94 Scientific Proceedings, Royal Dublin Society. 



the same cow fat before calving maj' represent as much as a hundred gallons, 

 or even more, during a lactation. It was also found that, if a cow was got 

 in calf again too soon, her yield fell during that lactation : very seriously 

 when the " rest " was below six weeks. 



These points referred to above having been considered so far that their 

 influence might be estimated wliere necessai'y, the effect of a prolonged 

 lactation upon the yield was examined. 



A comparison of the records of the cows got in calf at the normal time, 

 that is three months after the previous calving, with those of the cows 

 running beyond that time, or not got in calf at all, showed that cows are, 

 on the average, usually about three months in calf before their being so 

 affects the yield appreciably. The yield of a normal cow drops fairly 

 quickly from about the sixth month after calving till about the tenth month, 

 when it ceases altogether. On the other hand, the yield of a cow that is not 

 in calf till more than three months after her last calving is so much later in 

 showing the quick drop which shows the yield is coming to an end. There 

 is a decline certainly, but it is small. Cousequeutly, a cow that goes thirteen 

 months from calf to calf milks for a month longer than one that goes twelve 

 months. And thus, for every month a cow is in milk beyond the normal, 

 tlie yields she gives during the seventh, the seventh and eighth, the seventh, 

 eighth and ninth months of her lactation, and so on, must be deducted from 

 the total yield in order to bring it to tlie normal. This deduction must be 

 made with some judgment, of course, because no cow will go on milking for 

 ever, and the drop at the end of a very long lactation will not be the same 

 as it would liave been had the lactation been normal. 



While examining the Irish records it was noticed that the daily yield of 

 a cow when at her maximum, from four to six weeks after calving, is a fair 

 index of what the total normal yield will be for the same lactation, provided, 

 of course, no illness or accident intervenes to alter the yield. A winter-calving 

 cow that gives a daily yield of six gallons at her maximum will rise to about 

 eleven or twelve gallons during the lactation; a cow that gives over five gallons 

 ■will rise to about a tliousand. Cows calving in spring or summer will not rise 

 so far. The calculation is to multiply the average daily yield in pounds over 

 two or three weeks at the maximum by about twenty, and the result gives 

 an approximate indication of the yield for the normal lactation in gallons. 

 A lower figure, say nineteen or eighteen, has to be used for cows calving in 

 spring or summer. Lower figures must be used also where cows are not 

 well fed and cared for. In the case of cows that dry up very early, say in 

 six or seven mouths, this calculation is misleading ; but the number of such 

 cows is not large — far less than is frequently asserted. 



