Use of different levels of ground endophyte-infected tall fescue seed during heat stress to separate characteristics of fescue toxicosis1

Abstract

Studies of fescue toxicosis using whole seed diets show reduced feed intake and thermoregulatory ability, but much of the seed passes undigested through the animal. Cattle were fed ground tall fescue seed at different levels to potentially facilitate digestion and absorption of toxins and identify toxin sensitivity for major characteristics of the condition [i.e., hyperthermia, reduced feed intake (FI), reduced blood prolactin]. Steers (n = 18; 350 kg BW) were housed in the Brody Climatology Laboratory at thermoneutrality (TN; 19°C) and randomly assigned to daily diet treatments with either ground endophyte-infected [E+; low and high doses at 20 and 40 μg ergovaline/(kg BW/d), respectively] or endophyte-free [E-; control at 0 μg ergovaline/(kg BW/d)] tall fescue seed. After 12 d at TN, animals received 2 d of transition to heat stress (HS; 36°C daytime, 25°C nighttime) and maintained for 14 more days. Cattle were fed twice daily at 0800 and 1600 h, with water ad libitum. Feed intake was measured at 0700 h, with skin and rectal temperatures, and respiration rate at 0600, 1100, 1600, and 2100 h. Blood was sampled on selected days for prolactin and leptin determinations. Steers fed ground E+ diet decreased (P ≤ 0.0001) FI below controls at TN, with no dose effect. Maximum FI reduction with E+ treatment was 25% at TN, with an additional 46% decrease during HS (P ≤ 0.05). By the end of HS, E+ FI increased (P > 0.05) to that of E-, suggesting recovery. Prolactin was reduced (P ≤ 0.05) in high E+ cattle below controls at study end. Leptin blood concentrations were unaffected by E+ treatment (P > 0.05) but was reduced (P ≤ 0.05) by the end of HS. Pattern of rectal temperature response to HS showed a more rapid initial increase and decline for both E+ groups compared with controls (P ≤ 0.05). Skin temperature was the only variable that identified E+ dose differences. Although there were no treatment differences at TN, skin temperature was lower (P ≤ 0.05) for high E+ steers compared with controls during HS when air temperature was reduced each day. In general, FI was more responsive to E+ toxins than body temperature or blood prolactin, declining even at TN and exhibiting dynamic activity during HS. Although body temperature response to E+ toxins appears to stabilize during HS, this is misleading as rapid change in air temperature exposes effects on skin temperature.

Interactions between animal temperament and exposure to endophytic tall fescue: Effects on cell-mediated and humoral immunity in beef heifers

“…This allowed for equalization of dry matter intake among treatments. As mentioned previously, decreased intakes are commonly associated with cattle consuming E+ feedstuffs (Schmidt et al, 1982;Paterson et al, 1995;Spiers et al, 2012). Increased titer responses to vaccination against horse red blood cell and keyhole limpet haemocyanin have been reported in calves fed on a lower plane of nutrition (Pollock et al, 1994).…”

“…At the start of P2, ambient temperatures were set to cycle between 33.3°C during the day and 22.2°C at night. This was to simulate average temperature fluctuations experienced by cattle in Kentucky during July and August, when effects of fescue toxicosis are at their most severe (Hemken et al, 1981) and has been previously shown to be sufficient for inducing signs of fescue toxicosis in cattle during periods of tall fescue seed consumption (Spiers et al, 2012). Temperature humidity index (THI) was calculated as described by Hahn (1999): Increased THI conditions continued through P3, when heifers were provided their respective endophyte seed treatments.…”

“…However, alkaloid compounds produced by this fungus are detrimental to grazing animals, resulting in decreased gains and overall poor performance (Stuedemann and Hoveland, 1988). The negative effects of the fungal alkaloids are compounded during times of heat stress (Spiers et al, 2012).…”