丁酸钠对犊牛胃肠道发育的研究进展

丁酸钠是一种绿色新型饲料添加剂，目前在动物饲料中应用广泛，且效果良好。作者主要介绍了丁酸钠的生物学功能、对犊牛胃肠道发育的影响及其在犊牛日粮中的应用效果。重点总结了丁酸钠促进犊牛胃肠道发育的影响机制，包括作为胃肠道组织的能量来源调控激素和生长因子的分泌，提高消化和吸收相关酶的分泌及活性，提高肠道免疫细胞保护性蛋白的分泌等。现有研究表明，日粮干物质中添加0.3%丁酸钠就能达到促进犊牛生长和胃肠道发育的效果，但具体添加水平、添加阶段和方式等尚不明确。此外，日粮粗饲料水平、精料发酵所产生的内源丁酸对外源丁酸钠的作用效果是否有影响也鲜有报道，有待进一步开展研究。     

诱食剂对荷斯坦犊牛生长性能和部分血清激素水平的影响

试验旨在研究饲粮中添加不同水平诱食剂对7～150日龄荷斯坦犊牛增重、耗料增重比、体尺指标、部分血清激素水平的影响。选取60头体重（33±2）kg、（7±3）日龄的荷斯坦母犊牛,随机分为3组,每组5个重复,每个重复4头牛。对照组饲喂基础日粮,试验组分别在基础日粮中加入300 mg/kg和500 mg/kg诱食剂（γ-壬内酯、乙基香兰素）,试验预试期7 d,正试期136 d,其中60～67日龄为断奶过渡期。结果表明：试验全期各组犊牛的体重均无显著差异;14～60日龄时,2个试验组犊牛的干物质采食量均高于对照组（P<0.05）;91～150日龄时,300 mg/kg诱食剂组犊牛的干物质采食量低于其他各组（P<0.05）;在断奶过渡期内,500 mg/kg诱食剂组的耗料增重比优于其他各组（P<0.05）;在犊牛断奶前后的60～67、61～90日龄,500 mg/kg诱食剂组犊牛的部分体尺增长率高于其他各组（P<0.05）;试验全期各组平均体尺增长率均无显著差异;试验全期各组的血清胰岛素、生长激素、类胰岛素样生长因子-I、神经肽Y、5-羟色胺、γ-氨基丁酸含量之间均无显著...     

结构性饲料对哺乳期和断奶应激期犊牛采食量和生长性能的影响

试验旨在研究群饲犊牛自由采食酸化奶的条件下,结构性饲料对哺乳犊牛和断奶应激期犊牛生长性能的影响。选择3～5日龄、体重相近犊牛300头,随机分为6栏,每栏50头,随机选择3栏饲喂常规颗粒犊牛开食料(颗粒料组),其余3栏饲喂结构性犊牛开食料(结构料组)。两种日粮的配方完全一致。颗粒犊牛料中所有物料均经粉碎、混合、制粒,制成颗粒料。将饲粮配方中玉米和大麦取出,换为蒸汽压片玉米和带壳大麦,其余物料粉碎、混合、制粒,为颗粒浓缩料,再将颗粒浓缩料与蒸汽压片玉米、带壳大麦混合,制成结构性饲料。整个试验分为哺乳期和断奶应激期共计90 d,哺乳期试验第1 d饲喂酸化奶,第15 d供应开食料。颗粒料组犊牛在哺乳期饲喂开食料,断奶后补饲苜蓿干草。结构料组犊牛断奶后饲喂结构性生长料。将结构性开食料与20%苜蓿干草混合,制成结构性生长料。结果表明:哺乳期间,结构性饲料采食量比颗粒料组高40%(P<0.05),日增重高19%(P<0.01);断奶应激期间,结构性饲料采食量比颗粒料组高29%(P<0.01),日增重高25%(P<0.01),饲料利用效率高11%(P<0.05);试验结束时,结构料组犊牛体重更高(P<0.05)。综上所述,在哺乳期自由饮用酸化奶的条件下,结构性饲料在哺乳期和断奶应激期的效果均优于传统颗粒开食料,可促进犊牛生长,缓解断奶应激。     

