Corn Steep Liquor in Poultry Nutrition: Impacts on Performance, Metabolism, and Immunity

CSL supplementation in broiler diets has been extensively evaluated, with studies exploring various inclusion levels, processing methods (liquid vs. dried), and replacement strategies for conventional protein sources such as SBM and fish meal. Early trials demonstrated that low-level CSL inclusion could improve body weight (BW) in broiler chicks. Camp et al. (1957) reported that the inclusion of 3—10% liquid CSL in diets based on yellow corn and SBM significantly enhanced BW of Lancaster × New Hampshire broiler chicks, with no further benefit beyond 3%, suggesting that a low inclusion level is sufficient to provide the unidentified growth factors present in CSL. Similarly, CSL dried on corn germ meal or corn gluten feed also preserved these growth-promoting effects, indicating that the drying process does not compromise CSL’s bioactive components. Subsequent studies assessed CSL as a partial substitute for plant- and animal-based proteins. Russo and Heiman (1959b) demonstrated that replacing 5% of corn meal and SBM with CSL (23% CP) increased BW in White Leghorn cockerels, regardless of feed form (pelleted or crumbled), although feed conversion ratio (FCR) remained unaffected. Interestingly, CSL could partially replace animal-derived protein sources such as condensed fish solubles and dried whey, fully restoring broiler body weight gain (BWG) and FCR (Russo and Heiman, 1959a). Moreover, Russo et al. (1960) found that fermentation improved CSL’s efficacy; fermented corn solubles yielded better feed efficiency compared with unfermented counterparts, highlighting the importance of fermentation-derived organic acids.

Dried CSL has also been evaluated in broilers. Tsang and Schaible (1960) reported that 3% dried CSL improved BW in White Plymouth Rock cockerels after 8 weeks, while replacing fish meal with 1.5—3.0% dried CSL enhanced BWG and improved FCR at 5 weeks of age. Likewise, Waldroup et al. (1970) observed that dried CSL inclusion up to 15% had no negative effects on BWG, feed intake (FI), or FCR; however, higher levels (20—25%) reduced BW and FI while increasing FCR. These detrimental effects were likely due to excessive dietary acidity or nutrient imbalance rather than palatability, as FI was not markedly lower in high-CSL diets. Recent studies have further clarified the inclusion threshold for CSL in broiler diets. Yazdanyar et al. (2015) showed that CSL inclusion above 10% negatively impacted BWG, FI, and FCR, likely due to high diet viscosity and lactic acid levels causing digestive discomfort. In contrast, moderate inclusion (≤10%) improved growth performance, possibly by acidifying the gut environment and enhancing nutrient digestibility. Ullah et al. (2018) similarly reported that 10% CSL yielded the highest BWG and best FCR in Hubbard × Hubbard broilers, while 15% CSL maintained BWG but did not further improve feed efficiency.

The beneficial effects of moderate CSL supplementation during the starter phase have been consistently observed. For instance, Ebrahimpour et al. (2022) found that 4% dried CSL enhanced FI and BWG in Ross 308 broilers during the first 10 days, likely due to improved palatability and gut health from CSL’s organic acids. However, long-term inclusion beyond the starter phase did not produce additional growth benefits. Similarly, Hamidifard et al. (2023) reported that low-dose liquid CSL (1 cc/kg) numerically improved BW and FI during the first 21 days without significantly affecting overall performance, supporting the notion that early-life gut acidification contributes to initial growth responses. Overall, evidence suggests that CSL inclusion at 3—10% supports growth and feed efficiency in broilers, likely through unidentified growth factors, lactic acid-driven gut acidification, and improved nutrient digestibility. However, excessive levels (>15%) can impair performance, potentially due to metabolic stress and reduced nutrient utilization.

