Plasma IGF-I binding proteins in sheep: effect of recombinant growth hormone treatment and nutritional status

The effect of maternal nutrition on foetal serum potency in cell culture

The influence of pre-slaughter nutrition on the potency of foetal serum in cell culture was studied. Ewes carrying late-gestation foetuses (120-day gestation) were either fasted for 66 h (F), fasted for 66 h but drenched with Ketol, a propylene glycol preparation, (5 × 120 ml doses; FK), given food ad libitum (A), or given food ad libitum and drenched with Ketol (5 × 120 ml doses; AK). Following slaughter foetal blood was collected for the determination of potency in cell culture using industry-standard cell culture bioassays: cloning efficiency, plating efficiency and a 96 h cell proliferation assay. Foetal serum insulin-like growth factor (IGF) concentrations were also measured. Pre-slaughter fasting or drenching with Ketol had no effect on the potency of foetal serum in any of the cell culture bioassays. Fasting significantly lowered foetal plasma IGF-1 levels (F < 0·01). Foetal IGF-2 levels were unaffected by fasting or drenching with Ketol.

Effects of dietary protein and growth hormone-releasing peptide (GHRP-2) on plasma IGF-1 and IGFBPs in Holstein steers

This study was conduct to determine the influence of dietary protein on the response of plasma insulin-like growth factor-1 (IGF-1) and insulin-like growth factor binding proteins (IGFBPs) to exogenous growth hormone releasing peptide-2 (GHRP-2 or KP 102) in Holstein steers. Eight 16-month-old Holstein steers were grouped by liveweight to two feeding treatments; high protein (HP; CP 1.38 kg/day and TDN 4.5 kg/day DM intake, n=4) or low protein (LP; CP 0.66 kg/day and TDN 4.42 kg/day DM intake, n=4). The experiment was a single reverse design whereby each group was injected twice daily with GHRP-2 (12.5 microg/kg body weight (BW)/day) or saline solution into the jugular vein for a 6-day period. Plasma IGF-1 in the HP group were higher than in the LP group (P<0.05), but plasma 34 kDa IGFBP-2 was lower in the HP than the LP group (P<0.05). The amplitude of the maximum growth hormone (GH) peaks responding to GHRP-2 injection were higher at day 1 than at day 6 of saline or GHRP-2 treatment in both LP and HP steers (P<0.05). The area under the GH response curve for 180 min after the GHRP-2 injection was not significantly different between the LP and the HP groups at days 1 and 6. A response in plasma IGF-1 concentration to GHRP-2 treatment in the HP group was observed at day 1 (198.9+/-18.1 ng/ml), day 2 (195.2+/-21.1 ng/ml) and day 6 (201.3+/-14.8 ng/ml) (P<0.05). No increase in plasma IGF-1 was observed from GHRP-2 administration in the LP group. Although the response of plasma IGF-1 concentration to GHRP-2 administration was increased in the HP group (P<0.05), there was no apparent effect of GHRP-2 treatment on plasma 38-43 kDa IGFBP-3 and 34 kDa IGFBP-2 at days 2 and 6 of treatment. In conclusion, it is proposed that the 34 kDa IGFBP-2 is sensitive to dietary protein level and may play an important role in the regulation of circulating IGF-1 in ruminant. In addition, increased plasma IGF-1 concentration observed in the HP group in response to the GHRP-2 treatment did not appear to affect plasma IGFBPs.

Individual variation in the milk yield response to bovine somatotropin in dairy cows

