ANNUAL CYCLES IN NUMBERS OF THE SHEEP KED, MELOPHAGUS OVINUS (L.)

Abstract

Sheep ked [Melophagus ovinus (L.)] populations were studied on barren and pregnant ewes in 1953-54, and on rams, wethers, and pregnant, barren, and ovariectomized ewes continuously from 1954 to 1957. All sheep in the 1954–57 study were obtained as 5-months-old lambs. Number of keds on wethers and on barren and ovariectomized ewes rose consistently to peak levels in January-February and declined again to very low numbers in the summer months. This appeared to be the basic pattern. Keds on pregnant ewes that conceived in October-November continued to increase in numbers until parturition (March-April) but on ewes that conceived in December they reached peak levels at the usual time (January-February). Following parturition decline in numbers was sharp and very low levels of infestation were noted in the summer months. Rams maintained consistently higher numbers than all animals except pregnant ewes throughout most of the study. Ked numbers on all but pregnant ewes were smaller and tended to reach peak levels earlier in the second and third years of the animal’s life than in the first year It is postulated that some form of host resistance to ked infestation develops toward the end of the first year of life and that ked increases each autumn result from a partial breakdown of this resistance.