SERUM LEVELS OF INSULIN-LIKE GROWTH FACTOR-I, THYROID HORMONES, AND SKELETAL MUSCLE FIBER SIZE IN CASTRATED LAMBS WITH AND WITHOUT ANDROGEN TREATMENT

ABSTRACT
To test the influence of castration on sexually dimorphic muscle growth and the
interaction between testosterone and IGF-1, T3 and T4 in muscle growth in Awassi lambs, 12
male lambs were divided into 3 groups; Group W (4 lambs) were castrated at age less than 1
month, group WT (4 lambs) were castrated at the same age and treated with testosterone, and
group R (4 lambs) intact males served as control. Animals were weighed before any treatment
and monthly thereafter and whole blood samples were collected monthly until slaughtering.
Insulin-like growth factor-1, T3, and T4 concentrations were measured in the harvested serum
using ELISA commercially available kits. Lambs were slaughtered at 8 months of age and
semitendinosus and splenius muscles fiber areas were measured using digital image technique.
In WT and R groups, IGF-I concentrations were significantly higher (P<0.05) at 4 and 8 months
compared to IGF-I levels in group W. There was an effect of age on IGF-1 concentration in
groups WT and R. Serum T3 concentrations were significantly the lowest in group R compared
to groups W and WT at most sampling times. Group WT had intermediate serum levels of T3 in
most sampling times. There was a negative correlation between the concentration of T3 and age
in group R. Testosterone treatment resulted in marginally reduced T3 concentration in group
WT. Serum levels of T4 were not significantly affected by age in all groups until months 6 and 8
of age where in group R its concentrations were significantly higher than groups W and WT.
The highest daily weight gain was reported in group R (19.90 gm/day) followed by group W and
group WT. There was a significant difference in weight gain (P<0.05) between group R and
groups W and WT and no significant difference between groups W and group WT. In group R,
splenius muscle fiber area (1458±193 um2) was significantly higher (P < 0.05) than that of
groups W and WT while the muscle fiber area of the semitendonosus was not significantly
different among all groups.