Effectiveness of maifanite in reducing the detrimental effects of aflatoxin B1 on hematology,aflatoxin B1 residues,and antioxidant enzymes activities of weanling piglets

A feeding trial was conducted to evaluate the effectiveness of maifanite, which is mainly composed of aluminosilicate, in reducing the adverse effects of aflatoxin B₁ (AFB₁) on hematology, AFB₁ residues, and antioxidant enzymes activities in weaning piglets. A total of 32 (9.28±0.17 kg BW) individually housed crossbred piglets (Duroc×Landrace×Large white) were randomly allotted to 1 of 4 dietary treatments in a 2×2 factorial arrangement with 8 replicates per treatment. The dietary treatments included 2 AFB₁ levels (5.3 and 372.8 μg/kg) and 2 maifanite levels (0% and 1%). No differences in average daily gain, average daily feed intake, and gain to feed ratio were observed among treatments. Ingestion of the AFB₁-contaminated (AF) diets (372.8 μg/kg of AFB₁) reduced (P<0.05) the numbers of neutrophil, monocyte, and total leukocyte. There were no effects of AFB₁ on gamma glutamyltransferase, alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase activities, and total protein, albumin, urea N, total bilirubin, IgG, IgA, and IgM concentrations in serum. Aflatoxin B₁ was found in the liver and kidney of piglets fed the AF diets. Piglets fed the AF diets reduced (P<0.05) the total superoxide dismutase, glutathione peroxidase, and catalase activities in serum. However, total superoxide dismutase activity in the liver was increased (P<0.05) in piglets fed the AF diets compared with those fed the basal diets (5.3 μg/kg of AFB₁). There was an interaction (P=0.003) in erythrocyte, but piglets fed the diets containing maifanite had greater erythrocyte and lymphocyte (P=0.035) numbers than those fed the diets without maifanite. The AFB₁ levels in the liver and kidney of piglets fed the AF diet containing maifanite were 29.6% and 41.2% lower, respectively, than those of piglets fed the AF diet alone. Although there was an interaction (P=0.011), piglets fed the diets containing AFB₁ and maifanite had greater serum T-SOD activity compared with those fed the diets with no maifanite. In conclusion, the addition of maifanite to the AF diet resulted in partial restoration of hematology and antioxidant enzymes activities and reduced AFB₁ levels in the liver and kidney.     

QuEChERS-高效液相色谱-串联质谱法测定乳粉中黄曲霉毒素B1和M1

建立了QuEChERS结合高效液相色谱-串联质谱测定乳粉中黄曲霉毒素B₁(aflatoxin B₁,AFB₁)和黄曲霉毒素M₁(aflatoxin M₁,AFM₁)的检测方法。乳粉用水复溶,乙腈提取,十八烷基键合硅胶和无水硫酸镁净化,在InertSustain-C₁₈柱(2.1 mm×150 mm, 3μm)上分离,乙酸铵溶液-甲醇为流动相,梯度洗脱,电喷雾正离子模式扫描,多反应监测,基质添加外标曲线定量。乳粉中AFB₁和AFM₁在0.08～20μg/kg范围内线性关系良好,r>0.999。检出限为AFM₁0.02μg/kg, AFB₁0.03μg/kg,定量限均为0.05μg/kg。在定量限的1、5和10倍添加浓度下,平均回收率为91.5%～100.7%。本方法便捷高效、重现性好、结果准确,可以为日常检测乳粉中黄曲霉毒素提供技术参考。     

Serotonin receptor 1B (HTR1B) genotype associated with milk production traits in cattle

Serotonin receptor 1B (HTR1B) is one of the 14 different identified serotonin receptors which are involved in the regulation of behaviors such as sleep, fear, aggression, mood, and feeding. The aims of this study were to characterize polymorphisms in the 5' coding and the 3' flanking regions of the bovine HTR1B gene among Chinese Holsteins and to identify the association of HTR1B polymorphisms with milk production performance. SSCP was used to examine the polymorphisms at four loci and the fragments with different SSCP patterns were sequenced. A total of three single nucleotide polymorphisms (SNPs) were detected, among which the 205G>T mutation was found to cause a predicted amino acid change: from Ala to Ser at position 69. The polymorphism of G205T was identified to be associated with milk yield trait. Furthermore, the H1-C genotype was found to be associated with a significant increase in milk yield of 489kg vs. the H1-A genotype (P<0.05).     

