Bulletin 578 October 1956
UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATIONS
J. R. BECKENBACH, Director
Factors Affecting the Weaning Weight
of Range Calves
By FENTRESS M. PEACOCK, W. G. KIRK and MARVINN
Fig. 1.-Native and grade cows used in the original bree program.
INTRODUCTION .......-...-....... ...- ............-... ........... 3
REVIEW OF LITERATURE ...-.... .... .. .... ............. 3
MATERIALS AND METHODS ...................----.......... -....--........ 5
EXPERIMENTAL RESULTS .........--..-------........--....--.....--..-- ....--.... 8
Breeding of Dam -...--....-..----- ..-- --.-.. ---...--- ....--...-.....---.....- 8
Time of Calving ...... ---........------- -....-...-.....-- ..--....- ......... 8
Individual Sire Differences ..-.............-... .--. ---- ....- ----...... 8
DISCUSSION OF EXPERIMENTAL RESULTS ..........--.........----------.. --......... 8
Breeding of Dam ..-.... ...---------..- -------.....-...-... ..... --........... 8
Time of Calving ---....-...--------.. ----.. -...-...-......-- ...-..-...... 9
Sire Differences --.. ---............. -------------- -......- ..............- 10
SUMMARY AND CONCLUSIONS ...-.................--..-...........- ......-. ....... 11
LITERATURE CITED ..................-- --...................- .......- ................... 12
Factors Affecting the Weaning Weight
of Range Calves
By FENTRESS M. PEACOCK, W. G. KIRK and MARVIN KOGER
Weaning weight of calves is important to the beef cattle pro-
ducer, since gains from birth to weaning are more economical
than those made later. Producers of either slaughter or feeder
calves are especially interested in this weight, as their income
largely depends upon size and weight available for sale. Heavy
weaning weight in replacement animals is equally or more im-
portant, because it is related to mature size and future produc-
tion of the herd.
A number of factors influence the weight of calves at weaning.
This study is concerned with certain hereditary factors which
are influenced by the breeding program and with environmental
factors, such as the season of birth, on weight of calves at wean-
ing. Information on the factors affecting production and the
magnitude of their influence is essential to devise a program to
make the most efficient use of feed.
Limited data have been published on factors that influence
weaning weights of beef calves in Florida. Production records
of cattle at the Range Cattle Experiment Station, Ona, have
been kept since the founding of the Station in 1941. This study
is an analysis of records to determine the influence of breeding
of dam, influence of sires and season of calving on weaning
REVIEW OF LITERATURE
The calf's weaning weight is a useful measure of a cow's yearly
production, since this observation is taken at the end of the
period over which she exerts maximum influence on the growth
of the calf.
In crossbreeding work at the Everglades Station at Belle
Glade from 1943 to 1951, Kidder and Chapman (6)1 found the
reciprocal crosses of both Brahman-Angus and Brahman-Devon
matings to be superior in weight gains from birth to weaning
to any of the three purebred lines. Baker and Black (3), USDA
Livestock Experimental Farms, Iberia, Louisiana, found that
SItalic figures in parentheses refer to Literature Cited.
4 Florida Agricultural Experiment Stations
half-breed Brahman-Angus cows produced significantly heavier
calves at six months of age than did cows of pure breeding,
irrespective of sires. Their results indicate that the full value
of hybrid vigor, derived from mating Brahman and Aberdeen-
Angus cattle in a crossbreeding program, cannot be realized from
a calf production standpoint until the hybrid cows have pro-
From a study on slaughter calf production, Knapp et al. (7)
found the best slaughter calves of the 1950 Lufkin Station calf
crop to be 3/4 Hereford-1/ Brahman mothered by nine-year-old
1/2 Brahman-1/2 Hereford sired by a Hereford bull. Table 1 pre-
sents a summary of the 1950 calf crop at Lufkin.
TABLE 1.-SUMMARY OF 1950 CALF CROP AT LUFKIN, TEXAS.
Breeding of Dam Hereford Hereford 1B.-H. %H.-'%B. %H.-1B.
