Effect of pituitary somatotropin injections on plasma insulin-like growth factor I and somatotropin profiles in growing heifers

Effects of daily injections of pituitary-derived bovine somatotropin (bST) for 6 wk were evaluated in 10 growing heifers and compared to 9 placebo-treated control animals. Bovine somatotropin was injected at 50 micrograms/kg BW each day. Body weight and growth, plasma concentrations of insulin-like growth factor I (IGF-I) and somatotropin (ST) were assessed. To measure plasma concentrations of IGF-I, we validated a RIA in which bovine plasma samples were extracted with acid-ethanol, a method that resulted in greater than 90% recovery of IGF-I. Average daily gain was similar during the first 4 wk of the experiment in both control and bST-treated groups; however, at the end of the experimental period (wk 4 and 6) ADG was greater (P less than .05) in bST-treated heifers (1.24 +/- .21 kg/d vs .75 +/- .25 kg/d). Plasma IGF-I from wk 2 to wk 6 were increased in bST-treated animals (452 +/- 97 ng/ml at wk 2; 683 +/- 106 ng/ml at wk 6) compared with controls (293 +/- 62 ng/ml at wk 2 (P less than .01) and 293 +/- 115 ng/ml at wk 6 (P less than .001). Moreover, ADG over the 6-wk experimental period was correlated with mean IGF-I concentrations determined over the same period (r = .55; P less than .01). As expected, mean plasma ST concentrations were increased in bST-injected animals from wk 1 to 6. Gel chromatographic profiles of bovine plasma exhibit a 150,000 molecular weight ST-dependent binding protein-IGF-I complex and a 30,000 molecular weight non-ST-dependent complex. This study validates a method for measuring IGF-I in cattle, and shows a positive relationship among IGF-I and ADG after ST treatment. No correlation, however, was found between plasma ST and growth performance.     

Preliminary results on between and within twin set variation in insulin-like growth factor I (IGF-1) and some relationships with performance traits in identical twin heifers

Blood samples were collected from eight sets of Simmental crossbred identical twin heifers at 291. 328, 254, 656 and 684 days of age and were assayed for serum concentrations of insulin-like growth factor 1 (IGF-1). The between twin set intraclass correlation for IGF-1 at these ages was −0.08±0.38, 0.25±0.35, 0.62±0.23, 0.68±0.21 and 0.54±0.27, respectively. Residual correlations of serum IGF-1 concentrations with weights taken at the same ages ranged from 0.29 (P > 0.10) to 0.74 (P < 0.01). Heifers with higher serum IGF-1 concentrations at 291, 354, 656 and 684 days of age tended to be taller at 291 and 656 days of age with correlations ranging from 0.25 (P > 0.10) to 0.61 (P < 0.05). Correlations of IGF-1 with weight gains were variable in sign and generally nonsignificant. Results indicate that serum concentrations of IGF-1 are positively related to body weight and hip height of beef heifers.     

The influence of level of feeding on growth and serum insulin-like growth factor I and insulin-like growth factor-binding proteins in growing beef cattle supplemented with somatotropin

The objective of this study was to determine the effects of level of feeding on growth, feed efficiency (gain:feed; G:F), body composition (BC), and serum concentrations of somatotropin (ST), IGF-I, and IGF-binding proteins (BP) in growing beef cattle supplemented with bovine (b) ST. In each of two consecutive years, 40 growing beef cattle were blocked by weight (average BW: yr 1 = 316 kg, yr 2 = 305 kg) and used in a 2 x 2 factorial arrangement with main effects of bST (0 or 33 microg x kg BW(-1) x d(-1)) and level of feed intake (ad libitum [AL] or 0.75 AL). Relative to uninjected cattle, treatment with bST increased ADG 9.6% (1.14 vs 1.25 kg/d; P < 0.05) and increased G:F 8.1% (12.3 vs 13.3 gain [g]:feed [kg]; P < 0.05), whereas ADG in AL animals was 39% greater than that in 0.75 AL animals (1.39 vs 1.00 kg/d; P < 0.05). There was a tendency (P = 0.10) for a bST x level of feeding interaction, such that the increase in ADG with bST was greater in AL cattle than in 0.75 AL cattle (10.6 vs 7.8%; P = 0.10). Serum concentrations of ST were greater in 0.75 AL cattle than in AL cattle (13.0 vs 8.6 ng/mL; P < 0.05) and in bST-treated cattle than in uninjected cattle (16.3 vs 5.2 ng/mL; P < 0.05). Due to a bST x level of feeding interaction (P < 0.01), the magnitude of the increase in serum ST to exogenous bST was greater (P < 0.01) in 0.75 AL cattle than in AL cattle. Relative to uninjected cattle, treatment with bST increased (P < 0.05) serum concentrations of IGF-I and IGFBP-3 and reduced (P < 0.05) concentrations of IGFBP-2. Similarly, AL cattle had greater (P < 0.05) serum concentrations of IGF-I and IGFBP-3 and reduced (P < 0.05) IGFBP-2 compared with 0.75 AL cattle. In summary, treatment with bST increased growth rate and G:F and stimulated serum IGF-I and IGFBP-3 while reducing IGFBP-2. Feeding at 0.75 ad libitum intake reduced the magnitude of response for each of these variables. Thus, limit-feeding may reduce the effect of exogenous bST on growth rate by blunting bST-induced increases in IGF-I and IGFBP-3 and bST-induced decreases in IGFBP-2.     

