Effect of exogenous thyrotropin-releasing hormone (TRH) administration on plasma levels of triiodothyronine (T3), thyroxine (T4) and growth hormone (GH) in chronically catheterized suckling piglets.

The purpose of the present study was to determine experimental conditions to stimulate secretion of thyroid hormones (T₃ and T₄) with thyrotropin-releasing hormone (TRH) injections in suckling piglets during the first weeks of postnatal life. Three consecutive experiments were conducted. Four 10–20 d old piglets were i.m. injected with 0, 20, 100, 500 μg (experiment 1) or 0, 4, 20, 100 μg TRH/kg BW (experiment 2) according to a 4 × 4 latin square design involving different litters in each experiment. Blood samples were taken −15, −1, 15, 30, 45, 60, 90, 120 180 and 300 min after TRH injection in experiment 1, and −.25, −.08, .25, .5, 1, 2, 4, 6, 8, 12, 24, 30, 36, 48, 60 and 72 hr after TRH injection in experiment 2. T₃ and T₄ levels were significantly (P<.01) increased as soon as 30 and 45 min after TRH injection, respectively. Maximal levels of T₃ and T₄ were obtained 2 and 4 hr after the injection of 100 μg TRH. T₃ and T₄ returned to basal levels within 6 and 8 hr post injection, respectively. Plasma pGH levels were significantly (P<.001) increased 15 min after TRH injection in piglets injected with 500 μg. In experiment 3, 100 μg TRH/kg BW were injected i.m. either daily or every other day from .0 to 23 days of age. Results showed that T₄ response to TRH did not decrease after repeated injections. These results indicate that daily i.m. injections of 100 μg TRH/kg BW can be used to increase thyroid hormone levels for at least 13 d in the young suckling piglet.     

Relationships between the thyroid and somatotropic axes in steers I: Effects of propylthiouracil-induced hypothyroidism on growth hormone, thyroid stimulating hormone and insulin-like growth factor I

The effects of propylthiouracil (PTU)-induced thyroid hormone imbalance on GH, TSH and IGF-I status in cattle were examined. In the first study, four crossbred steers (avg wt 350 kg) were fed a diet dressed with PTU (0, 1, 2 or 4 mg/kg/d BW) in a Latin square design with four 35-d periods. On day 29 in each period, steers were challenged with an intrajugular bolus of thyrotropin releasing hormone (TRH, 1.0 μg/kg). Blood samples were obtained to assess the change in plasma GH and TSH as affected by PTU. Plasma IGF-I was measured from blood samples obtained before and after (every 6 hr for 24 hr) intramuscular injection of bovine GH (0.1 mg/kg, day 31). Doses of 1 and 2 mg/kg PTU increased plasma T₄ (P<.01). At 4 mg/kg, PTU depressed T₄ concentrations to 30% of control (P<.01). Plasma T₃ linearly decreased with increasing doses of PTU (P<.01). Plasma TSH increased when PTU was fed at 4 mg/kg (P<.05) while the TSH response to TRH declined with increasing PTU (P<.02). Neither basal nor TRH-stimulated plasma concentration of GH was affected by PTU; the IGF-I response to GH tended to increase at the 1 and 2 mg/kg PTU (P<.01). In a second study 24 crossbred steers were fed PTU (1.5 mg/kg) for 119 d in a 2 × 2 factorial design with implantation of the steroid growth effector, Synovex-S (200 mg progesterone + 20 mg estradiol), as the other main effect. Basal plasma GH and IGF-I were not affected by PTU treatment. Synovex increased plasma concentration (P<.01) of IGF-I without an effect on plasma GH. The data suggest that mild changes in thyroid status associated with PTU affects regulation of T₃, T₄ and TSH more than GH or IGF-I in steers.     

The drop in plasma thyrotropin concentrations in fasted chickens is caused by an action at the level of the hypothalamus: role of corticosterone