Breeding of Sire Hereford Brahman Hereford Hereford IBrahman
(pounds) ........ 399 433 561 397 475
Age at Weaning
(days) ......... 172 181 216 149 196
As in previous years, it appeared that the Brahman blood
should be on the side of the dam and that British-breed bulls
bred to crossbred cows may be expected to produce the heaviest
slaughter calves at weaning. Results obtained by Knapp et al.
(8) in 1949 were similar.
A study of slaughter calf production in the Brazos Valley,
Texas, was made by Roberts et al. (15). In 1946 Brahman and
Hereford bulls were bred to grade Hereford cows. Heifers from
these matings were bred to Angus bulls in 1949. Results of
this crossbreeding program are shown in Table 2.
Many investigators have reported on the effect of different
sires on weaning weight of calves. Knapp et al. (10) in 1942,
studying the growth and efficiency of production in Hereford
cattle under range conditions in Montana, found that sire differ-
ences accounted for approximately 14 percent of the variance in
weaning weights of calves. In general, they concluded that the
effect of sires increases as the calf becomes older. This agrees
with results reported by Koger et al. (13), who made a study
on the selection of bulls in which 13 years' records at the College
Factors Affecting Weaning Weight of Range Cattle 5
Station Ranch, New Mexico, were used. They found that bulls
influenced the weaning weight of calves, which is in agreement
with the results reported by Gerlaugh et al. (4).
TABLE 2.-WEANING WEIGHTS OF CALVES SIRED BY ANGUS BULLS OUT OF
GRADE HEREFORD AND GRADE HEREFORD X BRAHMAN COWS.
Breeding of Dams Age of Calves of Calves
Grade Hereford x Brahman -.... 240 465
Grade Hereford .......................-- 235 444
Knapp et al. (9) in 1944, in performance testing of beef cattle,
found that phenotypic characteristics of a bull are a poor indi-
cation of his breeding performance. They concluded that the
productive ability of a sire is indicated by the weaning weight
of his calves. On the other hand, Knapp and Black (11) in
1941 found that difference between progeny of different sires
cannot be demonstrated by rate of gain during the period prior
to weaning. Results of investigation by Gregory et al. (5) in
1950 were similar but they concluded the results were probably
due to the limited number of bulls used and the small size of sire
progeny groups available to evaluate the sires.
Gerlaugh et al. (4) observed that winter or early calves gained
at a faster rate than calves born later in the season.
MATERIALS AND METHODS
The data used in this study were obtained from the weaning
records of calves produced by the commercial herd at the Range
Cattle Station during the period 1945 through 1951. This area
is typical of much of the native grazing range found in central
Florida. Native vegetation consists of wiregrass and various
species of broadleaf paspalums, with a scattering of pine trees
and occasional wooded areas of oaks. Beginning in 1946, im-
proved pastures consisting of Pangolagrass and Bahiagrass were
made available for limited grazing as a part of the pasture
The commercial herd consisted of grade Brahman, Hereford,
Devon and Shorthorn cows. Purebred Brahman, purebred Short-
horn and crossbred Shorthorn x Brahman bulls were used in
6 Florida Agricultural Experiment Stations
the breeding program. Records included breeding, weight
changes and productivity of all cattle. Calves were weighed
at birth and all animals were weighed at 28-day intervals. The
data included records on 673 calves obtained from 254 cows
from this herd.
Weaning weights of calves were adjusted to a mean weaning
age of 180 days, based on a regression coefficient of 1.5 pounds
per day determined from the data. Approximate correction for
sex difference was made by adding 28.3 pounds to the weaning
weight of heifers. This difference in weight due to sex was
obtained from within sub-group averages and was in close agree-
ment with results reported by Koger and Knox (14), who found
a sex difference of 30 pounds in their data. Since the influence
of age of dam was of small magnitude in these data, no cor-
rection was made for this factor. The remaining sources of vari-
ability involved year-to-year effects, sire effects, seasonal effects
and breeding of dam.
The mathematical model assumed for the analysis was:
YljkU = m + yi + sj + tk + di + eijklm;
Yijim is the weight of the ijklmth calf;
m is the general mean;
Yi is the ith year effect;
sj is the effect of the jth sire;
tk is the effect of the kth time;
di is the effect of the lth breeding of dam;
eijkim is the error for the mth individual in the ijklth group.
