Fish Meal Supplementation Alters Uterine Prostaglandin F2a Synthesis in Beef Heifers having Low Luteal Phase Progesterone

An experiment was conducted at Colorado State University to determine the effects of SeaLac® fish meal supplementation on uterine prostaglandin (PG) F2α synthesis in beef heifers having low luteal phase progesterone. Twenty-five Angus heifers were housed in individual pens and fed a corn silage-based diet (Table 1). Diets were supplemented with 5% fish meal (n = 12 heifers) or 6% corn gluten meal (n = 13 heifers) and formulated to contain the same level of energy and protein which met or exceeded NRC (1996) requirements for heifers. After 25 days on experimental diets, estrous cycles were synchronized using PGF2α (Lutalyse; Pharmacia and Upjohn Co., Kalamazoo, MI). Randomly selected heifers from each dietary supplement group were given 3 additional injections of PGF2α at 12 h intervals beginning on day 3 after estrus to induce formation of corpora luteal that secrete low luteal phase progesterone. Jugular blood samples were collected from day 1 through 16 of the estrous cycle to monitor blood progesterone. Each heifer was given 100 IU of oxytocin on day 16 of the estrous cycle to stimulate uterine PGF2α secretion. Jugular blood samples were collected before (-60, -30, -15 and 0 min time points; basal secretion) and after oxytocin administration (15, 30, 45, 60, 90, and 120 min time points; oxytocin-stimulated secretion) to determine concentrations of 13, 14, dihydro-15-keto PGF2α (PGFM; the stable metabolite of PGF2α).