041 Chronic Exposure to Ergot Alkaloids Suppresses Growth Hormone in Beef Steers

• Published in: Journal of animal science Vol. 95; no. suppl_1; p. 20
• Main Authors: Bostian, A. W., Lyons, S. E., Mackey, J. C., Pickworth, C. L., Poore, M. H., Poole, D. H.
• Format: Journal Article
• Language: English
• Published: Oxford University Press 01.12.2016
• Subjects: Growth hormone; Fescue toxocosis; beef steers
• ISSN: 0021-8812; 1525-3163
• DOI: 10.2527/ssasas2017.041

Abstract Tall fescue [Lolium arundinaceum (Schreb.) Darbysh] is the predominant grass that cattle graze throughout the southeastern United States. Due to its association with the fungus, Epichloë coenophiala, the grass becomes endophyte-infected and produces ergot alkaloids. Ergot alkaloid exposure causes a whole host of physiological problems in cattle including increased body temperature and heart rate, as well as decreased growth and blood flow to the extremities. Together, these symptoms are called fescue toxicosis and the exact pathway by which it occurs is not well understood. Crossbred Angus steers (n = 8) were placed in Calan gates and were randomly assigned to receive either endophyte-infected fescue seed (EI) or non-infected fescue seed (EF; control) for 60d. Weekly measurements and blood samples were taken to monitor the steer's physiological responses during exposure to ergot alkaloids. Data were analyzed using repeated measure in the MIXED procedure of SAS. Statistical significance was determined at P < 0.05 and a tendency at 0.05 < P < 0.10. Upon completion of the feeding period, animals were euthanized and tissue harvested to analyze impact on organ weight. Respiration rate, rectal temperature, surface temperature assessed by thermal camera, temperament, hair coat and shedding scores (1 to 5 scale) did not differ between treatment groups (P > 0.05). Systolic and diastolic blood pressure as well as caudal vein diameter were not different (P > 0.05). However, there was decreased heart rate (67.43 vs. 73.72 beats/min) and increased caudal artery diameter (35.58 vs. 34.38 mm2) in EI animals compared to EF (P < 0.05). Body weight and average daily gain (BW 425.8 vs 409.5 kg; ADG 0.99 vs 1.14 kg/d) tended to increase in the EF group compared to EI (P = 0.09). Body condition score tended to be greater in the EF group compared to EI (5.46 vs, 5.39; P = 0.07). Hematocrit was not different between treatment groups (P > 0.05). Heart, liver, spleen, kidney and pancreas weights did not differ between treatment groups (P > 0.05). Circulating luteinizing hormone (LH) concentrations were no different between treatment groups (P > 0.05) during chronic exposure to ergot alkaloids whereas, circulating growth hormone (GH) concentrations were reduced in the EI 1.3 ng/ml) group when compared to the EF controls (7.2 ng/ml; P < 0.05). Growth hormone could play an important role in the reduced weight gain that is seen in animals that are chronically exposed to ergot alkaloids. Determining exactly how ergot alkaloids are functioning along the hypothalamic-pituitary axis to alter GH production could help to further elucidate the mechanisms that leads to losses associated with fescue toxicosis.