Body weight changes and subsequent lambing rates of western whiteface ewes grazing winter range

The objective was to describe body weight change (BWC) and subsequent lambing performance of Columbia, Polypay, Rambouillet, and Targhee ewes that grazed shrub-dominated range in winter of 1989, 1990, and 1991. In December (winter), after breeding each year (yr; October to December), ewes were moved to range. Depending upon severity of climatic conditions and vegetation accessibility, ewes grazed winter range for 30 to 60 days (d). Body weights were measured 2 d before grazing commenced (initial) and 2 to 7 d after ewes were transported off range (exit). Total BWC was calculated by subtracting finial BW from initial BW. All data were analyzed within each breed, as repeated measures using mixed models with age and year included in the model. For all breeds, 2-yr-old ewes were lightest going on to winter range and had the lowest lambing rate. Ewes lost weight while grazing winter range, but mature BW, once achieved, was restored annually with the exception of the 7-yr-old Columbia and Targhee ewes. Regardless of breed or age, ewes were able to achieve lambing rates > 1.5 lambs following early- and mid-pregnancy weight loss. Lambing rates were greater in older ewes, which generally experienced substantial negative BWC during winter grazing.     

冷季放牧补饲对甘肃高山细毛后备母羊瘤胃代谢参数及瘤胃微生物数量的影响

旨在筛选出甘肃高山细毛羊后备母羊科学合理的补饲料,改变牧区由于营养供给不足导致甘肃高山细毛羊2.5岁才能配种的饲养方式。试验选择甘肃高山细毛羊(12月龄)48只,随机分为试验a(1号料)、b(2号料)、c(3号料)组和对照组(不补饲),进行90 d放牧补饲试验。结果表明,1)瘤胃pH试验a组和b组差异极显著(P<0.01)、c组显著(P<0.05)低于对照组,瘤胃氨态氮、蛋白氮、总氮浓度试验组均极显著高于对照组(P<0.01),总挥发性脂肪酸(VFA)试验a组和b组均极显著高于对照组(P<0.01),b组显著高于c组(P<0.05);乙酸和丙酸摩尔比a组极显著高于对照组(P<0.01),b和c组显著高于对照组(P<0.05);丁酸摩尔比a组极显著高于c组(P<0.01);乙/丙b组显著低于对照组(P<0.05)。2)瘤胃纤维降解菌和原虫数目试验组均极显著(P<0.01)或显著(P<0.05)高于对照组。综上所述,补饲均能正向影响甘肃高山细毛羊后备母羊瘤胃代谢参数及瘤胃微生物数量,以1号料补饲效果最优,2号料也能起到理想效果。     

放牧强度对高寒草地产草量及羊体质量增加的影响

以托云牧场高寒草地为研究对象,通过设置3个放牧样地,一个对照样地,研究不同强度放牧对草地地上生物量的影响以及在不同放牧压力下羊体质量增加的效果。结果表明,1）托云牧场是以银穗草（Leucopoa albida）、羊茅（Festuca arioides）、点地梅（Androsace umbellata）和棘豆（Oxytropis falcatae）为优势种的高山草地;2）高寒草地地上生物量较低,禁牧区7月地上生物量（干物质）仅830 kg·hm-2;3）放牧活动对地上生物量有较大影响,重度放牧能显著降低牧场地上生物量;4）以羊体质量增加值为评价指标,该高寒牧场在载畜量为1.05羊单位·hm-2时能获得较好的体质量增加效果。     

不同日龄阿勒泰大尾羊脂肪组织形态学及血脂指标的比较

为了研究阿勒泰大尾羊不同部位脂肪组织沉积的变化规律,本试验选取90和270日龄健康、雄性阿勒泰大尾羊各6只,分别采集了90和270日龄时肾周脂、尾脂、腹部皮下脂肪组织样和血清,采用冰冻脂肪组织切片油红O滴染技术和Motic显微数字图像处理系统,测定脂肪细胞面积,并采用放射性免疫技术和酶联免疫法测定了血脂指标.结果显示,90日龄时,阿勒泰大尾羊尾脂脂肪细胞面积极显著高于肾周脂脂肪细胞面积(P<0.01),270日龄时,尾脂和腹部皮下脂肪脂肪细胞面积均极显著高于肾周脂脂肪细胞面积(P<0.01),但脂肪细胞的面积在尾脂和皮下脂肪之间无显著差异(P>0.05);与90日龄相比,270日龄阿勒泰大尾羊肾周脂脂肪细胞面积显著增高(P<0.05),而尾脂脂肪细胞面积极显著降低(P<0.01);90日龄阿勒泰大尾羊血清中leptin和HSL含量极显著高于270日龄(P<0.01),而血清中AST和ALT含量极显著低于270日龄(P<0.01).结果表明,阿勒泰大尾羊从90日龄生长至270日龄时,肾周脂脂肪细胞面积呈增加的趋势,而尾脂脂肪细胞的面积呈减少的趋势,这种变化可能与血清瘦素、激素敏感脂肪酶、天门冬氨酸氨基转氨酶和丙氨酸氨基转移酶含量有关.     