Each observation was assumed to be the sum of the influences
of effects of the variables as follows: Weaning weight = general
mean + year differences + sire differences + time of calving +
breeding of dam + error. This linear combination of effects is
similar to that used by Koch (12).
The least squares solution for disproportionate frequency dis-
tribution was employed for these data. Based on the mathe-
matical model given above, 21 simultaneous equations evolved
from these data. The method of analysis employed was the
Abbreviated Doolittle method from which estimates of treat-
ment effects were obtained and analysis of variance for the
treatment effects were determined (Anderson and Bancroft,
Factors Affecting Weaning Weight of Range Cattle 7
TABLE 3.-ANALYSIS FOR THE ADJUSTED EFFrCTS OF BREEDING OF DAM,
SIRES AND TIME OF CALVING.
Sums of I Mean
Source of Variation d. f. Squares I Squares
Total ............... .................... 672 1,559,338
"Treatment" ................................ 135 989,300
SSR' ...........................-..... ........... 16 509,977
Years ........................................ 6 369,534
Sires (Y,T,D) ........................ 5 34,164 6,833
Time (Y,T,D) ...-.............- ..... 1 29,906 29,906**
Breeding of Dam (Y,S,T) .. 4 84,026 21,006**
Residual ................................... 119 479,323 4,028
W within .......................................... 537 570,038 1,061
** Significant at the .01 level of probability.
TABLE 4.-EFFECT OF BREEDING OF DAM ON WEANING WEIGHT OF CALVES
ADJUSTED FOR YEARS, SIRES AND TIME OF CALVING.
Dam Number of Mean from Mean
S Calves (Pounds) (Pounds)
English Breed ........................ 221 367.9 -3.8
1/32 15/32 Brahman ............ 114 381.7 +10.0
% Braham ....----............................ 267 394.6 +23.0
17/32 31/32 Brahman .......... 58 377.0 +5.3
Florida Native Cow ............... 13 337.1 -35.0
TABLE 5.-EFFECT OF TIME OF CALVING ON WEANING WEIGHT OF CALVES
ADJUSTED FOR YEARS, SIRES AND BREEDING OF DAM.
Time Adjusted Deviation from
Means (Pounds) Mean (Pounds)
W inter ................................................. 378.7 + 7.0
(December, January and February)
Spring .................----- ------............. -. 364.6 7.0
(March, April and May)
TABLE 6.-EFFECT OF SIRES ON WEANING WEIGHT OF CALVES ADJUSTED
FOR YEARS, TIME OF CALVING AND BREEDING OF DAM.
Number Adjusted Deviation
Sires of Means from Mean
Calves (Pounds) (Pounds)
Floppy (Brahman) ...........-................ 105 391.2 +19.6
Smoky (Brahman) .....................-...... 276 376.2 +4.6
Polled Shorthorn ..-...........-- .....-....-.. ... 73 373.0 +1.4
Emperor (Brahman) ......----.....--....-.. 87 366.9 -4.7
David (Brahman) .--......................---.. 86 361.0 -10.6
Crossbred (Shorthorn x Brahman) 46 361.5 -10.2
8 Florida Agricultural Experiment Stations
BREEDING OF DAM
A summary of the analysis of variance is given in Table 3.
The adjusted mean square for breeding of dam was highly sig-
nificant, the F value being 5.2. The adjusted means for dams
of different breeding are shown in Table 4.
The heaviest weaning weights of calves were from cows of
one-half Brahman breeding, with production being lower in cows
containing less than one-half and those containing more than
one-half Brahman breeding. This behavior suggests that hybrid
vigor was evident in the F1 cows. Native cows produced the
lightest calves in this study. However, the numbers were small
in this group. Figure 1 shows a group of native and grade
cows, while Figures 2 and 3 are calves sired by Brahman bulls
and Figure 4, calves sired by a Polled Shorthorn bull.
TIME OF CALVING
The estimated effect of time of calving, together with adjusted
means, is shown in Table 5. Calves born during December,
January and February were 14 pounds heavier at 180 days of
age than calves born during March, April and May. This differ-
ence was highly significant.
INDIVIDUAL SIRE DIFFERENCES
The adjusted mean square for sire effects was non-significant
when the F test was computed by using the residual as error
for general inferences. The estimated sire effects, together
with adjusted sire means, are shown in Table 6.
