SFLORIDA AGRICULTURAL EXPERIMENT STATION
Dairy Science Mimeo Report 63-3
September 1, 1962
Effect of season and year of freshening on milk production
C. J. Wilcoxl. and H. W. Young.
Large increases have been made in Florida recently in average milk
production. These increases have occurred partly as the result of the
genetic improvement of the dairy cow and partly because of the develop-
ment of better management techniques.
To continue this increase in milk production, it is necessary to
know the effect of various factors on milk yields. Better understanding
of the effects of these factors will aid the dairyman in developing
better management techniques and in selecting A.I. sires. The objectives
of this investigation were to measure and evaluate two of these factors,
year and season of freshening.
Climate affects milk production directly by affecting the physio-
logical functions of the cow and indirectly by influencing the quantity
and quality of the feed consumed. Johnston et al. (9) reviewed the
effects of southern climate on milk production and found that at an air
temperature of 950F. feed consumption and milk production may be only
50% of feed consumption and milk production at 600F. Increasing air
temperature also drastically increased body temperature and respiration
rate. High-producing cows suffered more under high temperature than
cows which were poor producers even under the best conditions. High
humidity and solar radiation were also found to have an adverse effect
on milk yield.
1. Assistant Dairy Husbandman.
2. Working under the auspices of the National Science Foundation Summer
Science Research Participation Program for Secondary Students.
Many investigators have studied milk yields of cows freshening in
different months or seasons of the year and results have been somewhat
variable. In 1923, Hammond and Sanders (7), with Shcorthorn records from
various regions of England, found that monthly milk production reached
a maximum in November and a minimum in February. They noted that
production was quite low during the summer months also. In the same
year, Turner (16) showed that milk production of cows from different
regions of the United States which freshened in the fall and winter
months was higher than that of comparable cows which freshened in the
summer. Sanders (14) in 1927 found that English cattle calving between
October and February produced more than those calving in June in Norfolk,
England, but in Penrith, England, the best time of year for calving was
between the months of August and November. The difference in optimum
calving period was attributed to climatic differences.
In 1933, Cannon (5) found that those cows which freshened in
November had the highest total yield and those which freshened in June,
the lowest total yield. Frick et al. (6) in 1947 found in Connecticut
that cows freshening in February had the highest total yield and those
which freshened in July had the lowest total yield. In Washington,
Annis et al. (1) in 1959 found a significant effect of season of calving
on milk yields. Reaves (13) in a study of 6142 DHIA lactation records
in Florida recently found that January was the best month for freshening
and that July, with an average production 1320 lb. less than January,
was the poorest month for freshening. Johnson and Touchberry (8)
reported in 1962 on DHIA records in Illinois and showed that Holsteins
calving in December, January, and February had the highest total milk
production and those calving in June, July and August had the lowest
total milk production.
On the other hand, Wylie (20) studied 2900 records from the American
Jersey Cattle Club of cows freshening in 1921 and found that cows freshen-
ing in certain months produced more milk than cows freshening in certain
other months, but that the difference was not significant. In a study
of 15,442 DHIA lactation records in 1945, Woodward (19) found no
significant difference in total milk yields of cows freshening in dif-
An early study of Arnold and Becker (3) covered 319 lactations of
Jersey cows in the Fla. Agr. Exp. Sta. herd during the years 1917-32.
Differences in milk yields among seasons were small, with only spring
(March through May) deviating much from the over-all mean. Spring
fresheners produced about 10% less than cows freshening in other seasons.
Changes in average yield from year to year result from changes in
environment (a gradual improvement in dairy cattle management over the
years), and changes in the genetic merit of the herd. The USDA (17)
reported an increase in average milk yield from 4508 lb. per cow in 1931
to 7004 lb. per cow in 1960 for the United States as a whole. In
Florida, the average milk yield has increased at a faster rate, from
2880 lb. per cow in 1931 to 6700 lb. in 1960.
