Wilson — The Inheritance of Milk- Yield in Cattle. 95 



It was also noticed tliat tlie yield of a cow calved six months and in 

 calf about tlie normal time is approximately 50 to 60 per cent, of the yield at 

 its maximum. That is to say, a cow whose maximum is sixty pounds a day, 

 gives from thirty to five and thirty pounds when six months calved. The 

 percentage is higher for a winter-calved cow, and lower for a cow calving in 

 spring. 



This and the previous observation can be used to reduce a prolonged 

 lactation to the normal when only the total yield is known. For instance, 

 thousand-gallon cows give over 5 gallons a day. At six months calved they 

 give 2J to 3 gallons a day. If the lactation has. been prolonged, say, a 

 month, then 75 to 90 gallons (2| x 30 days or 3 x 30 days) have to be 

 deducted from the total yield to reduce it to the normal, according to the 

 time the cow calved and other affecting circumstances. 



The last point to be determined before milk-yields could be compared 

 was the rate at which they increase with age. This is perhaps the most 

 important of all the points dealt with, since there are more young cows than 

 old, and since the young ones are perhaps more satisfactory for the purpose 

 of comparing yields than the old ones. The younger the cow the less are 

 the chances that her yielding-capacity may Iiave been damaged by one or 

 more of the causes liable to do so. At the same time it should be noted that 

 the yield of an immature heifer, say one poorly nurtured or under about 

 two and a half years' old, is probably an unreliable guide. At any rate, 

 none such is relied upon in this paper. 



In working through the records at the Department of Agriculture's farms 

 at Glasnevin, Clonakilty, and Loughrea, it became apparent that a cow's 

 yield generally increases from the birth of her first calf, when she is a 

 three-year-old (that is, from about thirty-three to forty-two montiis old) till 

 the birth of her fourth or fifth, when she is six or seven years old, and that 

 the total increase from the first to the fourth or fifth calf is on the average 

 about 50 percent. That is, assuming no interference, a cow that starts at 300 

 gallons will rise approximately to about 450 ; another tliat starts at 500 will 

 rise to about 750 ; and another that starts at 700 will rise to about 1,050. 



This estimate was also found to hold as regards Danisii and Dutch cows. 

 The records in the first three volumes, containing over 400 cows, of the Herd- 

 book of the red Danish breed (Kostambog Koer af roed dansk Malkerace), 

 published 1907, 1908, and 1910, were gone through carefully, and the results 

 were found to be generally in accordance with the rale. There were 

 exceptions, but these were usually explained by such things as illness or 

 abortion. Among the liighest grade of cows, there was one kind of exception 

 whicli was very suggestive. There were a number of three-year-old cows 



