Hair Sheep Production in the Southeast U.S.

Numbers of hair sheep in the U.S. have increased in the past few years because of their ease of management and marketability. These sheep shed their hair, thus require no shearing, and many are resistant to parasites, a trait of growing importance, especially in the southeastern U.S. Because of resistance of gastrointestinal nematodes to chemical dewormers, use of resistant genotypes represents an important control measure for these parasites. U.S. hair breeds include American and Barbados Blackbelly, Dorper, Katahdin, and St. Croix.

Out-of-season breeding is an important characteristic of sheep in the eastern and southeastern U.S. Marketing potential increases when more than one breeding season is included in reproductive management because of the increased supply of lamb at different times of the year. Because sheep are seasonally polyestrus, traditionally ewes are bred in the fall to lamb in the spring. Length of the breeding season is dependent largely on breed, latitude and photoperiod.

There is some evidence that St. Croix ewes are capable of breeding in the spring in Arkansas, but at a reduced rate compared with other times of the year. Dorper ewes are capable of year-round breeding in South Africa, but out-of-season capability in the U.S. has not been determined. Prolificacy is another important trait of sheep in this area. Lambing rate of St. Croix ewes can range from 140 to 212% and lambing rate of Katahdin ewes can reach 168%. Prolificacy of Dorper ewes in South Africa was 141% and has not been reported in the U.S.

In the current study, Dorper, Katahdin, and St. Croix ewes were bred in late summer (August/September), winter (December), or spring (April/May) in Arkansas to assess ability to breed out-of-season during a 30-day breeding period to respective ram breed after a 21-day exposure to vasectomized teaser rams.

Figure 1. Pregnancy loss for summer, winter, and spring bred ewes

Figure 2. Pregnancy rates of summer, winter, and spring bred ewes

Figure 3. Litter weaning weights for summer, winter, and spring-bred ewes

Dorpers were developed in warm, arid climates. The climate of Arkansas during summer months is warm and humid. Surprisingly, pregnancy (more than 20%) and newborn lamb losses (more than one-third) were greater and lamb birth weights lighter for Dorper ewes bred in the spring compared with Katahdin and St. Croix ewes (Figure 1). It was noted that body condition was good during this period, suggesting that heat stress, rather than poor nutrition, contributed to these losses. This suggests that Dorper ewes were more susceptible to heat stress than Katahdin and St. Croix ewes which had no changes in lamb losses or birth weights among seasons. Similarly, the summer breeding period for Dorper and Katahdin ewes resulted in reduced pregnancy rates compared with winter breeding with no further losses in mid to late pregnancy. There may have been an initial heat stress with increased early embryonic mortality or delayed resumption of the estrous cycle.

Pregnancy rate was similar between summer and winter breeding for St. Croix ewes (Figure 2), suggesting a greater tolerance to heat stress. However, pregnancy rate was reduced during spring breeding. This was likely attributed to an inability to breed out-of-season in a greater proportion of ewes for all breeds. There were more St. Croix than Katahdin ewes pregnant at this time, but lambing rate was similar among the breeds within a season and was similar among breeds and seasons when considering only ewes that lambed.

Average birth weights of a litter for Dorper, Katahdin and St. Croix ewes were similar when breeding occurred in the spring, but otherwise were greater for Dorper and Katahdin ewes. Total weight of lambs born per ewe was not affected by season and was greater for Katahdin ewes. Total weaning weights at 60 days of age were greatest when breeding occurred in the summer for Dorper and Katahdin ewes and were similar between these breeds (Figure 3). Average weaning weights were lighter for St. Croix compared with other breeds bred in summer and spring, but were similar to Dorper and Katahdin in winter.

Forage quality and quantity are often greater during late winter and early spring in Arkansas, contributing to greater weaning weights. The St. Croix ewes appeared to be less affected by changes in forage quality throughout seasons compared with Dorper and Katahdin ewes. In contrast, a previous study at this location determined that weaning weights of St. Croix lambs were lighter during fall lambing. Supplemental feeding was offered throughout late gestation and lactation for all seasons in the current study, but not between May and September in the previous study, which likely accounts for differences between studies.

The forage base for this flock included endophyte-infected tall fescue, which reduced pregnancy and calving rates in beef heifers and increased body temperature of cattle. We reported decreased pregnancy rates in yearling, but not mature ewes, grazing tall fescuecompared with bermudagrass at this station. In addition to reduced ability for out-of-season breeding, reduced pregnancy rates in summer and spring breeding in the current study could have been attributed to fescue toxins. Tropically-adapted breeds of cattle were less sensitive to fescue toxins than English breeds, likely because of greater heat tolerance. This could be true of St. Croix compared with Katahdin ewes, although this was not examined. Rectal temperatures of St. Croix ewes were lower than that of Targhee at elevated ambient temperatures, indicating greater heat tolerance of St. Croix.

Conclusion
In conclusion, all hair breeds in this study were capable of out-of-season breeding and early pregnancy rates were highest during winter breeding. Pregnancy rates and pregnancy and newborn lamb losses were greater for Dorper ewes bred in spring compared with late summer or winter, likely due to heat stress. Lambing rate for ewes lambing was similar among breeds and seasons. Weaning weights of St. Croix lambs were not influenced by season, but were greater for Dorper and Katahdin lambs born in winter.

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