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

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 NH(3)-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.

INTRODUCTION

The significance of the symbiotic relationship between the ruminant microflora and host animal is not well appreciated by the casual observer. However, when one considers that in the United States alone, over 42.8 million beef and dairy cows comprise the national herd and provide over 11.9 billion kg of beef and 82.5 billion kg of milk (USDA-NASS, 2007a,b), the economic importance of maintaining a healthy symbiotic relationship is staggering. Utilization of grain in ruminant diets leads to modifications of the rumen microflora that cause alterations in rumen fermentation patterns and health of the rumen and animal (Russell and Rychlik, 2001). The development of microbial manipulation techniques to maintain efficient production levels and a healthy rumen environment has been a priority for the ruminant nutritionist. New technologies to select for or against specific ruminal microorganisms can permit rumen microbe manipulation consistent with future constraints on antimicrobial use and environmental concerns.

Immunization against lactic acid-producing bacteria was effective in decreasing the risk of acidosis in cattle and sheep fed high-grain diets (Shu et al., 1999; Gill et al., 2000). Feeding colostrum powder or egg yolk from cows and hens immunized against bovine coronavirus was effective in decreasing bovine coronavirus-induced diarrhea in neonatal calves (Ikemori et al., 1997). These studies demonstrate the potential for immunization techniques to provide protection against specific pathogens (Ikemori et al., 1992; Lee et al., 2002).

Preparations of polyclonal antibodies (PAP) against Streptococcus bovis (PAP-Sb) or Fusobacterium necrophorum (PAP-Fn) also have decreased ruminal counts of target bacteria and increased ruminal pH of steers fed high-grain diets (DiLorenzo et al., 2006). Our objective was to evaluate the effects of feeding PAP against S. bovis and F. necrophorum on performance, carcass characteristics, and fermentation patterns of feedlot steers.

MATERIALS AND METHODS

All animal care personnel were trained, and animals were cared for according to the guidelines established by the University of Minnesota Institutional Animal Care and Use Committee.

PAP

Procedures described in DiLorenzo et al. (2006) were used to generate the PAP used in the present studies. Polyclonal antibodies are produced under patented procedures (Camas Inc., Le Center, MN) described herein. Immunogens were extracted from model bacteria grown under proprietary conditions ideal for expression of surface antigens. Antigens then were purified from the culture, and isolated adherin immunogens were made for injection into egg-laying hens with no adjuvant. The model organisms for this study were S. bovis (ATCC 9809, Manassas, VA) and F. necrophorum (ATCC 27852). These organisms were used for the initial testing, to which wild-type organisms isolated from the rumen of 16 high-grain-fed cattle were later included. More than 600 hens were immunized with each immunogen. Eggs collected were analyzed weekly by specific ELISA test plates (Corning Inc., Corning, NY) to monitor antibody binding.

For the study preparations, approximately 200 immunized hens were randomly selected from the total group of hens used for egg collection. Eggs were collected for 3 d, and the product was made from eggs pooled from this collection. The PAP product was made using a mixture of whole egg, molasses, soy oil, and PBS at pH 7.4. At the single dose, the PAP product was fed at 2.5 mL/d. Approximately 2 mL of whole egg was present in each 2.5-mL aliquot of the PAP product. Titers by ELISA averaged between 1:50,000 and 1:1,000,000. The preparations contained immunoglobulin Y, immunoglobulin M, and immunoglobulin A. Counts of 1018 antibody molecules/mL of whole egg were observed. This included approximately 10 to 20% of the preparation that was not active. Because antibodies against many bacteria are found in most eggs, commercially available egg products or eggs were tested for antibodies to specific microbes using the same protocols used to produce egg protein. The ELISA titers did not detect binding to the specific attachment factors.

Exp. 1.

During 2 consecutive years, 226 or 192 Angus and Angus crossbred steers with an initial average BW of 272 or 259 kg were stratified by BW and randomly assigned to 1 of 16 or 1 of 12 pens for yr 1 and 2, respectively. Steers were fed a common diet for 153 or 166 d in yr 1 and 2, respectively. Diets were supplemented with soybean hull pellets mixed or not mixed with PAP resulting in a 2 × 2 factorial arrangement as follows: control, 240 g of soybean hull pellets/d; PAP-Fn, 2.5 mL of a PAP against F. necrophorum mixed with 240 g of soybean hull pellets/d; PAP-Sb, 2.5 mL of a PAP against S. bovis mixed with 240 g of soybean hull pellets/d; PAP-Fn + PAP-Sb, 2.5 mL of PAP-Fn and 2.5 mL of PAP-Sb mixed with 240 g of soybean hull pellets/d.

