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Effect of Milking Time on Solids in Milk from Holsteins1
EFFECT
OF M I L K I N G T I M E ON S O L I D S I N MILK FROM HOLSTEINS ~
W. S. NICHOLSON, JR., H. S. WILLARD, W. R. THOMAS, AN]) D. C. BROWN
Dairy Depavtment~ U~dversity of Wyoming, Laramie Variations in the solids between mornings' and evenings' milk of 40 Holsteins were studied for two consecutive miikings during three years. There were significant differences among cows for pounds of milk, fat, solids-not-fat and total solids and for their percentages in milk. Significantly more milk was produced in the morning and there were significant differences in the amount of solids in mornings' and evenings' milk. Editor.
I n recent years, the dairy industry has placed increasing emphasis on the nonfat solids portion of milk, and attention has been focused on the scarcity of comprehensive data illustrating the characteristics of solids in milk. This study was conducted for the purpose of determining variations of the solid-milk components, between the morning and evening milk of individual cows. Whether milk f r o m an individual cow is sampled during" the morning or evening milking m a y have an effect on its solids content. Citations of Peterson (5), T u r n e r (8), and W i n g (9), on milk yield and fat test of morning and evening milk, have led to the conclusion that when the interval was even, there was a greater milk yield but a lower f a t test in the morning milk. Bailey (1) and Bartlett (2) showed a v e r y slight decline in solids-not-fat of morning herd milk over evening herd milk. Eekles and Shaw (3), reporting on the average production of five cows for 14 consecutive days, showed that the solids-not-fat content was higher in the evening milk for two Holsteins, but lower in the evening milk for one Ayrshire and two Jersey cows. Spreeht et al. (7) found no significant difference in the morning and evening milk f r o m 12 individual Jersey cows, milked regularly with an ] l l ~ - h r . night-time interval. However, they found a significant difference in favor of the morning milk yield. EXPERINIENTAL
PROCED~JI~E
Milk for this study was obtained from the University of Wyoming p u r e b r e d Holstein-Friesian herd. Samples were collected monthly f r o m individual cows during two consecutive milkings. Tile herd was milked regularly with a 12-hr. interval between morning and evening milking times. This interval would sometimes v a r y by 30 rain. Milk f r o m 40 cows was analyzed over.a period of three years, to discount effects of all factors except those being studied. The following determinations were made on milk samples f r o m individual cows: fat content Received for publication June 14, 1957. 1published with approval of the Director, Wyoming Agricultural Experiment Station, as Journal Paper No. 95. 1480
EFFECT
OF
I~IILKING
TIME
ON
SOLIDS
IN
51ILK
1481
by the Babcock method; total solids by the Dietert method (4), using the Dietert speed oven for d r y i n g the milk samples, and solids-not-fat by difference between total solids and fat. Data were tested statistically b y the analysis of variance teehniques as outlined by Snedecor (6). RESULTS AND DISCUSSION
