Impact of cattle grub (Hypoderma spp.) (Diptera: Oestridae) infestations on performance of beef cattle.

Abstract

Forty-five weaned Angus steer calves, Bos taurus , were obtained from a ranch at the interface between a large area (southern Alberta, Canada) with a history of several years’ treatment with systemic insecticides for cattle grubs, Hypoderma lineatum (Villers) and Hypoderma bovis (L.), and an area where there had been treatment for only 1 yr. Thus, we expected that these animals would receive different levels of cattle grub infestation pressure and have different numbers of encysted larvae. The steers were not exposed to systemic insecticides; they were evaluated for the effects of the cattle grubs on performance. Peak numbers of cattle grubs that appeared in the backs of these animals ranged from 2 to 39. The influence of level of cattle grub infestation on the performance of these steers during the period when the larvae were migrating to and emerging from the animals’ backs did not influence the steers’ rate of gain, feed intake, or feed-to-gain ratio. The entire growth period from weaning to slaughter was divided and analyzed as three distinct periods: the period before the cattle grubs appeared in the animals’ backs, the period when cattle grubs were present in the warbles, and the period following drop-out of cattle grubs. In addition, cattle grub infestation did not influence carcass grade, backfat thickness, marbling score, or rib eye area when steers were slaughtered 13 wk after the last cattle grub had emerged. Results suggest that relatively low numbers of cattle grubs did not produce measurable effects on performance of cattle that were placed on feed as soon as 15 wk before Hypoderma spp. encystment.