Bulletin 773 (technical)
GROWTH AND REPRODUCTION
IN RAMBOUILLET AND
FLORIDA NATIVE SHEEP
P. E. Loggins, D. E. Franke, and C. G. Hurley
Institute of Food and Agricu
S University of Florida, G
J. W. Sites, Dean for
I : -~I II
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Cover: A Rambouillet ewe and her set of twins with two extra visitors in
FACTORS INFLUENCING GROWTH AND
REPRODUCTION IN RAMBOUILLET
AND FLORIDA NATIVE SHEEP
P. E. Loggins, D. E. Franke, and C. G. Hurley
Mr. Loggins is a Professor and Dr. Franke is an Associate
Professor in the Animal Science Department, University of
Florida, Gainesville. Mr. Hurley's present address is High
This public document was promulgated at an annual cost
of $451.76, or a cost of 300 per copy to provide basic infor-
mation on the production traits of sheep in the lower South-
east area of the United States.
Sheep production in Florida is limited primarily to small
flocks of "Native" sheep maintained for a local lamb supply and
with minor income from sale of wool. These sheep are considered
tolerant to hot and humid conditions that prevail in the Southeast
and to the high exposure rate of internal parasites, particularly
the stomach worm Haemonchus contortus. Columbia, Hampshire,
and Rambouillet sheep have been raised experimentally to deter-
mine if they could compete with the "Florida Native" under
Florida environmental conditions. Of these, Rambouillet ap-
peared most promising, although it was quite susceptible to H.
contortus (14, 1, 8).
The production data presented here are from a study de-
signed to evaluate response to selection for resistance to the
stomach worm H. contortus in Rambouillet and Florida Native
flocks. Production data included birth weight, 60 and 120-day
weight, ewe fertility, and lamb survival rate. Although these
traits have been evaluated extensively at other experiment sta-
tions, the subtropical environment and genetic makeup of the
Florida Native warrant additional study.
Materials and Methods
Florida Native sheep have been in existence in Florida for
several centuries. They are descendants of sheep of mixed breed-
ing developed largely through natural selection under native
range conditions. Rambouillet utilized in this study were from
foundation flocks established in 1962 from commercial herds in
Texas and Alabama.
Blood hemoglobin values were determined routinely on ewes
prior to this study. Prior to the 1966 breeding season ewes with-
in the Rambouillet and Florida Native flocks were divided equally
into low hemoglobin (LH) and high hemoglobin (HH) groups.
Ewes with average monthly hemoglobin values below the breed
mean were assigned to the LH group; those with average hemo-
globin values above the breed mean were assigned to the HH
group (Table 1). Replacement ewe lambs were selected within
each high or low group and were assigned to their respective low
or high groups depending upon their average hemoglobin values
measured periodically between 4 and 18 months of age. Rams
also were selected on high and low average values within their
The flocks were managed for spring lamb production. Ewes
were maintained as one flock except during a 45-day breeding
TABLE 1. AVERAGE HEMOGLOBIN LEVELS OF RAMBOUILLET AND FLORIDA NATIVE
EWES FOR THE FIRST BREEDING SEASON, 1966.
Breed Low High
Florida Native 8.66 + .08 9.68 + .14
Number 60 60
Rambouillet 8.03 + .10 8.94 + .15
Number 30 30
season beginning July 1 each year. All lambs were weaned at ap-
proximately 60 days of age. Ewes were maintained on Bermuda-
grass pastures and were supplemented to meet their nutritional
requirements in all seasons. Use of anthelmintics to control in-
ternal parasites was restricted initially for all groups. However,
it became necessary in the second year of the study to treat Ram-
bouillet LH ewes to maintain the group with a high exposure
rate to H. contortus infections. After the third year all Rambouil-
let ewes were treated routinely for H. contortus.
Least squares analysis of variance (6) was utilized to esti-
mate effects of environmental factors on responses and to obtain
least squares constants for these effects. Effects of year, breed,
hemoglobin group, birth type (single or twin), ewe age, and sex
were included in a model to explain variation in weight responses.
First order interactions between these effects were included in
preliminary analyses and in general found not to be important.
Age of lamb was included as a linear covariance term in analysis
for 60 and 120-day weight. All main effects except sex and birth
type were included in the model for ewe fertility. Sex of lamb
and birth weight were included for lamb survival to weaning.
Results and Discussion
Average hemoglobin levels for the LH and HH groups of
Rambouillet and Florida Native ewes at the onset of the study
are shown in Table 1. Results of analysis of variance for hemo-
globin values indicated significant differences (P<.01) existed
between breed, hemoglobin groups, and breed x hemoglobin
group interaction subclasses.