F o r t y cows were tested for the following factors of milk production: milk yield, b u t t e r f a t yield, solids-not-fat yield, total solids yield, b u t t e r f a t percentage, solids-not-fat percentage, and total solids percentage. There was an average of 10.1 observations per cow. The mean yields per cow for each milking, morning and evening, are shown (Table I ) . Tile over-all milking-time means for yield also are included in the table. Mil~: yield. When the differences among cows for milk yield were tested according to the analysis of variance (6), cow differences were significant at the 1% level. The mean morning and evening milk yields were 18.56 and 16.47 lb., respectively: milking-time differences also were significant at the 1% level, with an " F " value of 23.57. No evidence was found for interaction between cows and milking time. The difference between morning and evening milkings is in agreement with previous reports (5, 7-9). With a slight difference in the intervals between milkings, an even greater difference in milk yield between milkings would be expected. W i n g (9) reported differences in milk yield even when the intervals between milkings were equal. Butterfat yield. Differences among cows for b u t t e r f a t yield were highly significant. Butterfat-yield milking-time means were 0.68 lb. for morning milk and 0.62 lb. for evening milk. Significant differences at the lc/c level were found between milkiug times, with an " F " value of 11.86. Evidence of an interaction between cows and milking time for b u t t e r f a t yield was not found. B u t t e r f a t yield followed closely the p a t t e r n found for milk yield. This should be expected, except that there have been reports of a higher b u t t e r f a t percentage in the evening's milk yield (9). A lower b u t t e r f a t percentage in tile morni n g ' s milk yield m i g h t tend to reduce differences in b u t t e r f a t yield, owing to the milk-yield differenees. However, tile reduced b u t t e r f a t percentage did not offset the differences in yield. S.N.F. yield. Tile yield of solids-not-fat was fomid to be highly significantly different among' cows. An " F " value of 17.85 was significant at the 1% level between milking times. Solids-not-fat yield means for morning and evening milk were 1.60 and 1.42 lb., respectively. Interaction between milking time and cows was not found. There have been very few reports concerning the solids-not-fat portion of individual cows in respect to morning and evening milkings. Although Eckles and Shaw (3) reported a higher solids-not-fat yield for two Holsteins, not one of the 40 cows in this study had a higher solids-not-fat yield for the evening milking (see Table 1).
W. S. NICHOLSON, JR. ET AL
1482
TABLE 1
Average y.ields of mil]~ components, by individual cows a~d time of mill:ing Cow No.
Months of observations
Milk Morning Evening
Butterfat Morning Evening
Solids-not-fat l~{orning E v e n i n g
T o t a l solids Morning Evening
(zb.) 1 2 3 4 5 6 7 8 9 I0 11 12 13 14 15
12 10 8 9 10 8 17 10 18 9 11 11 6 12 9
20.31 18.08 21.41 16.64 19.08 17.19 22.30 21.10 1,6.84 19.20 19.05 23.92 21.67 23.65 24.92
18.85 17.06 19.94 14.1~ 15.89 15.25 19.83 18.53 15.22 17.90 15.31 21.37 18.90 20.92 23.96
0.73 0.66 0.83 0.60 0.64 0.64 0.77 0.79 0.61 0.65 0.79 0,90 0.69 0.76 0.87
0.65 0.62 0.74 0.53 0.60 0.59 0.71 0.66 0.51 0.64 0.58 0.89 0.67 0.71 0.95
1.77 1.59 1.86 1.46 1.61 1.45 1.89 1.81 1.42 1.57 1.68 2.08 1.89 2.03 2.24
1.62 1.48 1.70 1,28 1.35 1.31 1.66 1.57 1.28 1.48 1.35 1.86 1.60 1.77 2.13