The experimental diet described in Table 1 was delivered once daily at 0900 h. A supplement containing protein, vitamins, and minerals (Table 1) was formulated to deliver 100 mg of laidlomycin propionate per steer daily. Steers were implanted (VetLife, West Des Moines, IA) with 120 mg of trenbolone acetate, 24 mg of estradiol, and 29 mg of tylosin tartrate (Elanco Animal Health, Greenfield, IN) initially and were reimplanted 78 d (yr 1) or 76 d (yr 2) before slaughter.

Table 1.

Composition and analyzed nutrient content of the diets consumed by steers fed avian-derived polyclonal antibody preparations

	Experimental diet
Item	Exp. 1	Exp. 2
Ingredient, % of DM
Corn grain	33.81	82.73
High-moisture corn	33.81	—
Corn silage	19.10	12.73
Soybean meal	4.35	—
Supplement	8.93	4.54
Supplement composition, % as fed
Cracked corn	58.63	—
Calcium carbonate	21.25	33.7
Soybean meal	—	22.5
Urea	10.07	22.3
Dyna-K1	3.71	10.5
Trace mineral salt	5.62	8.6
Mineral oil	—	1.0
Vitamin and mineral mix	0.602	0.83
Cattlyst-504	0.12	—
Rumensin-805	—	0.38
Tylan-406	—	0.22
Nutrient content, % of DM
CP, %	9.13	10.17
NEg, Mcal/kg	1.42	1.43
Ca, %	0.65	0.65
P, %	0.35	0.35

Provided KCl (International Minerals & Chemical Corp., Terre Haute, IN; minimum 95% KCl).

Composition of vitamin and minerals mix: 0.08% ZnSO4, 0.06% CuSO4, 0.02% MnO2, 20,000 IU of vitamin A, 2,000 IU of vitamin D, and 62 IU of vitamin E.

Composition of vitamin and minerals mix: 0.4% Zn, 0.8% Mn, 0.1% Cu, 0.002% Se, 30,000 IU of vitamin A, 3,000 IU of vitamin D, and 91 IU of vitamin E.

Provided 12.5 mg of laidlomycin propionate (Alpharma Inc., Fort Lee, NJ) per kilogram of diet DM.

Provided 30 mg of monensin (Elanco Animal Health, Greenfield, IN) per kilogram of diet DM.

Provided 8.8 mg of tylosin (Elanco Animal Health) per kilogram of diet DM.

Steers were dewormed, vaccinated against viral and bacterial diseases (infectious bovine rhinotracheitis, bovine viral diarrhea virus, parainfluenza-3 virus, bovine respiratory syncytial virus, 7-way Clostridium sp., and Haemophilus somnus; Pfizer Animal Health, New York, NY), and adapted to pens and diets for a 4-wk period. Animals were housed in a confinement barn bedded with straw at least once weekly; bedding was allowed to accumulate for the duration of the feeding period. Concrete surface areas in the pen were scraped twice weekly. Feed ingredients and dietary treatments were added to and mixed in a truck-mounted mixer. Feed offerings were made according to a visual assessment of feed orts that also considered the preceding 3-d running feed delivery and bunk scores to achieve ad libitum feeding.

Exp. 2.

Sixteen ruminally cannulated crossbred steers (665 ± 86 kg of BW) were used in a completely randomized design with a 2 × 2 factorial arrangement of treatments. Factors were inclusion or not of PAP-Fn or PAP-Sb, both at a dose of 2.5 mL/d each, and the combination of PAP-Fn and PAP-Sb. The experimental diet (Table 1) was fed once daily at 0900 h, and soybean hull pellets with either PAP or a control solution (50:50 mixture of a PBS solution and molasses) added were top-dressed. Steers were gradually adapted to the diet over a 7-d period before initiation of treatments; after adaptation, steers were permitted to consume feed ad libitum. Each PAP or control solution was sprayed onto 120 g of soybean hull pellets/d using a 10-mL syringe; thus, each steer received a total of 240 g of soybean hull pellets/d. A supplement containing protein, vitamins, and minerals (Table 1) was formulated to deliver 300 mg of monensin (Elanco Animal Health) and 90 mg of tylosin/d (Elanco Animal Health). Steers were housed in each of 2 concrete-surfaced pens (7.3 × 9.8 m) in a total confinement barn. Pens were bedded as needed with hardwood sawdust to minimize bedding consumption. Each pen was fitted with a Calan-Broadbent System (American Calan, Northwood, NH) that accommodated 12 individual bunks (0.61 m wide). Steers had free-choice access to a shared water trough (0.91 m).