Effect of prepartum administration of growth hormone-releasing factor on somatotropin, insulin-like growth factor I, milk production, and postpartum return to ovarian activity in primiparous beef heifers.

Forty-one primiparous beef heifers were used over 2 yr to evaluate the effect of prepartum administration of a growth hormone-releasing factor analog (GRF-A) or growth hormone-releasing factor (GRF(1-29)-NH2) on somatotropin (ST), insulin-like growth factor I (IGF-I), milk production, heifer BW, and postpartum (PP) return to ovarian activity. Beginning on d -11 +/- 1 from parturition, heifers were administered (s.c.) GRF-A ([desNH2-Tyr1,D-Ala2,Ala15]GRF(1-29)-NH2, 2.5 micrograms/kg; Yr 1) or GRF(1-29)-NH2 (12.5 micrograms/kg; Yr 2) (GRF; n = 17) or vehicle (CON; n = 24) for seven consecutive days. Blood samples were collected at 20-min intervals from -60 to 300 min from the first and fourth injections. Samples were also collected at 20-min intervals for 6 h on d 25 and 69 +/- 1 PP. Area under the curve of ST (nanograms.minute-1.milliliter-1) was greater (P less than .01) in GRF than in CON heifers (9,671 +/- 677 vs 2,611 +/- 237). Increases in ST after GRF-A or GRF(1-29)-NH2 were similar. On d 25 +/- 1 PP, frequency of ST release (pulses per 6 h) was greater (P less than .01) in CON (3.3 +/- .2) than in GRF (2.1 +/- .2) heifers. Milk production was similar (P greater than .1) for the two treatments. Heifer BW loss from d -16 to 81 after parturition was greater (P less than .01) in GRF (88 +/- 5) than in CON (68 +/- 5) heifers. Postpartum return to ovarian activity (progesterone greater than 1 ng/mL for two consecutive weeks) was delayed (P less than .05) in GRF (97 +/- 14) vs CON (71 +/- 8) heifers. After accounting for variation due to treatment and year, a negative (P less than .02) correlation (r = -.39) was detected between concentrations of IGF-I during the first 30 d PP and PP interval to ovarian activity. These results indicate that prepartum administration of GRF altered the release pattern of ST after parturition and was associated with greater PP BW loss and delayed PP return to ovarian activity in heifers.     

Effect of dietary energy source and level on serum growth hormone, insulin-like growth factor 1, growth and body composition in beef heifers

Effects of fiber vs starch energy supplements on endogenous growth hormone (GH), insulin-like growth factor (IGF-1) and animal performance from weaning to breeding age were evaluated in 18, 9-mo-old beef heifers. Heifers had ad libitum access to wheat silage plus an average daily supplement intake of 1) 4.08 kg corn-soybean meal (SBM) (high energy-starch, HS), 2) 4.54 kg soyhulls (SH)-SBM (high energy-fiber, HF) or 3) 1.36 kg SH-SBM (low energy-fiber, LE). Serum samples were collected via jugular puncture every 10 d and were analyzed for IGF-1 by RIA. On d 45 and d 176, four heifers per treatment were fasted 18 h and serial blood samples collected via jugular cannulas every 15 min for 6.5 h. Arginine (.5 g/kg BW) was administered intravenously (ARG) to induce release of GH, and four additional samples of blood were collected. Samples were analyzed by RIA for GH. Mean fasted GH (6.4 +/- .4, 8.3 +/- .4 and 13.8 +/- .4 ng/ml for HS, HF and LE, respectively) varied with energy source and level (P less than .01). Mean GH following ARG was higher (P less than .01) in heifers receiving LE (46.2 +/- 4.7) than in those receiving HS and HF (23.5 +/- 4.4 and 24.1 +/- 4.6 ng/ml). Basal GH concentration and peak amplitude were higher (P less than .05) in LE than in HS and HF treatments. Diet did not influence number or frequency of GH peaks.(ABSTRACT TRUNCATED AT 250 WORDS)     

