butter fat; a very good dairy cow, on the other hand, will yield over twice this amount, and exceptional producers will give more than quadruple the figures stated. But the average quality of milk of cows of the same breeds also differs greatly. The variations are probably larger within the Jersey and Guernsey breeds than in any other breed; there are thus cows or families within these breeds that produce milk of an average fat content above 6 per cent during the entire lactation period, while individuals of other families will generally not go over 4 per cent. In the same way, we find some Holstein cows producing milk with over 4 per cent fat, and others whose milk will contain less than 2.8 per cent, on the average, for a considerable period of time.

Age of Cows. This is not, on the whole, an important factor

far as the quality of the milk is concerned. As a general rul heifers and young cows will give milk of a somewhat higher fat content than older cows, but the differences in the average quality of the milk for a long period of time, say one year, are only within a few tenths of one per cent in the fat content, and there are some individuals whose milk changes with advancing age in the opposite direction from that stated.

The production of milk and butter fat increases with advancing age of cows till they are past maturity. A dairy cow ordinarily produces about 30 per cent more milk or butter fat at full age than she did as a heifer with her first calf. The maximum production, as a rule, comes at an age of six to eight years, differing somewhat with the different breeds and with individual cows, according to the method of feeding and management, and the constitutional vigor of the cows. Good dairy cows will continue to be profitable producers till ten or twelve years old and, in exceptional cases, considerably longer.

Stage of Lactation Period.—This is of greater importance than the age

of the cow. The quality of the milk is, in general, higher during the first few weeks after parturition than later on, and remains fairly constant from this time on until toward the close of the lactation, when the milk becomes richer in solids and fat as the yield decreases (Fig. 44). The following compilation of 300 cows in the Wisconsin Dairy Cow Competition, 1909–1911,4 will illustrate the changes in production of dairy cows during the progress of the lactation period :

5

The normal decrease in the flow of milk in well-managed dairy herds is about 5 per cent a month during the second to seventh month of the lactation period, about 10 to 12 per cent during the eighth and ninth months, and 20 per cent for the tenth and subsequent months.

Condition.—The physical condition of a cow will influence the quality and amount of her milk secretion. A dairy cow in good flesh will give more milk and of richer quality than cows in poor condition. Where cows in a fleshy body condition are placed on official tests shortly after parturition their milk may contain 1 to 2 per cent fat above normal during the first 2 to 3 weeks, as has been shown by Eckles and the author;" cows in good flesh directly after parturition will also produce milk of a higher fat content throughout the lactation period than cows that are thin and poor at the beginning of the lactation.

Frequency of Milking.-Under otherwise similar conditions, the shorter the interval between milkings, the less milk is obtained and the higher are the percentages of solids and butter fat contained therein. Where the interval between milkings is nearly equal, the differences in quality will, as a rule, be small. If the cows are milked three times a day, the noon milking is richest and the morning milking generally lowest in butter fat, while the amount of milk is least at noon and heaviest in the morning.

Excitement.-A feverish condition is generally accompanied

by a decrease in milk flow and an increase in the fat content; in cases of severe illness, the percentage of butter fat in the milk, will, however, be abnormally low. Cows in heat, or handled roughly, chased by dogs, or excited through other causes, will, as a rule, give a greatly diminished amount of milk, which will test very high.

Temperature and Weather.-Both excessively high temperatures and cold, heavy rain storms are likely to cause a marked decrease in the percentage of butter fat in the milk. Periods of drought, according to Van Slyke, cause a decrease in the flow of milk and in the contents of casein and albumen, especially the latter, while either no change or an increase in the percentage of butter fat will occur.

Season of Year.–The percentage fat content of milk appears to be subject to certain seasonal influences that are independent of the stage of lactation period, the breed of cows, or the system of feeding. The lowest fat content of the milk will, in general, occur during hot weather, in June or July, and from this time on a regular increase occurs, which reaches its maximum in December or January, and a general gradual decrease then takes place until toward midsummer. This seasonal influence appears to depend on the temperature of the air, and is, therefore, to be expected from what was said in the preceding paragraph.