Fasting has severe effects on thyroid metabolism in the chicken: plasma thyroxine (T₄) concentrations increase, whereas 3′,5,3-triiodothyronine (T₃) concentrations decrease. In the present report we studied the effect of fasting at the level of: 1) the pituitary (plasma thyrotropin (TSH) concentrations; the sensitivity of thyrotrophs to corticotropin-releasing hormone (CRH) and TSH-releasing hormone (TRH)); and 2) the hypothalamus (TRH content). A regulatory role of corticosterone is discussed. One day of fasting resulted in a drop in plasma TSH concentrations. Fed and nonfed animals were treated with ovine CRH (oCRH) or TRH. The sensitivity of thyrotrophs to the respective hypothalamic hormones was increased when animals were subjected to a 1-d period of fasting. A 75% (TRH) and 50% (oCRH) increase in plasma TSH was recorded in fasted animals, whereas both secretagogues did not evoke any response in their fed counterparts. The drop in plasma TSH cannot, therefore, be attributed to a loss in sensitivity of thyrotrophs to hypothalamic stimulatory control. In an identical experiment, plasma TSH concentrations decreased, whereas hypothalamic TRH content was higher in fasted animals, suggesting a decreased hypothalamic TRH release toward the pituitary. In both fasting experiments, plasma corticosterone concentrations were increased after 1 d of fasting. Because an iv injection of corticosterone-elevated hypothalamic TRH contents and decreased plasma TSH concentrations, a corticosterone-induced TSH decrease during fasting is suggested through an action at the level of the hypothalamus.     

Extrathyroidal thyroxine-5′-monodeiodinase activity in cattle

The monodeiodination of thyroxine (T₄) to triiodothyronine (T₃) was studied in vitro using liver, kidney, and muscle obtained from two-year old Angus and Hereford steers. Tissues were homogenized in .1 M phosphate buffer-.25 M sucrose - 5 mM EDTA, pH 7.5, and centrifuged at 2000 × g for 30 min. Supernatants were incubated with T4 (1.3 μM) at 37 C and T₃ generated was measured by radioimmunoassay of an ethanol extract of the incubation mixture. The T₄ to T₃ conversion in Angus liver homogenate was dependent upon pH, temperature, duration of incubation (5–120 min), homogenate (.025–.20 g-eq tissue/ml), and substrate concentration (.32–6.43 μM T₄). The apparent K_m and V_max of the conversion were .64 μM T₄ and 1.87 ng T₃ generated/hr/mg protein, respectively. Mean T₄ to T₃ conversion in Angus liver and kidney was 1.37 and .22 ng T₃/hr/mg protein. The presence of 2 mM dithiothreitol (DTT), a sulfhydryl protective agent, significantly increased T₃ generation in liver and kidney (5.12 and 4.58 ng/hr/mg protein) and also revealed activity in muscle (05 ng/hr/mg protein). In liver and kidney from Hereford steers conversion activity was 2.89 and .48 in absence and 10.91 and 5.38 ng T₃/hr/mg protein in presence of DTT, respectively. These results demonstrate the presence of a very active enzymatic system responsible for the peripheral 5′-monodeiodination of T₄ to T₃ in cattle.     

Acute and chronic hormone and metabolite changes in lambs fed the beta-agonist, cimaterol

The objective of this study was to determine if acute and chronic changes in circulating metabolic hormone and metabolite concentrations are associated with β-agonist-induced nutrient repartitioning in young growing lambs. Two groups of 12 Dorset and Dorset-Finn cross ram lambs weighing 36 or 33 kg live weight were assigned to 3- or 6-week treatment intervals, respectively, to achieve similar slaughter weights. Six lambs within each treatment interval were fed ad libitum a complete mixed high-concentrate diet containing either 0 or 10 ppm cimaterol. During the first 12 hr of cimaterol administration plasma somatotropin (ST), thyroxine (T₄), and triiodothyronine (T₃) concentrations were not altered by treatment, but plasma insulin, glucose, non-esterified fatty acids (NEFA) and glycerol concentrations were elevated 2 hr after ingestion. These acute responses suggest direct stimulation of glycogenolysis and lipolysis by cimaterol, which is characteristic of β-adrenergic alteration of carbohydrate and lipid metabolism. Chronic administration of cimaterol significantly decreased insulin concentrations by 36% and 52% at 3 and 6 weeks, respectively, while glucose concentrations remained unchanged. Serum IGF-I concentrations were not significantly altered by cimaterol. T₄ levels were reduced 22.1% after 3 weeks of cimaterol treatment. Although plasma NEFA concentrations were chronically elevated 56% to 65% in lambs fed cimaterol, plasma glycerol concentrations remained at baseline levels. The relative changes in plasma NEFA and glycerol concentrations are consistent with a decreased rate of lipogenesis, rather than an increase in lipolysis.     

