungs
- vaporization from the skin
- water lost in feces
- water lost in urine
why is it difficult to delineate the water requirements of an animal?
b/c numerous dietary & environmental factors affect water absorption & excretion — water is important in regulation of body temperature
what is the relationship between dry matter consumption & water consumption as long as the animal is not in heat stress?
water consumption is linearly related to heat production when the animal is not in heat stress
describe how heat stress can affect water needs for animals. give a concrete example.
heat stress can cause a decrease in feed consumption & an increase in water consumption greatly.
i.e cattle at 40F, the water consumption per unit of dry matter consumption is at 0.35 gal/lb. vs. at 100F, the water consumption per unit of dry matter is at 1.9 gal/lb.
what happens to water consumption in relation to water need on lush pastures?
there is a higher water consumption than needed when the forage is lush with high water content.
how does protein intake affect water intake?
protein increases water requirements b/c of urea that is toxic & must be diluted to prevent it from damaging the kidney
how does urea consumption affect urine volume?
urea requires a good deal of water for excretion. uric acid requires very little water so poultry species don’t have volumous urine
milk is mostly water. why do nursing animals need more water?
the high content of protein in milk results in high obligatory urinary water loss & w/out additional water performance will be reduced
how does fat consumption affect water intake?
increase intake of fat will also cause an increase in water intake
what is the effect of salt consumption on water consumption & excretion?
salt increases consumption & excretion of water greatly
generally speaking, how much water do animals need per quantity of dry feed consumed?
2-5 kg H2O/kg dry feed consumed
what is the normal ration of water consumption to dry matter consumption for cattle? sheep? why do cattle need more?
cattle: 4:1 — need more b/c they aren’t as efficient at storing water
how does the water consumption of birds compare to mammals?
birds require less water consumption mammals
how does young vs. adult affect for how much water is required?
young animals require more water per unit of body weight than adults
how does activity affect how much water is required?
nervous animals will consume more water than less active ones
how does milk production affect water consumption in cattle?
water consumption will be increased by milk production
is there a valid reason for not allowing an animal unlimited access to water?
calves: death may result due to large amounts of water suddenly ingested due to kidneys slow adaptation to sudden high water load.