催乳中药组方对产后缺乳模型大鼠的催乳作用研究

目的 探讨一种催乳中药组方的催乳效果,研究其作用机制.方法 取产仔时间前后相差不超过24 h的50只母鼠,按母鼠体重随机分为正常组、模型组、催乳药物高、低剂量组和阳性对照组,每组10只母鼠.自分娩第2日起每天上午腹腔注射左旋多巴2 mg/kg,连续注射7d.于造模当日开始,每日下午给药,正常组蒸馏水灌胃,每日1次,连续给药14d.从给药第2日开始,每日测定母鼠泌乳量,并于给药14d后,处死动物,酶联免疫吸附测定法（ELISA法）检测血清泌乳素（PRL）和下丘脑5-羟色胺（5-HT）水平,同时取乳腺福尔马林固定,并进行病理形态学观察.结果 造模后正常组单次泌乳量和总泌乳量均显著高于模型组,表明产后缺乳大鼠造模成功.催乳药高、低剂量组的单次泌乳量、总泌乳量和血清PRL含量均显著高于模型组.催乳药高剂量组下丘脑5-HT含量高于模型组.结论 该催乳中药组方具有促进哺乳大鼠泌乳的作用,催乳机制可能是通过提高产后缺乳模型大鼠的血清PRL及下丘脑5-HT水平,使乳腺组织呈高度泌乳状态,从而促进乳汁分泌.     

新橙皮苷对3T3-L1前脂肪细胞分化的影响及其作用机制

为探讨新橙皮苷对脂肪细胞脂肪形成的影响及其作用机制,采用MTS法检测新橙皮苷对3T3-L1前脂肪细胞的细胞活力的影响,确定新橙皮苷的作用浓度后,油红O染色法和分光光度法测定3T3-L1脂肪细胞的分化及胞内甘油三酯的含量,RT-PCR测定脂肪形成相关基因CCAAT增强子结合蛋白α（CCAAT/enhancer binding proteinα,C/EBPα）和过氧化物酶体增殖激活受体γ（Peroxisome proliferators-activated receptorγ,PPARγ）mRNA表达,Western蛋白印迹法检测蛋白激酶B（Protein kinase B,PKB/Akt）、糖原合成酶激酶3β（Glycogen synthase kinase3β,GSK3β）和糖原合成酶（Glycogen synthase,GS）的磷酸化水平;利用GSK3β选择性的抑制剂LiCl作用3T3-L1脂肪细胞后,检测新橙皮苷对3T3-L1细胞分化、胞内甘油三酯含量、C/EBPα、PPARγ及aP2蛋白表达的影响。结果表明,新橙皮苷能极显著抑制脂肪细胞分化和胞内甘油三酯的形成（P<0.01）,激活Akt信号通路,促进p-Akt和p-GSK3β水平增加,极显著抑制C/EBPα、PPARγ、aP2 mRNA和蛋白表达（P<0.01）。新橙皮苷的这些影响部分地被GSK3β抑制剂LiCl所抑制（P<0.01）。新橙皮苷能够通过激活Akt/GSK3β信号通路抑制脂肪细胞分化。     

不同热加工工艺对巴氏杀菌乳中乳清蛋白的影响

以牛乳乳清蛋白为研究对象,探究不同热加工工艺（72 ℃/15 s、75 ℃/15 s、80 ℃/15 s、85 ℃/15 s）对巴氏杀菌乳乳清蛋白中3 种活性蛋白（α-乳白蛋白、β-乳球蛋白和乳铁蛋白）的影响,以及测定并分析杀菌温度对各样品菌落总数和嗜冷菌的影响。结果表明：随着热加工强度的提升,牛乳中的菌落总数随之减少,当杀菌温度在80 ℃以上时牛乳中的菌落总数小于10 CFU/mL;当杀菌温度在72 ℃以上时样品中的嗜冷菌数均小于10 CFU/mL;72 ℃/15 s 和75 ℃/15 s对α-乳白蛋白、β-乳球蛋白和乳铁蛋白影响较小,当杀菌温度达到80 ℃以上时,巴氏杀菌乳中的α-乳白蛋白、β-乳球蛋白和乳铁蛋白含量显著下降（P＜0.05）。综上,热加工的时间和温度与乳清蛋白的关系密切,72～75 ℃/15 s 的热加工工艺能更好地保留乳清蛋白中的3 种活性蛋白。     