2.50 2.25 2.69 2.06 2.25 2.09 2.66 2.59 2.03 2.22 2.46 2.98 2.58 2.79 3.11
2.27 2.10 2.44 1.81 1.95 1.90 2.37 2.23 1.79 2.12 1.93 2.75 2.27 2.48 3.08
16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
10 3 11 10 12 13 10 9 8 8 9 9 10 9 10
23.35 13.03 20.29 16.47 13.98 16.85 20.11 17.20 14.11 20.46 16.73 19.61 14.06 17.41 21.72
20.36 10.13 17.20 15.43 13.61 14.51 17.80 14.79 12.54 17.14 14.97 16.78 11.71 15.06 20.25
0.81 0.55 0.78 0.72 0.56 0.59 0.69 0.67 0.53 0.77 0.58 0.68 0.46 0.61 0.92
0.68 0.45 0.63 0.61 0.57 0.63 0.60 0.61 0.50 0.67 0.54 0.61 0.44 0.54 0.91
2.02 1.15 1.79 1.53 1.20 1.33 1.63 1.49 1.10 1.79 1.43 1.75 1.09 1.45 1.92
1.72 0.92 1.49 1.39 1.17 1.15 1.44 1.25 1.10 1.52 1.28 1.50 0.98 1.36 1.75
2.83 1.70 2.56 2.25 1.77 1.92 2.32 2.17 1.73 2.55 2.01 2.43 1.55 2.06 2.84
2.39 1.37 2.12 2.00 1.73 1.78 2.04 1.86 1.60 2.19 1.82 2.11 1.42 1.90 2.66
31 32 33 34 35 36 37 38 39 40
11 11 12 12 8 9 9 12 12 8
15.75 16.70 14.92 23.78 9.69 20.11 15.73 17.25 14.64 15.14
15.25 13.89 13.35 20.62 8.81 18.27 14.01 15.32 13.14 12.38
0.65 0.63 0.68 0.73 0.38 0.75 0.53 0.57 0.59 0.58
0.68 0.50 0.58 0.73 0.34 0.63 0.51 0.54 0.54 0.46
1.40 1.41 1.34 1.99 0.91 1.77 1.35 1.48 1.22 1.34
1.37 1.20 1.23 1.70 0.82 1.57 1.19 1.32 1.10 1.10
2.05 2.04 2.03 2.73 1.29 2.52 1.88 2.05 1.81 1.91
2.05 1.70 1.81 2.43 1.16 2.20 1.70 1.87 1.63 1.55
10.1
18.56
16.47
0.68
0.62
1.60
1.42
2.28
2.03
Mean
Total solid.s yield. Cow differences in total solids yield were significant at the 1% level. The mean morning and evening total solids yields were 2.28 and 2.03 lb., respectively. The " F " value of 20.88 for milking time was significant at the 1% level. The interaction between cows and milking time was not significant. With higher yields of b u t t e r f a t and solids-not-fat in the morning milk yield, the yield in total solids must be greater in the morning milk. Thus., butterfat, solids-not-fat, and total solids yields have paralleled milk yield. Butterfat percentage. When tested by the analysis of variance (6), differences among cows for b u t t e r f a t percentage were found to be highly significant. The over-all milking-time butterfat-percentage weighted means were 3.66% for
EFFECT
OF
MILKING
TIME
ON
SOLIDS
IN
MILK
1483
morning milk and 3.76% for evening milk. The differences in b u t t e r f a t percentages for milking times were significant at the 5'% level, with an " F " value of 4.51. No evidence was found of an interaction between cows and milking time for b u t t e r f a t percentage. The results fo~md here f o r b u t t e r f a t percentage agree with those reported b y Wing (9). With the morning milk yield higher than the evening milk yield, the b u t t e r f a t percentage was less than in the evenfi)g milk yield. Solids-not-fat percentage. The differences between cows for solids-not-fat percentage were significant at the 1% level. An " F " value of 0.88 f o r milking times did not approach the 5% level of significance. The morning and evening solids-not-fat percentage averages were 8.60 and 8.59%, respectively. No evidence for an interaction between cows and nlilking time was found. F i n d i n g no difference in solids-not-fat percentage between morning and evening milk yields indicates a complete departure from the trends found in the other phases of this study. The differences in solids-not-fat yield that were f o u n d are then due to the differences found in milk yield alone.
