猪生长激素释放因子基因质粒对猪生长发育的影响

试验选用 30头杜洛克×太湖和汉普夏×太湖二元杂仔猪 ,平均 4 4日龄断奶 ,体重 (10 .30± 1.80 )kg ,研究了经腿部肌肉注射 0 ,0 .2 5 ,0 .5 ,1.0和 2 .0mg猪生长激素释放因子 (pGRF)基因质粒对猪生产性能、胴体品质和血液参数的影响。试验结果表明 ,pGRF基因质粒对猪不同生长阶段生产性能的影响不同 ,10～ 4 0kg阶段促生长效果好于 4 0～ 10 0kg阶段 ,且促生长效果与剂量有关。相对于促生长效果 ,在猪整个生长阶段pGRF基因质粒对饲料利用率的改善效果更明显。 10 0kg体重屠宰 ,2mg组对胴体品质改善最明显 ,但对肉质无影响 ;血液中GH、IGF I、GRF及血糖浓度和血清尿素氮与对照组均无显著差异     

肌肉注射高剂量pGRF基因质粒对猪生产性能及血液激素水平影响的研究

为探讨高剂量注射pGRF基因质粒对动物生产性能及血液激素水平的影响,本试验选取平均体重为(6．78± 0．47)kg的断奶仔猪24头,随机分为3个处理,每个处理4个重复。在试验开始时按不同处理分别注射0、2．2 mg和 4．4mg的pGRF基因质粒。结果表明:注射2．2 mg和4．4 mg的pGRF基因质粒对动物的生产性能具有一定的改善作用(P<0．05或P>0．05),注射高剂量(4．4 mg)pGRF基因质粒相对于2．2 mg剂量并不能进一步改善动物的生产性能。高剂量(4．4 mg)pGRF基因质粒可相对延长其在动物体内的作用时间,可有效提高动物生长后期血浆GRF浓度。高剂量(4．4 mg)的pGRF基因质粒具有促进内源生长抑素(SS)分泌的作用,因而不利于其生物学效应的发挥。     

pGRF基因质粒对猪胴体性状和肌肉品质的影响

为研究猪生长激素释放因子(pGRF)基因质粒对猪胴体性状和肌肉品质的影响,试验选用24头大白×长白二元杂交去势公猪平均体重(17.25±0.62)kg,随机分为4个处理,每个处理6个重复,分别经臀部注射0、4.0 mg、6.0 mg和8.0 mg的pGRF基因质粒。结果表明:注射4.0 mg和6.0 mg的pGRF基因质粒有提高猪宰前活重、眼肌面积、屠宰率、胴体直长、胴体斜长及降低背膘厚的趋势,其中6.0 mg组宰前活重和胴体斜长与对照组相比差异显著(P0.05)。注射pGRF基因质粒对猪肌肉品质无显著影响(P0.05)。     

银耳孢子发酵物及与pGRF基因质粒合用对断奶仔猪生长、部分免疫指标及肠道菌群的影响

本研究探讨了银耳孢子发酵物(TSF)及与猪生长激素释放因子(pGRF)基因质粒合用对断奶仔猪生长、部分免疫指标以及肠道菌群的影响,同时与饲用抗生素效果作比较.选用48头(28±2)日龄的断奶D×L×Y三元杂交仔猪,采用单项分类试验设计,按体重相近、性别一致的原则随机分到对照组、抗生素组(吉他霉素40 mg/kg+硫酸抗敌素20 mg/kg)、TSF(4 000 mg/kg)组和TsF(4 000 mg/kg)+pGRF组4个组中,TSF+pGRF组中pGRF基因质粒是在试验开始时于每头猪后腿肌肉注射1 mg.试验期28 d.结果表明:与对照组相比,3组均显著提高了断奶仔猪的日增重(P<0.05)及改善饲料转化效率(P<0.05).添加有TSF的2组较对照组和抗生素组能显著提高血清IL-2浓度(P<0.05)、T淋巴细胞转化率(P<0.05)和血清猪瘟抗体滴度(P<0.05);T淋巴细胞数量也有明显的提高(P=0.10).添加有TSF的2组乳酸杆菌和双歧杆菌均显著高于抗生素组(P<0.05),与对照组差异不显著(P=0.07).由结果证明,TSF有促生长的作用,而且效果与吉他霉素+硫酸抗敌素相当;同时TSF还能提高断奶仔猪的免疫功能,优化肠道菌群;TSF与pGRF基因质粒合用有进一步提高生长性能的趋势,但对免疫功能和肠道菌群没有进一步的改善作用.     

