力克斯种母兔营养水平研究

本研究旨在探讨繁殖母兔的能量、粗蛋白等营养需要量.试验设高能量高蛋白(第1组:DE11.31MJ/kg,CP 18.73%)、低能量高蛋白(第2组:DE 10.71MJ/kg,CP 19.54%)、高能量中蛋白(第3组:DE11.31MJ/kg,CP 17.02%)和低能量中蛋白(第4组:DE 10.47MJ/kg,CP 17.48%)4个组.繁殖127窝测定结果表明:怀孕母兔饲粮营养水平为消化能10.47MJ/kg、粗蛋白17.48%、粗纤维14.62%时,产仔数、产仔成活率、初生窝重最高;哺乳母兔饲粮营养水平为消化能10.71MJ/kg、粗蛋白19.54%、粗纤维12.52%时,有利于35日龄断奶仔兔数和断奶窝重的提高.     

青年獭兔消化能、粗蛋白水平研究

用 72只 10 0日龄左右青年獭兔进行能量、粗蛋白等营养需要量试验 ,设高能量高蛋白 (第 1组 :DE 11 17MJ/kg ,CP18 44 % )、高能量中蛋白 (第 2组 :DE 10 98MJ/kg ,CP 16 2 9% )、低能量高蛋白 (第 3组 :DE 10 5 3MJ/kg ,CP 19 2 9% )和低能量中蛋白 (第 4组 :DE 10 2 6MJ/kg ,CP 16 0 5 % ) 4个组。 74天生长发育和被毛质量测定结果 :①饲喂消化能为10 98～ 11 17MJ/kg的饲料 ,有利于青年獭兔生长速度和饲料利用率的提高 ,也有利于屠宰率的改善。其中以消化能为11 17MJ/kg、粗蛋白 19 2 9%的饲料 ,其生长速度和饲料利用率最好。②饲喂消化能为 10 2 6～ 10 5 3MJ/kg、粗蛋白16 0 5 %～ 19 2 9%的饲料 ,有利于毛皮质量的提高。③综合本研究结果 :生产优质商品兔皮的青年兔饲喂含消化能为10 2 6～ 10 5 3MJ/kg、粗蛋白 16 0 5 %～ 19 2 9%的饲料为宜。     

日粮能量、蛋白水平对断奶仔猪生长性能、血液生化指标及激素水平的影响

本试验选用300头(28±1)日龄断奶的杜长大仔猪,按体重、胎次相近的原则分为5组,分别饲喂能量蛋白质水平不同的日粮,研究日粮能量和蛋白质水平对断奶仔猪生长性能、血液生化指标和激素水平的影响。结果表明:断奶仔猪日粮CP 19%,DE 13.59 MJ/kg时平均日增重最佳,CP 18%,DE 13.38 MJ/kg时饲料转化率最高,不同能量蛋白水平对仔猪血清尿素氮、胃泌素和皮质醇含量有显著影响(P<0.05)。     

饲粮能量水平对高山美利奴断奶公羔生长发育和屠宰性能的影响

试验旨在研究饲粮能量水平对高山美利奴（Ovis aries）断奶公羔生长发育和屠宰性能的影响。选择4月龄断奶体重相近（24 kg）的高山美利奴公羔45只，随机分为3组，每组15只，分别单笼饲喂高能量水平饲粮（10.5 MJ/kg）、中能量水平饲粮（10.1 MJ/kg）和低能量水平饲粮（9.7 MJ/kg）。研究结果表明，正试期第84天，饲喂高能量组试验羊体高显著高于低能量组（P<0.05）；正试期第28天和第56天，饲喂高能量组和中能量组试验羊平均日采食量显著低于低能量组（P<0.05）；饲喂高能量组试验羊胴体重显著高于低能量组（P<0.05）；饲喂中能量组试验羊屠宰率显著高于低能量组（P<0.05）。因此，在本试验条件下，高山美丽奴断奶公羔的适宜饲粮代谢能水平为10.5 MJ/kg。     

添加纤维素复合酶制剂对羔羊日粮营养物质消化的影响

为研究纤维素酶制剂对羔羊消化性能的影响,选取体重相近、健康断奶的萨福克羊与小尾寒羊杂交一代4月龄羔羊60只,随机分为5组,分别为对照组(CP 18.54%,DE 13.04 MJ/kg)、低蛋白日粮加酶组(Ⅰ组CP 16.44%,DE 13.04 MJ/kg,复合纤维素酶0.2%)、低蛋白日粮组(Ⅱ组CP 16.44%,DE 13.04 MJ/kg)、低能量日粮加酶组(Ⅲ组CP18.54%,DE 12.26 MJ/kg,复合纤维素酶0.2%)、低能量日粮组(Ⅳ组CP 18.54%,DE 12.26 MJ/kg).饲喂30天后,采用全收粪法收集粪样.结果表明日粮能量水平和蛋白质水平影响羔羊对日粮营养物质的消化.降低日粮蛋白或能量水平显著降低了日粮DM、CP、EE、CF的消化率以及钙、磷吸收率.比较而言,能量水平对各种养分消化率的影响更大.同时,酶制剂作用效果受日粮能量水平的影响大于日粮蛋白质水平对其的影响;低蛋白日粮加入复合纤维素酶制剂有提高粗纤维消化率的趋势(但未达到显著水平,P＞0.05),不能提高粗脂肪的消化率和钙磷的吸收率;而低日粮能量水平添加加酶制剂,可以显著提高(P＜0.05)粗脂肪的消化率、钙的吸收率,但不能提高粗纤维的消化率,也不能改善磷的吸收率.     