Sample Collection

Feed offerings and refusals were measured daily. Monthly composites of samples collected weekly were stored frozen (−20°C) until they were analyzed for DM, CP (methods 930.15 and 990.02, respectively; AOAC, 1997), NDF, and ADF. Concentrations of NDF (with heat-stable a-amylase and sodium sulfite) and ADF were determined using a fiber analyzer (model 200, Ankom Technology, Fairport, NY). Initial BW was the average of the BW of 2 consecutive days after withholding food and water for 16 h. Interim BW were taken every 28 d before feed delivery. Final BW was obtained before slaughter or derived from HCW (adjusted) divided by the mean dressing percentage of 62.5 or 62.7 for yr 1 and 2, respectively. Steers were marketed when 55% of the steers in the pen reached Choice grade as assessed visually. Steers were processed at a commercial abattoir by USDA-approved procedures. Longissimus muscle area, percentage of KPH fat depot, fat depth, and liver abscess incidence were measured by university personnel. Liver abscess incidence and liver abscess scores were only measured in yr 2. Quality and yield grades were measured by USDA graders assigned to the plant.

Samples of diet offered and feed ingredients, including pellets, were collected weekly, and those of feed refusals were collected daily. Diet, ingredient, and refusal samples were composited and stored frozen (−20°C) until they were analyzed for DM (6 h at 104°C, Thiex and Richardson, 2003), CP (method 990.02, AOAC, 1997), NDF, and ADF. Concentrations of NDF (with heat-stable a-amylase and sodium sulfite) and ADF were determined using a fiber analyzer (model 200, Ankom Technology). After the adaptation period, steers were sampled (d 0) for measuring ruminal pH and bacterial populations (S. bovis and F. necrophorum) in the morning before delivery of feed and PAP treatments. A second collection took place 19 d later, again before feed delivery. On d 12, ruminal fluid samples were collected at 0, 2, 4, 6, 9, 12, 15, 18, 21, and 24 h after feeding to be analyzed for pH, NH3-N, and VFA. Ruminal fluid (200 mL) was collected by hand from different locations in the rumen and strained through 4 layers of cheesecloth. A subsample (approximately 100 mL) was transferred into a glass beaker, and ruminal pH was measured immediately using a model 345 Corning pH meter equipped with an immersible probe (Corning Inc., Corning, NY). From the remaining 100 mL, 2 subsamples of 25 mL each were transferred into 50-mL vials containing 5 mL of 25% (wt/vol) HPO3 or 1 mL of 9 M H2SO4 to be analyzed for VFA and NH3-N, respectively. Samples were stored at −20°C until they were further processed.

Ruminal Bacterial Enumerations

Ruminal fluid (150 mL) was collected by hand from 3 areas in the rumen and strained through 4 layers of cheesecloth. A subsample (approximately 48 mL) was transferred to a 50-mL vial, held at 39°C, and immediately transported to the microbiology laboratory. Vials were introduced into an anaerobic glove box (Coy Laboratories Inc., Grass Lake, MI) containing an O2-free atmosphere of CO2 (98%) and H2. Vials were vortexed inside the glove box, and a 20-μL aliquot was transferred to each of 3 wells in a 96-well microtitration plate containing 180 μL of minimal medium (Russell et al., 1981) or modified lactate medium (Tan et al., 1994) for quantification of S. bovis or F. necrophorum, respectively.

Serial 10-fold dilutions were performed in triplicate to determine the most probable number (MPN) of S. bovis or F. necrophorum per milliliter of ruminal fluid. A final (conclusive) test for confirmation was performed using API 20 Strep strips or API 20A strips (bioMerieux Inc., Hazelwood, MO) for S. bovis or F. necrophorum, respectively. A complete description of the ruminal bacteria quantification procedures as well as the composition of the media utilized was reported by DiLorenzo et al. (2006).

Laboratory Methods

Samples for NH3-N analyses were thawed and centrifuged at 5,000 × g for 15 min, and NH3-N was measured in the supernatant fluid by steam distillation with MgO using a Kjeltec 2300 Analyzer Unit (Tecator, Hoganas, Sweden). Samples for VFA analyses were thawed and centrifuged at 5,000 × g for 15 min, the supernatant fluid was transferred into a glass vial, and the sample was frozen. The centrifugation process was repeated 3 times until ruminal fluid was clarified.

The VFA and lactic acid were analyzed using a gas chromatograph (model 6890, Hewlett Packard, Palo Alto, CA) with a 4% Carbowax 20M80/120 Carbopack B-DA column (Supelco, Bellefonte, PA) using oxalic acid as the internal standard. Samples were run at 175°C with flow rates of 24, 40, and 450 mL/min for N2, H2, and air, respectively.