Total solids perce~,tage. Total solids percentage paralleled b u t t e r f a t percentage clos:ely. Differences among cows for total solids percentage were highly significant. The means for total solids percentage were 12.'26 and 12.36%, for morning and evenirlg milking times, respectively. Milking-time differences were significant at the 5% level, having an " F " value of 4.00. As in all previous analysis in tills study, no interaction was found between cows and milking time. These differences in percentage of total solids are the result of the differences in b u t t e r f a t percentage. With a rise in b u t t e r f a t percentage and no change in solids-not-fat percentage in the evening milk yield compared to the morning milk yield, a paralleled rise in total solids, therefore, is obtained. This study f u r t h e r indicates the importance of milk yield as opposed to butterfat, solids-not-fat, and total solids percentages, increased percentage of the solid components of Holstein-Friesian cows' milk with a decreased milk yield does not balance the effect of decreased yield. Actual yield of the solid components of milk depends p r i m a r i l y upon the quantity of milk yield, as indicated in this study. A p p a r e n t l y , there are no cow differences in this respect, since all phases of interaction between cows and s:olid components were not significant. F i n d i n g highly significant differences among cows for each milk-solid component indicates that, f u r t h e r study of the components is required on an indidividual basis. Although the differences between milkings and the interaction between cows and milkings were not significant ~%r solids-not-fat percentage, the differences among cows need f u r t h e r investigation. These differences among cows m a y be due to differences in milk yield, or any of the solid components. Heredi t a r y influences should be considered, also. SUMS[ARY
AND CONCLUSIONS
This study was conducted for the purpose of determining variations of the solid-milk components, between morning and evening milk of individual cows.
W. S. NICHOLSON,
1484
gI%. ET
AL
F o r t y p u r e b r e d H o l s t e i n - F r i e s i a n cows were s a m p l e d m o n t h l y , d u r i n g two consecutive milkings, over a p e r i o d of three years. Milk samples were a n a l y z e d for fat, solids-not-fat, a n d t o t a l solids. S i g n i f i c a n t differences a m o n g cows were o b t a i n e d for p o u n d s of milk, fat, solids-not-fat, a n d total solids, a n d p e r c e n t a g e of fat, solids-not-fat, a n d total solids. A s i g n i f i c a n t l y l a r g e r q u a n t i t y of m i l k was p r o d u c e d at the m o r n i n g m i l k i n g . No s i g n i f i c a n t difference i n p e r c e n t a g e of solids-not-fat b e t w e e n m o r n i n g a n d e v e n i n g m i l k was f o u n d . S i g n i f i c a n t differences b e t w e e n m o r n i n g a n d e v e n i n g milk were o b t a i n e d for p o u n d s of fat, solids-not-fat, a n d total solids, a n d p e r c e n t a g e of f a t a n d total solids. No evidence of i n t e r a c t i o n b e t w e e n cows a n d m i l k i n g time was f o u n d i n a n y p a r t of this study. ACKNOWLEDGMENT The authors wish to express their appreciation to E. C. Bryant, Head, Statistics Department, for aid in the statistical analysis of the data. REFERENCES
(I) BAILEY,
G. L. Variations 893. 1952.
in the Solids-not-fat
Fractions
of Milk. Dairy Sei. Abstr., 14:
(2) BAI~TL~T'r,S. Yariations in tile Solids-not-fat Content of Milk. J. Dairy t~esearch, 5: 113. 1934. (3) ECKLES, C. H., A.N3)SHAW, R. H. The Influence of Breed and Individuality on the Composition and Properties of Milk. USDA, Bur. Animal Industry. Bull. 157. 1913. (4) I.I]~EII), B. O. Testing ~viilk and Milk Products for Fat and Total Solids. Univ. of Illinois, Circ. $30: 61. 1948. (5) PETZRSO~,W. E. Dairy Seie~we. 2nd ed. p. 340. J. B. Lippincott Co., Chicago, Illinois. 1950. (6) SI¢~]~e~)g,GF~RGEW. Statistical MetItods. 5th ed., Iowa State College Press, Ames. 1956. (7) St)~HT, L. W., B ~ N ~ , J. 1~., M.~I)])~,~, D. E., ANI) RALSTON, N. P. The Influence of Several Factors on the Protein and Solids-not-fat Content in the Milk of Jersey Cows. J. Dairy Sci., 39: 1337. 1956. (8) TuRx~a, C. W, Factors Affecting the Composition of Milk. Missouri Agr. Expt. Sta., Bull. 365. 1936. (9) WI.~-G, H. H. Mil]~ and Its Prod twts. p. 28. Macmillan Publ. Co., New York. 1913.
