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Most sheep are seasonal breeders as a result of their sensitivity to the changing daylength and are most fertile in the fall. However some breeds are less seasonal or have extended breeding seasons like the Dorset Horn, Merino and Rambouillet. This makes these breeds more suitable for an accelerated lambing program.
Accelerated lambing refers to ewes lambing more frequently than once per year. Such intensive reproductive management can reduce maintenance costs of breeding stock per offspring reared, will often increase net return and will provide a more uniform supply of lamb throughout the year. It is not possible at present to increase the frequency of lambing and avoid the complication of seasonal restrictions. However, a knowledge of reproductive physiology, selection, and useful management practices has led to successful intensive management systems under some conditions. These systems usually require higher resource and management inputs and should be considered only when a producer can provide skilled management, as well as adequate nutrition for the ewe and the lamb. The accelerated lambing systems most commonly used are three lamb crops per ewe every two years and five lamb crops per ewe every three years (STAR breeding program).
The three lamb crops per ewe every two years system is an attempt to have an average lambing interval of eight months, or 1.5 lambings per ewe per year. This system is generally characterized by a fixed mating and lambing schedule such as May mating/October lambing, January mating/June lambing and September mating/February lambing. It can also be modified slightly to 7-7-10 or 7-8-9 month intervals to better fit climatic, management and feed resources.
Some producers have developed a variation of this system that provides for a more continuous lambing schedule. The flock is divided into four groups on a staggered eight-month lambing interval schedule. If a ewe fails to conceive with her group, she has a second chance to mate two months later. Producers using this staggered two-month interval schedule have reported up to 40 percent increase in lamb production over previous conventional systems. They also suggest that by dividing the flock into four groups substantial savings in facilities costs are possible. Increased management attention can be given to critical lambing and early lactation periods since all ewes are not lambing at the same time.
This system was developed by Cornell University and is often called the STAR system. It was developed to maximize production of market lambs on a continuous basis year-round basis. The calendar year is divided into five segments (the points of the star) that each represent one-fifth of a year, or 73 days. The star can be rotated to give the most suitable dates. Two-fifths of a year is 146 days, which is approximately the gestation length of a ewe. There are five lambing periods in each year. There are always three groups in the flock; breeding and pregnant ewes and the rams, lambing and/or lactating ewes and their lambs, and growing lambs (market and replacements). These three groups are kept and managed separately.
If a ewe skips a breeding, she can still lamb three times in two years. The STAR system is a natural system that does not use hormones or light control to achieve out-of-season breeding. It involves selecting sheep that breed during any season of the year. More detailed information on this system can be found on Cornell’s website.
For the above systems to work, out-of-season breeding techniques must be used. These techniques assist in the shortening of the lambing period and allow the ewes to come into heat out of season so that they can be bred in the spring for an accelerated lambing program.
Important management concerns:
There are three out-of-season breeding methods:
Day length appears to be the primary factor in controlling breeding season in sheep. Day length can be artificially controlled to induce estrus and ovulation out-of-season. However, total confinement and light control are required, which greatly increases management costs and restricts feeding options.
The ram effect occurs when ewes are induced to begin cycling though the spontaneous introduction of a ram. Separate rams and ewes completely for 60 days prior to breeding. This must be complete separation of the ram and ewes – no contact, sight, sound or smell for the entire isolation period. This increases the number of ewes bred the first week of breeding.
MGA is a feed additive, containing hormone, that is commonly used in feedlot heifer rations. It is not licensed for use in sheep and requires a veterinary prescription for use. MGA is formulated into the ewe ration and is fed twice daily, with feedings as close to 12 hours apart as possible. MGA is fed for 12-16 days and five hours after the last feeding, PMSG should be given. The timing of MGA feeding and PMSG administration should be strictly followed. Rams should be introduced to the ewes 48 hours after the last feeding of MGA. A veterinarian should be consulted for full protocols. A major drawback to this program is feeding the ewes twice daily. For more information consult the fact sheet on MGA.
Vaginal sponges that contain progesterone may also be used for out-of-season breeding. On day 1, insert the sponges. On day 12-16, remove the sponges and inject with PMSG (only if out-of-season breeding). Introduce rams 42-48 hours after sponge removal. Use harnesses to determine breeding. All ewes should be bred within three days. Either leave rams in, or turn in again about 14-16 days later.
Accelerated lambing will increase lambing frequency, providing a more uniform supply of lambs throughout the year, which may result in a more even cash flow to the producer. It is possible when a number of factors are available:
For further information on accelerated lambing, contact your local Manitoba Agriculture and Food office.