不同诱食剂对安格斯犊牛生长性能、养分表观消化率及部分血清激素的影响

试验旨在研究日粮中添加不同诱食剂对安格斯犊牛生长性能、养分表观消化率及部分血清激素的影响。采用单因子随机区组设计,选用平均体重165.1 kg±35.5 kg、约6月龄的健康安格斯肉犊牛24头,随机分为A、B、C、D 4组,每组6个重复。A组为对照组,饲喂全混合日粮（TMR）;B、C、D组分别饲喂TMR+0.24%绿色素、TMR+1.2 g/d XTRACT^® 7065（香味剂）、TMR+0.4%甜蜜素。预饲期10 d,正饲期30 d。结果显示,与对照组相比,B、C、D组平均干物质采食量（ADMI）均显著提高（P < 0.05）。各诱食剂均能提高犊牛营养物质表观消化率,但各诱食剂的影响程度不同,其中B组酸性洗涤纤维（ADF）表观消化率显著高于其他诱食剂组（P < 0.05）,B组中性洗涤纤维（NDF）表观消化率显著高于对照组（P < 0.05）。在试验第31天采食后1 h,各组间神经肽Y（NPY）和5-羟色胺（5-HT）含量差异均不显著（P > 0.05）,B、D组NPY含量高于对照组,C组则低于对照组,B、D组5-HT含量均低于对照组,而C组则高于对照组。综合考虑,日粮中添加绿色剂、香味剂及甜味剂均可在一定程度上提高犊牛生长性能及营养物质消化率;绿色剂和甜味剂可以提高犊牛血清中NPY含量,而香味剂则使犊牛血清中5-HT含量升高。     

犊牛人工乳哺育试验

本试验选用1～3日龄的黑白花公犊9头,随机分为3组,即对照组、试验Ⅰ组和试验Ⅱ组。对照组喂常乳,试验Ⅰ组喂混合乳,试验Ⅱ组喂人工乳。试验结果表明,对照Ⅱ组的平均日增重比对照组提高10%,试验Ⅰ组的平均日增重比对照组降低了12.5%,饲养成本分别降低了21.8%和41.7%,而且生长发育各项指标差异不显著(p>0.05);与常乳比,试验Ⅱ组的乳肉比15.7∶1,小于试验。Ⅰ组的19.6∶1和对照组的17.5∶1,说明人工乳完全代替牛乳不仅能适合犊牛早期营养需要,而且对犊牛早期生长发育有较好的促进和补偿作用,并可减少疾病的发生,降低饲养成本,提高经济效益。     

不同结构性开食料对犊牛生长性能的影响

试验旨在研究开食料中添加糖蜜对犊牛生长性能及腹泻率的影响。选用24头3日龄健康荷斯坦奶牛犊牛作为试验动物,按体重相近原则随机分为4组,每组6头,对照组和试验1、2、3组分别饲喂不同方式处理的犊牛颗粒料。结果表明,在30日龄时,试验2组犊牛体重显著高于对照组(P<0.05);60日龄时,试验2、3组犊牛体重显著高于对照组(P<0.05),试验2组犊牛体高和胸围显著高于对照组(P<0.05);在整个试验期,试验2、3组犊牛采食量显著高于试验1组和对照组(P<0.05);在腹泻率方面,对照组最低,试验1组最高。因此,从对生长性能及体尺指标来看,颗粒料、玉米压片和小麦压片按7:2:1比例且再加5%糖蜜进行喷涂处理的犊牛开食料要优于其他各组,且饲料利用率最高。     