天然放牧条件下性别对苏尼特羊肌肉组织中胆固醇、脂肪酸含量和血清生化指标的影响

试验旨在研究不同性别的苏尼特羊血清生化指标及肌肉组织中脂肪酸与胆固醇含量存在的差异.试验选择在天然草场放牧的8月龄羯羔、母羔各8只,禁食12h、禁水2h进行屠宰,测定背最长肌、臂三头肌、股二头肌、臀肌中的脂肪酸、胆固醇等指标.结果 显示,母羔血清中白蛋白(ALB)和钙(Ca)含量显著高于羯羔(P＜0.05),而碱性磷酸...     

复合营养调控剂对冷季放牧绵羊生长性能、屠宰性能和血清生化指标的影响

试验旨在研究不同营养调控剂对冷季放牧绵羊生长性能、屠宰性能和血清生化指标的影响。采用单因素完全随机区组试验设计,将48只健康、体重相近(28.01±1.70)kg的7月龄放牧母羊随机分为4组,Ⅰ组不补饲;Ⅱ组补饲常规精料;Ⅲ组补饲常规精料+复合配方1 (0.30%苹果酸、0.06%半胱胺、0.08%糖萜素);Ⅳ组补饲常规精料+饲料复合配方2 (0.60%苹果酸、0.12%半胱胺、0.16%糖萜素)。其中每组3个重复,每个重复4只,进行45 d饲养试验。结果表明:①试验Ⅲ组末重最高,较Ⅱ组和Ⅳ组分别提高6.26% (P>0.05)、3.69% (P>0.05);试验Ⅲ组平均日增重最高,较Ⅱ组和Ⅳ组分别提高26.32% (P<0.01)、5.74% (P>0.05)。②试验Ⅲ组的屠宰率较Ⅱ组提高4.68% (P>0.05);试验Ⅲ组的净肉率较Ⅰ组、Ⅱ组和Ⅳ组分别提高18.46% (P<0.05)、10.97% (P>0.05)和4.40% (P>0.05);试验Ⅲ组的胴体净肉重较Ⅰ组、Ⅱ组和Ⅳ组分别提高49.74% (P<0.01)、13.22% (P>0.05)和18.27% (P<0.05);试验Ⅲ组的胴体净肉率较Ⅰ组、Ⅱ组和Ⅳ组分别提高10.42% (P<0.01)、6.00% (P>0.05)和3.37% (P>0.05)。③在血清GLU、Ca、P、HDL、LDL、GPT、IgG含量中,试验Ⅰ、Ⅱ、Ⅳ和Ⅲ组依次呈上升趋势,而其A/G、TG含量依次呈下降趋势。综上,补饲复合营养调控剂可改善冷季放牧绵羊的生长性能、屠宰性能和血清生化指标,其中补饲复合配方1组(试验Ⅲ组)作用效果最佳。     

冷季牦牛和黄牛采食行为、血清生化指标与瘤胃发酵参数的比较研究

本试验为研究冷季营养匮乏对放牧牦牛和黄牛血清生化指标、瘤胃发酵参数及放牧行为的影响,选取体重相近、健康无病的4岁母牦牛和母黄牛各10头,分别于2018年11月、2019年1和3月佩戴MOOnitor监测系统对其放牧行为进行研究.在试验期末(2019年3月)采集牧草样品、瘤胃液和血液,用于牧草营养成分、血清生化指标和瘤胃...     