EGF、Gln和pGRF基因质粒对早期断奶仔猪生产性能、免疫功能及相关激素水平的影响

为探讨表皮生长因子（EGF）、谷氨酰胺（Gln）和pGRF基因质粒不同组合形式对早期断奶仔猪生产性能、免疫功能及相关激素（皮质醇、生长激素）分泌的影响，选择同日龄断奶仔猪42头，随机分为7个处理，每个处理3个重复，每个重复2头猪，做一对比试验，试验期21d。结果表明，EGF、Gln和pGRF基因质粒的不同组合形式在促进仔猪生长、增强免疫功能及调节激素分泌方面均表现出良好效果，其中以三者联合使用的效果最为突出：仔猪末重和全期日增重分别提高48．02％（P〈0．01）与1．68倍（P〈0．01），料肉比降低50．75％（P〈0．01）；日粮粗蛋白表观消化率增加1．13倍（P〈0．01）；毛色分数提高14．03（P〈0．05），而且全期未发生腹泻，其作用远优于两两组合及各自单独使用。对免疫功能的调节效果以EGF＋pGRF基因质粒和EGF＋G1n＋pGRF基因质粒两种组合形式较为明显：断奶后第1周，试验组血清IgG水平分别比对照组增加11．71％（P〈0．05）和11．24％（P〈0．1）；第2周则分别减少9．53％（P〈0．01）和5．06％（P〈0．1）。对仔猪内分泌的影响，亦以三者联合使用的作用最为显著：其血清皮质醇水平在断奶后1～2周分别比pGRF基因质粒单独使用及其与EGF两者合用降低40．40％和88．57％；生长激素水平的变化与皮质醇呈相反趋势，但变化规律与皮质醇相似。     

生长肥育猪骨骼肌注射表达pGRF基因质粒的效应研究

将猪的GRF基因表达质粒注射于猪的骨骼肌后,研究其促生长效应与机理。选用始重6.3kg的44头去势长白×太湖仔猪,分6组,采用2×3因子安排的完全随机区组设计,按6～10kg、10～20kg、20～50kg、50～100kg4个阶段饲养。4个饲养阶段的饲粮低蛋白水平分别是20.70%,17.90%,15.03%,13.00%;高蛋白水平分别是23.70%,20.90%,18.02%,16.00%。pGRF基因质粒注射剂量设0mg、0.5mg、1.0mg3个水平,于试验开始与试验猪体重达60kg时共注射基因质粒2次。测定各阶段日增重,饲料消耗量,耗料增重比以及30、70、100kg时血液中GH、GRF、IGF-I的浓度。100kg时屠宰进行胴体品质测定。结果表明:饲粮蛋白水平对各阶段及全期试验猪日增重均有显著影响(P<0.05或P<0.01),对50～100kg阶段与全期日采食量和耗料增重比有显著影响(P<0.05或P<0.01)。注射pGRF基因质粒对各阶段及全期日增重均有显著影响(P<0.05),对6～10kg、10～20kg、50～100kg3阶段及全期日采食量有显著影响(P<0.05),对6～10kg阶段、50～100kg阶段及全期耗料增重比有显著影响(P<0.05)。注射pGRF基因质粒对30kg及70kg体重时猪血液中GRF、GH、IGF-I浓度均有显著影响(P<0.05)。提高饲粮蛋白水平与注射pGRF基因质粒均可明显降低超声波测膘厚及屠宰测膘厚、增大眼肌面积(P<0.05)。     

