Neuroendocrine regulation of growth hormone secretion in sheep. II. Effect of somatostatin on growth hormone and glucose levels.

The effect of intravenous (iv) and intracerebroventricular (icv) administration of somatostatin on the plasma levels of growth hormone (GH) and glucose was studied in sheep. Intravenous somatostatin decreased (P less than 0.001) circulating GH when infused at the rate of 5 micrograms/min (150 ng/kg/min) over 1 hr, but when used at 1 microgram/min there was no effect on plasma GH levels during infusion. At both doses used there was an indication of an increase in GH following the cessation of somatostatin infusion. Somatostatin given at both these doses iv had no effect on plasma glucose levels. When given icv neither 1.8 micrograms, 18 micrograms nor 180 micrograms somatostatin had any significant effect of plasma GH levels, although there was a significant (P less than 0.05) elevation in GH levels 75 min after 180 micrograms somatostatin icv. Plasma glucose levels did not increase following injection of somatostatin icv at 1.8 or 18 micrograms, but there was a clear hyperglycaemic episode following 180 micrograms icv. Despite a lack of effect of somatostatin on GH release when given icv, there was a clear elevation (P less than 0.05) in plasma GH levels immediately following icv administration of a somatostatin antiserum. These data indicate that iv administration of somatostatin at pharmacological levels can depress unstimulated GH levels in sheep while administration icv does not. Central administration of somatostatin increases plasma glucose levels only at high doses and seems unlikely to be of physiological importance in glucose homeostasis.     

Effects of plane of nutrition, growth hormone and unsaturated fat on mammary growth in prepubertal lambs.

Effects of plane of nutrition, growth hormone treatment and dietary polyunsaturated fat on mammary development were assessed in prepubertal ewe lambs. Ten lambs (15.6 kg initial body weight) were assigned to each of four treatment groups. Treatments included: (A) lambs given ad libitum access to a high-energy ration; (G) fed as group A but injected s.c. daily with bovine growth hormone (.08 mg/kg BW); (R) feed intake restricted to achieve a growth rate of about 120 g/d; and (S) given ad libitum access to a ration including a formaldehyde-protected sunflower seed supplement. Diets were isonitrogenous and isocaloric and were fed from about 7 to 22 wk of age. At slaughter, the udder was removed and divided into halves. One udder half was trimmed and the parenchyma was dissected from surrounding stroma for compositional analyses. Final body weight and rate of gain averaged 41.2, 42.8, 27.3 and 46.0 kg, and 251, 267, 112 and 311 g/d for groups A, G, R and S, respectively. In the same treatment order, mammary parenchymal weight averaged 15.3, 20.3, 14.2 and 25.6 g. Parenchymal dry, fat-free tissue and DNA content were 1.7, 2.5, 1.3 g and 12.6, 24.1, 10.4 and 18.8 mg, respectively. Mammary parenchymal development was stimulated by polyunsaturated fat but was not affected by plane of nutrition. Supplemental dietary lipid may promote mammogenesis in ruminants.     

Effects of thyrotropin-releasing hormone and a thyrotropin releasing hormone analog on growth and selected plasma hormones in lambs

