EFFECT
OF UNEQUAL MIL~ING
INTERVALS
ON L A C T A T I O N M I L K ,
MILK FAT, AND TOTAL SOLIDS PRODUCTION
OF COWS
G. 1=[. SCttMIDT AND G. W. TRIMBERGER Department of Animal Husbandry, Cornell University, Ithaca, New York SUmmARY
Cows of three breeds were milked at 12- and 12-hr, 14- and 10-hr, and 16and 8-hr daily intervals for complete lactations~ to deternfine the effect of milking intervals on the milk, milk fat, and total solids production. Thirty-five trios were used over a 2-yr period in the experiment. The mature equivalent milk records of cows milked at 14- and 10-hr intervals were 0.3% lower, and those of cows milked at 16- and 8-hr intervals were 1.3% lower, than the records of cows milked at equal intervals. The mature equivalent milk production records of all cows averaged over 13,500 lb milk. No significant differences occurred between any two groups in the milk fat and total solids percentages or yields. There was some indication that the 16- and 8-hr intervals had a greater adverse effect on higher-producing cows in comparison to lower-producing cows, and on first-calf heifers in comparison to older cows; however, the evidence was not conclusive. Unequal intervals had no effect on udder health or the incidence of ketosis.
The object of this experiment was to determine the effect of unequal milking intervals on the production of milk, milk fat, and total solids by high-producing cows during complete lactations.
The milking of cows at equal intervals has been advocated for a long time because of the observations that the milk secretion rate during a long milking interval is lower than that during a short milking interval. This has resulted in long working days for the dairy farmer. Experiments at Minnesota (2) and in New Zealand (5) and Australia (7) indicated that unequal daily intervals of 14 and 10 hr and 16 and 8 hr did not cause a decrease in milk production in comparison with equal intervals. The production of these cows was relatively low in comparison with the average production of the higher-producing cows in the United States. Hansson et al. (1) found that cows milked at 15- and 9-hr intervals and 16- and 8-hr intervals produced slightly less milk than those milked at 12- and 12-hr intervals, ttighproducin~ cows were not more adversely affected than the lower-producing cows. Linnerud et al. (4) also found that cows milked at 16- and 8-hr intervals produced slightly less milk than those milked at equal intervals. I n a previous report from this laboratory (6)~ it was found that the milk secretion rate declined at a 16-hr interval, but the reduction in secretion rate was slight in cmnparison to 8and 12-hr intervals. The secretion rate of highproducing cows was affected less by the long intervals than was that of the lower-producing
EXPERIMENTAL PROCEDURE
One hundred seventeen cows of the Ayrshire, Brown Swiss, and Holstein breeds from the Cornell University dairy herd were divided into 39 trios. Before calving, the cows were assigned to trios according to lactation number, breed, season of calving, and previous production. First-calf heifers were assigned to trios according to breed and season of calving and no attempt was made to predict their producing ability from their pedigrees. The memb e ~ of each trio were assigned at random to one of the three milking intervals. Cows on the 12- and 12-hr daily intervals were milked at 5 ~ and 5 P~; those on the 14- and 10-hr intervals were milked at 6 A~ and 4 P~; and those on the 16- and 8-hr intervals were milked at 7 A~ and 3 P~. Two years were required to complete the experiment. Twenty-three trios were used during the first year, starting with the fall freshening period of 1959, and 16 trios were used the second year. The cows were fed hay and silage ad libitum and grain according to milk production. Dally milk weights were recorded and separate night and morning milk samples were taken biweekly for milk fat and total solids determinations. The milk fat was analyzed by the Babcock method and the total solids were
COWS.
Received for publication September 13, 1962. 19
G. H. SCHMIDT AND G. W. TRIMBERGER
20
TABLE 1 Effect of milking intervals on mature equivalent milk, milk fat, and to~al solids production of cows for complete lactation periods Daily intervals
(hr) 12-12 14-10 16- 8
No. trios 35 35 35
Milk
Milk fat
(lb )
(%)
13,760 13,716 13,582
3.78 3.91 3.86
determined with the Watson lactometer (8) and the milk f a t test. The average daily milk fat and total solids tests were calculated by weighting the separate samples according to the milk yields. The mature equivalent milk production was calculated using the New York State age-correction factors. Two cows died during the experiment and two had to be sold because of severe mastitis. These records were extended by the conversion factors of Lamb and McGilliard (3). All records used in the analysis were terminated as 305-day lactation records. F o u r first-calf heifer trios were eliminated from the analysis because one member in each trio produced at least 4,000 lb less milk than either one of her trio mates. This low production apparently was due to inheritance and was not a treatment effeet. Data on 35 trios are included in the analysis. RESULTS AI~D DISCUSSION
The mature equivalent lactation records are given in Table 1. The M.E. milk production of cows milked at 14- and 10-hr intervals was about the same as that of cows milked at 12and 12-hr intervals; however, the milk fat percentage was slightly higher. These differences were not significantly different (P > 0.05). The M.E. milk records of cows milked
Total solids
(lb ) 520 536 524
(%) 12.41 12.~6 12.40
(lb ) 1,707 1,709 1,684
