82 Breeding for Increase of Milk in Dairy Cattle 



steadier level so that I believe that in the end the cows calving between 

 October and May ultimately yield just about the normal amount. On 

 the other hand, cows calving in July, August and September start their 

 physiological rise on the seasonal fall and I believe that their yield is 

 lessened. I am aware that the Irish Department of Agriculture states 

 the exact reverse but they do not give the evidence upon which they 

 base their view. 



Temperature has a marked effect on yield. I have come to the con- 

 clusion that the optimum lies between 50" — 60° Fahrenheit. Wind 

 direction and intensity also affects yield as does sunshine: both are to be 

 avoided, though light is most desirable. The general character of the 

 season, whether wet or dry (the first is to be preferred), the nature of 

 the fodder or roots used, the skill of the milkers, the temper of the 

 byreman, all leave their mark on the milk record, and the effect of the 

 most transitory illness is at once visible in the amount registered. 



One source of inaccuracy can be corrected more or less adequately. 

 A cow running twelve months neat between calves gives a normal 

 lactation, but if this period is shortened or lengthened the lactation 

 ceases to be quite normal. Here, however, we must remember the 

 following facts. Some cows will remain in milk for two years between 

 calves, some will go out of milk at the end of ten months or thereby 

 even if yeld. 



Some cows if run dry will give more milk than they would have, 

 had they been put in calf, and some will give less. After much study 

 I have come to the conclusion that the proper correction is to take the 

 total lactation figure and divide it by the total of days between calving 

 dates and multiply the quotient by 365, This decreases the figure of 

 yield for the long lactations and increases it for the short ones. All the 

 figures of yield in these tables have been thus obtained. The butterfat 

 percentages are averages for the whole lactation. 



This correction which may appear arbitrary to workers unfamiliar 

 with data afforded by the consideration of large numbers of records is, 

 I am convinced, a fair representation of the facts and it should be noted 

 that while it reduces the maximum range of difference in yield, it has 

 never occasioned the placing of good milkers in a low category nor the 

 reverse. 



The curve of butterfat exactly reverses the milk yield curve, falling 

 as long as the milk curve rises and rising when it falls. I have only one 

 exception to this rule, a case where the butterfat curve, if drawn, would 

 make an almost straight line rising slightly in the second half of the 



