Immobilization (restraint) stress in desert sheep and goats, and the influence of pretreatment with xylazine or sodium betaine thereon

Some behavioral, clinical, biochemical and haematological parameters were studied in Desert (Najdi) sheep and goats subjected to the acute and unavoidable stressful stimuli of immobilization. The effect of pretreatment with xylazine (n = 6) or sodium betaine (n = 6) on the responses of these animals has also been investigated. The immobilization stress resulted in increased vocalization and in variable and statistically insignificant increases in heart pulse and respiratory rates. In the two species, immobilization stress significantly elevated the plasma concentration of cortisol (from about 35.2 to about 83.8 mmol/L) and glucose (from 3.1 to 4.6 mmol/L), and decreased the concentration of magnesium (from 0.81 to 0.65 mmol/L). The endogenous thiocyanate concentration was unaffected. The immobilization stress also insignificantly decreased the haematocrit (PCV), and the number of lymphocytes, and increased the concentration of haemoglobin. Pretreatment of sheep and goats with xylazine at a dose of 0.01 mg/kg, via the intravenous route significantly alleviated the effects induced by the stressful stimulus. Pretreatment of the two species with sodium betaine (10 mg/kg/day for 3 days), however, produced variable and insignificant effects. There were no significant differences between sheep and goats in the responses to the immobilization stress, except in vocalization, which was more pronounced in sheep than in goats.     

Stress associated with road transportation in desert sheep and goats, and the effect of pretreatment with xylazine or sodium betaine

The present work investigates some clinical, endocrinological, biochemical and haematological variables in desert sheep and goats stressed in the course of individual road transportation, and the influence thereon of pretreatment with an established anti-stressor drug, xylazine HCl, and a test compound, sodium betaine (trimethylglycine). Road transportation for 2h resulted in variable and statistically insignificant increases in heart, pulse and respiratory rates in both control and experimental animals. Transportation stress significantly increased the concentrations of plasma cortisol, and glucose, and decreased that of magnesium. The endogenous thiocyanate concentration was unaffected. The stress also insignificantly decreased the haematocrit (PCV), and the number of lymphocytes, and increased the concentration of haemoglobin. Pretreatment of sheep and goats with xylazine at a single dose of 0.01 mg/kg by the intravenous route significantly ameliorated the effects induced by the stressful stimulus. The effects of pretreatment of the two species with sodium betaine (10 mg/kg) produced variable and insignificant effects.     

Tyrosine Ameliorates Some of the Clinical,Biochemical and Haematological Effects of Acute Stress Associated with Transportation of Desert Sheep

We studied some clinical, biochemical and haematological variables in Desert (Najdi) sheep acutely stressed in the course of individual road transportation, and the influence thereon of pretreatment with tyrosine. Transportation for 30 min resulted in variable but statistically insignificant increases in heart, pulse and respiratory rates. It also caused significant increases in the plasma concentration of cortisol (from 43.5 to 101.7 mmol/L) and glucose (from 3.1 to 4.5 mmol/L), and a decrease in that of magnesium (from 0.85 to 0.72 mmol/L). The endogenous thiocyanate level was unaffected. The transportation stress also decreased the haematocrit (PCV) and the number of lymphocytes, and increased the concentration of haemoglobin. Pretreatment of sheep with tyrosine at a dose of 100 mg/kg by the intravenous route significantly ameliorated the stress-induced clinical, biochemical and haematological changes. The treatment caused no overt adverse effects.     

