【正文】 rather salty taste. The content of catalase and peroxidase is high. ? Four to five days after calving the cow begins to produce milk of normal position, which can be mixed with other milk. ? 牛初乳組成 ? 根據(jù)大量研究資料表明 , 與常乳比較，牛初乳除了含有豐富的優(yōu)質(zhì)蛋白質(zhì)、維生素和礦物質(zhì)等營養(yǎng)成分外，還富含免疫因子、生長因子等活性功能組分。分娩以后，雌激素水平隨之降低。 ? 妊娠期間，由于母體黃體分泌大量的孕激素，反饋抑制了垂體促乳素的分泌，并使乳腺對促乳素的敏感性有所降低；孕激素分泌量的增加會抑制雌激素對促乳素分泌的刺激作用，也引起促乳素分泌的減弱。 到 300天時(shí) ， 產(chǎn)奶量比高峰時(shí)下降 1525%。 我國 810胎 ? After having given birth to some 5 calves, the cow is generally slaughtered. Secretion of milk（乳的分泌） ? Milk is secreted in the cow?s udder （ 乳房 ） ? A sectional view of the udder is shown in Figure. 乳房主要由： 腺體組織約占 75%～80%， 結(jié)締和脂肪組織占20%～ 25% 乳房內(nèi)部又都是由乳腺泡、乳導(dǎo)管、乳池、乳頭管和間質(zhì)構(gòu)成。第三篇 乳品工藝學(xué) 第一章 乳的基礎(chǔ)知識 第一節(jié) 奶牛的基礎(chǔ)知識 ? Milk production began 6 000 years ago or even earlier. ? The dairy animals of today have been developed from untamed animals which, through thousands of years, lived at different altitudes and latitudes exposed to natural and, many times, severe and extreme conditions. Table 表 1中是不同種類動(dòng)物乳汁的營養(yǎng)組成是平均數(shù)，影響因素還很多，包括： breed, feeding, climate, etc. ?牛乳 （ Cow milk） ? 乳是哺乳動(dòng)物生命之初唯一食物 ? Milk is the only food of the young mammal during the first period of its life. ? 乳可以提供能量 ， 并含有動(dòng)物生長所需的物質(zhì) ? The substances in milk provide both energy and the building materials necessary for growth. ? 乳也含有抗體 ? Milk also contains antibodies which protect the young mammal against infection. ? 1頭犢牛大約需要 1000L牛乳 ? A calf needs about 1 000 litres of milk for growth, and that is the quantity which the primitive cow produces for each calf. ? 1頭奶牛 1個(gè)泌乳周期大約分泌 6000L牛乳， ? 現(xiàn)在有些奶牛產(chǎn)奶量超過 14000L。 ? Before a cow can start to produce milk she must have calved first. Heifers（ 小母牛 ） reach sexual maturity （ 性成熟 ） at the age of seven or eight months but are not usually bred until they are 15 – 18 months old. ? ? 小母牛一般在 2歲前進(jìn)行自然或人工配種 ? The heifer is bred (naturally or by insemination) before the age of 2 years. ? 奶牛的孕期為 265300天 ? The period of gestation is 265 – 300 days ? 小母牛在 ? A heifer produces her first calf at the age of about 2 – years. ? 奶牛的懷孕時(shí)間 9個(gè)月 ? The gestation period is 9 months. ? 奶牛產(chǎn)犢后泌乳期為 10個(gè)月 （ 通常按 305天計(jì)算 ） ? After calving the cow gives milk for 10 months. ? 奶牛產(chǎn)犢后 12個(gè)月再進(jìn)行配種 ? 1 – 2 months after calving the cow will again be bred. ? 奶牛一生大約產(chǎn) 5胎后就宰殺 。 ? 乳房由含有能夠產(chǎn)生乳的腺體 ? The udder is posed of glandular（ 腺體 ） tissue which contains milkproducing cells. ? It is encased in muscular tissue, which gives cohesion to the body of the udder and protects it against injury from knocks and blows. ? The glandular tissue contains a very large number (about 20 億 ) of tiny bladder scalled alveoli （ 腺胞 ） . ? 每天大約有 90 000 L血液流經(jīng)乳房 ? Flow of blood through the udder approx. 90 000 l/day. ? 大約需要 800 – 900 L血液方能產(chǎn)生 1L乳 ? Approx. 