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ISSN : 2287-5824(Print)
ISSN : 2287-5832(Online)
Journal of The Korean Society of Grassland and Forage Science Vol.45 No.1 pp.59-64
DOI : https://doi.org/10.5333/KGFS.2025.45.1.59

Influence of Ruminal Metabolism and Physiology in Steers Fed Tall Fescue Seed

Ki-Won Lee1, Do Hyung Kim2*
1Grassland & Forages Division, National Institute of Animal Science, RDA, Cheonan 31000, Korea
2Department of Animal Science, Gyeongbuk Provincial College, Yecheon 36830, Korea
* Corresponding author: Do Hyung Kim, Department of Animal Science, Gyeongbuk Provincial College, Yecheon 36830, Korea
Tel: +82-54-650-0343, E-mail: dhkim@gpc.ac.kr
February 14, 2025 March 14, 2025 March 17, 2025

Abstract


This study assessed the effects of fescue toxicosis on ruminal metabolism and physiology in steers. Twelve ruminally cannulated Angus steers [body weight (BW) = 547 ± 9 kg] were blocked by BW and randomly assigned to six blocks. The steers were fed alfalfa cubes (1.5× NEm) and dosed (1 kg/d) with either endophyte-infected tall fescue seed (E+) or endophyte-free tall fescue seed (E-) via rumen cannula for 21 days. Ruminal dry matter (DM) content was tended to have a higher (p=0.052) in steers in E+ than in E- group. Total volatile fatty acid (VFA), acetate concentrations, as well as the acetate:propionate ratio, were higher (p=0.084, 0.095, and <0.001, respectively) in the E+ group, while propionate was lower (p<0.001). Ruminal pH and temperature were similar between treatment groups (p=0.62 and 0.95, respectively), but ruminal pressure was higher (p<0.001) in E-. Additionally, serum prolactin levels was lower (p<0.001) in the E+ group. These findings suggest that consumption of endophyte-infected tall fescue seed may impair ruminal VFA absorption, potentially due to changes in ruminal motility.


Steer , Ruminal metabolites , Tall fescue

초록

    Ⅰ. INTRODUCTION

    Tall fescue (Lolium arundinaceum, formerly Festuca arundinacea) is a widely cultivated perennial grass known for its adaptability and resilience. However, it is commonly infected with an endophytic fungus (Epichloë coenophiala; formerly Neotyphodium coenophialum), which produces ergovaline, a key ergot alkaloid associated with fescue toxicosis. This condition has been linked to reduced performance in ruminants (Stokes et al., 1988;Klotz, 2015) and summer syndrome, a physiological disorder exacerbated by high environmental temperatures (Hemken et al., 1984;Eisemann et al., 2014).

    Several physiological changes have been documented in ruminants consuming endophyte-infected tall fescue. Clinical symptoms of fescue toxicosis include reduced feed intake and body weight gain (Wagner, 2008), which are thought to result from the agonistic effects of ergot alkaloids on serotonergic receptors (Dyer, 1993;Valente et al., 2020). These alkaloids likely induce increased satiety, thereby suppressing feed intake (Simansky, 1996). Additionally, previous research has shown that ergot alkaloids induce vasoconstriction in the rumen (Foote et al., 2011) and mesenteric vasculature (Egert et al., 2014), reducing blood flow and impairing volatile fatty acid (VFA) absorption from the reticulorumen (Foote et al., 2013).

    Ergovaline, a predominant ergot alkaloid found in endophyteinfected tall fescue, has been shown to impair rumen epithelial blood flow and decrease ruminal VFA flux (Foote et al., 2013). Despite these findings, the specific effects of ergot alkaloids on rumen physiology remain insufficiently explored. Therefore, this study aimed to evaluate the impact of fescue toxicosis on rumen metabolism and physiology, with a particular focus on ruminal motility and VFA absorption.

    Ⅱ. MATERIALS AND METHODS

    All experimental procedures involving steers were approved by the University of Kentucky Institutional Animal Care and Use Committee (IACUC).