OF M I L K I N G T I M E ON S O L I D S I N MILK FROM HOLSTEINS ~
W. S. NICHOLSON, JR., H. S. WILLARD, W. R. THOMAS, AN]) D. C. BROWN
Dairy Depavtment~ U~dversity of Wyoming, Laramie Variations in the solids between mornings' and evenings' milk of 40 Holsteins were studied for two consecutive miikings during three years. There were significant differences among cows for pounds of milk, fat, solids-not-fat and total solids and for their percentages in milk. Significantly more milk was produced in the morning and there were significant differences in the amount of solids in mornings' and evenings' milk. Editor.
I n recent years, the dairy industry has placed increasing emphasis on the nonfat solids portion of milk, and attention has been focused on the scarcity of comprehensive data illustrating the characteristics of solids in milk. This study was conducted for the purpose of determining variations of the solid-milk components, between the morning and evening milk of individual cows. Whether milk f r o m an individual cow is sampled during" the morning or evening milking m a y have an effect on its solids content. Citations of Peterson (5), T u r n e r (8), and W i n g (9), on milk yield and fat test of morning and evening milk, have led to the conclusion that when the interval was even, there was a greater milk yield but a lower f a t test in the morning milk. Bailey (1) and Bartlett (2) showed a v e r y slight decline in solids-not-fat of morning herd milk over evening herd milk. Eekles and Shaw (3), reporting on the average production of five cows for 14 consecutive days, showed that the solids-not-fat content was higher in the evening milk for two Holsteins, but lower in the evening milk for one Ayrshire and two Jersey cows. Spreeht et al. (7) found no significant difference in the morning and evening milk f r o m 12 individual Jersey cows, milked regularly with an ] l l ~ - h r . night-time interval. However, they found a significant difference in favor of the morning milk yield. EXPERINIENTAL
PROCED~JI~E
Milk for this study was obtained from the University of Wyoming p u r e b r e d Holstein-Friesian herd. Samples were collected monthly f r o m individual cows during two consecutive milkings. Tile herd was milked regularly with a 12-hr. interval between morning and evening milking times. This interval would sometimes v a r y by 30 rain. Milk f r o m 40 cows was analyzed over.a period of three years, to discount effects of all factors except those being studied. The following determinations were made on milk samples f r o m individual cows: fat content Received for publication June 14, 1957. 1published with approval of the Director, Wyoming Agricultural Experiment Station, as Journal Paper No. 95. 1480
EFFECT
OF
I~IILKING
TIME
ON
SOLIDS
IN
51ILK
1481
by the Babcock method; total solids by the Dietert method (4), using the Dietert speed oven for d r y i n g the milk samples, and solids-not-fat by difference between total solids and fat. Data were tested statistically b y the analysis of variance teehniques as outlined by Snedecor (6). RESULTS AND DISCUSSION
