Polyclonal antibody preparations from avian origin as a feed additive to beef cattle: ruminal fermentation during the step-up transition diets

This study investigated the effects of feeding an avian-derived polyclonal antibody preparation (PAP; CAMAS, Inc.) against Streptococcus bovis, Fusobacterium necrophorum, and lipopolysaccharides (40%, 35%, and 25% of the preparation, respectively) on ruminal fermentation [pH, ammonia-N (NH3-N), lactate, and volatile fatty acids (VFA)] of beef steers during a 21-d step-up diet adaptation. Eight ruminally cannulated Angus crossbred beef steers (658 +/- 79 kg of body weight) were assigned in a crossover design to be transitioned from a diet containing ad libitum bermudagrass hay [Cynodon dactylon (L.) Pers.] plus 0.45 kg/d (as fed) of molasses with 0 (CON) or 3 g of PAP (PAP) to a high-grain diet. Transition consisted of three 7-d steps of increased inclusion of cracked corn (35%, 60%, and 82% of the diet DM for STEP1, STEP2, and STEP3, respectively). On each transition day and 7 d after STEP3 (STEP3-7d), ruminal fluid samples were obtained every 3 h for 24 h. Feeding 3 g of PAP daily increased (P < 0.01) average ruminal pH during STEP3 compared with CON steers (5.6 vs. 5.4 +/- 0.05, respectively). During STEP1, NH3-N concentration was greater (P < 0.01; 9.4 vs. 6.8 +/- 0.74 mM, respectively), and time (min/d) and area (time x pH) of ruminal pH below or equal to 5.2 was lesser (P <= 0.03) for steers consuming PAP compared with steers assigned to CON treatment (33.4 vs. 73.3 +/- 21.7 min/d and 187.4 vs. 406.3 +/- 119.7 min x pH/d, respectively). Steers consuming PAP had greater acetate:propionate ratio at 0, 3, and 6 h relative to diet change compared with CON (2.42, 2.35, 2.29 vs. 1.66, 1.79, and 1.72 +/- 0.17, respectively), whereas butyrate molar proportions increased (P = 0.02; 17.1 vs. 11 +/- 1.58 mol/100 mol for CON and PAP, respectively) when PAP was not fed at STEP2. Total ruminal lactate concentrations were not affected by PAP feeding (P > 0.11). In conclusion, feeding 3 g/d of polyclonal antibody preparation against S. bovis, F. necrophorum, and lipopolysaccharides was effective in increasing ruminal pH, A:P ratio, and NH3-N concentrations, possibly attenuating the risks of ruminal acidosis in steers during the step-up transition from forage to high-grain diets. LAY SUMMARY Feedlot cattle are fed high-grain diets that require a transition period with gradual increasing amounts of grain. Those diets are associated with changes in microbial populations of the gastrointestinal tract in favor of bacteria that can contribute to cause metabolic disorders by reducing ruminal pH. Feed additives are compounds added to the diet of feedlot cattle to improve animal health and performance by minimizing the effects of microbial changes. An alternative product, polyclonal antibody preparations (PAP), have emerged as a possible tool to ameliorate the effects of high-grain diets on cattle health and performance. Therefore, this research investigated the effects of PAP during diet transition to a high-grain in beef cattle. It was concluded that feeding PAP contributed to increase ruminal pH, which could result in reduced risks of metabolic diseases.