216 Scientific Proceedings^ Royal Dublin Society. 



Discussion of the Results. 



It is clear that the percentage of, and total milk fat can be increased, within 

 limits, by increasing the ration. Thus an increase in the starch diet in goat 1 

 (periods' D and E) from IJ to If lbs. produced considerable increases in milk 

 fat. There is a limit to the capability of the animal in this direction, and a 

 maximum milk fat yield is reached above which it is impossible to go. In goat 1 

 the feeding of 2^ lbs. of starch gave no better yield than the feeding of If lbs. 

 (pex-iods B and G). It is evident that the feeding of a ration constituted like 

 that given in period G, no matter in what quantity it is consumed, does not 

 enable the lactating animal to give the maximum return in milk fat. There 

 is some necessary constituent supplied in sub-minimal quantity, and we shall 

 see later that that material is fat. The results from goat 1 (periods B, C, and D) 

 and from goat 3 (periods A and B, and periods B and D) show that for the 

 production of milk fat, starch and protein, i.e. protein in excess of minimum 

 requirements, replace one another in equal quantities. The comparative value 

 is not so clear in the case of fat and starch. In goat 1 (periods E and F) the 

 substitution of fat for three and a half times its weight of starch caused an 

 increase in milk fat yield, and in the same goat (periods P and G) the replace- 

 ment of fat by four and a half times its weight of starch caused a decrease in 

 milk fat yield. Similarly in goat 2 (periods A and B) fat in the ration gave a 

 better yield of milk fat than two and a half times its weight of starch, and in 

 the same goat (periods E and F) fat gave a better result than three times its 

 weight of starch. Similar conclusions can be drawn from goat 3. 1:^ lbs. of 

 starch are inferior to i lb. of fat (periods C and D). The same relation seems 

 to hold between fat and protein, ^ lb. of fat being considerably superior to 

 1^ lbs. of casein for milk fat production — fig. 3 (periods B and C). When, 

 however, we consider the substitution of carbohydrate by fat, in rations already 

 containing a fair proportion of fat, we get quite different results. From the 

 results from goat 1 (periods H and I) it is seen that 1 lb. of fat is verj^ slightly 

 sui^erior for milk fat production to 1^ lbs. of starch, plus f lb. of fat — that is, 

 1| lbs. of starch is almost equal for that purpose to f lb. of fat, or 2 -Jj lbs. of 

 starch to 1 lb. of fat. In the same way it is determined from goat 3 (periods H 

 and I) that If- lbs. of starch almost serves the same purpose as ^ lb. of fat, or 

 2 yV lbs. of starch to 1 lb. of fat. A very slight increase in the starch figure 

 would render the results similar, so that it is justifiable to nominate the figure 

 2| for starch as being equivalent to 1 of fat. Since starch and protein replace 

 one another in equal parts, it might be reasonably concluded that fat and 

 protein replace one another in the proportion of 1 to 2f also. Though fat in 

 the ration is necessary to induce the maximum activity of the mammary gland 

 for milk fat secretion, a small proportion of fat is as efficacious in this direction 

 as a large quantity. Thus in goat 1 (periods G and H) |- lb. of fat, and in 

 goat 3 (periods G and H) ^ lb. of fat per day, in addition to the fat contained 

 in the basal ration, was sufficient to yield maximum results. Apparently less 

 than that quantity would suffice for the purpose of inducing maximum yield 

 of milk fat, for in goat 2 (periods E and IT) we see that the addition of even 

 -js lb. of fat per day increased the percentage of milk fat to a level higher 

 than was reached by that animal at any other period of her lactation; but 

 whether a higher level could be attained by feeding more fat, say 1 lb. per day, 

 as in goats 1 and 3 (period I), was not determined. The foregoing results 

 establish a definite relationship between proteins and carbohydrates for milk 

 fat production. It is shown in the case of fat that a certain quantity must be 