Effects of Complex Nutritional Regulation Additives on Growth Performance,Slaughter Performance and Serum Biochemical Indexes of Grazing Sheep in Cold Season

This experiment was conducted to investigate the effects of complex nutritional regulation additives on growth performance, slaughter performance and serum biochemical indexes of grazing sheep in cold season.A single factor random block design was used and 48 grazing ewes with the average weight (28.01±1.70) kg and 7 months old were randomly divided into 4 groups:Group Ⅰ without supplement;Group Ⅱ with concentrate;Group Ⅲ with concentrate+complex formulation 1 (0.30% malic acid, 0.06% cysteamine, 0.08% saccharicterpenin);Group Ⅳ with concentrate+complex formulation 2 (0.60% malic acid, 0.12% cysteamine, 0.16% saccharicterpenin)with 3 replicates per group and 4 grazing ewes per replicate.The results showed that:①The final weight of group Ⅲ was the highest and higher than group Ⅱ and Ⅳ by 6.26% (P>0.05)、3.69% (P>0.05), respectively.The average daily gain of group Ⅲ was highest, and higher than group Ⅱ and Ⅳ by 26.32% (P<0.01)、5.74% (P>0.05) respectively.②Comparing with group Ⅱ, the slaughter rate of group Ⅲ was increased by 4.68% (P>0.05).Compared with groupⅠ, Ⅱ and Ⅳ, the meat percentage of group Ⅲ was increased 18.46% (P<0.05), 10.97% (P>0.05) and 4.40% (P>0.05), while the net meat weight of carcass in group Ⅲ was increased by 49.74% (P<0.01), 13.22% (P>0.05) and 18.27% (P<0.05), respectively.Compared with groupⅠ, Ⅱ and Ⅳ, the net meat rat of carcass in group Ⅲ was increased 10.42% (P<0.01)、6.00% (P>0.05) and 3.37% (P>0.05), respectively.③There was a rising trend as the order of groupⅠ, Ⅱ, Ⅳ and Ⅲ in serum glucose, Ca, P, HDL, LDL, GPT and IgG, while A/G and TG showed a decreasing trend.Based on the above results, in this trial, supplementing complex nutritional regulation additives had good effects on growth performance, slaughter performance and serum biochemical indexes of grazing sheep in cold season.And supplementing complex formulation group 1 (group Ⅲ) was the best.     

绵羊肺腺瘤病毒内蒙毒株囊膜蛋白基医在大肠杆菌中的分段表达

为了建立原核高效表达体系，从自然感染绵羊肺腺瘤病毒内蒙毒株的肺肿瘤组织中提取基因组DNA，应用PCR技术分别扩增编码囊膜蛋白（env）基因的表面蛋白（surfaceprotein，su）和跨膜蛋白（transmembrane protein，TM）区域基因，通过T—A克隆的方法分别克隆入pGEM—TEasy载体中，然后利用设计的起始密码、终止密码以及相应酶切位点的引物，把env基因的SU区和TM区基因亚克隆到表达载体pGEX-4T～1中，分别构建SU和TM的重组表达质粒，经酶切、PCR及DNA测序鉴定后，将阳性质粒转化入大肠杆菌BL21CodonPlus中并在IPTG的诱导下表达，表达产物用SDS—PAGE分析鉴定。结果表明，该基因可以在大肠杆菌中以稳定的包涵体形式高效表达，表达的SU和TM融合蛋白表观分子质量约为68ku和46ku，表达量分别占全菌蛋白的25％和30％，并且从包涵体分离纯化得到的表达蛋白具有较高纯度，是一种理想的免疫原。     

绵羊肺腺瘤病毒内蒙毒株囊膜蛋白基因在大肠杆菌中的分段表达

为了建立原核高效表达体系,从自然感染绵羊肺腺瘤病毒内蒙毒株的肺肿瘤组织中提取基因组DNA,应用PCR技术分别扩增编码囊膜蛋白(env)基因的表面蛋白(surface protein,SU)和跨膜蛋白(transmembrane protein,TM)区域基因,通过T-A克隆的方法分别克隆入pGEM-TEasy载体中,然后利用设计的起始密码、终止密码以及相应酶切位点的引物,把env基因的SU区和TM区基因亚克隆到表达载体pGEX-4T-1中,分别构建SU和TM的重组表达质粒,经酶切、PCR及DNA测序鉴定后,将阳性质粒转化入大肠杆菌BL21 CodonPlus中并在IPTG的诱导下表达,表达产物用SDS-PAGE分析鉴定。结果表明,该基因可以在大肠杆菌中以稳定的包涵体形式高效表达,表达的SU和TM融合蛋白表观分子质量约为68 ku和46 ku,表达量分别占全菌蛋白的25%和30%,并且从包涵体分离纯化得到的表达蛋白具有较高纯度,是一种理想的免疫原。     

