Section 5 Only HQ (Milk Production and Quality)
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SECTION 5 MILK PRODUCTION and QUALITY 240 Section 5 | Chapter 48 CHAPTER 48 ANATOMY AND PHYSIOLOGY OF LACTATION “Remember a cow is a mother and her calf is a baby” Introduction Seen from the back, the udder is divided into a right and left half by the udder or intermammary Very early in the development of the dairy groove. From a side view, the fore and rear industry in Britain, the way to treat cows for quarters are more smoothly joined together milking was described as follows: not having such a distinctive groove. The hind quarters are usually larger than the fore “…She shall then milk the cow boldly, and not quarters and may secrete 25 to 50% more milk leave stretching and straining of her teates, till than the fore quarters with the ratio between one drop of milk more will come from them; back and fore quarters being 60 to 40%. for the worst point of housewifery that can be, is to leave a cow halfe milkt; for besides the The udder is attached to the body by the losse of milk it is the only way to make the cow following ligaments: dry, and utterly unprofitable for the dairy. The milkmaid, whilst she is milking, shall do nothing 1. The medial suspensory ligament, which rashly or suddenly about the cow which may divides the udder into a right and left half afright or amaze her; but as she came gently, (Figure 48.1), and so with all gentleness she shall depart.” From C. 2. The lateral suspensory ligaments, which Markham (1660). The English housewife – a way form a fibrous layer around the outside of to get wealth. the glands joining the medial suspensory ligaments on the lower surface of the The same principles still apply for present-day glands. dairies using modern equipment. The lateral suspensory ligaments are chiefly Anatomy of the udder fibrous, whereas the medial suspensory ligaments are more elastic fibres. Filling the The udder of a mature dairy cow normally udder therefore stretches the medial ligaments weighs about 10 to 25 kg and consists of four to enlarge the storing capacity of the udder. individual glands, also referred to as quarters. When these ligaments weaken, the udder Each quarter is drained by a teat at the bottom tends to separate from its close adherence to of the quarter. There is no flow of milk between the abdominal wall and the udder is described quarters. The total milk storage capacity of the to be breaking away. Connective tissue udder may be as high as 35 kg. penetrates and traverses each quarter, thus giving shape and further support to the udder. The udder is a skin gland connected to the A big udder may contain a large volume of abdominal cavity through the inguinal canal. connective tissues and little gland tissue; udder Blood and lymph vessels, as well as nerve fibres, size is, therefore, not always a true indication enter the udder from the abdominal cavity of the productive ability or capacity of a cow. through this canal, which forms a tube about 10 cm long. 241 Skin Median suspensory ligament Lamellae Lateral suspensory ligament Figure 48.1. The suspensory apparatus of the udder of a dairy cow The udder should ideally shrink during the milking canal, which is 0.5 to 1.0 cm long, prevents process and must therefore be completely dirt entering the udder and milk escaping elastic when empty. before milking commences. The diameter of the streak canal and the tonus of the sphincter It is important for the udder to extend well muscle determine the ease of milking a cow. forward for the maximum utilisation of the At the upper end of the streak canal loose space available underneath the body. This folds of tissue, called the Furstenberg’s Rosette, feature is essential, since the udder must be press down against the opening of the streak large enough to contain all the milk that may canal and assist in preventing the escape of be secreted between milking sessions. This milk from the udder. results in the udder expanding, i.e. becoming larger, by about one-third of its normal size. This The teat cistern has a diameter of about 1 expansion increases the milk-carrying capacity cm with a capacity of 30 to 50 mℓ of milk of the udder by approximately 60%, while the immediately above the teat opening. In the remaining 40% of the milk secreted can be teat cistern, several fairly well-defined circular accommodated in the natural storage spaces membranes are found. This may sometimes of the udder. form a septum across the teat, preventing the flow of milk. If this happens, the septum has to The shape and size of the teats that drain the be pierced with a special needle to enable four glands are independent of the shape normal milk flow. and size of the udder. In addition to the four normal teats, about 40% of cows have one The udder cistern, also called the lactiferous or more supernumerary teats, usually without cistern, with a capacity of 100 to 400 mℓ of the presence of glandular tissue. These teats milk, follows immediately beyond the teat usually occur behind the rear teats. cistern and is situated in the udder. There is no definite separation between these two cisterns Milk collecting system resulting in their being more or less continuous. From the gland cistern five to 20 large milk The teat opening, or streak canal, is situated collecting ducts branch and rebranch into in the lower end of the teat and is surrounded very small collecting tubules, each eventually by a sphincter muscle. This muscular walled ending in an alveolus (Figure 48.2). 