NET ENERGY 
Adapting the Net Energy Equation 
The net energy equation, as formulated by 
Winchester and Hendricks (1953), was 
adapted to pasture conditions by the addition 
of a travel (walking) component for which the 
energy coefficient was adopted from Brody 
(1945). Coefficients for maintenance and gain 
were adopted from the results of Garrett et al. 
(1959). Thus, when animal liveweight, gain, 
and travel are known, the total amount of net 
energy (NE,,.,) received daily from pasture 
can be estimated by solution of the net-energy 
equation: 
NE,» =388W: (1+0.45G) +0.33 WT, (7) 
where W _ represents animal liveweight in 
pounds, G represents animal daily gain in 
pounds, and T represents the distance traveled 
in miles. 
Prorating this total amount of net energy re- 
ceived to a unit weight of forage dry matter 
was accomplished according to the theory of 
separate values for maintenance and produc- 
tion proposed by Lofgreen (1963). We chose to 
express forage quality to a value for mainte- 
nance at zero production (Hyder et al. 1966b). 
This procedure, of course, has no connection to 
water intake, except through the use of the 
water-intake method of estimating forage in- 
take. Since the net-energy equation is not ex- 
pected to apply specifically to a single animal 
over any given period of time, the problem 
of sample size is equivalent to that encountered 
with respect to water-intake rates. 
Forage Quality 
Yorage quality can be evaluated and quanti- 
fied (in part) in several ways, such as by dry- 
matter digestibility, organic-matter digestibil- 
ity, total digestible nutrients, digestible en- 
ergy, metabolizable energy, starch equivalents, 
and net energy. The net-energy value is most 
definitive but indicates animal as well as 
forage characteristics. However, dry-matter di- 
gestibility is least definitive but most limited to 
forage characteristics. In the practical sense, 
forage value (as opposed to “quality”) can be 
expressed in terms of the efficiency of forage 
conversion to beef. which is a function of for- 
age intake as well as quality. For example, 
normal (that is, modal) forage conditions on 
blue grama range for yearling Hereford steers 
ane ee by the following results (Hyder 
TOE 
Normal forage conditions 
Forage conversion rate ___-_ = 10.5 1)b./Ib 
Steer daily gain = 2.2 1b./day 
Forage intake _- aij See ee eee 28 Ob e/davy, 
Adjusted forage intake _____. = 19.0 lb./day 
Net energy value of forage __._._.. = 690 kcal./lb 
Crude protein content of forage = 12.7 percent 
Amount of herbage standing ___- = 400 Ilb./acre 
124 
Inefficient forage conversion rates were en- 
countered in May, when the adjusted forage 
intake was only 14.2 lb./day and the net energy 
value was only 410 keal./lb., and in October, 
when the adjusted forage intake was less than 
14 lb./day and the net energy value was greater 
than 600 keal./lb. In May, forage intake was 
limited by the small amount of herbage stand- 
ing (120 lb./a.), but in October it was limited 
apparently by low moisture (less than 50 per- 
cent) and low crude protein (less than 8 per- 
cent) contents of forage. Beef production per 
acre could be increased an estimated 40 per- 
cent by omitting inefficient pasturing condi- 
tions. However, economic advantage would also 
depend on the cost and efficiency of alternate 
practice. 
Sampling Problems 
The use of the net-energy equation to esti- 
mate the apparent net-energy quality of forage 
requires the measurement of forage intake, an- 
imal liveweight, daily gain, and daily travel. 
Sampling requirements have not been evalu- 
ated in detail, but the critical and sensitive 
parts of the calculations have become obvious 
—these are animal daily gain and forage in- 
take. Yearling Hereford steers have a daily 
water turnover of about 80 pounds. Weather 
and forage conditions sometimes induce 
changes in liveweight of greater than 30 
pounds in a single day. Yet, we need to mea- 
sure daily gains over short intervals, at least 
biweekly, to properly associate animal per- 
formance with existing herbage conditions. 
The point of view is that the animals deter- 
mine forage intake and quality, and these two 
factors can then be interpreted for the develop- 
ment of more efficient grazing practices. When 
we devote a considerable expenditure of time 
and money in our research programs to live- 
stock, and have within our grasp the ultimate 
manifestation of forage value, the deficiency of 
measurement techniques and of fundamental 
data about animal-forage relations is intolera- 
ble. Since animal daily gain is essential to this 
approach, we must find a way to measure it. 
The prospect is not entirely dismal. Difficulties 
in measuring daily gain appear to arise pri- 
marily from variations in the amount of water 
contained in the animal, although we cannot 
disregard variability in the dry-matter content 
of the gut. Liveweight is composed of up to 
about 70 percent water, and cattle appear to 
have a water turnover rate that is two to three 
times greater than that of other ruminants 
(Macfarlane 1965). Morris et al. (1962) re- 
ported that the total body water content of 
sheep varied from 50 to 67 percent of live- 
weight. Animal liveweights presumably should 
be adjusted to a constant total-body-water per- 
centage. Research methods applicable to this 
