Department of Animal Scienc le [ i I I') ,V Florida Agricultural
Research Report No. AL-175--1 ft Experiment Station
February, 1975 Gainesville, Florida
A DISCUSSION OF GROWTH CURVES OF
ANGUS, BRAHMAN, HEREFORD AND SANTA GERTRUDIS COWS
[.F .S. Univ. of i-oiK 1
:. E.F-ranke and W."C. Burns
Body weights of beef cattle at birth, weaning, yearling, 24 months and other
ages and rates of gain between certain ages or over specified time periods have
been studied by numerous researchers (1, 2, 4, 7, 11). Many of these studies
were concerned with genetic and environmental influences affecting specific weights
or rates of gain prior to maturity. Characteristics such as rate and degree of
maturity or mature size cannot be measured on immature animals, yet they are im-
portant in understanding lifetime growth of individuals (3). The use of immature
and mature weights to characterize growth curves of individuals and study of the
association of growth curve parameters to individual body weights and other fac-
tors aids in evaluating aspects of animal growth. The objective of this report
is to present growth curves of Angus, Brahman, Hereford and Santa Gertrudis cows
and to discuss the factors which influence and are associated with them.
Materials and Methods
Quarterly weight data collected at the Brooksville Beef Cattle Research Sta-
tion from 1953 to 1973 were made available to study growth curves of 184 Angus,
96 Brahman, 181 Hereford and 62 Santa Gertrudis cows. Cows included in the study
were at least four years of age, having at least 4 years of quarterly weight data.
Quarterly weights were taken in March-immediately after calving season, June,
August-at weaning of all calves and December.
The Brody Model,
Yt = A Bekt (1)
was fitted to each set of cow weight data. In the Brody Model, Yt is the pre-
dicted weight at age t, A is an estimate of mature weight, B is an estimate re-
lated to growth to be made after birth and k is an estimate of earliness of ma-
turing. Therefore, estimates of A, B and k were computed for each female.
Associate Professor (Associate Geneticist), Animal Science Department, Univer-
sity of Florida, Gainesville 32611, and Location Leader, USDA Beef Cattle Re-
search Station, Brooksville 33512.
This public document was promulgated at an annual cost of
$ 195.59 or .13 cents per copy to inform county agricul-
ture directors, ranchers and growers of research results
in cattle growth.
Department of Animal-Science
Institute of Food and Agricultural Sciences
Management practices at the Brooksville location were similar for all cows.
Heifer calves at weaning were placed on pasture with supplemental feed to ensure
normal growth, but not fattening, to approximately 20 months of age. At this
time they were evaluated on weight per day of age, body soundness and condition.
From 10 to 25% of the 20-month-old heifers in any given year were culled for low
weight per day of age, unsoundness or poor quality. All heifers saved for re-
placements were bred to calve first at three years of age. Cows and replacement
heifers which did not become pregnant during the breeding season were culled in
the fall of each year. The breeding season ranged from approximately 90 days
in early years to 65 days in more recent years and occurred such that calves
were dropped in December, January and February. Some cows which lost calves
during the nursing period were culled if they were pregnant when palpated during
most of the preweaning period. The effect of not lactating during most of the
preweaning period on cow weight change is not known.
Least squares statistical procedures were utilized to obtain best estimates
of A, B and k for each breed and to determine the influences of year of cow birth,
dam of cow age and sire of cow on the growth curve parameters and birth, 7 month
weaning, 24 month and 48 month weight. Paternal half-sib components of variance
and covariance, pooled across breeds, were used to estimate heritabilities of and
genetic correlations between growth curve parameters and weights.
Results and Discussion
Best estimates of A, B and k for the four breeds are given in table 1. These
data showed that at maturity, Hereford cows were heaviest, weighing 1081 pounds,
Santa Gertrudis cows were next heaviest, weighing 1003 pounds and Brahman and
Angus cows weighed the least at maturity, 952 and 904 pounds, respectively. Growth
curves predicted from best estimates of A, B and k for the four breeds of cows are
shown in figure 1. Also shown in figure 1 is the fact that Santa Gertrudis cows
grew at a faster rate than cows of the other three breeds. The k values in table 1
define rate of maturity, that is how fast an animal approached its mature weight.
The higher k value for Santa Gertrudis females indicates that they were reaching
maturity earlier than the other breeds, with Angus and Brahman fei, '- approaching
maturity at similar rates and the Hereford approaching maturity at tne slowest
rate, as indicated by the lowest k value. Brown et al. (5), reported in an Arkansas
study that Hereford cows were heavier at maturity than Angus cows (1056 vs. 972
pounds) but reached maturity at a slower rate than Angus cows (0.0437 vs. 0.0566
for k values). Carpenter and Fitzhugh (8) in Texas reported that Hereford cows
weighed about the same at maturity (1150 pounds) as Brahman x Hereford crossbred
cows but reached the mature weight at a much slower rate. Joandet (10) also re-
ported that Hereford cows reached maturity at a slower rate than various types of
Brahman x Hereford crossbred cows.