Analgesic and systemic effects of ketamine,xylazine, and lidocaine after subarachnoid administration in goats

OBJECTIVE: To determine the effects of ketamine hydrochloride, xylazine hydrochloride, and lidocaine hydrochloride after subarachnoid administration in goats. ANIMALS: 6 healthy goats. PROCEDURE: In each goat, ketamine (3 mg/kg), xylazine (0.1 mg/kg), lidocaine (2.5 mg/kg), and saline (0.9% NaCI) solution were injected into the subarachnoid space between the last lumbar vertebra and first sacral vertebra (time 0). Analgesic, ataxic, sedative, cardiovascular, and respiratory effects and rectal temperature were evaluated before (baseline) and 2, 5, 10, 15, and 30 minutes after administration and at 30-minute intervals thereafter as needed. RESULTS: Administration of anesthetics induced varying degrees of analgesia. Onset of the analgesic effect was more delayed for xylazine (mean +/- SD, 9.5 +/- 2.6 minutes) than for ketamine (6.7 +/- 2.6 minutes) or lidocaine (3.5 +/- 1.2 minutes). Duration of analgesia induced by xylazine (88.3 +/- 15 minutes) was twice as long as the duration of analgesia induced by ketamine (48.8 +/- 13.5 minutes) but similar to that induced by lidocaine (66.5 +/- 31 minutes). Xylazine induced bradycardia, whereas ketamine caused a nonsignificant increase in heart rate. Xylazine induced a reduction in arterial pressure, whereas ketamine or lidocaine did not affect arterial pressure. CONCLUSIONS AND CLINICAL RELEVANCE: Subarachnoid administration of xylazine in goats resulted in longer duration of analgesia of the tail, perineum, hind limbs, flanks, and caudodorsal rib areas than administration of ketamine or lidocaine. However, xylazine caused bradycardia and respiratory depression. Additional studies are needed to determine whether the analgesia would be sufficient to allow clinicians to perform surgical procedures.     

热应激状态下羊的体温调节

热应激是由高温环境所引起的,在炎热的气候条件下,当环境有效温度超过羊的等热区上限温度时,羊就会出现热应激。由热应激引发的不良影响广泛存在,不仅严重影响羊的生存质量,而且导致羊体温升高、生长性能降低、免疫力减弱以及肉品质下降。本文综述了导致羊产生热应激的因素以及热应激条件下的体温调节机制。在热应激的情况下,机体通过吸收环境辐射热和累积机体代谢产热,使机体获得很高的热负荷,超过了机体的散热能力。暴露在高温环境中的羊只,可通过增加机体散热消除过多的热负荷。当空气温湿度发生变化时,作为恒温动物,绵羊和山羊可以通过调整自身的产热量、采食量、饮水量、呼吸频率和行为等方式,来维持机体产热和散热的平衡。总之,羊可以利用复杂有效的散热机制维持体温平衡,适应高温环境。     

Comparison of xylazine and lidocaine effects for analgesia and cardiopulmonary functions following lumbosacral epidural injection in goats

The present study was carried out in order to compare the effects of xylazine and lidocaine on analgesia and cardiopulmonary parameters following epidural injection in goats. Twelve healthy Small East African goats of both sexes (mean +/- SD; 15.6 +/- 1.9 kg body weight) were used. The goats were randomly assigned to two groups of five and seven animals. The first group (n = 5) was given 2% lidocaine-HCl at 4400 micrograms/kg body weight. The second group (n = 7) was administered 2% xylazine-HCl at 150 micrograms/kg body weight. All drugs were diluted in 5 ml of sterile water and were injected epidurally through the lumbosacral interspace with the injection taking over 20 s. Both drugs induced analgesia within 5 min. Signs of sedation, cardiopulmonary changes and lateral recumbency developed within 5-7 min after administration of epidural xylazine. Tail flaccidity and hind limb paralysis developed 3 min after epidural administration of lidocaine. The time from recumbency to regaining normal stance was 60 and 158 min for xylazine- and lidocaine-treated animals respectively. Xylazine induced adequate analgesia of the flank and perineum, which extended to the head and forelimbs. In contrast, lidocaine induced adequate bilateral flank and perineal analgesia extending up to the third thoracic vertebra. For both drugs, analgesia of the flank and perineum persisted for the entire 180-min observational period. Epidural injection of xylazine and lidocaine caused variable depression effects on the cardiopulmonary values but was not so low as to cause concern. It is concluded that lumbosacral epidural injection of xylazine at 150 micrograms/kg body weight in 5 ml of water for injection offers the most desirable sedation and analgesia of the flank and perineum. The longer duration of analgesia may be useful for postoperative analgesia and relief of continuous straining in goats.     