    1. Animals, treatments, and feeding

    Twelve Angus steers were surgically fitted with a ruminal cannula (Bar Diamond Inc., Parma, ID, USA) and blocked by initial body weight (BW = 547 ± 9 kg), with two steers per block, resulting in six blocks. Steers were provided ad libitum access to water and were fed once daily (07:00 h) with alfalfa cubes formulated to meet 1.5× net energy for maintenance (NEm) based on individual BW. The chemical composition of the alfalfa cubes (DM basis) was as follows: crude protein (CP) = 16.5%, acid detergent fiber (ADF) = 37.2%, neutral detergent fiber (NDF) = 51.9%, and NEm = 5.19 MJ/kg. A mineral premix (Kentucky Nutrition Service, Lawrenceburg, KY) was top-dressed on the feed, containing NaCl (92%), Zn (5500 mg/kg), Fe (9275 mg/kg), Mn (4790 mg/kg), Cu (1835 mg/kg), I (115 mg/kg), Se (18 mg/kg), and Co (65 mg/kg).

    Steers were assigned to one of two treatment groups and received a ruminal dose (1 kg/d) of either endophyte-infected (E+, 4.45 mg ergovaline + ergovalinine/kg DM) or endophytefree (E-) tall fescue seed for a 21-day treatment period.

    The tall fescue seed was ground using a grinder mixer with a 1.25 cm screen and dosed directly into the rumen via the cannula immediately after feeding. To standardize slaughter timing, dosing and feeding was staggered across individual steers, with one steer from each block slaughtered per day, completing one block each week.

    2. Ruminal fluid collection

    Ruminal fluid samples were collected using a suction strainer attached to a 1 m × 6 mm outer diameter stainless steel tube, enabling sampling from multiple locations within the rumen. Sampling was performed on day 14, both immediately before feeding and at 2-hour intervals over an 8-hour period.

    For volatile fatty acid (VFA) analysis, a 5 mL aliquot of ruminal fluid was preserved with 0.5 mL of 50% (w/v) metaphosphoric acid and 0.5 mL of 2-ethylbutyrate (85 mM) as an internal standard. Before analysis, VFA samples were centrifuged (39,000 × g for 20 min at 4℃), and the supernatant was analyzed for VFA concentrations according to the method described by Koontz et al. (2015).

    For ammonia (NH₃) concentration analysis, an additional 5 mL aliquot of ruminal fluid was preserved with 0.5 mL of 25% (w/v) metaphosphoric acid, then centrifuged (39,000 × g for 20 min at 4℃). The supernatant was analyzed for NH₃ concentration using a Konelab 20XT Clinical Analyzer (Thermo Scientific, Waltham, MA, USA).

    3. Blood collection

    Blood samples were collected from the jugular vein via catheter on day 14, immediately before feeding and at 2-hour intervals over an 8-hour period. Samples were allowed to clot for 24 h at 4℃, then centrifuged (2,000 × g for 20 min).

    Serum prolactin concentration was measured using a radioimmunoassay (RIA) procedure, as described by Bernard et al. (1993). The intra- and inter-assay coefficients of variation (CV) were 6.6% and 7.1%, respectively.

    4. Rumen evacuation, and ruminal pH, temperature and pressure measurement

    Rumen fill was evaluated by determining the dry matter (DM) content of ruminal contents. On day 16, ruminal contents were manually evacuated via the cannula before morning feeding, and the total contents were weighed. A 1-kg subsample was collected and dried in a forced-air oven at 60℃ until a constant weight was achieved for DM determination. After subsampling, the remaining ruminal contents were reintroduced into the rumen. To continuously monitor ruminal pH, temperature, and pressure, a wireless probe was inserted into the rumen, with data recorded every 15 min from day 17 to day 21.

    5. Fescue seed and diet analysis

    The ergot alkaloid concentration in tall fescue seed was quantified using ultra-performance liquid chromatography (UPLC) coupled with tandem mass spectrometry (MS-MS), following the procedure described by Foote et al. (2012). Analysis was performed using an Acquity UPLC-TQD triple quadrupole mass spectrometer (Waters, Inc., Milford, MA, USA).

    Feed samples were dried in a forced-air oven at 60℃ for 48 h, then ground using a Wiley mill (Model 4; Thomas Scientific, Swedesboro, NJ, USA) with a 2-mm screen. The dried and ground samples were analyzed for DM and crude protein (CP) according to AOAC methods (AOAC, 2005).

    Neutral detergent fiber (NDF) and acid detergent fiber (ADF) concentrations were determined following the procedure outlined by Van Soest et al. (1991). The NDF analysis included the use of heat-stable amylase and sodium sulfite, with results expressed as ash-free NDF values.

    Metabolizable energy (ME) values were calculated using tabular values, while net energy for maintenance (NEm) was determined using equations from the NRC (2000).