饲粮能量和蛋白质水平对61～120日龄湖羊羔羊生长性能、氮代谢和血清生化指标的影响

本试验旨在研究饲粮能量和蛋白质水平对61~120日龄断奶湖羊羔羊生长性能、氮代谢及血清生化指标的影响。采用2×2两因素两水平试验设计,选取64只61日龄体重相近的纯种湖羊羔羊,随机分为4组,饲喂不同能量和蛋白质水平的饲粮,分别为高能量[代谢能(ME)为10.92 M J/kg]高蛋白质[粗蛋白质(CP)为15.74%]组、高能量(M E为10.92 M J/kg)低蛋白质(CP为11.78%)组、低能量(ME为8.64 MJ/kg)高蛋白质(CP为15.72%)组、低能量(ME为8.64 M J/kg)低蛋白质(CP为11.82%)组,每组4个重复,每个重复4只,公母各占1/2。试验期60 d。结果表明:1)饲粮能量与蛋白质水平对羔羊生长性能指标不存在交互作用(P0.05);饲粮高能量高蛋白质水平显著提高了羔羊61~90日龄的平均日增重(P0.05),显著降低了料重比(P0.05)。2)饲粮高蛋白质水平显著提高了81~90日龄、111~120日龄羔羊氮摄入量(P0.05);饲粮低能量高蛋白质水平显著提高了81~90日龄、111~120日龄羔羊尿氮排出量(P0.05),并且以低能量高蛋白质组尿氮排出量最高;对于81~90日龄羔羊,饲粮高能量高蛋白质水平显著提高了氮沉积(P0.05),而饲粮低能量或高蛋白质水平显著降低了氮生物学效价(P0.05)。3)羔羊120日龄时,饲粮低能量水平显著降低了血清葡萄糖含量(P0.05),显著提高了血清尿素氮含量(P0.05);饲粮低蛋白质水平显著提高了血清胰岛素样生长因子Ⅰ含量(P0.05)。综上所述,61~90日龄阶段,饲粮高能量高蛋白质水平可促进羔羊生长;91~120日龄阶段,可适当降低饲粮蛋白质水平以节约生产成本,不会对生长性能产生不利影响。     

天津白猪生长肥育期饲粮适宜能量蛋白质水平的研究

试验选用96头天津白猪(去势公猪,母猪各半),采用双因子(能量、蛋白质)两水平(高、低)2×2交叉随机化区组设计,通过饲养试验研究天津白猪生长(20～60kg)和肥育(60～90kg)阶段适宜的饲粮消化能浓度和蛋白质水平.结果表明,天津白猪母猪全期平均日增重较去势公猪略高,但未达到显著水准.饲粮消化能浓度在全期显著地影响猪日增重和饲料转化率,高能饲粮(DE13.39MJ/kg)处理显著大于低能饲粮(DE12.55MJ/kg)处理.饲粮蛋白水平在生长期显著影响日增重,高蛋白水平组(CP16%,566g)显著大于低蛋白组(CP13%,519g),但全期二者间日增重(619gvs 597g)差异不显著;蛋白质水平对饲料转化率没有影响.采用高营养饲养方式有利于提高猪日增重和饲料转化率,建议天津白猪饲粮的适宜消化能浓度为13.39MJ/kg,蛋白质水平为生长期16%、肥育期13%.     

日粮营养限制及补偿对蒙古羔羊瘤胃内环境的影响

试验选用80只自然断奶的3月龄健康蒙古羔羊,平均体质量(14.72±1.10)kg,试验羊按各组体质量差异不显著的原则随机分为4个试验组。试验分为限饲期和补偿期,限饲期8周,各组日粮分别为:对照组(ME 10.88 MJ/kg,CP 15%)、低蛋白组(ME 10.88 MJ/kg,CP 10%)、低能量组(ME 9.41 MJ/kg,CP 15%)和双低组(ME 8.62 MJ/kg,CP 5.7%);限饲结束后进入补偿期,为期13周,各组日粮能氮水平相同(ME 9.75 MJ/kg,CP 12%)。试验结果表明:限制期及补偿期结束时,低能量组和对照组各内环境指标无显著差异。低蛋白组限制期氨态氮(NH3-N)质量浓度显著低于对照组;乙酸、丙酸及总挥发性脂肪酸(TVFA)质量浓度显著高于对照组;补偿期结束时,乙酸及TVFA质量浓度显著低于对照组。双低组限制期乙酸、丙酸、TVFA质量浓度和NH3-N质量浓度显著高于对照组,瘤胃菌体蛋白质量浓度显著低于对照组;补偿期乙酸、丙酸、TVFA质量浓度和NH3-N质量浓度显著低于对照组。说明在试验日粮限制条件下,蛋白营养限制和能量蛋白同时限制显著影响了瘤胃内环境,而能量限制对瘤胃内环境影响不显著。     

