Farm Animal Metabolism and Nutrition

in muscle colour score. Objective colour

measurements of fresh loin and ham show

significant reductions in ‘a’ value (redness)

and ‘b’ value (yellowness) with no effect on

‘L’ value (lightness; Table 4.4). A reduction

in the ‘a’ value suggests that the concentra-

tion of myoglobin may be reduced in pigs

fed ractopamine. The reason is probably

due to a shift in muscle fibre type in

ractopamine-treated pigs, increasing the size

and percentage of white fibres (Aalhus et al.,

1992; Table 4.5). This shift is accompanied

by an improvement in WHC (Uttaro et

al., 1993; Table 4.6). This benefit was

unexpected but may be related to greater

functionality of muscle protein from muscle

with high white fibre content (Parsons and

Knight, 1990), translating to decreased cook-

ing losses and increased processing yields

(Uttaro et al., 1993; Table 4.6).

Fat composition

Variable and minor effects of ractopamine

feeding on fatty acid profiles in swine have

been reported (Engeseth et al., 1992;

Perkins et al., 1992). A reduction in choles-

terol content in muscle of pigs treated with

ractopamine was reported by Perkins et al.

(1992). These authors measured cholesterol

content in longissimus dorsimuscles of 144

pigs representing two different trials. Two

levels of ractopamine (10 or 20 mg kg^1 )

were fed in each trial. Ractopamine treat-

ment reduced cholesterol content in both

trials, with an overall reduction of 9%.

Engeseth et al. (1992) reported a similar

trend, but with variable responses from

limited numbers of pigs. A significant inter-

action affecting cholesterol content was

identified between ractopamine treatment

and sex by Uttaro et al. (1993). The feeding

of ractopamine resulted in a 14% decrease

in the cholesterol content of longissimus

dorsimuscle of barrows, but did not affect

cholesterol content of gilts. The difference

between ractopamine-treated and control

pigs without considering the sex interaction

was 8.6%, which is similar to that reported

by Perkins et al. (1992).

Mode of Action of

Phenethanolamines

Adipose tissue

The effects of phenethanolamines on adi-

pose tissue are facilitated by 
-adrenergic

74 D.E. Moody et al.

Table 4.4.Objective colour measurements of fresh

pork loin and ham muscles (adapted from Uttaro et

al., 1993).

Ractopamine (mg kg^1 )

020

Loin (longissimus dorsi)

L value (lightness) 46.32 45.84

a value (redness) 7.59 6.48a

b value (yellowness) 3.14 2.42b

Ham (gluteus medius)

L value (lightness) 44.37 43.47

a value (redness) 9.57 8.22a

b value (yellowness) 3.98 3.05a

aP< 0.01; bP< 0.05.

Table 4.6.Effect of ractopamine on quality

characteristics of loin and ham in pigs (adapted

from Uttaro et al., 1993).

Ractopamine (mg kg^1 )

020

Loin drip loss (%) 6.4 4.3

Loin cooking loss (%) 25.7 24.4a

Ham processing yield 96.4 99.5b

Bacon processing yield 95.5 97.1

aP< 0.05; bP< 0.01.

Table 4.5.Effect of ractopamine on myofibre

distribution and diameter in swine (adapted from

Aalhus et al., 1992).

Ractopamine treatment

(mg kg^1 )

020

Number of animals 23 22

Red (%) 14.38 12.35

Intermediate (%) 12.86 10.39a

White (%) 72.81 77.26b

Red (μ^2 ) 2480 2564

Intermediate (μ^2 ) 1783 2216 b

White (μ^2 ) 3467 4048 b

aP< 0.01; bP< 0.05.

04 Farm Animal Metabolism 04 20/4/00 12:02 pm Page 74