Levodopa attenuates the feed intake reduction caused by ergot alkaloids in cattle

Authors: VALENTE, ERITON E. - Western Paraná State University; Klotz, James; MARKMANN, RYANA - Western Paraná State University; TROTTA, RONALD - University Of Kentucky; EDWARDS, JANICE - University Of Tennessee; MAY, JOHN - University Of Kentucky; HARMON, DAVID - University Of Kentucky

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/13/2024
Publication Date: 3/19/2024
Citation: Valente, E.L., Klotz, J.L., Markmann, R.C., Trotta, R.J., Edwards, J.L., May, J.B., Harmon, D.L. 2024. Levodopa attenuates the feed intake reduction caused by ergot alkaloids in cattle. Journal of Animal Science. 102. Article skae078. https://doi.org/10.1093/jas/skae078.
DOI: https://doi.org/10.1093/jas/skae078

Interpretive Summary: Dopamine plays important roles in many biological systems and those are involved with reward sensations and energy nutrition are of interest. This is of value in livestock where control of feed intake is desired. The role of dopamine in control of feed intake is very complex and not completely understood. The dopamine precursor compound L-DOPA can be used to increase dopamine synthesis, and has been shown to be effective at increasing dopamine in cattle. Ergot alkaloids are toxins that cause fescue toxicosis in grazing livestock. One of the symptoms of fescue toxicosis is decreased feed intake. The objective of this study was to see if giving L-DOPA to cattle with fescue toxicosis would raise dopamine levels and offset some of the negative symptoms like lower feed intake. L-DOPA given to cattle did raise blood dopamine levels and did not cause any negative effects. Further, the L-DOPA treatment moderately increased feed intake in cattle with fescue toxicosis. This research will be of interest to other researchers that study problems like fescue toxicosis in grazing animals and to producers interested in improving control of feed intake of their livestock.

Technical Abstract: Consumption of ergot alkaloids from endophyte-infected tall fescue results in losses to the livestock industry in many countries and means to mitigate these losses are needed. The objective of this study was to evaluate intra-abomasal infusion of the dopamine precursor, levodopa (L-DOPA), on dopamine metabolism, feed intake, and serum metabolites of steers exposed to ergot alkaloids. Twelve Holstein steers (344.9 ± 9.48 kg) fitted with ruminal cannulas were housed with a cycle of heat challenge during daytime (32 °C) and thermoneutral at night (25 °C). The steers received a basal diet of alfalfa cubes containing equal amounts of tall fescue seed composed of a mixture of endophyte-free (E') or endophyte-infected tall fescue seeds (E+) equivalent to 15 µg ergovaline/kg BW for 9-d followed by intra-abomasal infusion of water (L-DOPA') or levodopa (L-DOPA+; 2 mg/kg BW) for an additional 9-d. Afterward, the steers were pair-fed for 5-d to conduct a glucose tolerance test. The E' treatment decreased (P = 0.005) prolactin by approximately 50%. However, prolactin increased (P = 0.050) with L-DOPA'. Steers receiving E+ decreased (P < 0.001) DMI; however, when supplemented with L-DOPA+ the decrease in DMI was less severe (L-DOPA x E, P=0.003). Also, L-DOPA+ infusion increased eating duration (L-DOPA x E, P = 0.012) when steers were receiving E+.The number of meals, meal duration, and intake rate were not affected (P > 0.05) by E' or L-DOPA'. The L-DOPA+ infusion increased (P < 0.05) free L-DOPA, free dopamine, total L-DOPA, and total dopamine. Conversely, free epinephrine and free norepinephrine decreased (P < 0.05) with L-DOPA+. Total epinephrine and total norepinephrine were not affected (P > 0.05) by L-DOPA+. Ergot alkaloids did not affect (P > 0.05) circulating free or total L-DOPA, dopamine, or epinephrine. However, free and total norepinephrine decreased (P = 0.046) with E+. Glucose clearance rates at 15 to 30 min after glucose infusion increase with L-DOPA+ (P < 0.001), but not with E+ (P = 0.280). Administration of L-DOPA as agonist therapy to treat fescue toxicosis provided a moderate increase in DMI and eating time for cattle with E+ seed exposure and increased plasma glucose clearance.