The objective was to relate the short-term milk yield response (MYR) following use of exogenous bovine somatotropin (bST) to changes in plasma concentrations of metabolites and hormones. Twenty-four Holstein cows (52 +/- 4.1 d postpartum) received daily subcutaneous injections of saline for 1 wk followed by subcutaneous injections of 33 mg/d of bST for 2 wk (Trial 1). The difference in milk yield between wk 1 and 3 for each cow was used to determine the 5 cows with the highest (HR) and 5 with the lowest responses (LR) to bST. These 10 cows were then used in 3 further trials of the same design (Trials 2, 3, and 4, conducted at 122, 181, and 237 +/- 7.6 d postpartum, respectively). Blood samples were taken 2 h after the administration of bST on d 1, 3, 5, 15, 17, and 19 of each trial. The HR group had consistently greater MYR to bST than the LR group throughout their lactation. The LR group had a higher milk yield and lower plasma insulin like growth factor-I (IGF-I) concentrations during the saline treatment in all trials. The increase in plasma somatotropin concentrations following injections of bST was greater for the LR group, whereas the difference in plasma IGF-I level between wk 1 and 3 was greater for the HR group. The HR group had lower levels of 3-hydroxy-butyrate and nonesterified fatty acids before bST treatment. Low short-term response to bST was associated with plasma concentrations of hormones and metabolites that indicate negative energy balance, although other factors may be involved.

Effects of growth hormone and feeding level on endocrine measurements, hormone receptors, muscle growth and performance of prepubertal heifers

Prepubertal Friesian heifer calves (n = 24, initial BW = 195 +/- 5 kg) were assigned to a 2 x 2 factorial block design and used to evaluate the effects of daily GH treatment (0 or 15 mg/d) at either a low or a high feeding level in a 5-wk treatment period on endocrine measurements, hormone receptors, muscle growth, and overall performance. In the pretreatment period, a low feeding level was employed for all calves. During the treatment period, animals at the low feeding level had free access to a roughage-based mixture, whereas animals at the high feeding level had free access to a concentrate mixture and were offered 2 kg/d of the roughage-based mixture. Blood samples were collected weekly starting 3 wk before treatment. Longissimus (LM) and supraspinatus (SS) muscles were obtained at slaughter. Metabolizable energy intake was 81% higher, digestible CP intake was 140% higher, and ADG was 115% higher (all P < 0.001) at the high vs. low feeding level. Feed (DMI, ME, and protein) intake was not affected by GH treatment, but ADG was 18% higher (P < 0.13) in GH-treated than in control heifers at both feeding levels. Although of different magnitudes, the muscle anabolic effects of GH treatment and high vs. low feeding level were additive, and both treatments increased carcass weights (P < 0.02 and P < 0.001, respectively), LM (P < 0.05 and P < 0.001), and SS (P < 0.06 and P < 0.003). The anabolic effect of GH treatment was similar in both muscles, whereas the effect of feeding level was most pronounced in LM. Overall, GH treatment increased plasma GH, IGF-I (both P < 0.001), and IGFBP-3 (P < 0.02); however, GH treatment increased total IGF-I, free IGF-I, and IGFBP-3, and decreased IGFBP-2 mainly at the high feeding level (GH x feeding level interaction; P < 0.02, 0.01, 0.03, and 0.10, respectively). The high feeding level increased insulin, free and total IGF-I, and IGFBP-3 (all P < 0.001), but decreased GH and IGFBP-2 (both P < 0.001). High feeding increased type-1 IGF receptor density (P < 0.02), mainly in LM, in accordance with the largest anabolic response in this muscle, whereas GH treatment had no effect on type-1 IGF receptors. The results suggest that in skeletal muscle, the anabolic effects of exogenous GH are related to endocrine changes in the GH-IGF axis, whereas the effects of feeding level also seem to rely on IGF receptor density in the muscles.

The effect of growth hormone-releasing peptide-2 (KP102) administration on plasma insulin-like growth factor (IGF)-1 and IGF-binding proteins in Holstein steers on different planes of nutrition