Serum copper concentrations in beef cows and heifers

OBJECTIVE: To characterize serum copper status of cows and heifers in beef cow-calf herds throughout the United States and to evaluate use of copper supplements in those herds. DESIGN: Cross-sectional survey. ANIMALS: 2,007 cows and heifers from 256 herds in 18 states. PROCEDURES: Producers participating in a health and management survey conducted as part of the National Animal Health Monitoring System voluntarily allowed serum samples to be obtained from cows and heifers for determination of copper concentration. Results were categorized as deficient, marginally deficient, or adequate. The proportion of cattle and herds (on the basis of mean value of the tested cattle) in each category was determined. Copper concentrations were compared between herds that reportedly used copper supplements and those that did not. RESULTS: Overall, 34 of 2,007 (1.7%) cows and heifers were deficient in copper, and 781 (38.9%) were marginally deficient. In each region, at least a third of the cattle were deficient or marginally deficient. For herds, 92 of 256 (35.9%) were marginally deficient, and 22 (0.8%) were deficient. Approximately half of the producers reported use of copper supplements, but a sizeable proportion of those producers' cattle and herds were classified as marginally deficient or deficient. CONCLUSIONS AND CLINICAL RELEVANCE: Copper deficiency is not restricted to a single geographic region of the United States. Copper deficiency can persist despite reported use of supplements by producers. Veterinarians dealing with beef cow-calf herds that have problems consistent with copper deficiency should not rule out copper deficiency solely on the basis of geographic region or reported use of copper supplements for the herd.     

Genetic parameter estimates for serum insulin-like growth factor I concentrations, and body weight and weight gains in Angus beef cattle divergently selected for serum insulin-like growth factor I concentration

Data for the current study were obtained from a divergent selection experiment in which the selection criterion was the average serum IGF-I concentrations of 3 postweaning blood samples collected from purebred Angus calves. Multiple-trait derivative-free REML procedures were used to obtain genetic parameter estimates for IGF-I concentrations and for BW and BW gains measured from birth to the conclusion of a 140-d postweaning performance test. Included in the analysis were 2,674 animals in the A(-1) matrix, 1,761 of which had valid records for IGF-I concentrations. Direct heritability estimates +/- SE for IGF-I concentration at d 28, 42, and 56 of the postweaning period and for mean IGF-I concentrations were 0.44 +/- 0.07, 0.51 +/- 0.08, 0.42 +/- 0.07, and 0.52 +/- 0.08, respectively. Heritability estimates for maternal genetic effects ranged from 0.10 +/- 0.05 to 0.20 +/- 0.06. The proportion of total phenotypic variance due to the maternal permanent environmental effect was essentially zero for all measures of IGF-I concentrations. Genetic correlations of IGF-I concentrations with weaning and post-weaning BW ranged from 0.07 +/- 0.12 to 0.32 +/- 0.11 and generally demonstrated an increasing trend during the postweaning period. Averaged across the various measures of IGF-I, the genetic correlation of IGF-I with preweaning gain was 0.14, whereas the genetic correlation with postweaning gain was 0.29. Genetic correlations between IGF-I and BW gain were positive during all time intervals, except between weaning and the beginning of the postweaning test and from d 84 to 112 of the postweaning period. Environmental and phenotypic correlations of IGF-I with BW and BW gains were generally positive, but small. These results indicate that postweaning serum IGF-I concentration is moderately to highly heritable and has small positive genetic, environmental, and phenotypic correlations with BW other than birth weight and with pre- and postweaning gain. Therefore, if IGF-I proves to be a biological indicator of an economically important trait (e.g., efficiency of feed use for growth) in beef cattle, it should be possible to rapidly change IGF-I concentrations via selection without significantly altering live weight or rate of gain.     

Effect of active immunization against growth hormone releasing factor on concentrations of somatotropin and insulin-like growth factor I in lactating beef cows.