不同营养水平日粮对海南黑山羊肥育羔羊生长性能和器官指数的影响

试验旨在研究不同营养水平日粮对海南黑山羊肥育羔羊生长性能和器官指数的影响。采用2×3析因设计,将24只3月龄、体重为(10.56±1.28)kg海南黑山羊随机分成6个处理组,每个处理组4只羊(公、母各半),每只羊为1个重复。6个不同营养水平精饲料处理组分别为:试验1组粗蛋白质(CP)水平为15%、消化能(DE)水平为11.72 MJ/kg,试验2组CP 15%、DE 12.55 MJ/kg,试验3组CP 15%、DE 13.39 MJ/kg,试验4组CP 17%、DE 11.72 MJ/kg,试验5组CP 17%、DE 12.55 MJ/kg,试验6组CP 17%、DE 13.39 MJ/kg,试验期90 d。结果表明,精饲料粗蛋白质水平对试验羊平均日增重影响显著(P<0.05),17% CP日粮组试验羊有较高的平均日增重(P<0.05)和较低的料重比(P<0.05);日粮精饲料蛋白质和能量水平对心脏、肝脏、脾脏、肺脏、肾脏、胃的脏器指数影响均不显著(P>0.05),随着精饲料消化能水平的增加,肠道的脏器指数逐渐减小(P<0.05)。结果提示,补饲不同营养水平精饲料对3月龄海南黑山羊育肥期羔羊平均日增重和料重比均有显著影响(P<0.05),对黑山羊肠道重量及肠道器官指数影响显著(P<0.05),而对其他内脏器官指数无显著影响(P>0.05)。     

营养水平对肉犊牛营养物质消化率和血清指标的影响

研究不同能量、蛋白质水平的代乳品对南方地区哺乳期肉用犊牛营养物质消化和血清指标的影响,进而确立代乳品能量和蛋白质参数,为南方地区肉犊牛的饲料配制提供数据支持。采用2×2因子设计,犊牛代乳品的能量水平为16、14 MJ/kg,粗蛋白水平为25%、22%,共计4种。选取新生犊牛40头,21日龄断母乳并根据日龄和体重一致原则分为4个处理组,每组10头犊牛,分别饲喂上述4种代乳品,于77~85日龄进行消化试验并静脉采集血液。结果显示相同能量水平,犊牛对代乳品中粗脂肪和钙的表观消化率随粗蛋白水平的升高而提高(P0.05);较低粗蛋白水平代乳品,随其能量水平的升高,粗蛋白消化率显著提升(P0.05);低能低蛋白组(DE:14 MJ/kg,CP:22%)营养物质消化率略小于其它各组。饲喂低能量水平代乳品时,随其粗蛋白水平的升高,犊牛血清中尿素氮含量显著降低(P0.05);而饲喂高能量水平代乳品时,随其粗蛋白水平的升高,犊牛血清谷草转氨酶含量显著提高(P0.05);代乳品能量和粗蛋白水平对犊牛其它血清指标均无显著影响(P0.05)。高能量水平(DE:16 MJ/kg)有助于犊牛粗蛋白质消化吸收,高蛋白水平(CP:25%)有助于犊牛对粗脂肪和钙的利用,低能低蛋白水平(DE:14 MJ/kg,CP:22%)日粮不利于犊牛营养物质消化吸收。     

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.     

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.     

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

Tropical Animal Health and Production -     

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.     

Prevalence of gastric lesions in racing Alaskan sled dogs

Human and equine athletes are reported to have a high prevalence of gastric disease, and anecdotal evidence suggests a similar phenomenon applies to racing sled dogs. To investigate the prevalence of gastric disease in racing sled dogs, we conducted 2 gastroscopy studies on dogs competing in the annual Iditarod Sled Dog Race. A pilot study of dogs that were either dropped from the 2000 Iditarod Sled Dog Race because of illness or that finished the race indicated that, approximately 5 days after competing, 10 of 28 dogs (35%) had endoscopic evidence of gastric ulceration, erosion, or hemorrhage. The next year, an endoscopic study of 73 dogs participating in the 2001 Iditarod race was performed in order to evaluate a larger population of dogs. Data from 70 of these dogs could be used; 34 (48.5%) had ulceration, erosion, gastric hemorrhage, or some combination of these findings. When this group of 70 dogs was compared retrospectively to a control group of 87 dogs presented to the Texas A&M University (TAMU) Veterinary Medical Teaching Hospital, the Iditarod sled dogs had a significantly higher prevalence (P = .049) of gastric lesions. These findings suggest that, similar to athletes of other species, elite canine athletes have an increased prevalence of gastric disease compared to the canine population at large.     

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.     

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.     

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.     

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.