Production traits of St. Croix White and Dorper x St. Croix ... - Inra

R.W. Godfrey, R.E. Dodson and R.C. Ketring
University of the Virgin Islands,
Agricultural Experiment Station,
St. Croix, VI

Background
• The Sheep research Facility at the University of the Virgin Islands
Agricultural Experiment Station was established in 1986
• The flock originally consisted of St. Croix White and Barbados Blackbelly
hair sheep, and a small flock of Gulf Coast Native wool sheep was kept for a
few years to evaluate parasite tolerance
• Hair sheep in the tropics do not exhibit seasonal breeding patterns like
most breeds of wool sheep in temperate regions making them very well
suited for use in accelerated lambing systems
• Seasonal pattern of rainfall in the USVI and limited land area make pasture
management a critical aspect of small ruminant farm management

Background
• Breeds of hair sheep in the Caribbean produce relatively small lambs with
light carcass weights at slaughter
• Previous attempts in our lab to increase carcass weight by crossing with
wool breeds have met with limited success
• Suffolk X St. Croix White lambs had higher average daily gain but lower
feed efficiency when compared to purebred St. Croix White lambs
(Godfrey and Collins, 1999)
• Lamb mortality of ¼ Suffolk x ¾ St. Croix White lambs was 57.1%
compared to 33.3% for St. Croix White lambs while grazing gunieagrass
pasture during the rainy season (Godfrey et al., 2000)
• Therefore, we saw the need for evaluation of other breeds to be crossed
with indigenous hair sheep

Introduction of Dorper Sheep
PROS
• Hair type sheep
• Developed in South Africa
• Adapted to hot climate
• Heavy muscled
CONS
• Lack parasite tolerance of hair sheep
• Not adapted to humid tropics
• Expensive to purchase purebreds
• Not as prolific as hair sheep

Dorper x St. Croix White Crossbreds
• Dorper x St. Croix White lambs grow faster and yield heavier carcasses than
St. Croix White lambs when they are raised on either a concentrate or
forage ration after weaning (Dodson et al., 2005; Godfrey and Weis, 2005)
• There were some issues with parasite susceptibility of the crossbred lambs
(Dodson et al., 2005)

Caveat
• Many farmers are using Dorper to crossbreed with local breeds of sheep
• Taking advantage of increased growth rates, higher feed efficiency and
better carcass quality
• Be careful not to wipe out local breeds of sheep by crossbreeding
• Local hair breeds still have a place in the industry
• Prolificacy
• Hardiness
• Parasite tolerance

Objective
• The objective of this study was to compare production traits of
St. Croix White and Dorper x St. Croix White ewes managed in
an extensive management and accelerated lambing system in
the tropics.

Animals
•The Dorper x St. Croix White ewes (DRPX; n = 17-25) were
compared to an established St. Croix White flock (STX; n = 20-
27) for 6 lamb crops (387 lambings)
•The DRPX ewes were bred in October 2003 for their first
lambing in March 2004
•Subsequent lamb crops were produced in November 2004, July
2005, March 2006, November 2006 and July 2007
•The STX ewes were older than DRPX ewes at the March 2004
lambing (3.5 vs. 1.1 yr, respectively)

Management
•Ewes grazed guinea grass (Panicum maximum) pastures at
a stocking rate of 7-8 ewes/ha in a rotational grazing
system during breeding, gestation and lactation
•Single sire breeding for 35 d in Oct 2003, June 2004, Feb
2005, Oct 2005, Jun 2006 and Feb 2007
•Same breed rams used at a ram:ewe ratio of ~1:20
•Lambs weaned at 63 d of age

JAN
DEC
FEB
BREED
LAMB
NOV
MAR
LAMB
BREED
OCT
APR
SEP
MAY
AUG
JUL
LAMB
JUN
BREED

Results

Litter birth weight
7
6
b
c
DRPX
STX
a,b P < 0.006
c,d P < 0.003
Breed x Time P < 0.003
5
d
4
a
3
2
1
0
Mar-04 Nov-04 Jul-05 Mar-06 Nov-06 Jul-07
Lambing

Litter size at birth
2.5 DRPX
STX
b
a,b P < 0.0002
d c,d P < 0.02
2.0
Breed x Time P < 0.008
c
1.5
a
1.0
0.5
0.0
Mar-04 Nov-04 Jul-05 Mar-06 Nov-06 Jul-07
Lambing

Litter weaning weight
30
25
b
c
DRPX
STX
a,b P < 0.02
c,d P < 0.0001
Breed x Time P < 0.0001
a
20
d
15
10
5
0
Mar-04 Nov-04 Jul-05 Mar-06 Nov-06 Jul-07
Lambing

Litter size at weaning
2.5 DRPX
STX
a,b P < 0.004
b
c,d P < 0.02
2.0
d
Breed x Time P < 0.005
1.5
a
c
1.0
0.5
0.0
Mar-04 Nov-04 Jul-05 Mar-06 Nov-06 Jul-07
Lambing

Ewe Efficiency
(litter weaning weight/ewe wt at weaning)*100
60
c
DRPX
STX
a,b P < 0.03
c,d P < 0.0001
Breed x Time P < 0.0004
a
Efficiency, %
50
40
b
d
30
Mar-04 Nov-04 Jul-05 Mar-06 Nov-06 Jul-07
Lambing

Weaning rate
100
80
DRPX
STX
Percent
60
40
20
0
Full
Weaning Rate
Partial

Summary of production traits of St. Croix White and
Dorper x St. Croix White ewes
Ewe Breed
St. Croix White Dorper x St. Croix White P
Number of lambs born 1.8 0.1 1.6 0.1 0.03
Number of lambs weaned 1.6 0.1 1.5 0.1 n.s.
Litter birth weight, kg 5.2 0.2 5.0 0.2 n.s.
Litter weaning weight, kg 19.6 0.6 22.6 0.6 0.0004
Ewe efficiency, % 46.8 1.5 50.2 1.4 0.09

Reproductive traits of St. Croix White and Dorper x St. Croix
White ewes
Ewe Breed
St. Croix White Dorper x St. Croix White P
Multiple lambs at birth, % 69.8 58.6 0.08
Ewe fertility a , % 83.8 2.6 92.7 2.9 0.05
Ewe prolificacy b , % 1.7 0.1 1.6 0.1 n.s.
Ewe fecundity c 1.4 0.1 1.5 0.1 n.s.
a
Ewes lambing / ewes exposed
b
Lambs born / ewe lambing
c
Lambs born / ewe exposed

Summary
• Even though the Dorper x St. Croix White ewes had fewer
lambs born than St. Croix White ewes they produced heavier
litter weaning weights
• The Dorper x St. Croix White ewes were able to achieve
production rates similar to St. Croix White ewes as they
matured as shown by heavier litter weaning weights and
greater ewe efficiency
• Within 1 lambing of being introduced into the flock the Dorper
x St. Croix White ewes had production traits similar to those of
the St. Croix White ewes

Conclusion
• These results indicate that Dorper x St. Croix White ewes can
be used in an accelerated lambing system under tropical
conditions and will achieve production rates similar, and even
superior, to those of indigenous sheep breeds

Questions