Two experiments were conducted to determine the effects of immunoneutralization of growth hormone-releasing factor [GRF(1-29)-NH2] on concentrations of somatotropin (ST) and insulin-like growth factor I (IGF-I) in lactating beef cows. In Experiment 1, multiparous Hereford cows were immunized against 2 mg GRF(1-29)-(Gly)4-Cys-NH2 conjugated to human serum albumin (GRFi, n = 3) or 2 mg human serum albumin (HSAi, n = 3) at 52 +/- 1 d prior to parturition. Boosters (1 mg) were administered on days 12, 40 and 114 postpartum (pp). Serum samples were collected at 15-min intervals for 5 hr on days 18, 46 and 120 pp, followed by administration (IV) of an opioid agonist (FK33-824; 10 micrograms/kg) and an antagonist (naloxone; .5 mg/kg) at hours 5 and 7, respectively. A GRF-analog ([desamino-Tyr1, D-Ala2, Ala15] GRF (1-29)-NH2; 3.5 micrograms/kg) and arginine (.5 g/kg) were administered at hour 10 on days 47 and 121, respectively. Percentage binding of [125I]GRF (1:100 dilution of serum) 28 d after primary immunization was greater in GRFi (14.3 +/- 4.9) than in HSAi (.7 +/- .3) cows. Binding increased to 29.3 +/- 6.5% after first booster in GRFi cows. Episodic release of ST was abolished by immunization against GRF; concentration and frequency of release of ST were lower (P less than .05) in GRFi than in HSAi cows on all days pp. Concentrations of IGF-I were lower in GRFi than in HSAi cows throughout lactation. Serum ST failed to increase following FK33-824 or arginine in GRFi; however, ST increased after both compounds in HSAi cows. Concentrations of ST following GRF-analog were greater (P less than .05) in HSAi than in GRFi cows. Experiment 2 was conducted to determine if a lower dose of antigen and a single booster would be sufficient to lower ST and IGF-I in lactating cows. Multiparous Hereford and Angus cows were assigned to GRFi (n = 6) or HSAi (n = 6). Primary (1.2 mg) and booster (.5 mg) immunizations were administered -14 and 8 d from calving, respectively. Cows were restricted to 60% of recommended intake of energy during lactation in order to elevate concentrations of ST. Serum samples were collected at 15-min intervals for 6 hr on days 26, 50, 73, 90 and 109 pp. Two of six GRFi cows had binding less than 10% (1:1,000 dilution of serum) and were omitted from further analyses.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effect of active immunization against growth hormone-releasing factor on growth and onset of puberty in beef heifers.

Angus and Charolais heifers (195 +/- 7 kg) were actively immunized against growth hormone-releasing factor (GRF) to evaluate the effect on concentrations of somatotropin (ST), insulin-like growth factor I (IGF-I), insulin (INS), growth, and onset of puberty. Primary immunizations were given at 184 +/- 7 d of age (d 0 of experiment) by injecting (s.c.) 1.5 mg of GRF-(1-29)-Gly-Gly-Cys-NH2 conjugated to 1.5 mg of human serum albumin (GRFi, n = 22) or 1.5 mg of human serum albumin (HSAi, n = 21). Booster immunizations of .5 mg of antigen were given on d 62, 92, 153, and 251. Antibody binding (percentage at 1:2,000 dilution) to [125I]GRF on d 69 was greater (P less than .01) in GRFi (53.7 +/- 4.5) than in HSAi (10.1 +/- .6) heifers. Serum concentration (ng/ml) and frequency (peaks/5 h) of ST release, respectively, on d 78 were lower (P less than .01) in GRFi than in HSAi heifers (3.3 +/- .1 vs 5.6 +/- .2 and .9 +/- .3 vs 2.3 +/- .2). Serum IGF-I (ng/ml) was lower (P less than .01) in GRFi than in HSAi heifers on d 69 (41 +/- 5 vs 112 +/- 4). Serum INS (microU/ml) on d 78 was lower (P less than .05) in GRFi (2.2 +/- .1) than in HSAi (3.8 +/- .2) heifers. Feed intake, ADG, and feed efficiency were lower (P less than .05) in GRFi than in HSAi heifers. Hip height was lower (P less than .01) and fat thickness was greater (P less than .05) in GRFi than in HSAi heifers by d 132 and 167, respectively. Percentage of heifers attaining puberty (progesterone greater than 1 ng/ml for two consecutive weeks) by d 209 and 379 (12.9 and 18.5 mo of age), respectively, was lower (P less than .05) in GRFi (40.9 and 45.5) than in HSAi (81.0 and 100). In conclusion, growing heifers were successively immunized against GRF. Active immunization against GRF resulted in decreased serum concentration of ST, IGF-I, and INS. In addition, GRF immunization led to lowered feed intake, ADG, and feed efficiency, increased fat depth, and delayed onset of puberty in heifers. We propose that ST and IGF-I are important metabolic mediators involved in the initiation of puberty in heifers.     