F o r t y cows were tested for the following factors of milk production: milk yield, b u t t e r f a t yield, solids-not-fat yield, total solids yield, b u t t e r f a t percentage, solids-not-fat percentage, and total solids percentage. There was an average of 10.1 observations per cow. The mean yields per cow for each milking, morning and evening, are shown (Table I ) . Tile over-all milking-time means for yield also are included in the table. Mil~: yield. When the differences among cows for milk yield were tested according to the analysis of variance (6), cow differences were significant at the 1% level. The mean morning and evening milk yields were 18.56 and 16.47 lb., respectively: milking-time differences also were significant at the 1% level, with an " F " value of 23.57. No evidence was found for interaction between cows and milking time. The difference between morning and evening milkings is in agreement with previous reports (5, 7-9). With a slight difference in the intervals between milkings, an even greater difference in milk yield between milkings would be expected. W i n g (9) reported differences in milk yield even when the intervals between milkings were equal. Butterfat yield. Differences among cows for b u t t e r f a t yield were highly significant. Butterfat-yield milking-time means were 0.68 lb. for morning milk and 0.62 lb. for evening milk. Significant differences at the lc/c level were found between milkiug times, with an " F " value of 11.86. Evidence of an interaction between cows and milking time for b u t t e r f a t yield was not found. B u t t e r f a t yield followed closely the p a t t e r n found for milk yield. This should be expected, except that there have been reports of a higher b u t t e r f a t percentage in the evening's milk yield (9). A lower b u t t e r f a t percentage in tile morni n g ' s milk yield m i g h t tend to reduce differences in b u t t e r f a t yield, owing to the milk-yield differenees. However, tile reduced b u t t e r f a t percentage did not offset the differences in yield. S.N.F. yield. Tile yield of solids-not-fat was fomid to be highly significantly different among' cows. An " F " value of 17.85 was significant at the 1% level between milking times. Solids-not-fat yield means for morning and evening milk were 1.60 and 1.42 lb., respectively. Interaction between milking time and cows was not found. There have been very few reports concerning the solids-not-fat portion of individual cows in respect to morning and evening milkings. Although Eckles and Shaw (3) reported a higher solids-not-fat yield for two Holsteins, not one of the 40 cows in this study had a higher solids-not-fat yield for the evening milking (see Table 1).
W. S. NICHOLSON, JR. ET AL
1482
TABLE 1
Average y.ields of mil]~ components, by individual cows a~d time of mill:ing Cow No.
Months of observations
Milk Morning Evening
Butterfat Morning Evening
Solids-not-fat l~{orning E v e n i n g
T o t a l solids Morning Evening
(zb.) 1 2 3 4 5 6 7 8 9 I0 11 12 13 14 15
12 10 8 9 10 8 17 10 18 9 11 11 6 12 9
20.31 18.08 21.41 16.64 19.08 17.19 22.30 21.10 1,6.84 19.20 19.05 23.92 21.67 23.65 24.92
18.85 17.06 19.94 14.1~ 15.89 15.25 19.83 18.53 15.22 17.90 15.31 21.37 18.90 20.92 23.96
0.73 0.66 0.83 0.60 0.64 0.64 0.77 0.79 0.61 0.65 0.79 0,90 0.69 0.76 0.87
0.65 0.62 0.74 0.53 0.60 0.59 0.71 0.66 0.51 0.64 0.58 0.89 0.67 0.71 0.95
1.77 1.59 1.86 1.46 1.61 1.45 1.89 1.81 1.42 1.57 1.68 2.08 1.89 2.03 2.24
1.62 1.48 1.70 1,28 1.35 1.31 1.66 1.57 1.28 1.48 1.35 1.86 1.60 1.77 2.13
2.50 2.25 2.69 2.06 2.25 2.09 2.66 2.59 2.03 2.22 2.46 2.98 2.58 2.79 3.11