注射pGRF基因质粒对由脂多糖或三联疫苗诱导的免疫应激仔猪生长和免疫指标的影响

为研究猪生长激素释放因子(pGRF)基因质粒对由脂多糖或三联苗诱导的免疫应激仔猪生长性能和免疫指标的影响,选用36头(28±2)d断奶的杜长大(Duroc×Landrace×Yorkshire,DLY)三元杂交仔猪,按体重相近、阎公猪和母猪各1/2的原则,分为对照组(不注射pGRF基因质粒、大肠杆菌LPS或三联苗)、注射pGRF组、注射脂多糖(LPS)组、注射pGRF+LPS组、注射三联疫苗组(猪瘟兔化弱毒,猪丹毒杆菌G4T10弱毒,猪源多杀性巴氏杆菌E0630弱毒)和注射pGRF+三联疫苗6个处理,每个处理6个重复,每个重复1头猪.试验开始时,pGRF组、pGRF+LPS组、pGRF+三联疫苗组的仔猪大腿肌肉分别注射1.0 mg pGRF基因质粒;试验的第11天给LPS组、pGRF+LPS组仔猪注射100 ug/kg LPS生理盐水溶液,三联疫苗组以及pGRF+三联疫苗组注射2头份三联苗生理盐水溶液,对照组和pGRF组注射生理盐水;第18天时按照第11天的操作重复进行.结果表明,在2次注射LPS或三联苗后,即10～17 d和17～24 d阶段,pGRF+LPS组仔猪的ADG显著(10～17 d,P<0.05)或极显著(17～24 d,P<0.01)高于LPS组,F/G均显著低于LPS组(P<0.05);pGRF+疫苗组仔猪ADG均显著高于疫苗组(P<0.05),F/G显著低于疫苗组(P<0.05).在第11天和第18天,pGRF+LPS组仔猪的血清细胞因子(IL-1、IL-6)水平均极显著低于LPS组(P<0.01),类胰岛素生长因子(IGF-I)和IgG浓度均极显著高于LPS组(P<0.01);pGRF+疫苗组仔猪的血清IL-1和IL-6浓度显著低于疫苗组(P<0.05),lgG浓度极显著(11 d,P<0.01)或显著(18 d,P<0.05)高于疫苗组,IGF-I浓度显著(11 d,P<0.05)或极显著(18 d,P<0.01)高于疫苗组.证明pGRF基因质粒能缓解由LPS或三联疫苗免疫应激引起的仔猪生长抑制;能够抑制由脂多糖或三联苗诱导的血清IL-1和IL-6浓度的上升和血清IGF-I浓度的降低,同时能提高免疫应激仔猪的血清IgG浓度.     

猪生长激素释放因子基因对早期断奶仔猪生产性能、免疫功能及消化道发育的影响

为探讨注射猪生长激素释放因子基因 (pGRF)对早期断奶仔猪生产性能、肠粘膜及免疫功能的影响 ,选取 4周龄杜长大同窝断奶仔猪 8头 (6 .2 7± 1 .1 9kg) ,等分为两组 ,日粮分高、低两个水平 ,做一对比试验 ,试验期 2 1天。结果表明 :断奶后注射组仔猪ADG第 1、2周及 1～ 2周分别增加 2 8.57g、2 5 .0 1g和 2 6 .79g ;饲料转化率 1、2周分别提高 33 .80 %和 1 7.33 % ;N沉积率第 1、2及 1～ 2周分别增加 3 .67%与 5 .1 3 %和 1 6 .96 % ;绒毛长度增加 1 9.71 % ;血清IgG含量在断奶时、第 1周末和第 2周末分别增加 3 .82 %、9.90 %和 8.1 9%。     

pGRF基因质粒对免疫应激断奶仔猪生长抑制的缓解作用

旨在研究pGRF基因质粒对免疫应激断奶仔猪生长的影响,探讨pGRF基因质粒缓解免疫应激引起的生长抑制作用及其可能的机理。选取18头日龄为（35&#177;2）d、体质量为（7.86&#177;0.59）kg未去势的杜洛克&#215;长白&#215;大白（DLY）三元杂交断奶仔猪,采用单向分类试验设计,按体质量相近、性别一致的原则配对,分为3个处理,即pGRF（pGRF基因质粒）组、pGRF＋LPS（脂多糖）组和LPS组,每个处理6个重复,每个重复1头猪。结果表明：pGRF基因质粒可以缓解因注射LPS导致的日增质量的降低（P〈0.05）,饲料转化率有所改善（P〉0.05）;能够抑制由LPS诱导的细胞因子（IL-1I、L-6）浓度的上升（P〈0.05或P〈0.01）和血清IGF-I浓度的降低（P〈0.05或P〈0.01）,同时显著提高血清IgG的浓度（P〈0.05）。结论：pGRF基因质粒缓解了断奶仔猪因注射脂多糖引起的生长抑制,降低了血清IL-1和IL-6的水平,提高了血清IgG的浓度,提高了仔猪的抗病力,从而缓解了断奶仔猪的免疫应激;pGRF基因质粒缓解免疫应激的作用与其促进IGF-I的分泌密切相关。     

