An examination of potential indices of fasting time in commercially slaughtered sheep

A total of 215 market lambs was slaughtered either directly off grass or after 12, 24, 36, 48 or 72 h from food withdrawal. They had access to water at all times. Half the animals were given a moderate exercise and were subjected to venepuncture about 0.5 h before slaughter. Samples of blood were collected at exsanguination and samples of liver and muscle subsequently removed during carcass dressing. Blood packed cell volume and the concentrations of plasma glucose, lactate, free fatty acids, beta-hydroxybutyrate and total protein, and glycogen in liver and muscle, were examined as potential indices of fasting time. Fasting caused significant changes in all parameters but only beta-hydroxybutyrate increased progressively with longer food-withdrawal times and was unaffected by exercise or the stress of venepuncture. The pattern of response to fasting could be described by an equation of the Gompertz form. Sex of animal did not affect fasting responses but origin of blood (venepuncture or at exsanguination) influenced absolute levels of all the measured blood components except total plasma protein.