黄曲霉毒素B1残留ELISA试剂盒的研制及应用

本研究采用间接竞争酶联免疫吸附试验(ELISA)检测黄曲霉毒素B₁(aflatoxins B₁,AFB₁)残留量。将AFB₁与蛋白质载体牛血清蛋白(BSA)和卵清白蛋白(OVA)偶联制备了AFB₁-BSA和AFB₁-OVA偶联物,以AFB₁-BSA作为免疫原制备特异性抗体,并成功建立了AFB₁残留间接竞争ELISA检测方法及检测试剂盒。试剂盒IC₅₀为128.8 ng/L,检测线性范围为50~1800 ng/L,检测限不超过100 ng/kg;食用油、花生和谷物的平均添加回收率大于71.3%,批内、批间变异系数均小于14.2%。因此,本试剂盒具有操作简便、检测快速、灵敏度高等特点,将在植物性食品中AFB₁的残留检测中发挥重要作用。     

Fumonisin B1 Metabolism by Bovine Liver Microsomes

Only limited and contrasting information is available about the metabolic fate in cattle of fumonisin B₁, a mycotoxin produced by moulds of Fusarium. This study was carried out to evaluate the hepatic metabolism of fumonisin B₁ by bovine liver microsomes. No biodegradation or metabolization of the mycotoxin by liver microsomes was detectable after incubating fumonisin B₁ with bovine microsomes in the presence of a regenerating system for 1 h. No aminopolyol 1, aminopolyol 2 or aminopentol, metabolites of fumonisin B₁, were detected in any of the incubated samples. The tolerance of ruminants to fumonisin B₁ is apparently not dependent on its detoxification in the rumen.     

Vitamin B12 in the blood and in the liver of normal and of totally gastrectomized pigs

The concentration of vitamin R₁₂ in the blood was studied in five totally gastrectomized pigs followed for 10–18 months, and in four controls followed for 5¼–8 months. The concentration of vitamin B12 in the liver was investigated in three pigs of each group. The content of vitamin B₁₂ in the blood was of the same magnitude in both groups. Thus, removal of the stomach does not compromise the normal presence of this vitamin in the blood. The B₁₂ content in the liver was also unaffected by the operation, whereas it was increased after simultaneous administration of vitamin B₆.     

Aflatoxin B<Subscript>1</Subscript> Binding to Sorbents in Bovine Ruminal Fluid

A recent approach to the problem of contamination of agricultural products by aflatoxin B₁ (AFB₁) is to add non-nutritional adsorbents to animal diets in order to sequester ingested aflatoxins. We conducted in vitro experiments to develop a rapid and cheap model using ruminal fluid to assess the ability of sorbent materials to bind AFB₁. Seven sorbents (hydrated sodium calcium aluminosilicate; clinoptilolite; zeolite; two types of bentonite; sepiolite; and PHIL 75), commonly added to bovine diets were incubated in water and ruminal fluid in the presence of AFB₁. Hydrated sodium calcium aluminosilicate, sepiolite and one of the bentonites bound 100% of the AFB₁ in the presence of both ruminal fluid and water; clinoptilolite bound about 80% of AFB₁ in both liquids; whereas the affinities for the mycotoxin of zeolite (50%) and the other sample of bentonite (60%) in water seem to be increased by about 40% in ruminal fluid incubations. PHIL 75 had the poorest binding ability: about 30% in water and 45% in ruminal fluid. In view of the differences in toxin binding in water and ruminal fluid, it is preferable to use the ruminal fluid model for the in vitro pre-screening of sorbent materials potentially useful as adjuvants to ruminant feeds.     

The food contaminant fumonisin B1 reduces the maturation of porcine CD11R1+ intestinal antigen presenting cells and antigen-specific immune responses, leading to a prolonged intestinal ETEC infection

Consumption of food or feed contaminated with fumonisin B₁ (FB₁), a mycotoxin produced by Fusarium verticillioides, can lead to disease in humans and animals. The present study was conducted to examine the effect of FB₁ intake on the intestinal immune system. Piglets were used as a target and as a model species for humans since their gastro-intestinal tract is very similar. The animals were orally exposed to a low dose of FB₁ (1 mg/kg body weight FB₁) for 10 days which did not result in clinical signs. However, when compared to non-exposed animals, FB₁-exposed animals showed a longer shedding of F4⁺ enterotoxigenic Escherichia coli (ETEC) following infection and a lower induction of the antigen-specific immune response following oral immunization. Further analyses to elucidate the mechanisms behind these observations revealed a reduced intestinal expression of IL-12p40, an impaired function of intestinal antigen presenting cells (APC), with decreased upregulation of Major Histocompatibility Complex Class II molecule (MHC-II) and reduced T cell stimulatory capacity upon stimulation. Taken together, these results indicate an FB₁-mediated reduction of in vivo APC maturation.     

