Abstract
Objective was to examine the activity of cytochrome P450 (CYP), a liver enzyme that metabolizes ergot alkaloids which is hindered by this fescue toxin, as an indicator of fescue toxicosis in sheep. In spring and fall, ewes were blocked by age and BW, and randomly assigned to 1 kg/ewe/d of endophyte-infected (E+; 61% of diet in fall, 13% of diet in spring; 0.8 µg/g of ergovaline; and soy hulls, alfalfa pellets, cottonseed hulls, molasses) or non-infected (E-; same proportion of E+/season and same feeds) tall fescue seed supplement (n = 10/diet in each season) for 28 d, plus hay, mineral and water. Ewes were exposed to teaser, d -21 to 0, and intact rams, d 0 (first day of diet) to 30. Rectal temperature (RT), serum concentration of prolactin (using RIA), and CYP were determined every 7–14 d between d 0–28, and pregnancy status on d 56. PromegaTM P450-Glo assay was used to determine CYP from serum. Data were analyzed by using PROC MIXED with repeated measures (SAS). Rectal temperature of E+ compared with E- ewes was elevated on at least one day in fall and spring (diet × season × d, P < 0.001). Serum prolactin was lower in E+ compared with E- ewes (diet × d, P < 0.001) and lower in fall (P < 0.001). CYP was higher in E- ewes on d 28 in fall (diet × season × d, P = 0.008), but otherwise similar between diets, and higher in fall than spring (P < 0.001). There was an unexpected negative correlation between CYP and prolactin (R = -0.24; P < 0.009), but there appears to be a subpopulation of ewes with low prolactin and lower CYP. CYP activity in sera may not be a marker for fescue toxicosis in ewes.
111 Metsulfuron and variable nitrogen application rates on infected tall fescue: effects on stocker performance, forage yield, nutritive value, ergovaline concentration and botanical composition
