Farm Animal Metabolism and Nutrition

Feed intake versus energy balance

In the individual reports of Beever et al.
(1985, 1986), intake of ryegrass by cattle
progressively exceeded that of clover when
TDOMI exceed an intake in the order of
13 g TDOM kg^1 BW. Cammell et al.(1986)
observed that metabolizable energy (ME)
from clover versus ryegrass was used with
progressively greater efficiency for energy
retention as intake of ME exceeded 1.65
that of a maintenance requirement of 50 MJ
day^1. Consumption of ryegrass versus
clover reported by Beever et al.(1985, 1986)
was 1.21-fold greater at the highest level of
consumption of clover. This ratio of 1.21
was comparable with the observed ratio for
the partial efficiencies of ME utilization
from clover versus ryegrass (1.19, Table 5
of Cammell et al., 1986). Thus, differences
in TDOMI of ryegrass versus clover were
equivalent to differences in net availability

of ME required to provide the flux of net

energy accreted as body protein and fat.

Feed intake versus balance of

metabolizable amino acids

Feed intake appears related to the net

efficiency of metabolizable amino acid

utilization in an analogous manner to that

inferred above for net energy. In the data of

Hill (1991), TDOMI from grazed pastures

was unrelated to flux of MP associated

with supplemental proteins that differed in

both ruminal degradability and amino acid

composition (Ellis et al., 1995; and Figures

3 and 5 of Ellis et al., 1999). However,

intake was positively related to the chemical

score of MP expressed as the balance of

amino acid in the supplemental protein

relative to that in whole egg protein. Intake

of grazed pasture was positively correlated

340 W.C. Ellis et al.

0 1 2 3 4 5 6

40

30

20

10

0

Daily TDOMI (g kg

^1

BW)

Daily MP (g kg
^1 BW)

G

G

G

GG G

G

E

E

E

E

L

L

LL

L

MMMM

F

F

F

F

H

H

H

H

I

III

JJJJ

KKK

K

K

Fig. 16.2.Linear regressions for treatment means of TDOMI versus MP within experiments (A,B, ... M).
With the exceptions of two experiments (F and E), all regressions converge at approximately 1.4 g of MP
kg^1 BW or approximately 1.5 times the estimated MP requirements for maintenance. Divergences in the
slope above this convergence point are interpreted to reflect differences among experiments in digestive
yield of proportions of TDOM and MP and differences among animals in their productive requirement for
MP (see Table 16.2).