The role of temperature and light on inhibition of development of Cooperia oncophora.

Infective Cooperia oncophora larvae were temperature and light conditioned by holding them at various temperatures and daily light intensities for up to 56 days prior to administration to parasite-free calves via stomach tube. The calves were killed either on day 20 or day 21 postinfection. A marked (up to 80.5%) inhibition of development occurred in larvae held at 4 degrees C while little or no inhibition occurred in larvae held at room temperature or in fresh larvae. Marked inhibition also occurred in larvae held at 15 degrees C for 56 days while a low rate of inhibition occurred in larvae held at 17 degrees C for 42 days. Low incidence of inhibition was recorded in two of four calves given larvae held at ambient temperatures of mid-summer while appreciable inhibition of development of larvae occurred in two calves permitted to graze during the second and third week of September in 1975. Temperature conditioning of C. oncophora eggs for 27 days did not result in inhibition of development of infective larvae subsequently cultured from the eggs. Photoperiod or the presence of light did not have any appreciable effect on the development of inhibition of C. oncophora under the conditions of these investigations.