连续式微滤膜分离乳清蛋白的研究

文章研究了跨膜压力对连续式微滤膜分离技术工艺参数、分离效果及组分组成的影响。以脱脂乳为原料,使用0.1μm陶瓷微滤膜三级连续在线洗滤工艺分离乳清蛋白和酪蛋白。实验使用0.08、0.11、0.14 MPa 3个梯度,在50℃,3.5倍浓缩的条件下连续生产240 min。计算跨膜压力并且检测截留液和透过液中的α-乳白蛋白（α-La）,β-乳球蛋白（β-LG）含量及钾、钙、钠、镁等金属离子的含量。结果表明一级膜通量下降是导致整体膜通量下降的主要因素,经过240 min实验通量下降约17.2%。研究了不同跨膜压力下的膜通量变化情况,膜通量与跨膜压力呈正相关关系,水洗恢复率与跨膜压力呈负相关关系。随着实验时间的延长,膜表面形成不可逆的污堵层,乳清蛋白分离率下降,透过液中乳清蛋白含量下降,150 min后α-乳白蛋白浓度下降37%,β-乳球蛋白浓度下降36.5%。乳清蛋白中2种主要蛋白质比例会随着跨膜压力变化而变化,随着跨膜压力的升高β-乳球蛋白含量会逐渐升高。三级连续膜过滤后,乳清蛋白最高分离率90%左右（α-乳白蛋白为90.4%,β-乳球蛋白为92.7%）。乳中蛋白质的形态和功能受金属离子影响...     

α-乳白蛋白提取工艺研究及副产物功能性质评价

研究了热附聚法结合凝乳酶处理从牛乳中直接提取α-乳白蛋白的工艺,得到富含α-乳白蛋白的乳清和副产物——附聚β-乳清蛋白的凝乳酶干酪素。富含α-乳白蛋白的乳清中α-乳白蛋白与β-乳球蛋白的浓度比达到3.03,达到了商业化产品的水平。副产物——附聚β-乳清蛋白的凝乳酶干酪素与市售凝乳酶干酪素在溶解性、持水性和乳化性方面存在的差异较小,将附聚β-乳清蛋白的凝乳酶干酪素作为原料应用于仿真干酪中,质构测定结果未显示出在质构方面与普通凝乳酶干酪素对照样品存在明显差异。     

壳寡糖对酒精诱导的大鼠肠道损伤的干预作用

目的：研究壳寡糖（chitooligosaccharide,COS）对慢性饮酒诱导的肠道损伤的干预作用。方法：将Wistar雄性大鼠随机分为空白对照组、模型组、COS低剂量组、COS中剂量组和COS高剂量组5 组,除空白对照组,其余各组通过连续42 d灌胃4.5 g/kg mb酒精构建肠道损伤模型,COS组酒精灌胃前灌胃COS。结果：与模型组相比,COS可以显著改善大鼠小肠平滑肌伸缩性（P＜0.05）,恢复小肠健康水平,降低血浆中D-乳酸水平、二胺氧化酶活力及白细胞介素（interleukin,IL）-1β、肿瘤坏死因子-α（tumor necrosis factor-α,TNF-α）、IL-6等促炎因子、丙二醛和蛋白质羰基水平（P＜0.05）以及抑制claudin-4蛋白的基因表达（P＜0.05）,高剂量COS可以显著提高紧密连接蛋白Occludin（P＜0.05）和ZO-1（P＜0.05）的基因表达,中、高剂量的COS可以显著降低小肠组织中炎症因子IL-6、IL-1β和TNF-α的基因表达量（P＜0.05）。结论：COS通过提高小肠健康水平、提高肠黏膜屏障、降低炎症反应及减缓氧化损伤,缓解慢性酒精导致的大鼠肠道损伤。     

