|Kane, K - NEW MEXICO STATE UNIV|
|Hawkins, D - NEW MEXICO STATE UNIV|
|Pulsipher, G - NEW MEXICO STATE UNIV|
|Denniston, D - NEW MEXICO STATE UNIV|
|Krehbiel, C - NEW MEXICO STATE UNIV|
|Thomas, M - NEW MEXICO STATE UNIV|
|Petersen, M - NEW MEXICO STATE UNIV|
|Hallford, D - NEW MEXICO STATE UNIV|
|Remmenga, M - NEW MEXICO STATE UNIV|
|Keisler, D - UNIV MISSOURI-COLUMBIA|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 24, 2003
Publication Date: January 15, 2004
Citation: 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., KEISLER, D.H. EFFECT OF INCREASING LEVELS OF UNDEGRADABLE INTAKE PROTEIN ON METABOLIC AND ENDOCRINE FACTORS IN CYCLING BEEF HEIFERS. JOURNAL OF ANIMAL SCIENCE. 82:283-291. 2004. Interpretive Summary: Undegradable intake protein supplementation has been reported to enhance reproductive performance in beef females by minimizing BW changes, hastening the onset of puberty, decreasing postpartum anestrus, and increasing pregnancy rates in cattle consuming dormant forage. However, high levels of undegradable intake protein have also been associated with impaired fertility in both beef and dairy cattle. The regulatory role undegradable protein supplementation has on reproductive function in beef cattle remains unclear and further work is needed to establish the mechanisms involved in nutritional modulation of reproduction. Present research indicates that alterations in reproductive performance with undegradable intake protein supplementation in beef cattle may be associated with changes in anterior pituitary gland synthesis, storage, and secretion of gonadotropins and(or) ovarian follicular dynamics.
Technical Abstract: The influence of three levels of undegradable intake protein (UIP) supplementation on metabolic and endocrine factors that influence reproduction was evaluated in 23 yearling crossbred heifers stratified by BW (362 ± 12 kg) and randomly assigned to one of three supplements: 1) low UIP (1,135 g'heifer-1'd-1; 30% CP, 113 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'heifer-1'd-1; 46% CP, 321 g UIP, n = 8). Heifers were estrually synchronized prior to 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 harvested. 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 in serum insulin or IGF-I among treatments (P > 0.10). At slaughter (d 10 to 12 of the estrous cycle), treatments did not influence corpus luteum weight, cerebral spinal fluid leptin or IGFBPs, serum estradiol-17ß, progesterone, leptin, IGF-I, and IGFBPs, or anterior pituitary content of IGFBPs (P > 0.10). Follicular fluid IGFBP-2 and -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 were similar (P > 0.10) following 28 d of supplementation (d 10 of the estrous cycle), yet basal serum FSH concentrations were greater in low and mid vs. high UIP heifers (5.2 and 5.2 vs. 4.6 ng/mL, respectively; P = 0.06) and FSH area under the curve was greater in low vs. high UIP heifers (P = 0.03). 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 were similar among treatments (P > 0.10). However, FSHß mRNA was increased approximately two fold (P = 0.03) in mid vs. low UIP. In summary, mid level UIP supplementation increased FSHß mRNA compared to low level UIP supplementation. In contrast, circulating concentrations of FSH were greater in low and mid level UIP supplemented heifers than in high UIP heifers. In addition, supplementation of UIP at high levels was associated with increased follicular fluid IGFBP-2 and -4. However, at the levels and duration fed of this study, UIP supplementation did not alter other metabolic and endocrine factors known to influence reproduction.