N-ethylmaliemide (NEM)-stimulated passive potassium transport in camel erythrocytes: inhibitory effects of age, furosemide, sodium fluoride and okadaic acid

The effects of age, and the inhibitory effects of furosemide, sodium fluoride, and okadaic acid on N-ethylmaliemide (NEM)-stimulated, ouabain-resistant potassium influx were investigated in camel erythrocytes. The NEM-stimulated influx which declined with the age of erythrocytes, was partially inhibited by 2 mmol/L furosemide, 20 mmol/L sodium fluoride, and completely inhibited by 150 nM okadaic acid. The effect of all chemical inhibitors was significant if added before the NEM pretreatment.     

Abortion in small ruminants in Switzerland: investigations during two lambing seasons (1996-1998) with special regard to chlamydial abortions

Abortion cases of 144 goats und 86 sheep were investigated etiologically during 2 lambing seasons (1996/1997, 1997/1998). Macroscopic inspection of fetus and placenta was completed by histopathology and bacteriological isolation of agents. In addition, immunohistologically the following antigens were labeled in formalin-fixed and paraffin-embedded tissue sections: Toxoplasma gondii, Neospora caninum, Chlamydophila abortus (formerly Chlamydia psittaci serovar 1) and Border Disease Virus. From farms with abortions caused by Chlamydophila abortus specific data were recorded. In 75% of abortion cases in sheep and in 59% of cases in goats an etiologic diagnosis could be substantiated. Chlamydophila abortus is the most commonly involved agent in the etiology of caprine and ovine abortion (sheep 39%, goats 23%), followed by Toxoplasma gondii (sheep 19%, goats 15%) and Coxiella burnetti (sheep 1%, goats 10%). All other agents are of minor importance. An infectious cause of abortion based on histopathologic findings without isolation of agents was observed in sheep (10%) and goats (21%). Malformation occurred in sheep (2%) and goats (3%) and lesions suggestive for Vitamin E/Selenium deficiency were seen in goats only (2%).     

Efficacy of intra-muscular analgesics for acute pain in sheep

The analgesic action of intramuscularly injected buprenorphine, methadone, flunixin meglumine and xylazine was examined in sheep, using algesimetry based on a leg withdrawal response to an electrical stimulus. No analgesic response was detected for buprenorphine, methadone or flunixin meglumine. Only the αaL2-adrenoceptor agonist, xylazine, produced an analgesic response. The current required to elicit a response increased by 170% (4.5±0.43 mA to 12.23±1.14 mA; mean±SE) after a dose of 0.05 mg/kg xylazine; by 180% (4.73±0.3 mA to 13.28±2.35 mA) after 0.1 mg/kg; and by 510% (4.52±0.29 mA to 27.63±3.89 mA) after 0.2 mg/kg. Intramuscular xylazine appears to be an effective analgesic agent for acute pain in the sheep and further investigation into ideal administration regimens and dosage may provide more detailed information on relationships between dose, analgesic and sedative effects. The findings also suggest that some common analgesic agents, and opioids in particular, may be ineffective for the management of acute pain in sheep and that any analgesic should be administered only on the basis of its proven efficacy in that species.     

Opioid peptides and behavioral and physiological responses of dairy cows to social isolation in unfamiliar surroundings

