S Agricultural Research Center, Ona *
- C Research Report RC-1973-33 ------ -. April, 1973

1- 3 HUME LIBRARY
REPRO UCTIVE EFFICIENCY OF COW-

F. M. Peacp W. .Aik, M. Koger d A. C. Warnick/

Frility one of AS Univ. of Florida
Fertility i one of : -co ic traits in beef cattle.

The low reproductive performance of beef cattle in thq-South has received

considerable attention from both cattlemen and research workers resulting

in coordinating efforts to obtain knowledge to improve this trait.

Temple3/ (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 percentage 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.

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


1/ To be presented at the 22nd annual Beef Cattle Short Course, University of

Florida, Gainesville Florida, May 3, 4 and 5, 1973.

.2/ Associate Animal Husbandman, Animal Scientist, Emeritus, Agricultural

Research Center, Ona. Animal Geneticist, Animal Physiologist, Animal

Science Department, University of Florida, Gainesville.

3/ Temple, R. S. 1965. Reproduction of Beef Cattle in the South. Presented

at the Florida Beef Cattle Short Course, University of Florida, Gainesville ,

May 6-7, 1965.








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Research Center, Ona, Florida were studied in an attempt to find causes of

this relatively low reproductive performance.

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 unsfeected population,

with all heifers, except strictly culls, going into the breeding herd to

increase numbers and many of the original cows kept to determine longevity

of production.

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, lactation status within age and breed

of bulls on calving, weaning and death loss of calves expressed by percentage

are given in Tables 1, 2 and 3, respectively.

Age of dam probably has the most influence of the non-environmental factors

affecting reproduction. Average percentage for cows of all ages was 74.3 for

calving, 71.5 for weaning and 3.8 for death loss of calves. Non-lactating

2 year olds calved.at 65.4%, increased to 85.7% for the non-lactating three

and four year olds. The 5 year olds calved at 91.7%, highest for the non-

lactating cows. Non-lactating cows from 6 through 17 years maintained a

relatively high calving rate. This study indicates a lack of sexual maturity

for the two year olds but by 3 years of age sexual maturity for this population
4/
had been attained. Research by Reynolds et al- (1963) showed the average

age at puberty to be 816 days for Brahman heifers, which supports these data.



4/ Reynolds, W. L., T. M. DeRouen and T. W. Hige, Jr. 1963. The age and

weight at puberty of Angus, Brahman and Zebu cross heifers. J. An.

Sci. 22:243.












Lactation exerted the greatest influence on reproduction. Lactating

three year old females had a 49.5% calving rate, increasing to 68.2% at 4

years and a further increase to 81.6% at 5 years of age. Lactating cows 6

to 12 years of age maintained a high calving rate of 78.7%, but from 13 to 17

years of age calving dropped to 68%. These data indicate the lack of

physiological maturity until approximately 5 years of age and a decline in

physiological state at 13 years of age under the prevailing management conditions

Death loss of calves was lowest in 5 to 17 year old cows. Non-lactating

cows had a higher average death loss than lactating cows but most of the

difference could be attributed to the high death loss for the non-lactating

three year old females. The higher death loss for the young cows indicates

a possible association between the physiological age of the cow and the prenatal

environment of the calf. Physiological immaturity of these females could have

affected size and nutrition of the fetus as well as difficulties at partuition.

The influence of breed of sire on reproductive behavior was negligible

except for death loss of calves, 5% for the Brahman and 2.78% for European bulls.

Data have been presented on 1038 observations for reproductive performance

of Brahman females being bred at 2 through 17 years of age relative to age,

lactation status within age and breed of bulls. The data indicates that two

year old females lacked sexual maturity for a high percentage calf crop but

at three years of age sexual maturity for the population had been attained.

From 3 through 17 years of age average calving rate was over 85% for the non-

lactating cow. Cows suckling calves increased in calving percentage to 5 years

of age indicating a lack of physiological maturity until approximately 5 years

old. A relatively high reproductive level was maintained through 12 years of

age, then dropped due to stress from lactation. There was a higher death loss

in Brahman sired calves than calves sired by European bulls.








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In studying these data it appears that these animals behaved relative.to

an environment that limited production until physiological adjustments to this

envirorf nt were made. faster physiological development brought about by

management and nutrition compatible with the genetic potential of the animal

should improve reproduction. Combining faster physiological developments with

selection of females with characteristics conducive to high fertility should

correct many of the deficiencies that have resulted in low reproductive

behavior of Brahman cows.





Table 1. INFLUENCE OF AGE OF DAM ON CALVING RATE, WEANING RATE AND DEATH LOSS
OF CALVES.


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


2 162 65.4

3 158 63.9

4 141 75.2

5 111 83.8

6 93 81.7

7 83 80.7

8 9 116 76.7

10 12 110 79.1

13 17 64 71.9


Total 1038 74.3


% %
Weaned Death loss,


62.4 4.7

59.5 6.9

70.9 5.7

82.0 2.2

80.7 1.1

79.5 1.2

73.3 3.5

77.3 1.8

70.3 1.6


71.5 3.8


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TABLE 2. INFLUENCE OF LACTATION


Age of Dam Lactation
when bred status


2 years Non-lactating

3 years Non-lactating


4 years



5 years


6-12 years


13-17 years


Lactating

Non-lactating

Lactating

Non-lactating

Lactating

Non-lactating

Lactating

Non-lactating

Lactating


STATUS WITHIN AGE OF DAM OR REPRODUCTIVE PERFORMANCE OF BRAHMAN COWS.


Number in
Breeding herd


162

63

95

56

85

24

87

69

333

14

50


Birth Rate
%I


65.4

85.7

49.5

85.7

68.2

91.7

81.6

82.7

78.7

85.7

68.0


Wean Rate
%


62.4

77.8

47.4

82.1

63.5

91.7

79.3

79.7

76.9

85.7

66.0


Death Rate
%


4.7

11.1

4.3

4.2

6.9

0.0

2.8

3.5

2.3

0.0

2.9


TOTAL Non-lactating 388 77.1 73.4 4.7

Lactating 650 72.6 70.3 3.2


_ _




, r


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TABLE 3. INFLUENCE OF BREED OF SIRES ON BIRTH RATE, WEAN RATE AND DEATH
LOSS OF CALVES


Breed of Sire No. exposed Birth Rate Wean Rate Death Rate


Brahman 457 74.40 70.68 5.00

European 581 74.18 72.12 2.78


This Research Report was promulgated at an annual cost of
$59.00, or 6 cents per copy, to inform ranchers on the
latest research work at this research facility.


RC-1973-3