Statistical Analyses

Data were analyzed after combining yr 1 and 2. Steer performance data were analyzed on a BW and carcass weight-adjusted final BW basis. Data were analyzed for effects of treatment using pen as the experimental unit in an ANOVA for a completely randomized design with a factorial arrangement of treatments using PROC MIXED (SAS Inst. Inc., Cary, NC). When main effects were observed, control for PAP-Fn was represented by the mean of the control (no PAP fed) + PAP-Sb treatment. Similarly, for main effects of PAP-Sb, control was represented by the mean of the control (no PAP fed) + PAP-Fn treatment. The model included the fixed effects of PAP-Fn, PAP-Sb, and their interactions and the random effect of year; the Satterthwaite method was used to approximate the degrees of freedom. For the analysis of liver abscess incidence and liver abscess scores, the GENMOD procedure of SAS was used. For the analysis of final BW, ADG, G:F, HCW, and dressing percentage, initial BW was included as a covariate. For the analysis of fat thickness, LM area, KPH, USDA yield grade, and marbling score, HCW was included as a covariate.

Data were analyzed for the effects of treatments using steer as the experimental unit in an ANOVA for a completely randomized design with a factorial arrangement of treatments using PROC MIXED of SAS. When main effects were observed, control for PAP-Fn was represented by the mean of the control (no PAP fed) + PAP-Sb treatment. Similarly, for main effects of PAP-Sb, control was represented by the mean of the control (no PAP fed) + PAP-Fn treatment. For the analysis of ruminal bacterial populations, data were converted before analysis using base-10 logarithm transformation and backtransformed to present arithmetic means. Data on populations of ruminal bacteria, ruminal pH, and ruminal NH3-N were analyzed by repeated measures procedures (Littell et al., 1998). Repeated factors included day, for ruminal bacteria populations, and hour for ruminal pH, NH3-N, and VFA analyses. Due to unequal sampling time intervals, the covariance structure utilized was spatial power of SAS. Ruminal pH, NH3-N, and VFA measurements after feeding also were averaged across time by calculating the area under the ruminal data vs. time curve and dividing by total time (Pitt and Pell, 1997). This analysis was conducted for both the initial 4-h postfeeding period and the 24-h postfeeding period.

RESULTS

Feedlot Performance

Results of the combined analysis of the 2-yr feedlot study (Exp. 1) are presented in Table 2 and Figure 1. No significant (P > 0.10) PAP main effects or interactions between PAP were observed for any of the feedlot performance variables or carcass characteristics with the exception of G:F (PAP-Fn × PAP-Sb interaction, P = 0.05), dressing percentage (PAP-Fn main effect, P = 0.01), and severity of liver abscesses (PAP-Fn main effect, P = 0.05). The PAP-Fn × PAP-Sb interaction for G:F on a BW basis yielded the following feed efficiencies: 0.180, 0.185, 0.186, and 0.184 for control, only PAP-Fn, only PAP-Sb, and both PAP, respectively. On a BW basis, steers fed only PAP-Sb were more efficient (P < 0.05) than those fed no PAP. Nevertheless, when PAP-Fn was fed with or without PAP-Sb, feed efficiency was similar (P > 0.10) to steers fed no PAP. No differences (P > 0.10) in feed efficiency (BW basis) were found between steers fed either or both PAP. The PAP-Fn × PAP-Sb interaction (P = 0.13) for G:F on a carcass-adjusted basis yielded the following feed efficiencies: 0.180, 0.181, 0.185, and 0.180 for control, only PAP-Fn, only PAP-Sb, and both PAP, respectively. When analyzed on carcass-adjusted basis, a tendency was found for steers fed only PAP-Sb to be more efficient than those fed both (P = 0.09) or no PAP (P = 0.07). No differences were found in feed efficiency (carcass weight-adjusted) between steers fed only PAP-Sb or PAP-Fn. This was partially due to a main effect of PAP-Fn feeding on dressing percentage. No effects of feeding PAP were observed for live and carcass weight-adjusted final BW, ADG (BW or carcass weight-adjusted basis), or DMI (Table 2). Regarding carcass characteristics, no significant (P > 0.10) PAP main effects or interactions between PAP were observed for HCW, fat thickness, LM area, KPH, yield grade, marbling score, quality grade, or percentage of abscessed livers. A significant (P < 0.05) main effect of PAP-Fn was found for dressing percentage, in which steers receiving PAP-Fn had a decreased dressing percentage when compared with steers receiving no PAP-Fn. Severity of liver abscesses was decreased when PAP-Fn (P = 0.04) was fed and no effect on severity of liver abscesses was observed (P > 0.10) when PAP-Sb was fed.

Table 2.