Response of young broiler chickens to chronic injection of recombinant-derived human insulin-like growth factor-I

The purpose of this study was to determine if exogenous insulin-like growth factor-I (IGF-I) would improve growth rate or body composition of young broiler chickens. Broiler cockerels were given a daily intramuscular (im) injection of sodium acetate buffer (buffer control), 100 or 200 μg recombinant-derived human IGF-I (rhIGF-I) per kg body weight from 11 to 24 days of age. Exogenous IGF-I did not affect the average daily gain, average daily feed consumption, or the gain-to-feed ratio of broiler chickens. Although daily injection of 200 μg/kg of rhIGF-I reduced (P<0.05) body ash content, there was no significant effect of IGF-I treatment on either body fat or protein content. Plasma GH levels were depressed (P<0.05) by chronic treatment with rhIGF-I. In contrast, plasma levels of T₃ and T₄ were not affected by rhIGF-I treatment. The half-life of rhIGF-I in plasma was determined at 25 days of age in naive control or chronically-injected chickens after a single intravenous dose of 50 μg rhIGF-I/kg. We found a single compartment, first-order disappearance pattern of rhIGF-I from chicken plasma. The half-life (t_1/2) of rhIGF-I in plasma was similar (t_1/2 = 32.5 min) for naive controls (injected once) or chronically-treated chickens which had received a daily injection of rhIGF-I (100 or 200 μg/kg) for 14 d. These data indicate that daily injection of IGF-I cannot be used to enhance growth performance or body composition of broiler chickens when given during the early growth period. The depression of plasma GH levels in rhIGF-I-injected chickens supports a negative-feedback role of IGF-I on pituitary GH secretion.     

The effect of insulin and relaxin upon mitosis (in vitro) in mammary tissue from pregnant and lactating pigs

The rate of cellular proliferation in the mammary glands of pigs during late gestation and lactation was assessed by measuring the incorporation of ³H-thymidine (T₁) into the DNA of mammary gland explants in vitro. The T₁ showed a linear response over the first 9 hr in vitro, and was not affected by the addition of 500 ng insulin/ml medium. From day 100 to parturition the T₁ rose, reached a peak at 2 d after parturition and declined during lactation to the lowest levels seen at day 21 of lactation.

The inclusion of 0–1000 ng relaxin/ml medium on T₁ at 24–72 hr in vitro had no effect in stimulating T₁ in mammary tissue explants taken from either pregnant or lactating pigs.     

Effect of daily injections of growth hormone-releasing factor and thyrotropin-releasing hormone on growth and endocrine parameters in chickens

The control of growth is a complex mechanism regulated by several metabolic hormones including growth hormone (GH) and thyroid hormones. In avian species, as well as in mammals, GH secretion is regulated by hypothalamic hypophysiotropic hormones. Since thyrotropin-releasing hormone (TRH) and growth hormone-releasing factor (GRF) are potent GH secretagogues in poultry, we were interested in determining the influence of daily intravenous administration of either peptide or both simultaneously on circulating GH and IGF-I concentrations and whether an improvement in growth rate or efficiency would be obtained.

Male broiler chicks were injected once daily for a period of 21 days with either GRF (10 μg/kg), TRH (1 μg/kg) or both GRF and TRH (10 and 1 μg/kg respectively) between four and seven weeks of age. On the last day of the experiment, following intravenous injection of TRH, GRF or a combination of GRF and TRH, plasma GH levels were significantly (P<.05) increased to a similar extent in control chicks and in those which had received daily peptide injections for the previous 21 days. Circulating GH levels between 10 and 90 min post-injection were significantly (P<.05) greater and more than additive than GH levels in chicks injected with both GRF and TRH when compared to those injected with either peptide alone. Mean plasma T₃ concentrations during that same time period were significantly elevated (P<.05) above saline-injected control chick levels in birds treated with TRH or GRF and TRH respectively, regardless of whether the chicks had received peptide injections for the previous 21 days. There was no evidence of pituitary refractoriness to chronic administration of either TRH or GRF injection in terms of growth or thyroid hormone secretion.

Despite the large elevation in GH concentration each day, growth rate, feed efficiency and circulating IGF-I concentrations were not enhanced. Thus the quantity or secretory pattern of GH secretion induced by TRH or GRF administration was not sufficient to increase plasma IGF-I concentration or growth.     