Grooming and Exercise. -Grooming and moderate exercise stimulate the circulation and tend to cause a slight increase in the milk production and in the percentage of butter fat in the milk. Results of German experiments on this points are somewhat more favorable than those of experiments conducted in this country.” The effect of grooming on the health of the animals and on the condition of the milk are, however, important factors. In dairies producing certified or sanitary milk the cows are curried and groomed regularly, and udders and hindquarters are washed. This, doubtless, is an effective means of promoting the health of the herd and lessening the bacterial content of the milk.

Influence of Feed on Quality of Milk.-Contrary to the opinion held quite generally by dairy farmers up to recent years, the feed does not exert any marked influence on the quality of the milk secretion, so long as the cow receives sufficient nutriment in her ration to maintain her body weight. Given fair amounts of protein and digestible nutrients in the ration, the quality of the milk is not affected by a more liberal system of feeding or by furnishing any special feed or combination of feeds. Underfed or starved cows produce milk of an abnormally low fat content, and this may be readily raised to the normal percentage for the individual cow by increasing the feed. On the other hand, by feeding rations high in protein, a cow will give milk of the highest fat content of which she is capable, but any improvement in quality that may be wrought by such feeding is small, within one or two tents of one per cent above normal at the most. A slight improvement in the composition of the milk has been observed in some cases by feeding single feeds, notably palm-nut meal and cocoanut meal, and by feeding fat or oil, but the evidence with regard to this point furnished by different experiments is often conflicting, and in cases where greater differences were found as a result of a certain system of feeding there was a gradual return to normal after a couple of weeks or before, when the cows became accustomed to the feed. In general, both dairy farmers and scientists are now agreed that it is impossible to change materially the percentage of fat in a cow's milk by the feed; no amount of rich feeding or supplying special feeds will change the milk of a Holstein to a composition similar to that of a Jersey, or make low-testing cows or families into “high testers.” The largest improvement in quality that can be hoped for would be within a few tenths of one per cent. “The quality of the milk which the cow produces is as natural to her as the color of her hair”; it is a practically fixed character that is intimately connected with the functional activity of the mammary gland.

Influence on Quantity of Milk. The feed eaten by a cow influences in a marked manner the quantity of milk secreted, and determines the preluction that the cow will make, up to the capacity of her mammary glands. The feed is, therefore, of primary importance in the management of a dairy, and the problem before the dairy farmer is to provide feed for his cows that will secure the largest production of which these are capable, at a minimum cost. As it is only the excess of feed caten over and above maintenance requirements that is used for productive purposes, it follows that the more a cow will eat without increasing appreciably in body weight, the larger returns she will yield per unit eaten (see Fig. 46). The old saying, “ Feed your cow and she will feed you, ” expresses the practical experience as to the relation of feed to product. With cows of the dairy type that respond to a more liberal system of feeding by an increase in milk production and not by a gain in body weight, this is a safe rule to follow in the management of a dairy. It is the heavy eaters that produce the largest yields and give the most economical production.10

The Value of High-producing Cows.—Results obtained in the Wisconsin Dairy Cow Competition, 1909–1911, illustrate in a striking manner the value of high-producing cows. The following table gives some of the main data for the highest, medium, and

:

MAINTENANCE MILK PRODUCTION GAIN IN WEIGHT LIBERAL RATION FED TO BEEF COWS

Fig. 45.- Liberal rations led to cows of beefy tendencies produce a pain in weight; such fed to good dairy cows i reduce ihe larķest picduction of milk or which they are capable. (Van Norman.) lowest producers among the 398 cows in the competition for which complete records of production for a full year were obtained. The cows were separated into three groups of the same number of cows within each of the dairy breeds represented, Holstein, Jersey, and Guernsey, according to their production of butter fat; the data for the different groups have been combined and are given in the following table:11

Returns from Cows of Different Producing Powers