There has been an increased interest in using Dorper sheep in crossbreeding programs with local sheep breeds in the USVI. The Dorper breed was chosen for its heavy muscling in an attempt to increase the growth rate and size of lambs produced for the local market.

Because of local interest in the use of Dorper sheep in crossbreeding programs we conducted a project, funded by the USDA-NIFA TSTAR Program. The results of that project showed that 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 (See Relevant Publications below).

The Dorper was developed for an arid environment and is not known for prolificacy, unlike the indigenous hair sheep in the Caribbean that have been selected for a humid environment and are prolific. There is little information on how Dorper x St. Croix White crossbred ewes will perform under tropical conditions found in the USVI and the greater Caribbean. A crossbred flock has been established to compare the production traits of Dorper X St. Croix White ewes to St. Croix White ewes under tropical conditions. Ewes are being managed in an extensive system, with rotational grazing and an accelerated lambing cycle.

In the accelerated lambing system currently being used, lambs are weaned at 63 days of age to allow the ewes a brief rest between lactation and rebreeding. Because the Dorper x St. Croix White lambs don't have the same level of parasite tolerance as the St. Croix White lambs there has been a relatively high mortality rate post weaning. A long-term project has just been initiated in 2008 to evaluate the impact of later weaning (90 or 120 days of age) on lamb and ewe production traits. Lamb growth and survival will be evaluated in lambs weaned at either 63, 90 or 120 days of age. Ewe productivity will also be evaluated, and will include weight change, fertility, cyclicity, milk production and ability to breed back.

Heat stress is a common problem in ruminant production throughout the tropics. Genetic selection has been used to develop breeds that are adapted to the tropical environment. On the island of St. Croix there are two breeds of adapted livestock, Senepol cattle and St Croix White hair sheep. Both of these breeds play a role in the agriculture industry of the US Virgin Islands and the wider Caribbean and Central and South America. Previously funded TSTAR research in our laboratory using thermal imaging to measure body temperature in St Croix White and Dorper X St Croix White hair sheep found no differences indicating that the crossbred sheep maintain the adaptation to the environment evident in the local breed of hair sheep.

Lab analysis for parasites   AI procedure in sheep   Day 40 sheep fetus
Relevant Publications

Behavioral and endocrine responses of hair sheep ewes exposed to different mating stimuli around estrus. Theriogenology 55:877-884

Effect of flushing hair sheep ewes during the dry and wet seasons in the U.S. Virgin Islands. J. Anim. Vet. Adv. 2:184-190

Effect of supplemental nutrition around lambing on hair sheep ewes and lambs during the dry and wet seasons in the U.S. Virgin Islands. J. Anim. Sci. 81:587-593

Evaluation of sexual behavior of hair sheep rams in a tropical environment. J. Anim. Sci. 76:714-717

Post-weaning growth and carcass traits of St. Croix White and Dorper X St. Croix White lambs fed a concentrate diet in the U.S. Virgin Islands. Sheep & Goat Research Journal 20: 32-36

Post-weaning growth and carcass traits of St. Croix White and Dorper X St. Croix White lambs grazing pasture during the dry and wet seasons in the U.S. Virgin Islands. Sheep & Goat Research Journal 20: 25-31
Plasma LH, FSH, testosterone, and age at puberty in ram lambs actively immunized against an inhibin -subunit peptide. Theriogenology 60: 933-901

 The effect of ram exposure on uterine involution and luteal function during the postpartum period of hair sheep ewes in the tropics. J. Anim. Sci. 76:3090-3094

Evaluation of ultrasonography to measure fetal size and heart rate as predictors of fetal age in hair sheep. Sheep & Goat Research Journal 25:60:65