日粮主要营养指标对奶牛乳尿素氮浓度影响的评价

通过对702头荷斯坦奶牛，118种日粮的试验结果进行统计分析，评价了日粮的主要营养指标（蛋白质水平、能量水平以及氮能比）对乳尿素氮浓度的影响。结果：由于日粮营养指标间的相关关系，使一般多元回归分析中存在严重的共线性；消除共线性影响后的岭回归分析结果表明在三个营养指标中日粮蛋白质水平是对MUN影响最大的因素，其次为氮能比，但能量水平的作用不显著。     

日粮蛋白质水平对奶牛乳尿素氮浓度及氮利用率的影响

采用4×4的拉丁方试验设计,将体重、奶产量和泌乳天数接近的4头经产荷斯坦牛饲喂四种等能量水平不同蛋白质水平(13.2%,14.1%,15.0%和16.2%,干物质基础)的日粮,来研究奶牛乳尿素氮浓度及氮利用率的变化情况。整个试验期共56d,每期14d,1-10d为调整期,11-13d为粪尿收集期。结果发现,随着日粮蛋白质水平的增加,乳尿素氮浓度极显著升高(P<0.01),而氮的利用率随着蛋白质水平的增加而显著下降(P<0.05);乳尿素氮和氮利用率间存在显著的二次曲线关系(P<0.01)。乳尿素氮可以作为反映奶牛日粮蛋白质水平变化的指标,也有可能作为估测奶牛氮利用率的指标发挥作用。     

简述奶牛乳尿素氮产生机理及其影响因素

通过对乳尿素氮的产生机理、生物学意义及影响牛奶尿素氮含量的因素进行了简要综述,为提高奶牛饲料氮素利用率,减少奶牛养分损失,降低饲料成本,提高经济效益提供参考.     

日粮营养因素对奶牛乳尿素氮浓度影响的研究进展

生产实践中,由于饲料贮存、饲喂过程中的损失以及在计算日粮配方等方面可能出现误差,使饲料分析结果不能完全代表奶牛实际的摄人情况（Hof等．1997）。这些问题引发了人们寻找一种可以在奶牛个体水平测量的生化指标来反映奶牛蛋白质营养状况。人们通常使用血液尿素氮（Blood urea nitrogen,BUN）、血清蛋白指标和免疫功能指标来对动物蛋白质营养状况进行检测。     

影响奶牛乳尿素氮的主要因素研究进展

牛奶中乳尿素氮(MUN)作为反映奶牛蛋白质营养状态和评价蛋白质利用效率的生物学指标已经被国内外研究人员广泛认可。综述了乳尿素氮的定义、检测方法、产生机制,以及影响乳尿素氮的营养和非营养性因素,以期为奶牛养殖生产提供参考。     

奶牛乳尿素氮影响因素及遗传参数估计的研究进展

乳尿素氮（Milk Urea Nitrogen,MUN）是奶牛生产性能测定（Dairy Herd Improvement,DHI）工作中常规的测定指标之一,其浓度通常用于监测奶牛营养状况,反映日粮能氮平衡、繁殖性能以及环境中氮的排放量。MUN浓度因个体和日粮构成而异,同时受多种因素影响。准确的MUN遗传参数估计不仅能够提高牛场经济效益,而且能加快奶牛的遗传进展,为选育优质奶牛提供理论依据。本文对国内外关于MUN的影响因素、遗传力以及与乳脂率、乳蛋白率、乳糖率、产奶量、体细胞评分等性状的遗传相关进行了综述,以期为MUN的深入研究应用提供参考。     

不同防腐剂对奶牛乳尿素氮和β-羟丁酸的影响

为检测在高温环境中不同防腐剂对乳尿素氮和β-羟丁酸的影响,在40℃高温环境保存牛奶7 d,通过Bentley红外线方法检测乳尿素氮及β-羟丁酸的含量变化,并与德国进口防腐剂比较。结果显示:牛群改良计划(DHI)测定专用防腐剂与进口防腐剂对尿素氮(MUN)、β-羟丁酸(BHBA)含量影响较小,能满足夏季DHI检测要求。重铬酸钾对MUN、BHBA含量检测影响较大,不适用于DHI检测。     

日粮营养调控对奶牛乳组成的影响

近年来,通过营养调控改变牛乳组成已经越来越受到研究人员的重视。作者综述了通过营养调控对奶牛牛乳乳脂肪、乳蛋白及乳糖的影响。     

通过乳尿素氮含量对奶牛日粮营养状况的评价

由于乳尿素氮(MUN)含量和血浆尿素氮含量之间具有一定的相关性,众多研究表明,通过乳尿素氮含量的变化可以反应出瘤胃降解蛋白(RDP)、过瘤胃蛋白(UDP)及能量的供应情况。因此,了解乳尿素氮含量的标准范围及其影响因素可以对蛋白质和能量摄入平衡状况进行评价,进而对牛群营养与饲养状况进行监控,对指导牛场生产和提高牛场经济效益具有重要意义。     