Perturbed metabolism and hormonal profiles in calves infected with Sarcocystis cruzi

Plasma concentrations of growth hormone (GH), thyroid stimulating hormone (TSH), insulin (IN), thyroxine (T₄), and triiodothyronine (T₃) in addition to metabolic parameters [N balance (NB), urinary 3-methylhistidine (TMH), urinary creatinine (CR), and urinary hydroxyproline (HP)] were measured in 4-mo-old Holstein steers divided equally among groups infected with Sarcocystis (I), noninfected ad libitum fed (C), and noninfected pair fed to I (PF) (7 steers per treatment). Effects of infection on these parameters beyond those attributable to altered dietary intake were determined using orthogonal contrasts (effect of intake, C vs I + PF; effect of infection, PF vs I). NB was higher in C than I and PF (P<.05) and lower in I than PF (P<.02). Hydroxyproline and CR were influenced by intake (P<.05) and HP excretion was reduced in association with infection (P<.05). Reduced intake was associated with lowered mean basal plasma concentrations of GH, IN, T₃ and T₄ (P<.05). Infection further reduced (P<.001) plasma T₃ concentration.

Triiodothyronine and T₄ responses following an intravenous bolus of thyrotropin releasing hormone (TRH) were measured. The magnitude of the responses in I and PF were lower than those observed in C (P<.05). Plasma T₃ responses were further reduced in association with infection (P<.05). Insulin responses to intravenous arginine infusion (ARG) were also low in association with reduced intake. Growth hormone responses to TRH or ARG were affected by the level of feed intake only. These data suggest that hormonal perturbations associated with the insult of infection further compromise metabolism and the direction of nutrient partitioning that would ordinarily be associated with developmental growth in young steers beyond those responses anticipated from solely the reduction of feed intake.     

The effect of dietary yeast and protected methionine on performance and trace minerals status of growing Awassi lambs

Eighteen growing Awassi lambs were used in this study to determine the effect of supplementing two levels of yeast and methionine (cyc-methionine) on the trace elements bioavailability, growth rate, and general performance. The lambs were divided to three groups. The dietary treatments were the control diet (C), control diet plus 2 g cyc-methionine/lamb/day (T₁) and control diet plus 4 g cyc-methionine/lamb/day (T₂).

Lambs fed 2 g/day of cyc-methionine (T₁) showed a significantly higher (P < 0.05) copper, zinc, and cobalt concentrations in liver and meat tissues, but not the same trend in kidney. No significant (P > 0.05) effect of time and time × treatment interaction on copper, zinc, cobalt, and manganese concentrations in blood serum, but cobalt and manganese concentration showed significant (P < 0.05) change by time. Moreover, a significantly (P < 0.05) higher total body gain, average daily gain, dressing percentage, and lower feed conversion were detected in lambs from T₁ compared with the control and T₂ groups.

Feeding 2 g of cyc-methionine to growing lambs increased the net profit by $6.017/lamb and only $3.52/lamb fed 4 g cyc-methionine/day when compared with the control group.

In conclusion, feeding growing Awassi lambs yeast and methionine in a form of cyc-methionine, with a low level of 2 g/day, improve the bioavailability of copper, zinc, and cobalt by growing lambs and their growth performance.     

Effect of progressive cachectic parasitism and growth hormone treatment on hepatic 5'-deiodinase activity in calves

Thyroid status is compromised in a variety of acute and chronic infections. Conversion of thyroxine (T₄) into the metabolically active hormone, triiodothyronine (T₃), is catalyzed by 5′-deiodinase (5′D) mainly in extrathyroidal tissues. The objective of this study was to examine the effect of protozoan parasitic infection (Sarcocystis cruzi) on hepatic 5′D (type I) activity and plasma concentrations of T₃ and T₄ in placebo- or bovine GH (bGH)-injected calves. Holstein bull calves (127.5±2.0 kg BW) were assigned to control (C, ad libitum fed), infected (I, 250,000 S. cruzi sporocysts per os, ad libitum fed), and pair-fed (PF, non-infected, fed to intake of I treatment) groups placebo-injected, and three similar groups injected daily with pituitary-derived bGH (USDA-B-1, 0.1 mg/kg, i.m.) designated as C_GH, I_GH and PF_GH. GH injections were initiated on day 20 post-infection (PI), 3–4 days prior to the onset of clinical signs of the acute phase response (APR), and were continued to day 56 PI at which time calves were euthanized for liver collection. Blood samples were collected on day 0, 28, and 55 PI. Alterations in nutritional intake did not affect type I 5′D in liver. Treatment with bGH increased (P<0.05) 5′D activity in C (24.6%) and PF (25.5%) but not in I calves. Compared to PF calves, infection with S. cruzi reduced 5′D activity 25% (P<0.05) and 47.8% (P<0.01) in placebo- and bGH-injected calves, respectively. Neither nutrition nor bGH treatment significantly affected plasma concentrations of T₄ and T₃ on day 28 and 55 PI. However, plasma thyroid hormones were reduced by infection. On day 28 PI, the average plasma concentrations of T₃ and T₄ were reduced in infected calves (I and I_GH) 36.4% (P<0.01) and 29.4% (P<0.05), respectively, compared to pair-fed calves (PF and PF_GH). On day 55 PI, plasma T₃ still remained lower (23.7%, P<0.01 versus PF) in infected calves while plasma T₄ returned to control values. The data suggest that parasitic infection in growing calves inhibits both thyroidal secretion and extrathyroidal T₄ to T₃ conversion during the APR. After recovery from the APR, thyroidal secretion returns to normal but basal and bGH-stimulated generation of T₃ in liver remains impaired.     

