In their comprehensive paper relating to the feeding of animals published in 1895, Lawes and Gilbert discussed amongst other questions that of milk production, and directed attention to the great difference in the demands made on the food—on the one hand for the production of meat (that is, of animal increase), and on the other for the production of milk. Not only, however, do cows of different breeds yield different quantities of milk, and milk of characteristically different composition, but individual animals of the same breed have very different milk-yielding capacity; and whatever the capacity of a cow may be, she has a maximum yield at one period of her lactation, which is followed by a gradual decline. Hence, in comparing the amounts of constituents stored up in the fattening increase of an ox with the amounts of the same constituents removed in the milk of a cow, it is necessary to assume a wide range of difference in the yield of milk. Accordingly, Table V. shows the amounts of nitrogenous substance, of fat, of non-nitrogenous substance not fat, of mineral matter, and of total solid matter, carried off in the weekly yield of milk of a cow, on the alternative assumptions of a production of 4, 6, 8, 10, 12, 14, 16, 18 or 20 quarts per head per day. For comparison, there are given at the foot of the table the amounts of nitrogenous substance, of fat, of mineral matter, and of total solid matter, in the weekly increase in live-weight of a fattening ox of an average weight of 1000 ℔—on the assumption of a weekly increase, first, of 10 ℔, and, secondly, of 15 ℔. The estimates of the amounts of constituents in the milk are based on the assumption that it will contain 12.5% of total solids—consisting of 3.65 albuminoids, 3.50 butter-fat, 4.60 sugar and 0.75 of mineral matter. The estimates of the constituents in the fattening increase of oxen are founded on determinations made at Rothamsted.

Table V.—Comparison of the Constituents of Food carried off in Milk, and in the Fattening Increase of Oxen.

[1 Gallon = 10.33 ℔]Nitrogenous
Substance.		Fat.Non-
Nitrogenous
Substance
not Fat
(Sugar).		Mineral
Matter.		Total
Solid
Matter.
In Milk per Week.
If:— ℔ ℔ ℔ ℔ ℔
 4 quarts per head per day 2.64 2.53 3.33 0.54  9.04
 6  ”    ”    ” 3.96 3.80 4.99 0.81 13.56
 8  ”    ”    ” 5.28 5.06 6.66 1.08 18.08
10  ”    ”    ” 6.60 6.33 8.32 1.35 22.60
12  ”    ”    ” 7.92 7.59 9.99 1.62 27.12
14  ”    ”    ” 9.24 8.86 11.65 1.89 31.64
16  ”    ”    ” 10.56 10.12 13.32 2.16 36.16
18  ”    ”    ” 11.88 11.39 14.98 2.43 40.68
20  ”    ”    ” 13.20 12.65 16.65 2.70 45.20
In Increase in Live-Weight per Week.—Oxen.
If 10 ℔ increase 0.75 6.35 .. 0.15  7.25
If 15 ℔ increase 1.13 9.53 .. 0.22 10.88

With regard to the very wide range of yield of milk per head per day which the figures in the following table assume, it may be remarked that it is by no means impossible that the same animal might yield the largest amount, namely, 20 quarts, or 5 gallons, per day near the beginning, and only 4 quarts, or 1 gallon, or even less, towards the end of her period of lactation. At the same time, an entire herd of, for example, Shorthorns or Ayrshires, of fairly average quality, well fed, and including animals at various periods of lactation, should not yield an average of less than 8 quarts, or 2 gallons, and would seldom exceed 10 quarts, or 2½ gallons, per head per day the year round.

For the sake of illustration, an average yield of milk of 10 quarts, equal 2½ gallons, or between 25 and 26 ℔ per head per day, may be assumed, and the amount of constituents in the weekly yield at this rate may be compared with that in the weekly increase of the fattening ox at the higher rate assumed in the table, namely, 15 ℔ per 1000 ℔ live-weight, or 1.5% per week. It is seen that whilst of the nitrogenous substance of the food the amount stored up in the fattening increase of an ox would be only 1.13 ℔, the amount carried off as such in the milk would be 6.6 ℔, or nearly six times as much. Of mineral matter, again, whilst the fattening increase would only require about 0.22 ℔, the milk would Carry off 1.35 ℔, or again about six times as much. Of fat, however, whilst the fattening increase would contain 9.53 ℔, the milk would contain only 6.33 ℔, or only about two-thirds as much. On the other hand, whilst the fattening increase contains no other non-nitrogenous substance than fat, the milk would carry off 8.32 ℔ in the form of milk-sugar. This amount of milk-sugar, reckoned as fat, would correspond approximately to the difference between the fat in the milk and that in the fattening increase.

It is evident, then, that the drain upon the food is very much greater for the production of milk than for that of meat. This is especially the case in the important item of nitrogenous substance; and if, as is frequently assumed, the butter-fat of the milk is at any rate largely derived from the nitrogenous substance of the food, so far as it is so at least about two parts of such substance would be required to produce one of fat. On such an assumption, therefore, the drain upon the nitrogenous substance of the food would be very much greater than that indicated in the table as existing as nitrogenous substance in the milk. To this point further reference will be made presently.

Table VI.—Constituents consumed per 1000℔ Live-Weight per Day, for Sustenance and for Milk-Production. The Rothamsted Herd of 30 Cows, Spring 1884.

Total
Dry
Substance.		 Digestible.
Nitrogenous
Substance.		Non-
Nitrogenous
Substance
(as Starch).		Total
Nitrogenous
and Non-
Nitrogenous
Substance.
℔ ℔ ℔ ℔
3.1 ℔ Cotton cake 2.76 1.07 1.50 2.57
2.7 ℔ Bran 2.33 0.33 1.09 1.42
2.8 ℔ Hay-chaff 2.34 0.15 1.18 1.33
5.6 ℔ Oat-straw-chaff 4.64 0.08 2.21 2.29
62.8 ℔ Mangel 7.85 1.01 5.73 6.74
  Total 19.92 2.64* 11.71* 14.35
Required for sustenance 0.57 7.40 7.97
Available for milk 2.07 4.31 6.38
In 23.3 ℔ milk 0.85 3.02 3.87
  Excess in food 1.22 1.29 2.51
Per 1000 ℔ Live-Weight.
℔ ℔ ℔ ℔
Wolff 24 2.5 12.5** 15.4
* Albuminoid ratio, 1-4.4.
** Exclusive of 0.4 fat; albuminoid ratio, 1-5.4.

Attention may next be directed to the amounts of food, and of certain of its constituents, consumed for the production of a given amount of milk. This point is illustrated in Table VI., which shows the constituents consumed per 1000 ℔ live-weight per day in the case of the Rothamsted herd of 30 cows in the spring of 1884. On the left hand are shown the actual amounts of the different foods consumed per 1000 ℔ live-weight per day; and in the respective columns are recorded—first the amounts of total dry substance which the foods contained, and then the amounts of digestible nitrogenous, digestible non-nitrogenous (reckoned as starch), and digestible total organic substance which the different foods would supply; these being calculated according to Lawes and Gilbert’s own estimates of the percentage composition of the foods, and to Wolff’s estimates of the proportion of the several constituents which would be digestible.

The first column shows that the amount of total dry substance of food actually consumed by the herd, per 1000 ℔ live-weight per day, was scarcely 20 ℔ whilst Wolff’s[3] estimated requirement, as stated at the foot of the table, is 24 ℔. But his ration would doubtless consist to a greater extent of hay and straw-chaff, containing a larger proportion of indigestible and effete woody fibre. The figures show, indeed that the Rothamsted ration supplied, though nearly the same, even a somewhat less amount of total digestible constituents than Wolff’s.