    6. Statistical analysis

    Data for body weight (BW), dry matter intake (DMI), and ruminal dry matter (DM) content were analyzed using a randomized complete block design (RCBD) with the ANOVA procedure of SAS (SAS Institute Inc., Cary, NC, USA). The individual steer served as the experimental unit. The statistical model included block, steer, and seed treatment, where steer and block were considered random effects, and treatment was treated as a fixed effect. Mean separation was performed using Tukey’s adjustment for multiple comparisons.

    Data for serum prolactin concentration, volatile fatty acid (VFA) and ammonia (NH₃) concentrations, and rumen environmental parameters (pH, temperature, and pressure) were analyzed using a randomized complete block design (RCBD) with the ANOVA procedure of SAS. The statistical model included block, steer, treatment, sampling hour, and the interaction between treatment and sampling hour. Block and steer were considered random effects, while treatment, sampling hour, and the treatment × sampling hour interaction were treated as fixed effects. Mean comparisons for treatment, sampling hour, and their interaction were conducted using least significant difference (LSD) with Tukey’s adjustment to control.

    Ⅲ. RESULTS AND DISCUSSION

    There were no significant differences in initial (p=0.82) or final body weight (p=0.28) between treatments. Additionally, dry matter intake (DMI) per unit of metabolic body weight was not affected by treatment (p=0.13; Table 1). However, steers dosed with endophyte-infected (E+) tall fescue seed tended to have a higher total dry matter (DM) percentage of ruminal contents compared to those receiving endophyte-free (E-) seed (p=0.052). In contrast, total ruminal content weight per unit of metabolic body weight (p=0.27) and total DM weight per unit of metabolic body weight (p=0.57) did not differ between treatments.

    Ruminal pH (p=0.62; Table 2 and Fig. 1) and temperature (p=0.95) were not influenced by treatment. However, mean ruminal pressure (p<0.001) was significantly lower in steers dosed with E+ seed compared to those receiving E- seed. Similarly, serum prolactin concentration was markedly reduced in steers consuming E+ seed (p<0.001), a common physiological response associated with ergot alkaloid exposure. A treatment × hour interaction was detected for ruminal pH (p=0.026), with steers receiving E+ seed exhibiting lower pH values between 14 and 24 h post-dosing.

    Steers dosed with E+ seed tended to have a higher total volatile fatty acid (VFA) concentrations (p=0.084; Table 2), along with a greater acetate:propionate ratio (p=0.001) than those receiving E- seed. The propionate proportion was significantly lower (p<0.001) in the E+ treatment, whereas the acetate proportion tended to have a higher (p=0.095) in steers consuming E+ seed. Additionally, ruminal ammonia (NH₃) concentration showed a tendency to be higher in E+ steers (p=0.11), potentially indicating alterations in nitrogen metabolism associated with ergot alkaloid exposure.

    Despite efforts to equalize dry matter intake (DMI), steers dosed with endophyte-infected (E+) tall fescue seed exhibited a higher total dry matter (DM) percentage in ruminal contents compared to those receiving endophyte-free (E-) seed. Several factors can influence the amount and DM content of ruminal digesta, including differences in digestibility, forage quality, ergovaline concentration, and alterations in ruminal flow kinetics. Goetsch et al. (1987) reported that digestibility increased in diets containing higher levels of E+ hay. Conversely, Aldrich et al. (1993) and Matthews et al. (2005) found that apparent DM digestibility was lower in steers consuming E+ hay compared to those fed E- hay. These conflicting findings highlight a fundamental challenge in fescue research—studies comparing E+ and E- forages often face confounding effects of forage source and endophyte presence. To mitigate this issue, the present study standardized the basal diet and introduced E+ or E- seed as an experimental treatment.

    The higher DM percentage observed in steers dosed with E+ seed aligns with previous findings by Foote et al. (2013) and Koontz et al. (2013). It has been hypothesized that increased ruminal DM content may be attributed to altered ruminal motility. Additionally, it is well established that serotonin influences peristalsis and gut motility, primarily through adrenergic signaling pathways (De Ponti et al., 1996;Hansen, 2003;Egert et al., 2014). The observed reduction in serum prolactin concentration in E+ steers further supports the known pharmacological effects of ergot alkaloids, which act on α1- and β2-adrenergic, serotonin-2, and dopaminergic receptors.