Association of single nucleotide polymorphisms in the growth hormone and growth hormone receptor genes with blood serum insulin-like growth factor I concentration and growth traits in Angus cattle

This study was conducted to identify polymorphisms in the promoter and coding regions of the bovine growth hormone and growth hormone receptor genes and to study association of polymorphisms identified in these genes with growth traits and serum insulin-like growth factor-I (IGF-I) concentration. The denaturing gradient gel electrophoresis method and sequencing were utilized to identify three new single nucleotide polymorphisms in the promoter region of the growth hormone gene in Angus cattle. Polymerase chain reaction-based restriction fragment length polymorphism procedures were developed for rapid determination of the single nucleotide polymorphism genotypes in the growth hormone and the growth hormone receptor genes among Angus calves from lines divergently selected for high or low blood serum IGF-I concentration. The IGF-I concentration and growth traits were analyzed using animal models. The single nucleotide polymorphism in the promoter region of the growth hormone receptor gene was associated with serum IGF-I concentration on d 42 of the postweaning test and with mean IGF-I concentration. The associated effects of the markers need to be verified in other populations.     

Serum insulin-like growth factor type 1 concentrations in healthy dogs and dogs with spontaneous primary hypothyroidism

Circulating insulin-like growth factor type 1 (IGF-1) concentrations in dogs have been correlated with standard breed bodyweight (SBBW or breed size). Thyroid and somatotropic functions, which have common effects and regulatory mechanisms, were investigated in hypothyroid dogs. IGF-1 was measured in 495 adult healthy dogs (N) and in 220 primary hypothyroid dogs (HOT) with clinical and biological signs of primary hypothyroidism. IGF-1 was determined as a function of SBBW (kg): ≤15 (group A); 1540 (group D). In HOT dogs, median fT4 and c-TSH values were 9pmol/L and 1.5ng/mL, respectively. A significant correlation between bodyweight (BW) and IGF-1 was observed in both HOT and N dogs. The median IGF-1 value (ng/mL) was significantly higher (P<0.01) in HOT dogs compared to N in groups B, C and D (230 vs. 182; 316 vs. 230; 606 vs. 306 respectively). In conclusion, IGF-1 concentration should be interpreted in the context of SBBW in dogs and increases in spontaneous primary hypothyroidism. However, it remains unclear if this association is directly due to hypothyroidism or is the result of the weight gain accompanying hypothyroidism.     

Effects of breed and wintering diet on growth, puberty and plasma concentrations of growth hormone and insulin-like growth factor 1 in heifers

Twenty-five Brangus (BR) and 15 Angus (AN) heifers were used to study the effects of breed and wintering diet on average daily gain (ADG), onset of puberty and plasma concentrations of growth hormone (GH) and insulin-like growth factor 1 (IGF-1). Wintering diets (fed for 107 days beginning November 15) consisted of the following: 1) native grass hay (NGH), 2) ammoniated NGH, 3) NGH plus cottonseed meal, 4) Diet 3 plus corn and 5) Diet 4 plus monensin. After wintering, heifers were transferred to ryegrass pasture for 70 days. Mean ADG during the wintering phase were -.20, -.10, .17, .29 and .39 kg for heifers fed Diets 1 through 5, respectively (P less than .01). ADG was greater (P less than .05) for BR than for AN heifers. Plasma concentrations of GH were higher (P less than .05) in heifers fed Diets 1 and 2 than in heifers fed Diets 3, 4 or 5. Plasma concentrations of IGF-1 were lowest in heifers fed Diet 1 and highest in heifers fed Diets 4 and 5. During ryegrass grazing, GH concentrations were similar for all groups. However, concentrations of IGF-1 were higher (P less than .05) in heifers fed Diets 3, 4 and 5 than in heifers fed Diets 1 and 2. Age at puberty (onset of cyclic progesterone concentrations) was greatest in heifers fed Diet 1 and lowest in heifers fed Diet 5. Weight at puberty was not affected (P greater than .10) by wintering diet but was greater (P less than .01) in BR than in AN heifers. Therefore, negative ADG appears to be associated with elevated plasma GH concentrations in heifers, and plasma IGF-1 concentration appears to be a more accurate indication of nutritional status than plasma concentrations of GH.     

