Studies on the spring rise phenomenon in ovine helminthiasis. I. Spring rise in stabled sheep.

Serial ova count studies were conducted to determine some of the characteristics of the spring rise in faecal shedding of nematode ova by parasitized sheep in flocks in the Montreal area. It was discovered that substantial spring rises occurred in most ewes following their lambing but that great variation existed in the magnitude, duration, and pattern of the rises. Although rams did not display increased ova counts, a slight but well-defined rise developed in one unbred ewe. Larval studies in ewes parasitized by a variety of nematode species, revealed that Haemonchus contortus was the major contributor to the spring rise in faecal ova output. Preparturient treatment of ewes with thiabendazole(1), at the rate of 100 mg./kg. of body weight, suppressed spring rise but failed to arrest completely the faecal shedding of nematode ova.