日粮类型对奶牛粪尿特性及氮排放的影响

通过研究不同类型日粮对泌乳奶牛粪尿及氮排放的影响,达到减少和控制氮排放的目的,本试验选用12头体重514 kg、年龄3～5岁的中国荷斯坦奶牛为试验动物,分为3组,分别饲喂粗料为干秸秆玉米,精粗比40∶60的A日粮、粗料为玉米青贮,精粗比分别是40∶60和60∶40的B和C日粮进行了对其粪尿特性及氮排放的试验研究。结果表明,日粮类型对奶牛粪便及尿液产生量均有一定的影响。粪便产生量结果为秸秆型A日粮>青贮型低精比B日粮>青贮型高精比C日粮。3种日粮的尿液产生量为C日粮>B日粮>A日粮。同时,日粮类型对奶牛氮平衡具有显著的影响,秸秆型日粮的乳氮、尿氮含量和氮的消化率极显著低于青贮型日粮低(P<0.01),粗料均为青贮玉米条件下,随日粮精料水平的提高,氮消化率和尿氮极显著增加(P<0.01),粪氮和乳氮增加不显著(P>0.05)。结果提示,秸秆型日粮的摄入氮主要是从粪中排出,粗料为青贮玉米时,随日粮精料水平的提高粪氮比例减少,而尿氮比例增加,粪氮和尿氮占总粪尿氮的比例基本一致。     

Factors affecting milk urea nitrogen and protein concentrations in Quebec dairy cows

Milk urea nitrogen (MUN), together with percentage milk protein (PROT), are increasingly used as indicators of the protein-energy balance and for monitoring nutrition and diagnosing feeding disorders. The goal of this study was to analyze the effects of parity, milk yield, days in lactation, somatic-cell count, and herd and feeding factors on MUN and PROT. In 10 dairy herds, one milk sample was taken from each of 418 cows, within +/- 2 days of the routine milk-test visit. We used a four-step multiple linear-regression model with backward elimination, including interactions between herd and the different factors. For both dependent variables, there were significant interactions with herd. Herd-specific models were markedly different; however, the daily amount of protein concentrates fed remained (and had a positive coefficient) in seven of 10 herd models for MUN. This factor is easy to record under field conditions and has to be considered in the evaluation of the ration by means of MUN and PROT. Overfeeding of rumen soluble protein can be easily diagnosed and corrected using MUN analyses. The relationships between MUN and PROT in respect of the factors parity, daily milk yield, and days postpartum also vary considerably among herds.     

Anti-Neospora caninum antibodies in milk in relation to production losses in dairy cattle

A comprehensive field study was carried out with the following objectives: (a) to assess the usefulness of individual and bulk tank milk analysis for determining Neospora caninum serostatus in individual cows and herds, and (b) to study the associations between N. caninum infection status (based on milk testing), and several productive and reproductive parameters in the animals. Antibodies were detected with a commercially available ELISA test (Bio K 192/5). Analysis of paired serum and milk samples from 1134 lactating cows on 38 farms revealed that 97.6% of the ELISA results were coincident, irrespective of whether serum or milk samples were used. Moreover, multiple linear regression analysis revealed that 86.0% of the variations in ELISA values in milk were due to variations in the serum. The measurement of antibodies in bulk tank milk was a good estimator of the herd level status of N. caninum infection, and enabled detection of infection in 94.7% herds with ≥10.0% seropositive cows and/or in all herds with >4% highly seropositive cows. The odds ratio for abortion in seropositive animals was 9.1 times higher than in seronegative animals. The infection serostatus was also a significant risk factor, as the odds ratio for abortion was even higher (12.0 times) in cows categorized as highly seropositive. ELISA values for the bulk milk from 387 randomly selected herds were negatively associated with average milk production. Moreover, milk production losses mainly occurred on farms categorized as highly positive (i.e. herds with ≥20.0% seropositive cows).     

Genetic structure of milk protein polymorphisms and effects on milk production traits in a local dairy cattle

The milk protein genetic structure of the Reggiana dairy local cattle with remarkable milk quality properties was analysed and compared with the structure of Italian Friesian and Italian Brown cattle. A total of 1138 individual milk samples from the three breeds were typed by isoelectrofocusing. Polymorphism was found at the α_s1‐casein (CSN1S1), β‐casein (CSN2), κ‐casein (CSN3), and β‐lactoglobulin (LGB) loci. High frequencies were observed for some casein alleles in Reggiana (CSN1S1*C, 25%; CSN2*B: 28%) with considerable differences to those observed in a survey carried out 30 years before. A great variation among breeds was observed for casein haplotype frequencies and high linkage disequilibrium was detected at the three polymorphic casein loci CSN1S1‐CSN2‐CSN3. The prevalent haplotypes were CA²B (23%; Reggiana), BA²A (48%; Italian Friesian) and BA²B (51%; Italian Brown). Higher G_ST values between breeds were observed when haplotype frequencies were considered instead of gene frequencies. In the Reggiana cattle, the occurrence of two casein alleles at a rather high frequency (CSN1S1*C, CSN2*B) allowed to estimate the effects of rare casein haplotypes on milk traits. The CA²B haplotype was associated with a significantly higher milk protein and fat content and a significantly higher protein per cent was found also for the BA¹B haplotype.     