242 Section 5 | Chapter 48 Alveoli Lobe Lobule containing alveoli Connective tissue Major duct Ducts Gland cistern Teat cistern Teat meatus Figure 48.2. The milk collecting system An alveolus consists of a single layer of milk tissue) and vascular (blood-vessel) network producing cells attached to the inside of a surrounds the alveolus (Figure 48.3). Each spherical basement membrane. This cell layer lumen drains into a small milk-collecting tubule. of epithelial cells surrounds the lumen, the These small tubes flow together forming larger hollow inside of the alveolus into which the milk milk ducts. is excreted. A dense myoepithelial (muscle Arteriole Myoepithelial cell Lumen Capillary Epithelial cell Venule Ducts Figure 48.3. The alveolus The alveoli occur in large numbers in the udder and have a diameter of 0.1 to 0.3 mm. They are grouped together in lobules by connective tissue; each lobule containing about 200 alveoli. All the lobules draining into the same milk duct are described as a lobe. 243 Milk secretion secretory products fill the interior spaces of the cells before leaving through the walls of the Each alveolus is surrounded by a dense apex to fill the lumen with milk. network of fine blood-vessels which provide the milk synthesising cells with a continuous supply About 500 kg of blood pass through the udder of nutrients for the synthesis of milk. There are during the production of one kg of milk. Some three phases identified during milk secretion: milk constituents move unchanged from the blood to the milk, while others are synthesised • Synthesis by the cells of the alveolar by the epithelium. Casein and lactose, for epithelium; example, are found only in milk, while milk fat • Discharge from the epithelial cells into the comprises glyceride combinations not found alveolar lumen; and elsewhere in the body. • Storage in the alveolar, ducts, and cisterns. Udder pressure and secretion rate Directly after milking, the lumina are almost empty, the epithelium folded, and the cells Changes in the secretion rate and themselves are largely devoid of any secretion. intramammary pressure in the udder during As the producing cells draw the raw materials milk secretion as affected by milking interval for milk synthesis from the blood, synthesised are shown in Figure 48.4. (a) (b) FigureFigure 48.4. 48. The4. The decrease decrease in in milk milk secretion secretion rates rates (a)(a) and increaseincrease in in udder udder pressure pressure (b) (b) as as affected by the length ofaffected the milking by the interval length of the milking interval MilkMilk is continually is continually synthesised synthesized atat aa raterate of ofabout about 1 to 224 m ℓhours./g glandular After tissueabout per 36 day. hours, At thewhen aboutcompletion 1 to 2 mℓ/g of milking, glandular when tissue all available per day. milk At hasudder been removed,pressure maypressure be withinas high the as teat about cistern 7 kPa the iscompletion at atmospheric of milking,levels, but when within all an available hour after milkingabove , atmosphericpressure within pressure, the udder increasesmilk secretion by milkabout has 1been kPa removed,as milk re siduepressures fill withinthe collapsed the stops teat andaltogether. udder cisterns. Thereafter, pressure teatinitially cistern increasesis at atmospheric slowly for levels, 5 to 6 but hours, within and then more rapidly at 2 to 4 kPa at the end of an hournormal after milking milking, intervals. pressure The within pressure the at udder this stage There depends are on theindications length of thethat interva thel betweenapparent increasesmilking by session abouts, 1udder kPa ascapacity milk residues, and the fill yield the of declinecows. The in pressuresecretion in therate udder of most is also of greater the milk collapsedin the hind teat quarters and udder than in cisterns. the front Thereafter, quarters, as wellconstituents, as in early lactation.as the milking increases, is due to pressure initially increases slowly for 5 to 6 hours, their absorption during storage, rather than a andMilk then is more secreted rapidly at an at inverse 2 to 4 ratekPa to at mammary the end pressure.true decline This relain secretiontionship is, rate.