Effects of polyclonal antibody preparations on rumen fermentation patterns, performance, and carcass characteristics of feedlot steers
ABSTRACT: In a previous study, preparations of polyclonal antibodies (PAP) against Fusobacterium necrophorum (PAP-Fn) or Streptococcus bovis (PAP-Sb) were successful in decreasing 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 variables 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 BW 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 decreased (P < 0.05) dressing percentage. Steers receiving PAP-Fn (alone or in combination with PAP-Sb) had a decreased severity of liver abscess (P < 0.05). No differences (P > 0.10) were observed in any other carcass characteristics.
In Exp. 2, sixteen 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 decreased (P < 0.05) ruminal counts of S. bovis when compared with 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 decreased by 98% (P < 0.05) after 19 d, when compared with the counts in control steers. Mean daily ruminal pH was greater (P < 0.05) in steers fed both PAP when compared with 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 less (P < 0.05) ruminal NH3-N concentrations in the first 4 h after feeding when compared with 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 decreased. 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.
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Figure 2. Effects of feeding an avian-derived poly- clonal antibody preparation against Streptococcus bo- vis (PAP-Sb) or Fusobacterium necrophorum (PAP-Fn) for 12 d on ruminal pH (A; SEM = 0.15), concentration of ruminal NH3-N (B; SEM = 0.92), and total VFA con- centration (C; SEM = 18) over time after feeding. Main effect of PAP-Fn on ruminal pH, P = 0.02. A significant PAP-Sb × time after feeding interaction was observed for ruminal NH3-N concentration (P = 0.05). A PAP-Fn × PAP-Sb × time after feeding interaction was observed for ruminal pH (P = 0.10) and NH3-N concentrations (P = 0.01). No main effects or interactions were observed for total VFA concentration (P > 0.10).
