Water Intake by Cattle as a Measure of Forage Intake and Quality 
D. N. HYDER? 
INTRODUCTION 
Semiarid grazing lands present numerous 
obstacles to adaptations of agronomic and nu- 
tritional methods to range research. Such 
lands are characterized by large acreages of 
natural vegetation, limited production of for- 
age, ecological variability in species composi- 
tion, species sensitive to herbage removal, 
great variations in the quantity and quality of 
forage eaten by grazing animals, and striking 
seasonal changes in diet composition. We must, 
of course, obtain the greatest possible advan- 
tage from the research methods that require 
artificial restrictions on land and animals. 
Also, we must have research methods that can 
be used without restricting land and animals. 
Economic limitations require a rather exten- 
sive type of land and animal husbandry in 
which ecological relations can seldom be re- 
placed by cultural practices. Consider, for ex- 
ample, the quantity and quality of forage eaten 
by grazing animals. Large pastures of natural 
vegetation generally offer a great variety of 
species and conditions from which the animals 
select food and cover that is favorable, or at 
least pleasing, to them. Thus, ecological inter- 
actions cannot be ignored, and experimental re- 
sults from greatly restricted situations can be 
unrealistic. So, one must have research meth- 
ods that can be used to determine the impor- 
tant factors and interactions of plants, ani- 
mals, and soils on semiarid grazing lands with- 
out excessive restriction. 
This need prompted our interest in the wa- 
ter-dry matter intake dependency of cattle as 
defined by Winchester and Morris (1956) ; and 
our interest in the net energy equation as ap- 
plied by Lofgreen (1963) and coworkers. Prog- 
ress in our research is summarized in this 
paper. Three topics are involved: (a) The wa- 
ter-intake method of estimating forage intake 
by grazing cattle; (b) the adaptation of the 
net-energy equation for estimating forage 
quality; and (c) the use of water-soluble tra- 
cers for estimating water use and partitioning. 
THE WATER-INTAKE METHOD 
Initial Development 
Derivation.—Our work began in 1964 with 
an interest in the possibilities of using the wa- 
ter-intake rates of cattle to estimate forage in- 
take by grazing cattle. Winchester and Morris 
(1956) gave water-intake rates (in gallons of 
* Range Scientist, Crops Research Div., ARS, USDA, 
Ft. Collins, Colo. 
120 
water consumed per pound of food dry matter 
eaten) as a function of ambient temperature. 
Since their work was based on a substantial 
number of data, the water-dry matter intake 
relations should be valid for a variety of condi- 
tions. The original data can be equated in the 
form: 
H =KF, (1) 
where H represents the total amount of water 
consumed (in gal), K represents the water-in- 
take rate (in gallons of water per pound of dry 
matter consumed at any given mean air tem- 
perature in degrees F.), and F represents for- 
age intake (in pounds of dry matter eaten per 
head daily. By solving for F, we obtained the 
desired expression: 
PS Headk (2) 
Equation 2, however, must be expanded to in- 
clude as separate components the water in for- 
age and the water taken by drinking. A table 
of forage-intake rates (in pounds of dry 
matter eaten per gallon of water drunk for any 
given set of mean air temperature in degrees 
F. and percentage of moisture content of for- 
age) was computed. Thus, a solution for forage 
intake was given as the product of the amount 
of water drunk and the forage-intake rate 
(Hyder et al. 1966a). The method requires the 
measurement of water drunk, mean air tem- 
perature, and the percentage of moisture in the 
forage. These measurements are nonrestric- 
tive. Drinking water is measured by metering, 
air temperatures are recorded by a thermo- 
graph, and moisture contents of forage are es- 
timated from hand-plucked samples of herbage 
collected while moving with and observing the 
selectivity of the grazing animals. 
Initial Testing.—The water-intake method 
was compared to the agronomic method of clip- 
ping before and after grazing in 1965. This ex- 
periment was arranged to facilitate the estima- 
tion of forage intake by the clipping method, 
even though such an arrangement was a disad- 
vantage in applying the water-intake method. 
Grazing by yearling Hereford steers was re- 
stricted to areas of about 1 acre for 3 days at bi- 
weekly intervals for a total of six trials in the 
summer of 1965. The mean forage intake was 
estimated to be 23.3 and 22.8 pounds of dry 
matter per head per day by clipping and wa- 
ter-intake methods, respectively. Since true 
forage intake is unknown, the reliability of the 
two methods must be judged on a statistical 
and intuitive basis. Two separate factors allow 
intuitive evaluations: one is animal size in 
