Roxarsone and
monensin are common poultry feed additives that are used alone or in combination with other drugs to improve growth and feed utilization in young birds. The effects of
monensin and
roxarsone on the physiology of flexoral tendons of broiler chickens were examined to understand their relationships to leg weakness that have been occasionally associated with these drugs. Day-old chickens were fed either
roxarsone or
monensin for a period of 6 wk with two regimens of each of the drugs (
roxarsone, 45.4 or 90.8 g/ton feed;
monensin, 100 or 150 g/ton feed). None of the treatments had any adverse effect on the growth of the birds or caused any significant leg problem.
Roxarsone at 45.4 g/ton caused a significant gain in
body weight. The biomechanical strength of digital flexoral tendons was measured in several ways. There were no statistical differences in load at break, the modulus of elasticity, or stress or strain levels between different treatment groups and birds that received no medication. There were no differences in
collagen,
proteoglycan, and
pyridinoline content of tendons. Sequential extraction of tendons with different
solvents revealed a significant increase in the percentage of
guanidine HCl extractible
collagens in
monensin-treated birds, and a decrease in the
acid extractible
collagen in both
roxarsone- and
monensin-treated groups. The relative content of
collagen in
acid extractible
collagens were significantly small relative to total
collagen content. Majority of
collagen (84 to 90%) was extractible with
pepsin. About 8 to 11% of total
collagen was resistant to
pepsin that was extractible with
collagenase; this did not differ between treatment groups.
Roxarsone treatment had no effect on the
guanidine soluble
collagen pool. The effect of
monensin on the increase in
guanidine soluble pool of
collagen may relate to its disruptive effects on cellular secretory processes, which may be of significance in modulating connective tissue function in conjunction with other factors. However, in the present study, neither
roxarsone nor
monensin alone produced any significant leg problems nor caused any significant differences in the physiology of flexoral tendons or altered their biomechanical properties.