Dietary fats varying in their fatty acid composition differentially influence follicular growth in cows fed isoenergetic diets.
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The working hypothesis was that dietary fats differing in fatty acid composition would differentially influence ovarian follicular growth. Cows (n = 27) were fed isoenergetic, isonitrogenous, and isofibrous diets containing no added fat (control; CT, n = 7) or diets supplemented with fats containing primarily saturated (SAT, n = 7), polyunsaturated (PU, n = 7), or highly polyunsaturated (HPU, n = 6) fatty acids. Coincident changes in serum lipid metabolites, insulin, and GH and the concentration of IGF-I in large and medium-sized follicles also were examined. Body weights and body condition scores remained similar for all groups throughout the study. Polyunsaturated fat increased (diet x day, P = .06) the number of medium-sized follicles on d 5 through 9 of a synchronized estrous cycle within 3 wk of onset of feeding and maximized (P < .001) this to a fourfold difference at ovariectomy after 7 wk. Fats with predominantly SAT and HPU tended (P < .10) to produce these effects after 7 wk. All fat-supplemented diets increased serum concentrations of total cholesterol (P < .05), GH (P < .05), and follicular fluid IGF-I in large follicles (P < .065) compared to CT but differentially influenced serum concentrations of insulin. Polyunsaturated fat stimulated a marked increase (P < .001) in serum insulin relative to controls within 3 wk, whereas SAT and HPU increased (P < .05) serum insulin only after 6 to 7 wk. We conclude that consumption of PU fatty acids stimulates a greater rate of ovarian follicular growth in cattle compared to CT, AT, and HPU. Future research should investigate the potential role of insulin in mediating PU effects on follicular growth.