DISCUSSION OF EXPERIMENTAL RESULTS
BREEDING OF DAM
The weaning weight of the calf is a useful measure of a cow's
yearly production, since this evaluation is obtained at the end
of the period over which the cow exerts maximum influence on
the growth of the calf. A cow influences the weaning weight
of her calf by the genes transmitted, by nourishment provided
in the milk and by other items of mothering ability. The en-
vironment a cow provides a calf probably exerts a stronger
influence on the weaning weight of the calf than do the genes
transmitted by the parents. This is because the major part of
Factors Affecting Weaning Weight of Range Cattle 9
the calf's ration is made up of milk during the period of rapid
Results from this study show significant differences in the
weaning weight of calves mothered by one-half Brahman cows
over weaning weights of calves out of cows with either more
or less than one-half Brahman breeding. They indicate that
hybrid vigor had a beneficial influence on mothering ability and
was reflected in increased weaning weights of the offspring.
Results of this study agree with those obtained by Knapp
et al. (7), who found that the highest grade of slaughter calves
was produced by nine-year-old crossbred Brahman x Hereford
TIME OF CALVING
Florida breeders have observed that early (winter) calves
grow faster than calves born in spring and summer. Results
of this study confirm this. There was a highly significant dif-
ference in weaning weights of calves born in December, January
and February over calves born in March, April and May.
The heavier weaning weights attained by calves born early
in the season probably were due to heavier milk flow of the
dams, and to calves having access to nutritious pasture forage
when they needed it for growth. Gains by calves born later
in the season were smaller, due to lower milk production of the
cow and to lack of high quality pastures when the calf was be-
ginning to graze.
Fig. 2.-Calves sired by Floppy, purebred Brahman bull, and out of
native and grade cows shown in Fig. 1.
10 Florida Agricultural Experiment Stations
This is supported by results reported by Arnold et al. (2)
showing that dairy cows freshening during the winter months
gave slightly more milk and were more persistent producers
than cows freshening at other times. Those calving in October
and November followed the winter group closely. Cows freshen-
ing in the summer (June to September) ranked below those in
milk yield, while the spring calving group (March to May) pro-
duced the least milk.
Results of this study show no significant influence of sires
on 180-day weight of calves. This is not surprising in view
of the limited number of bulls and the finding of previous in-
vestigators that sire differences tend to be small at weaning and
increase with age of offspring. Inherent growth potential of
various sire groups may have been partially masked because
the dam's milk supply was a limiting factor. Furthermore, the
breeding structure of the herd was such that sire differences
probably were minimized. There was a tendency for dams heavy
in Brahman breeding to be mated to British bulls and vice versa,
resulting in high grade cows of both Brahman and British breed-
ing raising a preponderance of crossbred calves.
Fig. 3.-Calves sired by Smoky, purebred Brahman bull, and out
of grade cows.
Factors Affecting Weaning Weight of Range Cattle 11
SUMMARY AND CONCLUSIONS
A study was made from records of 673 calves from 264 cows
at the Range Cattle Station, Ona, Florida, to determine: (a)
breeding of the dam which was most efficient in producing the
heaviest calves at weaning; (b) individual sire differences; and
(c) effect of time of calving on weaning weights of calves. The
period covered was from 1945 through 1951.
Results showed a highly significant difference between wean-
ing weights of calves mothered by dams of different breeding.
Cows with 1/2 Brahman breeding weaned the heaviest calves
with an adjusted mean of 395 pounds. Weaning weights of
calves from cows of 1/32 to 15/32 and 17/32 to 31/32 Brahman
breeding averaged 382 and 377 pounds, respectively. Cows of
predominantly European breeding, containing no Brahman blood,
weaned calves which averaged 368 pounds. Thirteen calves from
native cows averaged 337 pounds.
There was a highly significant difference in weaning weights
of calves born in winter (December, January and February)
over calves born in spring (March, April and May), with the
adjusted difference being 14 pounds.
There was no significant difference in weaning weights of
calves sired by six different bulls.
Fig. 4.-Calves sired by Polled Shorthorn bull and out of grade cows.
12 Florida Agricultural Experiment Stations
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