348
DAIRY-FARMING
the milk to have been derived largely, if not wholly, from the albuminoids of the food. It has been shown that although it is possible that some of the fat of a fattening animal may be produced from the albuminoids of the food, certainly the greater part of it, if not the whole, is derived from the carbohydrates. But the physiological conditions of the production of milk are so different from those for the production of fattening increase, that it is not admissible to judge of the sources of the fat of the one from what may be established in regard to the other. It has been assumed, however, by those who maintain that the fat of the fattening animal is formed from albuminoids, that the fat of milk must be formed in the same way. Disallowing the legitimacy of such a deduction, there do, nevertheless, seem to be reasons for supposing that the fat of milk may, at any rate in large proportion, be derived from albuminoids. Thus, as compared with fattening increase, which may in a sense be said to be little more than an accumulation of reserve material from excess of food, milk is a special product, of a special gland, for a special normal exigency of the animal. Further, whilst common experience shows that the herbivorous animal becomes the more fat the more, within certain limits, its food is rich in carbohydrates, it points to the conclusion that both the yield of milk and its richness in butter are more connected with a liberal supply of the nitrogenous constituents in the food. Obviously, so far as this is the case, it may be only that thereby more active change in the system, and therefore greater activity of the special function, is maintained. The evidence at command is, at any rate, not inconsistent with the supposition that a good deal of the fat of milk may have its source in the breaking up of albuminoids, but direct evidence on the point is still wanting; and supposing such breaking up to take place in the gland, the question arises—What becomes of the by-products'? Assuming, however, that such change does take place, the amount of nitrogenous substance supplied to the Rothamsted cows would be less in excess of the direct requirement for milk-production than the figures in the table would indicate—if, indeed, in excess at all. The figures in the column of Table YI. relating to the estimated amount of digestible non-nitrogenous substance reckoned as starch show that the quantity actually consumed was 11‘71 lb, whilst the amount estimated by Wolff to be required was 12‘5 lb, besides 0‘4 lb of fat. The figures further show that, deducting 7'4 lb for sustenance from the quantity actually consumed, there would remain 4 •31 lb available for milk-production, whilst only about 3’02 lb would be required supposing that both the fat of the milk and the sugar had been derived from the carbohydrates of the food; and according to this calculation, there would still be an excess in the daily food of 1 -29 lb. It is to be borne in mind, however, that estimates of the requirement for mere sustenance are mainly founded on the results of experiments in which the animals are allowed only such a limited amount of food as will maintain them without either loss or gain when at rest. But physiological considerations point to the conclusion that the expenditure, independently of loss or gain, will be the greater the more liberal the ration; and hence it is probable that the real excess, if any, over that required for sustenance and milk-production would be less than that indicated in the table, which is calculated on the assumption of a fixed requirement for sustenance for a given live-weight of the animal. Supposing that there really was any material excess of either the nitrogenous or the non-nitrogenous constituents supplied over the requirement for sustenance and milk-production, the question arises—
[FOOD AND MILK PRODUCTION.
Whether, or to what extent, it conduced to increase in live-weight of the animals, or whether it was in part, or wholly, voided, and so wasted 1 As regards the influence of the period of the year, with its characteristic changes of food, on the quantity and composition of the milk, the first column of the second division of Table VII. shows the average yield of milk per head per day of the Botham,sted herd, averaging about 42 cows, almost exclusively Shorthorns, in each month of the year, over six years, 1884 to 1889 inclusive; and the succeeding columns show the amounts of butter-fat, of solids not fat, and of total solids in the average yield per head per day in each month of the year, calculated, not according to direct analytical determinations made at Rothamsted, but according to the results of more than 14,000 analyses made, under the superintendence of Dr Yieth, in the laboratory of the Aylesbury Dairy Company in 1884;1 the samples analysed representing the milk from a great many different farms in each month. Table YII. Percentage Composition of Milk each Month of the Year; also Average Yield of Milk, and of Constituents, p)er Head per Day each Month, according to Rothamsted Dairy Records. Rothamsted Dairy. Average Composition of Milk each Month, 1884 (Dr Vieth—14,235 analyses). Estimated Quantity of Constituents in Average per Head per Per cent. Yield Milk of Milk Day each Month. per Head Specific Day, Gravity. Butter- Solids Solids Total Total per not not Solids. Fat. Fat. Solids. 6 Years. ButterFat. Fat. January February March April May June July August September October . November December
1-0325 1-0325 1-0323 1-0323 1-0324 1-0323 1-0319 1-0318 1-0321 1-0324 1-0324 1-0326
Per cent. 3-55 3-53 3-50 3-43 3-34 3-31 3-47 344-26 4-36 4-10
Per cent. 9-34 9-24 9-22 9-22 9-30 9-19 9-13 9-08 9-17 9-27 9-29 9-29
Per cent. 12-89 12-77 12-72 12-65 12-64 12-50 12-60 121313-53 13-65 13-39
lb 2022-81 2426-50 31-31 30-81 28-00 2522-94 2119-19 19-31
Mean . 1-0323 3-74 9-22 12-96 24-28
lb 0-72 0-80 0-85 0-91 1-05 1-02 0-97 0-97 0-94 0-89 0-84 0-79
lb 122-23 2-44 2-91 2-83 2-56 2-27 2-11 1-95 1-78 1-79
lb 2-62 233-35 3-96 3-85 3-53 3-24 3-05 2-84 2-62 2-58
0-90 2-24 3-14
- Average over five years only, as the records did not commence
until February 1884. It should be stated that the Rothamsted cows had cake throughout the year; at first 4 lb per head per day, but afterwards graduated according to the yield of milk, on the basis of 4 lb for a yield of 28 lb of milk, the result being that then the amount given averaged more per head per day during the grazing period, but less earlier and later in the year. Bran, hay and straw-chaff, and roots (generally mangel), were also given when the animals were not turned out to grass. The general plan was, therefore, to give cake alone in addition when the cows were turned out to grass, but some other dry food, and roots, when entirely in the shed during the winter and early spring months. Referring to the column showing the average yield of milk per head per day each month over the six years, it will be seen that- during the six months—January, February, September, October, November, and December —the average yield was sometimes below 20 lb, and on the average only about 21 lb of milk per head per day; whilst over the other six months it averaged 27"63 lb, and over May and June more than 31 lb, per head 1
The Analyst, April 1885, vol. x. p. 67.
