The aims and scope of the present investigation can therefore be briefly summarized as follows. Where necessary, the significance of the differences noted was determined by statistical analysis of the data. The whole problem of abnormal milk secretion centers around the composition of normal milk, the standard prescribed for milk, the anatomy of the udder and the physiology of milk secretion.
No effort was made to increase yield or quality of milk at high feeding. The average percentages of fat and solids-not-fat given in the appendix for the four-week periods are calculated from the results of the weekly and fortnightly tests. The solids-not-fat percentage was calculated by Richmond's formula from the fat percentage and the specific gravity of the milk obtained at 60°F.
The factors that were therefore studied in addition to the fat and non-fat solids are chloride, lactose, chloride-lactose index and cell content of the milk from the individual quarters. It is one of the three specific products of the mammary gland, which is synthesized in the alveolar epithelium from its precursor, glucose, in the blood. They consist of leukocytes derived from the blood circulating through the udder and epithelial cells due to desquamation of the epithelial lining of the alveoli and ducts.
Suspension of the udder. The primary means of support is provided by the lateral and median suspensory ligaments and the skin. As a result, filling the udder stretches the median ligament, causing the teats to protrude outward and downward at an angle. However, the three main components of milk, namely fat, lactose and casein, are specific products of the mammary gland and as such do not appear in the blood.
Intra-'1'/Wmmary pressure. One of the main factors affecting the composition of milk and the rate of its secretion is the milk pressure in the gland. The rate of milk secretion per unit time is determined by the intramammary pressure, which in turn is determined by the amount of milk present in the udder in relation to the capacity of the storage system. Ziegler (1941) and Swanson and Turner (1941) described the presence of cells beneath the secretory epithelium of the alveoli and in the interlobular spaces, which
It is now generally accepted that the release of milk is due to a reflex and according to Petersen (1942) stimuli from the nerves of the skin of the body; and tea. Thus the milk is forced out of the alveoli and tubules into the lar()'er milk ducts and. It appears that either the effect of factors known to suppress milk solids is more pronounced than it was.
This phenomenon has particularly attracted the attention of those workers in the field of mastitis research, who combine bacteriological methods of diagnosis with biochemical examination of the milk.
1 1 ABLE 2
Of the 1.4 76 determinations made, only 45 (3%) were below the minimum standard, and 18 of the 40 quarters consistently yielded milk with a fat content above the limit. The average fat content of each of the 40 quarters was well above 3 percent. Each of the 40 quarters secreted milk with an abnormal percentage of chloride at different times (Table 3).
Ten of the eleven quarters mentioned above that produced the majority of abnormal results also had an average chloride level of 0.150 percent. Accordingly, the appendix will show that for many of the samples with a high chloride content, and therefore a low lactose content, the latter was not recorded. With the exception of the right front quarter of 7921, the average lactose content of these twelve quarters was below 4.50 percent.
As in the case of fat-free solids and chloride, none of the forty quarters failed to pass all the tests for chloride-lactose index. The majority of samples come from seven quarters, namely 7909 R.F. A total of 12 quarters consisting of the 7 mentioned above in addition to 7912 L.F. has an average cell content in the milk that exceeded the prescribed limit. The left rear quarter of 7905 was the only one of the 40 that never had a score above the standard.
In other quarters the means again fell so far short of the prescribed standard and the percentage of abnormal responses to the tests used was so high that a classification of these quarters as abnormal was justified. Another important factor revealed by the data is that any quarter that did not have a mean equal to the standard prescribed for normality in any of the components studied also, with very rare exceptions, abnormal produced results in the majority of the tests applied for. the relevant ingredient. a) Composition.-When the average for the relative ingredient met the prescribed standard, it was indicated by N while ABN indicated that the average was below the limit. Although the averages for the fat and fat-free solids of these four quarters were above the legal standards, this could not be considered normal in view of the deviations shown by their milk in chloride, lactose, chloride-lactose index and cells . .
These are the only four cows in which one of the quarters showed significant differences in the composition of the milk compared to the other three quarters of the same udder, and this aspect will receive more complete attention in the relative section later in this work. Notwithstanding the fact that the averages for all the factors examined met the standards prescribed for normal milk, it was found that a very large percentage of the samples examined were of abnormal composition. Analysis of the data revealed that each of the 40 quarters produced substandard milk at different times.
The scope of this work has therefore been extended to include a study of the main factors that may be affected by the production of inferior quality milk. The determination of chloride in milk has often been recommended as one of the most reliable indirect tests for mastitis.