METHODS AND RESULTS
The data used were from Jersey cows of the Fla. Agr. Exp. Sta. over
a period of 30 years (1931-60, inclusive). The herd was located on
campus at Gainesville until September 16, 1949, when it was moved to its
present location, the Dairy Research Unit at Hague.
All records were adjusted for age of cow at time of freshening,
using correction factors of Kendrick (10). In some cases, where cows
had short calving intervals and were dried off before the 305th day of
the lactation, the records were extended by factors of Lamb and McGilliard
(11). Otherwise the records represented milk production for the first
305 days. Since all records were from Jersey cattle in the same herd,
no adjustments were necessary for breed or herd differences. Data were
screened for acceptability using guides suggested for regional research
in the South (2). Some 1370 records were judged normal and included in
Several preliminary analyses were undertaken to determine the most
efficient method of grouping months into seasons, criteria being those of
Bereskin and Freeman (4). Standard analysis of variance techniques
were used, as demonstrated by Snedecor (15). The most efficient grouping
proved to be winter (December, January and February), spring (March,
April and May), summer (June, July and August), and autumn (September,
October and November).
Because of unequal numbers of records in the year-season subclasses,
data were adjusted for non-orthogonality by the method of Patterson
(12). Both season and year effects were significant (P < 0.01). Season-
year interactions were not significant. There were four year-season
subclasses in which there were no data, so the tests for significance
for the interaction were approximate.
The variations due to season (shown in Table 1) were quite similar
to those of Reaves (13). Year effects have been removed from the season
Table 1. Average milk production in different seasons
Season Records yield effect.
(no.) (lb.) (lb.)
Winter 413 7566 +363
Spring 251 7152 +409
Summer 252 6514 -547
Autumn 454 7082 -225
Over-all 1370 7136 --
Freed of year effects. Differences among seasons
significant (P < 0.01).
effects, giving the adjusted estimates. Spring and winter were highest
and nearly alike, suggesting the possibility of grouping them as one
season. Cows freshening in summer had the lowest average yield. U. S.
Weather Bureau records (18) for 1931-60 give an average maximum tempera-
ture of 89.50F. for the summer months. Johnston et al. (9) pointed out
that milk production decreased rapidly with increasing temperature after
the air temperature exceeds 850F.
Season-year interactions were surprisingly low. This indicated that
season effects were about the same from year to year. Unfortunately,
the effects of recent changes in management during hot weather could not
be evaluated because no cows freshened in the spring from 1958-60, and
very few in the summer. Vacant cells were accounted for in the analyses
by deleting degrees of freedom for interactions.
Milk production increased steadily during the years (Table 2), with
Table 2. Average milk production in different years.
Milk Year Milk Year
Year Records yield effect Year Records yield effect
(no.) (l) ( (Ib.) (no.) (lb.) (lb.)
1931 16 6469 -422 1946 59 7000 -59
1932 25 5415 -1635 1947 47 6758 -518
1933 23 5720 -1608 1940 36 7882 +767
1934 24 6312 -865 1949 61 7457 +313
1935 28 5800 -1341 1950 64 7436 +206
1936 31 5992 -1128 1951 62 7247 +181
1937 45 6023 -1061 1952 60 7190 -64
1938 47 6247 -728 1953 52 7352 +368
1939 58 6440 -667 1954 61 7966 +920
1940 51 5710 -1311 1955 73 8383 +1349
1941 39 6537 -590 1956 48 7801 +695
1942 24 5884 -1057 1957 64 7795 +620
1943 30 5233 -1895 1958 44 7798 +297
1944 22 6620 -664 1959 73 8021 +733
1945 27 6737 -272 1960 76 9070 +1839
Differences among years significant (P < 0.01).
i. Freed of season effects.
minor fluctuations. The best measu.'e of change in yield, freed of the
effects of season, is the estimates of year effects. The years contain
the months December through November, in that order, and are not strictly
An estimate of the variability among cows freshening in the same
year-season was obtained. The standard deviation was 1591 lb. About
2/3 of the cows would be included in the range of the year-season mean
plus and minus the standard deviation.
