Effects of feeding diets containing endophyte-infected fescue seed on luteinizing hormone secretion in postpartum beef cows and in cyclic heifers and cows

Abstract

Two experiments were conducted to investigate the effect of feeding endophyte (Acremonium coenophialum)-infected fescue (Festuca arundinacea Shreb.) seed on LH secretion in postpartum beef cows and in cycling heifers and cows. In Exp. 1, spring-calving primiparous Angus cows (n = 16) were pair-fed for 75 d diets that contained endophyte-free or endophyte-infected (95%) fescue seed that contained 1.3 micrograms/g of ergovaline and 5.2 mg/g of saturated pyrrolizidines. Serial blood samples for basal and GnRH-stimulated serum LH analysis were obtained on d 7, 28, 42, and 56 of the study. The endophyte had no effect on LH secretion (basal, pulse frequency, and amplitude) or milk production. Average daily gain was decreased (P < .05) in cows that consumed infected fescue seed compared with controls (-.20 vs -.01 kg, respectively). Basal serum prolactin concentrations were reduced (P < .01) in treated compared with control cows (8.9 vs 25.4 ng/mL, respectively) on d 70. In Exp. 2, cycling Angus heifers (n = 8; age = 2 yr) and cows (n = 8; age = 4 yr) stratified by age were pair-fed for 40 d diets that contained the noninfected or the highly infected fescue seed. Estrus was synchronized by prostaglandin F2 alpha (d 18 and 28). Serial blood samples for serum LH analysis were obtained on d 28 (luteal phase) and d 30 (follicular phase). The endophyte did not affect LH (P > .28) or prolactin (P > .16) secretion, whereas ADG was decreased (P < .05) in treated compared with control animals (.32 vs .70 kg/d, respectively).

Reproductive characteristics of endophyte-infected or novel tall fescue fed ewes

“…A dual role of LH and prolactin has been suggested for CL maintenance both during the cycle and in early pregnancy (Tabarelli et al, 1982;Kann and Denamur, 1974). However, changes in luteinizing hormone were not observed in EI-fed heifers (Mizinga et al, 1992) or ewes administered an ergopeptide (Louw et al, 1974). The relevance of decreased prolactin in EI-fed animals has never been clearly demonstrated.…”

BOARD-INVITED REVIEW: St. Anthony's Fire in livestock: Causes, mechanisms, and potential solutions1,2

“…Preliminary work suggested both LH and FSH were diminished in 3-mo-old heifers when fed ergot alkaloid-contaminated hay (McKenzie and Erickson, 1991). However, changes in LH were not observed in ewes administered ergocornine hydrogen maléate subcutaneously (Louw et al, 1974) or in heifers fed endophyte-infected tall fescue seed diets for 75 d (Mizinga et al, 1992). In a series of intravenous ergot alkaloid-challenge studies.…”

Increased responsiveness to intravenous lipopolysaccharide challenge in steers grazing endophyte-infected tall fescue compared with steers grazing endophyte-free tall fescue

“…Prolactin Serum concentrations of PRL were determined by RIA procedures as in Mizinga et al (1992) with reagents supplied by the USDA Hormone Distribution Program (Beltsville, MD, USA). The intra-and interassay coefficients of variation (C.V.) were 3·7% and 7·3% respectively.…”