This study was conducted to investigate the nutrition-dependent changes in insulin-like growth factor (IGF)-1 and IGF-binding proteins (IGFBPs) with growth hormone releasing peptide-2 (D-Ala-D-betaNal-Ala-Trp-D-Phe-Lys-NH(2); GHRP-2 or KP102) treatment in growing Holstein steers. Eight 13 month-old Holstein steers were grouped on two levels of feed intake (high intake (HI); 2.43% body weight or low intake (LI); 1.22%) and each group was daily injected with KP102 (12.5 microg/kg body weight/day) or saline solution into the jugular vein during 6-day period. The concentration of plasma GH showed an increase after an i.v. bolus injection of KP102 on Day 1 and Day 6 in both the LI and HI groups. Plasma IGF-1 began to increase 10 hr following an i.v. bolus injection of KP102, but this was only observed in the HI group (P < 0.05). Also, the plasma IGF-1 in the HI group with daily injections was significantly greater than the LI group from Day 1 of KP102 administration (P < 0.05). It reached maximum values of 125.1 +/- 7.6 ng/ml after Day 2, and returned to pre-injection levels after Day 4, however, no change in plasma IGF-1 was observed in LI with administration of KP102. During 6 days of treatment, plasma 38-43 kDa IGFBP-3 and 24 kDa IGFBP-4 were significantly higher in KP102 treated steers but only in the HI group (P < 0.05). Plasma 34 kDa IGFBP-2 decreased in the HI group and did not show any change following an injection of KP102. In conclusion, the effect of stimulated endogenous GH with KP102 administration increased plasma IGF-1, 38-43 kDa IGFBP-3 and 24 kDa IGFBP-4 levels in the HI group of growing Holstein steers, but not in the LI one. Thus, we strongly believe that the plasma IGF-1 and IGFBPs response to KP102 treatment is modulated by the nutritional status of growing Holstein steers and the increased plasma IGF-1 concentration with KP102 treatment may be regulated by plasma 38-43 kDa IGFBP-3 and 24 kDa IGFBP-4 in Holstein steers.

Nutrition, development and efficacy of growth modifiers in livestock species

Somatotropin (ST) and synthetic beta-adrenergic agonists (beta-AA) are growth-modifying agents that increase the rate and sometimes, the efficiency of protein deposition in lean tissues of livestock species. The ST-induced increase in muscle protein deposition is effected by a relatively modest increase in protein synthetic rate. This is possibly mediated by the endocrine influence of marked increases in circulating IGF (insulin-like growth factor)-I, and other ST-dependent components of the IGF system; mediation by locally expressed IGF-I may also occur. Increased muscle protein accretion in animals treated with beta-AA seems to be directly mediated by binding of the synthetic agonist to muscle beta-1 or beta-2 receptors, leading to increased muscle protein synthesis, possibly accompanied or followed by decreased protein degradation. This response is transient, due to down-regulation of beta-adrenergic receptors. Maximal responses of muscle protein accretion to both ST and beta-AA are attenuated by feeding inadequate levels of total protein or specific, limiting amino acids. For ST, but not beta-AA, this effect in growing pigs is partially offset by increased efficiency of utilization of absorbed amino acids for protein deposition, with predictable consequences for dietary protein and amino acid requirements. Both ST and beta-AA are less efficacious in promoting muscle protein deposition in very young animals. For ST, this is related to postnatal development of the somatotropic axis; a mechanistic explanation for the similar lack of effect of beta-AA is lacking. In both cases, this phenomenon must be considered against the very high inherent capacity and efficiency of lean tissue protein accretion in the neonate.

The effect of bovine somatotropin and diet on somatotropin binding sites in hepatic tissue of lactating dairy cows

In the lactating cow, galactopoiesis is stimulated by treatment with recombinant bovine somatotropin (bST) and by an improved plane of nutrition. The present study determined the interaction between these variables and examined whether a positive galactopoietic effect was accompanied by a change in hepatic binding sites for bST. Lactating dairy cows received one of three diets with increasing nutrient density; diet 1, 150 g/kg of dry matter (DM) of crude protein (CP) and 10.5 MJ/kg of DM of metabolizable energy; diet 2, 170 g/kg of DM of CP and 11.3 MJ/kg of DM of metabolizable energy; and diet 3, 190 g/kg of DM of CP and 12.1 MJ/kg of DM of metabolizable energy. At 90 d after calving, half of the cows in each dietary group were treated with bST every 14 d for the rest of the lactation. Both nutrient density and administration of bST increased milk yield significantly in mid and late lactation; there was no significant treatment by diet interaction. Treatment with bST significantly increased plasma concentrations of insulin-like growth factor (IGF)-I compared with IGF-I concentrations in controls in both mid and late lactation. Comparisons within diet revealed that concentrations of IGF-I were significantly higher in cows fed diet 3 than in cows fed diets 1 and 2 at both stages of lactation. Increases in plasma insulin were confined to cows in late lactation, and no changes were observed for nonesterified fatty acids. Liver biopsies showed that concentrations of hepatic binding sites for bST were not affected significantly by bST treatment but were increased in midlactation for cows fed diet 3. Concentration of hepatic binding sites per unit weight of tissue were greater for cows in midlactation than for cows in late lactation. In summary, exogenous bST treatment and increased nutrient density were associated with elevated plasma IGF-I concentrations and increased milk yield; however, only nutrient density in midlactation increased the number of hepatic binding sites for bST. Exogenous bST treatment had relatively little effect on the concentration of hepatic bST receptors compared with nutrient density.

