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A method to produce latex cast model of cow's cistern and duct system was developed in order to clarify the internal structure of the udder and to measure the holding capacity of the milk storing system. Udders of ten lactating, ten dry Holstein cows and three growing heifers were collected and the latex casts of their cisterns and duct systems were prepared. The capacities of the milk storing systems, the numbers and location of the ducts, and the size and shape of cisterns were measured on the latex casts. 1) The technique used in the present study made it possible to fill the whole milk storing systems down to lobule level, using a latex solution with a suitable viscosity of the material. The cast can be used to estimate the size and shape of milk storing system in cows and growing heifers. 2) The average milk storing capacity of the left half for lactating cow's udder was 4.71±0.92l (Mean±SD). The fore quarters was 39.05% of the whole udder. The average milk storing capacity of left half for dry cow's udder was 2.85±0.96l while that of the fore quarters was 37.81% of whole udder. There was significant difference in milk storing capacity of the left half between dry and lactating cows (P<0.05). 3) Gland cisterns were classified into five types: divergent, ball, egg, columnar and part-divergent types, the percentages of which were 45, 12. 5, 10, 15, and 17.5%, respectively. The size of cistern greatly varied in different cows and in different quarters of the same udder. 4) The number of ducts in a quarter varied from 7 to 24, mean 16.7±1.3 in each quarter, and no difference in number of ducts was found between lactating and dry quarters. Major ducts, of which storing capacity exceeds ten percent of the whole milk storing capacity in a quarter, were mostly located toward the fore or rear directions. They occupied 75.56% and 72.14% of capacities of fore and rear quarters in lactating cows, and 77.32% and 66.02% in dry cows. For growing heifers, capacity of cistern and duct systems in fore quarters formed 44.02%, 47.83%, and 47.32% of those of whole udder, at the age of 10, 20, and 25 to 30 months, respectively. Duct system of udder developed uniformly in these heifers. The number of ducts in heifers at the age of 30 months had increased to similar number as in mature cows. Jpn. J. Zootech. Sci., 56 (9): 736-743, 1985 The udder is made up of series of systems which includes the supportive structures, a duct system for storage and conveyance of milk and secretory units of epithelial cells. Each of these components directly or indirectly to the synthesis of milk. It is well known that the synthesis of milk is controlled in part by the pressure in the alveoli lumina due to the accumulation of milk1). It is also assumed that the pressure within the teat cistern reflects that within the lumina of the alveoli2). From studies on the aqueous phase of milk and the electrochemical gradients between milk and extracellular fluid, LINZELL and coworkers3. 4. 5) proposed that in the Jpn. J. Zootech. Sci., 56 (9): 736-743 736 The Latex Cast of Caw's Udder ducts, maintenance of milk composition is achieved by the simple expedient of impermeability to ions and lactose but not to water, and the secretory cells are permeable to ions but not to lactose once secreted. The storage of milk means that we are really dealing with two mechanisms that produces and then maintain the composition of milk in the alveoli and ducts. SHINDE6) demmonstrated that the removal of milk from the duct system increases the milk yield by promoting the rate of proliferation and activity of secretory cells during early lactation and reduces the rate of involution after the peak. It seems that the storing capacity, form and location of the duct systems have effect upon mammary function in cows. Little works have been done in this area. The experiment reported here have been attempted to develop a method of latex cast model of milk storing system and to clarify the structure and holding capacity of the milk storing system. Materials and Methods Udders of ten lactating, ten dry Holstein cows and three growing heifers were collected. Immediatly after slaughter the udders were excised, rinsed to remove the blood clots and trimmed of any excess connective and fat tissues. Milk in the udders were removed as much as possible by physical massaging of the udder. The udders were separated into halves through the medial ligaments, then the halves were weighted. The injection medium used was latex (Neoprene 601-A, Kyoritsukasei Ldt) and diluted to 1:1 in volume with water. A glass bottle with an I. D. of approximately 10cm and 30cm in length was used to hold the latex. A piece of glass tubing which fit into the tubing on the teat cannula was inserted into a rubber stopper which was large enough to plug one end of the glass bottle. The latex was then poured into the open end of the bottle, taking care not to trap any air bubble, then allowed the latex to fill the glass tubing. The free end of the tubing connected to the teat cannula was filled with latex and connected to the bottle. Careful manipulation at this point prevented any air from entering the system. The latex was now allowed to flow into the udders from the bottle, which can be vertically clamped, above the udders. The latex had density slightly greater than water and filled the duct systems well beyond the point of branching, flowing under its own hydrostatic pressure. Optimum filling was ensured by a gradual rise in intramammary pressure to a maximum of about 150 mm Hg. When injection was completed, the tubing above the teat cannula was clamped and the bottle was removed off. After injection, the half of the udder was placed in a container filled with hydrochloric acid for vulcanization of latex and digestion of the tissue. When the corrosive solution was fresh, digestion was completed within 3 days and the cast was removed and rinsed in clean water. A short soaking in either diluted acid or base neutralized any remaining digestion fluid and a final wash completed the procedure.

The Latex Cast of Cistern and Duct System of Dairy Cow's Udder