Cobalt metabolism in horse. Serum level and biosynthesis of vitamin B12.

The levels of serum vitamin B₁₂ were determined on 16 mature partly warm-blooded, partly Finnish rural-race horses by the radioisotopic competitive inhibition assay method. The mean value from three samplings carried out in dupli- or triplicate was 1.54 ± 0.16 ng/ml. The utilization of serum inorganic cobalt for cyanocobalamin synthesis was studied on two geldings, which received a dose of 200 µCi ⁵⁸CoGl₂ i.v. A Sephadex G-100 gel filtration was carried out with the serum proteins from serial blood samplings at different time intervals 15 min. to 48 hrs. after administration. The gel filtration showed the presence of two labelled proteins in the serum, one of them appearing some time after administration and disappearing almost completely towards the end of the experimental period. The two elution peaks are considered to represent inorganic ⁵⁸Co and ⁵⁸Co labelled vitamin B₁₂. The appearance of labelling in serum vitamin B₁₂ indicates the passing of cobalt into the intestine, and reabsorption into blood in the form of vitamin B₁₂.     

Aflatoxin B1 in poultry: Toxicology, metabolism and prevention

Aflatoxins (AF) are ubiquitous in corn-based animal feed and causes hepatotoxic and hepatocarcinogenic effects. The most important AF in terms of toxic potency and occurrence is aflatoxin B₁ (AFB₁). Poultry, especially turkeys, are extremely sensitive to the toxic and carcinogenic action of AFB₁, resulting in millions of dollars in annual losses to producers due to reduced growth rate, increased susceptibility to disease, reduced egg production and other adverse effects. The extreme sensitivity of turkeys and other poultry to AFB₁ is associated with efficient hepatic cytochrome P450-mediated bioactivation and deficient detoxification by glutathione S-transferases (GST). Discerning the biochemical and molecular mechanisms of this extreme sensitivity of poultry to AFB₁, will contribute in the development of novel strategies to increase aflatoxin resistance. Since AFB₁ is an unavoidable contaminant of corn-based poultry feed, chemoprevention strategies aimed at reducing AFB₁ toxicity in poultry and in other animals have been the subject of numerous studies. This brief review summarizes many of the key recent findings regarding the action of aflatoxins in poultry.     

A Saccharomyces cerevisiae RC016-based feed additive reduces liver toxicity,residual aflatoxin B1 levels and positively influences intestinal morphology in broiler chickens fed chronic aflatoxin B1-contaminated diets

The present study was conducted to investigate the ability of Saccharomyces cerevisiae RC016 (Sc)-based feed additive to reduce liver toxicity, residual aflatoxin B₁ (AFB₁) levels and influence intestinal structure in broiler chickens fed chronic aflatoxin B₁-contaminated diets. A total of 100 one-day-old male commercial line (Ross) broiler chickens were divided into 4 treatments, with 5 pens per treatment and 5 broiler chickens per pen. Birds were randomly assigned to 4 treatments, which were namely treatment 1 (T₁), control diet (CD); T₂, CD + Sc at 1 g/kg; T₃, CD + AFB₁ at 100 μg/kg; T₄, CD + Sc at 1 g/kg + AFB₁ at 100 μg/kg. The liver histopathology of broiler chickens fed diets with AFB₁ showed diffused microvacuolar fatty degeneration. The addition of Sc showed normal hepatocytes similar to the control. The small intestine villi from AFB₁ group showed atrophy, hyperplasia of goblet cells, prominent inflammatory infiltrate and oedema. In contrast, the small intestine villi from birds that received the yeast plus AFB₁ showed an absence of inflammatory infiltrate, and atrophy; moreover, a lower number of goblet cells compared to the groups with AFB₁ was observed. The morphometric intestine studies showed that a significant decrease (P < 0.05) in the crypt depth values when Sc was applied to AFB₁-contaminated diets. Although the intestinal villus height and apparent adsorption area did not show significant differences (P > 0.05), there was a tendency to improve these parameters. The residual levels of AFB₁ in livers were significantly reduced (P < 0.05) in the presence of the yeast. The present work demonstrated that the addition of Sc alone or in combination with AFB₁ in the broiler chicken diets had a beneficial effect in counteracting the toxic effects of AFB₁ in livers besides improving the histomorphometric parameters and modulating the toxic effect of AFB₁ in the intestine.     