To test whether endogenous opioid peptides are involved in the behavioral and physiological responses of cattle to stress, 12 Holstein cows were either placed in social isolation in unfamiliar surroundings for 15 min or remained in their home stalls, either with or without naloxone treatment, following a Latin square design. Vocalizations (judged as high or low frequency), defecation/urination, and heart rate were recorded, latency to respond to local thermal stimulation of the leg by means of a laser was measured to detect pain sensitivity, and blood was sampled and assayed for cortisol concentrations. Naloxone in the home stall increased cortisol concentrations and tended to reduce response latencies to the laser but did not induce vocalization. Social isolation increased the incidence of high-frequency vocalization and of defecation/urination, heart rate, cortisol concentrations, and response latencies to the laser. Prior administration of naloxone increased the incidence of low-frequency vocalization in isolation, but it had no effect on heart rate or on responses to the laser and only limited effect on cortisol concentrations when the cows were isolated. Brief periods of social isolation in unfamiliar surroundings seem to be stressful to cows, as indicated by increased heart rate, hypothalamic-pituitary-adrenocortical axis activity, and vocalization. Isolation also reduces pain sensitivity, suggesting a stress-induced analgesia. However, we found no evidence that naloxone-sensitive opioid receptors were involved in these responses.     

Probable post-synaptic α2 adrenergic mediated effect of xylazine on goat uterine motility*

Perez, R., Cox, J.F., Arrue, R. Probable post-synaptic ot2 adrenergic mediated effect of xylazine on goat uterine motility. J. vet. Pharmacol. Therap. 17 , 59–63. Xylazine has been characterized as a selective α₂-adrenoceptor agonist, which has explained its central nervous system depressant and other pharmacological effects. In order to characterize the effect of xylazine on uterine motility during the oestrus cycle in goats intrauterine pressure changes were recorded in cycling goats using balloon-tipped catheters placed in the uterine horns and connected to pressure transducers and a recorder. The effect of xylazine on myometrial activity was studied by giving increasing doses of the drug (1.0, 10.0, 100.0 or 500.0 m̈g/kg) intravenously (i.v.) to animals either in the follicular or the luteal phase of the cycle. To establish the subtype of a adrenergic receptor mediating the action of xylazine, goats were pretreated with either prazosin (1.0 mg/kg, i.v.) or yohimbine (1.0 m̈g/kg, i.v.). To establish whether the effect of xylazine was pre- or post-synaptic, xylazine (100 mg/kg, i.v.) was administered to goats pretreated with reserpine (0.8 mg/kg, i.p.) to deplete presynaptic catecholamine stores. Xylazine induced a significant and dose-dependent increase on uterine motility in cycling goats, apparently mediated by postsynaptic oc₂-adrenoceptors.     

柴达木改良绒山羊红细胞钾型的研究

采用火焰光度法对94只柴达木改良绒山羊的红细胞钾型进行了调查研究。结果发现：（1）柴达木改良绒山羊红细胞钾浓度存在多态性，有高钾和低钾两种表型，以高钾型为优势表型（79．79％）；（2）高钾型山羊的红细胞钾浓度在37－83.2mmol/L之间，低钾型的在16－28．8mmol/L之间；（3）K^L和K^h等位基因频率分别为0．1068和0．8932，基因杂合度为0．1782。     

Comparative pharmacokinetics of amoxicillin/clavulanic acid combination after intravenous administration to sheep and goats

The pharmacokinetic behaviour of an amoxicillin/clavulanic acid combination was studied after intravenous administration of single doses (20 mg/kg per kg body weight) to five sheep and six goats. The objective was to determine whether there are differences between sheep and goats in the disposition of amoxicillin and clavulanic acid. The plasma concentration-time data were analysed by compartmental pharmacokinetic and non-compartmental methods. The disposition curves for both drugs were best described by a biexponential equation (two-compartment open model) in sheep and goats. The elimination half-lives of amoxicillin were 1.43 ± 0.16 h in sheep and 1.13 ± 0.19 h in goats, and of clavulanic acid were 1.16 ± 0.01 h and 0.85 ± 0.09 h in sheep and goats respectively. The apparent volumes of distribution of amoxicillin and clavulanic acid were similar in the two species. Body clearances of amoxicillin were 0.09 ± 0.01 L/h kg in sheep and 0.11 ± 0.01 L/h kg in goats, and of clavulanic acid were 0.07 ± 0.01 L/h kg and 0.12 ± 0.01 L/h kg in sheep and goats respectively. The half-lives and body clearances of amoxicillin and clavulanic acid differed significantly between sheep and goats. It was concluded that the disposition of amoxicillin and clavulanic acid administered intravenously as an amoxicillin/clavulanic acid combination to sheep and goats differed between the two ruminant species. Even though the differences in disposition kinetics of both drugs were statistically significant, the same intravenous dosing rate of this antimicrobial combination can generally be used in sheep and goats.     