Effects of a growth hormone-releasing factor analogue and an estradiol-trenbolone acetate implant on somatotropin, insulin-like growth factor I, and metabolite profiles in growing Hereford steers.

Hereford steers (290 +/- 6 kg of BW) were implanted (n = 4) with 140 mg of trenbolone acetate (TBA) and 28 mg of estradiol-17 beta (E2 beta) or nonimplanted (controls, n = 4). In Trial 1, effects of a single i.v. injection of 0, 20, 40, or 80 micrograms of a growth hormone-releasing factor (1-29 NH2) analogue (GRFa) on release of endogenous somatotropin (ST) were evaluated in a double 4 x 4 Latin square design. Plasma samples (n = 21) were obtained from -20 to 240 min after GRFa injection. Area under the ST response curve (AUC) increased (P = .009) in a dose-dependent manner (.2, 2.6, 3.6, 4.3 mg.min-1.mL-1, respectively). Mean ST concentration was not affected (P = .238) by implant but AUC was greater (P = .009) in implanted than in control steers. There was no interaction (P = .460) between dose of GRFa and presence of implant. In Trial 2, 80 micrograms of GRFa was administered at 12-h intervals to the same eight steers. Response of ST (AUC) to the first and last (13th) i.v. injection of GRFa was similar and not affected by implant. Before GRFa administration, plasma insulin-like growth factor I (IGF-I) concentrations were greater (P = .039) in implanted than in control steers (272 vs 164 ng/mL). Administration of GRFa increased plasma IGF-I (P = .0001), decreased plasma urea N (PUN) (P = .0001), and did not alter plasma glucose (P = .447) in both control and implanted steers. Data indicate that effects of GRFa and TBA/E2 beta on plasma IGF-I and PUN concentrations were additive in this study.     

Insulin-like growth factor I in follicular development and function in postpartum beef cows

The objective of this study was to determine whether nutrition affects follicular growth and(or) steroid and insulin-like growth factor I (IGF-I) concentrations in follicular fluid. Beginning 6 d after calving, Hereford-cross cows (n = 28) were fed either 14 (ad libitum) or 7 (restricted) kg.animal1.d-1 of chopped alfalfa-brome hay. Half the cows in each treatment were ovariectomized on d 20 (OVX-20) and the remaining half on d 35 (OVX-35) postpartum. Cow weight and condition score were recorded weekly, and blood was collected thrice weekly for determination of insulin, IGF-I, glucose, and free fatty acid (FFA) concentrations. At ovariectomy, follicular fluid from each follicle greater than or equal to 4 mm in diameter was aspirated for determination of IGF-I, progesterone (P4), and estradiol-17 beta (E2) concentrations. Restricted cows lost more weight after calving than did ad libitum cows (P less than .0001), although all cows lost similar amounts of body condition (time postpartum, P = .008). Concentrations of FFA were elevated (P less than .0001) in restricted cows from wk 2 through 5 after calving but did not change with time in ad libitum cows. Plasma concentrations of glucose were lower in restricted than in ad libitum cows (59.6 +/- .4 vs 61.8 +/- .4 mg/dl; P = .05), but insulin and IGF-I were similar (P greater than .10) between dietary treatments.(ABSTRACT TRUNCATED AT 250 WORDS)     

Interaction of insulin-like growth factor I with turkey satellite cells and satellite cell-derived myotubes

