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Effects of a Combination of Antibiotics Administered for Prevention of Pasture Bloat¹

Iowa State University, Ames

Abstract

The effect of daily feeding of a combination of penicillin, erythromycin, tylosin and streptomycin (PETS) in wheat middlings-molasses pellets was evaluated. In 474 animals treated with PETS, bloat was reduced by 67% when compared with 362 controls. Two factors which may have contributed to the occurrence of some bloat in treated groups were the decline in erythromycin activity in the pellets and the refusal of some animals to consume PETS pellets, particularly during the 1- to 4-day period after initiation of antibiotic feeding. Average weight gains were greater (0.19 lb. per animal daily) in 52 animals fed PETS pellets than in a similar number of controls. PETS in loose salt, and penicillin, erythromycin, tylosin, chloramphenicol and oxytetracycline in pellets appeared to be less effective than the same treatments in grain.

Transient diarrhea and swelling in the region of the vulva occurred occasionally in antibiotic-fed animals; these reactions were restricted almost exclusively to animals receiving high-grain diets. It was demonstrated with animals on high-grain diets that transient depression of appetite sometimes occurs when P, E and T were fed singly, but there was no evidence of this reaction when S was fed alone. Conversely, no adverse reactions were observed among animals fed primarily green chopped forage or alfalfa hay when as much as 2 gm. of the antibiotic mixture (PETS) was fed per animal daily.

No marked effect of antibiotic feeding on total counts of Gram positive or Gram negative rumen organisms was observed; however, concentration of total volatile rumen acids was sharply depressed for about 3 days after initiation of antibiotic feeding.

¹ Journal Paper No. J-4480 of the Iowa Agricultural and Home Economics Experiment Station, Ames, Iowa. Project No. 1267. Supported in part by funds provided by the Iowa State University Research Foundation.