Use of growth curve models to estimate weights of individuals allows evalua-
tion of weights at ages when actual weights may not have been taken. Predicted
weights for the four breeds of females at 4, 8, 12, 16, 20, 24, 36 and 48 months
of age are shown in table 2. These weights indicate that Angus females were
smaller at all ages than females in the other breeds. Hereford females were the
next smallest up to 16 months of age where they were similar to Brahman heifers.
After 16 months, Brahman females were smaller than Hereford and Santa Gertrudis
females. Santa Gertrudis females were heavier at all ages up to 48 months, when
Hereford females became heavier. Brown et al. (6) reported that Angus females
were heavier than Hereford females up to 36 months of age, at which time Hereforn
females became heavier and remained heavier through maturity.
Estimates of degree of maturity of the four breeds of females at various
ages are shown in table 3. Degree of maturity defines the percentage of mature
weight that an animal reaches at various ages and is obtained by dividing some
specified premature weight by mature weight and multiplying by 100. Degree of
maturity is related to rate of maturing. Cows which have reached a greater per-
centage of their mature weight at certain ages than other cows have higher rates
Degree of maturity percentages in table 3 indicate Santa Gertrudis females
reached a greater percentage of their mature weight earlier and at each age than
any other breed of cow. Hereford females, on the other hand, reached the same
percentage mature weight at older ages than the other breeds. Angus and Brahman
females had similar degrees of maturity at all ages. At 48 months of age, Santa
Gertrudis females were 97% mature, from a body weight viewpoint, whereas Hereford
females were only 91% mature. Herefords did not reach 97% of their mature weight
until about 84 months of age, even though they were gaining weight at a greater
rate than Angus. Brown et al. (6) also found Hereford females to reach the same
degree of maturity as Angus females at older ages. They also reported Angus fe-
males to gain faster up to 12 months of age at which time monthly gains of Hereford
females became greater.
Heritabilities of A, B, k, birth, 7 month, 24 month and 48 month weight and
genetic and phenotypic correlations between these measurements are given in table
4. Heritability estimates of A and k are of sufficient magnitude to indicate
that strict selection in a population of cattle could change rate of maturing or
mature size. Estimates obtained in these data are slightly higher than reported
previously in Angus and Hereford cattle (5). Genetic correlations between k and
birth, 7 month, and 24 month weight were positive, indicating that cattle with
heavier premature weights also tend to have genotypes reflecting rapid rates of
maturing. However, the genetic correlations between k and 48 month weight and A
(mature weight) were negative. This result suggests that animals which reach
mature weights earlier tend to have smaller mature weights. As mentioned earlier,
these heritabilities and genetic correlations were computed using sire components
of variance and covariance pooled across breeds. The estimates, therefore, re-
flect a general situation. Brown et al. (6) computed these genetic parameters
within Angus and Hereford breeds and found differences between the breeds. Al-
though phenotypic variation of various preweaning and mature weights were simi-
lar for the two breeds, additive genetic variation was smaller in the Angus breed
resulting in smaller estimates of heritability for weight in Angus cattle. Genetic
correlations between mature weight and preweaning weights were found to be small
in Angus whereas the same genetic correlations were large in Hereford cattle. Es-
timates of genetic correlations between k and A and between k and 8, 24 and 48
month weight found by Brown et al. (6) for Hereford cattle were similar to those
found in this study when pooled across Angus, Brahman, Hereford and Santa Gertru-
dis breeds. It is also recognized that k is computed and interpreted relative to
A, and therefore it is not completely independent of A. Therefore, the negative
associations between k and measures of mature size should be evaluated with some
amount of caution.
Growth curves were computed on 186 Angus, 96 Brahman, 181 Hereford and 62
Santa Gertrudis cows born at the Brooksville Beef Cattle Research Station between
1953 and 1973. Best fitting growth curves for the four breeds were obtained by
least squares analysis. Hereford cows were heavier at maturity, weighing 1081
pounds, followed by Santa Gertrudis at 1003, Brahman at 952 and Angus at 904
pounds. Santa Gertrudis cows matured more rapidly and Hereford cows less rapidly
with Angus and Brahman cows maturing at similar rates and intermediate to Santa
Gertrudis and Hereford cows. Rate of maturity of the four breeds was closely re-
lated to degree of maturity at various ages of the four breeds. Heritability
estimates of A, B, k, 7 month, 24 month and 48 month were large (all >.50).