Satellite cells, isolated from the superficial pectoralis muscle of growing Nicholas tom turkeys, were cloned to obtain a pure population of myogenic cells. These cells proliferated rapidly and differentiated (fused) into myotubes typically containing 92-98% fused nuclei. Competitive binding assays were performed on near-confluent satellite cell or myotube cultures in 35 mm diameter wells by adding [125I]IGF-I along with increasing concentrations of unlabeled IGF-I, IGF-II, or insulin. Following incubation, the cultures were washed to remove the unbound hormones, solubilized with 0.5 N NaOH, and the radioactivity specifically bound was determined. Total and fused nuclei number as well as total protein were determined in parallel cultures. Our results indicate that turkey satellite cell and myotube cultures possess specific binding sites for IGF-I. Displacement of [125I]IGF-I was in the order of IGF-I greater than IGF-II greater than or equal to insulin. Although the [125I]IGF-I association constants were similar for turkey satellite cells and myotubes, a 2.8-fold decrease in the number of receptors per nuclei was observed as satellite cells differentiated into myotubes. The 50% inhibition constants for IGF-I, IGF-II, and insulin were 3.7 X 10(-9) M, 7.5 X 10(-8) M, and 8.7 X 10(-8) M for satellite cells and 3.1 X 10(-9) M, 7.5 X 10(-8) M, and 9.6 X 10(-8) M for myotubes, respectively. Receptor cross-linking analysis using disuccinimidyl suberate was performed on near-confluent satellite cell cultures incubated with [125I]IGF-I in the presence or absence of 1 X 10(-7) M IGF-I, IGF-II, or insulin. Receptor subunit species of Mr 130 kDa and 98 kDa were observed under reducing conditions (100 mM dithiothreitol) and at a Mr greater than 300 kDa (native receptor tetramer) under non-reduced conditions. Autoradiographic bands were displaced with IGF-I but not with equimolar levels of IGF-II or insulin. The results suggest that turkey satellite cells possess a type I IGF receptor.     

Impact of blood serum insulin-like growth factor I on platelet-activating factor in bull spermatozoa

The objective of this study was to examine differences in platelet-activating factor [1-O-alkyl-2-acetyl-sn-glycero-3-phosphorylcholine; PAF] in spermatozoa between two lines of Angus beef cattle divergently selected for blood serum insulin-like growth factor I (IGF-I) concentration. Endogenous lipids were extracted from the spermatozoa and endogenous PAF content was determined by radioimmunoassay. The amount of PAF detected in spermatozoa obtained from high IGF-I bulls (n = 8) ranged from 0.145 to 3.571 pM/10(6) cells. The level of PAF extracted from spermatozoa obtained from low IGF-I- bulls (n = 5) ranged from 0.001 to 1.024 pM/10(6) cells. Polynomial regression analysis revealed a significant cubic relationship (R(2) = 0.374; F = 6.292; P < 0.05) between spermatozoa PAF content and blood serum IGF-I concentration. Spermatozoa-derived PAF levels (mean +/- SEM) were significantly higher (P < 0.05) in the high IGF-I group (1.90 +/- 0.39 pM/10(6) cells) than in the low IGF-I group (0.59 +/- 0.20 pM/10(6) cells). High IGF-I bulls have a greater than three-fold higher PAF content in their spermatozoa than low IGF-I bulls. The data demonstrate that not only is PAF present in bull spermatozoa but that levels are significantly higher in individuals with high serum IGF-I concentrations.     

An association between lifespan and variation in insulin-like growth factor I receptor in sheep

Longevity in livestock is a valuable trait. When productive animals live longer, fewer replacement animals need to be raised. However, selection for longevity is not commonly the focus of breeding programs as direct selection for long-lived breeding stock is virtually impossible until late in the reproductive life of the animal. Additionally the underlying genetic factors or genes associated with longevity are either not known, or not well understood. In humans, there is evidence that IGF 1 receptor (IGF1R) is involved in longevity. Polymorphism in the IGF1R gene has been associated with longevity in a number of species. Recently, 3 alleles of ovine IGF1R were identified, but no analysis of the effect of IGF1R variation on sheep longevity has been reported. In this study, associations between ovine IGF1R variation, longevity and fertility were investigated. Polymerase chain reaction-single strand conformational polymorphism (PCR-SSCP) was used to type IGF1R variation in 1,716 New Zealand sheep belonging to 6 breeds and 36 flocks. Ovine IGF1R C was associated with age when adjusting for flock (present 5.5 ± 0.2 yr, absent 5.0 ± 0.1 yr, P = 0.02). A general linear mixed effects model suggested an association (P = 0.06) between age and genotype, when correcting for flock. Pairwise comparison (least significant difference) of specific genotypes revealed the difference to be between AA (5.0 ± 0.1 yr) and AC (5.6 ± 0.2 yr, P = 0.02). A weak negative Pearson correlation between fertility and longevity traits was observed (r = -0.25, P < 0.01). The finding of an association between variation in IGF1R and lifespan in sheep may be useful in prolonging the lifespan of sheep.     

