Effects of Gastrointestinal Nematode Parasites on Performance in Feedlot Cattle

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Abstract
Two beef fattening experiments were conducted to investigate the effects of the gastrointestinal nematode parasites Ostertagia ostertagi and Cooperia spp. on performance. Data were recorded for 13 infected-control, 13 infected-medicated and 13 unexposed (worm-free) individually-fed steers in experiment one, and for 6 infected-control and 6 unexposed (worm-free) group-fed animals in experiment two. Fecal egg counts averaged 341 eggs per gm. at the start of the feeding period for the 32 steers that had been exposed to parasitic infection. After 22 days on feed (25% concentrate ration) the egg counts decreased 80% in the infected-controls and 99% in the infected-medicated group (7 days after treatment with an anthelmintic, thiabendazole). A transitory response to anthelmintic treatment was apparent in the average gain comparisons; however, the two infected groups in experiment one showed comparable weight gains and feed efficiencies after the 189-day drylot fattening period was completed. The unexposed groups gained more rapidly than their infected-control counterparts. Feed efficiency differences were small and not significantly different. Group-fed and individually-fed lots of steers on analogous treatments had nearly identical daily gains. Anorexia was noted to be the primary effect of parasitism. The parasites had their influence on performance over the first 70 days of feeding period. During the last 90 days on feed the infected-control groups underwent compensatory weight gain, which appreciably narrowed the gain advantages of the unexposed groups. The experiments indicated that worms per se can be an important source of economic loss in feedlot cattle. An important interrelationship between gastrointestinal nematode parasitism, concurrent disease and nutrition is postulated. The prevention of worm infections by the producer of feeder cattle is regarded as the best means of avoiding the losses and adverse interactions. Copyright © 1969. American Society of Animal Science . Copyright 1969 by American Society of Animal Science

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