An 8-wk growth trial was conducted to assess the effects of continuous infusion of thyrotropin-releasing hormone (TRH) and an active TRH analog less than Aad-His-Pro-NH2 (the less than Aad is L-pyro-alpha-aminoadipic acid) on growth trial performance, carcass composition and hormone profiles of growing lambs. Both drugs were infused at 600 micrograms X lamb -1 X d -1 with 16 lambs/treatment. Both TRH and less than Aad-His-Pro-NH2 decreased average daily gain (ADG; P less than .01) and increased feed conversion (FC; P less than .01) compared with saline infused controls. Average daily feed intake was not altered. Carcasses of lambs given TRH or less than Aad-His-Pro-NH2 contained fewer kilograms of moisture (P less than .05) and appeared to contain fewer kilograms of protein. Thyrotropin-releasing hormone and less than Aad-His-Pro-NH2 increased thyroid gland weights (P less than .05), but pituitary gland weights were not different. Plasma thyrotropin (TSH) concentrations were increased by both drugs compared with control lambs, peaking at 4 to 7 d after initiating infusion. However, by 14 d, TSH concentrations returned to control levels. Triiodothyronine (T3) and thyroxine (T4) were elevated by both drugs over the entire 8-wk trial, with peak levels reached at 10 d and maintained for the duration of the study. Both TRH and less than Aad-His-Pro-NH2 increased prolactin over the entire period. Growth hormone levels were not altered by either drug. The effects of less than Aad-His-Pro-NH2 infusion on growth trial performance, carcass composition and hormone profiles of growing lambs were very similar to TRH. The negative effects of TRH and less than Aad-His-Pro-NH2 infusion on ADG, FC and carcass protein appear to be the result of elevated T3 and T4 levels.     

Effects of plane of nutrition, growth hormone and unsaturated fat on growth hormone, insulin and prolactin receptors in prepubertal lambs

The influence of plane of nutrition, growth hormone (GH) treatment and dietary polyunsaturated fat on serum concentrations of GH and insulin (INS) and binding capacities of GH, INS and prolactin (PRL) in liver, mammary parenchyma and adipose tissue was assessed in prepubertal ewe lambs. Ten lambs were assigned to each of four treatment groups. Treatments included: (A) lambs with ad libitum access to a high-energy ration; (G) lambs fed as group A and treated with bovine GH (.08 mg/kg/d); (R) lambs with feed intake restricted to limit ADG to about 120 g; and (S) lambs with ad libitum access to a ration including formaldehyde-protected sunflower seed. Diets, all approximately isonitrogenous and isocaloric, were fed from about 7 to 22 wk of age. Weekly blood samples were collected during wk 6 to 14 of the trial. Averaged across sampling dates, mean serum concentrations of GH were elevated in G lambs (P less than .05) and INS concentrations differed in the order G greater than A greater than R = S (P less than .05). Crude membranes for binding assays were prepared from liver, mammary parenchyma and adipose tissue. Mean concentrations of GH receptors in liver and PRL receptors in mammary parenchyma were elevated in group S lambs (P less than .01). Dietary polyunsaturated fat increased the number of GH receptors in liver and PRL receptors in mammary parenchyma. Increased availability of receptors may mediate the stimulation of mammary growth observed in lambs fed polyunsaturated fat.     

Regulation of growth hormone-releasing hormone and somatostatin from perifused,bovine hypothalamic slices. III. Reciprocal feedback between growth hormone-releasing hormone and somatostatin

An in vitro perifusion system for bovine hypothalamic tissue was used to determine if growth hormone-releasing hormone (GHRH) and somatostatin (SRIF) modulate each other's release, and whether SRIF mediates D₁-agonist-induced suppression of GHRH in cattle. Up to three sagittal slices (600 μm) of bovine hypothalamus, immediately parallel to the midline, were cut in an oxygenated balanced salt solution at 4° C, placed in 5 cc syringe barrels, and perifused at 37° C with oxygenated minimum essential medium-α at a flow rate of 0.15 ml/min. Three experiments were conducted, and medium effluent was collected every 20 min before (two samples), during (one or three samples), and after (six samples) treatment. Areas under GHRH and SRIF response curves (AUC), adjusted by covariance for pretreatment values, were calculated from samples collected during the treatment/post-treatment period. Perifusion of SRIF at 10⁻⁶ M and 10⁻⁴ M decreased AUC for GHRH from 86.3 (control) to 65.4 and 59.5 ± 6.3 ng · ml⁻¹ min, but 10⁻⁸ M SRIF was ineffective. Relative to controls, 10⁻⁸, 10⁻⁶, and 10⁻⁴ M GHRH increased release of SRIF 190, 675, and 1,135%, respectively. Activation of D₁ receptors with 10⁻⁶ M SKF 38393 increased AUC for SRIF from 12.5 ng · ml⁻¹ min (control) to 484.9 ng · ml⁻¹ min and decreased AUC for GHRH from 36.4 ng · ml⁻¹ min (control) to 18.2 ng · ml⁻¹ min. Blockade of SRIF action with a SRIF antagonist, cyclo-[7-aminoheptanoyl-phe-d-trp-lys-thr(bzl)], increased release of GHRH 1.9-fold. In addition, the SRIF antagonist blocked SKF 38393-induced suppression of GHRH. We concluded that GHRH and SRIF interact within the bovine hypothalamus/pituitary stalk to modulate the release of the other. Moreover, SRIF mediates the inhibitory effects of activation of D₁ receptors on release of GHRH in cattle.     

