Impact of doramectin treatment at the time of feedlot entry on the productivity of yearling steers with natural nematode infections.
OBJECTIVE
To measure the reduction in fecal nematode egg counts and productivity impact of treatment of yearling steers with doramectin at entry into the feedlot, compared with control steers treated only with fenthion.


METHODS
6,096 crossbred yearling steers with a mean (+/- SD) body weight of 377.0 (+/- 37) kg.


METHODS
Steers were implanted with zeranol and alternately separated to fill each of 24 pens. Groups of steers within 12 matched pairs of pens were randomly allocated to treatment with doramectin or no treatment with doramectin for internal nematodes. Fecal samples were collected from approximately every twentieth steer from each pen at day 0 and at reimplant (approx day 60). Each steer was weighed on day 0 and at reimplant and then mean body weights of steers per pen were determined at 120 to 140 days after trial initiation.


RESULTS
Treatment steers had a significantly lower fecal egg count at reimplant than control steers. Treatment steers had a significantly greater mean daily gain during the study, significantly greater feed consumption, significantly lower feed-to-gain ratio, and significantly better quality carcass grades at slaughter.


CONCLUSIONS
Under the conditions of our trial, there was a significant fecal egg count reduction response to doramectin treatment, which resulted in significantly improved productivity. Results of economic analysis of return on investment indicated that even with low egg counts in heavy body weight cattle, nematode egg count reduction with doramectin significantly improved returns.
MacGregor
D S
DS
Livestock Consulting Services, Jerome, ID 83338, USA.
Yoder
D R
DR
Rew
R S
RS
D045930:Anabolic Agents / Q000008:administration & dosage; D000818:Animals; D000871:Anthelmintics / Q000627:therapeutic use*; D002417:Cattle / Q000254:growth & development* / Q000469:parasitology; D002418:Cattle Diseases / Q000188:drug therapy* / Q000469:parasitology; D004958:Estradiol / Q000008:administration & dosage; D004968:Estrogens, Non-Steroidal / Q000008:administration & dosage; D005243:Feces / Q000469:parasitology; D007559:Ivermectin / Q000031:analogs & derivatives / Q000627:therapeutic use*; D008297:Male; D008460:Meat; D009349:Nematode Infections / Q000188:drug therapy*; D010270:Parasite Egg Count / Q000662:veterinary; D011897:Random Allocation; D014204:Trenbolone Acetate / Q000008:administration & dosage / Q000031:analogs & derivatives; D015430:Weight Gain / Q000187:drug effects; D015029:Zeranol / Q000008:administration & dosage
D045930:Anabolic Agents; D000871:Anthelmintics; D004968:Estrogens, Non-Steroidal; D004958:Estradiol; D007559:Ivermectin; D015029:Zeranol; C084101:doramectin; D014204:Trenbolone Acetate