Effects of feeding an avian-derived polyclonal antibody preparation against Streptococcus bovis (PAP-Sb) or Fusobacterium necrophorum (PAP-Fn) on steer performance and carcass characteristics in 2 consecutive years (data pooled; Exp. 1)

	Main effect1
	PAP-Fn		PAP-Sb
Item	0 mL/d	2.5 mL/d	0 mL/d	2.5 mL/d	SEM	PAP-Fn × PAP-Sb P-value
Initial BW, kg	265	267	266	266	6.6	0.43
Final BW, kg	542	544	543	544	6.5	0.19
Carcass-adjusted final BW, kg	542	539	540	541	7.5	0.26
ADG, kg	1.72	1.73	1.72	1.73	0.10	0.17
Carcass-adjusted ADG, kg	1.71	1.70	1.70	1.71	0.11	0.23
DMI, kg/d	9.35	9.37	9.39	9.33	0.29	0.70
G:F	0.183	0.184	0.182	0.185	0.009	0.05
Carcass-adjusted G:F	0.183	0.181	0.181	0.183	0.009	0.13
HCW, kg	339	338	338	339	9.6	0.26
Dressing percentage2	62.7	62.2	62.5	62.4	0.13	0.58
Fat thickness, cm	1.44	1.46	1.43	1.48	0.04	0.14
LM area, cm2	78.96	79.55	78.90	79.61	0.85	0.55
KPH, %	2.16	2.16	2.15	2.17	0.26	0.49
Yield grade	2.98	3.01	2.97	3.02	0.52	0.26
Marbling score3	519	519	514	523	6.0	0.80
USDA quality grade,4 %
Choice or greater	61.7	61.2	61.4	61.5	—	0.79
Select	37.2	37.7	37.0	37.9	—	0.56
Standard	1.1	1.1	1.6	0.6	—	0.32
Abscessed livers, %	18.3	9.7	16.9	11.1	—	0.46
Liver abscess score5	0.267	0.111	0.240	0.124	0.068	0.11

For PAP-Fn, 0 mL/d was represented by the mean of the control (no PAP fed) and the PAP-Sb treatment. For PAP-Sb, 0 mL/d was represented by the mean of the control (no PAP fed) and the PAP-Fn treatment.

Main effect of PAP-Fn observed (P = 0.01).

300 = Slight 00; 400 = Small 00; 500 = Modest 00.

Quality grade category determined by USDA grader.

Main effect of PAP-Fn observed (P = 0.04). Liver abscess score: 0 (no abscesses present) = 0; -A (1 or 2 minor abscesses) = 1; A (2 to 4 well-established abscesses) = 2; and +A (large, active abscesses, may contain inflammation on the abscess periphery) = 3.

Figure 1.

Effects of feeding an avian-derived polyclonal antibody preparation against Streptococcus bovis (PAP-Sb) or Fusobacterium necrophorum (PAP-Fn) on feed efficiency of feedlot steers. A significant PAP-Fn × PAP-Sb interaction was observed (P = 0.05). Pooled SEM = 0.004. a,bMeans without common letters differ (P < 0.05).

Ruminal bacterial counts (Exp. 2) are reported in Table 3. Ruminal S. bovis counts showed no day effect (P = 0.23) or day × treatment interaction (P > 0.10); however, a significant (P = 0.02) PAP-Fn × PAP-Sb interaction was observed (Table 3). Steers receiving only PAP-Fn or PAP-Sb had less (P < 0.05) ruminal S. bovis counts than those in the control group. No significant differences (P > 0.10) were observed in ruminal S. bovis counts between steers receiving only PAP-Fn or PAP-Sb and those receiving both PAP. No significant differences (P > 0.10) were observed between steers in the control group or those receiving both PAP.

Table 3.

Effects of feeding an avian-derived polyclonal antibody preparation against Streptococcus bovis (PAP-Sb) or Fusobacterium necrophorum (PAP-Fn) for 19 d on ruminal S. bovis counts, in steers fed a high-grain diet (Exp. 2)

	PAP-Fn × PAP-Sb interaction
Item	Control	Only PAP-Fn	Only PAP-Sb	PAP-Fn + PAP-Sb	SEM
No. of steers	4	4	4	4
S. bovis,1 millions/mL	24.0b	5.5a	6.2a	12.4ab	1.4

For S. bovis counts, within rows, and for F. necrophorum counts, within rows and columns, means without common superscripts differ (P < 0.05).

PAP-Fn × PAP-Sb interaction (P = 0.02).

Day × PAP-Fn (main effect) interaction (P = 0.01).