    In agreement with the lower ruminal pressure and increased ruminal DM content observed in E+ steers, ruminal dosing of E+ seed resulted in higher total volatile fatty acid (VFA) concentrations, an increased acetate:propionate ratio, and a lower molar proportion of propionate in ruminal fluid. Although VFA concentrations in the rumen fluid do not always indicate absorption, ruminal epithelial metabolism can serve as an index of VFA absorption. Aschenbach et al. (2009) proposed that acetate uptake primarily occurs through protein-mediated transport rather than passive lipophilic diffusion. The absorption of VFA from the rumen is facilitated by two primary mechanisms: simple diffusion of undissociated VFA into ruminal epithelial cells, followed by intracellular dissociation, or facilitated transport of dissociated VFA via membrane transport proteins (Connor et al., 2010). These findings suggest that ergot alkaloids may influence VFA absorption dynamics, potentially through modifications in ruminal motility and epithelial transport mechanisms.

    Ⅳ. CONCLUSIONS

    Ergot alkaloids produced by endophyte-infected tall fescue may reduce blood flow to the absorptive surfaces of the rumen, thereby impairing VFA absorption. However, the specific effects of ergot alkaloids on rumen physiology remain inadequately explored. The findings of this study suggest that dosing with E+ seed can reduce VFA absorption in the rumen, possibly due to altered blood flow or changes in epithelial function. These differences in VFA absorption may also be influenced by variations in the surface area of ruminal papillae or differences in blood flow rates, which could affect the diffusion and transport of VFA from the rumen. To fully elucidate the underlying mechanisms, further research should focus on integrating ruminal kinetics with VFA absorption and passage dynamics (nutrient flux) to better understand the interactions between ergot alkaloids and ruminal metabolism.

    Ⅴ. ACKNOWLEDGMENTS

    This study was supported by the RDA Fellowship Program of National Institute of Animal Science, and Cooperative Research Program for Agriculture Science and Technology Development (Project No. PJ01592504), Rural Development Administration, Republic of Kore

    Figure

    KGFS-45-1-59_F1.gif

    Comparison of ruminal pH, temperature and pressure, and blood prolactin concentration between endophyte-infected tall fescue seed (E+) and endophyte-free tall fescue seed (E-).

    Table

    Body weight (BW), dry matter (DM) intake and rumen contents in Angus steers dosed with endophyte-free tall fescue seed (E-) or endophyte-infected tall fescue seed (E+)

    Serum prolactin concentration, ruminal physiology and ruminal volatile fatty acid (VFA) and ammonia concentrations in Angus steers dosed with endophyte-free tall fescue seed (E-) or endophyte-infected tall fescue seed (E+)

