"Spring rise" in fecal nematode egg counts in sheep in Maine

A "spring rise" in fecal nematode egg counts occurred in Maine sheep housed under conventional conditions during 2 years. Nematodes causing this increase were Haemonchus contortus in one year and Ostertagia sp in the other. The increase in egg counts was greater in sheep that lambed than in unbred sheep. Most of the eggs in the spring rise were probably produced by worms that passed the winter in developmental arrest in the sheep. Some of the female worms probably came from contaminated bedding and developed in the sheep without arrest in growth. Acquisition from contaminated bedding, therefore, should be considered as an additional factor in the epizootiologic character of the condition in Maine.