Management practices associated with Johne's bulk tank milk ELISA positivity

Johne's disease (JD) control is often based on the culling of positive animals and the adoption of management practices that minimize exposure of young stock to the pathogen (Mycobacterium avium ssp. paratuberculosis). Throughout 2010 to 2013, the province of Ontario, Canada, instituted a voluntary Johne's control program consisting of whole-herd testing and risk assessment. The JD risk assessment evaluated 5 management areas to characterize herd JD risk. Using a modified milk ELISA technique with an optical density cut-off of 0.089, province-wide bulk tank milk (BTM) testing was used to assess the prevalence of JD high-risk herds at the end of the control program and again 4 yr after its completion. Approximately 71% of Ontario bulk tanks were classified as positive in 2017 compared with roughly 46% in 2013. In 2019, the same JD risk assessment used in the original program was readministered on 180 Ontario dairy farms. Using this cross-sectional approach, logistic regression models were built using data from the original program risk assessment and follow-up risk assessment as well as the BTM ELISA results to determine management factors associated with the control of JD. We demonstrated that management of the maternity area is an important factor in the control of Johne's disease. Although it is believed that the highest risk group for JD infection is calves under 6 mo, the cleanliness scores of older heifers and their exposure to mature cow manure was significantly associated with JD control; farms with highly contaminated weaned and bred heifers and those that had exposure to mature cow manure were more likely to be unsuccessful in their JD control efforts. Careful management of young calves appears to be important for JD control, and this management should continue even after calves have left the maternity area.     

Bedding and bedding management practices are associated with mesophilic and thermophilic spore levels in bulk tank raw milk

Mesophilic and thermophilic spore-forming bacteria represent a challenge to the dairy industry, as these bacteria are capable of surviving adverse conditions associated with processing and sanitation and eventually spoil dairy products. The dairy farm environment, including soil, manure, silage, and bedding, has been implicated as a source for spores in raw milk. High levels of spores have previously been isolated from bedding, and different bedding materials have been associated with spore levels in bulk tank (BT) raw milk; however, the effect of different bedding types, bedding management practices, and bedding spore levels on the variance of spore levels in BT raw milk has not been investigated. To this end, farm and bedding management surveys were administered and unused bedding, used bedding, and BT raw milk samples were collected from dairy farms (1 or 2 times per farm) across the United States over 1 yr; the final data set included 182 dairy farms in 18 states. Bedding suspensions and BT raw milk were spore pasteurized (80°C for 12 min), and mesophilic and thermophilic spores were enumerated. Piecewise structural equation modeling analysis was used to determine direct and indirect pathways of association among farm and bedding practices, levels of spores in unused and used bedding, and levels of spores in BT raw milk. Separate models were constructed for mesophilic and thermophilic spore levels. The analyses showed that bedding material had a direct influence on levels of spores in unused and used bedding as well as an indirect association with spore levels in BT raw milk through used bedding spore levels. Specific bedding and farm management practices as well as cow hygiene in the housing area were associated with mesophilic and thermophilic spore levels in unused bedding, used bedding, and BT raw milk. Notably, levels of spores in used bedding were positively related to those in unused bedding, and used bedding spore levels were positively related to those in BT raw milk. The results of this study increase the understanding of the levels and ecology of mesophilic and thermophilic spores in raw milk, emphasize the possible role of bedding as a source of spores on-farm, and present opportunities for dairy producers to reduce spore levels in BT raw milk.     

高蛋白饮用型纯益生菌发酵乳的研制

以鲜牛乳和浓缩牛奶蛋白为主要原料,以酸度和感官评价为评价指标,通过单因素试验和正交试验确定高蛋白饮用型纯益生菌发酵乳的最佳发酵工艺条件。结果表明,高蛋白饮用型纯益生菌发酵乳的最佳发酵工艺条件为浓缩牛奶蛋白添加量6.0%,发酵剂接种量2.0%、发酵温度43 ℃、二次无菌均质压力4 MPa。在此优化条件下,制得的高蛋白饮用型纯益生菌发酵乳感官评分达到89分,酸度129.1 °T,口感清爽顺滑,组织状态良好,理化及微生物指标均符合国家相关标准。     

离子液体在无抗奶检测中的应用

采用复分解方法合成疏水性离子液体1-辛基-3-甲基咪唑六氟磷酸盐[(C_8MIM)(PF_6)],用活性炭和大孔树脂固相萃取小柱净化该离子液体,得到无色透明的[(C_8MIM)(PF_6)],产率87.6%。利用该离子液体萃取乳及乳制品中的青霉素及其酶解产物青霉素噻唑酸,并优化萃取条件。通过自建的高效液相色谱方法检测青霉素及青霉素噻唑酸的含量,间接判断乳及乳制品中是否为真正的"无抗奶"。离子液体萃取方法青霉素回收率为87.4%~92.6%,RSD为1.8%,检出限5ng/mL;青霉素噻唑酸回收率为83.5%~90.8%,RSD为2.4%,检出限5ng/mL,通过与杯碟法和液相质谱法作比较,更说明了该方法的优越性。     

