Influence of insulin and energy intake on ovulation rate, luteinizing hormone and progesterone in beef heifers.
Ovarian and gonadotropin responses to insulin and energy restriction were investigated in a 2 X 2 factorial experiment using 2-yr-old Brangus heifers. Thirty heifers were paired by weight and body condition, then assigned to treatment groups receiving 75 (LE) or 180% (HE) of NRC recommendations for dietary energy for maintenance. Diets were adjusted weekly to maintain daily .25 to .5 kg weight loss or 0 to .25 kg weight gain, respectively. On d 10 of the first estrous cycle subsequent to the initial 45 d of feeding, heifers within each dietary group were allocated to receive twice daily infusions of either 40 U insulin (I) or saline (C). Infusions began at 5 and 10 h postprandial and were given in six boluses, 20 min apart. Infusions continued daily until d 20 or estrus, whichever occurred first. On d 11, blood samples were collected at 15-min intervals for 12 h to determine luteinizing hormone (LH) and insulin concentrations. On d 16 to 20, twice daily im injections of 1 mg follicle stimulating hormone (FSH) were administered. Heifers were ovariectomized on d 11 after estrus. Number of corpora lutea (CL) in LE-I heifers was greater (P less than .05) in LE-C, HE-C or HE-I. Total CL weight (g) per heifer was greater (P less than .05) in HE-C and LE-I heifers than in LE-C. Individual CL wt was heavier in HE than in LE heifers (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)
D000818:Animals; D002417:Cattle / Q000502:physiology*; D002149:Energy Intake; D004734:Energy Metabolism; D004971:Estrus; D005260:Female; D005640:Follicle Stimulating Hormone / Q000494:pharmacology; D007328:Insulin / Q000502:physiology*; D007986:Luteinizing Hormone / Q000097:blood*; D010053:Ovary / Q000502:physiology; D010060:Ovulation; D010507:Periodicity; D010902:Pituitary Gland / Q000502:physiology; D011374:Progesterone / Q000097:blood*
D007328:Insulin; D011374:Progesterone; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone