A successful business needs to generate enough cash to cover expenses, current debt, and family living expenses, pay interest on owned and borrowed capital, maintain productivity, and earn a reasonable return for the operator. Income from sheep production is generally only part of a total farm and nonfarm income. Thus options, opportunity costs, and decisions regarding the sheep production enterprise are not isolated; they affect other agricultural enterprises. Sheep production consistently returns profits to producers, which makes it an enticing agricultural enterprise. There are advantages in raising sheep in Virginia, such as abundant, high-quality forage, moderate climate, pasture improvement, and good access to markets with high demand for lamb. The disadvantages to sheep production are unavailable and inexperienced labor and operators, predators, and inconsistent market demand and supply. Sheep producers have the opportunity to choose which lambing system fits their existing operations and lifestyle. The use of economic analysis enables operator to make sound business management decisions. To compare different lambing systems (spring, fall with winter clean-up, and high-fertility fall) in a systematic way, a simulation model was constructed with a fixed forage resource of 50 acres of pasture including typical Virginia mountain pasture plus various amounts of fescue for stockpiling. The simulation included a production calendar; nutritional requirements for ewes, lambs, and artificially reared triplets; growth rates for lambs; lambing distributions; forage growth; and enterprise budgets including income, costs, and returns. A economic analysis was performed for each lambing system with average prices or with plus or minus one standard deviation for prices of corn, SBOM, and market lambs, and price differentials for market lambs across lambing seasons. Comparisons of each lambing systems produced various results. In spring lambing, only 78 ewes could be maintained on the fixed forage resource, while the fall with winter clean-up and high-fertility fall lambing system each had 115 ewes. This result occurred because of limited forage in July and August and higher nutrient requirements for spring lambing in those months. The overall nutrient requirements were higher in the fall with winter clean-up and high-fertility fall lambing than in spring lambing as a result of the increased ewe and lamb numbers. Concentrate consumption by lambs was also greater for fall with winter clean-up and high-fertility fall lambing than for spring lambing because of the increased numbers of lambs. Because of the low number of ewes and lambs, spring system produced the most hay. Labor costs were highest in fall with winter clean-up lambing because of the two lambing seasons. In the economic analysis system, each lambing was compared. With 10-year average prices for market lambs, corn, and SBOM, high-fertility fall lambing had the greatest income ($17,467), followed by fall with winter clean-up lambing ($14,695), and spring lambing ($10,358). This result occurred because high-fertility fall and fall with winter clean-up lambing had more lambs sold at higher market lambs prices than spring lambing. With 10-year average prices for market lambs, corn, and SBOM, high-fertility fall lambing had the highest cost ($7,935), followed by fall with winter clean-up lambing ($7,360), and spring lambing ($6,084). This was the result of increased ewe and lamb numbers in high-fertility fall and fall with winter clean-up lambing than spring lambing. High-fertility fall lambing had the greatest returns ($6,210), followed by fall with winter clean-up lambing ($4,025), and spring lambing ($2,028). On a fixed forage resource, increasing fertility in fall lambing clearly results in increased returns. In this model, forage availability controlled the number of ewes that a lambing system can have because of limited summer growth and had a major impact on profits. Conclusions of Tolman (1993) differed from those found within this thesis. On a per ewe basis, she found that spring lambing to yielded the highest returns whereas this thesis found that high-fertility fall lambing yielded the highest returns. A key difference between this study and that of Tolman (1993) was after weaning this thesis feed fall lambs stockpiled fescue and she feed fall lambs feed in dry lot. / Master of Science

The objective of this study was to evaluate ewe and lamb performance in an accelerated lamb production system, and to compare the performance and lamb output between a conventional and an accelerated lamb production system. In the “Conventional” system, ewes were bred in March to lamb in August. The “Accelerated” system was based on the “STAR” system (Lewis et al., 1996), in which there were five breeding periods within each year. In the current experiment these were 14th January, 28th March, 9th June, 21st August and 2nd November. Progesterone was used to synchronise the breeding periods and during the non-breeding season, eCG was used to induce reproductive activity. Lambing began on each of these dates and weaning was 73 days later, coinciding with the next breeding period. The experiment ran over a three-year period beginning with breeding in March 2003 and was complete with the weaning of lambs from the January 2006-bred ewes. This resulted in 15 lambing and breeding periods over the three years in the Accelerated system and three lambing and breeding periods in the Conventional system. Average pregnancy rates were lower in the Accelerated system than in the Conventional system. Lamb growth rates were similar between the two systems, although lamb live weights at weaning were lower in the Accelerated system due to the age of the lambs at weaning (average = 69 vs 96 days). More lambs were born and weaned, resulting in more kilograms of lamb weaned in the Accelerated system relative to the Conventional system over the experimental period (26,200 vs 24,300 kg). Labour input was 35% higher in the Accelerated system, or 13% higher per lamb weaned. Average annual ewe energy requirements were 6% higher in the Accelerated system. Ewe energy requirements per kilogram of lamb weaned was lower (6%) in the Accelerated system due to more breeding and lambing periods per ewe per year. Laparoscopic observation of ewes’ ovaries at each breeding period revealed that most ewes had active ovaries and were therefore capable of successfully producing a viable foetus. In a subsequent experiment, blood samples were collected for analysis of progesterone concentrations from ewes bred during the spring and autumn breeding periods. Observations of data indicated that a small number of ewes conceived and lost their conceptus, or had abnormal corpora lutea. Results suggested that pregnancies were failing due to a lack of an appropriate signal from the embryo to the dam/uterus. Exposing Romney ewes to an artificial lighting regimen was unsuccessful for inducing reproductive activity during spring. In another experiment, melatonin implants administered to Romney ewes in spring and used in conjunction with eCG and progesterone, resulted in 61% more lambs born per ewe treated, compared to eCG and progesterone alone. This result indicated that melatonin implants, used with eCG and progesterone may be a suitable method for improving reproductive performance in sheep bred out of season in New Zealand. Delaying weaning of lambs and breeding lactating ewes can be used to obtain heavier lamb weaning weights in the Accelerated system. Spring-bred ewes had lambs weaned at either 69 days post partum or 90 days post partum. Reproductive performance was similar between the two groups of ewes, and lamb live weights in the later weaned group were heavier when lambs were 90 and 120 days of age. This research has shown that accelerated or out-of-season lamb production is an option for some New Zealand sheep farmers. However, the mechanisms associated with reproductive seasonality and methods of successfully circumventing this seasonality require further attention in order to achieve optimum reproductive performance.