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Effects of feeding polyclonal antibody preparations on rumen fermentation patterns, performance, and carcass characteristics of feedlot steers

N. DiLorenzo^*, C. R. Dahlen, F. Diez-Gonzalez, G. C. Lamb, J. E. Larson^* and A. DiCostanzo^*

^* Department of Animal Science , Department of Food Science and Nutrition, University of Minnesota, St. Paul 55108 , Northwest Research and Outreach Center, University of Minnesota, Crookston 56716and North Florida Research and Education Center, University of Florida, Marianna, 32446

dicos001{at}umn.edu

Abstract

In a previous study, preparations of polyclonal antibodies (PAP) against Fusobacterium necrophorum (PAP-Fn) or Streptococcus bovis (PAP-Sb) were successful in reducing ruminal counts of target bacteria and increasing ruminal pH in steers fed high-grain diets. The objective of this study was to evaluate the effects of feeding PAP-Fn or PAP-Sb on performance, carcass characteristics, and ruminal fermentation parameters of feedlot steers. In Exp. 1, during 2 consecutive years, 226 or 192 Angus and Angus crossbred steers were fed a high-grain diet containing either PAP-Sb or PAP-Fn or both. When measured on a live weight basis, steers fed only PAP-Sb had a greater G:F (P < 0.05) than those fed no PAP. Nevertheless, when both PAP were fed, feed efficiency was similar (P > 0.10) to steers fed no PAP or only PAP-Sb. Steers receiving PAP-Fn (alone or in combination with PAP-Sb) had a reduced (P < 0.05) dressing percentage. Steers receiving PAP-Fn (alone or in combination with PAP-Sb) had a reduced severity of liver abscess (P < 0.05). No differences (P > 0.10) were observed in any other carcass characteristics. In Exp. 2, 16 ruminally cannulated Angus crossbred steers (BW = 665 ± 86 kg) were fed a high-grain diet containing either PAP-Sb or PAP-Fn or both. Feeding only PAP-Fn or PAP-Sb for 19 d reduced (P < 0.05) ruminal counts of S. bovis when compared to steers fed both or no PAP. The ruminal counts of F. necrophorum in steers fed PAP-Fn alone or in combination with PAP-Sb were reduced by 98% (P < 0.05) after 19 d, when compared to the counts in control steers. Mean daily ruminal pH was greater (P < 0.05) in steers fed both PAP when compared to feeding either or no PAP. Ruminal pH in the first 4 h after feeding was greater (P < 0.05) for steers receiving PAP-Fn alone or in combination with PAP-Sb. Steers receiving either PAP alone or in combination had lower (P < 0.05) ruminal NH₃-N concentrations in the first 4 h after feeding when compared to those of control steers. Polyclonal antibody preparations against S. bovis were effective in enhancing G:F of steers fed high-grain diets, but dressing percentage was lowered. Mechanisms of enhancement of G:F remain unknown but may be related to changes in ruminal counts of target bacteria and associated effects on ruminal fermentation products.

Key Words: Streptococcus bovis • Fusobacterium necrophorum • Antibodies