Metabolizable Amino Acid Requirements of Feedlot Calves

One hundred ninety-two crossbred steers (229 kg) were used to evaluate the influence of metabolizable amino acid intake on growth performance and health during the initial 42-d receiving period. Treatments consisted of four levels of metabolizable lysine (23, 24, 25 and 26 g/kg diet DM). Morbidity averaged 36%, and was not affected (P > 0.20) by treatments. No steers died during the study. Increasing the metabolizable lysine supply increased DMI, ADG, gain efficiency, and dietary NE (linear effect, P < 0.01). Metabolizable amino acid supply of the basal diet was determined using 6 steers (214 kg) with cannulas in the rumen and proximal duodenum. Metabolizable amino acid supply of the diet was in close agreement with expected (R2 = 0.99;P < 0.0001) based on NRC (2000) [12] Level 1 model. The metabolizable amino acid supplies for treatments in Trial 1 were estimated by adding tabular metabolizable amino acid values for the respective supplemental proteins (cottonseed meal and fish meal) to the observed metabolizable amino acid supply of the basal diet. Treatment effects on metabolizable lysine supply explained 99% of the variation (P < 0.01) in ADG, and 91% of the variation in observed versus expected dietary NE. The biological value for the intestinal chyme was determined based on chemical score technique, using bovine tissue as the reference protein. Accordingly, methionine and lysine were closely co-limiting amino acids having ratios of 77% and 79%, respectively. We conclude that current NRC standards reliably predict both requirements and supplies of metabolizable amino acids for feedlot calves. Diet formulations that do not meet the metabolizable amino acid requirements may depress both ADG and the partial efficiency of utilization of metabolizable energy for maintenance and gain.

Extruded Corn Meal as a Partial Replacement for Steam Flaked Corn in Finishing Diets for Feedlot Cattle: Growth Performance and Digestive Function of Feedlot Cattle

Sixty-four Holstein steers (247 ± 4 kg) were used in a 70-d experiment to evaluate the effects of partial replacement of steam flake corn (SFC) with extruded corn meal (EC) on growth performance and dietary net energy. Treatments consisted of a steam flaked corn-based finishing diet containing 0%, 10%, 20%, or 30% EC, where EC replaced 0%, 15%, 30%, or 45% of SFC (DM basis). Replacement of SFC with increasing levels of EC did not affect (P > 0.10) ADG, DMI, and gain efficiency. When EC replaced 15% to 30% of SFC, observed dietary NE was 99% of expected. Whereas, when EC replaced 45% of SFC, observed dietary NE was 94% of expected. Four Holstein steers (210 ± 7 kg) with cannulas in the rumen and proximal duodenum were used in a 4 × 4 Latin square experiment to evaluate treatment effects on characteristics of digestion. Partial replacement of SFC with EC did not affect (P > 0.10) flow of undegraded feed N and microbial N and to the small intestine, and ruminal microbial N efficiency (g microbial N/kg OM fermented). Likewise, there were no treatment effects (P > 0.10) on ruminal digestion of OM, NDF, starch and feed N. As expected, total tract digestion of starch for all treatments exceeded 99%. However, partial replacement of SFC with EC decreased total tract digestion of DM and OM (linear effect, P = 0.02), and dietary DE (linear effect, P = 0.03). These effects were more pronounced where EC replaced 45% of SFC. Partial replacement of SFC with EC did not affect (P > 0.10) ruminal pH, total VFA concentration, molar proportions of acetate, propionate, and butyrate, and estimated methane production. It is concluded that partial replacement of SFC with EC does not have a beneficial effect on ruminal microbial efficiency and digestive function. The feeding value of extruded corn for feedlot cattle is comparable to that of steam flaked corn provided the inclusion rate does not exceed 20% of diet dry matter.

