untitled

protein, energy, or other nutrients can be estimated by observing what animals eat and

then determining the chemical composition of that diet. These indirect estimates of

intake are compared with an estimate of requirements either from direct physiolo-

gical experiments or inferred from the literature. Examples are from reindeer on South

Georgia Island (Leader-Williams 1988) and greater kudu (Tragelaphus strepsiceros)

in South Africa (Owen-Smith and Cooper 1989). Energy intake for the jerboa

(Allactaga elater) in north cis-Caspian, Russia (Fig. 4.1) dropped below requirements

in mid-summer and so body weight declined (Abaturov and Magomedov 1988).

Similarly, energy measured from fecal collections showed that energy intake of

moose during winter in Norway dropped below requirements by 25–30% (Hjeljord

et al. 1994). For greater kudu (Fig. 4.2), energy intake during winter was below require-

ments, but protein intake was sufficient. In contrast, protein intake of African buf-

falo in tropical dry seasons was below requirements (Fig. 4.3).

These indirect measures of food intake can often be inaccurate because they are

an amalgam of several different measurements. One way around this is to use a physi-

ological index from the animal to indicate the quality of the food it has eaten. Nitrogen

in the feces predicts nitrogen in the diet down to the minimum level of nitrogen

balance. If nitrogen intake falls below this level it is not reflected in the feces because

metabolic nitrogen (from microorganisms and gut cells) continues to be passed out

irrespective of intake.

FOOD AND NUTRITION 43

550

500

450

400

350

30

25

20

15

10

62

58

54

50

MAMJ J ASO

Month

Body weight (g)

Daily energy (kcal / individual)

Food energy(kcal / 100 g)

(a) Energy in forage

(b) Daily energy

(c) Body weight

Intake

Requirement

Fig. 4.1Seasonal
changes in energy and
body weight of the
jerboa (Allactaga elater)
in the cis-Caspian,
Russia, during 1985.
(a) Percentage energy
of forage in the
stomach. (b) Daily
energy intake, and daily
energy requirement.
(c) Body weight.
(After Abaturov and
Magomedov 1988.)