THE ROTHAMSTED FEEDING EXPERIMENTS: MILK PRODUCTION.

Otago Witness, 25 January 1900, Page 4

THE ROTHAMSTED FEEDING EXPERIMENTS: MILK PRODUCTION.

Now that dairy farming is regarded with so much favour, the results of the Rothamsted experiments in feeding for milk production .should have a special interest for those engaged in the industry. It will be seen that, from a colonial farmer's point of view, the Rothamsted dairy cows were specially well fed; nevertheless, the conclusions arrived at from the results apply as well in the case of cows supplied only with—but in abundance—the ordinary foods grown on the farm. The Rothamsted estimates are based on the assumption that milk will contain 12.5 per cent, of total solids, consisting of 3.65 albuminoids, 3.50 butter-fat, 4.60 sugar, and 0.75 mineral matter. But, as there is a very wide range of yield per head per day. it may be remarked that it is by no means impossible that the same animal might yield 20 quarts (or 5 gallons) at the 1 beginning, and only four quarts (or one gallon), oi even less, towaids the end of her period of lactation. At the same time an entiie held of, say, Shorthorns or Ayrshires, of fairly average quality, well fed, and including animals at various periods of lactation, should not yield an average of a^ht quarts (or two gallons), and would

seldom exceed 10 quarts (or 2£ gallons) per head per day the year round. For the sake of" illustration, then, an average yield is assumed of 10 quarts (or 2£ gallons) per head per day. ' and the amount of constituents in the weekly yield at this rate is compared with that of the weekly increase of the fattening ox at the assumed rate of 151b per 10001b live weight. Thus, whilst of the nitrogenous substance of food the amount stored up in the fattening increase of an ox will be only 1.131b, the amount carried off as suck in milk would be 6.61b, or nearly six times as much. Ot mineral matter, again, whilst the fattening increase would only require about 0.221b, the milk would carry off 1.351b, or again about six times as much. Of fat, however, whilst the fattening increase would contain_ 9.561b, the milk would contain only 6.65'.b, oi only about two-thirds as much. On the other hand, whilst the fattening increase contains no other non-nitrogenous substance th^n fat, the milk would carry off 8.321b in the form of milk-sugar. It may be observed that this amount of milk-sugar reckoned as fat would coirespond approximately to the difference between the fat in the milk and that in the fattening increase. From the foregoing comparison it is evident 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 nitrogenuous substance ; and if, as is irequently assumed, the butter-fat of tho milk is, at any rate, largely derived from the nitrogenous .substance of the food so far as it is so, at least two parts of such substance would bo 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 as existing as nitrogenous substance in the milk. The figures in the following table show the food consumed and the constituents therein, per 10G0 b live weight per day, in the case of the Sothamsted herd, then of 30 cows, in the spring of 1884. On the left hand are shown the actual amounts of the different foods consumed per 10001b live weight per clay ; and in the respective columns are recorded — first, the amounts of total dry sub-tance which the foe ds coptiined, 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 ct;lcul.ited recording to the Rothamsted estimates of the percentage composition of the ioods, 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 10001b live weight per daj' was scarcely 201b, whilst Wolff's estimated requirements, as stated at the foot of the table, is 241b. But his ration would doubtless consist in "larger proportion of hay and straw-chaff, containing a larger proportion of indigestible and effete woody fibre. The figures sLow, indeed, that the Rothamsted ration supplied, though nearly the same, even a somewhat less amount of total digestible constituents than Wolff's. Coi.i-titueats c n urceJ per 1000H) live-weight p?r day fur msienance »nri for mi k proiiiution ; the Rothamsted hi rd of 30 cows ; >pr nsr, 1881.