不同营养水平代乳料对夏南牛犊牛生长发育的影响

[目的]通过补饲代乳料提高夏南牛犊牛生长发育速度,培育优质健康犊牛,实现犊牛早期断奶。[方法]犊牛随机挑选并随机分成2个组,试验组使用B配方的饲料,对照组使用A配方的饲料,两组牛分圈饲喂,犊牛与母牛隔离饲养。代乳颗粒料自由采食,采取少给、勤给、逐渐增多的饲喂方法。试验期内测量犊牛体尺、体重,观察不同代乳料的适口性,记录疾病发生种类、次数和频率。[结果]试验组比对照组平均日增重提高17.78%,但差异不显著(P>0.05)。试验组比对照组体高、体斜长、胸围3项体尺分别增加了0.67 cm,1.04 cm和2.05 cm,差异不显著(P>0.05)。腹泻发病率试验组23.08%,对照组22.22%,两组均没有发生其他疫病和死亡。[结论](1)A、B两种代乳颗粒料均可以取代代乳粉,作为夏南牛犊牛的补饲料。(2)较高营养水平的代乳颗粒料,可以提高夏南牛犊牛日增重。试验用代乳颗粒料优于犊牛精料补充料。(3)B配方的代乳颗粒料适口性较好。     

高饲料成本下断奶犊牛培育的营养调控措施

目的 为了解决奶牛养殖企业在降低断奶犊牛培育饲料成本上存在的难点。方法 本试验在天津嘉立荷牧业集团有限公司断奶犊牛饲养管理技术水平上,对犊牛前期配合料进行营养水平调整,研发新的犊牛后期配合料,并对比两种犊牛颗粒料在断奶犊牛中的饲喂效果。结果 饲喂两种犊牛颗粒料,断奶犊牛日粮总采食量、日增重、日增体高、日增体斜长和日增腹围无差异（P>0.05）,其中平均日粮总采食量分别为5.70 kg和5.90 kg,平均日增重分别为1.20 kg和1.22 kg,平均日增体高分别为0.23 cm和0.22 cm,平均日增体斜长分别为0.27 cm和0.28 cm,平均日增腹围分别为0.43 cm和0.44 cm;饲喂了犊牛后期配合料,断奶犊牛腹泻率降低了0.20 个百分点,日粮采食成本可节约133.98 元/头·d;日增重成本可节约24.36元/头·d。结论 犊牛后期配合料既能降低断奶犊牛培育的饲养成本,又能满足断奶犊牛生长发育营养需要。     

豆乳作为新型代乳料促使犊牛采食开食料并可降低断奶日龄及成本

作者研究了豆乳替代部分母乳对断奶前犊牛生产性能和断奶成本的影响。试验选用27头新生荷斯坦犊牛(18头公,9头母)作为试验动物(体重:41.6±1.6 kg)。所有犊牛出生后3 d内饲喂初乳而后转为过渡期哺乳。试验采用完全随机试验设计,分为3个处理组,分别为对照组(饲喂全母乳)、75%母乳 25%豆乳组(S25)和50%母乳 50%豆乳组(S50),哺乳量为犊牛体重的10%(湿重基础)。犊牛日采食开食精料量达到900 g时,视为断奶标准。试验期前2周,各处理组犊牛采食开食料量和粪值间无显著差异,此时S25日粮组,犊牛体重接近于全母乳犊牛体重。在犊牛49日龄时,S25日粮组犊牛体重仍与对照组相似。S25和S50日粮组分别提前对照组10 d和12 d达到断奶标准。犊牛饲喂豆乳促进了犊牛对开食精料的采食量,因此相对于对照组哺乳量有降低现象。由于牛奶成本高于豆乳和开食精料50%之多,因此犊牛饲喂豆乳代替部分母乳可降低断奶成本近35%。虽然新生犊牛对非乳蛋白和植物抗营养因子及其敏感,但本试验中,犊牛在2至4周龄时,即便豆乳替代母乳高达50%,仍维持了犊牛的生理健康。研究结果显示,豆乳可作为经济有效的代乳料,益于提高犊牛饲养效价。     