A significant day × PAP-Fn main effect (P = 0.01) was observed for ruminal F. necrophorum counts (Table 3). Feeding PAP-Fn alone or in combination with PAP-Sb for 19 d decreased (P < 0.01) F. necrophorum counts from 1.8 × 104 MPN/mL of ruminal fluid to 4.1 × 102 MPN/mL of ruminal fluid. When no PAP-Fn was fed, F. necrophorum ruminal counts were not significantly different (P > 0.10) after 19 d of high-grain feeding. No significant differences (P > 0.10) were observed in ruminal F. necrophorum counts between steers at d 0.

No significant treatment effects or interactions (P > 0.10) were observed for DMI in Exp. 2 (data not shown). A day effect was observed (P = 0.03), in which DMI increased from 9.54 kg/d (d 0) to 10.64 kg/d (d 19).

Ruminal Fermentation Variables

Ruminal fermentation variables (Exp. 2) are presented in Table 4 and Figure 2. A significant main effect of PAP-Fn (P = 0.03) was observed for ruminal pH in the first 4 h after feeding, in which steers receiving PAP-Fn alone or in combination with PAP-Sb had a greater ruminal pH (Table 4). An interaction between PAP-Fn and PAP-Sb was observed for mean daily ruminal pH (P = 0.07), with a greater (P < 0.05) ruminal pH observed in steers receiving both PAP when compared with the rest of the treatments. Analyzing this interaction for mean daily ruminal pH, feeding both PAP resulted in greater (P < 0.05) mean daily ruminal pH than the rest of the treatments. Mean daily ruminal pH was 5.79, 5.85, 5.72, and 6.23 for control, only PAP-Fn, only PAP-Sb, and both PAP, respectively.

Table 4.

Effects of feeding an avian-derived polyclonal antibody preparation against Streptococcus bovis (PAP-Sb) or Fusobacterium necrophorum (PAP-Fn) for 12 d on ruminal fermentation variables, in steers fed a high-grain diet (Exp. 2)

	Main effect
	PAP-Fn		PAP-Sb
Item	0 mL/d	2.5 mL/d	0 mL/d	2.5 mL/d	SEM	PAP-Fn × PAP-Sb P-value
Mean daily ruminal pH1	5.76	6.04	5.82	5.98	0.08	0.07
Mean daily ruminal NH3-N, mM	4.0	2.1	3.4	2.8	0.79	0.74
Mean daily total VFA, mM	127	124	135	117	13	0.94
Mean daily VFA, mol/100 mol
Acetate	48.5	48.3	48.3	48.6	2.6	0.38
Propionate	29.8	32.3	30.6	31.5	2.7	0.12
Butyrate	14.1	12.0	13.7	12.4	1.1	0.14
2-Methyl butyrate	3.3	3.8	3.6	3.4	0.83	0.12
Isobutyrate	0.93	0.93	0.93	0.93	0.09	0.07
Valerate	2.42	1.90	1.97	2.36	0.59	0.07
Isovalerate	0.88	0.76	0.82	0.82	0.09	0.45
Lactate	ND2	ND	ND	ND
Acetate:propionate	1.73	1.68	1.69	1.72	0.29	0.32

PAP-Fn main effect, P = 0.03.

ND = not determined.

Figure 2.

Effects of feeding an avian-derived polyclonal antibody preparation against Streptococcus bovis (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 concentration (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).

An interaction between PAP-Fn and PAP-Sb was observed (P = 0.06) for ruminal NH3-N concentrations in the first 4 h after feeding. Ruminal NH3-N concentrations in the first 4 h after feeding were less (P = 0.05) for all the treatments receiving PAP when compared with control (8.43, 4.03, 3.63, and 4.39 mM for control, only PAP-Fn, only PAP-Sb, and both PAP, respectively). Analyzing the PAP-Fn × PAP-Sb interaction for ruminal NH3-N concentrations in the first 4 h after feeding, no differences were observed (P > 0.10) between steers fed diets containing only PAP-Fn, only PAP-Sb, or both PAP. For mean daily ruminal NH3-N concentrations, no main effects or interactions (P > 0.10) were observed between treatments (Table 4).

No significant main effects or interactions (P > 0.10) were observed for total VFA concentrations both during the first 4 h after feeding or for mean daily values. Mean daily total VFA concentrations ranged from 117 to 135 mM.

No significant main effects or interactions (P > 0.10) were observed for mean daily acetate, propionate, butyrate, or branched-chain VFA concentrations. No significant main effects or interactions (P > 0.10) were observed for mean daily molar proportions of acetate, propionate, butyrate, 2-methyl butyrate, isovalerate, or actetate:propionate ratio. An interaction between PAP-Fn and PAP-Sb was observed for the mean daily molar proportions of isobutyrate (P = 0.07) and valerate (P = 0.07). However, when means were separated, no treatment differences (P > 0.10) were observed for isobutyrate mean daily molar proportions, and only a trend (P < 0.10) was observed for steers receiving only PAP-Sb to have greater valerate mean daily molar proportions when compared with control and both PAP. Ruminal lactate was not detected in steers fed any of the treatments at any of the sampling times.