Effect of Supplemental Calcium Levels on Feedlot Growth Performance and Dietary Net Energy Utilization during the Receiving Feeding Period of Calf-Fed Holstein Steers

Ninety-six calf-fed Holstein steer (127 kg) were used to evaluate the influence of supplemental dietary calcium (Ca) on growth-performance, and dietary net energy (NE) utilization during the initial 112-d of receiving period. Treatments consisted of steam flake corn-based growing-finishing diets supplemented with limestone to achieve 0.60%, 0.70%, 0.80%, or 0.90% dietary Ca (DM basis). Morbidity was low (6.3%) and it was not affected (P > 0.87) by dietary treatments. During the initial 84-d period (181 kg average BW), increasing dietary Ca did not influence (P > 0.10) DMI, ADG, gain efficiency or observed/expected DMI. Observed DMI was 19% greater than expected based on diet formulation and growth. Estimated metabolizable protein and methionine supply during the initial 84-d period averaged 92% and 79% of the required, respectively. The apparent decrease in efficiency of energy utilization in the present study is in close agreement with previous studies involving calf-fed Holstein steers in the early growing phase fed conventional growing-finishing diet that is otherwise deficient in metabolizable amino acids. Thus, it is considered that the anticipated growth-performance responses to dietary Ca treatments may have been masked by expected inefficiencies due to metabolizable amino acid deficiency. During the final 28-d period (256 kg of average BW), increasing supplemental Ca reduced feed intake (linear effect, P = 0.04) and enhanced gain efficiency (linear effect, P = 0.03). During this period, predicted ([1] Level 1) metabolizable protein and methionine supply were 110% and 94% of the required, respectively. Nevertheless, improvements in gain efficiency during the final 28-d period with increasing levels of supplemental Ca were not sufficient to influence (P > 0.10) overall 112-d growth-performance. It is concluded dietary Ca requirements of calf-fed Holstein steers during the initial 112-d feeding period appear to be secondary to deficiencies of conventional steam-flaked corn-based diets in meeting metabolizable amino acid requirements. However, when those requirements are met during the early growing phase, gain efficiency responses are optimized at approximately 0.90% dietary Ca.

Determination of Particulate Matter Emissions from Cattle Feedlots Using Wind-Trax and the Flux-Gradient Technique

Large commercial cattle feedlots are significant sources of particulate matter (PM) emissions. This research compared WindTrax and the flux-gradient technique in estimating emissions of PM with aerodynamic diameter < 10 μm (PM10) from cattle feedlots. Meteorological conditions were measured and PM10 concentrations were profiled vertically (i.e., 2.0 to 7.62 m) at a large commercial beef cattle feedlot in Kansas from May through September 2011. Results show that between the two methods evaluated, WindTrax was least sensitive to changes in heights and number of heights used in the emission estimation, with calculated PM10 emission rates varying by up to 18% only. On the other hand, PM10 emission rates produced by the flux-gradient technique varied by almost 56% when changing either heights and/or number of heights in emission calculation. Both methods were sensitive to height settings, with their respective PM10 emission rates higher when the lowest height setting (2.0 m) was included. Calculating PM10 emission rates with the 7.62-m height led to lower estimates for the flux-gradient technique but no significant change in estimates was observed for WindTrax. As demonstrated in this study, for the flux-gradient technique, settings for the lowest and highest heights were the most critical in emission estimation;exclusion of other heights in between showed only to 2% to 6% change in calculated PM10 emission rates. In general, the higher PM10 emission rates were obtained with the flux-gradient technique. However, eliminating the lowest height (2.0 m) in the calculation and, at the same time, using a specific set of formulations for the flux-gradient technique made its calculated PM10 emission rates slightly lower (but not significantly different) than those from WindTrax.

Impact of Feedlot on Soil Phosphorus Concentration

Raising cattle in feedlots is becoming more common in Argentina, but there is little information available about the effects of this practice on soil phosphorus (P) dynamics. In this study, concentrations of water and Bray -1 extractable soil P were quantified in a feedlot (upper and lower slope positions in the feedlot pen), runoff area and pasture during 2006 - 2008. The feedlot showed higher P concentrations in all P forms, soluble reactive P, soluble nonreactive, total soluble P, and Bray-P1 when compared to runoff area and pasture. Most of the total soluble P was soluble reactive P from the soil in the feedlot and the runoff area, while soluble nonreactive P predominated in the pasture. Concentrations of total soluble P were elevated in the feedlot at the soil surface, ranging on average from 158.71 to 245.86 mg?P?kg?1, and had a rapid decrease within the first 20 cm and remained relatively low, about 25.53 - 27.33 mg?P?kg?1. The evidence that total soluble P concentration in the feedlot was significantly (p < 0.05) higher than that registered in the pasture at 20 - 40 and 40 - 60 cm soil depth suggests a potential transfer of P through the soil from the surface. Although the feedlot had a moderate increase of 23.05 to 24.55 mg?P?kg?1 from the background concentration, it may represent a long-term source of increased nutrient loading to groundwater. Soil extractable Bray-1 P in the top 0 - 2.5 cm fluctuated from 659.26 to 45.36 mg?P?kg?1 in the feedlot and pasture, respectively. The relationship between soil P extracted by test and TSP was linear, and correlation coefficient was r2 = 0.95.

