Effect of low temperature storage on the haemolytic complement of cattle and sheep

Sera from cattle and sheep stored at −70, −20 and −10°C were examined for haemolytic complement at Days 0, 37, 54, 86, 133 and 245. The decline in complement followed a similar trend, both by classical pathway (CPW) and alternative pathway (APW) assay methods. Both cattle and sheep sera retained 80% of their complement activity till Day 245 at −70°C whereas at −20°C cattle sera had lost 67% and sheep sera 80% of the activity. At −10°C the decline in complement levels was, in general, similar to −20°C. The complement level of sheep sera declined more rapidly than that of cattle. For reliable results, it is suggested that sera of cattle and sheep should be assayed for complement within 4–5 months at −70°C and within a month at −20 or −10°C.