2.27 2.10 2.44 1.81 1.95 1.90 2.37 2.23 1.79 2.12 1.93 2.75 2.27 2.48 3.08
16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
10 3 11 10 12 13 10 9 8 8 9 9 10 9 10
23.35 13.03 20.29 16.47 13.98 16.85 20.11 17.20 14.11 20.46 16.73 19.61 14.06 17.41 21.72
20.36 10.13 17.20 15.43 13.61 14.51 17.80 14.79 12.54 17.14 14.97 16.78 11.71 15.06 20.25
0.81 0.55 0.78 0.72 0.56 0.59 0.69 0.67 0.53 0.77 0.58 0.68 0.46 0.61 0.92
0.68 0.45 0.63 0.61 0.57 0.63 0.60 0.61 0.50 0.67 0.54 0.61 0.44 0.54 0.91
2.02 1.15 1.79 1.53 1.20 1.33 1.63 1.49 1.10 1.79 1.43 1.75 1.09 1.45 1.92
1.72 0.92 1.49 1.39 1.17 1.15 1.44 1.25 1.10 1.52 1.28 1.50 0.98 1.36 1.75
2.83 1.70 2.56 2.25 1.77 1.92 2.32 2.17 1.73 2.55 2.01 2.43 1.55 2.06 2.84
2.39 1.37 2.12 2.00 1.73 1.78 2.04 1.86 1.60 2.19 1.82 2.11 1.42 1.90 2.66
31 32 33 34 35 36 37 38 39 40
11 11 12 12 8 9 9 12 12 8
15.75 16.70 14.92 23.78 9.69 20.11 15.73 17.25 14.64 15.14
15.25 13.89 13.35 20.62 8.81 18.27 14.01 15.32 13.14 12.38
0.65 0.63 0.68 0.73 0.38 0.75 0.53 0.57 0.59 0.58
0.68 0.50 0.58 0.73 0.34 0.63 0.51 0.54 0.54 0.46
1.40 1.41 1.34 1.99 0.91 1.77 1.35 1.48 1.22 1.34
1.37 1.20 1.23 1.70 0.82 1.57 1.19 1.32 1.10 1.10
2.05 2.04 2.03 2.73 1.29 2.52 1.88 2.05 1.81 1.91
2.05 1.70 1.81 2.43 1.16 2.20 1.70 1.87 1.63 1.55
10.1
18.56
16.47
0.68
0.62
1.60
1.42
2.28
2.03
Mean
Total solid.s yield. Cow differences in total solids yield were significant at the 1% level. The mean morning and evening total solids yields were 2.28 and 2.03 lb., respectively. The " F " value of 20.88 for milking time was significant at the 1% level. The interaction between cows and milking time was not significant. With higher yields of b u t t e r f a t and solids-not-fat in the morning milk yield, the yield in total solids must be greater in the morning milk. Thus., butterfat, solids-not-fat, and total solids yields have paralleled milk yield. Butterfat percentage. When tested by the analysis of variance (6), differences among cows for b u t t e r f a t percentage were found to be highly significant. The over-all milking-time butterfat-percentage weighted means were 3.66% for
EFFECT
OF
MILKING
TIME
ON
SOLIDS
IN
MILK
1483
morning milk and 3.76% for evening milk. The differences in b u t t e r f a t percentages for milking times were significant at the 5'% level, with an " F " value of 4.51. No evidence was found of an interaction between cows and milking time for b u t t e r f a t percentage. The results fo~md here f o r b u t t e r f a t percentage agree with those reported b y Wing (9). With the morning milk yield higher than the evening milk yield, the b u t t e r f a t percentage was less than in the evenfi)g milk yield. Solids-not-fat percentage. The differences between cows for solids-not-fat percentage were significant at the 1% level. An " F " value of 0.88 f o r milking times did not approach the 5% level of significance. The morning and evening solids-not-fat percentage averages were 8.60 and 8.59%, respectively. No evidence for an interaction between cows and nlilking time was found. F i n d i n g no difference in solids-not-fat percentage between morning and evening milk yields indicates a complete departure from the trends found in the other phases of this study. The differences in solids-not-fat yield that were f o u n d are then due to the differences found in milk yield alone.