The distribution of drinking water-to-cattle ratios in the summer across four feedlots in the Texas High Plains

In this short communication, we report the findings of a cross-sectional pilot study of the amount of water available per head of cattle (water-to-cattle ratio) and the associated feedlot and environmental factors across 26 pens in four Texas feedlots. The water-to-cattle ratio varied greatly among pens within and between feedlots. Mixed-effect linear regression modeling with feedlot as a random effect indicated that water in troughs with a higher water-to-cattle ratio was generally warmer when compared with water in troughs with a lower water-to-cattle ratio. This may have implications in the transmission and persistence of pathogens in feedlot cattle, such as Shiga toxin-producing Escherichia coli and Salmonella, because warmer water has been reported to favor the growth of these pathogens. Therefore, future field studies in feedlot cattle are warranted to assess whether the water-to-cattle ratio affects the prevalence of these pathogens in the water itself or in feces shed by the animals.

Wheat silage partially replacing oaten hay exhibited greater feed efficiency and fibre digestion despite low feed intake by feedlot lambs

This study aimed to investigate the feeding effect of wheat silage on growth performance,nutrient digestibility,rumen fermentation,and microbiota composition in feedlot lambs.Sixty-four male crossbred Chinese Han lambs(BW=27.8±0.67 kg,3 months of age)were randomly assigned to four ration groups with wheat silage replacing 0%(WS0),36%(WS36),64%(WS64),and 100%(WS100)of oaten hay on forage dry matter basis.The concentrate-to-forage ratio was 80:20 and the feeding trial lasted 52 d.Increasing wheat silage inclusion linearly decreased dry matter intake by 4%to 27%(P<0.01).However,increasing the wheat silage replacement of oaten hay by no more than 64%improved the feed efficiency by 14%as noted by the feed-to-gain ratio(P=0.04).Apparent digestibility of organic matter(P<0.01),neutral detergent fibre(P=0.04)and acid detergent fibre(P<0.01)quadratically increased.Ammonia nitrogen(P=0.01)decreased while microbial protein production(P<0.01)increased with the increase of wheat silage inclusion.Total volatile fatty acids concentration increased quadratically with the increase of wheat silage inclusion(P<0.01),and the highest occurred in WS64.The molar proportion of acetate(P<0.01)and acetate-to-propionate ratio(P=0.04)decreased while butyrate(P<0.01)and isovalerate(P=0.04)increased.Increasing wheat silage inclusion increased the Firmicutes-toBacteroidota ratio by 226%to 357%,resulting in Firmicutes instead of Bacteroidota being the most abundant phylum.The relative abundance of cellulolytic Ruminococcus numerically increased but that of amylolytic Prevotella(P<0.01)decreased as increasing wheat silage inclusion.Taken together,increasing wheat silage replacement of oaten hay by no more than 64%exhibited greater feed efficiency and fibre digestion despite low feed intake by feedlot lambs due to the change of Firmicutes-to-Bacteroidota ratio in the rumen.

Diet and monensin influence the temporal dynamics of the rumen microbiome in stocker and finishing cattle

Background Stocker cattle diet and management influence beef cattle performance during the finishing stage,but knowledge of the dynamics of the rumen microbiome associated with the host are lacking.A longitudinal study was conducted to determine how the feeding strategy from the stocker to the finishing stages of production affects the temporal dynamics of rumen microbiota.During the stocker phase,either dry hay or wheat pasture were provided,and three levels of monensin were administrated.All calves were then transported to a feedlot and received similar finishing diets with or without monensin.Rumen microbial samples were collected on d 0,28,85 during the stocker stage(S0,S28 and S85)and d 0,14,28,56,30 d before slaughter and the end of the trial during the finishing stage(F0,F14,F28,F56,Pre-Ba,and Final).The V4 region of the bacterial 16S rRNA gene of 263 rumen samples was sequenced.Results Higher alpha diversity,including the number of observed bacterial features and the Shannon index,was observed in the stocker phase compared to the finishing phase.The bacterial amplicon sequence variants(ASVs)differentiating different sampling time points were identified.Dietary treatments during the stocker stage temporally impact the dynamics of rumen microbiota.For example,shared bacteria,including Bacteroidales(ASV19)and Streptococcus infantarius(ASV94),were significantly higher in hay rumen on S28,S85,and F0,while Bacteroidaceae(ASV11)and Limivicinus(ASV15)were more abundant in wheat.Monensin affected rumen microbial composition at a specific time.Transportation to feedlot significantly influenced microbiome structure and diversity in hay-fed calves.Bacterial taxa associated with body weight were classified,and core microbiotas interacted with each other during the trial.Conclusions In summary,the temporal dynamics of the rumen microbiome in cattle at the stocker and finishing stage are influenced by multiple factors of the feeding strategy.Diet at the stocker phase may temporarily affect the microbial composition during this stage.Modulating the rumen microbiome in the steers at the stocker stage affects the microbial interactions and performance in the finishing stage.