复合菌颗粒料对犊牛瘤胃发酵参数及菌群结构的影响

为研究复合菌颗粒料对犊牛瘤胃发酵参数及菌群结构的影响,试验选择出生后健康且体重相近的20头安格斯犊牛随机分为2组,每组10个重复,每个重复1头牛。对照组饲喂颗粒料不添加任何复合菌,试验组添加1%复合菌颗粒料（酵母菌、枯草芽孢杆菌、植物乳杆菌,活菌数为3×108cfu/g）。试验期共100 d,其中预饲期10 d,正试期90 d。试验结束后抽取犊牛瘤胃液并测定相关指标。结果表明：试验组微生物蛋白（MCP）含量和Simposon指数显著高于对照组（P <0.05）;试验组Shannon指数和Chao指数极显著高于对照组（P <0.01）;试验组Sobs指数、Ace指数显著高于对照组（P <0.05）。门水平上,2组的优势菌门主要是拟杆菌门（Bacteroidota）和厚壁菌门（Firmicutes）。而属水平上2组的优势菌属为Prevotella,两组第二优势菌属不同：对照组为理研菌科＿RC9肠道群（Rikenellaceae＿RC9＿gut＿group）,试验组为未分类＿f＿Muribaculaceae(norank＿f＿Muribaculaceae)。由此可见,复合菌...     

用杀鼠剂和饵料对达乌尔黄鼠进行防治正交试验研究

为筛选出防治达乌尔黄鼠的杀鼠剂及其施用技术,用3种杀鼠剂、3个用药浓度、3个投饵量和3种饵料进行L9(34)正交试验,经方差分析和F检验发现,各因子对灭洞率的有效性自大至小顺序为:杀鼠剂用药浓度投饵量饵料种类。以灭洞率为评价指标,对不同因子各水平进行SSR测验证明:3种参试杀鼠剂的有效性依次为溴鼠灵(87.56%)C型肉毒梭菌生物毒素(80.00%)敌鼠钠盐(73.89%);灭洞率随用药浓度和投饵量变化,用药浓度越大、投饵量越多,灭洞率亦越高;用玉米、苜蓿草颗粒和玉米秸秆草颗粒作饵料灭洞率差异不显著,表明用苜蓿草颗粒和玉米秸秆草颗粒代替粮食作达乌尔黄鼠的饵料是可行;A2B3C2D3(0.15%的溴鼠灵、苜蓿草颗粒作饵料、每个有效洞口投25粒毒饵)是最佳处理组合。     

不同处理方式的苜蓿草对犊牛生长性能、瘤胃发酵及微生物蛋白合成的影响

文章旨在评估苜蓿草的不同处理方式及饲料形式对犊牛生长性能、瘤胃发酵及微生物蛋白合成的影响.试验将60头均重为40.01 kg的刚出生犊牛随机分为4组,每组5个重复,每个重复3头牛.试验日粮采用多因素方差设计,2种苜蓿草处理方式(切碎和制粒)和2种饲料形式(粉料和颗粒料).T1组为切碎苜蓿草+粉料,T2组为制粒苜蓿草+粉...     

新疆维吾尔自治区应用C·肉毒杀鼠素灭鼠试验报告

Ｃ·肉毒杀鼠素（下称毒素）０．１％浓度毒饵，对新疆的主要害鼠大沙鼠和黄兔尾鼠进行灭治，校正灭洞率分别为９７．４％和９０．２％，均可取得良好效果。常用农药０．５％甘氟毒饵的灭治效果分别为９８．５％和６７．１％。因此，毒素能够代替甘氟在新疆草地灭鼠中应用；以小麦和草颗粒作载体与０．１％毒素拌制毒饵，灭杀大沙鼠和黄兔尾鼠灭洞率分别为９８．２％、９９．３％和９０．２％、９１．７％，两种载体均可使用；新疆草地的害鼠四月份正值数量低峰期，废弃洞数量很大，有效洞率大沙鼠为９．３７％、黄兔尾鼠为１４．７０％。     

Efficacy of sustained release needle-less ceftiofur sodium implants in treating calves with bovine respiratory disease

