Department of Animal Science Florida Agriculture
Research Report AL-1981-11 Experiment Station
November 1981 Gainesville, Florida
THE PERFORMANCE OF FLORIDA NATIVE, ST. CROIX
AND ST. CROIX x FLORIDA NATIVE F1 CROSSBRED SHEEP
P. E. Loggins and Kodjo P. Abassa
The term "Florida Native" is used to identify a type of sheep that has
been developed in Florida primarily through natural selection. For several
centuries they have survived on native range and are characterized by small
body size with white to dark brown color, refined bone structure, open faces,
and clean legs and underlines. These sheep have developed a degree of
resistance to high exposure rate of internal parasites and to the climatic
conditions prevailing in the Southeast. Because of these characteristics,
Florida Native sheep offer promise for increased sheep production in subtropical
areas and the Southeastern United States. The objective of this study was
to measure the productivity of straightbred Florida Natives and their crosses
with the St. Croix, a hair breed of sheep from the Virgin Island, St. Croix
in the West Indies.
Data were collected over a three-year period (1978-1980) from the sheep
flock at the Florida Agricultural Experiment Station at Gainesville. The
Florida Native ewes were divided into two breeding groups which were maintained
as a single flock except during the 40-day breeding season beginning on
July 15. One group of ewes was bred to Native rams and the other to St.
Croix rams. A small flock of St. Croix ewes were straighbred. A total of
317 ewes and 348 lambs were used in the analysis. Ewe weights and hemoglobin
levels were collected during the breeding season, during the 4th month of
pregnancy and at the 60-day weaning date of the lambs. The lamb data included
birth, weaning and postweaning (120 days) weight and hemoglobin levels at
60 days and 120 days.
Least squares methods were used in the analysis of fertility of the
ewes, survival of the lambs at birth (48 hours), weaning (48 hours to 60
days) and to 120 days. The birth weight, weaning weight and postweaning
(120 days) weight of the lambs were used in the analysis. The models for
growth traits included the effects of year, age of the ewe, sex of the lamb,
breed of the lamb, birth type and appropriate interactions. Year, age of
dam and ewe breed were the effects used for fertility analysis. The models
also allowed for regression of appropriate traits on weight of ewes, hemo-
globin levels, lamb age and lamb birth weight.
RESULTS AND DISCUSSION
The breed of ewe significantly (P<.05) affected the pregnancy rate
91.5 percent for Native ewes when compared to 67.7 percent for St. Croix
ewes (table 1).
TABLE 1. EFFECT OF BREED ON FERTILITY1
BREED NUMBER FERTILITY
Florida Native 282 91.46 4.84**
St. Croix 40 67.68 6.73
Fertility expressed as percentage ewes bred.
The lambing rate per ewe lambing was significantly increased (P<.05) for
each mg increase in hemoglobin levels at the beginning of the breeding season
as shown in table 2.
TABLE 2. EFFECT OF HEMOGLOBIN & WEIGHT ON EWE PERFORMANCE
ST. CROIX RAMS
FLORIDA NATIVE EWES
Number of Ewes 142 140 40
Hemoglobin Levels1 9.76 2.04 9.65 2.06 10.92 1.70
Weight kg2 38.82 4.24 38.88 4.47 35.97 3.87
Number of Ewes Lambing 129 128 28
Number of Lambs Born3 156a 151a 41b
Mean hemoglobin levels at the beginning of the breeding season.
2Mean ewe weight at the beginning of the breeding season.
3'a'bMeans with the same letter as subscript do not differ significantly at the
Lamb survival rates at birth of straightbred Native Lambs, crossbred
lamb (St. Croix x Native) and Straightbred St. Croix lambs were not signif-
icantly different (table 3). The survival rate was not significantly affected
(table 3) by breed type and age of ewe. Survival to weaning of the F1 lambs
was not statistically different from the straightbred Native lambs. The
straight St. Croix lambs, however, had lower survival rates (P<.01) than the
other breed groups (69% vs 95.4% or 97.7%) (table 3). Survival rate of lambs
born from St. Croix x Native matings were nonsignificant from those of straight-
bred Native matings. The survival rate of St. Croix lambs was lower (P<.O1)
than that of lambs of other breed types.
TABLE 3. PERCENT LAMB SURVIVAL RATE BY BREEDING GROUP
BREEDING AT BIRTH WEANING (48 hours SURVIVAL (60 to 120 DAYS)
GROUPS (48 hours) to 60 days) 1978 1979 1980
Native 94.55 .03a 95.39 .03a 89.45 .06 97.53 .05 91.61 .05
St. Croix a a
SNative 97.50 .03a 97.74 .04a 94.14 .06 98.20 .05 94.82 .05
st.XCroix 76.99 .05b 69.05 .05b 89.45 .10 68.31 .08 46.18 .09
Means with the same letter as subscript do not differ significantly at the .05
There was an interaction between year and sex on lamb survival rate. Ewe
lambs born in 1978 had higher survival rates than those born in 1979 and 1980
as shown in table 4. On the other hand, ram lambs born in 1978 had lower
survival rates than those born in 1979 and 1980. Ewe lambs had a higher
survival rate in 1978 than ewe or ram lambs in any year. However, the lowest
level was found in the 1980 ewe lambs. Ram lambs born in 1978 had the lowest
survival rate when compared with ewe lambs (P<.01) and ram lambs (P<.05) of
any of the other years. On the other hand, ewe lambs born in 1978 had the
highest survival rate at birth (table 4).