β-乳球蛋白与邻苯醌类物质反应效率分析

乳清蛋白作为营养健康食品的重要原料或成分,可能与多酚氧化形成的邻苯醌类物质反应,即发生蛋白-多酚共价相互作用。乳清蛋白与邻苯醌类物质的反应效率是阐明两者反应行为的重要科学依据。以乳清蛋白主要成分β-乳球蛋白（β-Lactoglobulin,β-LG）作为研究对象,利用循环伏安技术研究了不同条件下β-LG与邻苯醌类物质的反应效率。结果表明：在pH值7.0,扫描速率50 mV/s条件下,β-LG（0.03 mmol/L）与非黄酮型邻苯醌的反应效率顺序为：原儿茶酸（54.72%）>咖啡酸（47.01%）>迷迭香酸（41.86%）>绿原酸（39.29%）>邻苯二酚（27.36%）>4-甲基邻苯二酚（22.51%）>原儿茶酸乙酯（19.24%）,与黄酮型邻苯醌的反应效率的顺序为：木犀草素（19.34%）>槲皮素（14.68%）>芦丁（12.50%）≈儿茶素（11.97%）>表儿茶素（6.66%）。研究表明：邻苯醌类物质的结构会影响其与β-LG的反应效率,醌环上含有给电子基团的邻苯醌类物质反应效率高于醌环上含有吸电子基团的邻苯醌类物质;此外,醌环上取代基的空间位阻会削弱邻苯醌类物质与β-LG的反应效率。     

小鼠乳腺中FGF7及其受体的表达与作用

为了从蛋白水平研究成纤维细胞生长因子7（FGF7）及其受体（KGFR）在哺乳动物乳腺发育、泌乳及退化过程中表达定位的动态变化,揭示FGF7及其受体表达变化与乳腺发育及泌乳功能的关系,本研究利用激光扫描共聚焦显微系统对昆明鼠乳腺中FGF7及其受体的表达进行了免疫荧光检测,利用体外培养不同发育时期的小鼠乳腺组织研究了FGF7在乳腺中的作用。结果表明：FGF7主要定位于乳腺导管上皮细胞以及腺泡上皮细胞外周,同时在基质中有弱的表达。KGFR主要出现在导管上皮细胞以及腺泡上皮细胞上,在乳腺发育的个别时期细胞外基质中有弱表达。FGF7在退化4d达到最高值;KGFR在泌乳4d达到最高值。除青春期和妊娠期外,添加FGF7均能显著诱导乳腺上皮细胞产生KGFR。FGF7能促进小鼠乳腺上皮细胞的增殖分化,降低乳腺上皮细胞的细胞凋亡。     

牛乳体细胞数与乳蛋白含量相关性的研究

对呼和浩特郊区一牧场30头荷斯坦乳牛进行6个月单个采样，共得427个有效样本，检测乳样中体细胞数、酪蛋白（包括α-酪蛋白、β-酪蛋白、κ-酪蛋白）、乳清蛋白、总蛋白、游离氨基氮、酪蛋白／总蛋白和乳清蛋白／总蛋白。结果表明，乳中总蛋白、游离氨基氮含量及乳清蛋白／总蛋白与SCC呈显著正相关；酪蛋白／总蛋白与SCC呈显著负相关；乳清蛋白含量与SCC呈极显著正相关。酪蛋白、α-酪蛋白／酪蛋白、β-酪蛋白／酪蛋白、κ-酪蛋白／酪蛋白与SCC的相关性不显著。酪蛋白含量与总蛋白含量呈极显著的正相关，与游离氨基氮含量、乳清蛋白／总蛋白呈极显著的负相关。乳清蛋白含量与游离氨基氮、总蛋白含量呈极显著正相关。     

