|Bishop, Cecily - OREGON STATE UNIV|
|Stormshak, Fredrick - OREGON STATE UNIV|
Submitted to: Trade Journal Publication
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 13, 2006
Publication Date: June 8, 2006
Citation: Burke, J.M., Bishop, C., Stormshak, F. 2006. Reproductive characteristics of endophyte-infected or novel tall fescue fed ewes. Livestock Science. 104:103-111. Interpretive Summary: Pregnancy rates are often reduced in female ruminants grazing endophyte-infected tall fescue and costs the beef industry millions of dollars annually. Changes in reproductive function that lead to decreased pregnancy rate are unclear and cost-effective supplements to increase pregnancy rates have not been found. The current study determined that there was a decrease in oxytocin-induced prostaglandin F2alpha, which indicates a change in uterine function, and an asynchrony in reproductive tissue function, but supplementary fish meal did not alleviate these problems. These results provide an insight into mechanisms for reproductive failure in females grazing endophyte-infected tall fescue, information that is important to producers, extension agents, and scientists.
Technical Abstract: Reduced pregnancy rates often occur in ruminants grazing endophyte-infected (EI) tall fescue. The objectives were to characterize basal and oxytocin-induced PGF2' concentrations in serum and reproductive function in ewes fed tall fescue and to determine whether addition of fish meal (FM) to a diet of EI fescue would alter PGF2' production. In Experiment (Exp) 1, ewes were fed an EF or EI seed diet (50%) for 30 d and in Exp 2, ewes were fed a diet with NE or EI seed containing either corn gluten mean (CG) or FM. Serum concentrations of prolactin, a measure of severity of fescue toxins, were reduced in ewes fed EI compared with EF forage seed or NE and were greater in NEFM than NECG-fed ewes. Size and number of CL, determined by trans-rectal ultrasonography, were similar between diets. Serum concentrations of progesterone were reduced in ewes fed EI compared with EF seed or EI compared with NE-fed ewes with two CL. Follicle numbers changed, but not consistently between Exp 1 and 2. Oxytocin-induced PGFM concentrations during the luteal phase were determined as a measure of uterine function. On the day of oxytocin administration, in Exp 1, EF-fed ewes did not appear to respond, but peak PGFM was reached at 20 min in EI-fed ewes. In Exp 2, peak plasma concentrations of PGFM were reduced in EI compared with NE-fed ewes. Estrous cycle length was more variable in EI than NE-fed ewes in Exp 2. Luteal function and follicle dynamics were altered by consumption of EI compared with EF or NE tall fescue seed. There appears to be hormonal asynchrony between EF/NE and EI fed ewes leading to changes in uterine responsiveness to oxytocin. Inclusion of FM did not alter uterine responsiveness to oxytocin.