Blood metabolite and regulatory hormone concentrations and response to metabolic challenges during the infusion of mimosine and 2,3-dihydroxypyridine in Alpine goats

A. Al-Dehneh, S. G. Pierzynowski, M. Smuts, T. Sahlu, and J. M. Fernandez

Sixteen Alpine wethers (average BW 35 ± kg) were used to evaluate the effect of continuous 48-h intravenous infusions of saline (CON), mimosine (MIM; 200 mg · kg^0.75·d^-1), 2-hydroxy-3(1H)-pyridine (2,3-DHP; 200 mg · kg^0.75·d^-1), or MIM + 2,3-DHP (100 mg of MIM plus 100 mg of 2,3-DHP · kg^0.75·d^-1) on hepatic function and selected blood metabolite and circulating hormone concentrations. Neither MIM nor 2,3-DHP affected plasma ammonia N, glucose, cortisol, or insulin concentrations over time (P > 0.10). Jugular plasma total protein concentration was greater in the MIM group (P < 0.07). Plasma triiodothyronine (P < 0.01) and thyroxine (P < 0.08) concentrations were higher in the goats receiving the MIM, 2,3-DHP, and MIM + 2,3-DHP infusions than in the goats receiving the CON infusion. Plasma urea N concentration was decreased by MIM (P < 0.10) and MIM + 2,3-DHP (P < 0.03) compared with the CON infusion. A Propionate Load Test was conducted at 24 to 28 h into the infusion to assess the toxins' effects on the liver's ability to increase circulating glucose concentrations in the presence of elevated propionate levels. The results indicated that neither 2,3-DHP nor MIM reduced the liver's ability to respond to a bolus dose of propionate (P > 0.10). Following a Urea Load Test, circulating ammonia N and glucose concentrations in the MIM, 2,3-DHP, and MIM + 2,3-DHP treatments had lower peak values than that in the CON treatment (P < 0.01). It is concluded that continuous short-term infusion of MIM and 2,3-DHP increased circulating thyroid hormone concentrations in goats and improved the goats' ability to detoxify a bolus dose of urea N without affecting its glucogenic capacity in response to elevated propionate levels.