Utilizing polyclonal antibodies to improve rumen function
ABSTRACT: Polyclonal antibody preparations (PAP) can contribute to reduce antimicrobial resistance and improve rumen function by targeting specific bacteria or molecules. Avian-derived antibodies (IgY) from egg yolks offer advantages over traditional mammalian-sourced PAP including higher antibody concentrations, reduced welfare concerns and cross-reactivity, cost-effectiveness, stability, and the absence of host immune complement activation. The mechanism of action involves agglutinating bacteria, inhibiting their adhesion to epithelial cells, suppressing virulence factors, and neutralizing toxins. IgY have been studied for their effects on rumen microbial populations, particularly during high-grain feeding. Research shows PAP-IgY targeting Streptococcus bovis and Fusobacterium necrophorum inhibits bacterial growth, prevents the decrease of ruminal pH, and reduces liver abscess severity. Limited studies have shown improvements in feed efficiency in beef steers and increased milk production in dairy cows. However, findings on nutrient digestibility have been inconsistent, and no benefits regarding the mitigation of systemic inflammation have been observed. While promising, further research is needed to optimize dosage, antibody combinations, and evaluate broader impacts on rumen and livestock performance. This review explores current research and practical applications of PAP as feed additives with a focus on mechanism, preparation, and potential for improving rumen function while identifying gaps in the literature to guide future research.
Keywords: avian-derived IgY, cattle performance, feed additives, passive immunization
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Fig. 1. Proposed mechanism of action of the polyclonal antibody preparation (PAP) IgY in inhibiting bacterial activity. The IgY antibody features a “Y”-shaped structure consisting of two identical heavy chains and two identical light chains. Each chain contains four constant heavy regions (C H ), one constant light region (C L ), and one variable region (V), all linked by disulfide bonds. The antigen-binding domains are located at the tips of the arms (Fab regions), while the effector domains are found at the base (Fc region). Binding to antigens occurs through the Fab regions, which then trigger effector functions via the Fc region. The proposed mechanisms by which IgY inhibit bacterial activity include bacterial agglutination, adherence-blockade, toxin neutralization, and opsonization followed by phagocytosis (created in BioRender (Silva 2025), https://BioRender.com/q54y723).
Use of PAP to improve rumen function
Investigations of PAP applications in beef cattle
Polyclonal antibody preparations in beef cattle diets have been evaluated to a limited extent (Table 1), highlighting the need for further research to better understand and quantify their effects on growth performance, ruminal health, and carcass characteristics.
The primary goal of incorporating PAP into beef cattle diets has been to improve health outcomes during high-grain feeding, with a particular focus on targeting Streptococcus bovis and Fusobacterium necrophorum due to their recognized pathogenic potential, economic detriment to livestock production, and their relation to acidosis and liver abscesses (Nagaraja et al. 2005; Fubini et al. 2018). Blanch et al. (2009) found that a PAP against a mix of microorganisms may help prevent ruminal acidosis in heifers transitioning to high-concentrate diets by maintaining a higher pH before feeding. Similarly, Silva et al. (2022a) observed that feeding PAP targeting Streptococcus bovis, Fusobacterium necrophorum, and LPS reduced the risk of ruminal acidosis by increasing ruminal pH of steers fed a transition diet. In agreement, DiLorenzo et al. (2006) observed reductions in the bacterial counts (most probable number/mL of ruminal fluid) of Streptococcus bovis and Fusobacterium necrophorum when feeding PAP to steers fed a high-grain diet. DiLorenzo et al. (2008) observed a reduction in Streptococcus bovis counts and lower liver abscess scores in PAP-fed cattle. Also, Pacheco et al. (2012) observed reduced rumen lesions for PAP-fed steers than for monensin-fed steers. Con- versely, Silva et al. (2021) did not observe a reduction in circulating inflammatory markers in cannulated crossbred steers fed a transition diet (three steps 35%, 60%, 82% cracked corn grain, respectively). Altogether, PAP appears to be a viable strategy to assist in the ruminal and liver health of beef cattle fed high-grain diets.