硝呋烯腙对断奶仔猪生产性能的影响

选用 1 80头 2 8日龄三元杂交 (杜×长×大 )断奶仔猪 ,平均体重约为 7.0kg ,小母猪和去势公猪各占一半 ,按性别和体重随机分为 6组 ,每组 3个重复 ,每个重复 1 0头猪。各组基础日粮一致。对照组 (第 1组 )饲喂基础日粮 ;试验组按 2～ 6组分别添加 90mg kg的喹乙醇、2 0mg kg的速大肥、1 0mg kg的硝呋烯腙、2 5mg kg硝呋烯腙和 50mg kg的硝呋烯腙于基础日粮中。试验结果表明 ,试验组第 5组效果最好 ,较对照组日增重提高了 34 .9% (P <0 .0 5) ,饲料转化率提高了 2 0 .9% (P <0 .0 5) ,腹泻率降低了 76 .3 % (P <0 .0 5) ;第 2组、第 3组、第 4组、第 6组与对照组相比差异均不显著(P >0 .0 5) .第 5组与第 2组相比 ,日增重提高了 2 1 .6 % (P <0 .0 5) ,饲料转化率提高了 1 8.9% (P <0 .0 5) ,腹泻率降低了72 .3 % (P <0 .0 5) ;试验组第 2组～第 6组与对照组相比 ,采食量差异均不显著     

白术、微米白术和白术多糖对断奶仔猪生长性能和肠道形态及微生态区系的影响

试验选用96头平均体重14.82 kg左右的杜×长×大断奶仔猪,随机分成4组,每组3栏,每栏8头(公母各半)。对照组饲喂基础日粮,试验1、2、3组分别添加1%80目白术、0.2%白术多糖和1%微米白术。试验期30 d。结果表明:在生长性能方面,与对照组相比,1%微米白术添加组可显著提高日增重(P0.05)、降低饲料增重比和腹泻率,而且效果优于1%80目白术组和0.2%白术多糖组,在肠道形态和肠道微生态区系方面,与对照组相比,日粮添加1%80目白术、0.2%白术多糖、1%微米白术均可不同程度的提高十二指肠和空肠的绒毛高度,加深十二指肠和空肠的隐窝深度,并且增加肠道微生态区系的多样性,其中以1%微米白术添加组的效果最佳。     

Prevalence and seasonal incidence of nematode parasites and fluke infections of sheep and goats in eastern Ethiopia

Sissay, M.M., Uggla, A. and Waller, P.J., XXXX. Prevalence and seasonal incidence of nematode parasites and fluke infections of sheep and goats in eastern Ethiopia. Tropical Animal Health and Production, XXXX. A 2-year abattoir survey was carried out to determine the prevalence, abundance and seasonal incidence of gastro-intestinal (GI) nematodes and trematodes (flukes) of sheep and goats in the semi-arid zone of eastern Ethiopia. During May 2003 to April 2005, viscera including liver, lungs and GI tracts were collected from 655 sheep and 632 goats slaughtered at 4 abattoirs located in the towns of Haramaya, Harar, Dire Dawa and Jijiga in eastern Ethiopia. All animals were raised in the farming areas located within the community boundaries for each town. Collected materials were transported within 24 h to the parasitology laboratory of Haramaya University for immediate processing. Thirteen species belonging to 9 genera of GI nematodes (Haemonchus contortus, Trichostrongylus axei, T. colubriformis, T. vitrinus, Nematodirus filicollis, N. spathiger, Oesophagostomum columbianum, O. venulosum, Strongyloides papillosus, Bunostomum trigonocephalum, Trichuris ovis, Cooperia curticei and Chabertia ovina), and 4 species belonging to 3 genera of trematodes (Fasciola hepatica, F. gigantica, Paramphistomum {Calicohoron} microbothrium and Dicrocoelium dendriticum) were recorded in both sheep and goats. All animals in this investigation were infected with multiple species to varying degrees. The mean burdens of adult nematodes were generally moderate in both sheep and goats and showed patterns of seasonal abundance that corresponded with the bi-modal annual rainfall pattern, with highest burdens around the middle of the rainy season. In both sheep and goats there were significant differences in the mean worm burdens and abundance of the different nematode species between the four geographic locations, with worm burdens in the Haramaya and Harar areas greater than those observed in the Dire Dawa and Jijiga locations. Similar seasonal variations were also observed in the prevalence of flukes. But there were no significant differences in the prevalence of each fluke species between the four locations. Overall, the results showed that Haemonchus, Trichostrongylus, Nematodirus, Oesophagostomum, Fasciola and Paramphistomum species were the most abundant helminth parasites of sheep and goats in eastern Ethiopia.     