施肥和地膜覆盖对黄土高原旱地冬小麦籽粒品质和产量的影响

在黄土高原旱作农业区,地膜覆盖的广泛应用有效地解决了水分不足对冬小麦生产的制约,并使单位面积产量大幅度提高。如何调优品质已经成为该区域冬小麦生产中亟待解决的首要问题。本研究以不施任何肥料(T₀)为对照,选择常规化肥(T₁)、等量化肥+地膜覆盖(T₂)、等量化肥+有机肥(T₃)、高量化肥+地膜覆盖(T₄)、高量化肥+有机肥(T₅)5种不同的施肥(有机+无机)和覆盖模式,采用随机区组设计,研究不同“施肥+地膜覆盖”模式对旱地冬小麦籽粒加工品质、产量及其构成要素的影响,并分析产量与品质之间的相关性。结果表明,“施肥+地膜覆盖”组合显著影响小麦籽粒的加工品质和产量。比较对照T₀,不同“施肥+地膜覆盖”模式(T₁~T₅)显著提高籽粒产量(GY)、蛋白质(PC)、湿面筋含量(WA)和沉降值(SDS),增加面团吸水率(WG)、延伸性(EX)和淀粉糊化粘度,相反降低了面团稳定时间(ST)和拉伸阻力(RE)。两年平均产量依次为T₃>T₅>T₄>T₂>T₁ >T₀,T₁、T₂、T₃、T₄、T₅比T₀分别增加85.60%、90.99%、118.32%、102.30%和106.65%。增施有机肥(T₃、T₅)对籽粒产量和加工品质的改善优于地膜覆盖(T₂、T₄)。籽粒产量的提高是叶面积(LA)、千粒重(TGW)、穗长(SL)、穗粒数(SGN)协同增加的结果,加工品质的改变部分归因于蛋白质含量的变化。生育期降水量和分布影响谷物产量和品质。本研究结果证实,等量化肥+有机肥(T₃)不仅能达到地膜覆盖的增产效果,而且有利于小麦加工品质的改善,在降水量500 mm左右的黄土高原半干旱雨养农业区是更加持续、稳产、优质的冬小麦栽培模式。     

乳黄消口服液滋阴、扶正及祛邪功效的研究

为探讨乳黄消口服液滋阴、扶正及祛邪的功效,本研究观察乳黄消口服液对阴虚模型大鼠临床症状、饮食量、饮水量、体重、胸腺指数、脾脏指数、总三碘甲状腺原氨酸(T_3)、总甲状腺素(T_4)和促甲状腺激素(TSH)含量的影响,以及对小鼠巨噬细胞吞噬功能及对大肠杆菌、金黄色葡萄球菌、无乳链球菌和副乳房链球菌抑制作用的影响。结果显示,试验组大鼠在乳黄消口服液给药后精神正常,易抓取,但被毛光泽仍较差,有脱毛现象,大便正常。与模型组相比,试验组大鼠体重(P>0.05)、胸腺指数(P>0.05)、脾脏指数(P>0.05)、TSH含量(P<0.05)上升,饮食量(P<0.05)、T_3(P<0.05)、T_4含量(P>0.05)下降,但均与阴性对照组差异不显著(P>0.05);与模型组相比,试验组大鼠饮水量显著下降(P<0.05),但仍显著高于阴性对照组(P<0.05)。乳黄消口服液给药后高、中、低剂量组与阴性对照组间吞噬指数均差异显著(P<0.05),乳黄消口服液高、中剂量组与阴性对照组相比吞噬百分比差异显著(P<0.05);乳黄消口服液对大肠杆菌、金黄色葡萄球菌、无乳链球菌及副乳房链球菌的最小抑菌浓度(MIC)分别为12.50、1.56、0.20和0.39 mg/mL。综上所述,乳黄消口服液可改善大鼠阴虚临床症状,增强巨噬细胞吞噬功能,抑制奶牛乳房炎主要病原菌,具滋阴、扶正和祛邪的功效,可用于奶牛乳房炎的治疗。     