盐碱混合胁迫下抗碱盐生植物碱地肤的生长及其茎叶中溶质积累特点

将中性盐NaCl、Na2SO4和碱性盐NaHCO3、Na2CO3按不同比例混合,模拟出25种盐度、碱度各不相同的复杂盐碱条件,并对抗碱盐生植物碱地肤幼苗进行盐碱混合胁迫处理。测定其茎叶中溶质含量及日相对生长率等9项胁变指标,并分析了有机酸组分。以探讨混合盐碱胁迫下,碱地肤的生长及其茎叶中溶质积累特点。结果表明,适当的中性盐胁迫(80 mmol/L)对其生长有促进作用,而后随着盐度或碱度的增强其日相对生长率逐渐下降。在本实验条件下,碱地肤幼苗可耐受的最高盐碱混合胁迫强度为盐度400 mmol/L、pH值10.70,可见碱地肤是一种高度抗碱的盐生植物。在各种盐碱混合胁迫下,碱地肤茎叶中各种溶质的积累表现出了与众不同的特点。大量积累以Na 、K 为主的无机离子。Na 、K 含量均随盐度增强而上升,而且K /Na 基本保持不变(约为0.49),表明了碱地肤对K 、Na 吸收可能不存在拮抗作用。盐度是影响Na 、K 含量的主导因素,而碱度的影响较小。大量积累的有机溶质是甜菜碱和有机酸。随着盐度或碱度的增强甜菜碱的含量逐渐上升,最高含量可达干重的6%。盐度对甜菜碱积累的影响大于碱度。在积累的有机酸中,草酸的比例高达90%以上。有机酸含量不仅随盐度增高而上升,而且碱度对其也有明显的提高作用。只有在盐度大于240 mmol/L或pH值超过9.8的高强度的盐碱胁迫下,脯氨酸才有所积累,而且其积累量平均仅为甜菜碱的1/74左右。这一现象表明碱地肤茎叶中脯氨酸的积累可能不是一种单纯的对渗透胁迫的生理响应。     

外源NO对NaCl胁迫下燕麦幼苗氧化损伤的保护作用

用不同浓度的外源一氧化氮(NO)供体SNP处理100 mmol/L NaCl胁迫下一年生燕麦草幼苗,研究了外源NO对NaCl胁迫下燕麦幼苗氧化损伤的影响.结果表明,外源NO可缓解NaCl胁迫造成的燕麦幼苗膜质过氧化产物丙二醛(MDA)含量的升高,促进脯氨酸(Pro)积累,提高超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和过氧化物酶(POD)活性,并能缓解叶绿素含量的降解,提高可溶性糖的含量.而且NO的这种作用存在明显的剂量效应,其中以0.2 mmol/L SNP处理效果最为显著.     