Internal Parasites and Haematological Values in Cattle Slaughtered in Buea Subdivision of Cameroon

Tropical Animal Health and Production -     

Phase I evaluation of CCNU (lomustine) in tumor-bearing cats

1-(2-Chloroethyl)3-cyclohexyl-1-nitrosourea (CCNU) is an alkylating agent in the nitrosourea subclass. A prospective evaluation of CCNU was done to determine the maximally tolerated dosage of CCNU in tumor-bearing cats. Response data were obtained when available. Twenty-five cats were treated with CCNU at a dosage of 50-60 mg/m3 body surface area. Complete hematologic data were available for 13 cats. Neutropenia was the acute dose-limiting toxicity. The median neutrophil count at the nadir was 1,000 cells/microL (mean, 2,433 cells/microL; range, 0-9,694 cells/microL). The time of neutrophil nadir was variable, occurring 7-28 days after treatment, and counts sometimes did not return to normal for up to 14 days after the nadir. Based on these findings, a 6-week dosing interval and weekly hematologic monitoring after the 1st treatment with CCNU are recommended. The nadir of the platelet count may occur 14-21 days after treatment. The median platelet count at the nadir was 43,500 cells/microL. No gastrointestinal, renal, or hepatic toxicities were observed after a single CCNU treatment, and additional studies to evaluate the potential for cumulative toxicity should be performed. Five cats with lymphoma and 1 cat with mast cell tumor had measurable responses to CCNU. Phase II studies to evaluate antitumor activity should be completed with a dosing regimen of 50-60 mg/m3 every 6 weeks.     

Chemotaxis of macrophage in inflammation

Our particular attention in this article was given to natural mediators for macrophages isolated from the sites of tissue injury. A number of chemotactic factors, which may satisfy many criteria making them acceptable as inflammatory leucocyte chemotactic factors, has been separated. Among them, our laboratory has isolated three macrophage (monocyte) chemotactic factors (MCF-a, -b and -c). Their purification, characterization and functional specificity are discussed.     

Y‐chromosomal variation of local goat breeds of Turkey close to the domestication centre

Genetic variations in chromosome Y are enabling researchers to identify paternal lineages, which are informative for introgressions and migrations. In this study, the male‐specific region markers, sex‐determining region‐Y (SRY), amelogenin (AMELY) and zinc finger (ZFY) were analysed in seven Turkish native goat breeds, Angora, Kilis, Hair, Honaml?, Norduz, Gürcü and Abaza. A SNP in the ZFY gene defined a new haplotype Y2C. All domestic haplogroups originate from Capra aegagrus, while the finding of Y1A, Y1B, Y2A and Y2C in 32, 4, 126 and 2 Turkish domestic goats, respectively, appears to indicate a predomestic origin of the major haplotypes. The occurrence of four haplotypes in the Hair goat and, in contrast, a frequency of 96% of Y1A in the Kilis breed illustrate that Y‐chromosomal variants have a more breed‐dependent distribution than mitochondrial or autosomal DNA. This probably reflects male founder effects, but a role in adaptation cannot be excluded.     

Furosemide continuous rate infusion in the horse: evaluation of enhanced efficacy and reduced side effects

Continuous rate infusion (CRI) of furosemide in humans is considered superior to intermittent administration (IA). This study examined whether furosemide CRI, compared with IA, would increase diuretic efficacy with decreased fluid and electrolyte fluctuations and activation of the renin-angiotensin-aldosterone system (RAAS) in the horse. Five mares were used in a crossover-design study. During a 24-hour period, each horse received a total of 3 mg/kg furosemide by either CRI (0.12 mg/kg/h preceded by a loading dose of 0.12 mg/kg IV) or IA (1 mg/kg IV q8h). There was not a statistically significant difference in urine volume over 24 hours between methods; however, urine volume was significantly greater after CRI compared with IA during the first 8 hours ([median 25th percentile, 75th percentile]: 9.6 L [8.9, 14.4] for CRI versus 5.9 L [5.3, 6.0] for IA). CRI produced a more uniform urine flow, decreased fluctuations in plasma volume, and suppressed renal concentrating ability throughout the infusion period. Potassium, Ca, and Cl excretion was greater during CRI than IA (1,133 mmol [1.110, 1,229] versus 764 mmol [709, 904], 102.7 mmol [96.0, 117.2] versus 73.3 mmol [65.0, 73.5], and 1,776 mmol [1,657, 2.378] versus 1,596 mmol [1,457, 1,767], respectively). Elimination half-lives of furosemide were 1.35 and 0.47 hours for CRI and IA, respectively. The area under the excretion rate curve was 1,285.7 and 184.2 mL x mg/mL for CRI and IA, respectively. Furosemide CRI (0.12 mg/kg/h) for 8 hours, preceded by a loading dose (0.12 mg/kg), is recommended when profound diuresis is needed acutely in horses.     