As a secondary effect, growth performance may be affected by feeding PAP to beef cattle. Silva et al. (2022b) reported that feeding 1 g/day of a PAP improved average daily gain during the first 14 days and increased DMI during the first 28 days of feeding in backgrounding heifers fed a growing diet. Such improvement in feed intake and gain may be related to the enhanced fiber digestibility observed with PAP in this study. Similarly, DiLorenzo et al. (2008) showed that feeding a PAP against Streptococcus bovis increased gain to feed ratios in steers fed a finishing diet. Pacheco et al. (2012) observed similar effects on feed efficiency of PAP-fed and monensin- fed steers. In agreement, Rodrigues et al. (2013) observed improved average daily gain, reduced the cost of gain, and improved feed conversion in finishing steers during the first 84 days of feed.
Interestingly, PAP may affect carcass rib eye area and dressing percentage, probably as a result of enhanced health and efficiency of nutrient utilization. Only a few studies have evaluated the effects of PAP on carcass characteristics. Millen et al. (2015) found that PAP-fed steers had a 4% greater ribeye area as compared to monensin-fed steers. Pacheco et al. (2012) found that PAP-fed steers had a minor reduction in dressing percentage as compared to monensin-fed steers. In contrast, Dilorenzo et al. (2008) and Rodrigues et al. (2013) did not find any effects of PAP on carcass characteristics of steers.
Investigations of PAP applications in dairy cattle and in vitro systems
Other studies have explored the use of PAP in dairy cattle to evaluate their effects on rumen function, nutrient digestibility, and the mitigation of metabolic challenges such as acidosis through ruminal pH, with or without the comparison to monensin (Table 2). Similar to the beef cattle studies, the major bacteria targeted were Streptococcus bovis and Fusobacterium necrophorum. Marino et al. (2011) investigated the effects of PAP targeting Streptococcus bovis, Fusobacterium necrophorum, Clostridium aminophilum, Peptostreptococcus anaerobius, and Clostridium sticklandii, compared to monensin, on ruminal fermentation patterns and in vivo digestibility in ruminally cannulated dairy cows. The study found that starch digestibility was negatively impacted in PAP-treated cows compared to both the control and monensin-treated cows. Interestingly, no differences in ruminal pH were observed between monensin and PAP-treated cows; however, both treatments resulted in higher pH levels 4 h post-feeding compared to control cows. In contrast, Pacheco et al. (2023) compared PAP targeting Streptococcus bovis, Lactobacillus spp., Fusobacterium necrophorum, E. coli O157H:7, and endotoxins to monensin and found that cattle treated with monensin exhibited higher mean ruminal pH values compared to those receiving PAP. Barros et al. (2019) testing two forms of PAP–powdered (7 g/day) and liquid (21 mL/day)–targeting Streptococcus bovis, Fusobacterium necrophorum, E. coli, and endotoxins during dietary transition in dairy cattle. When liquid PAP was fed, it improved apparent dry matter and neutral detergent fiber digestibility and effectively prevented a ruminal pH drop compared to both powdered PAP and the control group (Barros et al. 2019). However, Marino et al. (2011) detected a reduction in apparent total tract digestibility of starch for Holstein cows consuming high-grain diets with the addition of PAP at 10 mL/day compared with cows consuming the control treatment (95.3 or 96.8%, respectively). When four doses (0, 1.5, 3, and 4.5 g/day) of spray-dried PAP were formulated against 26% Streptococcus bovis, 12% Fusobacterium necrophorum, 48% against the proteolytic bacteria (Clostridium aminophilum, Peptostreptococcus anaerobius, and Clostridium sticklandii), and 14% E. coli O157:H7 and administered to Holstein cows fed high-concentrate diets, Bastos et al. (2012) did not observe differences in nutrient digestibility. The variability in nutrient digestibility results across experiments suggests that the effectiveness of PAP as a feed additive is influenced by several factors, including dosage (Silva et al. 2022a, 2022b) and its physical form. These findings highlight that animal responses to PAP can vary significantly depending on the diet fed to the animals, the mode of delivery, the preparation and purification of the PAP, and the bacterial species targeted.