The effect of passive immunization against somatostatin on marker retention time in lambs

The effects of passive immunization against somatostatin on retention time of marker have been investigated in sheep using Cr2O3 as a marker. The mean transit time for clearance of 50% of the marker was significantly retarded in all the anti-somatostatin-treated animals by approximately 19.0 h, as compared with control lambs given a nonspecific antiserum. The findings suggest an important role for circulating somatostatin in the regulation of the rate of flow of digesta through the gastrointestinal tract in lambs. Moreover, it enhances the claim of the immunological approach as a new technique to investigate factors controlling food utilization in farm livestock.     

Plasma somatotropin response to exogenous growth hormone releasing factor in lambs

Two experiments were performed to examine the ability of human pancreatic growth hormone releasing factor (hGRF) administration to stimulate endogenous growth hormone (GH) secretion in lambs. Each study utilized eight Dorset wether lambs in replicated 4 X 4 Latin square experiments. Growth hormone response (integrated area under the curve for 150 min post-injection) for 0, 1, 5 and 10 micrograms hGRF/kg body weight averaged 13, 23, 92 and 134 units, respectively. While the 1-microgram hGRF dose was not different (P greater than .05) than the response to saline injection, there was an increased (P less than .01) GH response to 5 or 10 micrograms hGRF. Overall the GH response increased in a log dose-response fashion. There was distinct variation between lambs in their response to hGRF. Study II examined the optimal method to administer 40 micrograms hGRF/kg body weight to maximize GH concentration over 24 h. Continuous infusion (CI) was compared with eight (8X), four (4X), or two (2X) injections/d. Hourly blood samples were obtained from all lambs. Growth hormone response (area under the curve for 24 h) was 162, 305, 306 and 220 units for CI, 8X, 4X and 2X, respectively. Growth hormone response to CI was inferior to discrete injections, and the GH response to 4X or 8X was superior to 2X/d. Results demonstrate that, in spite of lamb-to-lamb variation, one can utilize exogenous hGRF to enhance GH secretion in lambs. Thus, the ability of exogenous hGRF to enhance growth performance merits further study.     

Effects of immunization against two inhibin antigens on daily sperm production and hormone concentrations in ram lambs