    Reference

    1. Aldrich, C.G., Paterson, J.A., Tate, J.L. and Kerley, M.S. 1993. The effects of endophyte-infected tall fescue consumption on diet utilization and thermal regulation in cattle. Journal of Animal Science. 71:164-170.
    2. AOAC. 2005. Official methods of analysis (16th ed.). AOAC International, Washington. DC.
    3. Aschenbach, J.R., Bilk, S., Tadesse, G., Stumpff, F. and Gabel, G. 2009. Bicarbonate-dependent and bicarbonate-independent mechanisms contribute to nondiffusive uptake of acetate in the ruminal epithelium of sheep. American Journal of Physiology-Gastrointestnal and Liver Physiology. 296:G1098-G1107.
    4. Bernard, J.K., Chestnut, A.B., Erickson, B.H. and Kelly, F.M. 1993. Effects of prepartum consumption of endophyte-infested tall fescue on serum prolactin and subsequent milk-production of Holstein cows. Journal of Dairy Science. 76:1928-1933.
    5. Connor, E.E., Li, R.W., Baldwin, R.L. and Li, C. 2010. Gene expression in the digestive tissues of ruminants and their relationships with feeding and digestive processes. Animal. 4:993-1007.
    6. De Ponti, F., Giaroni, C., Cosentino, M., Lecchini, S. and Frigo, G. 1996. Adrenergic mechanisms in the control of gastrointestinal motility: From basic science to clinical applications. Pharmacology & Therapeutics. 69:59-78.
    7. Dyer, D.C. 1993. Evidence that ergovaline acts on serotonin receptors. Life Sciences. 53:223-228.
    8. Egert, A.M., Kim, D.H., Schrick, F.N., Harmon, D.L. and Klotz, J.L. 2014. Dietary exposure to ergot alkaloids decreases contractility of bovine mesenteric vasculature. Journal of Animal Science. 92: 1768-1779.
    9. Eisemenn, J.H., Huntington, G.B., Williamson, M., Hanna, M. and Poore, M. 2014. Physiological responses to known intake of ergot alkaloids by steers at environmental temperatures within or greater than their thermoneutral zone. Frontiers in Chemistry. 96:1-9.
    10. Foote, A.P., Harmon, D.L., Brown, K.R., Strickland, J.R., McLeod, K.R., Bush, L.P. and Klotz, J.L. 2012. Constriction of bovine vasculature caused by endophyte-infected tall fescue seed extract is similar to pure ergovaline. Journal of Animal Science. 90:1603-1609.
    11. Foote, A.P., Harmon, D.L., Strickland, J.R., Bush, L.P. and Klotz, J.L. 2011. Effect of ergot alkaloids on contractility of bovine right ruminal artery and vein. Journal of Animal Science. 89:2944-2949.
    12. Foote, A.P., Kristensen, N.B., Klotz, J.L., Kim, D.H., Koontz, A.F., McLeod, K.R., Bush, L.P., Schrick, F.N. and Harmon, D.L. 2013. Ergot alkaloids from endophyte-infected tall fescue decrease reticuloruminal epithelial blood flow and volatile fatty acid absorption from the washed reticulorumen. Journal of Animal Science. 91:5366-5378.
    13. Goetsch, A.L., Jones, A.L., Stokes, S.R., Beers, K.W. and Piper, E.L. 1987. Intake, digestion, passage rate and serum prolactin in growing dairy steers fed endophyte-infected fescue with noninfected fescue, cover or wheat straw. Journal of Animal Science. 64:1759-1768.
    14. Hansen, M.B. 2003. Neurohumoral control of gastrointestinal motility. Physiological Research. 52:1-30.
    15. Hemken, R.W., Jackson Jr, J.A. and Boling, I.A. 1984. Toxic factors in tall fescue. Journal of Animal Science. 38:1011.
    16. Klotz, J.L. 2015. Activities and effects of ergot alkaloids on livestock physiology and production. Toxins. 7:2801-2821.
    17. Koontz, A.F., Kim, D.H., Foote, A.P., Bush, L.P., Klotz, J.L., McLeod, K.R. and Harmon, D.L. 2013. Alteration of fasting heat production during fescue toxicosis in Holstein steers. Journal of Animal Science. 91:3881-3888.
    18. Koontz, A.F., Kim, D.H., McLeod, K.R., Klotz, J.L. and Harmon, D.L. 2015. Effect of fescue toxicosis on whole body energy and nitrogen balance, in situ degradation and ruminal passage rates in Holstein steers. Animal Production Science. 55:988-998.
    19. Matthews, A.K., Poore, M.H., Huntington, G.B. and Green, J.T. 2005. Intake, digestion, and N metabolism in steers fed endophyte-free, ergot alkaloid-producing endophyte-infected, or nonergot alkaloidproducing endophyte-infected fescue hay. Journal of Animal Science. 83:1179-1185.
    20. NRC. 2000. Nutrient requirements of beef cattle (7th rev. ed.). Natl. Acad. Press, Washington. DC.
    21. Simansky, K.J. 1996. Serotonergic control of the organization of feeding and satiety. Behavioural Brain Research. 73:37-42.
    22. Stokes, S.R., Goetsch, A.L., Nejad, H.H., Murphy, G., Jones, A.L., Mashburn, S., Beers, K.W., Johnson, Z.B. and Piper, E.L. 1988. Effects of supplemental bermuda grass hay or corn on intake, digestion and performance of cattle consuming endophyte-infected fescue. Journal of Animal Science. 66:204-212.
    23. Valente, E.E.L., Klotz, J.L., Ahn, G., McLeod, K.R., Herzing, H.M., King, M. and Harmon, D.L. 2020. Ergot alkaloids reduce circulating serotonin in the bovine. Journal of Animal Science. 98:1-8.
    24. Van soest, P.J., Robertson, J.B. and Lewis, B.A. 1991. Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. Journal of Dairy Science. 74:3583-3597.
    25. Wagner, J.F. 2008. Neotyphodium effects on cattle. In: H.A. Fribourg and D.B. Hannaway (Eds), Tall fescue on-line monograph. Oregon State University Extension Service, Corvallis, and University of Tennessee Agricultural Experiment Station. Knoxville.
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