. Journal of agricultural research . ercentage. Age (in years). Mean fat percentage. Observed. Calculated. Observed. Calculated. 2 3- 10 3-5993. 606 3-5953-5933-590 T, II 4 12 C I? 6 14 I q 7 8 16 9- • From an examination of the observed figures it appears that in generalthe fat percentage tends to decline with advancing age until the tenth 3i8 Journal of Agricultural Research voi. x\ai. no. 6 year is reached. From that point on, allowing for chance fluctuationsand t
. Journal of agricultural research . ercentage. Age (in years). Mean fat percentage. Observed. Calculated. Observed. Calculated. 2 3- 10 3-5993. 606 3-5953-5933-590 T, II 4 12 C I? 6 14 I q 7 8 16 9- • From an examination of the observed figures it appears that in generalthe fat percentage tends to decline with advancing age until the tenth 3i8 Journal of Agricultural Research voi. x\ai. no. 6 year is reached. From that point on, allowing for chance fluctuationsand the fact that the numbers dealt with get progressively smaller, thefat percentage appears to remain about constant for the rest of the cowsmilking life. Consequently, it has seemed best to break the curve at thelo-year point and fit the two parts separately, each with a straight resulting figures are given in the calculated column of Table XI,and are shown graphically in figure 6. The equations to the two lines 4,000 FiQ. 6.—Showing the observed (zigzag line) and calculated (straight line) changes ia the mean fat per-centage of the milk of Ayrshire cows with advancing age. are as follows, the fitting having been done by the method of leastsquares. From 2 to lo years of age: ;^ = ID to i6 years of age: y= — 8x. SUMMARY This paper presents the results of a biometrical analysis of variation inthe quantity per unit of time, and the quality, as indicated by fat per-centage, of the milk of Ayrshire cows. Its purpose is to establish normalconstants for interindividual variation in these characters, to serve as abase of reference in future genetic studies on milk production. Sept. IS, 1919 Variation in Milk of Ayrshire Cows 319 The chief results of this first part of the investigation may be sum-marized as follows: (i) The mean weekly yield and fat percentage of the milk change in aconsiderable degree and definite manner with increasin
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectagricul, bookyear1913