乳清蛋白的特性及在乳制品生产中的应用

乳清蛋白是酪蛋白沉淀在分流时保留在清液中的多种蛋白质,乳清蛋白主要由β-乳球蛋白、α-乳白蛋白、血清白蛋白、免疫球蛋白以及脉胨等构成。随着社会的发展,干酪或干酪素逐渐出现在人们的生活中,两者在生产过程中会产生大量液态副产品乳清,经过特殊工艺进行浓缩,就可以得到不同蛋白质浓度的乳清浓缩蛋白（WPC）或乳清分离蛋白（WPI）。乳清蛋白优点显著,如高蛋白、低脂肪、低胆固醇。     

Milk nutrition and childhood epilepsy: An ex vivo study on cytokines and oxidative stress in response to milk protein fractions

We present a pilot study on the effects of milk protein fractions [α_S1-casein (CN), α_S2-CN, κ-CN, β-CN, and a mix of α-lactalbumin (α-LA) and β-lactoglobulin (β-LG)] from different animal species (bovine, ovine, and caprine) on pro- and anti-inflammatory cytokines and oxidative status in cultured peripheral blood mononuclear cells from children with generalized epilepsy. Peripheral blood mononuclear cells (PBMC) were obtained by density gradient from blood of 10 children with generalized epilepsy (5 males; mean age 33.6 ± 5.4 mo) and 10 controls (5 males; mean age 35.6 ± 6.8 mo). Children with epilepsy were grouped according to cytokine levels as follows: children with epilepsy having low levels of cytokines not different from those of control children (LL-EC); children with epilepsy having cytokine levels at least 5-fold higher (medium levels) than those of control children (ML-EC); and children with epilepsy having cytokine levels at least 10-fold higher (high levels) than those of control children (HL-EC). The production of tumor necrosis factor-α (TNF-α), IL-10, IL-6, and IL-1β was studied in cultured PBMC incubated with α_S1-CN, α_S2-CN, κ-CN, β-CN, and a mix of α-LA and β-LG from bovine, caprine, and ovine milks. The levels of reactive oxygen and nitrogen species (ROS/RNS) and catalase activity were assessed in cultured supernatant. In the HL-EC group, β-CN from small ruminant species (ovine and caprine) induced the highest levels of TNF-α, whereas PBMC incubated with α_S2-CN from ovine milk and the mix of β-LG and α-LA from all tested milk species had the lowest levels of TNF-α. Within the HL-EC group, production of IL-1β was higher for bovine and ovine α_S2-CN fractions and lower for caprine and ovine β-CN and κ-CN. In the HL-EC group, IL-6 was higher in cultured PBMC incubated with α_S2-CN from bovine and ovine milk than from caprine milk. The cytokine IL-10 did not differ among milking species. The highest levels of ROS/RNS were found after incubation of PBMC with the β-CN fraction in bovine milk. Catalase activity was higher in PBMC cultured with β-CN isolated from bovine and caprine milk and with α_S1-CN from ovine milk.     

Mechanism underlying the modulation of milk production by incomplete milking

Mammary gland secretory activity is modulated by systemic and local factors; however, the relationship between these factors is unknown. The aim of this study was to determine how a local factor, such as incomplete milking, affects mammary epithelial cell activity, number, and responsiveness to blood prolactin (PRL). Eight cows in mid-lactation were differentially milked (i.e., their right quarters were milked incompletely at approximately 70%, and their left quarters were milked completely, twice daily for 4 wk). Throughout the experiment, milk yield was measured at the quarter level. Milk samples were collected from each quarter once a week to assess the milk components, and epithelial cell concentrations, as well as to isolate milk fat globule RNA. In the weeks before and after the experiment, mammary gland functional capacity was evaluated by measuring the volume of milk harvested after complete filling of the gland. At the end of the last experimental week, mammary gland biopsies were performed on each rear quarter. The milk production of quarters milked completely remained stable during the treatment period, whereas, as expected, the milk production of quarters milked incompletely was only 53% of completely milked quarters at the end of the period. Accordingly, the expression of genes related to milk synthesis (CSN2, LALBA, and ACACA) in milk fat was lower in the quarters that were milked incompletely. Incomplete milking decreased the milk lactose content, indicating a loss of integrity of tight junctions. The total yield of epithelial cells in milk was not affected, but their concentration in milk, the BAX:BCL2 gene expression ratio, and the loss of mammary functional capacity were greater in the quarters milked incompletely, suggesting an acceleration of involution in those quarters. The expression of the short isoform of the PRL receptor gene (PRLR) tended to be lower, and the expression of STAT5A and STAT5B tended to decline in the quarters milked incompletely. In mammary gland biopsy samples, the number of both short and long isoforms of the PRLR were not affected, nor were the amount and activation of STAT3 and STAT5. However, the ratio of PRLR short isoform to PRLR long isoform was lower in the quarters milked incompletely. The decrease in milk yield induced by incomplete milking is rapid and associated with a decrease in mammary epithelial cell activity and a decrease in the number of secretory epithelial cells. The results of this experiment provide only limited support for the hypothesis that modulation of the mammary gland's responsiveness to PRL is part of the mechanism by which local factors, such as incomplete milking, modulate milk synthesis.     