Lack of effects of growth hormone administration on ovarian function of lactating goats

Exogenous growth hormone (GH, 5 mg d-1) was given daily to lactating goats for 4 weeks (Experiment 1) and 100 days (Experiment 2). Treatment effects on milk production and milk composition were assessed. At the end of treatment, goats were slaughtered and one ovary was processed for histological analysis while the largest follicles of the other ovary were dissected, measured and incubated in vitro (Experiment 1). In Experiment 2, following a synchronisation treatment, a superovulatory regime of pregnant mare's serum gonadotrophin (eCG) was given and ovulation rate measured at laparoscopy. In both experiments, GH administration raised milk yield (28.6% and 17% in Experiments 1 and 2 respectively). Circulating IGF1 concentrations were also increased following treatment. In contrast, no treatment effects were detected on the ovaries. In Experiment 1, the total population of antral follicles, their atresia, the number in specific size classes and the size of the largest healthy or atretic follicles were similar in control and GH treated ovaries. In addition, steroidogenesis (oestradiol and testosterone) by large follicles was also unaffected by treatment. In Experiment 2, eCG induced ovulation rate (control 6.9 +/- 7.6, treated 4.2 +/- 2.8) was also similar between groups. It is concluded that GH administration to lactating goats, while increasing milk production has no detrimental or positive consequences on ovarian function.

Effect of selenium and lodine supplementation on growth rate and on thyroid and somatotropic function in dairy calves at pasture

The effects of Se and I supplementation on growth rate and on thyroid and somatotropic function were examined for heifer calves from two herds fed pasture. Supplementation of calves with intraruminal Se pellets increased the basal plasma concentration of 3,5,3'-triiodothyronine and reduced the basal plasma concentration of thyroxine for both herds. For one herd, supplementation with Se increased the triiodothyronine response to challenge with thyrotropin-releasing hormone, increased BW gain, and tended to increase the plasma concentration of IGF-I. The plasma concentration of growth hormone was unaffected by Se supplementation. Supplementation with I increased the response of thyroid hormones to thyrotropin-releasing hormone but did not increase BW gain. Interaction between Se and I treatment within the herds was not apparent for any outcome variable. These data suggest that the effects of Se deficiency in grazing calves may be mediated by alterations in thyroid hormone metabolism but apparently are not mediated through modulation of the peripheral concentration of growth hormone.

The ontogeny of serum insulin-like growth factor-I concentration in foals: effects of dam parity, diet, and age at weaning