甘肃高山细毛羊及其杂种羔羊育肥效果分析

为了解祁连山高寒牧区的羔羊育肥效果,给建立天祝县高寒牧区肥羔生产优化体系提供技术支撑。选择甘肃高山细毛羊和波德代(♂)×甘肃高山细毛羊(♀)F1代羔羊(简称波甘F1代)各40只,进行为期60 d的全舍饲高效育肥,系统观测育肥期内2个群体的4类生长结果、5个屠宰性能指标和6个肉品质指标,计算育肥经济效益。结果表明,经60 d短期育肥,波甘F1代平均日增重213.5 g/只,胴体重18.1 kg,屠宰率49.7%,均优于甘肃高山细毛羊。波甘F1代和甘肃高山细毛羊的熟肉率、肉色、剪切力、失水率和pH均无明显差异(P>0.05)。波甘F1代的大理石纹评分为3.73,显著高于甘肃高山细毛羊的2.86(P<0.05)。波甘F1代和甘肃高山细毛羊育肥期内的纯收入分别为308.2、182.0元。可见,2个群体经60 d的短期育肥,均取得了明显的效果,且波甘F1代在育肥期内的生长结果和屠宰性能均优于甘肃高山细毛羊。

Impact of Chromium Propionate Supplementation and Days of Adaptation on Energy Status in Newly Weaned Steer Calves*

The objective of this research was to evaluate the influences that supplemental dietary chromium propionate (CrP;0 or 0.4 mg·kg-1 added to the total diet on a DM basis) has on plasma indicators of energy status in newly weaned steers upon introduction to the feedlot. For this experiment single source, Angus steers (n = 28;BW = 289 ± 12.0 kg) from a ranch in Western South Dakota were weaned and immediately shipped 579 km to the Ruminant Nutrition Center (RNC) in Brookings, SD. Steers were allotted to one of four 7.6 m × 7.6 m pens (2 pens/diet;7 steers/pen) at 4 d post-arrival to the RNC and test diets were initiated. No anabolic implant was used in this study. Subsequent BW measurements were obtained at 1400 h, to accommodate a post-prandial timing for blood sampling. This was 4 h after initial access to feed, and immediately prior to the afternoon feed delivery. Weights and blood sampling occurred on d 5, 12, 19, and 33. Whole blood samples were collected from all steers via jugular venipuncture and separated as plasma. There were no diet x day interactions (P ≥ 0.51) for plasma glucose, insulin, or urea-N. Plasma glucose, insulin, and urea-n levels were similar between diets (P ≥ 0.35). Plasma glucose and urea-n levels were not different across days (P ≥ 0.59). Insulin levels differed as a result of days of adaptation and were greatest (P = 0.01) on d 12 regardless of diet. There tended (P = 0.12) to be a diet x day interaction for NEFA levels. Plasma NEFA levels tended to be lower (P = 0.13) for calves fed CrP on d 5, and were greater (P = 0.09) on d 12 in calves fed CrP. The shift in NEFA on d 12 coincided with the spike in insulin levels. Both events occurred at the time that NEg intake was approaching the acclimated plateau and neither event impacted glucose status. In non-ruminants, elevated insulin concentrations decrease circulating NEFA levels. We detected minimal differences in regard to plasma indicators of lipid metabolism in this study due to chromium supplementation. These data indicate that ruminants may differ from non-ruminants in the regulation and maintenance of glucose status and body fat catabolism during the post-absorptive state.