800 – 900 l of blood needed for formation of one litre of milk. The lactation cycle（哺乳期） ? Secretion of milk in the cow?s udder begins shortly before calving ? 奶牛產(chǎn)犢后連續(xù) 300天的乳的分泌 ， 這個(gè)期間叫哺乳期 ? The cow then continues to give milk for about 300 days. This period is known as lactation. ? 產(chǎn)奶量在產(chǎn)犢后不斷上升 ， 后又不斷下降 。 ? 引起泌乳發(fā)動(dòng)的原因很多，目前一般認(rèn)為，分娩前后血液中激素濃度的變化是導(dǎo)致泌乳發(fā)動(dòng)的主要誘因。在分娩當(dāng)天外周血液中促乳素的濃度可達(dá)到妊娠期的 2～ 5 倍 , 此后也比妊娠期高 1 倍以上。 ? The first milk that a cow produces after calving is called colostrum. ? ? 初乳在組成和特性方面與常乳有很大區(qū)別 ， 特別是乳清蛋白含量 ， 因此初乳受熱很容易凝固 ? It differs greatly from normal milk in position and properties. One highly distinctive characteristic is the high content of whey proteins – about 11% pared to about % in normal milk。主要包括：胰島素樣生長因子 (IGF1)；神經(jīng)營養(yǎng)生長因子 (NGF)；表皮生長因子 (EGF)；轉(zhuǎn)化生長因子 (TGF)；纖維細(xì)胞生長因子(FGF)；促性腺激素 釋放激素 (GnRH)及其締合肽 (GAP)；生長激素 (GH)。 奶牛的排乳反射一般維持 4 min～ 7min 后消失 ? A hormone called oxytocin must be released into the cow?s bloodstream in order to start the emptying of the udder. This hormone is secreted and stored in the pituitary gland. When the cow is prepared for milking by the correct stimuli, a signal is sent to the gland, which then releases its store of oxytocin into the blood stream. In the primitive cow the stimulus is provided by the calf?s attempts to suck on the teat. The oxytocin is released when the cow feels the calf sucking. A modern dairy cow has no calf but is conditioned to react to other stimuli, . to the sounds, smells and sensations associated with milking. ? The oxytocin begins to take effect about one minute after preparation has begun and causes the musclelike cells to press the alveoli. This generates pressure in the udder and can be felt with the hand。 優(yōu)點(diǎn)是造價(jià)較低 ， 缺點(diǎn)是擠乳員仍須彎腰操作 ， 影響勞動(dòng)效率 。 一般適于中等規(guī)模的奶牛場 。 其優(yōu)點(diǎn)是奶?？蛇B續(xù)進(jìn)入擠乳 臺，擠乳員在 入 口處沖洗乳房 、 套奶杯 ， 不必來回走動(dòng) ， 操作方便 ， 每轉(zhuǎn)一圈 7 min ～10min， 轉(zhuǎn)到出口處已擠完乳 ， 勞動(dòng)效率高 ， 適于較大規(guī)模奶牛場。異常乳可分為生理異常乳、化學(xué)異常乳微生物污染乳及經(jīng)濟(jì)等異常乳幾大類。 它們的直徑約為~20um，平均大小為 3~4um。 C/10 min or 75176。 Proteins in milk ? Proteins are giant molecules built up of smaller units called amino acids. ? A protein molecule consists of one or more interlinked chains of amino acids, where the amino acids are arranged in a specific order. ? A protein molecule usually contains around 100 – 200 linked amino acids, but both smaller and much larger numbers are known to constitute a protein molecule. ? Proteins are built from a supply of approx. 20 amino acids, 18 of which are found in milk proteins. ? The electrical status of milk proteins Classes of milk proteins ? 乳中含有上百種蛋白質(zhì) ， 他們中的大多數(shù)含量較低 ， 蛋白質(zhì)按照其化學(xué) 、 物理和生物功能進(jìn)行分類 ? Milk contains hundreds of types of protein, most of them in very small amounts. The proteins can be classified in various ways according to： ? chemical properties ? physical properties ? biological functions. Table Concentration