Some 1370 Jersey milk records from the Fla. Agr. Exp. Sta. were
analyzed. Season and year of freshening affected milk production
significantly (P < 0.01). Milk yield averaged 7136 lb., with a standard
deviation of 1591 lb.,during the years 1931-60. Spring and winter
months were the best months to freshen, and summer was poorest, with an
average yield about 1000 lb. less than spring. Yearly average yields
were found to have increased steadily to a high of about 9000 lb. in
1960. It was found most efficient to group months into four 3-month
seasons: winter (December, January, February), spring (March, April,
May), summer (June, July, August), and autumn (September, October,
November). No significant season-year interactions were found.
The authors wish to acknowledge the support of the National Science
Foundation. Milk production records during the period were collected
under the supervision of P. T. D. Arnold and R. B. Becker.
REVIEW OF LITERATURE
(1) ANNIS, D. J., ERB, R. E., and WINTERS, W. R. Influence of month
and season of calving on yields of milk and fat. Wash. Agr. Exp.
Sta. Bull. 606. 1959.
(2) ANONYMOUS' Guides to the collection of data for the regional project.
Mimeo Report, Regional Dairy Cattle Breeding Technical Committee for
the Southern States and Puerto Rico. January 1, 1961.
(3) ARNOLD, P. T. D. and BECKER, R. B. The effect of season of the year
and advancing lactation upon milk yield of Jersey cows. J. Dairy
Sci., 18:621. 1935.
(4) BERESKIN, B., and FREEMAN, A. E. Effect of month of calving in herds
at three levels of production. J. Dairy Sci., 44:1196. 1961.
(5) CANNON, C. Y. Seasonal effect on yield of dairy cows. J. Dairy
Sci., 16:11. 1933.
(6) FRICK, G. E., MANN, A. I., and JOHNSON, S. The relation of season
of freshening to milk production. J. Dairy Sci., 30:631. 1947.
(7) HAMMOND, J., and SANDERS, H. G. Some factors affecting milk yield.
J. Agr. Sci., 13:74. 1923.
(8) JOHNSON, R. V., and TOUCHBERRY, R. W. Influence of month of calving
on lactation milk yields. J. Dairy Sci., 45:678. 1962.
(9) JOHNSTON, J. E., McDOWELL, R. E., SHRODE, R. R., and LEGATES, J. E.
Summer climate and its effects on dairy cattle in the southern
region. Southern Cooperative Series, Bull. 63. 1959.
(10) KENDRICK, J. F. Standardizing Dairy Herd Improvement Association
records in proving sires. USDA Bull. ARS-52-1. 1955.
(11) LAMB, R. C., and McGILLIARD, L. D. Variables affecting ratio factors
for estimating 305-day production from past lactations. J. Dairy
Sci., 43:519. 1960.
(12) PATTZRSON, R. E. The use of adjusting factors in the analysis of
data with disproportionate subclass numbers. J. Am. Stat. Assn.,
(13) REAVES, C. W. Effect of month of freshening on yearly production of
Florida DHIA cows. DHI Newsletter, Fla. Agr. Exp. Sta. July 5, 1961.
(14) SANDERS, H. G. The variations in milk yields caused by season of the
year, service, age and dry period and their elimination. J. Agr.
Sci., 17:339. 1927.
(15) SNEDECOR, G. W. Statistical methods. Iowa State College Press,
(16) TURNER, C. W. Seasonal variations in milk and fat production.
J. Dairy Sci., 6:198. 1923.
(17) UNITED STATES DEPARTMENT OF AGRICULTURE. Dairy statistics through
1960. Economic Research Service, Statistical Bull. 303, Washington,
(18) UNITED STATES WEATHER BUREAU. Decennial census of United States
climate monthly normals of temperature, precipitation and heating
degree days, Florida. U.S. Govt. Printing Office, Washington,D.C. 1962.
(19) WOODWARD, T. E. Some studies of lactation records. J. Dairy Sci.,
(20) WYLIE, C. E. The effect of season on the milk and fat production
of dairy cows. J. Dairy Sci., 8:127. 1925.