Effects of milk protein variants on the protein composition of bovine milk

The effects of β-lactoglobulin (β-LG), β-casein (β-CN), and κ-CN variants and β-κ-CN haplotypes on the relative concentrations of the major milk proteins α-lactalbumin (α-LA), β-LG, α_S1-CN, α_S2-CN, β-CN, and κ-CN and milk production traits were estimated in the milk of 1,912 Dutch Holstein-Friesian cows. We show that in the Dutch Holstein-Friesian population, the allele frequencies have changed in the past 16 years. In addition, genetic variants and casein haplotypes have a major impact on the protein composition of milk and explain a considerable part of the genetic variation in milk protein composition. The β-LG genotype was associated with the relative concentrations of β-LG (A » B) and of α-LA, α_S1-CN, α_S2-CN, β-CN, and κ-CN (B > A) but not with any milk production trait. The β-CN genotype was associated with the relative concentrations of β-CN and α_S2-CN (A² > A¹) and of α_S1-CN and κ-CN (A¹ > A²) and with protein yield (A² > A¹). The κ-CN genotype was associated with the relative concentrations of κ-CN (B > E > A), α_S2-CN (B > A), α-LA, and α_S1-CN (A > B) and with protein percentage (B > A). Comparing the effects of casein haplotypes with the effects of single casein variants can provide better insight into what really underlies the effect of a variant on protein composition. We conclude that selection for both the β-LG genotype B and the β-κ-CN haplotype A²B will result in cows that produce milk that is more suitable for cheese production.     

Short communication: Effect of kefir grains on proteolysis of major milk proteins

The effect of kefir grains on the proteolysis of major milk proteins in milk kefir and in a culture of kefir grains in pasteurized cheese whey was followed by reverse phase-HPLC analysis. The reduction of κ-, α-, and β-caseins (CN), α-lactalbumin (α-LA), and β-lactoglobulin (β-LG) contents during 48 and 90 h of incubation of pasteurized milk (100 mL) and respective cheese whey with kefir grains (6 and 12 g) at 20°C was monitored. Significant proteolysis of α-LA and κ-, α-, and β-caseins was observed. The effect of kefir amount (6 and 12 g/100 mL) was significant for α-LA and α- and β-CN. α-Lactalbumin and β-CN were more easily hydrolyzed than α-CN. No significant reduction was observed with respect to β-LG concentration for 6 and 12 g of kefir in 100 mL of milk over 48 h, indicating that no significant proteolysis was carried out. Similar results were observed when the experiment was conducted over 90 h. Regarding the cheese whey kefir samples, similar behavior was observed for the proteolysis of α-LA and β-LG: α-LA was hydrolyzed between 60 and 90% after 12 h (for 6 and 12 g of kefir) and no significant β-LG proteolysis occurred. The proteolytic activity of lactic acid bacteria and yeasts in kefir community was evaluated. Kefir milk prepared under normal conditions contained peptides from proteolysis of α-LA and κ-, α-, and β-caseins. Hydrolysis is dependent on the kefir:milk ratio and incubation time. β-Lactoglobulin is not hydrolyzed even when higher hydrolysis time is used. Kefir grains are not appropriate as adjunct cultures to increase β-LG digestibility in whey-based or whey-containing foods.     