Of digestible nitrogenous substance, the food is 2.641b per day. Avhilst the amount estimated to be required for sustenance merely is 0.571b, leaving, therefore, 2.071b available for milk production. The 23.31b of milk yielded per 10001b live weight per ' day would, however, contain only 0.851b : and there would thus remain an apparent excess of 1.22 ib of digestible nitrogenous substance in the food supplied. But, against the amount of 2.641b actually con.sumed, Wolff's estimate of the amount required for sustenance and for milk production is 2.51b, or but little less than the amount actually consumed at Rothamsted. On the assumption that the expenditure of nitrogenous substance in the production of milk is only in the formation of the nitrogenous substance of the milk, there would appear to have been a considerable excess given in the food. But Wolff's estimate assumes no excess of supply, and that the whole is utilised ; the fact being that he supposes the butter-fat of the milk to have been derived largely (if not wholl3 r ) from the albuminoids of the food. As compared with fattening increase — which may in a sense be said to be a 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 ricii in carbohydiatcs, 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. Assuming, however, that saeh. is the case, that such change does take place, the amount of nitrogenous substance 'supplied to the Eothamsted 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. It should be stated that the Rothamsted cows had cake throughout the year ; afe first 41b per head per day, but afterward? graduated according to the yield of milk, on. the basis of 41b for a yield" of 281b of milk, the result being thot then the amounts 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 cows were not tinned out to grass. The general plan was, therefore, to give cake alone in addition when the cows were turned out to grass, but some oilier dry food and roots when entirely in the shed during the winter and early spring months. A table is given showing the influence of period of the year, with its characteristic changes of food, on the quantity and c imposition of the milk in each month of the year over six years (1884-1889) inclusive. Referring to _the column showing the average yield of milk per head per day over six years, it will be seen that the mean was 24.281b, and thai during the six months — January, February, September, October, November, and December — the average was sometimes below 203b. and on the average only about 211b of milk per head per day ; whilst over the other six months it averaged 27.631b, and over May and June more than 311b par head per day. That is to .say, the quantity of milk yielded was considerably greater during the grazing period than when the animals had more dry food and roots instead of grass. iSText, referring to the particulars of composition, it is &cen that the specific gravity of the milk w^s only average, or lower than average, during the grazing period, but rather higher in the earlier and later months of the year. The percent-age of total solids was rather lower than the average at the beginning of the year, lowest during the chief gracing months, but considerably higher m the" later months of the year, when the animal,? were kept in the sheds and received more dry food. The percentage of butter fat follows very closely that of the total solids, being the lowest during the best gracing months, but considerably higher than the average during the lasfc four or five months of the year, when more dry focd was given. The percentage ox solids, not fat, was considerably the lowest during the later months of the grazing pariod, but average, or higher than average, during the earlier and .later months of ihe year. It may be observed that Recording to the average percentages given in the - table, a gallon of milk will contain more of both- total solids and of butter fat in the later months. Turning to the last three columns of the table, it is seen that although, as has been, shown, the percentage of the constituents in the milk is lower during the grazing months, the actual amounts contained in the quantity of milk yielded per head are distinctly greater during those months. Thus, the amount of butter fat yielded per •head per day is above the average of the year from April to September 'inclusive ; the amounts of solids, not fat. are over average from April to August inclusive; and the amounts of total solids yielded are average or over average from April to August inclusive. From the foregoing results, it cannot be doubted that the quantity of milk yielded per luad is very much the greater daring the grazing months of the year ; but that the percentage composition of the milk rs lower during that period of higheV yield, and considerably higher during the months of more exclusively dry -food feeding. Nevertheless, owing to the much greater quantity of milk yielded during the grazing months, the actual quantity of constituents yielded per cow is greater during those months than during the months of higher percentage composition but lower yield of milk per. head. It must be added' that a careful" consideration of the number of newly-calved cows brought into the Rothamsted herd each month shows the results, as aUove stated, were perfectly distinct, independently of any influence of the period of la cation" of the different individuals of the herd. With regard to the influence of variation in the quantity and composition of the fond on the quantity and composition of the milk yielded, the Rothamsted authorities say : — • " Exercising such care and reservation in regard to the numerous results of ourselves and others which are at command, it may be taken as clearly indicated that, within certain limits, high feeding, and especially high nitrogenous feeding, does increase both the yield and richness of the milk. Bufc it is evident that when high feeding is pushed beyond a comparatively limited range, the tendency is to increase the weight of the animal ; that is, to favour the development of the individual rather than to enhance the activity of the functions connected with the reproductive system." It may be observed that direct experiments at Rothamsted confirm the view, arrived at by common experience, that roots, and especially mangel, have a favourable effect on the flow of milk. Further, the Rothamsted experiments have shown th.ifc a higher percentage of butter fat, of other solids, and of total solids, was obtained with mangel than with silage as the succulent food. The yield of milk was, however, in a much greater degree increased by grazing than by any other change in the food, and at Rothamsted, at any rate, the influence of roots comes next in order

to that of grass) though far behind it in this respect. But with grazing, as has, been shown, the percentage composition of the milk is considerably reduced, though owing to the greatly increased quantity . .yielded, the amount of constituents removed ■ in tbe milk whilst grazing may, nevertheless, be greater per head per day than under any other conditions. | Lastly, it has been clearly illustrated how very much greater is the demand upon the food, especially for nitrogenous and for mineral constituents, in the production of niilk than in that of fattening increase. j

Total Dry Substance. Nit rogerou Stntt'nce uitrcteo' us ub Toisl | Nitr - : prenous jit Nonj iiitrc- {< nous I Sub- . s-tance stance (as ftaivh). 3'llh cotton cikt 2 71b bran caKe 2* 8 b hay chaff... s'tilb oat-straw eh ff 62 81bn3a>.gcl .. lb. 2 7K 2 33 2 3-i lb. l(-7 0 33 0-i5 lb. 1-5) 1-09 1-J8 lb. 2 57 1-1-2 133 4'fi4 7-S5 OTB 1-01 221 57.1 2-21 6 74 To'al Requited form - tei ance 19-92 2-C4 0-57 1171 14 35 7-W 7 40 Available for milk In 23 31b milk... 2-07 OSS 4-31 3-02 6SS 3W Excess in f00d...' I\2 129 2 51 Pef 10001b )ivr d weight. Wolff's lation „ I lb. ...I *24 I 11.. 25 I lb. 125 lb. 154