5-hydroxytryphophan mitigates ergot alkaloid-induced suppression of serotonin and feed intake in cattle

Abstract

The impact of ergot toxicosis on livestock industries is detrimental and treatments are needed in many countries. The objective of this study was to evaluate the effects of acute exposure to ergot alkaloids and 5-hydroxytryptophan (5-HTP) supplementation on feed intake, serotonin metabolism, and blood metabolites in cattle. Eight Holstein steers (538 ± 18 kg) fitted with ruminal cannulas were used in a replicated 4 × 4 Latin Square design experiment with a 2 × 2 factorial treatment structure. The treatments were the combination of 0 (E-) or 15 µg ergovaline/kg BW (E+) and 0 (5HTP-) or 0.5 mg of 5-hydroxy-l-tryptophan/kg BW (5HTP+) administered daily for 6 d. Toxic endophyte-infected tall fescue seed was used to supply the daily dose of ergovaline. Endophyte-free seed was used to equalize seed intake between treatments. Ground seed was placed into the rumen immediately before feeding. The 5-HTP was dissolved in water and infused into the abomasum via the reticulo-omasal orifice. Blood was collected from a jugular vein catheter at 0, 1, 2, 4, 8, and 24 h after treatment administration. Ergovaline without 5-HTP (E+/5HTP-) decreased dry matter intake (DMI) in comparison to steers without ergovaline and 5-HTP (E-/5HTP-). However, 5-HTP infusion in association with ergovaline (E+/5HTP+) normalized the DMI. Although E + did not affect (P > 0.05) the area under the curve (AUC) of serum 5-HTP, 5-hydroxyindoleacetic acid, tryptophan, and kynurenine, serum and plasma serotonin concentrations were decreased (P < 0.05). The infusion of 5-HTP increased (P < 0.05) the AUC of serum 5-HTP, serum and plasma serotonin, and serum 5-hydroxyindoleacetic acid. In conclusion, acute exposure to ergot alkaloids reduced DMI and circulating serotonin in cattle but 5-HTP administration showed potential to normalize both circulating serotonin and feed intake.

Keywords: bovine; ergovaline; fescue; serotonergic receptor.

Figure 1.

Dry matter intake of steers receiving ergot alkaloids (E+) and 5-hydroxytryptophan (5-HTP). Means (A) and over time (B), vertical dot line indicates when treatments started. Data are means ± SEM for N = 8 steers/group. P-value for E+ = 0.269, 5HTP+ = 0.0729, E+*5HTP = 0.003, day < 0.001.

Figure 2.

Serum prolactin of steers receiving ergot alkaloids (E+) and 5-hydroxytryptophan (5-HTP). Data are means ± SEM for N = 8 steers/group. P-value for E+ < 0.001, 5HTP = 0.303, E+*5HTP = 0.789.

Figure 3.

Changes in serum 5-hydroxytryptophan (5-HTP, A), serum serotonin (5-HT, B), plasma 5-HT (C), and 5-hydroxyindoleacetic acid (5-HIAA, D) in steers receiving ergot alkaloids (E+) and 5-hydroxytryptophan (5-HTP). Data are means ± SEM for N = 8 steers/group. P-value for (A) E+ = 0.957, 5HTP = <0.001, E+*5HTP = 0.550, time = <0.001; (B) E+ = <0.001, 5HTP = 0.0729, E+*5HTP = 0.872, time = 0.017; (C) E+ <0.001, 5HTP = 0.068, E+*5HTP = 0.347, time = 0.017; (D) E+ = 0.394, 5HTP < 0.001, E+*5HTP = 0.242, time < 0.001.

Figure 4.

Changes in serum tryptophan (A), serum kynurenine (B), and kynurenine × 100/tryptophan ratio (KYN × 100/TRP, C) in steers receiving ergot alkaloids (E+) and 5-hydroxytryptophan (5-HTP). Data are means ± SEM for N = 8 steers/group. (A) E+ = 0.969, 5HTP = 0.002, E+*5HTP = 0.700, time = 0.014; (B) E+ = 0.009, 5HTP < 0.001, E+*5HTP = 0.155, time = 0.003; (C) E+ = 0.007, 5HTP = 0.002, E+*5HTP = 0.051, time = 0.012.

Figure 5.

Changes in plasma glucose (A) and plasma non-esterified fatty acids (NEFA, B) in steers receiving ergot alkaloids (E+) and 5-hydroxytryptophan (5-HTP). Data are means ± SEM for N = 8 steers/group. (A) E+ = 0.581, 5HTP = 0.790, E+*5HTP = 0.202, time = 0.004; (B) E+ = 0.609, 5HTP = 0.254, E+*5HTP = 0.202, time < 0.001.