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Senepol Show Resilience on
Endophyte-Infected Tall Fescue
Richard Browning, Jr.
Cooperative
Agricultural Research Program
Seminar Series
Tennessee State University, Nashville, TN
October 2, 2002
Growth
rates are known to be reduced in cattle when grazing tall fescue (Festuca
arundinacea Schreb.) infected with a fungal endophyte (Neotyphodium
coenophialum). Cattle also exhibit signs of exaggerated heat stress
when consuming this grass. Hyperthermia may contribute to poor cattle
growth rates recorded on endophyte-infected tall fescue diets. Research
was conducted to determine how heat tolerant cattle would respond to an
endophyte-infected tall fescue diet. Heat-sensitive Hereford and
heat-tolerant Senepol steers (Bos taurus) were fed tall fescue or
orchardgrass (Dactylis glomerata L.) in two studies over three
summers (2000, 2001 and 2002) to assess breed differences in growth and
thermoregulatory responses to the endophytic forage. Data in 2000 and
2001 were from 30 Hereford and 28 Senepol steers, whereas data in 2002
were from 14 Hereford and 14 Senepol steers. Chemical analysis of the
forages fed during the project indicated that energy and protein content
of the experimental diets were similar. In 2000, tall fescue increased
(P < 0.01) respiration rates and daytime shade use in Hereford and
Senepol steers compared to orchardgrass-fed contemporaries and tended to
increase skin temperatures (P = 0.09). In 2001, tall fescue did not
alter respiration rates, shade use or skin temperatures in either breed.
In 2002, tall fescue tended to increase (P < 0.1) skin temperatures in
both breeds. Tall fescue reduced (P < 0.01) growth rates of Hereford
steers by 50, 82 and 240% in 2000, 2001 and 2002, respectively, compared
to Hereford contemporaries on orchardgrass. Hereford steers on tall
fescue lost more weight than the Herefords on orchardgrass gained during
the 8-wk study period in 2002. Variation in growth rates between Senepol
steers fed tall fescue or orchardgrass were not statistically
significant in either year. Numerically, mean growth rates for Senepol
on tall fescue were 4, 2, and 52% lower in 2000, 2001 and 2002,
respectively, compared to cohorts fed orchardgrass. Senepol and Hereford
steers responded to the experimental diets similarly in terms of
thermoregulatory traits. However, the Senepol exhibited an ability to
gain weight in spite of the endophyte challenge. The use of
heat-tolerant breeds such as Senepol may be beneficial in tall
fescue-based cattle production systems to reduce economic resulting from
fescue toxicosis.
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