A\ Agricultural Research Center
S Mimeo Report RC-1972-9 Ma rIU E LIBRARY


INFLUENCE OF BREEDING ON REPRODUCTIVE
PERFORMANCE OF HEIFERS BRED AS YEARLI JGS N 2 91972

F. M. Peacock, E. M. Hodges, W. G. K rk
M. Koger and A. C. Warnick A.S.- Univ. of Florida

There has been increased interest in south Florida in

breeding heifers to calve at two years of age instead of the

conventional three. This has come about by intensification

of management practices and the awareness of cattlemen of the

time and cost in carrying a cow until she is three years of

age before calving.
The concept that early pregnancy, commensurate with

physiological state and nutritional status, would aid in
improving reproductive efficiency of cattle, resulted in

the initiation of a study at the Agricultural Research Center,
Ona of breeding crossbred heifers as yearlings. The main

purpose of this study was evaluation of reproductive performance

of various European Brahman FL crosses and backcrosses.

EXPERIMENTAL PROCEDURE

Crossbred heifers between 11 and 14 months of age, similar

to those commonly used in commercial production were exposed

to Charolais bulls for 100 days. The breeding season in this

experiment began and ended two weeks before the regular breeding

season. Breed groups of heifers studied included various


1/ Associate Animal Husbandman, Agronomist, Animal Scientist
Emeritus, Agricultural Research Center, Ona.
Animal Geneticist, Animal Physiologist, Animal Science
Department, Gainesville.





2.

combinations of the Angus, Brahman, Charolais and Shorthorn

breeds, with major emphasis being on Brahman-European crosses.

Related breed groups in the Charolais x Brahman classi-

fication and also the Charolais x Shorthorn breed groups

were combined for presentation because of small numbers.

Heifers in the other cross category were not related by

breed. Due to the small numbers within breed groups, inferences

as to reproduction of the specific breed group could not be

made but are presented as items of interest.
Results and Discussion

Reproduction data by breed groups over a four year

period are given in the following table. All true F1 heifers

had a relatively high calving rate, with the I Angus a

Brahman highest at 100% and the I Brahman J Shorthorn at 85%.

The I Charolais mix breed group dropped from the levels

of the F1 heifers to 71%, indicating a genetic variance relative

to conception at this age.
Calving percentage of the backcross 3/4 Shorthorn

Brahman was second to the J Angus Z Brahman heifers with

a 90 calving percentage while the 3/4 Brahman x 1 Shorthorn

was lowest at 43%. These results clearly demonstrate the

potential of the European breeds for breeding at a young age

and the apparent later sexual maturity of animals of predo-

minant Brahman breeding.

Weaning percentage being relative to both calving and

survival resulted in the Angus Brahman being highest,

even though calf survival of 90% was not highest in the










INFLUENCE OF BREEDING OF CROSSBRED
HEIFERS CALVING AT TWO YEARS OF
AGE ON PERCENT CALVING, WEANING
AND CALF SURVIVAL


No. Calf
Heifers Calving Weaning Survival
Breeding of Heifer Exposed % % %


J Angus I Br
1 Sh Br

3/4 Sh Br
3/4 Br Sh
I Ch Mixl/
A 3/8 Br 1/8 Sh
Ch x Br Crosses
Ch x Sh Crosses
Other Crosses


Totals


100


91
100
90

57


11


207


1/ Ch A B
2 Ch t Sh B B








experiment. The combined Charolais Brahman females were

next in order at 78% due to a 100% survival rate. The one-
half Shorthorn one-half Brahman heifers weaned-the same

percentage of calves as the 3/4 Shorthorn Brahman at

77, with calving and survival percentage differences balancing
each other out. Small numbers in the Charolais x Brahman

groups limits inferences by specific breeding but a 100o
survival rate is of interest and indicates these heifers

are less subject to calving problems than other heifers

in this study when bred to bulls of large breeds. However,

management plays an important role in this practice. After

conception, until the calf is weaned, management determines

to a high degree the overall production in calving heifers

at two years of age.

SUMMARY

Reproduction data of various breed combinations on breed-

ing as yearlings and calving at two years of age have been

presented. The J Angus Brahman heifers had the highest
calving and weaning rate of all breed groups studied. However,
results showed the Fl, Shorthorn x Brahman, 3/4 Shorthorn -
4 Brahman, Angus x Brahman x Shorthorn and predominantly

Charolais x Brahman heifers have the potential to breed as

yearlings and wean a relatively high calf crop. Calf survival

was low in this study, averaging 88% and ranging from 57
to 100%. This can be partially corrected by selecting

individual bulls that are known to combine well with young

cows.