Least squares means, standard errors, and tests of signi-
ficance for sources of variation included in the models describing
weight at birth, 60 days and 120 days are given in Table 2. Sig-
nificant (P<.01) influence exerted on birth weight were sex,
TABLE 2. LEAST SQUARES MEANS, STANDARD ERRORS AND TESTS OF SIGNIFICANCE FOR
BIRTH, 60- AND 120-DAY WEIGHT.
Number of Birth
Observations Weight (lb)
627 7.6 .06
156 7.7 .1
107 7.7 .1
116 7.7 .1
119 7.5 .1
129 7.5 .1
311 7.8 t .1
316 7.5 .1
108 7.6 .1
519 7.7 .1
Weight (ib) Weight (Ib)
34.5 1 .7
32.9 .5 50.3 + .7
29.8 .5 45.8 .7
32.0 .6 48.3 .9
30.6 + .4 47.8 + .6
Hemoglobin group (ewe)
Regression on age
Breed x Group
Florida Native low
Florida Native high
298 7.7 .1
329 7.6 .1
520 8.3 .1
107 6.9 + .1
133 6.8 .1
118 7.3, .1
112 7.3 .1
77 7.9 .1
47 7.8 + .2
62 7.8 .2
33 7.9 .2
31 8.0 .2
14 7.8 .3
0.35 .02 0.40 .04
7.7 + .2
7.5 + .2
7.6 + .1
7.7 + .1
birth type, and ewe age. At birth male lambs were 0.24 pounds
heavier than ewe lambs, and single born lambs 1.39 pounds
heavier than twins. Ewes 2, 3, and 4 years old gave birth to
smaller lambs than aged ewes, as previously described by Sidwell
and Miller (10). The advantage in birth weights of single over
twin born lambs has been well documented in other flocks. Birth
weights of Rambouillet lambs were similar to those of Florida
30.1 + .6
27.8 + .7
31.3 + .7
48.3 + .9
29.3 + .9
30.8 + .5
48.2 + .7
47.3 + .7
Native lambs; however, the least squares mean birth weight of
7.6 pounds for Rambouillet lambs was lower than that reported
for Rambouillet lambs by several other workers (3,4,11). Birth
weights were similar to those reported by Shelton (12) and
Gould and Whiteman (5) for fall born lambs. Shelton (13)
demonstrated that high environmental temperatures during ges-
tation adversely affected lamb birth weights. Most ewes in Flori-
da are in the first and second trimesters of gestation during
August and September, usually two of the hottest months. These
high temperatures may have contributed to the low birth weights
found in this study.
Significant (P<.01) influences on 60-day weight were year,
sex, hemoglobin group, birth type, ewe age, regression of weight
on age, and breed x hemoglobin group interaction. Male lambs
were 3.1 pounds heavier than female lambs, and single reared
lambs 7.1 pounds heavier than twins. Two-year-old ewes weaned
lambs smaller than more mature ewes. The linear regression of
weight on age of 0.35 was similar to that reported by Basset et al.
(2). Preliminary analysis indicated the quadratic regression of
weight on age was not a significant source of variation. Ram-
bouillet and Florida Native lambs weighed approximately the
same at 60 days, although smaller than the 70-day weight of
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Figure 1. The 1970 Florida Native and Rambouillet ewe flocks two weeks
following the late March shearing.
54.3 pounds reported by Gould and Whiteman (5). Lambs born
in the LH group were heavier than those in the HH group; how-
ever, since the breed x hemoglobin group interaction was sig-
nificant, main effect significance has less meaning. It is apparent
the Rambouillet LH group accounted for the significant advan-
tages of the LH group main effect. Loggins, Swanson, and Koger
(8) and Jilek and Bradley (7) suggested that high hemoglobin
levels in ewes were indications of resistance to the stomach worm
H. contortus. It seems reasonable to assume that ewes under less
stress should be superior producers; however, this was not evi-
dent in the Rambouillet flock. Ewes in the Rambouillet LH flock
were drenched periodically to prevent death loss from H. con-
tortus infections, and of those surviving many produced lambs.
Thus, the drenched ewes, even though more susceptible to H.
contortus, may have been able to become sufficiently better pro-
Lamb 120-day weight was significantly influenced by the same
sources of variation as for 60-day weight except for ewe age. The
least squares mean for 120-day weight of 48.0 pounds was lower
than that reported for Rambouillet lambs in the Southern Region
(11). Heavier weights in Southern states other than Florida
prompted Loggins et al. (8) to suggest that Florida Native sheep
were unsatisfactory for commercial sheep production because of
low growth rates in lambs. Results in this study indicated that
Rambouillet lambs reared under the same conditions as Florida
Natives did not perform significantly better (48.3 pounds versus
47.7 pounds at 120 days). This may indicate they are unable to
perform at their genetic potential for growth due to environ-
mental conditions of high heat, humidity, and parasitic infections.
