Caloric Restriction/veterinary; Horses/physiology; Insulin-Like Growth Factor Binding Protein 3/metabolism; Insulin-Like Growth Factor II/metabolism; Insulin-Like Growth Factor I/metabolism; Ovarian Follicle/growth & development; Signal Transduction; Animals; Blood Glucose/analysis; Caloric Restriction/adverse effects; Female; Follicular Fluid/chemistry; France; Glucose/analysis; Gonadotropins, Equine/analysis; Gonadotropins, Equine/blood; Gonadotropins, Equine/metabolism; Growth Hormone/analysis; Growth Hormone/blood; Growth Hormone/metabolism; Horses/blood; Horses/growth & development; Insulin-Like Growth Factor Binding Protein 3/analysis; Insulin-Like Growth Factor Binding Protein 3/blood; Insulin-Like Growth Factor Binding Proteins/analysis; Insulin-Like Growth Factor Binding Proteins/blood; Insulin-Like Growth Factor Binding Proteins/metabolism; Insulin-Like Growth Factor I/analysis; Insulin-Like Growth Factor II/analysis; Insulins/analysis; Insulins/blood; Insulins/metabolism; Ovarian Follicle/diagnostic imaging; Ovarian Follicle/metabolism; Proestrus; Progesterone/analysis; Progesterone/blood; Progesterone/metabolism; Ultrasonography