The effects of dam parity, age at weaning, and preweaning diet were examined in the ontogeny of serum insulin-like growth factor-I (IGF-I) concentrations in foals. Foals born to 13 primiparous and 19 multiparous draft-cross mares were weighed and bled near birth. About one-half of the foals in each group were weaned early (about 13 wk old); the remaining foals were weaned late (about 16 wk of age). Pooled values for serum IGF-I concentrations between birth and 17 wk of age were higher (P < 0.065) for foals born to multiparous (386 ng/ml) than to primiparous mares (237.5 ng/ml). Colts (378 ng/ml) had higher (P < 0.05) serum IGF-I concentrations than fillies (254.5 ng/ml), regardless of dam parity. Colts (173.5 kg) also tended (P = 0.12) to be heavier than fillies (159.2 kg). Weaning, whether at 13 or 16 wk of age, reduced (P < 0.05) growth rates and serum IGF-I concentrations. Serum IGF-I values recovered to preweaning values within 1-3 wk postweaning concurrent to an improved weight gain. Fifteen 1-d-old foals in a second study were fed milk replacer for 7 wk and were compared with five foals that nursed their mares for 8 wk. During the first 2 wk, replacer-fed foals (0.46 kg/d) did not gain as rapidly (P < 0.03) as mare-nursed foals (1.73 kg/d). The associated serum IGF-I values for replacer foals (139.4 ng/ml) were lower (P < 0.0001) than values for mare-nursed foals (317.4 ng/ml). Despite similarity in gains for both groups there-after, serum IGF-I concentrations of replacer-fed foals were only 36 and 60% of values obtained for mare-nursed foals at 8 (weaning) and 18 wk of age, respectively. The intrinsic differences between mare-nursed and milk-replacer foals in serum IGF-I concentrations persisted to 1 yr of age despite similarities in dietary management and body weight of the foals. At 1 yr of age, the serum IGF-I concentration of mare-nursed foals (1,203 ng/ml) was 48% higher than that of replacer-fed foals (815 ng/ml). These data indicate that dam parity, sex of foal, and preweaning nutrition affect the ontogeny of serum IGF-I concentration in the foal. The chronic, persistent difference in serum IGF-I values created by the early nutritional management of growing animals has implications in the interpretation of longitudinal serum IGF-I studies in all species.

Zinc deficiency-induced anorexia influences the distribution of serum insulin-like growth factor-binding proteins in the rat

Zinc (Zn) deficiency can result in severe growth retardation in mammals, and in a number of animal model systems it leads to low circulating insulin-like growth factor-I (IGF-I) concentrations. Using a weanling male rat model and a number of feeding schemes, we show that in addition to lower circulating IGF-I concentrations, Zn deficiency leads to alterations in the distribution of serum IGF-binding proteins (IGFBPs). Serum from Zn-deficient animals labeled in vitro with [125I]IGF-I displayed three peaks of tracer activity: 150 kd (IGFBP-3), 37 kd (IGFBP-2 and -1), and 8 kd (free [125I]IGF-I). Relative to controls, Zn-deficient animals demonstrated more tracer binding in the 37-kd region, whereas less was found in the 150- and 8-kd peaks. Serum from chronically calorie-restricted fed animals displayed [125I]IGF-I binding profiles similar to Zn-deficient serum, implicating Zn deficiency-induced anorexia as the principle factor underlying both the lower circulating IGF-I and the alterations in IGFBP profiles. Concentrations of IGFBP-4 were unaffected by diet manipulation based on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE)/Western ligand blot (WLB) analysis.

IGF1 and 2 in two models of adrenal growth

Insulin-like growth factors (IGFs) 1 and 2 were measured in the adrenal glands of rats undergoing either compensatory growth following left unilateral adrenalectomy or adrenal regeneration following bilateral adrenal enucleation. In normal rat adrenal gland, the tissue concentration of IGF2 (7.45 +/- 0.99 pg/micrograms protein) wa higher than IGF1 (1.26 +/- 0.23 pg/micrograms protein), both peptides being more abundant in the inner zones of the adrenal gland compared to the capsule-glomerulosa. During compensatory growth of the right adrenal gland, IGF1 and 2 increased significantly compared with control right adrenal glands at 24 h following left unilateral adrenalectomy (P less than 0.001). At 68 h, the increase remained significant for IGF1 (P = 0.012). The two peptides were measured in the regenerating adrenal gland at 7, 14 and 21 days following bilateral enucleation. Whilst there was a trend towards an increase in the IGF1 and 2 content of regenerating adrenal glands, the increase was significant only for IGF2 in the left adrenal gland at 21 days following enucleation. Plasma IGF1 and 2 did not increase compared to controls during the experiments (110.97 +/- 1.95 and 46.33 ng/ml, respectively), suggesting that the changes in tissue IGF reflect increased local production during rapid growth of the adrenal gland.