The gonadal hormone inhibin regulates daily sperm production (DSP) indirectly through negative feedback control of FSH secretion and may also affect DSP via direct actions within the testis. Studies attempting to increase DSP through the immunization against inhibin have yielded equivocal results. The current study compared 2 inhibin antigens for effects on DSP and hormone secretion. Hampshire ram lambs (BW = 42 +/- 2 kg; age = 113 +/- 3 d) were assigned randomly to 3 groups: 1) control (n = 4); 2) alpha-peptide conjugate (PTC, n = 6); and 3) alpha-subunit (SUB, n = 6). Antigen PTC consisted of an alpha-inhibin, N-terminal, 25-amino acid peptide conjugated to ovalbumin. Antigen SUB was the complete inhibin alpha-subunit. Lambs were immunized on d 0 (June 19, 2006), 18, 38, and 63. Body weight was recorded on immunization days and scrotal circumference on d 63. Blood samples were collected on d 0, 7, 14, 18, 28, 35, 38, 49, 56, 63, and 70. Rams were slaughtered on d 71. Testes were weighed, and parenchyma was obtained for DSP determination. Plasma alpha-inhibin antibody titer and LH, FSH, and testosterone concentrations were measured. alpha-Inhibin antibody titer was first detectable on d 14 in both PTC- and SUB-immunized ram lambs and generally increased thereafter. Mean DSP per gram of testis (DSP/g) was increased (P < 0.01) 26% in PTC- and SUB-immunized ram lambs over that in control ram lambs. Total DSP per ram lamb and testes weight did not differ among the 3 treatment groups. Variation in DSP per ram lamb and testes weight were greater (P = 0.05) in PTC- and SUB-immunized ram lambs than in control ram lambs. Plasma FSH concentrations were similar in PTC- and SUB-immunized ram lambs. Immunization against either alpha-inhibin antigen did not alter LH, testosterone, BW, or scrotal circumference. Findings indicate that 1) the 2 alpha-inhibin antigens increase DSP/g to similar extents; 2) alpha-inhibin antibody may act at least in part through an intratesticular mechanism because DSP/g was increased in some animals without concomitant increases in FSH; and 3) immunization against alpha-inhibin may affect testes weight by actions independent of those that regulate DSP/g.     

Effects of immunization against α-inhibin using two adjuvants on daily sperm production and hormone concentrations in ram lambs

Twenty-five ram lambs were immunized against α-inhibin peptide emulsified in Freund's adjuvant (FRA), Emulsigen (EML) containing an oligodeoxynucleotide as an immunostimulant, or adjuvant without α-inhibin antigen (control). Four immunizations were administered during an 85-d period, after which testes were obtained for determination of daily sperm production (DSP) and histological evaluation. α-Inhibin antibody (Ab) titers were 70-fold greater in lambs treated with FRA than in EML-treated ram lambs. α-Inhibin immunization had no effect on testes weight or on plasma concentrations of follicle-stimulating hormone (FSH), luteinizing hormone (LH), and testosterone. Mean DSP/g tended (P = 0.1) to be greater in α-inhibin–immunized (EML = 17.6 × 10⁶; FRA = 15.8 × 10⁶) ram lambs than in control animals (14.4 × 10⁶). One of the 8 control ram lambs had an elevated DSP/g, which was a statistical outlier. Without data from this lamb, DSP/g was increased (P < 0.01) in α-inhibin–immunized ram lambs by 28% over controls. No association was found between the titer of α-inhibin Ab developed and DSP/g. Histologically, the percentage of testicular area occupied by seminiferous tubules differed (P = 0.01) by treatment and was greatest (82%) in EML-treated ram α-inhibin–immunized lambs and lowest (74%) in control animals. Percentage tubular area and DSP/g were correlated (r = 0.57, P = 0.003). Findings show that (1) the extent of the increase in DSP/g is not dependent on the titer of α-inhibin Ab; (2) the increase in DSP/g is achieved through an increase in the mass of seminiferous tubules; and (3) FRA elicits a greater α-inhibin Ab titer than EML containing an oligodeoxynucleotide.     

