Nov. 2005 -- Broad diversity among breeds of sheep is a precious industry resource. This breed diversity can be managed to increase performance and profit through use of crossbred ewes mated to rams of a terminal sire breed. Differences among breeds in performance for survival, growth, carcass, wool, and reproductive traits are due to the unique genetic history associated with each breed. Beneficial genetic effects of each breed can best be realized in terminal crossbreeding systems that use sire breeds to complement characteristics of maternal line crossbred ewes, thus greatly improving efficiency of commercial lamb production. Evaluation of breeds for important traits is necessary to determine their appropriate use in terminal crossbreeding systems designed for specific production and marketing situations. The relative performance of breeds can best be determined from large-scale experiments that are designed to give unbiased results.
The above fundamental genetic concepts provided justification for an experiment to comprehensively evaluate five breeds of sheep. The experimental objective was to determine differences among Romanov, Finnsheep, Dorset, Texel, and Montadale for survival, growth and carcass traits of crossbred lambs and for reproductive traits of crossbred ewes in both fall and spring breeding seasons. The practical goal was to provide unbiased information so that producers can select and use breeds that maximize profits in terminal crossbreeding systems.
Romanov, Finnsheep, Dorset, Texel, and Montadale rams were mated to western whiteface and Composite ewes. The MARC Composite flock, created in 1980, has a breed composition of half Columbia, quarter Hampshire and quarter Suffolk. The crossbred offspring of these five breeds were compared in three distinct phases of the experiment. In the first phase, differences among crossbred lambs for survival, growth and carcass traits were evaluated in 1991 through 1993. In the second phase, crossbred ewes were appraised for reproductive traits after mating in August, October and December of 1991 through 1995 to lamb at one, two, and three years- of-age. In the third phase, 4-, 5- and 6-year-old crossbred ewes were mated during March and May of 1995 through 1999 to investigate differences for percentage of ewes lambing after mating in the spring.
Lambs were born in an enclosed building. Ewes giving birth to triplets or quadruplets were generally limited to rearing only two lambs, with excess lambs artificially reared in a nursery. Male lambs were castrated at about 14 days-of-age, at which time all lambs were offered a total-mixed creep diet. Dam-reared lambs were weaned at about 56 days-of-age and nursery-reared lambs at about 32 days-of-age. All lambs were switched to a total-mixed growing diet at about 10 weeks-of-age. Lambs were reared in a drylot facility with access to an open-front building. Lambs were weighed at birth, weaning, 10 and 20 weeks-of-age. Productivity of ewes (litter weight) is often measured to weaning, but dam- and nursery-reared lambs were weaned at different ages in this experiment. Therefore, it was not reasonable to summarize weights of dam- and nursery-reared lambs at weaning. We chose to measure ewe productivity at 20 weeks-of-age, when lambs of both rearing types were weighed. Also, litter weight at 20 weeks of age is a better indicator of income per ewe rather than litter weight at weaning.
Crossbred Lambs. Romanov and Finnsheep crossbred lambs had higher survival to weaning than crossbred lambs by Dorset, Texel and Montadale, whereas differences among all crossbred types in weight at 20 weeks-of-age were slight. When compared at a common carcass weight of 63 pounds, Romanov and Finnsheep crossbred lambs had lower dressing percentages than other crossbreds. Crossbred lambs by Dorset and Montadale had the least fat depth at the 12th rib and the longest carcasses. Carcasses of Texel crossbred lambs were most compact, being shortest in length and having the largest rib-eye area. Finnsheep crossbred lambs had the smallest rib-eye area, followed by Romanov crossbred lambs.
Crossbred Ewes in Fall Breeding. Crossbred ewes by Dorset and Montadale were the heaviest at three years-of-age and ewes of the other crossbred types were similar in weight. The percentage of ewes lambing fell into four groups: Romanov crossbred ewes had the highest percentage lambing, followed by Finnsheep, then Texel and Dorset, and crossbred ewes by Montadale were lowest. As expected, crossbred ewes by Romanov and Finnsheep produced the greatest number born per ewe lambing. Romanov crossbred ewes had the heaviest litters at 20 weeks-of-age per ewe lambing for both dam- and nursery-reared lambs, followed by Finnsheep, then Dorset and Montadale, and finally Texel. Fleeces of crossbred ewes by Montadale and Texel were heaviest. Stayability was measured as the percentage of sound ewes remaining in the breeding flock at three-and-a-half years-of-age. Romanov and Montadale crossbred ewes stayed in the flock at a higher rate than crossbred ewes by Finnsheep, Dorset and Texel.
Crossbred Ewes in Spring Breeding. Differences among crossbred types in percentage of ewes lambing depended on breeding season. In March breeding, percentage lambing was 92 percent for crossbred ewes by Romanov, 91 percent for Finnsheep, 90 percent for Texel, 88 percent for Montadale and 83 percent for Dorset. In May breeding, a more challenging month, percentage lambing was 89 percent for Romanov, 72 percent for Finnsheep, 62 percent for Dorset and 52 percent for both Texel and Montadale.
