Animal Husbandry Investigations in 1919. 251 



Guernsey Milk Yield=668i. 5 + 104.422c — 5. 284x^4- 2846.5 log x. 

 where x equals the age in units of six months commencing at 

 one year and three months of age for the zero point. 



Jersey Milk Yield=4586.5-|-307.55x — I2.65x 2 -f-22i6.6 log x. 

 where x equals the age in units of six months commencing at 

 nine months of age for the zero point. 



These equations furnish the information necessary to 

 answer the above question ; the only question which arises is 

 how best to present the facts. Breeders have long recognized 

 that the average milk production for the breeds differs consid- 

 erably. It appears best, therefore, to get some means of ex- 

 pressing the relationship desired which shall eliminate this dif- 

 ference in the absolute yields. This may be done by determining 

 for a given breed the curve for the amount by which the milk 

 productions at the different ages, beginning at say 1 year and 9 

 months, should be multiplied to give the milk production at a 

 constant age, say 8 years. Concretely considered if the mean 

 milk production of the 2 year old group is 12862 pounds and 

 the mean milk production of the 8 year old group is 19023 



19023 



pounds the multiplication factor will be — — or I.47Q; if the 



12862 ^' y 



mean 3 year old milk production was 14857 the factor will be 



19023 



— — =1.281. Generalized this means that if a, b, c, d 



equal the mean milk productions at 2, 3, 4, 5 years of age 



and K equals the mean milk production at 8 years of age the 



T7 T£ XT" T7 T7 



curve for the breed may be found by — — , — — — Such a 



a b c d n 



curve for each breed gives the information desired for these 

 curves will be entirely comparative and comparative on the 

 same basis. Figure 26 page 252 shows this curve. 



The three curves in Figure 26 show a striking similarity 

 in shape. This similarity is even more striking where the large 

 variability of milk production is taken into consideration. It 

 is true that the Guernsey breed differs somewhat from the other 

 breeds in reaching its maximum yield later in life and having a 

 lower rate of decline in milk yield after maturity. This dif- 

 ference is, however, probably only slightly significant, based as 

 it is on the rather small numbers of this end of the curve. The 

 curves of Figure 26 show that age increases or decreases the 

 milk yield of the high producing breeds more than the milk 

 yield of the lower producing breeds. This increase or decrease 