Growth response to increasing doses of microencapsulated vitamin B12 and related changes in tissue vitamin B12 concentrations in cobalt-de cient lambs

AIM: To investigate growth responses of cobalt-deficient lambs to increasing doses of microencapsulated vitamin B₁₂, and to measure associated changes in serum and liver vitamin B₁₂ concentrations over 243 days.

METHODS: From a flock grazing pastures that had low cobalt (Co) levels (about 0.06 mg Co/kg dry matter), 4-6-week-old lambs (n=137) were assigned to four groups and received either no treatment or a subcutaneous injection of 3.0, 4.5 or 6.0 mg of microencapsulated vitamin B₁₂ on Day 1. At approximately monthly intervals, all lambs were weighed and blood samples were collected from a selection (n=10) of monitor animals, up to Day 243. Liver biopsies were also carried out on the monitor lambs (n=8) on Days 1, 124 and 215.

RESULTS: The vitamin B₁₂-treated lambs grew significantly faster (p<0.001) than untreated animals. Liveweights after 243 days were 28, 45, 45 and 47 kg for the untreated, 3.0, 4.5 and 6.0 mg vitamin B₁₂-treated lambs, respectively. Of the initial group of untreated lambs, 68% had to be removed before the end of the trial because of substantial weight loss, but none of the treated animals were similarly afflicted. Serum vitamin B₁₂ concentrations increased in all vitamin B₁₂-treated lambs, reaching a peak at Day 25, and those of the 4.5 and 6.0 mg vitamin B₁₂-treated lambs remained significantly higher (except at Day 124) than the untreated lambs to Day 187. However, at Day 124, but not Day 215, the liver vitamin B₁₂ concentrations of treated lambs were two to three times higher than those of controls.

CONCLUSIONS: The growth rates of Co-deficient lambs were markedly improved by injection of 3.0, 4.5 or 6.0 mg of microencapsulated vitamin B₁₂, and liveweights were maintained for at least 243 days. Serum vitamin B₁₂ concentrations were related to this growth response; concentrations of <220 pmol vitamin B₁₂/l were associated with a 95% probability that lambs were Co-deficient and would thus respond to Co/vitamin B₁₂ supplementation. Based on these data, the current New Zealand reference criteria for Co deficiency should be reviewed.

CLINICAL SIGNIFICANCE: An injection of 3 mg microencapsulated vitamin B₁₂2 given to lambs at tailing will treat Co deficiency and will increase and maintain liveweights in a flock for up to 8 months.     

Inductive expression of the NOD1 signalling pathway in chickens infected with Salmonella pullorum

1. The aim of this study was to describe the role of Nucleotide-binding oligomerization domain-containing protein 1 (NOD1) receptor signalling in chicken.

2. Tissue-specific expression analysis of NOD1, receptor-interacting serine-threonine kinase 2 (RIPK2), nuclear factor kappa B (NF-κB) and mitogen-activated protein kinase 11 (MAPK11 or p38) by quantitative real-time PCR (qRT-PCR) revealed their wide distribution in various organs and tissues.

3. Salmonella pullorum infection activated NOD1 receptor signalling in vivo and in vitro, resulting in significant induction of downstream signalling molecules RIPK2, NF-κB/p65, MAPK11/p38 and the effector molecules IL-1b and IL-8.

4. Activation of NOD1 by its agonist bacterial γ-D-glutamyl-meso-diaminopimelic acid (iE-DAP) in HD11 cells induced the adapter molecular RIPK2 and activated the NF-κB/p65 and MAPK11/p38 pathways, resulting in an increase in IL-8 but not IL-1β. Additionally, inhibition of NOD1 using NOD1-shRNA resulted in downregulation of RIPK2, MAPK11 and IL-8, while NF-κB/p65 and IL-1β were unaltered.

5. These results highlight the important role of NOD1 receptors in eliciting the innate immune response following pathogenic invasion in chicken.     