Concentrations of Prolactin, LH, Testosterone, TSH and Thyroxine in Normospermic Dogs of Different Breeds

Concentrations of prolactin (PRL), LH, testosterone (T), TSH and thyroxine (T₄) were determined before and at 20, 120 and 180 min after a single iv injection of thyrotropin-releasing hormone (TRH) in eight Beagles, eight Fox Terriers, six Labrador Retrievers and five Great Danes that were normospermic. Mean basal PRL concentrations were lower in the Fox Terriers compared with the Great Danes (p < 0.05). Mean LH concentrations were higher in the Fox Terriers than in the Beagles, and T was lower in the Fox Terriers at some times but not others (p < 0.05). Thyroid Stimulating Hormone (TSH) concentrations did not differ among breeds, while mean basal T₄ values were lower in Fox Terriers compared with Labrador Retrievers and Great Danes (p < 0.05). Stimulation of T₄ secretion 120 and 180 min after iv TRH injection was most pronounced in the Beagles and less in the Fox Terriers (p < 0.05). The results of the present study indicate that potential breed differences in circulating concentrations of PRL, LH, T, TSH and T₄ in male dogs with apparently normal fertility can be encountered, but further studies are needed to determine whether the observed differences are typical features of these breeds, reflect subsets of dogs within breeds, or are in part because of possible uncontrolled parameters such as sample timing, ambient photoperiod, housing conditions or diet.     

荒漠灌区苜蓿后茬轮作不同作物对土壤细菌群落的影响

为阐明荒漠灌区苜蓿（Medicago sativa）后茬轮作不同作物对土壤细菌群落的影响,本研究以6年生苜蓿地为对照（CK）,以5年生苜蓿地翻耕灭茬分别种植1年小麦（Triticum aestivum）（T₁）、油菜（Brassica chinensis）（T₂）、葵花（Helianthus annuus）（T₃）、玉米（Zea mays）（T₄）为处理,采用高通量测序技术,分析不同处理下土壤细菌群落的变化特征。结果表明,T₁,T₂微生物量碳含量显著大于CK,T₄微生物量氮含量显著高于CK（P<0.05）;T₃,T₄土壤呼吸显著大于CK（P<0.05）;T₁,T₂,T₃,T₄脲酶、碱性磷酸酶、过氧化氢酶、蔗糖酶活性分别是CK的1.44,1.13,1.36,1.54倍,1.53,7.78,4.25,7.28倍,1.09,1.28,1.14,1.06倍,1.11,1.38,1.14,1.74倍;与CK相比,轮茬后变形菌门、放线菌门、芽单胞菌门相对丰富呈降低、而酸杆菌门相对丰富呈增加趋势,这4个菌门为不同处理的优势菌门,占所有菌门的82.67%;T₁,T₂土壤细菌群落丰富度指数（Chao1和ACE）均显著高于CK（P<0.05）。综上,荒漠灌区轮茬较苜蓿连作更有助于提高土壤酶活性,稳定细菌群落结构,提高土地生产力。     

Total and free iodothyronine levels of growing Thoroughbred foals: Effects of weaning and gender

The aim of this study was investigate the effect of growing associated with different gender on circulating total and free iodothyronine concentrations during the first 13 mo of age in foals. In addition, we investigated the evolution of circulating concentrations of thyroid hormones during the first 3 d of weaning. Blood was collected from 13 clinically healthy Thoroughbred foals every month. All foals were weaned at the 4 mo and blood samples were taken also at 24, 48 and 72 h after weaning. The results obtained showed growing effects for tri-iodothyronine (T₃), thyroxine (T₄), free tri-iodothyronine (fT₃) and free thyroxine (fT₄) values (P < .001).