畜禽养殖基地磺胺类喹诺酮类和大环内酯类抗生素污染特征

利用固相萃取-高效液相质谱-串联质谱(HPLC-MS/MS)技术,调查了福建厦门市和莆田市畜禽养殖场的畜禽粪便、粪肥、作物土壤、沟渠底泥和人工湿地土壤共27份样品中8种抗生素的污染特征。结果表明:从样品类型来分析,除了大环内酯类在畜禽粪便中的平均检出浓度大于有机肥之外,样品中抗生素浓度顺序为有机肥>畜禽粪便>作物土壤、沟渠底泥和人工湿地;从抗生素种类来分析,喹诺酮类抗生素(QNs)的检出浓度最高,单个样品总含量∑QNs在粪肥中最高达到2967.6μg·kg-1,在作物土壤中最高达到579.0μg·kg-1;值得注意的是,14份作物土壤样品中有50%样品的∑QNs超过生态毒性效应浓度(100μg·kg-1);磺胺类抗生素(SAs)和大环内酯类抗生素(MLs)的检出浓度相对较低,单个作物土壤样品∑SAs和∑MLs都低于100μg·kg-1;从检出平均值和检出率来分析,磺胺类污染以磺胺二甲嘧啶(SM2)为主,大环内酯类以罗红霉素(ROX)为主,喹诺酮类检测浓度环丙沙星(CIP)最高,检出率恩诺沙星(ENR)最高。畜禽养殖基地的抗生素污染问题应该引起重视。

喷雾与纵向负压通风相结合的封闭牛舍降温效果

喷雾与纵向负压通风相结合的降温方式在猪舍、禽舍应用广泛,但在肉牛舍应用较少,该试验对喷雾与纵向负压通风相结合在封闭肉牛舍的运行模式进行了探究,并与喷雾结合扰流风机在开放肉牛舍的降温效果进行比较。该试验选用栓系饲养平均体质量273.4 kg的锦江黄牛杂交牛作为试验牛。处理舍安装低压两级雾化喷雾,配合卷帘和风机进行纵向负压通风降温;对照舍安装高压喷雾,结合扰流风机进行降温。两舍喷雾降温系统运行30 d,对环境条件、肉牛生理指标进行测定。结果表明低压两级喷雾在封闭牛舍纵向负压通风条件下喷雾与停止最佳时间均为5-10 min;经两舍喷雾系统降温后,处理舍的日平均温度为（30.4±0.1）℃,比对照舍和舍外分别降低了2.2、6.2℃（P〈0.01）,而相对湿度为89.7%±0.9%,较对照舍和舍外分别升高了11.3%、35.2%（P〈0.01）;处理舍试验牛的直肠温度为（38.28±0.03）℃,比对照舍低0.26℃（P〈0.01）;躺卧比为0.87±0.02,比对照舍高12%（P〈0.01）;日平均呼吸频率为（43±1）次/min,与对照舍没有显著差异（P〉0.05）;平均日增质量为（1.38±0.23）kg/d,比对照舍高0.19 kg/d（P〉0.05）;处理舍售牛可获利1042.39元/（月·头）,比对照舍高72.67元/（月·头）。可见封闭牛舍喷雾与纵向负压通风相结合降温效果显著,可改善牛舍环境,有效缓解肉牛热应激,提高生产性能。

猪场土壤中5种四环素抗性基因的检测和定量

近年来由于四环素在畜禽养殖业中的大量使用,诱导了环境中四环素抗性微生物的产生,然而有关四环素抗性基因在土壤中存在、迁移和扩散的研究目前还很少.论文提取了北京一规模化养猪场周边土壤的微生物DNA,利用普通PCR检测到5种四环素抗性基因(tet(B/P)、tet(M)、tet(O)、tet(T)、tet(W)),这5种基因都属于编码核糖体保护蛋白的一类.进一步建立了定量PCR程序对这5种基因进行了定量.结果显示,除tet(T)和tet(M)含量接近外(p=0.367),其余几种基因含量之间均差异显著(p<0.05),其中tet(W)的含量最高((2.16±0.20)×108copies·g-1(干土)),比含量最低的tet(B/P)((2.89±0.54)×106copies·g-(1干土))高出约两个数量级.抗性基因tet(W)、tet(T)、tet(M)、tet(O)含量均较高,为猪场土壤中优势抗性基因.这些基因曾被报道广泛存在于猪和牛的肠道中,显示抗性基因很可能是通过基因横向转移(HGT)等机制从养殖动物体内传播到周围土壤中土著微生物体内的.论文所建立的实验方法为进一步系统研究抗生素抗性基因在土壤中的环境行为及其生态风险提供了基础.