Phenotypic and genetic correlations between k and 7 and 24 month weights were
positive whereas they were negative between k and 48 month weight and A. These
genetic parameters indicate that selection could be effective for changes in
mature size and rate of maturing; however, selection for increased mature size
could reduce rate of maturing.
(1) Blackwell, R. L., H. H. Knox, C. E. Shelby and R. T. Clark. 1962. Genetic
analysis of economic characteristics of young Hereford cattle. J. Anim.
(2) Brinks, J. S., R. T. Clark, N. M. Kieffer and J. J. Urick. 1964. Estimates
of genetic, environmental and phenotypic parameters in range Hereford fe-
males. J. Anim. Sci. 23:711.
(3) Brody, S. 1945. Bioenergetics and Growth. Reinhold Pub. Co. N.Y.
(4) Brown, C. J., M. L. Day, W. Gifford and R. S. Hones. 1956. Growth and
development of Aberdeen Angus cattle. Ark. Agr. Exp. Sta. Bul. 571.
(5) Brown, J. E., C. J. Brown and W. T. Butts. 1972a. A discussion of the
genetic aspects of weight, mature weight and rate of maturing in Hereford
and Angus cattle. J. Anim. Sci. 34:525.
(6) Brown, J. E., C. J. Brown and W. T. Butts. 1972b. Relationships among
weights, gains and earliness of maturing in Hereford and Angus females. J.
Anim. Sci. 35:507.
(7) Butts, W. T., M. Koger, O. F. Pahnish, W. C. Burns and E. J. Warwick. 1971.
Performance of two lines of Hereford cattle in two environments. J. Anim.
(8) Carpenter, J. A., Jr., H. A. Fitzhugh, J. E. Brown and E. K. Crouch. 1971.
Relationships among growth parameters and measures of productivity in beef
cows. Tex. Agr. Exp. Sta. Prog. Rep. No. 2975.
(9) Fitzhugh, H. A. and St. C. S. Taylor. 1971. Genetic analysis of degree of
maturity. J. Anim. Sci. 33:717.
(10) Joandet, G. E. 1967. Growth patterns and efficiency of TDN utilization in
beef cattle. Ph. D. Dissertation. Texas A & M University, College Station.
(11) Kidder, R. W., M. Koger, J. H. Meade and J. R. Crockett. 1964. Systems of
crossbreeding for beef production in Florida. Fla. Agr. Exp. Sta. Bul. 673.
FIGURE 1. GROWTH CURVES OF ANGUS(A), BRAHMAN (B.), HEREFORD (H)
AND SANTA GERTRUDIS (SG) COWS.
24 48 72 96
MONTHS OF AGE
TABLE 1. ESTIMATES OF A, B, AND k FOR ANGUS,
BRAHMAN, HEREFORD AND SANTA GERTRUDIS COWS.
Breed A B k
Angus 904 856 0.064
Brahman 952 888 0.062
Hereford 1081 1016 0.050
Santa Gertrudis 1003 925 0.071
TABLE 2. PREDICTED WEIGHTS FOR ANGUS, BRAHMAN, HEREFORD AND SANTA GERTURIDS COWS.1
Age in Months
Breed Birth 4 8 12 16 20 24 36 48
A 54 230 390 505 590 670 715 815 860
B 58 260 410 530 620 695 750 855 905
H 65 245 405 525 620 705 775 910 988
SG 65 305 485 610 705 780 830 930 970
TABLE 3. DEGREE OF MATURITY OF ANGUS,
GERTRUDIS COWS AT PREMATURE AGES.1
BRAHMAN, HEREFORD, AND SANTA
Age in Months
Breed Birth 4 8 12 16 20 24 36 48
A 6 25 43 56 65 74 79 90 95
B 6 26 43 56 65 73 79 90 95
H 6 23 37 49 57 65 72 84 91
SG 6 30 48 61 70 78 83 93 97
TABLE 4. HERITABILITIES, PHENOTYPIC AND GENETIC CORRELATIONS POOLED
7 month wt.
24 month wt.
43 month wt.
-.39 0.23 0.32 0.39
Heritabilities on diagonal, genetic correlations
phenotypic correlations below diagonal.
TABLE 5. LEAST SQUARES ANALYSES OF VARIANCE SIGNIFICANCE
above diagonal and
Source df A B k wt. wt. wt. wt.
Breeds 3 ** ** ** ** ** ** **
Sires/Breeds 85 ** ** ** ** ** ** **
Years, L 1 ** *
Q 1 ** *
C 1 ** -
Cow Age, L 1 ** ** *
Q 1 ** -