A critical evaluation of serum methylmalonic acid and vitamin B12 for the assessment of cobalt deficiency of growing lambs in New Zealand

AIM: To derive reference ranges for serum methylmalonic acid (MMA) for the diagnosis of cobalt/vitamin B₁₂-responsiveness in lambs and critique existing serum vitamin B₁₂ reference ranges.

METHODS: Individual animal data from earlier supplementation trials, involving 225 ewes, 106 suckling lambs, 301 lambs during the suckling and post-weaning periods and 414 weaned lambs, for which weight gain to supplementation was observed, were used to derive relationships between serum vitamin B₁₂ and MMA, and liveweight gain.

RESULTS: Serum MMA concentrations were rarely elevated above the norm of <2 µmol/L when serum vitamin B₁₂ concentrations were >375 pmol/L, and not elevated into the range where a liveweight response to supplementation occurred (>10 µmol/L) unless serum vitamin B₁₂ concentrations were below 200 pmol/L. Suckling lambs were able to maintain high growth rates despite elevated serum MMA concentrations (>20 µmol/L).

CONCLUSIONS: The current reference ranges used in New Zealand for serum vitamin B₁₂ are set conservatively high. Serum MMA concentrations appear to allow better differentiation of a responsive condition than vitamin B₁₂ concentrations. Serum MMA concentrations <13 µmol/L indicate responsiveness to supplementation whilst concentrations <7 µmol/L indicate unresponsiveness. In the range 7–13 µmol/L, variation in response was observed and predictability of response is less certain, but supplementation is advisable.

CLINICAL RELEVANCE: The current reference ranges for vitamin B₁₂ responsiveness are conservatively high and lead to over-diagnosis of vitamin B₁₂ deficiency in ill-thriftiness of sheep.     

Development of a specific radioimmunoassay for vitamin B12 and its application in the diagnosis of cobalt deficiency in sheep

A radioimmunoassay (RIA) for vitamin B₁₂ is described. Antisera were raised in rabbits using a conjugate between 5-O-succinyl cyanocobalamin and chicken serum albumin. The antibody is largely specific for the (upper) face of the vitamin B₁₂ molecule. The RIA can detect vitamin B₁₂ down to concentrations of 37 pmol/L and correlated well (r=0.980, p<0.001) with a commercial radioassay. The use of this RIA, together with an assay for plasma methylmalonic acid, in the diagnosis of cobalt/vitamin B₁₂ deficiency in sheep is described.     

Deletion of sodCI and spvBC in Salmonella enterica serovar Enteritidis reduced its virulence to the natural virulence of serovars Agona, Hadar and Infantis for mice but not for chickens early after infection

Salmonella enterica serovars Typhimurium, Enteritidis, Dublin, Choleraesuis or Gallinarum can colonise liver and spleen in particular hosts while infections with serovars Infantis, Agona, Hadar, etc. are usually limited to gastrointestinal tract. Reasons for this behavior are unknown, although it has been shown that sodCI and spv genes exhibit a strict distribution between more and less virulent serovars and they influence Salmonella virulence. However to what extent the presence or absence of these genes is associated with the increased virulence of serovars which possess them has never been addressed experimentally. In this study we therefore first confirmed the exclusive association of spvB and sodCI genes with the former group of serovars. In the next step we removed these two genes from S. Enteritidis genome and compared the virulence of such a mutant with the virulence of S. Infantis, S. Agona and S. Hadar for chickens and highly sensitive Balb/C mice. Single strain infection showed that the deletion of these two genes from S. Enteritidis resulted in the reduction of its virulence for mice but not for chickens. Mixed infection further confirmed these observations and indicated that in mice but not in chickens the virulence of sodCI and spv mutant was reduced to the natural virulence of serovars Infantis, Agona and Hadar. Although sodCI and spv genes do not influence S. Enteritidis virulence for chickens directly, they may be of an indirect effect through the increased persistence of S. Enteritidis in mice and increased probability of the reintroduction of S. Enteritidis into poultry flocks.     