A multi-species model to assess the effect of refugia on worm control and anthelmintic resistance in sheep grazing systems

Objective Develop a computer simulation model that uses daily meteorological data and farm management practices to predict populations of Trichostrongylus colubriformis, Haemonchus contortus and Teladorsagia (Ostertagia) circumcincta and the evolution of anthelmintic resistance within a sheep flock. Use the model to explore if increased refugia, provided by leaving some adult sheep untreated, would delay development of anthelmintic resistance without compromising nematode control. Procedures Compare model predictions with field observations from a breeding flock in Armidale, NSW. Simulate the impact of leaving 1–10% of adult sheep untreated in diverse sheep‐grazing systems. Results Predicted populations of Tr. colubriformis and T. circumcincta were less than those observed in the field, attributed to nutritional stress experienced by the sheep during drought and not accounted for by the model. Observed variation in faecal egg counts explained by the model (R²) for these species was 40–50%. The H. contortus populations and R² were both low. Leaving some sheep untreated worked best in situations where animals were already grazing or were moved onto pastures with low populations of infective larvae. In those cases, anthelmintic resistance was delayed and nematode control was maintained when 1–4% of adult stock remained untreated. Conclusions In general, the model predicted that leaving more than 4% of adults untreated did not sufficiently delay the development of anthelmintic resistance to justify the increased production risk from such a strategy. The choice of a drug rotation strategy had an equal or larger effect on nematode control, and selection for resistance, than leaving 1–10% of adults untreated.     

Minimising the development of anthelmintic resistance, and optimising the use of the novel anthelmintic monepantel, for the sustainable control of nematode parasites in Australian sheep grazing systems

Objective To compare the risk of different treatment scenarios on selecting for anthelmintic resistance on Australian sheep farms. Design A computer simulation model predicted populations of Trichostrongylus colubriformis, Haemonchus contortus or Teladorsagia (Ostertagia) circumcincta, and the frequency of anthelmintic resistance genes. Method Nematode populations and the progression of drug resistance for a variety of treatment options and management practices in sheep‐rearing areas of Western Australia (WA), Victoria (VIC) and New South Wales (NSW) were simulated. A scoring system was devised to measure the success of each option in delaying resistance to each anthelmintic and in controlling nematode populations. Results The best option at all sites was combining the new anthelmintic (monepantel) with a triple mixture of benzimidazole, levamisole and abamectin (COM). The next best option was: in NSW, rotation at each treatment between monepantel, moxidectin and COM; in VIC, rotation at each treatment between monepantel and COM; and in WA, rotation at each treatment between monepantel (used in winter) and COM or moxidectin (used in summer–autumn). In WA, rapid selection for resistance occurred as a consequence of summer–autumn treatments; however, if a small percentage of adult stock were left untreated then this selection could be greatly reduced. Despite purposely assuming relatively high resistance to benzimidazole and levamisole, COM was still effective in controlling worms and delaying resistance. Conclusions Because of cost constraints, it may not be feasible or profitable for producers to always use the combination of all drugs. However, the second‐ and third‐best options still considerably slowed the development of anthelmintic resistance.     

Effects of supplemental protein sources during the grazing period on performance, ruminal characteristics and blood constituents in early weaned growing Wagyu steer calves

We investigated the effects of grazing and supplemental protein sources during the grazing period on growth performance, ruminal characteristics and blood constituents in 15 growing Wagyu steer calves weaned at 3 months of age. Each animal was allotted one of three treatments: (1) GSBM, soybean meal (SBM) supplemented as a protein source during a grazing period; (2) GCGM, corn gluten meal (CGM) supplemented as a protein source during a grazing period; or (3) NG, no grazing, in which steers were fed hay and GSBM concentrate only. The estimated rumen undegradable protein (RUP) concentration of CGM was higher than that of SBM. High RUP supplementation during the grazing period did not influence feed intake or growth performance. Compared with the NG treatment, the average daily gain in GSBM and GCGM calves was significantly depressed (P < 0.05). Bodyweight/withers height ratio in the NG calves tended to be greater than in the GSBM and GCGM calves. Final paunch girth/heart girth ratio in the GSBM and GCGM calves was significantly greater (P < 0.05) than in the NG calves. Supplementation with CGM did not influence ruminal ammonia nitrogen and blood constituents. These results indicate that CGM supplementation during the grazing period did not enhance the growth of Wagyu calves because the CGM diet probably did not elevate the metabolizable protein supply to the grazing calves above that of the SBM diet in our conditions.     