Serum T₃ concentrations averaged respectively 2.89 and 0.29 nmol/L at 7 and 9 mo. Serum T₄ concentrations averaged respectively 100.17 and 21.77 nmol/L at 1 and at 10 mo. Serum fT₃ concentrations averaged respectively 6.96 and 1.50 pmol/L at 1 and 4 mo. Serum fT₄ concentrations averaged respectively 31.40 and 4.93 pmol/L at 1 and 9 mo. Significant correlations between T₃, T₄, fT₃ and fT₄ with body weight (BW) and between T₃, T₄ and fT₄ with age were observed.

Weaning effects (P < .001) were shown for T₃ and fT₄ levels. No differences (P > .05) in T₄ and fT₃ levels were observed over the 3-day period. Gender effects (P < .001) were shown for T₃, T₄, fT₃, and fT₄ levels. Significant correlations between T₄ and fT₄ with BW and age were observed in colts and fillies. T₃ concentrations were correlated with age only in colts and fT₃ with BW only in colts. The results obtained seem to lend support to the recognized effects of growing and weaning in modulating the thyroid function of Thoroughbred foals. In fact, significant and differentiated effects of growing and weaning on total and free iodothyronine levels have been demonstrated.     

Dietary fatty acids modulate hormone repsonses in lactating cows: Mechanistic role for 5′-deiodinase activity in tissue

Supplemental dietary fat provides excess fatty acids (FA), which can alter circulating concentrations of several hormones. To test the effects of fatty acid isomer type and possible sites of regulation, we abomasally infused fat mixtures high in cis-C_18:1 FA (iTRS) or no infusion (NI) and performed intravenous arginine (ARG) and intramuscular thyrotropin-releasing hormone (TRH) challenges. The experimental design was a replicated 3 × 3 Latin square. Challenges were conducted on Days 10 (ARG) and 12 (TRH) after initiation of fat infusion on each of three 4-wk experimental periods. Plasma concentrations of IGF-I were lower (P < 0.01) when cows received iCIS or iTRS compared with NI. Plasma insulin concentrations increased with ARG but responses were not affected by FA. Plasma growth hormone (GH) was unchanged after ARG. Peak plasma GH and thyroid-stimulating hormone (TSH) responses to TRH were blunted (P < 0.05 and P < 0.1, respectively), whereas thyroxine (T₄) and triiodothyronine (T3) responses were augmented post-TRH (P < 0.01) when cows received either FA isomer. Prolactin responses to TRH were not different between infusion treatments, although basal plasma concentrations before TRH were higher in cows infused with iTRS (P < 0.05). To focus on fat regulation of the thyroid axis, we tested directly in vitro the ability of fatty acids dissolved with sodium taurocholate to affect Type-I 5'-deiodinase (5'D) activity in bovine liver homogenates. Homogenate 5'D was not affected by C_2:0---C10:0 fatty acids, but decreased linearly (P < 0.01) with increasing concentrations of C_12:0---C_16:0 and C_18:1 isomers. CisC_18:1 decreased 5′D more than the trans-isomer (P < 0.01), the difference was only apparent at concentrations greater than 0.25 mM. The data suggest that various aspects of pituitary hormone regulation are differentially affected by FA composition. Fatty acid infusion may accentuate end organ responses in the thyroid axis and decrease IGF-I in the somatotropic axis. The data also suggest that FA isomer may alter patterns of extrathyroidal generation of thyroid hormones via direct influences on 5′D.     

