RESUMO
The associations between the muscle glycogen concentration and form and the rate of post-mortem glycolysis in ovine muscle were investigated. Twenty-two merino wethers (18-24 months) were allocated to either roughage or concentrate pelleted diets for 34 days prior to slaughter. An exercise depletion/repletion model was applied four days prior to slaughter to generate differences in muscle glycogen levels at slaughter. Muscle biopsies were taken from the m. semimembranosus (SM) and m. semitendinosus (ST) prior to and immediately after exercise for muscle glycogen determination. At slaughter, one side was electrically stimulated and both sides were conventionally chilled for 24h. The pH response to electrical stimulation (ΔpH) and the rate of pH decline adjusted to a constant temperature of 38°C over the initial 6h post-mortem period was determined in three muscles (m. longissimus thoracis et lumborum LTL, SM and ST). In addition, the concentrations of glycogen, proglycogen (PG), macroglycogen (MG) and lactate in the three muscles immediately after slaughter were determined. The glycogen loss due to exercise was influenced by diet (P<0.01; concentrate 63% and roughage 73%) but did not differ between muscles. The rates of repletion significantly varied between muscles (SM>ST) and diet (concentrate>roughage). The available glycogen (glycogen(A)) and MG concentrations at slaughter varied significantly depending on the diet (P<0.01) and muscle (P<0.001). The percentage of MG relative to MG+PG varied between muscles (46%, 50% and 57% for the ST, LTL and SM). The concentration and form of available glycogen at slaughter did not influence the response to electrical stimulation after adjusting for pre-stimulation pH (P<0.01). The ΔpH varied significantly between muscles (0.39±0.03, 0.26±0.02 and 0.20±0.03 for the ST, LTL and SM) after adjusting for pre-stimulation pH. Differences in the temperature adjusted rate of pH decline were observed between the muscles (LTL>SM>ST). Importantly, a positive linear association (P=0.05) was found between muscle glycogen(A) concentration at slaughter and the rate of pH decline (temperature adjusted).
RESUMO
OBJECTIVE: To examine the effect on wool growth of physiological changes associated with experimental flystrike in superfine Merino wethers. DESIGN: An animal house study comparing experimentally fly struck sheep with non-infected control groups that were pair fed or fed ad libitum. PROCEDURE: Sheep in the blow fly larval challenge group were each artificially infected with 500 first instar larvae per day for 8 days. Infections were terminated with insecticide on day 10. For all sheep, live weight change, feed intake and body temperature were monitored and blood collected for analysis of haematology, cortisol, serum haptoglobin, serum amyloid A and the pro-inflammatory cytokines, TNFa, IL-1 b, IL-6 and IL-8. Wool growth and staple strength were examined 4 months after infection. RESULTS: Experimental fly strike included moderate fever, depressed feed intake, and elevated cortisol, IL-6, serum amyloid A and haptoglobin. Staple strength was significantly decreased in struck sheep and did not differ between wool from sites adjacent to and remote from strike lesions. CONCLUSIONS: The results suggest that depression in feed intake alone is not sufficient to account for the decline in staple strength seen during fly strike. Cortisol, IL-6 and metabolic consequences of the acute phase response are likely to be major contributors to the systemic effects of blowfly strike on wool.