Results averaged over both March and May breeding seasons were calculated. Percentage lambing was highest for crossbred ewes by Romanov, intermediate for Finnsheep, and lowest for Dorset, Texel and Montadale. The same ranking of breeds was detected for number born. The 20-week litter weight of dam-reared lambs per ewe lambing was heaviest for crossbred ewes by Romanov, intermediate for Finnsheep, Dorset, and Montadale and lowest for Texel. Romanov and Finnsheep crossbred ewes produced the heaviest litters of nursery-reared lambs.
To focus on traits that most affect production efficiency and to summarize results in a simple manner, crossbred types are classified for four key traits in Table 1. This approach clearly separates Romanov and Finnsheep from Dorset, Texel and Montadale. Furthermore, based on actual performance, Dorset, Texel and Montadale are fairly similar to one another. In contrast, Romanov and Finnsheep plainly differ from each other, with Romanov crossbred ewes outperforming crossbred ewes by Finnsheep for percentage lambing, number born and length of seasonal fertility, as well as stayability.
Small advantages of breeds for individual traits can accumulate to create a large effect on overall product value, much as money compounded over time can increase several fold. To account for differences among crossbred types in percentage of ewes lambing, number born, lamb survival, lamb growth and ewe stayability, a comprehensive trait was calculated. Total weight of lambs produced from one to three years-of-age by each ewe entering a fall-breeding flock was calculated as the sum of 20-week weights for dam- and nursery-reared lambs. At one extreme, a ewe that died before lambing at one year-of-age would have a total weight value of zero pounds. A ewe that produced one lamb (88 pounds at 20 weeks-of-age) at one year-of-age, two lambs (75 and 82 pounds) at two years-of-age, and two lambs (80 and 85 pounds) at three years-of-age would have a value of 410 pounds for total weight. To account for length of seasonal fertility, total weight was also calculated in a similar manner for each mature ewe in the spring-breeding flocks (total weight of lambs produced from four to six years-of-age by each ewe entering a spring-breeding flock). Values of crossbred types for total weight in fall- and spring-breeding seasons are illustrated in Figure 1.
Total weight of lambs produced by Romanov crossbred ewes in fall breeding (394 pounds) was 24-percent greater than Finnsheep crossbred ewes (318) and 63-percent greater than the average of crossbred ewes by Dorset (242), Texel (228), and Montadale (252). Crossbred ewes by Finnsheep were 32-percent more productive, on average, than crossbred ewes by Dorset, Texel and Montadale.
In the spring breeding flocks, mature Romanov crossbred ewes (312 pounds) produced 55-percent more lamb weight than crossbred ewes by Finnsheep (201) and 110-percent more weight than the average of crossbred ewes by Dorset (171), Texel (117), and Montadale (157). The advantage of Finnsheep crossbred ewes relative to Dorset, Texel and Montadale crossbred ewes averaged about 36 percent.
Whereas differences among young Dorset, Texel and Montadale crossbred ewes in total lamb weight in fall breeding were minor, mature Texel crossbred ewes were considerably less productive in spring breeding. Considering these and other research results, Texel rams should be used as terminal sires to complement characteristics of crossbred ewes in terminal crossbreeding systems. The appropriate use of Dorset and Montadale sheep is likely for crossing with prolific breeds to make crossbred ewes. Recognizing this crossbreeding role, the development and application of appropriate selection procedures by producers of purebred Dorset and Montadale sheep would improve the usefulness of the Dorset and Montadale breeds for commercial producers.
Romanov and Finnsheep should provide the reproductive foundation for maternal lines used in terminal crossbreeding systems. As the number born to purebred Romanov and Finnsheep ewes is often too high for practical use by commercial producers, these breeds are typically used to produce crossbred ewes. The crossbred ewes can be produced by first cross (F1), rotation, or composite mating systems so that breed composition is optimized to match production resources such as labor, facilities, land, feedstuffs, managerial skill, etc. The Polypay breed is an example of a maternal composite based on one-quarter Finnsheep genetics.
Romanov crossbred sheep had superior performance for lamb survival, percentage of ewes lambing, number born, and length of seasonal breeding. In addition, stayability of crossbred ewes by Romanov was greater than Finnsheep crossbred ewes. Two issues with Romanov bear attention. First, the behavior of purebred Romanov ewes in intensive production situations is often described as ?flighty.? Second, decreased wool and pelt values are associated with this breed. Nonetheless, we strongly recommend greater industry use of Romanov crossbred ewes as maternal lines in terminal crossbreeding systems, especially for annual or accelerated production systems that breed in the spring. Research is underway at MARC to evaluate the Dorset, Rambouillet, Dorper, and Katahdin breeds for their ability to complement Romanov genetics as crossbred ewes in fall- and spring-breeding production systems.