The effects of bovine growth hormone and thyroxine on growth rate and carcass measurements in lambs

The effects of bovine growth hormone (GH) and thyroxine (T4) on growth and carcass characteristics were assessed in Dorset ram lambs. Lambs in four groups (n = 10/group) were treated for 30 d as follows: controls, 3.33 mg (6 IU) GH/d (s.c.); 5-mg T4 implant (s.c.) on d 1 and a 10-mg T4 implant 21 d later; GH + T4. Blood samples were collected at 3-d intervals for analysis of GH, T4, triiodothyronine, somatomedin-C and testosterone concentrations. Six lambs/group were slaughtered for carcass measurements and composition. Daily GH injections increased (P less than .005) baseline plasma GH levels 10-fold, whereas plasma T4 concentrations were increased 10% (P less than .10) by the implants. Somatomedin-C increased with time in all groups, but the increments from d 0 to d 30 were higher (P less than .05) with GH treatment. Average daily gain (mean = 352 g/d), feed consumption and feed to gain ratio were not affected (P greater than .1) by GH or T4 treatment in ram lambs. Hot carcass weight and dressing percentage were increased (P less than .05) by T4. Growth hormone increased carcass protein content (P less than .005) and muscle weights while reducing carcass fat (P less than .05). Carcass composition was not altered by T4 alone, and the T4 x GH interaction was not significant; however, the combination of T4 and GH resulted in greater muscle and protein weight than did either hormone alone or no hormone administration. There were no differences in bone length or in the metacarpal growth plate width among groups. The beneficial effects of GH on carcass composition were not further enhanced by administration of thyroxine.     

Effects of growth rate and compensatory growth on body composition in lambs

Fifty lambs were used in a comparative slaughter experiment to determine the effects of growth rates and compensatory growth on body composition. The study consisted of a growing and a finishing phase. During the growing phase, lambs (20 to 30 kg) were fed three different concentrate levels (30, 50 or 70%) to gain at three different rates (slow, medium and rapid). The finishing phase was evaluated in two periods (early, 30 to 38 kg; late, 38 to 45 kg). All lambs received 70% concentrate diets during the finishing phase. Groups of five lambs were sacrificed at 20, 30, 38 and 45 kg fleece-free weights for whole-body chemical analysis. At 30 kg live weight, lambs on a rapid growth diet were the fattest (P less than .01) and contained the least protein (P less than .05) in their empty bodies. The slower the lambs gained during the growing phase, the greater (P less than .05) was the response in rate of gain and feed efficiency during both periods of the finishing phase. Compensatory growth occurred in two stages; a greater proportion of protein gain was made early while a greater proportion of the fat gain was made during the late period of the finishing phase.     

Growth hormone, insulin, prolactin and glucose levels in ewe and ram lambs during normal and compensatory growth

Two trials were conducted to determine the effect of compensatory growth on plasma glucose and serum growth hormone (GH), prolactin (PRL) and insulin concentrations in lambs. The trials consisted of a normal growth (NG) period (4 to 7 mo of age), a restricted feed/weight loss period and a compensatory growth (CG) period. The lambs in Trial 1 were 13 mo of age and in Trial 2, 11 mo of age at the start of the respective CG periods. Compensatory growth rate was 61 to 67% greater than NG rate in Trial 1 and 2, respectively. Twenty-four hour blood collections were performed during NG and CG in each trial. Normal growth blood collection for Trial 1 was performed in April (ram, n = 7; ewe, n = 6) and the CG blood collection in November (ram, n = 6; ewe, n = 6) while for Trial 2 blood collection dates were November (ram, n = 6; ewe n = 6) and March (ram, n = 4; ewe, n = 5). Trial 1 ram lambs had lower plasma glucose concentrations during CG than during NG while plasma glucose concentration was not altered in ewe lambs. Type of growth had no effect on plasma glucose in Trial 2. There was a type of growth by sex interaction for insulin in both Trial 1 and Trial 2. Insulin concentration decreased during CG in ram lambs but remained unchanged (Trial 1) or increased in ewe lambs (Trial 2) during CG. The effect of CG on PRL concentration in Trial 1 was confounded by photoperiod and the only effect in Trial 2 was a small decrease in the amplitude of PRL peaks during CG. The overall mean GH concentration (GHmn) was increased (P less than 0.01) two fold during CG in Trial 1. This effect was also seen in Trial 2 but the increase was sex dependent (P less than 0.005) with the effect of CG on GHmn in ram lambs being six times that seen in ewe lambs. The GH profile characteristics responsible for the increase in GHmn during CG differed between sexes and trials.     

