Seasonal Influences on Parasitism

Lambing when parasites are less active is often suggested as a means of controlling parasites. USDA researchers in Arkansas compared parasitism in Katahdin lambs born in the winter (Jan-Feb) vs. those born in the fall (Oct-Nov).

Body weights and FAMACHA© scores were determined at approximately 60, 90, 120, and 150 days of age. Fecal egg counts and packed cell volumes were determined at approximately 90, 120, and 150 d of age. Lambs were dewormed if their FAMACHA© score was greater than 3. Haemonchus contortus was the predominate parasite on most days in both seasons.

Fecal egg counts were higher in fall-born lambs at 90 days of age, but similar at 120 and 150 days of age. Packed cell volumes were lower in winter born lambs on days 120 and 150. Fall-born lambs had lower (better) FAMACHA© scores on all days. Winter born lambs were more subject to anemia and had a greater need for deworming. Fall lambs had lower body weights than winter lambs.

In Arkansas, parasites were more manageable in fall lambs, but winter born lambs weighed more, possibly due to seasonal differences in forage quality.

Source: Journal of Animal Science Supplement, May 2021. Read abstract.