Eimeria acervulina infection elevates plasma and muscle 3-methylhistidine levels in chickens

TO assess muscle breakdown during avian coccidiosis, the level of the nonme tabolizable amino acid 5-methylhistidine (3MH) was determined in muscle, pl asma and excreta from chickens infected with Eimeria acervulina. The change s in 3MH levels during infection were assessed at 1-29 days postinoculation (DPI) in animals given 5 X 10(5) oocysts per bird. The effect of levels of parasitism were evaluated at 8 DPI in birds receiving 5 x 10(3), 5 x 10(4) , 5 x 10(5) or 1 x 10(6) oocysts each. The 3MH levels of plasma, muscle, an d excreta samples were determined by high-pressure liquid chromatography af ter derivatization with fluorescamine. Weight gains, breast muscle weight, eviscerated weight, plasma carotenoid levels, dry weight of muscle, and gro ss lesion scores were also determined. Infected birds had significantly ele vated plasma and muscle 3MH at 4 and 8 DPI following a single dose of E. ac ervulina. The increase in 3MH levels had an inverse relationship with the t ime course of weight gain and plasma carotenoid levels. Plasma and muscle 3 MH levels returned to control values by 15 DPI and remained unchanged from control values through the remainder of the experiment (29 DPI). Breast wei ght was decreased in infected birds, but the ratio of breast weight to evis cerated body weight was unchanged. Excretion of 3MH decreased relative to c ontrols at 4 and 8 DPI and returned to control levels on 15 DPI. The plasma and muscle levels of 3MH were related to severity of infection; however, l evels of excreted 3MH were not. The results suggested that muscle breakdown , as assessed by plasma and muscle levels of 3MH, increased during the acut e stage of E. acervulina infection. The underlying causes for this muscle b reakdown was unclear but could involve a physiological response to anorexia and decreased food intake during the acute phase of infection. Levels of e xcreted 3MH did not increase during infection and this may be the result of decreased excreta output during infection. Plasma and muscle levels of 3MH were correlated with severity of E. acervulina infections but may not be a s sensitive an indicator of infection as plasma carotenoid levels or other physiological parameters.