DISCUSSION

Feeding avian-derived PAP against F. necrophorum and S. bovis was effective in enhancing feed efficiency and modifying ruminal counts of target bacteria and ruminal fermentation variables in steers fed high-grain diets. Effects observed in animal performance in Exp. 1 may be partially explained by alterations in ruminal fermentation patterns documented in Exp. 2 when feeding PAP-Fn and PAP-Sb.

The improvement in feed efficiency on a BW basis over control steers when feeding only PAP-Sb (Exp. 1) was due to a combined effect of a slight numerical increase in ADG, as well as a slight numerical decrease in DMI. When analyzing the G:F response on a carcass-adjusted basis, the differences with the BW basis responses were largely due to the main effect of PAP-Fn on dressing percentage, in which PAP-Fn seemed to increase weight of noncarcass components. Average daily gain of cattle treated with PAP-Fn was numerically less when calculated from HCW than when calculated from BW. This difference reflects the decreased dressing percentage of the PAP-Fn treatment. Reasons for this effect on dressing percentage remain unknown. Because the only other variable in the 2 experiments with a similar response (PAP-Fn main effect) was severity of abscessed livers, we suggest a possible link between liver metabolism and final weight of noncarcass components. The economic significance of a treatment that affects dressing percentage without concurrent effects on HCW is minimal, because the unit of sale typically is carcass mass, not percentage. Carcass-adjusted ADG reflects carcass rates of gain (Goodrich and Meiske, 1971), and the lack of difference in HCW or carcass-adjusted ADG demonstrates that, in spite of the decreased dressing percentage, cattle fed PAP-Fn had similar carcass ADG as cattle fed no PAP-Fn. The reduction in severity of liver abscesses observed when feeding PAP-Fn alone or in combination with PAP-Sb when compared with control or steers receiving only PAP-Sb may be directly related to the reduction in ruminal counts of F. necrophorum observed in Exp. 2 when feeding PAP-Fn. Fusobacterium necrophorum is the primary etiological agent in the development of liver abscess (Nagaraja and Chengappa, 1998), and strategies that inhibit F. necrophorum in the rumen, the liver, or both decrease the liver abscess incidence (Nagaraja et al., 1999).

When comparing feedlot performance results in Exp. 1 with the 24-h ruminal pH, NH3-N, and total VFA data from Exp. 2, we might attribute some of the differences in performance to ruminal pH and NH3-N patterns during the first 4 h after feeding. A greater ruminal pH in the first 4 h after feeding was observed for all the treatments receiving PAP-Fn along with less ruminal NH3-N concentration for all the PAP treatments. A lesser ruminal pH (below 6.0) in the early hours after feeding in steers not fed PAP-Fn may have decreased fiber and protein digestibility. As reported by Kovacik et al. (1986), a ruminal pH of 6.0 has been established as the threshold below which both proteolytic and cellulolytic activities are greatly decreased. This ruminal pH response up to 4 h after feeding may partially explain the feed efficiency differences between steers fed no PAP and those fed PAP-Sb.

One additional explanation for an enhanced feed efficiency for steers fed only PAP-Sb when compared with control also may be related to the reduction in ruminal S. bovis counts observed in steers fed only PAP-Sb when compared with control steers in Exp. 2. Streptococcus bovis is perhaps the primary etiological agent in the development of ruminal acidosis and also is involved in other detrimental metabolic processes such as wasteful deamination and excess production of lactic acid (Russell et al., 1981; Owens et al., 1998; Griswold et al., 1999). Indeed, in the first 4 h after feeding, steers fed either PAP had less rumen NH3-N than those fed no PAP. Thus, feeding PAP-Sb may have decreased deamination and prevented a decline in rumen pH associated with feeding, thereby leading to greater efficiency of N capture as protein and enhanced digestion during at least the first 4 h after feeding. Steers fed PAP-Fn also had less rumen NH3-N and greater pH during the first 4 h after feeding, and their G:F was intermediate relative to that of those fed no PAP and those fed PAP-Sb.