体外产气法评价生薯条加工副产品-稻草混贮与全株玉米青贮组合效应的研究

旨在探究生薯条加工副产品-稻草混贮（以下简称“薯稻混贮”）与全株玉米青贮间的组合效应。“薯稻混贮”是按照1∶2混合（混贮后的干物质含量为35%）、添加青贮添加剂、用搅拌机混匀、打捆裹包机裹包、发酵60 d制成。根据“薯稻混贮”与全株玉米青贮的不同比例分为7个组合，分别为T₀组（0∶100）、T₂₀组（20∶80）、T₄₀组（40∶60）、T₅₀组（50∶50）、T₆₀组（60∶40）、T₈₀组（80∶20）、T₁₀₀组（100∶0），每个组合3个重复。通过体外产气法，测定各组合发酵48 h干物质降解率（DMD）、pH、氨态氮（NH₃-N）浓度、微生物蛋白（MCP）产量以及挥发性脂肪酸（VFA）浓度等指标，测定各组合在发酵2、4、6、8、10、12、24、36和48 h的产气量（GP）。并计算每个单项组合效应指数（SFAEI）及综合效应指数（MFAEI）。结果表明：1）GP和DMD随“薯稻混贮”比例增加显著或极显著降低（P<0.05或P<0.01）。SFAEI中T₅₀和T₈₀组的GP和DMD最低，GP和DMD最高值均出现在T₂₀组。2）不同组合发酵后的pH值为6.46~6.59，其中T₈₀组pH最高，显著或极显著高于除T₁₀₀组外的其他组别（P<0.05或P<0.01），SFAEI在T₈₀组最高。3）各组合间NH₃-N浓度、MCP产量无显著差异（P>0.05），但均以T₄₀组最高，而SFAEI分别以T₄₀和T₈₀组最高。4）乙酸、丙酸、戊酸和TVFA浓度均以T₀组最高，T₁₀₀组最低，且两组间差异极显著（P<0.01）；丁酸也以T₀组浓度最高，但以T₈₀组浓度最低。SFAEI指标中，乙、丙、丁酸分别以T₈₀、T₂₀和T₆₀组最高。通过MFAEI指数评定得出，两种饲料组合均产生正组合效应，其中T₄₀组（40∶60）最优，其次是T₅₀组（50∶50）。     

Relationship of thyroid status to growth hormone and insulin-like growth factor-I (IGF-I) in plasma and IGF-I mRNA in liver and skeletal muscle of cattle

Steers were made hyperthyroid or hypothyroid to study the effects of physiological alterations in thyroid hormone status on plasma growth hormone (GH) profiles, plasma insulin-like growth factor-I (IGF-I) concentrations, and relative abundance of IGF-I mRNA in skeletal muscle and liver. Eighteen yearling crossbred steers (360 to 420 kg) were randomly allotted to hyperthyroid (subcutaneous injection 0.6 μg/kg BW L-thyroxine for 10 d), hypothyroid (oral thiouracil; 0.25% diet plus 12.5 g capsule/d for 17 d), or control (subcutaneous injection 0.9% NaCl) treatment groups. Blood samples were taken for measurement of GH, IGF-I, thyroxine (T₄) and triiodothyronine (T₃) by RIA. Samples of liver and skeletal muscle were taken by biopsy for measurement of IGF-I mRNA by solution hybridization. Steers receiving thiouracil had 57 and 53% (P<.05) lower T₄ and T₃, respectively, than control steers (84.1 and 1.7 ng/ml). The hyperthyroid steers had 228 and 65% greater (P<.05) T₄ and T₃ than control steers. Neither increased nor decreased thyroid status had any significant effects on plasma GH profiles, liver IGF-I mRNA, or plasma concentration of IGF-I. There was no effect of thyroid hormone alteration on skeletal muscle IGF-I mRNA concentrations. The results of this study suggest that short-term changes in thyroid status of cattle had no major impact on the GH-IGF-I axis or skeletal muscle IGF-I mRNA.     

Effects of dietary T3 on growth parameters and hormone levels in normal and sex-linked dwarf chickens

Tri-iodothyronine (T₃) has been administered in the diet, from day of hatch until 8 weeks of age, to sex-linked dwarf and normal chicks of both sexes from a brown-egg slow-growing strain. Feed was supplemented with either 0.1 ppm or 0.5 ppm T₃. A significant genotype by treatment interaction was observed on body weight: the effect of T₃ in males was significantly positive for dwarfs and null for normals, the effect in females was null for dwarfs and significantly negative for normals. Feed efficiency was rather decreased by the treatment in both genotypes. Abdominal fatness was decreased in a dose-dependent manner in both genotypes, while rectal temperature was raised in dwarf chicks only. Plasma T₃ was raised to normal levels in dwarfs receiving 0.1 ppm exogenous T₃, while the 0.5 ppm dose yielded hyperthyroid levels. Plasma GH levels were decreased in a dose-dependent manner by the T₃ treatment, the effect being larger in dwarfs. Surprisingly, plasma IGF-I was unchanged in spite of the GH decrease, whatever the genotype or the sex. It was concluded that exogenous T₃ alone can have a stimulatory effect on growth in dwarfs but can not fully restore a normal growth rate. Both T₃ and IGF-I are important for a normal growth and the relationships between T₃ and IGF-I production should be further investigated in order to better understand the physiological modifications due to the sex-linked dwarf gene.