Title page for ETD etd-12232009-020514
|Type of Document
||Genetic variation of susceptibility to fescue toxicosis in cattle
||Master of Science
|Hohenboken, William D.
|McGilliard, Michael L.
|Sponenberg, Daniel Phillip
- Toxicological interactions.
|Date of Defense
Fifteen calves of two sires were fed endophyte infected (E + ) fescue seed to quantify differences in
susceptibility to fescue toxicosis among sire groups. One of the sires, a Polled Hereford, had a
commercial reputation of producing calves with less severe symptoms of tall fescue toxicosis than
their contemporaries. The control sire, also a Polled Hereford, had unknown merit with regard to
offspring susceptibility to fescue toxicosis. The study was divided into five phases, two in which
endophyte-infected fescue seed was included in the diet (phases two and four) and three in which
fescue seed was not in the diet (phases one, three, and five). All calves were treated similarly and
given the same opportunities for water, shade and socialization. Susceptibility to fescue toxicosis
was measured by appetite (amount of feed consumed per day per unit of metabolic body weight),
serum prolactin, cholesterol, and alkaline phosphatase concentrations, ability to maintain
homeotherny (afternoon minus morning rectal temperature), ability to dissipate core body heat
(afternoon minus morning surface temperature), and heat-transfer inefficiency (afternoon rectal
minus afternoon surface temperatures). Appetite was decreased by the E + fescue seed, but the sire
groups did not differ in their response to or recovery from E + fescue seed. The E + fescue seed
caused prolactin to decrease (P < .0001) but the sire groups did not differ in their responses to addition
or withdrawal of E + fescue seed from the diet. Cholesterol levels were lower overall
(P < .001) when the E+ fescue seed was fed, and the sire groups recovered from the fescue toxicity
at different rates (P < .001). Alkaline phosphatase concentrations were lower during the phases
when E + fescue seed was fed; calves from the control sire were less resistant to the E + fescue seed
effects than the Missouri calves (P < .0001). Ability to maintain homeothermy was reduced by the
E + fescue seed, but the reduction did not differ between sire groups. Surface temperature changes
and heat-transfer inefficiencies were not indicative of fescue toxicosis in this study. It was concluded
that serum cholesterol and serum alkaline phosphatase concentrations may be accurate indicators
of differences among paternal half sib groups of cattle in susceptibility to fescue toxicosis.
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