外源甜菜碱处理对干旱胁迫下半夏氮代谢及相关酶活性的影响

为探讨喷施外源甜菜碱溶液对干旱胁迫下半夏体内相关次生代谢产物及氮代谢相关酶活性的影响,采用盆栽控水法研究了外源甜菜碱对D(干旱处理,含水量35%±2%)、D₂₀(干旱处理并加喷20 mmol/L的甜菜碱)、D₄₀(干旱处理并加喷40 mmol/L的甜菜碱)各处理组半夏体内谷氨酸合酶(GOGAT)活性、谷氨酰胺合成酶(GS)活性、谷氨酸脱氢酶(GDH)活性、硝态氮、可溶性蛋白、总生物碱、鸟苷和腺苷含量的变化规律。结果表明随着干旱胁迫时间的增加,D₄₀中GOGAT活性及GS活性降低幅度均小于D、D₂₀,GDH活性呈先升高后降低的趋势,对照组(CK组,含水量75%±2%)变化不明显。在处理第9~27天时,D₄₀与D₂₀相比,总生物碱含量分别提高了6.3%,10.3%,12.3%,差异显著。腺苷和鸟苷含量随时间增加呈上升趋势,且D₄₀含量均高于D₂₀,CK组含量最高,腺苷在第27天时有降低趋势。在第27天时,D₄₀可溶性蛋白含量分别比D、D₂₀提高了7.3%和3.1%。表明40 mmol/L的外源甜菜碱溶液能提高干旱胁迫条件下氮代谢相关酶的活性,从而加快无机氮的同化,有利于促进次生代谢物质的积累,同时也增强了半夏抵御干旱胁迫的能力。     

湿热应激对藏绵羊和山羊生长性能、抗氧化能力以及免疫功能的影响

本试验旨在研究藏绵羊和山羊在相同营养及湿热应激条件下血清激素、抗氧化和免疫指标的变化规律,考察湿热应激对藏绵羊和山羊生长性能、抗氧化能力以及免疫功能影响的差异。选取年龄和体重[(45.83±3.54)kg]相近的藏绵羊与山羊(波尔山羊×本地黄羊)各6只,试验共进行135 d,其中预试期15 d,正试期120 d。每日测定温湿度指数(THI),每月测定藏绵羊和山羊的血清相关指标。结果表明:1)5—7月份,羊舍THI随月份的增加显著升高(P0.05),6—8月份羊舍THI均大于72,因此将6—8月份定为湿热应激期。2)7、8月份藏绵羊和山羊直肠温度和呼吸频率均显著高于5月份(P0.05),且湿热应激期内藏绵羊直肠温度和呼吸频率均显著高于山羊(P0.05)。3)正试期内,湿热应激使得藏绵羊和山羊的干物质采食量最大降幅分别为10.70%和10.44%,平均日增重(ADG)最大降幅分别为50.00%和47.82%。4)羊舍THI由71.17(5月份)升高到76.82(7月份),藏绵羊和山羊血清皮质醇和胰岛素浓度显著升高(P0.05),血清葡萄糖和三碘甲状腺原氨酸浓度显著降低(P0.05)。湿热应激下,藏绵羊血清中生长激素和甲状腺素浓度的最大降幅均大于山羊。5)除藏绵羊7月份和山羊8月份血清总抗氧化能力,藏绵羊和山羊7、8月份的血清超氧化物歧化酶、谷胱甘肽过氧化物酶活性和总抗氧化能力均显著低于5月份(P0.05)外,血清丙二醛浓度均显著高于5月份(P0.05)。湿热应激下,山羊血清超氧化物歧化酶活性、总抗氧化能力和丙二醛浓度变化幅度均大于藏绵羊。6)与5月份相比,藏绵羊和山羊8月份的血清免疫球蛋白A、免疫球蛋白M、免疫球蛋白G和白细胞介素-2浓度显著降低(P0.05),而血清肿瘤坏死因子-α浓度则显著升高(P0.05)。湿热应激下,藏绵羊血清免疫球蛋白、白细胞介素-2和肿瘤坏死因子-α浓度的变化幅度均大于山羊。综上所述,湿热应激状态下藏绵羊和山羊的呼吸频率和直肠温度升高,抗氧化能力和免疫功能降低,从而导致生长性能降低。藏绵羊生长性能和免疫功能受湿热应激影响较大,而山羊抗氧化能力受湿热应激影响较大。     

Analgesic and systemic effects of xylazine, lidocaine and their combination after subarachnoid administration in goats