More recent studies have evaluated the inclusion of PAP targeting LPS in dairy bulls transitioned from a forage-based diet (11 days of orchard and timothy mixed hay) to a high-grain diet (2 days of 50% concentrate and 50% soybean flakes) to induce a subacute ruminal acidosis challenge (Mizuguchi et al. 2021). In this study, 0, 2, or 4 g of PAP was directly adminis- tered into the ruminal fistula. Inclusion of PAP significantly reduced ruminal LPS activity, and Holsteins bulls receiving PAP showed higher ruminal pH levels compared to controls. However, no significant differences were observed in rumen fermentation parameters or peripheral blood metabolites among the treatment groups (Mizuguchi et al. 2021). Another study investigating the effects of a pure LPS-targeting PAP on dairy cows found no differences in inflammatory markers, such as haptoglobin and ceruloplasmin. However, milk production was increased in early lactation dairy cows treated with PAP, suggesting potential benefits in milk production despite the lack of changes in inflammation (Ibarbia 2014).
In vitro studies have been performed to investigate the application of PAP in ruminant diets. Tondini et al. (2023) conducted an in vitro study to evaluate the effectiveness of avian derived PAP in inhibiting specific cellulolytic bacteria. The study utilized a cellobiose-containing growth medium to cultivate Ruminococcus albus 7, Ruminococcus albus 8, and Fibrobacter succinogenes S85, with the aim of testing the impact of increasing doses of PAP (0 mg/mL (CON), 1.3 × 10−4 mg/mL (LO), 0.013 mg/mL (MD), and 1.3 mg/mL (HI) of medium) on bacterial growth. The results demonstrated that PAP effectively inhibited the growth of the targeted cellulolytic bacteria. Interestingly, the antibodies also exhibited some inhibitory effects on non-targeted bacterial strains, indicating a broader spectrum of activity. This study highlights the feasibility of developing PAP to selectively suppress specific ruminal bacteria, offering a promising avenue for manipulating microbial populations to optimize rumen function. Similarly, Edwards et al. (2017) evaluated the ability of PAP to inhibit lipolytic activity in ruminal bacteria. The study focused on key ruminal lipase-contributing species, including Anaerovibrio lipolyticus, Butyrivibrio fibrisolvens, Propionibacterium avidum, and Propionibacterium acnes. An anti-Pseudomonas lipase antibody was generated to test whether targeting a purified protein could enhance inhibitory effects. The PAP was applied at increasing doses (0, 0.2, 1.0, 2.5, and 5.0 mg), and the results showed that the anti-lipase antibodies effectively inhibited lipolytic activity across various bacterial species. This suggests significant cross-reactivity among lipases secreted by different ruminal bacteria, demonstrating the potential of PAP to broadly reduce lipolysis within the rumen.
Conclusion: The use of polyclonal antibody preparations in beef and dairy cattle diets shows promising potential for improving rumen function, health outcomes, and growth performance, particularly during high-grain feeding. While the research on PAP applications in cattle is still limited, studies indicate that PAP can help mitigate ruminal acidosis, enhance nutrient utilization, and improve feed conversion efficiency by targeting key pathogens such as Streptococcus bovis and Fusobacterium necrophorum. In beef cattle, PAP has been associated with improved growth performance, increased dry matter intake, and enhanced feed efficiency, especially during the early stages of high-grain feeding. Furthermore, preliminary evidence suggests that PAP may positively influence carcass characteristics in some cases, although more research is needed in this area.
In dairy cattle, PAP’s effectiveness in improving rumen health and metabolic responses remains variable, with studies showing mixed results on nutrient digestibility. Despite these inconsistencies, some studies report beneficial effects, such as improved ruminal pH and potential increases in milk production. Additionally, in vitro studies highlight the promising application of PAP in selectively inhibiting specific ruminal bacteria, offering new possibilities for optimizing ruminal microbial populations.
While the potential of PAP as a feed additive in livestock diets is evident, further research is necessary to refine its application, optimize dosages, test different preparations, and better understand its broader effects on rumen and cattle health and performance. Furthermore, additional exploration is needed into various scenarios, including research on the potential of PAP for methane mitigation, reduction of systemic inflammation, and its effects during the backgrounding phase. Lastly, studies investigating PAP derived to target key pathogens should examine potential bacterial hierarchy and functionality cross-over when specific abundances are reduced.