Effect of increasing levels of undegradable intake protein on metabolic and endocrine factors in estrous cycling beef heifers

• Published in: Journal of animal science Vol. 82; no. 1; pp. 283 - 291
• Main Authors: Kane, K.K, Hawkins, D.E, Pulsipher, G.D, Denniston, D.J, Krehbiel, C.R, Thomas, M.G, Petersen, M.K, Hallford, D.M, Remmenga, M.D, Roberts, A.J
• Format: Journal Article
• Language: English
• Published: Savoy, IL Am Soc Animal Sci 2004; American Society of Animal Science
• Subjects: Animal Nutritional Physiological Phenomena; Animal productions; Animals; binding proteins; Biological and medical sciences; Cattle - physiology; dietary protein; Dietary Proteins - administration & dosage; Dietary Proteins - metabolism; Dose-Response Relationship, Drug; Estrus - physiology; Female; Follicle Stimulating Hormone - blood; Follicle Stimulating Hormone - genetics; follicle-stimulating hormone; Food industries; Fundamental and applied biological sciences. Psychology; Insulin-Like Growth Factor Binding Proteins - metabolism; insulin-like growth factor I; luteinizing hormone; Luteinizing Hormone - blood; Luteinizing Hormone - genetics; Meat and meat product industries; protein supplements; Random Allocation; Reproduction - physiology; RNA, Messenger - metabolism; Terrestrial animal productions; Vertebrates; Bovine; Animal feeding; Meat product; Ox; Metabolism; Beef Heifers; Insulin; Protein; Vertebrata; Insulin like growth factor; Mammalia; Undegradable Intake Protein; Follicle-Stimulating Hormone; Luteinizing hormone; Heifer; Artiodactyla; Beef; Ungulata; Insulin-Like Growth Factor-I; Follicle stimulating hormone
• ISSN: 0021-8812; 1525-3163
• DOI: 10.2527/2004.821283x

To determine the influence of three levels of undegradable intake protein (UIP) supplementation on metabolic and endocrine factors that influence reproduction, 23 yearling crossbred heifers (body condition score = 4.5 ± 0.5; initial BW = 362 ± 12 kg) were stratified by BW and assigned randomly to one of three supplements: 1) low UIP (1,135 g·heifer-1·d-1; 30% CP, 115 g UIP, n = 7); 2) mid UIP (1,135 g·heifer-1·d-1; 38% CP, 216 g UIP, n = 8); or 3) high UIP (1,135 g[round bullet, filled]heifer-1·d-1; 46% CP, 321 g UIP, n = 8). Heifers were estrually synchronized before initiation of supplementation. Supplement was individually fed daily for 30 to 32 d, at which time heifers were slaughtered (d 12 to 14 of the estrous cycle) and tissues collected. Heifers were fed a basal diet of sudan grass hay (6.0% CP) ad libitum. On d 28 of supplementation (d 10 of the estrous cycle), no differences were observed (P > 0.10) in serum insulin or IGF-I among treatments. At slaughter (d 10 to 12 of the estrous cycle), treatments did not influence corpus luteum weight, cerebral spinal fluid leptin, or IGFBP; serum estradiol-17β, progesterone, leptin, IGF-I, and IGFBP; or anterior pituitary content of IGFBP (P > 0.10). Follicular fluid IGFBP-2 and IGFBP-4 were greater in high-UIP heifers than low- or mid-UIP heifers on d 12 to 14 of the estrous cycle (P < 0.05). Basal serum LH concentrations and LH area under the curve (every 15 min for 240 min) did not differ (P > 0.10) following 28 d of supplementation (d 10 of the estrous cycle); however, basal serum FSH concentrations were greater (P = 0.06) in low- and mid- vs. high-UIP heifers (5.2 and 5.2 vs. 4.6 ng/mL, respectively), and FSH area under the curve was greater (P = 0.03) in low- vs. high-UIP heifers. At slaughter (d 12 to 14 of the estrous cycle), anterior pituitary LH and FSH content and steady-state mRNA encoding , LHss, and GnRH receptor did not differ (P > 0.10) among treatments. However, FSHβ mRNA was increased approximately twofold (P = 0.03) in mid vs. low UIP. In summary, low and mid levels of UIP supplements fed to estrous cycling beef heifers seemed to enhance pituitary expression and/or secretion of FSH relative to high levels of UIP. Moreover, high-UIP supplementation was associated with increased low-molecular-weight IGFBP compared with supplementation of low and mid levels of UIP. These data suggest that differing levels of UIP supplementation may alter pituitary and ovarian function, thereby influencing reproductive performance in beef heifers.