Three experiments were conducted to determine preliminary efficacy of sustained release needle-less implants in effecting cure in calves with bovine respiratory disease. One hundred and twenty beef calves with a rectal temperature > or = 40 degrees C and shallow or labored respiration and coughing were used in these experiments. Four groups (1-ceftiofur sodium injections [days 1, 2, and 3], 2-ceftiofur sodium needle-less implants [days 1, 2, and 3], 3-ceftiofur sodium needle-less implants [days 1 and 3], and 4-ceftiofur sodium needle-less implants [day 1] were included. All treatments contained 250 mg of ceftiofur sodium and were administered intramuscularly in the neck after diagnosis of bovine respiratory disease. Experiment 1 included 20 calves (group 1-10 calves and group 3-10 calves; 213 to 255 kg) and calves were monitored for clinical efficacy. Experiment 2 included five calves per group (all four groups; 164 to 192 kg) and calves were bled frequently after treatment for desfuroylceftiofur (the primary ceftiofur metabolite) concentrations. Experiment 3 included 20 calves per group (all four groups; 160 to 205 kg) and calves were monitored for clinical efficacy. Blood desfuroylceftiofur concentrations remained above the minimum inhibitory concentration for Pasteurella haemolytica, Pasteurella multocida, and Haemophilus somnus for 24 hours after injection and 72 hours after implantation (P < 0.05). Mortalities and the number of calves with a positive response and relapse response were similar (P < 0.25) among the four groups. In summary, the administration of one-250 mg ceftiofur sodium needle-less sustained release implant was as efficacious in treating bovine respiratory disease as three daily 250 mg injections of ceftiofur sodium.     

Effect of castration technique on beef calf performance, feed efficiency, and inflammatory response

The objective of this experiment was to examine the effect of castration technique on daily feed intake (DFI), daily water intake (DWI), growth performance, residual feed intake (RFI), and inflammatory response in weaned beef calves. Seventy-five beef calves (214 ± 3.2 kg; 200 ± 26 d of age) were housed in a GrowSafe 4000 feed intake facility 7 d post weaning (15 calves/pen). Calves were offered a total mixed ration (TDN = 67.3% and CP = 12.2%, DM = 89%) for ad libitum consumption. On d 0, calves were assigned to 1 of 5 treatments (n = 15 calves/treatment): 1) steers castrated surgically pre-weaning (52 d of age; CON); 2) intact bulls (BULL); 3) bulls castrated by the Callicrate Bander on d 0 (No-Bull Enterprises LLC.; BAN); 4) bulls castrated by the Henderson Castrating Tool on d 0 (Stone Mfg & Supply Co.; HEN); and 5) bulls castrated surgically utilizing an emasculator on d 0 (SUR). Average daily gain, DFI, and DWI were recorded over 84 d. Blood was collected from a sub-sample of calves (n = 45) on d 0, 2, 6, 9, 12, and 15 relative to castration. Castration decreased (P = 0.06) ADG for castrates compared with CON from d 0 to 14 but not d 0 to 84. Daily feed intake and DWI were similar (P > 0.10) among treatments during d 0 to 84. Gain:feed was not affected by castration technique; however, RFI tended (P = 0.09) to be negative for CON and BULL compared with castrates on d 0 to 14 but not d 0 to 84. Acute phase protein analyses indicated that surgical castration (SUR or HEN) elicited a short-term inflammatory response in calves, whereas calves castrated with BAN elicited a delayed response. Calves castrated pre-weaning had improved d 0 to 14 ADG, feed intake, and inflammation response compared with calves castrated at weaning. Banding elicited a delayed negative response in ADG, DWI, and inflammation. In weaned calves, castration method did not affect performance, DFI, DWI, or inflammatory response during the 84-d trial.     