Total solids perce~,tage. Total solids percentage paralleled b u t t e r f a t percentage clos:ely. Differences among cows for total solids percentage were highly significant. The means for total solids percentage were 12.'26 and 12.36%, for morning and evenirlg milking times, respectively. Milking-time differences were significant at the 5% level, having an " F " value of 4.00. As in all previous analysis in tills study, no interaction was found between cows and milking time. These differences in percentage of total solids are the result of the differences in b u t t e r f a t percentage. With a rise in b u t t e r f a t percentage and no change in solids-not-fat percentage in the evening milk yield compared to the morning milk yield, a paralleled rise in total solids, therefore, is obtained. This study f u r t h e r indicates the importance of milk yield as opposed to butterfat, solids-not-fat, and total solids percentages, increased percentage of the solid components of Holstein-Friesian cows' milk with a decreased milk yield does not balance the effect of decreased yield. Actual yield of the solid components of milk depends p r i m a r i l y upon the quantity of milk yield, as indicated in this study. A p p a r e n t l y , there are no cow differences in this respect, since all phases of interaction between cows and s:olid components were not significant. F i n d i n g highly significant differences among cows for each milk-solid component indicates that, f u r t h e r study of the components is required on an indidividual basis. Although the differences between milkings and the interaction between cows and milkings were not significant ~%r solids-not-fat percentage, the differences among cows need f u r t h e r investigation. These differences among cows m a y be due to differences in milk yield, or any of the solid components. Heredi t a r y influences should be considered, also. SUMS[ARY
AND CONCLUSIONS
This study was conducted for the purpose of determining variations of the solid-milk components, between morning and evening milk of individual cows.
W. S. NICHOLSON,
1484
gI%. ET
AL
F o r t y p u r e b r e d H o l s t e i n - F r i e s i a n cows were s a m p l e d m o n t h l y , d u r i n g two consecutive milkings, over a p e r i o d of three years. Milk samples were a n a l y z e d for fat, solids-not-fat, a n d t o t a l solids. S i g n i f i c a n t differences a m o n g cows were o b t a i n e d for p o u n d s of milk, fat, solids-not-fat, a n d total solids, a n d p e r c e n t a g e of fat, solids-not-fat, a n d total solids. A s i g n i f i c a n t l y l a r g e r q u a n t i t y of m i l k was p r o d u c e d at the m o r n i n g m i l k i n g . No s i g n i f i c a n t difference i n p e r c e n t a g e of solids-not-fat b e t w e e n m o r n i n g a n d e v e n i n g m i l k was f o u n d . S i g n i f i c a n t differences b e t w e e n m o r n i n g a n d e v e n i n g milk were o b t a i n e d for p o u n d s of fat, solids-not-fat, a n d total solids, a n d p e r c e n t a g e of f a t a n d total solids. No evidence of i n t e r a c t i o n b e t w e e n cows a n d m i l k i n g time was f o u n d i n a n y p a r t of this study. ACKNOWLEDGMENT The authors wish to express their appreciation to E. C. Bryant, Head, Statistics Department, for aid in the statistical analysis of the data. REFERENCES
(I) BAILEY,
G. L. Variations 893. 1952.
in the Solids-not-fat
Fractions
of Milk. Dairy Sei. Abstr., 14:
(2) BAI~TL~T'r,S. Yariations in tile Solids-not-fat Content of Milk. J. Dairy t~esearch, 5: 113. 1934. (3) ECKLES, C. H., A.N3)SHAW, R. H. The Influence of Breed and Individuality on the Composition and Properties of Milk. USDA, Bur. Animal Industry. Bull. 157. 1913. (4) I.I]~EII), B. O. Testing ~viilk and Milk Products for Fat and Total Solids. Univ. of Illinois, Circ. $30: 61. 1948. (5) PETZRSO~,W. E. Dairy Seie~we. 2nd ed. p. 340. J. B. Lippincott Co., Chicago, Illinois. 1950. (6) SI¢~]~e~)g,GF~RGEW. Statistical MetItods. 5th ed., Iowa State College Press, Ames. 1956. (7) St)~HT, L. W., B ~ N ~ , J. 1~., M.~I)])~,~, D. E., ANI) RALSTON, N. P. The Influence of Several Factors on the Protein and Solids-not-fat Content in the Milk of Jersey Cows. J. Dairy Sci., 39: 1337. 1956. (8) TuRx~a, C. W, Factors Affecting the Composition of Milk. Missouri Agr. Expt. Sta., Bull. 365. 1936. (9) WI.~-G, H. H. Mil]~ and Its Prod twts. p. 28. Macmillan Publ. Co., New York. 1913.