饲粮能量和蛋白质水平对21～60日龄湖羊生长、消化性能及血清指标的影响

旨在研究饲粮能量和蛋白质水平对21～60日龄湖羊羔羊生长、消化性能和血清指标的影响。本研究采用两因素两水平试验设计,选取64只17日龄体重相近、健康的湖羊羔羊,随机分为高能高蛋白(HE-HP)、高能低蛋白(HE-LP)、低能高蛋白(LE-HP)、低能低蛋白(LE-LP)4组,每组4个重复,每重复4只羊。试验预试期3d,21日龄起所有羔羊断母乳,饲喂代乳粉、补饲开食料。正试期40d。每天记录羔羊采食量,每隔20d晨饲前称重、颈静脉采血测定血清指标;31～40和51～60日龄期间采用全收粪法进行消化试验。结果表明:1)饲粮能量与蛋白水平对羔羊生长性能无显著交互作用(P>0.05),但羔羊日增重与饲料转化效率均随饲粮能量或蛋白质水平的降低而显著降低(P<0.05)。2)饲粮能量和蛋白质水平对羔羊31～40日龄干物质和总能消化率存在显著交互作用(P<0.05),表现为饲喂高能量饲粮时羔羊对饲粮干物质和和总能消化率随蛋白质水平的降低而显著降低(P<0.05)。3)40日龄羔羊血清葡萄糖含量随能量水平降低而显著降低(P<0.05);60日龄时,降低蛋白质水平显著降低了羔羊血清尿素氮含量(P<0.05)、提高了血清生长激素含量(P<0.05),降低饲粮能量水平显著提高了血清尿素氮和三酰甘油含量(P<0.05)。综上所述,能量和蛋白质水平对21～60日龄羔羊生长性能有显著影响,适当的能量和蛋白水平能够改善羔羊生长和消化性能。     

Comparison of blood electrolyte and biochemical parameters between single infections of rotavirus and Cryptosporidium parvum in diarrheic Hanwoo calves

BackgroundNeonatal calf diarrhea is a major problem in the cattle industry worldwide. Rotavirus and Cryptosporidium parvum are the primary causative agents, especially during the first three weeks of the calf’s life.ObjectivesThis study investigated the differences in acid-base, electrolytes, and biochemical parameters of diarrheic calves with infection of either rotavirus or C. parvum.MethodsA total of 61 Korean native calves (≤ 20 days old) were divided into two groups based on rotavirus or C. parvum infections: rotavirus infection (n = 44) and C. parvum infection (n = 17). The calves with at a specific blood pH range (pH 6.92–7.25) were chosen for comparison. The acid-base, electrolyte, chemistry, and serum proteins were analyzed, Further, fecal examinations were performed.ResultsCompared to C. parvum-infected calves, the rotavirus-infected calves showed lower levels of total carbon dioxide, bicarbonate (HCO₃ ⁻), anion gap, total protein, and albumin/globulin ratio, and significantly lower levels of potassium, globulin, and α2-globulin (p < 0.05). The C. parvum-infected calves (r = 0.749) had stronger correlations between pH and HCO₃ ⁻ than the rotavirus-infected calves (r = 0.598). Compared to rotavirus-infected calves, strong correlations between globulin and α2-globulin, α2-globulin and haptoglobin were identified in C. parvum-infected calves.ConclusionsThis study is the first to investigate acid-base, electrolyte, and biochemical parameters in calves in response to infections of rotavirus and C. parvum. Although rotavirus and C. parvum cause malabsorptive and secretory diarrhea in similar-aged calves, blood parameters were different. This would help establish the diagnostic and treatment strategies.     