Influence of dietary protein concentrations on performance and nitrogen repletion in stressed calves

Three trials were conducted to determine the influence of dietary CP concentration on health and performance of market-transport-stressed feeder calves (Exp. 1 and 2) and on repletion of nutrients lost during a 3-d feed and water deprivation period in steers fed at maintenance energy intake (Exp. 3). In Exp. 1 (84 calves) and 2 (256 calves), feeder calves averaging 184 kg were transported from Tennessee to Texas. In Exp. 1, calves were fed receiving diets containing either 12 or 16% CP. In Exp. 2, calves were fed diets containing 12 or 16% CP and .8 or 1.3% potassium in a 2 x 2 factorial arrangement of treatments. In Exp. 3, four Hereford steers averaging 253 kg were used in an N balance trial. Steers were deprived of feed and water for 3 d and then were limit-fed (1 x maintenance energy requirements) diets calculated to meet 100, 120, 140 or 160% of CP maintenance requirements for 14 d in a 4 x 4 Latin square design. In Exp. 1, calves fed the 16% CP diet had faster (P less than .05) daily gains and higher (P less than .10) feed consumption than calves fed the 12% CP diet during the first 14 d. In Exp. 2, calf performance was not affected by diet CP or K content. Calves fed the 16CP-1.3K diet had lower (P less than .10) mortality than calves on the remaining treatments. In Exp. 3, N balance and serum urea N increased linearly (P less than .05) with increasing dietary CP. Results of these studies are interpreted to indicate that the CP requirement (g/d) of market-transport-stressed feeder calves is similar to requirements of nonstressed calves; however, the CP concentration of the diet of stressed calves may need to be increased when feed intakes are low.     

Farming practices in Sweden related to feeding milk and colostrum from cows treated with antimicrobials to dairy calves

Background

Milk produced by cows in receipt of antimicrobial therapy may contain antimicrobial residues. Such antimicrobial-containing waste milk must be withdrawn from human consumption and is therefore sometimes used as calf feed. Unfortunately, this approach might promote selection of antimicrobial resistant bacteria in the calves’ intestinal microbiota. The objectives of this study were therefore to obtain an overview of waste milk feeding practices on Swedish dairy farms and to investigate if these practices were associated with certain farm characteristics. A representative group of 457 Swedish dairy farmers participated in a web-based survey with questions about the use of colostrum and milk from cows treated with antimicrobials at dry off or during lactation, respectively, as calf feed.

Results

Colostrum (milk from the first milking after calving) and transition milk (milk from the second milking to the fourth day after calving) from cows treated with antimicrobials at dry off was fed to calves on 89% and 85% of the farms in the study, respectively. When antimicrobial therapy was given to cows during lactation, 56% of the farms fed milk that was produced during the course of treatment to calves, whereas milk that was produced during the subsequent withdrawal period was fed to calves on 79% of the farms. Surveyed farmers were less prone to feed such milk if the antimicrobial therapy was due to mastitis than other infections. In Sweden, a majority of antimicrobial treatments during lactation are systemic administration of benzylpenicillin and thus, the bulk of waste milk in Sweden is likely to contain residues of this drug. Feeding waste milk to calves was more common on non-organic farms, and on farms located in Southern Sweden, and was less common on farms with cows housed in cold free stalls barns.

Conclusions

Waste milk that may contain antimicrobial residues is, at least occasionally, used as feed for calves on a majority of surveyed Swedish dairy farms. Future work should focus on the effect of waste milk feeding on the occurrence of antimicrobial resistant bacteria in the calves’ intestinal microbiota.     

Effect of a trainer cow on health, behavior, and performance of newly weaned beef calves