Even though effects on ruminal NH3-N were transient and restricted to the first 4 h after feeding, effects of PAP on protein metabolism may partially explain the performance differences observed in Exp. 1. A reduction in ruminal NH3-N in the first hours after feeding may indicate a decreased dietary protein deamination in the rumen (Russell et al., 1981) by steers supplemented with either PAP alone or in combination. A reduction in the rate of ruminal protein degradation in situ was described previously when PAP-Sb was fed alone or in combination with PAP-Fn (DiLorenzo et al., 2005). Excess of ruminal NH3-N may lead to greater concentrations of NH3 circulating in blood and an associated energetic cost for converting excess NH3 into urea for excretion (McBride and Kelly, 1990); this in turn can affect animal performance (Russell et al., 1981; Legleiter et al., 2005). Hristov and Broderick (1994) reported optimum ruminal NH3-N concentrations for bacterial protein synthesis in the range of 3.6 to 6.1 mM. The effects of feeding only PAP-Fn or PAP-Sb on ruminal S. bovis counts support the theory that deamination was decreased, which would have enhanced N metabolism in rumen. Besides its main role in the development of ruminal acidosis and starch fermentation, S. bovis has been recognized widely as one of the main proteolytic organisms in the rumen (Russell et al., 1981; Griswold et al., 1999). When feeding PAP-Fn only, or PAP-Sb only, significant reductions in ruminal S. bovis counts were observed; however, when both PAP were combined, S. bovis ruminal counts were similar to those in the control group. The nature of the interaction between the 2 PAP remains unknown, but similarities in terms of interactions on ruminal S. bovis counts and on feed efficiency are of interest.

The effect on ruminal S. bovis counts when feeding only PAP-Sb (Exp. 2) agrees with findings by DiLorenzo et al. (2006). The hypothetical mechanisms by which the reduction in target ruminal bacterial counts is exerted also was described by DiLorenzo et al. (2006) and may be related to the binding activity of the antigen (S. bovis) to PAP-Sb and inhibition of bacterial growth. An inhibitory effect of specific avian-derived antibodies on target microorganisms has been demonstrated previously both in vitro and in vivo (Kuroki et al., 1997; Sunwoo et al., 2002; Cook et al., 2005). Ruminal counts of F. necrophorum (Exp. 2) were in agreement with those reported in previous studies, in which similar doses of monensin and tylosin were fed (Coe et al., 1999; DiLorenzo et al., 2006). Because 300 mg of monensin/d and 90 mg of tylosin/d were fed to all steers from the beginning of the experiment, and were not part of the treatments as in DiLorenzo et al. (2006), ruminal F. necrophorum counts in Exp. 2 at d 0 were less (for all treatments) than those reported by DiLorenzo et al. (2006) when no tylosin was fed. Reductions in ruminal counts of F. necrophorum were not observed after an additional 19 d of tylosin feeding (control diet). However, feeding PAP-Fn (alone or in combination with PAP-Sb) for 19 d caused a further reduction in ruminal counts of F. necrophorum. This effect may be due to differences in the modes of action of tylosin and PAP-Fn that could produce additive or synergistic effects when both feed additives are fed.

Even though a modification in ruminal counts of S. bovis was observed when feeding only PAP-Sb, daily total VFA concentrations or molar proportions were not altered. This could be explained by the fact that, in spite of playing a major role in the development of lactic acidosis, the contribution of S. bovis to the total counts of ruminal microorganisms is relatively small, as has been observed on recent studies that utilize modern molecular techniques for quantification of rumen microorganisms (Stevenson and Weimer, 2007). The lack of detection of ruminal lactic acid in any of the treatments (Exp. 2) is in agreement with previous studies reporting similar ranges in ruminal pH (Coe et al., 1999; Cardozo et al., 2006). The lack of accumulation of lactate in ruminal fluid may be explained by the high mean daily ruminal pH observed in Exp. 2 (5.76 to 6.04). At a ruminal pH greater than 5.5, fermentation of lactate by ruminal bacteria typically exceeds the rate of lactic acid production (Asanuma and Hino, 2005), but once the ruminal pH decreases below 5.5, ruminal lactate-utilizing bacteria are inhibited so ruminal lactate can accumulate (Kung and Hession, 1995; Owens et al., 1998; Nagaraja and Titgemeyer, 2007).

In our study, PAP against S. bovis enhanced feed efficiency of steers fed high-grain diets without negatively affecting carcass characteristics. Enhanced feed efficiency (BW basis) occurred when only PAP-Sb was fed. When both PAP were fed in combination, no effects on animal performance were observed. Effects on animal performance may be explained partially by changes in the ruminal microbial ecosystem related to reductions in counts of S. bovis and some effects on ruminal fermentation metabolism. Feeding PAP-Fn alone or in combination with PAP-Sb led to decreased severity of liver abscesses. Avian PAP present an alternative new technology with the potential to enhance feed efficiency and decrease liver abscesses. Further research is needed to determine the mechanisms by which beneficial effects are achieved as well as development of more effective preparations targeting these and other rumen bacteria that may adversely affect cattle performance.