The objective of the study was to determine the analgesic and systemic effects of subarachnoid administration of xylazine hydrochloride (XY), lidocaine hydrochloride (LI) and their combination (XYLI) in goats. Six healthy goats were used in a prospective randomised study. Three treatments were administered to each goat, with 1-week intervals between each treatment. Treatments consisted of 0.1 mg/kg xylazine, 2.5 mg/kg lidocaine and a combination of xylazine 0.05 (mg/kg) and lidocaine (1.25 mg/kg). Analgesia, ataxic, sedative, cardiovascular and respiratory effects, and rectal temperature were evaluated before (baseline) and at 5, 10, 15, and 30 min after subarachnoid injection, and then at 30-min intervals until loss of analgesia occurred. Lidocaine induced analgesia in 3.1 +/- 1 min (mean +/- SD), which lasted for 66 +/- 31 min. Heart and respiratory rates and blood pressure remained unchanged after lidocaine-induced analgesia. Xylazine induced analgesia in 9.5 +/- 2.6 min and xylazine-lidocaine in 3.2 +/- 1.2 min. Xylazine-lidocaine-induced analgesia lasted longer (178.3 +/- 37 min) than that induced by xylazine (88.3 +/- 15 min). The XYLI treatment induced prolonged motor blocking (115 min), more than the XY (80 min) and LI (90 min) treatments. Both xylazine and xylazine-lidocaine caused significant decreases in the heart and respiratory rates, but not in blood pressure. The combination of xylazine (0.05 mg/kg) and lidocaine (1.25 mg/kg) can be administered subarachnoidally (between last lumbar vertebra and 1st sacral vertebra) to produce prolonged (> 2.5 h) analgesia of the tail, perineum, hind limbs, flanks and caudodorsal rib areas in goats. Despite the prolonged analgesia, using this combination is desirable for relieving postoperative pain, but it may be a disadvantage due to a motor block when dealing with goats.     

Effects of xylazine on the stress response to transport in male goats.

A 20-min van journey increased plasma cortisol concentrations to 15-25 ng/ml in male goats, blood glucose concentrations were not affected, but respiratory rates and heart rates were increased, the latter by 40 beats per min. A 2-h van journey increased plasma cortisol to greater than 25 ng/ml and blood glucose to greater than 5 mmol/l. Respiratory rates were increased to greater than 40 breaths per min and heart rates by greater than 100 beats per min. Xylazine alone (0.01 mg/kg) suppressed resting plasma cortisol concentrations, increased blood glucose concentrations to 4.5 +/- 0.8 mmol/l and suppressed respiratory rates by 5-10 breaths per min and heart rates by 20 beats per min. Cortisol concentrations were suppressed by xylazine treatment if given before a 20-min van journey, and for approximately 60 min if given 20 min after the start of a 2-h journey. When combined with transport, xylazine caused an additive effect on glucose concentrations, but suppressed respiratory and heart rates. However, for the latter criteria the timing of suppression was different depending on the time of onset and duration of the stressor. Injection of 50 micrograms ovine corticotrophin releasing factor (CRF) caused an immediate elevation of cortisol concentrations (but not glucose) which lasted for at least 6 h compared with the return to baseline within 60 min after either length of journey. Xylazine pretreatment did not alter the cortisol response to CRF, suggesting that xylazine must act centrally above pituitary level when blocking the cortisol response to transport. It is proposed that under resting conditions the hypothalamus is under alpha 2-adrenergic suppression. Stimulation of cortisol secretion in response to a stressor can be inhibited by an alpha 2-adrenergic agonist.     

The influence of chronic pain on the analgesic effects of the α2-adrenoceptor agonist, xylazine, in sheep

A comparison of the analgesic potency of the alpha 2-adrenoceptor agonist, xylazine, in control healthy sheep and sheep suffering chronic pain from footrot, indicated that the analgesic effectiveness of xylazine was significantly reduced in the animals experiencing chronic pain. This was measured by recording the threshold to a mechanically applied pressure stimulus. Furthermore, when the condition was apparently resolved, by conventional treatment over a period of 2 to 3 weeks, the decreased analgesic effectiveness of the alpha 2-agonist was still apparent although the animals were clinically cured of the footrot.