Haematology and blood biochemistry during the course of psoroptic scabies in sheep

Haematology and blood biochemistry were monitored during the development and regression of psoroptic scabies in sheep. There were rises in numbers of neutrophils and eosinophils and in the fibrinogen concentrations, with lowered haemoglobin concentrations any lymphocyte numbers. The only biochemical parameters that were affected were the estimated serum globulin concentration, which rose during the disease process, and the serum albumin concentration, which fell. All of these changes reverted to normal soon after treatment.Abbreviations CK creatine kinase - Diff WBC differential white blood cell - E eosinophils - GOT asparate aminotransferase - GT glutamyl transferase - Hb haemoglobin - Ly lymphocytes - M monocytes - N neutrophils - WBC white blood cell count     

日粮硝酸盐水平对湖羊瘤胃硝态氮动态消失率、发酵参数及血液高铁血红蛋白含量的影响

本试验研究日粮硝酸盐的添加量对湖羊瘤胃还原硝态氮程度和对发酵参数及血液高铁血红蛋白的影响。试验选取6头湖羊,采用随机区组试验设计,每期分别饲喂含0%,1%,2%,3%,4%,5%硝酸钾的日粮。测定喂后0,0.5,1.0,1.5,2.0,4.0,6.0,8.0 h瘤胃液硝酸盐和亚硝酸盐含量及瘤胃发酵参数。晨饲后2.0 h通过颈静脉采血,测定高铁血红蛋白含量。结果表明,湖羊在采食1.0 h后硝酸盐含量达到最高(0.952.14 g/L),之后快速消失,亚硝酸盐含量在喂后1.5 h达到最高(0.936.22 μmol/L),之后降低。高铁血红蛋白的含量随硝酸盐添加量的增加而显著升高(P<0.01),最高达0.32%。添加硝酸盐显著提高瘤胃液pH值(P<0.01)和2.0 h的氨态氮含量(P<0.01)以及乙酸/丙酸,添加量高于3%会降低微生物蛋白和总挥发性脂肪酸的浓度,2%的硝酸盐添加量微生物蛋白和总挥发性脂肪酸的合成量最高,最有利于微生物发酵。     

The effect of exercise on blood parameters in standardbred and Finnish-bred horses

Serum enzyme activities, albumin, protein, urea, cholesterol, triglyceride, free fatty acid, glucose and lactate concentrations as well as hematocrit values were measured in standardbred and Finnish-bred horses at rest and after (i) a short controlled exercise and (ii) a trotting competition. There were no breed differences in the enzyme activities at rest and the 2 breeds responded in the same manner to the exercise. Only after the race proper significant increases in the enzyme activities were found. The activities rose more in the standardbred horses than in the Finnish-bred horses. Urea and cholesterol concentrations did not change after either exercise. Protein and albumin concentrations as well as hematocrit values increased significantly after the exercise. At rest hematocrit values were significantly higher in the standardbred horses and the difference persisted throughout the exercise. After the race proper also albumin and protein concentrations were higher in the standard-bred than in the Finnish-bred horses. Free fatty acid and triglyceride concentrations increased significantly during the exercise. Although glucose and lactate concentrations increased in both breeds, the behaviour of these parameters differed. Glucose concentrations remained increased for a longer period and the recovery from the increased lactate level was faster in the standardbred than in the Finnish-bred horses. The observed differences suggest that the standardbred horses have higher anaerobic capacity than the Finnish-bred horses.     

Sheep performance under intensive continuous grazing of native grasslands of <Emphasis Type="Italic">Paspalum notatum</Emphasis> and <Emphasis Type="Italic">Axonopus compressus</Emphasis> in the subtropical region of the Highlands of Central Mexico

Liveweight gain was evaluated in tropical Dorper X Pelibuey lambs under intensive continuous grazing of native grasslands dominated by Paspalum notatum (PN) or Axonopus compressus (AC) in the subtropics of Central Mexico. Two trials were undertaken. Trial 1 lasted 12 weeks with 10 lambs (initial weight 18 +/- 2.57 kg, 3 months old) per treatment in 2002, and Trial 2 for 13 weeks with 8 lambs (initial weight 24.0 +/- 2.0 kg, 4 months old) per treatment. Lambs were weighed once per week, and liveweight change was estimated by linear regression over day of the experiment, using individual regression coefficients as unbiased estimates of daily liveweight change; analysed in a random block design. Lambs on Trial 1 gained 0.061 kg/lamb/day on PN and 0.047 kg/lamb/day on AC (P > 0.05) at an overall mean stocking rate of 25 lambs/ha. In Trial 2, liveweight gain was significantly larger in PN (0.060 kg/lamb/day) than on AC (0.043 kg/lamb/day) (P < 0.05), at a mean stocking rate of 21.5 lambs/ha. It is concluded that intensive continuous grazing of native grasslands in the subtropics of the highlands of Central Mexico enables moderate liveweight gains for weaned lambs during the rainy season; with better results in grasslands dominated by Paspalum notatum.