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paired observations, and the other is seasonal 
changes. In each of six trials spaced at 2-week 
intervals through the season, the steers were 
grouped into uniform liveweight classes called 
small and large. 
The forage-intake equation is as follows 
(Hyder et al. 1966a): 
Let: K =the water-intake rate in 
gallons of water per pound 
of dry matter consumed by 
European breeds of cattle 
at any given degree F. 
mean air temperature 
(Winchester and Morris 
1956). 
H =total water intake in gal- 
lons per day. 
H,=the gallons of water drunk. 
H,=the water content of forage 
in gallons per pound of dry 
matter = (% water+ %dry 
matter) + 8.345 lb./gal. 
F =forage intake in pounds of 
dry matter per day. 
F,=the forage-intake rate in 
pounds of dry matter per 
gallon of water drunk. 
Thus: PsN: pointers ot al a (1) 
1 Do Aes: ee ee a2.) 
Substituting: F =(H,+FH;)+K ______ (8) 
Solving for F: FK=H,+ FH; 
FK-—FH;=H, 
F(K—H,) =H, 
Bie ay te = He) <2. (4) 
Let H,=1.0 gal: 
F,=1.0+ (K—H,) ____-__. (5) 
Forage-intake rates (F.) were calculated for 
various combinations of mean air temperature 
°F.) and moisture contents of forage (%). 
Thus, the final solution for forage intake (F) 
is given by: 
F = << A, 
Application to lactating animals is accomplished 
Py subtracting the water content of milk from 
de 
Trial 2 also included a medium-size class. In 
table 1 the results obtained are grouped by size 
classes and trials. The authors (Hyder et al. 
1966a) believe that forage intake by size 
classes and trials (for seasonal changes) was 
estimated in a more consistent and reasonable 
way by the water-intake method than by the 
clipping method. Even with this restriction in 
area and duration of grazing, the clipping 
method is rated as only slightly successful. Its 
weakness was surely due to the small standing 
crops, which imposed an extremely high re- 
quirement in sampling precision. As we shall 
see from results of subsequent research, the 
restrictions upon area, grazing duration, and 
number of animals made the water-intake 
method disadvantageous. 
TABLE 1.—Forage intake as estimated by water- 
intake and herbage-clipping methods 
in 1965 
Forage intake, by method and 
Mean- size class 
live- 
weight, 
by size class Herbage clipping Water intake 
Trial Small Large Small Large Small Large 
(Lb./ (Lb./ (Lb./ © (Lb./ 
head/ head/ head/_ head/ 
Lb Lb. day) day) day) day) 
1 515 646 36.0 27.4 26.3 29.2 
2 545 691 16.8 22.1 20.6 26.2 
3 641 719 28.1 28.8 25.3 25.1 
4 610 752 16.4 20.0 17.0 22.2 
5 652 755 15.8 14.8 13.8 20.1 
6 679 787 25.0 18.6 15.3 29:2, 
Mean 607 725 23.0 22.0 19.7 24.2 
Adjusted Forage Intake.—Since we desire 
to reveal the effects of changing pasture con- 
ditions on forage intake, the estimates ob- 
tained should be adjusted to compensate for 
the differences and seasonal increases in year- 
ling liveweight. We chose to make this adjust- 
ment according to the function of animal meta- 
bolic size. Thus, the adjusted forage intake 
(F.4;) was that proportional part of the ob- 
served forage intake prorated to a yearling 
metabolic size (W:*°) of 100 (see equation (8) ; 
Hyder et al. 1966a). With animal size dis- 
counted, the variability among estimates indi- 
cates sampling precision. However, sampling 
precision among the estimates of adjusted for- 
age intake is more exactly defined by the resid- 
ual variance after removing the seasonal ef- 
fect among trials. In this way, the mean ad- 
justed forage intake and standard deviation 
are estimated to be 17.5 +4.0 and 16.9 +1.6 
pounds per day by clipping and water intake, 
respectively. (Note: These calculations were 
made without including the data for the me- 
dium-size class of trial 2.) Although sampling 
precision can be irrelevant to sampling accur- 
acy, it is nevertheless highly important in com- 
paring methods. 
Sampling Requirements 
Methods.—The encouraging results obtained 
in 1965 prompted a more intensive experiment 
in 1966—one planned to fulfill the objective of 
defining the sampling requirements and inher- 
ent limitations of the water-intake method 
(Hyder et al. 1968a). Twelve yearling Here- 
ford steers were allowed to graze a half-sec- 
tion, blue-grama pasture continuously from 
May 17 to October 5, 1966. The first 2 weeks 
were reserved for preconditioning and training 
of steers. Metered drinking water was pro- 
vided in individual pens to which the steers 
121 
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