In laying hens, CSL supplementation has been primarily evaluated for its effects on egg production, internal and external egg quality, and long-term metabolic health. Early investigations by Waldroup and Rutherford (1971) showed that dried CSL (31.5% CP, 7.8% lactic acid) could replace up to 25% of yellow corn and SBM in layer diets without negatively affecting hen-day egg production (HDEP), egg weight (EW), FCR, or Haugh units (HU). Interestingly, prolonged feeding (48 weeks) with 10—25% CSL improved HU and yolk color due to increased dietary xanthophyll levels. Further studies confirmed CSL’s positive impact on internal egg quality. Waldroup and Hazen (1979) reported that Babcock hens receiving 20% dried CSL showed significantly improved HU scores, indicating enhanced albumen integrity. However, in older hens (>12 months in production), high CSL inclusion (20%) occasionally reduced HDEP, likely due to the stress associated with dietary changes and handling.

Long-term trials by Lilburn and Jensen (1984) evaluated CSL (2.5—20.0%) in Single Comb White Leghorn hens. CSL supplementation improved HU scores at 10—20% inclusion levels without affecting HDEP, EW, or FI. Interestingly, hens fed CSL exhibited reduced liver lipid content and relative liver weight, suggesting improved lipid metabolism. These findings highlight CSL’s potential dual benefit in layers: enhancing albumen quality while supporting hepatic lipid regulation. In summary, CSL inclusion up to 20% can be safely used in laying hen diets to maintain egg production and improve internal egg quality, particularly HU scores. However, caution is advised in older layers where dietary stress may transiently affect egg production at very high inclusion levels.

Moreover, a recent study demonstrated that supplementing dried CSL at a moderate level (3% of the diet) in Hy-Line Brown hens improved laying performance, including higher HDEP, egg mass (EM), and feed efficiency during the later weeks of the trial, while 0.5% CSL showed no significant effects (Lee et al., 2025). Significantly, CSL supplementation did not alter external or internal egg quality parameters such as eggshell thickness, strength, albumen height, HU, or yolk color. These results suggest that a 3.0% inclusion of CSL can partially replace SBM without compromising egg quality, while providing additional benefits to production performance.

The use of CSL in turkeys has been less extensively studied, but available data indicate similar responses to those observed in broilers. Waldroup and Rutherford (1971) investigated CSL in turkey breeder hens and found that dried CSL (5—20%) replacing yellow corn, SBM, and alfalfa meal did not affect HDEP, FCR, fertility, or hatchability, indicating its safety and acceptability in breeder diets. In meat-type turkeys, Potter and Shelton (1978) evaluated the inclusion of 2.5% and 5.0% corn fermentation solubles in Large White turkeys over seven weeks. CSL supplementation improved BW by 6.6% (2.5% CSL) and 8.4% (5.0% CSL) and increased FI by 6.7% and 10.2%, respectively. However, feed efficiency slightly declined at the higher inclusion level (5.0%), suggesting a threshold beyond which CSL’s benefits on FI and BW may not translate into improved FCR. Thus, CSL can be used in turkey diets at low-to-moderate levels (≤5%) to improve growth performance and FI without compromising reproductive performance or egg quality in breeder hens.

CSL supplementation has been shown to influence lipid metabolism and liver health in poultry. In laying hens, Lilburn and Jensen (1984) reported that feeding liquid CSL for four to six months significantly reduced liver and plasma lipid levels compared to basal diets. In Babcock layers, the highest inclusion level of CSL resulted in a marked decrease in hepatic lipid accumulation, while Shaver layers fed 5%, 10%, or 20% CSL exhibited significantly lower liver lipid content than the controls. Interestingly, relative liver weight was unaffected in one trial but was reduced considerably in birds receiving the highest CSL inclusion in another, suggesting that CSL may modulate hepatic lipid metabolism through its bioactive compounds. Similar trends were observed in broilers. Yazdanyar et al. (2015) found that inclusion levels above 10% in Ross 308 broilers reduced relative liver weight, indicating possible alterations in metabolic activity or nutrient partitioning at higher dietary acidity levels. Moreover, Hamidifard et al. (2023) observed reduced plasma triglycerides and elevated high-density lipoprotein cholesterol (HDL-C) in birds receiving 1 cc/kg liquid CSL, likely due to the actions of CSL-derived organic acids and lactic acid bacteria in modulating bile acid metabolism and cholesterol homeostasis. Collectively, these findings suggest that moderate CSL inclusion supports lipid metabolism and may prevent excessive hepatic lipid deposition. In contrast, too high levels may lead to altered liver morphology or metabolic stress.