Changes in proportion of canine urinary calculi composed of calcium oxalate or struvite in specimens analyzed from 1981 through 2001

The objective of this report was to characterize 20-year changes in proportion of calcium oxalate (CaOx) calculi and struvite calculi in dogs, and associations with breed, age, and sex. In this retrospective study, results of analysis of urinary calculi from dogs were reviewed for specimens received between July 1, 1981, and December 31, 2001. Breed, sex, age, year of submission of the specimen, and mineral type(s) were analyzed statistically. CaOx or Struvite or both were contained in 18,966 of 20,884 (91%) specimens. For both sexes, a 20-year statistically significant increase was observed in the proportion of calculus specimens that contained CaOx. The increase in this proportion was greater in females (1% to 31%) than in males (18% to 82%). From 1998 to 2001, when proportions may have plateaued, the odds of specimens containing CaOx were markedly higher in 18 breeds, markedly lower in 5 breeds, and not significantly different in 13 breeds compared with crossbreds. For both sexes, a 20-year statistically significant decrease was observed in the proportion of calculus specimens that contained struvite. This decrease in proportion was greater for males (79-16%) than for females (97-68%). From 1998 to 2001, when proportions plateaued, the odds of calculi containing struvite were markedly lower in 20 breeds, markedly higher in 1 breed, and not significantly different in 15 breeds when compared with crossbreds. Breed, age, and sex were associated statistically with CaOx or struvite urolithiasis. In conclusion, there appears to have been a long-term increase in the proportion of specimens of canine urinary calculi that contain CaOx as well as a long-term decrease in the proportion of specimens of calculi that contain struvite for both male and female dogs. The rate of change appeared to begin leveling off in the period 1998 to 2001. The recent proportion of dogs with either CaOx- or struvite-associated urolithiasis may depend on breed, age, and sex, and on interactions among these 3 factors.     

Smart Phone Assisted City-scale Wireless Sensor Network Deployment for Transportation System Monitoring

<正>1.INTRODUCTION Ensuring transportation network security is one Of the most daunting challenges confronting homeland security agencies today.Significant research has been dedicated.To model and analyze the vulnerability of transportation systems,while notably fewer studies propose specific strategies for deploying defensive technologies to safeguard these systems.     

The Epidemiology of Gastrointestinal Nematodes of Dairy Cattle in Central Kenya

The epidemiology of H. placei and of other gastrointestinal nematodes in yearling dairy cattle was examined on two farms in Kiambu District, central Kenya during each of 13 one-month periods from April 1993 to April 1994. On each farm, 32 newly weaned dairy calves were given a single dose of albendazole and then placed on experimental pastures. Twelve of the animals were designated for bi-monthly slaughter (n = 2) and analysis of worm population characteristics and 20 were designated for blood and faecal collection and for weighing. Two parasite-free tracer calves were grazed alongside the weaner calves each month throughout the study period and were also slaughtered for analysis of worm populations. Faecal egg counts, haematological and serum pepsinogen determinations, herbage larval counts, and animal live weight changes were recorded monthly. The study revealed that Haemonchus placei, Trichostrongylus axei, Cooperia spp. and Oesophagostomum radiatum were responsible for parasitic gastroenteritis and that H. placei was the predominant nematode present in the young cattle on both farms. Faecal egg counts from resident cattle and necropsy worm counts revealed that pasture larval levels were directly related to the amount of rainfall. The total worm burdens in the animals were highest during the rainy season (March–June and October–December) and lowest during the dry seasons (July–September and January–February). The very low recovery of immature larvae of H. placei from the tracer calves indicated that arrested development is not a feature of the life cycle of this parasite in central Kenya. The maintenance of the parasite population depended on continuous cycling of infection between the host and the pasture. The agroclimatic conditions of the study area were such that, in general, favourable weather conditions for the development and survival of the free-living stages of gastrointestinal nematodes existed all year round.