at 16- and 8-hr intervals averaged 178 lb less milk, but the milk f a t yield was slightly higher than the records of cows milked at equal intervals. The differences among treatments in milk yield and milk f at percentages are not significantly different (P > 0.05). The differences due to trios in the analysis of variance were significant at the 1% level of probability. The standard deviation of the M.E. milk records was 1,689 lb and the coefficient of variation was 12.3%. No significant differences (P > 0.05) in total solids percentage or yield resulted between any two of the three groups. The average percentage decreases in milk production for the 14~ and 10-hr and 16- and 8-hr intervals were 0.3 and 1.3%, respectively, compared to the cows milked at equal intervals. The reduction at 16- and 8-hr intervals was somewhat lower than the 4.1% predicted in a previous paper (6). Hansson (1) found that cows milked at 16- and 8-hr intervals produced 3.1% less milk than those at 12- and 12-hr intervals. The percentage of the total milk production that was obtained at the morning milking was 52.2 for the 12- and 12-hr intervals, 57.2 for the 14- and 10-hr intervals, and 61.7 f o r the 16- and 8-hr intervals. The 16-hr interval represents 67% of the total time in the day, whereas only 61.7% of the milk was obtained
TABLE 2 l~ature equivalent lactation milk yields of cows grouped according to the highest~production record in each trio Percentage reduction from 1~-12 hr intervals
Milk yields (lb) Production of highest member
Intervals (hr)
Intervals (hr)
No. trios
12-12
14-10
16- 8
14-10
21 8 2 4
15,402 13,153 9,677 8,394
15,227 12,874 11,156 8,745
14,733 12,999 11,877 9,554
1.1 2.1 +15.3 + 4.2
16- 8
(lb) 15,000 13,000-14,999 11,000-12,999 11,000
4.3 1.2 +2'2.7 +13.8
21
EFFECT OF UNEQUAL MILKINGS ON PRODUCTION
TABLE Mature equivalent lactation nfilk yields from Holstein first-calf heifers and older cows
Age of cows in trios First-calf heifers Older cows
Milk yield (lb)
Percentage reduction from 12-12-hr intervals
Intervals (hr)
Intervals (hr)
No. trios
12-12
14-10
16- 8
14-10
16- 8
7 19
14.,954 15,027
15,2~1
13,926 14,457
+1.9 2.7
6.9 3.8
14,615
a f t e r this interval. This led some of the earlier workers to conclude that the milk secretion rate was decreased during a long interval between milkings. However, these workers failed to account f o r the greater amount of residual milk left in the udder a f t e r a longer interval. I n a previous r e p o r t (6) it was r e p o r t e d that the milk-secretion rate of higher-producing cows was affected less by the longer intervals than was that of the lower-producing cows. To determine whether this is true, the trios were grouped according to the production record of the highest-producing member of each trio (Table 2). I t will be noted that the cows producing over 15,000 lb milk had slightly higher reductions in M.E. milk production at the 16- and 8-hr intervals t h a n the 13,00014,999 lb group. However, the number o f trios in the last three groups is so limited and the variations are so g r e a t that the differences between any two means in the table are not significant ( P > 0.05). All of the trios producing over 15,000 lb milk were Holsteins; therefore, the Holstein trios were divided into first-calf heifer and older cow trios. I n Table 3 it will be noted that the 16- and 8-hr intervals caused a greater d r o p in milk production of the first-calf heifers than of older cows; however~ the difference was not significant ( P > 0.05). The n u m b e r of trios in the other breeds was too small to analyze the differences between age groups.
Twenty-one o f the cows were on different intervals during the second year. This is shown in Table 4. I t will be noted that the milk p r o duction f o r the cows varied somewhat, b u t there was no significant trend f o r lower production at the unequal intervals. F r o m these results it is impossible to conclude that unequal intervals have a different effect on highand low-producing cows. The unequal intervals had no adverse effects on the health o~ the cows. The number of cows with clinical mastitis was 20, 24, and 20, and with ketosis 7, 5, and 6 f o r the 1 2 - a n d 12-hr, 14- and 10-hr, and 16- and 8-hr intervals, respectively.
TABLE 4 Mature equivalent lactation milk and milk fat yields of cows milked aV two different intervals during the 2-yr experiment
(5)
No. cows
Intervals
Milk
(hr)
(lb)
(lb)
4
12-12 14-10
14,158 14,265
522 548
7
12-12 16- 8
13,626 14,612
483 542
1O
14-10 16- 8
13,890 13,214
552 506
REFERENCES
(1) HXNSSON, A., C ~ z s s o ~ , O., Br:dNN~Ne, E., AN-I) GUSTAFSSO17, N. Studies on Monozygous Cattle Twins. XVL Milking Intervals in Relation to Yield of Milk and Milk Constituents. Aeta Agr. Seand., 8 : 296. 1958. (9.r) KOSHI, J . H., AND PEI~E~SE~, W . E.
(3)
(4~)
(6)
Milk fat (7)
(8)
The
Effect of the Length of Intervals Between Milking on the Milk and Butterfat Production. J. Dairy Sci., 37: 673. 1954. LAMB, R. C., ~ND McGIM,~rm, L. D. Variables Affecting Ratio Factors for Estimating 305-Day Production from Part Lactations. J. Dairy Sei., 43: 519. 1960. LIN1VE~UI~, A. C., WIZLL~MS, J. B., AND DOlVKI~, J. D. Eight to Sixteen vs. 12-12 Hour Milking Intervals. J. Dairy Sci, 4,5: 696. 1962. McMEEKAlV, C. P., AND BI~UMBY, P. J. Milk Production and Interval Between ~[ilking. Nature, 178: 799. 1956. SC~MID% G. tL Effect of Milking Intervals on the Rate of Milk and F a t Secretion. J. Dairy Sci., 43: 213. 1960. TURNF~, H. G. The Effect of Unequal Intervals Between Milkings upon Milk Production and Diurnal Variation in Milk Secretion. Australian J. Agr. Research, 6: 530. 1955. WATSON, P. D. Determination of the Solids in Milk by a Lactomctrie Method at 102°F. J. Dairy Sci., 40: 394. 1957.