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Agricultural Research Center, Ona ** **
MyX..IMimeo Report RC-1972-10 May, 1972
HUME LIBRARY
INFLUENCE OF AGE ON REPRODUCTIVE
EFFICIENCY OF BRAHMAN C 29 ?2f 2

F. M. Peacock, W. G. Kirk., M. Koer
and A. C. Warnick / .
and A. C. Warnic .F.A.S. Univ. of Florida

Fertility is one of the most important economic traits
in beef cattle. The low reproductive performance of beef
cattle in the South has received considerable attention-from
both cattlemen and research workers resulting in coordinating
efforts to obtain knowledge.to improve this trait.
Temple (1965) from a survey of herds contributing to the
Southern Regional Beef Cattle Breeding Project., S-10, reported
for all breeds a 76.5 calving percentage and 67.8 percent for
calves weaned. Brahman cows in this survey had a 74.5 calving
percentag- and weaned a 58.8 percent calf crop. This weaning
value for Brahman cows was lower than all other breed groups
studied. For Florida, Temple (1965) also reported a 74.7
calving and 71.3 weaning percent for all breeds of cattle
contributing to the project.


1/ Associate Animal Husbandman, Animal Scientist, Emeritus,
Agricultural Research Center, Ona. Animal Geneticist,
Animal Physiologist, Animal Science Department, Gainesville.
2/ Temple, R. S. 1965. Reproduction of Beef Cattle in the
South. Presented at Florida Beef Cattle Short Course,
University of Florida. Gainesville May 6-7, 1965.










In view of the importance of the Brahman breed in Florida

as well as other areas of the U. S. and foreign countries,

records at the Agricultural Research Center, Ona, Florida
were studied in an attempt to find causes of this relatively

low reproductive performance.

EXPERIMENTAL PROCEDURE

The breeding program began with the purchase of 5 two

year old Brahman heifers in each of the 4 years, 1942, 1943,

1944 and 1945. The Brahman herd during the period of this
study was essentially an unselected population, with all
heifers, except strictly culls, going into the breeding herd,
to increase numbers. Heifers with infantile genitalia were
kept to study their reproductive behaviour and many of the

original cows purchased were kept to determine longevity of

production.

RESULTS

These data represent 1038 observations during 24 years

and include ages ranging from females first bred as two year
olds to cows bred at 17 years of age. Data on influence of

age of cow on calving, weaning and death loss of calves ex-

pressed by percentage are given in Table 1.
Age of dam probably has the most influence of the non-

environmental factors affecting reproduction. Average percen-
tage for all ages was 74.3 calving, 71.5 weaning and 3.8 for
death loss of calves. There was an increase in calving and

weaning percentages from females exposed at 2 to 5 years of










age with the exception of calving 3 year olds that dropped

slightly below the performance of heifers bred at two years

of age.
The increase from 65.4 calving percentage for heifers

bred as two year olds to 83.8 for cows being bred at 5 years

of age indicates that Brahman heifers, under the prevailing
management conditions, did not reach full sexual maturity at
two years of age. The increase in reproduction until 5 years
of age also indicates that physiological maturity was not
attained until the cows were near this age. Even though sexual

maturity is attained, nutrition and the physiological status
of the cow must be in balance to obtain maximum reproduction.
The relatively high level of reproduction from 5 through

12 years of age indicates that these are the peak productive

ages and dropping -rod this level after 13 years of age is
the normal biological process of aging.
Death loss of calves, 3.8%, is relatively low compared
to other studies. This study shows death loss ofcalves

highest in cows calving at 3, 4 and 5 years of age, with a
lower loss for older cows. The higher death loss for the young
cows and lowest for cows 6 through 18 years of age indicates
a possible association between the physiological age of the
cow and the prenatal environment furnished the calf.

SUMMARY

Data was presented on 1038 observations for reproductive

performance of Brahman females being bred between 2 and 17










years of age. The low conception rate at 2 and 3 years of age
with 5 years being the highest indicates that these heifers
were slow in maturing sexually and physiologically under the
management conditions prevailing during this period. Reproduc-
tion dropped after 13 years of age, which is a normal biological
process. Death loss of calves was relatively low for all ages
but highest in cows calving at 3, 4 and 5 years of age.


Table 1. INFLUENCE OF AGE OF
RATE AND DEATH LOSS


DAM ON CALVING
OF CALVES.


RATE, WEANING


Age of Dam No. in % % %
when bred Breeding herd Calving Weaned Death loss

2 162 65.4 62.4 4.7

3 158 63.9 59.5 6.9
4 141 75.2 70.9 5.7
5 111 83.8 82.0 2.2
6 93 81.7 80.7 1.1
7 83 80.7 79.5 1.2
8 9 116 76.7 73.3 3.5
10 12 110 79.1 77.3 1.8

13 17 64 71.9 70.3 1.6

Total 1038 74.3 71.5 3.8


RC-1972-10
5/22/72-200