蛋白水平及Lys/Met对早期断奶藏羔羊生长发育的影响

旨在研究藏羔羊早期断奶料蛋白水平及Lys/Met配比对其生长发育的影响。试验选取(55±2)日龄断奶、体重(10.85±0.65)kg藏羔羊98只,随机分为7组,每组14只,公母各半。分别饲喂不同蛋白水平和Lys/Met配比的藏羔羊早期断奶料,试验期20 d。结果:藏羔羊早期断奶料蛋白水平在15%～21%,随断奶料蛋白水平的提高,采食量和日增重增加、腹泻率降低、血清蛋白含量增加;18%蛋白,Lys/Met配比为3.1∶1的日粮最为合理,可以替代21%高蛋白断奶料;在15%蛋白水平的日粮,Lys/Met配比为3.1∶1最为合理,可以替代18%中蛋白断奶料。结果提示:早期断奶料营养水平影响藏羔羊早期的生长发育和血清指标,本试验推荐的早期断奶藏羔羊断奶料适宜的配比为18%蛋白水平和Lys/Met配比为3.1∶1。     

生长抑素基因工程苗和半胱胺对放牧羔羊增重效果的影响

选择 4～ 5月龄体重相近的杂种羔羊 90只 ,随机分成对照、添加半胱胺 (CS87)和生长抑素 (SS)苗免疫共 3组 ,每组公母各半。CS87按每千克体重 80mg每周添加 1次 ,持续 6周 ;SS苗按 1mL/只一次性免疫 ,9周结束。结果显示 ,添加CS87组 0～ 2 1d增重提高 1 6 46 % (P <0 0 5) ,2 1～ 42d增重提高 1 5 95 % (P <0 0 5) ;SS苗免疫组在 2 1～ 42d提高 5 86 % (P >0 0 5) ,42～ 63d提高 1 7 5 % (P <0 0 5) ,母羊效果优于公羊。     

酵母硒和酵母铬对羔羊生长性能、胴体品质、血液激素及代谢产物的影响

文章旨在研究日粮添加酵母硒和酵母铬对羔羊生长性能、胴体品质、血液相关指标的影响。试验选择平均体重为(26±4.75)kg的呼伦贝尔羔羊60只,随机分为6组,每组10只,每只羊作为1个重复。日粮采用2×3多因子设计,其中2个酵母硒水平(0和0.3 mg/kg,以硒计)和3个酵母铬水平(0、0.2和0.3 mg/kg,以铬计),试验共进行12周。随着酵母铬添加水平的升高,羔羊采食量显著线性升高(P <0.05)。酵母硒组羔羊末重、总增重和日增重随酵母铬添加水平的升高显著线性升高(P <0.05)。无酵母硒组随酵母铬添加水平的升高,血浆葡萄糖水平显著线性升高(P <0.05)。血浆甘油三酯和胰岛素水平随酵母铬添加水平的升高表现为显著二次曲线效应(P <0.05)。酵母硒组血浆甘油三酯和胰岛素水平随酵母铬添加水平的升高显著线性升高(P <0.05),而血浆尿酸含量显著线性下降(P <0.05)。无酵母硒组随酵母铬添加水平的升高,眼肌面积和胴体蛋白沉积量显著线性升高(P <0.05)。酵母硒组添加酵母铬对羔羊胴体相关指标均具有显著影响(P <0.05),其中屠体重、热胴体和冷胴体重、眼肌面积和能量沉积量随酵母铬添加水平表现为显著二次曲线效应(P <0.05),而脂肪含量和脂肪沉积量显著线性降低(P <0.05)。综上所述,硒酵母与铬酵母联合使用可以提高羔羊生产性能和改善胴体组成,改善血液激素和代谢产物,从而提高羊肉品质。