Experiments were conducted to investigate the effects of the presence of a trainer cow on behavior, performance, health, and feeding patterns of newly weaned beef calves. In Exp. 1,252 weaned calves (270+/-18 kg) were allocated to 22 pens (11 to 15 calves per pen). A trainer cow was randomly assigned to each of 11 pens. Calves were weighed prior to feeding on d 0, 3, 7, 14, 21, and 28. Rectal temperatures were taken on each of these days (except d 28) and blood samples were collected on d 0, 3, and 7 and subsequently analyzed for serum haptoglobin and leukotoxin antibody titers. Instantaneous scan observations of calf behavior were made at 10-min intervals between 0730 and 1730 on d 1, 2, 4, 5, and 6. A similar protocol was used in Exp. 2, in which 297 calves (258+/-17 kg) were allocated to 24 pens. Blood analyses included haptoglobin, white blood cell counts (WBC), and neutrophil:lymphocyte (NL) ratios. In Exp. 3, the above protocol was followed and patterns of feed bunk attendance of individual calves were also monitored using radio frequency identification by passive transponder ear tags. Trainer cows did not influence (P > .10) calf rectal temperatures, requirements for antibiotic therapy, WBC, NL ratios, or leukotoxin antibody titers. Pooled across treatments, NL ratios were lower (P < .01) on d 0 (.31) than on d 3 (.36) or d 7 (.39). Although differences in weight gain were detected in some periods within the three experiments, there were no differences (P > .10) overall (d 0 to 28). Trainer cows did not affect (P > .05) frequency or duration of bunk visits by the calves. Averaged across treatments, frequency and duration of bunk visits increased (P < .001) from 9.6 visits/d and 56.7 min/d between d 0 and 3 to 12.3 visits/d and 108.9 min/d between d 15 and 21. The number of calves observed eating during scan sampling observations also increased from 16.4% on d 1 to 25% on d 4 (P < .10) and 29% on d 5 and 6 (P < .05). More (P < .05) calves were observed lying on d 1 (41.7%) and d 2 (45.3%) than on d 4 (37.5%), d 5 (34.8%), or d 6 (36.2%). With a trainer cow present, fewer (36.7% vs 41.5%; P < .001) calves were observed lying and more (11.7% vs 10.2%; P = .08) were observed walking than when no cow was present. Trainer cows did not improve calf health, time spent at the feed bunk, or performance of newly weaned calves.     

两用（粮食和饲料）作物研究现状及发展前景

随着经济发展和收入水平的提高，居民对粮食消费量出现降低和对畜产品需求量出现增加的现象并存，但优质饲料的缺乏阻碍了畜牧业的发展。两用（粮用和饲用）作物增加了冬季饲料供应，其已成为一些国家或地区农业生产系统中的重要组成部分（主要分布于农牧交错区）。梳理近年来国内外关于两用作物生产和利用的现状及发展趋势，重点概述的内容有：1）两用作物的利用背景；2）两用作物的概念；3）代表性地区；4）饲草、籽粒产量和经济收益；5）动物利用和畜产品等。同时，对当前两用作物生产系统中面临的问题和应对举措进行了展望，包括：1）播种时间和播种量的选择；2）放牧或刈割后的氮肥管理；3）作物放牧或刈割的适宜生育期；4）种质资源的选择等。总体而言，两用作物生产管理（包括放牧时间、施氮量、播种量和放牧强度等）不当增加了籽粒产量降低的风险，但基于农业生产系统的综合效益，作物以两用的形式进行生产和利用是有利可图的。     

Infectious agents associated with diarrhoea of calves in the canton of Tilarán, Costa Rica

A case-control study of calves under 3 months of age was carried out by weekly visits to 15 farms in the canton of Tilarán, Costa Rica. Most farms were dedicated to beef or dual-purpose (DP) production. Faecal samples were collected over a 6-month period from a total of 194 calves with clinical signs and from 186 animals without clinical signs of diarrhoea as assessed by a scoring system. The samples were investigated for the presence of viruses, bacteria and parasites. Torovirus was detected for the first time in Costa Rica and was present in 14% of calves with diarrhoea and in 6% of the controls. Coronavirus and Rotavirus were less frequently encountered in either one of the groups (in 9 and 7% of scouring calves and in 1 and 2% of controls, respectively). Escherichia coli was detected in 94% of all the faecal samples, but isolates from only three samples from calves with diarrhoea contained the K99 antigen. Similarly, Salmonella was found only in scouring calves. Cryptosporidium oocysts were detected in animals with signs of diarrhoea, while other coccidia oocysts, Strongylida and Strongyloides eggs were frequently found in animals both with and without diarrhoea. A conditional logistic regression (CLR) analysis to compare healthy and scouring calves showed a significant difference with regard to the presence of Torovirus, Rotavirus and Coronavirus.