CSL supplementation also modulates immune function and oxidative status. Ebrahimpour et al. (2022) demonstrated that broilers fed 6% dried CSL had significantly higher antibody titers against Newcastle disease (ND), infectious bronchitis (IB), and avian influenza (AI), implying that CSL-derived organic acids may improve gut microbiota balance and stimulate both mucosal and humoral immunity. In addition, CSL’s high CP content likely supports immunoglobulin synthesis. Antioxidant effects were also reported by Atabak et al. (2021), finding that diets containing 8.5% dried CSL increased glutathione peroxidase (GPX) and ferric reducing ability of plasma (FRAP) while reducing lipid peroxidation markers, indicating improved oxidative stress resilience. Similarly, Hamidifard et al. (2023) showed enhanced humoral immune responses to AI vaccination at day 42 in birds supplemented with liquid CSL, although early vaccination titers were not significantly different. These findings collectively highlight CSL’s role in supporting immune responsiveness and mitigating oxidative stress, likely through its organic acids, bioactive peptides, and potential prebiotic effects on gut microbiota.

The influence of CSL on gut physiology and nutrient digestibility appears dose-dependent. Ullah et al. (2018) reported that broilers fed 5% and 10% CSL exhibited significantly higher dry matter (DM) and CP digestibility during the starter phase, likely due to CSL’s high soluble protein content improving nutrient availability. Ether extract (EE) digestibility was also enhanced at moderate inclusion levels. However, beyond the starter phase, further improvements were not observed, suggesting early-life benefits may be more pronounced. Similar findings were noted by Tauqir et al. (2022), where birds fed 3% CSL had the highest DM, CP, and EE digestibility, while higher inclusion levels did not confer additional benefits. Moreover, Hamidifard et al. (2023) showed that liquid CSL supplementation lowered the pH of ileal digesta, supporting an acidifying effect that can inhibit pathogenic bacteria and promote beneficial microbial colonization. Interestingly, while villus height (VH), crypt depth (CD), and the VH:CD ratio were not significantly altered, a numerically lower VH in CSL-fed birds suggested a reduced pathogen load and decreased intestinal cell turnover. Overall, moderate CSL inclusion may enhance early gut health by improving nutrient digestibility and lowering gut pH, thereby creating a more favorable intestinal environment.

High CSL inclusion can induce adverse effects on organ development and tissue integrity. In Ross 308 broilers, Yazdanyar et al. (2015) observed that inclusion levels above 10% significantly reduced the relative weights of the liver, Bursa of Fabricius, spleen, and gizzard, indicating potential impacts on immune organ development and mechanical digestion. Similarly, Ullah et al. (2018) reported that birds fed 15% CSL exhibited moderate-to-severe hypertrophy and hyperplasia of the crop mucosa, likely due to persistent irritation from the low dietary pH. Histological changes included swelling of enterocytes, leukocyte infiltration in intestinal intervillous spaces, and extensive necrosis of renal tubular epithelial cells, suggesting nephrotoxicity related to increased uric acid accumulation from CSL’s high non-protein nitrogen content. Interestingly, while hematological parameters such as erythrocyte count, leukocyte count, hemoglobin concentration, and erythrocyte sedimentation rate (ESR) remained unaffected, serum uric acid levels rose significantly with increasing CSL inclusion. Hamidifard et al. (2023) also found a transient increase in heterophil-to-lymphocyte (H:L) ratio at 14 days with higher CSL doses, suggesting mild stress responses, although this effect diminished over time. Despite these changes, carcass yield and giblet weights were largely unaffected at moderate inclusion levels (Tauqir et al., 2022), indicating that low-to-moderate CSL inclusion remains safe. Overall, while moderate inclusion supports organ development and immune function, excessive levels may induce crop irritation, renal stress, and reduced immune organ size.