Effects of GnRH in combination with PGF2α on the dynamics of follicular and luteal cells in post-pubertal Holstein heifers

Holstein heifers were randomly allotted by weight, age and body condition score to one of three treatments to test the hypothesis that GnRH administration concurrent with PGF_2α injection would advance follicle or corpus luteum (CL) development parallel to an induced luteolysis of the pre-existing CL. Heifers in the control group (n = 14) received two treatments of PGF_2α(25 mg, im) given 10 days apart. Groups 2 (n = 14) and 3 (n = 14) received an additional treatment of GnRH (100 μg, im) after the first and second PGF_2α respectively. Estrus detection began immediately after PGF_2α and continued for 80 h. Blood sampling was initiated 7 days prior to the first PGF_2α (day − 7) and continued on days 0, 7, 10 (prior to the second PGF_2α), 17 and 24. Heifers were artificially inseminated after the second PGF_2α and pregnancy diagnosed at 60 days. There was a trend (P < .10) toward a lower estrus response in group 3 when compared to the other groups. Pregnant heifers in group 2 had lower progesterone (0.44 ± 0.09 vs. 1.72 ± 0.56 ng/ml) a week after the second PGF_2α than the non-pregnant animals in that group (P < .05). Similar results were observed in the control group but only within the responding heifers (0.61 ± 0.08 vs. 0.93 ± 0.03 ng/ml; P < .05). Progesterone in heifers in group 2 remained high on day 0, 7, and 10 (1.48 ± 0.37, 1.23 ± 0.39, 1.96 ± 0.36 ng/ml) in spite of the treatment with PGF_2α. This data suggest that administration of GnRH following PGF_2α alters bovine luteal and/or follicular cell function.     

Age at primary infection with Salmonella enterica serovar Typhimurium in the chicken influences persistence of infection and subsequent immunity to re-challenge

Salmonella enterica remains one of the most important food-borne pathogens of humans and is often acquired through consumption of infected poultry meat or eggs. Control of Salmonella infections in chicken is therefore an important public health issue. Infection with S. enterica serovar Typhimurium results in a persistent enteric infection without clinical disease in chickens of more than 3 days of age, and represents a source for contamination of carcass at slaughter and entry into the human food chain. Data presented indicate a profound effect of age at initial exposure on the persistence of infection and a lesser effect on the development of effective immunity to re-challenge. The percentage of birds positive for Salmonella was high until 8–9 weeks of age, regardless of the age at which the birds were infected (1, 3 or 6 weeks). The birds infected at 3 and 6 weeks of age produced a more rapid and higher antibody response (IgY and IgA) than those infected at 1 week of age, but in all cases infection persisted for a considerable period despite the presence of high antibody levels. Following a re-challenge infection with S. Typhimurium, all three previously-infected groups had fewer bacteria in the gut, spleen and liver compared with age-matched birds receiving a parallel primary infection. However, the birds primary infected at 3 and 6 weeks of age cleared infection more rapidly than those infected at a younger age. Interestingly older-primed birds had higher specific T lymphocyte proliferative responses and specific circulating levels of IgY antibody at time of re-challenge. Although birds initially infected at 1 week of age and those that were previously uninfected produced a stronger antibody response following re-challenge, they were slower to clear Salmonella from the gut than the older-primed groups which expressed a stronger T lymphocyte response. The data presented indicate that clearance of Salmonella from the gut is age-dependent and we propose that this relates to the increased competence of the enteric T cell response. The findings that Salmonella persists beyond 8–9 weeks, irrespective of age at exposure, has implications for the broiler sector and indicates the need to remain Salmonella free throughout the rearing period. Moreover, the re-challenge data demonstrates that infection at a young age is less effective in producing protective immunity than in older chickens. This feature of the development of protective immunity needs to be considered when developing vaccines for the broiler sector of the poultry industry.     

Effects of α2-adrenergic drugs on small intestinal motility in the horse: An in vitro study

The effects of selective α₂-agonists (xylazine, detomidine and medetomidine) and antagonists (yohimbine and atipamezole) on in vitro small intestine motility in the horse were evaluated. Samples of equine jejunum were placed in isolated organ baths and drug-induced modifications of motility were measured by means of an isotonic transducer. All tested α₂-agonists dose-dependently reduced both spontaneous and electrically-evoked phasic contractions. Conversely, α₂-antagonists were ineffective when tested alone, and showed a heterogeneous and dose-independent ability to inhibit agonist activity. In particular, the antagonism exerted by higher concentrations of both yohimbine and atipamezole against α₂-agonists was weaker than when lower concentrations were used. The data are indicative of the presence of both pre- and post-synaptic α₂-adrenoceptors with inhibitory activity on equine jejunum motility, and support a possible therapeutic utility of these drugs in horse intestinal disorders associated with hypermotility.