原料乳嗜冷菌的危害分析及控制

从相关的8个牧场的原料乳样品中分离纯化得到嗜冷菌分离物。然后重点探讨嗜冷菌对原料乳的危害及对嗜冷菌的生长控制。对嗜冷菌数动态增加与蛋白酶和脂肪酶活力变化、pH值的变化和总醛类物质浓度增加的相关性进行了分析研究。结果表明，壳聚糖和二氧化氯对嗜冷菌有较好的抑菌作用。     

西藏乳及发酵乳制品中乳酸菌与酵母菌分布

西藏当地牦牛乳及发酵乳制品中的微生物分布备受科研人员的关注,而且重点多集中在其中的乳酸菌和酵母菌。本文对西藏当地乳及乳制品中乳酸菌与酵母菌的分布做了详细的介绍,包括原料乳、曲拉和藏灵菇乳中的乳酸菌和酵母菌的研究现状,并对今后的发展趋势做了分析。      

Use of PCR-restriction fragment length polymorphism analysis for identification of yeast species isolated from bovine intramammary infection

This study reports a rapid PCR-based technique using a one-enzyme RFLP for discrimination of yeasts isolated from bovine clinical and subclinical mastitis milk samples. We analyzed a total of 1,486 milk samples collected over 1 yr in south Sardinia and northern Italy, and 142 yeast strains were preliminarily grouped based on their cultural morphology and physiological characteristics. Assimilation tests were conducted using the identification kit API ID 32C and APILAB Plus software (bioMérieux, Marcy l’Etoile, France). For PCR-RFLP analysis, the 18S-ITS1-5.8S ribosomal(r)DNA region was amplified and then digested with HaeIII, and dendrogram analysis of RFLP fragments was carried out. Furthermore, within each of the groups identified by the API or PCR-RFLP methods, the identification of isolates was confirmed by sequencing of the D1/D2 region using an ABI Prism 310 automatic sequencer (Applied Biosystems, Foster City, CA). The combined phenotypic and molecular approach enabled the identification of 17 yeast species belonging to the genera Candida (47.9%), Cryptococcus (21.1%), Trichosporon (19.7%), Geotrichum (7.1%), and Rhodotorula (4.2%). All Candida species were correctly identified by the API test and their identification confirmed by sequencing. All strains identified with the API system as Geotrichum candidum, Cryptococcus uniguttulatus, and Rhodotorula glutinis also produced characteristic restriction patterns and were confirmed as Galactomyces geotrichum (a teleomorph of G. candidum), Filobasidium uniguttulatum (teleomorph of Crypt. uniguttulatus), and R. glutinis, respectively, by D1/D2 rDNA sequencing. With regard to the genus Trichosporon, preliminary identification by API was problematic, whereas the RFLP technique used in this study gave characteristic restriction profiles for each species. Moreover, sequencing of the D1/D2 region allowed not only successful identification of Trichosporon gracile where API could not, but also correct identification of misidentified isolates. In conclusion, the 18S-ITS1-5.8S region appears to be useful in detecting genetic variability among yeast species, which is valuable for taxonomic purposes and for species identification. We have established an RFLP database for yeast species identified in milk samples using the software GelCompar II and the RFLP database constitutes an initial method for veterinary yeast identification.     

Free fatty acids and oxidative changes of a raw goat milk cheese through maturation

Free fatty acids (FFA) and lipid and protein oxidation changes were studied throughout maturation process of a raw goat milk cheese with protected designation of origin. Cheeses were analyzed at 4 different times of maturation, at 1, 30, 60, and 90 d. All FFA significantly increased during maturation and the relative increase was higher for long-chain than medium- or short-chain FFA. At the end of maturation, oleic (C18:1 n9), butyric (C4:0), and palmitic (C16:0) acids were the most abundant. The higher levels of short-chain fatty acids (SCFA) regarding total FFA obtained at the end of Ibores cheese ripening compared with other raw goat milk cheeses, highlight the notable role of SCFA on the flavor of this cheese owing to their low-odor thresholds. Lipid oxidation values significantly increased during maturation process but low levels of malondialdehyde were reported; however, protein oxidation did not significantly change during ripening.     

固相萃取-流动注射化学发光法测定奶粉中的三聚氰胺

建立一种快速测定奶粉中三聚氰胺的新方法,利用鲁米诺-高锰酸钾化学发光体系,结合流动注射技术,对样品中的微量三聚氰胺进行测定。结果表明：三聚氰胺对鲁米诺-高锰酸钾化学发光体系具有显著的抑制作用,在最佳实验条件下,方法的线性范围为1×10-11～1×10-6mol/L,检出限(3RSN)为4.0×10-8mg/L,RSD为1.1%(n=11),样品加标回收率为96.1%～102.2%,用于奶粉中三聚氰胺含量的测定,结果令人满意。