Interactions of milk proteins during heat and high hydrostatic pressure treatments — A Review

Pressure treatment of β-lactoglobulin (β-LG), whey protein concentrate (WPC), whey protein isolate and skim milk has been explored by many groups using a wide range of techniques. In general terms, heat treatment and pressure treatment have similar effects: denaturing and aggregating the whey proteins and diminishing the number of viable microorganisms. However, there are significant differences between the effects of the two treatments on protein unfolding and the subsequent thiol-catalysed disulfide-bond interchanges that lead to different structures and product characteristics. Application of a range of techniques has given insight into the subtle differences between the pathways from native proteins to the final product mix. This review covers some of the techniques used and their strengths, and the probable pathways from native protein to the final products. β-LG is one of the most pressure-sensitive proteins and α-lactalbumin (α-LA) is one of the most pressure resistant. In a heated WPC system, bovine serum albumin is very sensitive and β-LG is more resistant. In a heated milk system, β-LG reacts with κ-casein (κ-CN) and not with α_S2-CN, but, in pressure-treated milk, β-LG forms adducts with either κ-CN or α_S2-CN. In both treatments, the role of β-LG is central to the ongoing reactions, involving α-LA and κ-CN in heated systems but involving κ-CN, α_S2-CN and α-LA in pressurized systems.Industrial relevanceHigh hydrostatic pressure (HHP) processing, as opposed to heat treatment, has received much attention recently as a means of processing milk proteins. This review examines the differences in the denaturation pathways that give rise to different final products.     

Relationship between glucocorticoids and prolactin during mammary gland stimulation in dairy cows

The objectives of this study were to determine the role of glucocorticoids in the regulation of prolactin (PRL) release induced by mammary gland stimulation and to investigate whether the milk depression induced by glucocorticoids in dairy cows is due to a decrease in PRL release. In experiment 1, 8 dairy cows were used in a 4 × 4 Latin square design. Four hours after the morning milking, the cows received 1 of the following treatments: (1) a 5-min manual stimulation of the mammary gland; (2) an i.v. injection of 1 mg of dexamethasone; (3) 2 infusions of 2.5 g of metyrapone (an inhibitor of cortisol biosynthesis) in the omasum 4 and 2 h before a 5-min stimulation of the mammary gland; or (4) no treatment. Sixty minutes later, the mammary gland of each cow was stimulated for 5 min. Blood samples were collected from 20 min before to 120 min after the start of the treatment. When the mammary gland was stimulated twice in 60 min, less PRL and cortisol were released during the second stimulation. Metyrapone did not affect PRL or cortisol release. Dexamethasone decreased serum cortisol concentration but did not affect PRL concentration. In experiment 2, 16 cows were used in a crossover experimental design consisting of 2 experimental weeks separated by 1 resting week. During the first week, cows were treated as follows: (1) 4 cows were injected with 0.5 g of domperidone (a PRL secretagogue) in canola oil on d 1 and 2 and 20 mg of dexamethasone on d 1; (2) 4 cows were injected with 0.5 g of domperidone on d 1 and 2; (3) 4 cows were injected with canola oil on d 1 and 2 and with 20 mg of dexamethasone on d 1; and (4) 4 cows were injected with canola oil on d 1 and 2. During the second experimental week, the same 4 treatments were repeated, except the cows that did not receive dexamethasone in the first week received it on d 1 of the second week, and cows that did receive it in the first week did not receive it in the second week. On d 1 and 2 of each week, blood samples were collected during morning milking for PRL determination. Dexamethasone reduced milk production and decreased both basal and milking-induced PRL release. It also increased milk fat and protein percentages and decreased milk lactose content. Domperidone increased basal PRL levels in serum and milk but did not affect milk yield. Although we cannot rule out the possibility that inhibition of PRL secretion or reduction of mammary gland PRL responsiveness play a role in the inhibition of milk production by glucocorticoids, the fact that enhancement of PRL secretion by domperidone could not prevent the depression of milk yield suggests that other mechanisms are involved.     