The effect of pregnancy on visceral growth and energy use in beef heifers

Beef heifers (24 mo; 378 +/- 32 kg of BW; 22 pregnant, PR; 17 nonpregnant, NP) were grouped in common pens and fed corn silage- and hay-based diets formulated to provide an ADG of 0.45 kg in NP heifers. Both PR and NP heifers were slaughtered on d 40, 120, 200, and 270 of the study. Intestinal and hepatic tissues were analyzed for protein, DNA, RNA (mg/g of fresh tissue), and in vitro oxygen use. Jejunal samples were analyzed for cellular proliferation via immunohistochemical analysis. For ileum, DNA, which provides an estimate of cell number per unit of tissue, revealed an interaction (P = 0.06) between pregnancy and slaughter day; both PR and NP decreased with time, but NP increased on d 270 (P = 0.09). Cell number in the ileum was reduced at d 200 and 270 in the PR heifers (P < 0.09). Liver protein concentration was less (P = 0.07) in PR than in NP heifers (NP = 291.1 vs. PR = 210.5 +/- 33.9 mg/g). Hepatic protein:DNA ratio was not affected (P > 0.10) by pregnancy or day. Energy use (kcal/d) of duodenum and jejunum, calculated from in vitro oxygen consumption, increased linearly (P < 0.02) with time for both PR and NP. Pregnant and NP ileal energy use increased linearly (P < 0.01), but ileal energy use by PR was less throughout gestation (P = 0.07) than ileal energy use by NP. Cellular proliferation in the crypt region of the jejunum was decreased on d 120 and 200 (P < 0.02). These data indicate that the small intestine and liver of PR heifers may conserve energy expenditure compared with NP heifers. Energy conservation can partially be explained by differences in growth and cell proliferation and by energy use of the liver and small intestine.     

The relationship of insulin-like growth factor-I with postweaning performance in Angus beef cattle

This study was designed to evaluate the ontogeny of serum IGF-I (SI) concentrations and its relationship to animal performance in a 140-d postweaning feeding trial. Ninety-eight progeny representing six sires (three high and three low feed conversion) and two sexes (43 bulls and 55 heifers) with ad libitum access to feed were allocated by sire and sex to monitor individual weights and pen feed consumption. Blood serum samples were obtained at the beginning of test (average age of 230 d) and every 28 d thereafter until each animal reached a fat thickness (estimated by sonoray) of 8.9 mm. Individual serum samples were acid-ethanol extracted and measured for IGF-I peptide by heterologous RIA. Serum IGF-I concentrations differed (P less than .10) between high (H) and low (L) feed conversion progeny groups at the end of the first 28-d period (125.12 vs 89.52 ng/ml) and tended to differ at the conclusion of the second 28-d period (P less than .15). Weight gains of H and L groups tended to differ in the second and third 28-d periods (P = .11 and .10, respectively). Serum IGF-I concentrations differed (P less than .05) between bulls and heifers for the first through fourth 28-d periods (P less than .01, P less than .05, P less than .10 and P less than .01, respectively). Phenotypic correlations indicated that pens with higher mean SI concentrations at the beginning of the test consumed less feed and had lower cumulative feed:gain ratios.(ABSTRACT TRUNCATED AT 250 WORDS)     

Growth and reproductive traits in beef heifers implanted with zeranol

Weaned replacement heifers were implanted with zeranol at 8 and 11 mo of age in two trials to evaluate growth and reproductive traits. Approximately 100 beef heifers were used in each trial, and the heifers were divided into categories of heavier than average (H) and lighter than average (L) weaning weight. Weight categories were further divided into control (HC and LC) and zeranol-implanted (HI and LI) groups. Heifers were kept in drylot from weaning to just before the start of the breeding season and were fed to reach a predetermined body weight by the start of the breeding season and were fed to reach a predetermined body weight by the start of the breeding season. Rates of gain in the drylot were greater in implanted than in control heifers in both trial 1 (.53 vs .48 kg/d; P less than .09) and trial 2 (.70 vs .63 kg/d; P less than .01). Pelvic areas were greater (P less than .01) in implanted than in control heifers of both trial 1 (175 vs 159 cm2) and trial 2 (175 vs 164 cm2). This increase in pelvic size was still present at the end of the summer pasture period, which followed the drylot period. Zeranol had no major effect (P greater than .10) on age of weight at puberty. Fall pregnancy rate was 16% lower in implanted heifers than in control heifers in trial 1 (62 vs 78%, P = .08) but did not differ in trial 2 (88 vs 87%, I and C, respectively).