TABLE 4. EFFECT OF YEAR AND SEX OF LAMB ON PERCENT SURVIVAL RATES1
AT BIRTH WEANING (48 SURVIVAL (60
YEAR AND SEX (48 hours) hours to 60 days) to 120 days)
1978 Ram Lamb 79.0 4.9 84.5 5.5 85.3 6.1
1978 Ewe Lamb 94.5 4.9 98.8 5.6 96.8 6.1
1979 Ram Lamb 91.2 4.4 87.1 4.9 89.7 5.3
1979 Ewe Lamb 92.3 3.9 85.4 4.6 86.4 4.9
1980 Ram Lamb 90.3 4.2 86.2 4.7 81.4 5.2
1980 Ewe Lamb 91.0 5.0 82.4 5.5 73.7 6.3
Mean differences were not tested.
The type of birth did not significantly affect survival rate to the 120
day of age. Single-born lambs were significantly heavier (P<.O1) than twin-
born lambs. However, breed effect on birth weight of lambs was not significant
(table 5). Significant differences in weaning weight due to sex of lamb,
birth type and lamb breed were observed. Ram lambs and single-born lambs were
significantly heavier than ewe lambs and twin-born lambs, respectively.
Straightbred Native lambs achieved heavier weights at weaning (60 days) than the
F1 lambs (St. Croix x Native) (P<.05) and straightbred St. Croix lambs (P<.01).
Straightbred Native lambs were 1.4 kg heavier than St. Croix lambs and .49 kg
heavier than F1 lambs (table 6).
TABLE 5. EFFECT OF SEX AND BIRTH TYPE ON THE GROWTH OF THE FLOCK1
SEX BIRTH TYPE
ITEMS EWE LAMB RAM LAMB SINGLE TWIN
Birth Weight (kg) 2.49 .086 2.39 .086 2.95 .05 2.31 .04
Weaning Weight (kg) 10.82 .31 10.05 .31 12.98 .19 9.42 .23
Average Daily Gain (kg) .15 .004 .15 .004 .16 .004* .14 .004
Flock was composed of 3 breeding groups; Native, St. Croix and St. Croix rams x
TABLE 6. GROWTH PERFORMANCE BY BREEDING GROUPS
POSTWEANING WEIGHT (kg)
BREEDING BIRTH WEANING WEIGHT (kg) (120 DAYS)
GROUPS WEIGHT (kg) (60 DAYS) RAM LAMBS EWE LAMBS
Native 2.50 .08a 11.06 .294a 17.98 .550 14.83 .550
St. Croix a b
Nativex 2.40 .09a 10.57 .33b 16.66 .610 15.09 .60
St. Croix 2.42 .13a 9.66 .51bc 14.85 1.050 15.83 1.460
abCMeans with the same letters as superscripts do not differ significantly
at the .05 level.
Mean differences not tested.
The 1979 lambs were significantly (P<.01) heavier, 16.9 kg at 120 days
of age, than the 1978 lambs, 15.2 kg, and the 1980 lambs, 15.6 kg (table 7).
Again birth type significantly influenced the trait. Single-born lambs were
3.6 kg heavier than twin-born lambs at weaning (table 5). Postweaning weight
was also affected byan interaction of sex and breed of the lamb. The F, ewe
lambs were .26 kg heavier than straightbred Native lambs, whereas the Native
ram lambs were 1.3 kg heavier than St. Croix x Native FI ram lambs (table 6).
Ewe lambs from straight St. Croix x St. Croix crosses were heavier than the
ewe lambs from the other two breed types (Native; St. Croix x Native), whereas
ram lambs from St. Croix x St. Croix matings were lighter than ram lambs from
the other matings as shown in table 6. The gain from heterosis in the F1 was
approximately 2 percent. Weaning weights were significantly heavier (P<.01)
for the 1979 lambs, 10.8 kg versus 10.4 kg and 10.1 kg (table 7) respectively.
The 1979 lambs were significantly (P<.01) heavier at 120 days, 16.9 kg, than
those of 1978 and 1980 lambs, 15.2 and 15.6 kg respectively (table 7). How-
ever birth weights were not significantly different for the three years.
TABLE 7. EFFECT OF YEAR ON LAMB GROWTH IN THE FLOCK~-
ITEMS 1978 1979 1980
Birth Weight (kg) 2.44 .10 2.52 .08 2.36 .09
Weaning Weight (kg) 10.41 .39 10.83 .33* 10.06 .38
Average Daily Gain (kg) .14 .004 .15 .004 .15 .004
Postweaning Weight (kg) 15.15 .64 16.90 .52** 15.58 .78
1/Flock was composed of 3 breeding groups; Native, St. Croix, and Native x
Performances of Florida Native ewes mated to Native and St. Croix rams
were compared with straightbred St. Croix in North Central Florida (Gainesville).
The pregnancy rates were 67.7% and 91.5% for the St. Croix and Native ewes,
respectively. Significant differences in survival rate at birth and to weaning
were found between the lambs of Native and St. Croix ewes. Lambs sired by
St. Croix rams were significantly lighter (.5 kg) than those sired by Native
rams. This difference may be attributed to the smaller mature size of the
St. Croix sheep as the purebred St. Croix lambs weighed (1.4 kg) less than
the straightbred Native lambs at weaning. Survival rate and preweaning growth
of crossbred (St. Croix x Native) lambs did not surpass that of straightbred
Native lambs. The gain from heterosis in the F1 was approximately two percent
and the crossbreeding program was dropped from the 1980 breeding season. Due
to the increase in death losses and the overall condition of the straight-
bred St. Croix flock, they were removed from the study on July 3, 1980.