were admitted daily from about 11 a.m. to 4 
p.m. Records of water drunk were omitted for 
days when rainwater was ponded on the pas- 
ture. Air temperatures were recorded contin- 
uously by thermograph. Hand-plucked samples 
of herbage were collected while moving with 
and observing the selectivity by the steers each 
morning and evening 3 days each week. The 
data obtained were used to estimate forage in- 
take for each 2-week period, and to determine 
the sampling requirements of each type of 
measurement. 
Forage intake-—The mean adjusted forage 
intake varied from 16.1 to 25.4 lb./day, with 5 
percent confidence limits based on differences 
among steers varying from +1.1 to +3.5 
lb./day. Increases and decreases in forage in- 
take among periods coincided with increases 
and decreases in the moisture content of forage 
(table 2). The relation of forage intake to 
moisture content of forage has been defined 
more completely elsewhere (Hyder 1967). For- 
age intake probably was overestimated in graz- 
ing periods 2, 6, 7, and 8 (1966), when the 
steers ate much Russian thistle (Salsola kali 
L.) as well as blue grama (Bouteloua gra- 
cilis (HBK) Lag. ex Steud.). There is no rea- 
son to suspect a bias in the estimate of forage 
intake when the moisture content of forage 
was less than 60 percent. 
TABLE 2.—Adjusted forage intake and moisture 
content of forage in 1966 
Adjusted Moisture content 
Grazing period forage intake of forage 
Pounds/day Percent 
1. 5/31-6/14 16.7 48 
2. 6/14-6/28 25.4 71 
38. 6/28-7/12 17.8 58 
4, 7/12-7/26 a Ey 3) 49 
5. 7/26-8/9 17.2 51 
6. 8/9-8/23 23.5 69 
7. 8/23-9/6 24.1 70 
8. 9/6-9/20 24.8 68 
9. 9/20-10/4 16.1 56 
Amounts of water drunk.—Mean water-dry 
matter intake relations are presumed not to 
apply to a single animal for any time inter- 
val, or to a single day for any number of an- 
imals. In other words, the proper application 
of mean water-dry matter intake relations re- 
quires an appropriate sample size stated with 
respect to number of animals and number of 
days. Individual animal-day observations are 
needed for the computation of variance compo- 
nents and sample structure. Since we cannot 
readily obtain under pasturing conditions the 
ratios of water to dry matter consumed, this 
analysis is based on the amounts of water 
drunk. As estimated from the separate compo- 
nents of variance for differences among steers 
and for differences among consecutive days 
within a week, a sample should include: 11 
122 
head over 14 days, 15 head over 7 days, or 16 
head over 4 days. 
Mean air temperature-—Mean air tempera- 
tures derived from daily minimum and maxi- 
mum values were compared with means de- 
rived from temperatures recorded at 83-hour in- 
tervals. Weekly means expressed to the nearest 
degree F. were nearly always identical by the 
two procedures, and never differed by more 
than one degree. Therefore, the simple proce- 
dure of averaging minimum and maximum 
daily temperatures is retained. 
Moisture contents of forage-—Weeks and 
time of day were sources of highly significant 
differences in the moisture contents of hand- 
plucked herbage. The residual mean square 
provides an evaluation of sampling precision 
that may be used to estimate the number of 
samples needed in a 2-week grazing period. 
Under the conditions encountered in 1966, 31 
samples would have been appropriate. Thus, 
when only 12 samples are taken in each graz- 
ing period, this characteristic was. under- 
sampled. The difficulty one encounters in 
hand-plucking to estimate the mean moisture 
content of forage consumed can vary from 
slight to extreme, increasing with an increase 
in the moisture content of forage. The kinds of 
variability encountered require a systematic 
daily (morning and evening) observation and 
collection of herbage. Although one develops 
confidence in this procedure, the accuracy at- 
tained in duplicating the animal diet cannot be 
determined in absolute value. 
Inherent Limitations 
High temperatures.—A limitation is inher- 
ent in the basic relations defined by Winchester 
and Morris (1956). High temperatures in- 
crease the requirement for water in the control 
of body temperature, and decrease the relative 
importance of the dry-matter function. Thus, 
the amount and variability in the amount of 
water required per pound of dry matter con- 
sumed increased with increased temperature. 
This variability becomes excessive at constant 
temperatures greater than 90 F., but our high- 
est 14-day mean temperature is about 75 F. 
High moisture contents of forage.—Theoret- 
ically the complete water requirement of cattle 
can be supplied by the water contained in the 
forage (Hyder et al. 1966a). In that event, the 
amount of water drunk theoretically would be 
zero, and forage intake could not be estimated. 
As the moisture content of forage increases, 
the relative importance of drinking water de- 
creases. The limiting effect of high-moisture 
forage can be shown by calculating the errors 
in forage intake that would result from an 
error in estimating the moisture content of for- 
age. Take, for example, an error of just +2 
percent in estimating the moisture content of 