应用反演式气体扩散技术测定奶牛场甲烷的排放特征

为了准确揭示奶牛场的甲烷排放特征,在我国首次采用国际上最新的反演式气体扩散技术与开路式激光仪相结合的研究方法,分别于2009年冬季和2010年春季测定了保定市某奶牛养殖基地甲烷的排放特征,测定期间养殖基地的动物总量平均为1200头。结果表明,奶牛养殖场尺度的甲烷排放在冬季和春季均呈现出规律性的日排放特征,即养殖场甲烷日排放高峰出现在0500、1130和1630,排放高峰的出现时间与上料时间基本吻合;冬季和春季试验期间该养殖场的反刍和粪尿甲烷总排放量分别为0.31t.d-1和0.36t.d-1,养殖基地内整个牛群平均每头牛的反刍和粪尿甲烷日排放总量分别为0.26kg.d-1和0.30kg.d-1,春季的甲烷日排放量比冬季约高16.7,初步揭示了奶牛场尺度甲烷排放的季节性差异。

北京地区畜禽养殖场周边蔬菜地生食蔬菜抗生素耐药基因(ARGs)的赋存特性

我国畜禽养殖废水灌溉农田广为应用,其中携带的抗生素耐药基因(ARGs)给环境及人类健康带来了潜在的危害,亟需了解畜禽养殖场周边蔬菜地生食蔬菜可食部ARGs的赋存特性.本文选取北京地区畜禽场周边农田中10份蔬菜样品,采用非细菌培养方法直接提取细菌总DNA,通过PCR扩增,考察了5类(磺胺类、四环素类、大环内酯类、氯霉素类、喹诺酮类)ARGs的赋存特性.结果表明,蔬菜样品残留的磺胺类ARGs、四环素类ARGs存在范围最广(蔬菜表面、内部的检出率分别为100%、70%),喹诺酮类ARGs次之(蔬菜表面、内部的检出率分别为100%、60%).无论在种类还是数量,蔬菜样品表面携带的ARGs均比内部丰富;并且蔬菜样品表面及内部均检出已被禁用多年的氯霉素类ARGs(cml A).这说明畜禽养殖场周边蔬菜地生食蔬菜可食部分残留ARGs严重,可能会导致生食蔬菜大量附生及内生细菌的耐药,并通过食物链危害人类健康,应引起高度重视.

畜牧业污水中大环内酯和拟除虫菊酯类驱虫剂物质的LCMSMS检测

采用无需衍生化的固相萃取为前处理手段,高效液相色谱-串联四极杆质谱联用技术(LCMSMS)为检测手段,在电喷雾电离正离子模式下,对澳大利亚畜牧业污水中常见的大环内酯和拟除虫菊酯两类共7种驱虫剂物质的残留,建立了一次进样下的有效快速分析方法。经一系列优化试验,确定了以50%丙酮+50%乙腈为洗提剂、每次4 mL共8 mL的洗提方法。结果表明,该固相萃取技术(SPE)的加标回收试验结果较好,各化合物的平均回收率为95.50%～108.00%,相对标准差范围为0.73%～8.82%。以含10 mmol/L醋酸铵、0.1%甲酸的超纯水和甲醇混合溶液为流动相,以准分子离子峰[M+NH4]^+、[M+H]^+作为母离子的定量离子对,所建立的1～500 ng/mL范围内的8点校正曲线中,各物质的相关系数均高于0.998 0,定量限范围为0.03～2.47 ng/mL。实际样品测定时,不同处理流程中各化合物的残留浓度有较好地体现。