Male lambs were 4.4 pounds heavier than ewe lambs at 120 days,
and lambs born in low hemoglobin groups were heavier than
those born in high hemoglobin groups across as well as within
breeds. Single reared lambs were 6.8 pounds heavier at 120 days
than twin reared lambs. The pre- and post-natal effects of twin-
ning were still prevalent 60 days after weaning, whereas age of
dam effects were not significant 60 days after weaning.
Phenotypic correlations of 0.35 and 0.32 were observed be-
tween birth and 60 and 120-day weights, respectively, and 0.83
between 60 and 120-day weights. Ercanbrack and Price (4) re-
ported a correlation of 0.46 between birth and 120-day weight in
Least squares means, standard errors, and tests of signifi-
cance for factors influencing ewe fertility and lamb survival rate
are shown in Table 3. Fertility rate is defined as the percentage
TABLE 3. LEAST SQUARES MEANS, STANDARD ERRORS AND
FOR FERTILITY RATE AND LAMB SURVIVAL.
TESTS OF SIGNIFICANCE
Fertility Rate Lamb Survival
Variable No. 2 SE No. % SE
789 77.6 + 1.7
70.9 + 3.2
73.5 + 3.3
712 83.8 1.6
84.0 + 2.6
75.5 + 2.9
85.9 + 3.1
88.4 + 3.0
Breed x Group
Florida Native low
Florida Native high
188 66.5 2.7
601 88.7 1.8
382 81.2 2.4
407 74.0 + 2.3
134 80.3 + 2.7
578 87.4 + 1.6
349 82.0 2.1
363 85.7 2.?
73.2 + 3.3
73.8 + 5.1
83.9 + 5.7
85.3 + 6.3
74.9 + 7.5
85.0 + 3.6
82.6 + 4.5
81.2 + 3.7
86.2 + 5.3
78.8 + 3.8
81.7 + 3.8
85.2 + 2.0
89.7 + 2.0
356 83.0 1.9
356 84.7 1.9
of ewes exposed which lambed. A 77.6% rate was observed for
789 ewe exposures and was similar to a 79% rate reported for
fine wool ewes in the lower South (11). Analyses indicated that
year, breed, hemoglobin group, and breed x hemoglobin group
were significant (P<.05 or P<.01) sources of variation influenc-
ing fertility rate. The most important effect appeared to be breed
of ewe. Florida Native ewes lambed at an 88.7% rate whereas
Rambouillet ewes lambed only 66.5% of the time. The fact that
breed x hemoglobin group interaction was significant does not
discount the advantage shown by Florida Native ewes, since the
highest fertility rate in the Rambouillet groups was lower than
fertility in the Florida Native groups. This strongly points out
the reproductive performance of sheep in areas where they are
not well adapted, particularly with respect to being relatively
resistant to H. contortus.
Of 712 lambs born, 83.8% survived to weaning. Year, breed,
and the linear effect of birth weight were significant (P<.05 or
P<.01) sources of variation on lamb survival. More Florida
Native lambs survived (7.1%) than Rambouillet lambs. Birth
weight was an important effect in that an increase in birth
weight of 2.2 pounds increased the probability of survival by 3%.
Shelton (12) discussed the effect of lamb birth weight on survi-
val and found those lambs weighing at least 5.5 pounds had a
75% chance of surviving. Death losses in these flocks because of
large lambs at birth were few.
Summary and Conclusions
Weights at birth, 60 days and 120 days were recorded on 627
Rambouillet and Florida Native lambs born from 1967 through
1971. An analysis of weights and reproductive performance of
the ewes revealed the following:
1. Rambouillet and Florida Native lambs had similar weights
at birth, 60 and 120 days.
2. Ram lambs were heavier at all three ages than ewe lambs.
3. Lambs born as singles were 1.4 pounds heavier at birth,
7.0 pounds heavier at 60 days, and 6.9 pounds heavier at 120
days than twin born lambs.
4. Overall ewe fertility was 77.6% ; however, Florida Native
ewes lambed 88.7% of the time as compared to 66.5% for Ram-
5. Of 712 lambs born alive, 83.8% survived to 60 days; 7%
more Florida Native lambs survived than Rambouillet lambs.
6. Rambouillet ewes had to be treated routinely following
the second year of the study for internal parasites in order to
7. Rambouillet ewe reproduction and lamb growth rates
were below the average for the breed in more temperate areas of
the United States.
8. This study indicates that Florida Native sheep are very
competitive in production traits for this area, and the fact that
they are less susceptible to internal parasites is a major factor.
9. Those interested in sheep production in this area need to
investigate selection of a breed very thoroughly before beginning
such an enterprise.
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1967. Estimates of genetic and phenotypic parameters of weanling
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3. Bell, T. D., L. E. Orme, C. W. Hodgson, R. E. Christian, and D. 0.
Everson. 1967. Weaning and carcass characteristics of purebred and
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JUN 2 1975