DIETARY FATS VARYING IN THEIR FATTY-ACID COMPOSITION DIFFERENTIALLY INFLUENCE FOLLICULAR-GROWTH IN COWS FED ISOENERGETIC DIETS

The working hypothesis was that dietary fats differing in fatty acid c omposition would differentially influence ovarian follicular growth. C ows (n = 27) were fed isoenergetic, isonitrogenous, and isofibrous die ts 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. Coin cident changes in serum lipid metabolites, insulin, and GH and the con centration of IGF-I in large and medium-sized follicles also were exam ined. 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 maximiz ed (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 concen trations of total cholesterol(P < .05), GH (P < .05), and follicular f luid IGF-I in large follicles (P < .065) compared to CT but differenti ally influenced serum concentrations of insulin. Polyunsaturated fat s timulated a marked increase (P < .001) in serum insulin relative to co ntrols within 3 wk, whereas SAT and HPU increased (P < .05) serum insu lin only after 6 to 7 wk. We conclude that consumption of PU fatty aci ds stimulates a greater rate of ovarian follicular growth in cattle co mpared to CT, AT, and HPU. Future research should investigate the pote ntial role of insulin in mediating PU effects on follicular growth.