3种四环素耐药基因型肉牛肠道大肠杆菌对四环素类抗生素的耐药性分析

以低于治疗水平的氯四环素(CT)及低于治疗水平的氯四环素和治疗水平的氧四环素组合(CT-OX)两种方式分别对肉牛进行抗生素处理,研究其对肠道大肠杆菌耐药基因型的影响。从粪便样品分离大肠杆菌,并通过抗菌药物纸片法和稀释法敏感性试验测试分离出的大肠杆菌对四环素、氧四环素和氯四环素的敏感性。利用针对耐药基因tet(A)、tet(B)和tet(C)的引物对176个四环素耐药或中介的细菌样品进行多重PCR试验,结果发现所有样品均携带一种或两种耐药基因,tet(A)在两组样品中的流行基本相同,但CT组中tet(B)的流行比例显著小于CT-OX组(P<0.05),而tet(C)的流行比例则显著CT-OX组(P<0.05)。同时,在对四环素表现为中介的52个样品检测结果中,发现其中92.3%携带tet(C)基因。另外,最小抑菌浓度值(MICs)结果表明,药物敏感性同时取决于四环素类别和耐药基因型两方面。利用real-time PCR在转录水平上对tet(C)基因进行分析,发现耐药型与中介型并非上游调控造成。对tet(C)基因的测序分析结果发现,耐药型的第1063位碱基由T突变为G。由上述数据可知,对肉牛的四环素饲喂种类可以影响到大肠杆菌的耐药基因流行。

奶牛场氨排放特征的光谱检测

为实现奶牛场氨气减排,改善生态环境,需要在线监测氨挥发浓度并准确揭示氨排放特征。采用开放式可调谐半导体激光吸收光谱（TDLAS）技术设计了开放式氨气在线监测系统,结合反演式气体扩散技术开展相关研究,于2013年秋季和冬季在保定市某奶牛厂进行了氨排放浓度在线监测和排放特征分析工作。监测结果表明,秋季氨气浓度峰值为6.11×10-6%,冬季氨气浓度峰值为6.56×10-6%,氨浓度具有日变化趋势,基本呈白天浓度低,夜晚浓度高的特点。由反演气体扩散模型得到秋冬季氨排放特征,氨排放峰值均出现在中午,秋季氨排放速率为1.48~130.6kg/head/hr,冬季氨排放速率为0.004 5~43.32kg/head/hr,秋季的排放速率高于冬季,说明奶牛场尺度下的氨排放存在一定的季节性差异。该方法可以有效获得大范围、高灵敏、免采样、快速气体排放特征结果,为奶牛厂的氨排放监测和科学养殖提供技术支持。

舍饲与放养饲养方式下蕨麻猪肉的挥发性成分对比

利用气相色谱质谱联用技术(GC-MS),研究甘肃甘南藏族自治州舍饲(谷物饲料)与放养(天然草料)6月龄蕨麻猪背最长肌中的挥发性风味化合物。两者的差异主要体现在醛类化合物上(舍饲组38.33%,放养组25.19%)。对于来源于美拉德反应的挥发性化合物而言,甲硫基丙醛(呈肉香)与苯并噻唑(呈肉汤味)在舍饲组的含量分别比放养组多23%和122%。舍饲组脂肪氧化产物总相对含量显著高于放养组(P<0.05),且两组肉样中脂肪氧化产物的种类差异很大。放养组蕨麻猪肉中的萜类含量显著高于舍饲组(P<0.05)。结果表明,饲养方式会对蕨麻猪肉挥发性化合物产生影响,进而可能会影响到蕨麻猪肉的风味。

云岭黑山羊与波云F_1代山羊的育肥及肉质性能的研究

通过对9月龄波×师F1代、波×文F1代、波×楚F1代、师宗黑山羊、文山黑山羊、楚雄黑山羊进行育肥和屠宰试验,结果表明,在放牧+补饲条件下,波×师F1代、波×文F1代和波×楚F1代羊的平均日增重(分别为137.2、133.1和132.3g)明显高于师宗黑山羊、文山黑山羊和楚雄黑山羊的平均日增重(分别为103.6、102.3和101.6 g),且差异极显著;在全放牧条件下,波×师F1代、波×文F1代和波×楚F1代羊的平均日增重(分别为74.2、72.1和73.5 g)也高于师宗黑山羊、文山黑山羊和楚雄黑山羊的平均日增重(分别为48.7、47.8和46.1 g),差异极显著(P<0.01);对放牧+补饲育肥条件下的波×师F1代、波×文F1代、波×楚F1代、师宗黑山羊、文山黑山羊、楚雄黑山羊每组随机抽取6只做屠宰测定,师宗黑山羊、文山黑山羊、楚雄黑山羊的屠宰率、净肉率、眼肌面积等都低于波×师F1代、波×文F1代、波×楚F1代羊,差异显著(P<0.05)。羊肉品味评定综合口感差异不显著(P>0.05),表明各波杂F1代羊肉的品质与云岭黑山羊羊肉的品质近似。