title: Insulin-like growth factor I in growing thoroughbreds.
abstract: The objective of this longitudinal study was to characterize growth and plasma insulin-like growth factor I (IGF-I) concentrations in pasture-raised thoroughbreds fed two sources of dietary energy. Mares and foals were randomly assigned to either a sugar and starch (SS) or fat and fibre (FF)-rich feed, and plasma IGF-I and growth were measured once a month from 1 to 16 months of age. These dependent variables were also compared with day length and ambient temperature. There was an association between plasma IGF-I concentration and average daily gain (ADG) (r = 0.32, p < 0.001). There were also clear seasonal patterns in both ADG and plasma IGF-I, with high values in June and May, and a low value in March. Plasma IGF-I and ADG were positively associated with day length and temperature. Plasma IGF-I was never higher (p > 0.10) in the FF group when compared with the SS group, and was higher in the SS group during a rapid growth phase in the spring of year 2 (p < 0.10). The results establish an association between ADG and IGF-I in the horse and indicate that environment and age may influence this relationship. In addition, plasma IGF-I is influenced by dietary energy source at particular times of year. This link has important implications in designing feeding management strategies that are aimed at addressing skeletal development.
authors.affiliation: Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA. wstaniar@vt.edu
authors.forename: W B
authors.initials: WB
authors.lastname: Staniar
authors.forename: D S
authors.initials: DS
authors.lastname: Kronfeld
authors.forename: R M
authors.initials: RM
authors.lastname: Akers
authors.forename: P A
authors.initials: PA
authors.lastname: Harris
mesh_terms: D000375:Aging / Q000097:blood; D000704:Analysis of Variance; D000821:Animal Feed; D000824:Animal Nutritional Physiological Phenomena / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn; D004041:Dietary Fats / Q000008:administration & dosage / Q000378:metabolism; D004043:Dietary Fiber / Q000008:administration & dosage / Q000378:metabolism; D019422:Dietary Sucrose / Q000008:administration & dosage / Q000378:metabolism; D005260:Female; D006736:Horses / Q000097:blood* / Q000254:growth & development*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008137:Longitudinal Studies; D009752:Nutritional Status; D011863:Radioimmunoassay / Q000379:methods / Q000662:veterinary; D012621:Seasons; D013213:Starch / Q000008:administration & dosage / Q000378:metabolism; D013696:Temperature; D015430:Weight Gain
chemical_list: D004041:Dietary Fats; D004043:Dietary Fiber; D019422:Dietary Sucrose; D007334:Insulin-Like Growth Factor I; D013213:Starch