奶牛氨基酸营养及其对乳蛋白分泌的影响

乳蛋白是一种营养价值很高的蛋白质 ,它的氨基酸含量和构成比例基本上与人体所需氨基酸的数量、比例相近。然而长期以来我国奶牛育种工作过分强调产奶量和乳脂率两项生产性能指标 ,而忽视了乳蛋白的选育 ,因此奶牛乳蛋白浓度始终较低。近些年随着研究的不断深入 ,人们发现 ,牛奶中含有大量的高度饱和脂肪酸助长了胆固醇的循环水平 ,增加了心血管疾病的发生率 ,同时人们也发现 ,乳蛋白除给新生动物和人类提供蛋白、氨基酸外 ,某些乳蛋白及其消化产生的肽类活性物质还具有特定的生理功能。目前世界很多国家低脂乳销售比例均在逐年增加 ,并且世…     

Comparison of three methods for gastrointestinal nematode diagnosis determination in grazing dairy cattle in relation to milk production

Development of resistance to anthelmintic drugs has motivated the search for diagnostic methods to identify animals for targeted selective treatments. We compared three methods for the diagnosis of nematode infection in relation to milk production in a fully grazing dairy herd of 150 cows in the humid Pampa (Argentina). Animals had feces, blood and milk sampled during the first postpartum month for EPG, pepsinogen and anti-Ostertagia antibody determination, respectively. With the results obtained two groups of cows, divided in high and low parasite burden, were conformed for each method, and milk production was then compared between groups. When cows were separated by the EPG method (EPG=0 (N=106) vs. EPG>0 (N=44)) a difference of nearly 800 l of milk per cow per lactation was found (P<0.05). On the other hand, milk production between groups separated by Pepsinogen (mUtyr ≤ 1000 vs. mUtyr > 1000) or by anti-Ostertagia (ODR ≤ 0.5 vs. ODR > 0.5) results did not differ. Interestingly, proportion of cows in each group differed between methods (P<0.0001), and the anti-Ostertagia method yielded significantly more cows in the high index group compared to results using the EPG or Pepsinogen method. No correlations were found between parasite indexes determined by the different methods. High parasite burden estimation found may be ascribed to the production system, fully grazing all year round, and to the sampling time, at the beginning of lactation with cows in negative energy balance and depressed immunity. The fact that the cows were born and reared outside, on pasture with continuous nematode larvae exposure, may also account for the results obtained. In conclusion, EPG counting during the first postpartum month may be a useful tool for the diagnosis of production impairment induced by high nematode burden in adult grazing dairy cows. The anthelmintic treatment of only the EPG-positive recently calved cows would improve milk production, while reducing selective pressure on nematode population for the development of resistance.     

大豆黄酮对奶牛产奶量和乳中常规成分的影响

研究口服大豆黄酮对不同泌乳期奶牛产奶量和乳中常规成分的影响。结果表明,1)大豆黄酮能明显提高泌乳中期奶牛的产奶量;2)大豆黄酮可显著提高泌乳晚期奶牛乳蛋白含量和乳脂率;另外对乳糖的影响是泌乳早期和泌乳晚期上升,而泌乳中期有所下降。     

Extruded urea could reduce true protein source in beef cattle diets

Rumen micro‐organisms are capable of producing microbial protein from ammonia and carbon skeleton, and non‐protein nitrogen (NPN) may be one of the sources of ammonia. Alternative source of NPN is the slow release of ammonia sources in which the product is the extrusion of starch with urea. This work aimed to determine the effects on nutrient intake, ingestive behaviour, digestibility, nitrogen balance, ruminal pH, rumen ammonia nitrogen, volatile fatty acids (VFA) and blood parameters with increased levels of extruded urea (50, 60, 70 and 80 g/100 kg of body weight [BW]) in beef cattle diet. Four rumen cannulated crossbred steers with initial mean weight of 336 ± 47 kg in a 4 × 4 Latin square design were distributed. Diets were formulated with 400:600 g/kg roughage:concentrate ratio on dry matter based and provided once per day, being used whole corn silage as roughage. There were no effects on nutrient intake (kg/day), ingestive behaviour, apparent digestibility, nitrogen balance, volatile fatty acid (VFA) and blood parameters in extruded urea treatment groups. Similar results were observed on time spent on feeding, rumination and idleness. There were positive linear effects (p = 0.022) on rumen pH in the time of 8 hr after feeding and also on plasma concentration of the extruded urea levels (p = 0.039); whereas a linear negative effect (p = 0.030) was observed on ammonia nitrogen for the collection time of 2 hr after feeding. Increased levels of extruded urea could maintain nutrient intake, digestibility, ingestive behaviour, rumen pH and blood parameters in normal conditions. In conclusion, we recommend the extruded urea use with values up to 80 g/100 kg BW in confined beef cattle that receive balanced diets with 140 g/kg of crude protein.