Whole-genome association study for milk protein composition in dairy cattle

Our objective was to perform a genome-wide association study for content in bovine milk of α_S1-casein (α_S1-CN), α_S2-casein (α_S2-CN), β-casein (β-CN), κ-casein (κ-CN), α-lactalbumin (α-LA), β-lactoglobulin (β-LG), casein index, protein percentage, and protein yield using a 50K single nucleotide polymorphism (SNP) chip. In total, 1,713 Dutch Holstein-Friesian cows were genotyped for 50,228 SNP and a 2-step association study was performed. The first step involved a general linear model and the second step used a mixed model accounting for all family relationships. Associations with milk protein content and composition were detected on 20 bovine autosomes. The main genomic regions associated with milk protein composition or protein percentage were found on chromosomes 5, 6, 11, and 14. The number of chromosomal regions showing significant (false discovery rate <0.01) effects ranged from 3 for β-CN and 3 for β-LG to 12 for α_S2-CN. A genomic region on Bos taurus autosome (BTA) 6 was significantly associated with all 6 major milk proteins, and a genomic region on BTA 11 was significantly associated with the 4 caseins and β-LG. In addition, regions were detected that only showed a significant effect on one of the milk protein fractions: regions on BTA 13 and 22 with effects on α_S1-CN; regions on BTA 1, 9, 10, 17, 19, and 28 with effects on α_S2-CN; a region on BTA 6 with an effect on β-CN; regions on BTA 13 and 21 with effects on κ-CN; regions on BTA 1, 5, 9, 16, 17, and 26 with effects on α-LA; and a region on BTA 24 with an effect on β-LG. The proportion of genetic variance explained by the SNP showing the strongest association in each of these genomic regions ranged from <1% for α_S1-CN on BTA 22 to almost 100% for casein index on BTA 11. Variation associated with regions on BTA 6, 11, and 14 could in large part but not completely be explained by known protein variants of β-CN (BTA 6), κ-CN (BTA 6), and β-LG (BTA 11) or DGAT1 variants (BTA 14). Our results indicate 3 regions with major effects on milk protein composition, in addition to several regions with smaller effects involved in the regulation of milk protein composition.     

Effectiveness of mid-infrared spectroscopy for the prediction of detailed protein composition and contents of protein genetic variants of individual milk of Simmental cows

Mid-infrared (MIR) spectroscopy was used to predict the detailed protein composition of 1,517 milk samples of Simmental cows. Contents of milk protein fractions and genetic variants were quantified by reversed-phase HPLC. The most accurate predictions were those obtained for total protein, casein (CN), α_S1-CN, β-lactoglobulin (LG), glycosylated κ-CN, and whey protein content, which exhibited coefficients of determination between predicted and measured values in cross-validation (1-VR) ranging from 0.61 to 0.78. Less favorable were results for β-CN (1-VR = 0.53), α_S2-CN, and κ-CN (1-VR = 0.49). Neither the content of α-LA nor that of γ-CN was accurately predicted by MIR. Predicting the content of the most common milk protein genetic variants (κ-CN A and B; β-CN A¹, A², and B; and β-LG A and B) was unfeasible (1-VR <0.15 for the content of κ-CN genetic variants and 1-VR <0.01 for the content of β-CN variants). The best predictions were obtained for β-LG A and β-LG B contents (1-VR of 0.60 and 0.44, respectively). Results indicated that MIR is not applicable for predicting individual milk protein composition with high accuracy. However, MIR spectroscopy predictions may play a role as indicator traits in selective breeding to enhance milk protein composition. The genetic correlation between MIR spectroscopy predictions and measures of milk protein composition needs to be investigated, as it affects the suitability of MIR spectroscopy predictions as indicator traits in selective breeding.