As sheep breeders, we aim to produce large numbers of quality sheep and make real genetic advancement. Not all breeders agree as to what method is best. Essentially there are 3 ways of producing quality lambs.
Naturally Here, quality ewes are mated to the best ram available. Ewes give birth usually in their second year of life, after an average gestation of 145 days. Most ewes can be expected to lamb each year up to about 6 years of age and less reliably after that. On average, about every third gestation in many breeds produces twins. Using these figures, each ewe would on average produce six to eight lambs before 6 years of age. As just under half of all lambs born are ewes, statistically three of these are likely to be ewes. As these young ewes are bred from quality mothers, mated to the best ram available, their standard, in turn, should be high. A quality ram should always be able to produce a son better than himself. With the best sons of the original ram being incorporated into the breeding plan or new rams being imported into the program, gradually the flock quality is increased.
Upgrading In this process, the best possible ram is mated to many ewes, often of variable quality. This is done repeatedly, gradually elevating the overall standard of the flock as the better individuals are retained. Quality steadily rises over the generations. This system does have particular application where an exotic breed is trying to be established. It is also useful when quality ewes are limited or finances restrict their availability. It is the preferred method for some breeders. The main disadvantages of this system are that it takes years and produces significant numbers of lesser value animals. To increase the numbers of a rare breed such as a Persian, for example, the process essentially works like this. 1/Ewes, usually Dorpers, are chosen to mate to a Persian ram. As Dorpers are approximately half Persian, they represent the first cross (or F1 Persian hybrids). If 20 Dorper ewes (for example) are mated to a Persian ram, on average this is likely to produce 10 ewe lambs (which are second-cross, i.e. F2 Persian hybrids) and 10 ram lambs. The 10 ram lambs are discarded from the breeding program. 2/ The 10 second-cross (F2) ewe lambs are then mated to another Persian ram. On average, this is likely to produce 5 ewe lambs and 5 ram lambs. The 5 ram lambs are discarded from the breeding program. 3/ The 5 third-cross (or F3) ewe lambs are then mated to another Persian ram. On average, this produces 2-3 ewe lambs and 2-3 ram lambs. The ram lambs are discarded from the breeding program. 4/ The 2- 3 fourth-cross (or F4) ewe lambs are mated to a Persian ram . On average, this produces 1 or 2 ewe lambs and 1or 2 ram lambs. The ram lambs are again discarded from the breeding program. 5/ The 1 or 2 fifth-cross (or F5) ewe lambs are submitted for assessment and may be considered for registration as a Persian sheep. The ram lambs are discarded from the breeding program. If each ewe lamb is mated to produce a lamb at around her first birthday, the time involved to produce the one or two F5 ewes is 4 years.
The principal costs involved are: a/ purchase of 20 Dorper ewes – sound, well-structured 2 to 4 year old ewes in good health from a recognised breeder = $ 7000, b/ purchase of Persian rams – 3 or 4 (ideally) would be required; these would need to be of a reasonable quality, otherwise the entire breeding program would be a waste of time. $500 each (very conservatively) approximately = $1500 to $2000 c/ cost of feeding, general care, worming, vaccination of all sheep involved—very hard to quantify but over 4 years $2000 would be extremely conservative to produce the 40 lambs involved and care for the mothers.
Upgrading to increase numbers of an uncommon breed produces large numbers of crossbred animals and very low numbers of “purebreds”. In the example above, statistically 18 to 20 crossbred rams would be produced, and 18 to 20 crossbred ewes would be produced. One to two 97% pure Persian ewes are produced and one to two, 97% pure Persian rams are produced.
Another potential disadvantage is that gene sharing is not always even. If a registered Persian ram is crossed with a ewe of another breed, the lambs are not all 50% Persian. This is the average amount of gene sharing and is the level found actually in only 1% of lambs. In reality, the lambs are anywhere between 1% and 99% Persian. When you get to F5, the lambs in theory could be anywhere from 5% to 95% Persian. Many of these F5 crossbred animals will look like Persians but as many genes are carried recessively they will not be visible phenotypically. These recessive genes will become apparent as these animals are bred from, particularly if these animals are mated together.
Based on the above figures, the two or three Persians produced would cost about $11,000 to produce. Statistically, half would be ewes. For this cost, only one F5 ewe may be produced. This of course makes no allowance for the breeder’s time and ignores unpredictable problems such as the death of a ewe or lamb. This cost is offset by the sale of the one or two F5 rams produced, resale of the Dorper ewes, resale of the purchased Persian rams and disposal of the crossbreds.
Embryo Transfer (ET) The aim of this technique is to produce large numbers of lambs from ewes of exceptional genetic quality. ET allows for very rapid genetic advancement. In this technique, initially a progesterone vaginal implant is inserted into all of the donor and recipient ewes. This serves to synchronise the reproductive cycles of all of the ewes. In the donor ewes, after approximately 10 days, injections of a hormone, PMSG , are given twice daily. This hormone stimulates the development of many follicles on the ovaries. A single injection of another hormone, HCG, is then given, which stimulates these follicles to ovulate. At this time, the vaginal implant is removed from all ewes. Two days later, the donor ewes are inseminated. This is not allowed to occur naturally. Normal mating may only fertilise 60% or less of the ova. Obviously, as many embryos as possible are wanted. Rams are artificially ejaculated. Collected semen is placed in an extender fluid. Each donor ewe is anaesthetised and the semen deposited via endoscope directly into the fallopian tubes where fertilisation occurs. A week later, the donor ewes are again anaesthetised. This time, guided by an endoscope, the embryos are flushed from the uterus into a Petri dish. The vaginal implant has prepared the recipient ewes hormonally so that their cycles match those of the donor ewes. After microscopic examination, embryos are selected for transfer. The recipient ewes are anaesthetised and two donor embryos are place endoscopically into the uterus of each ewe. Most of the donor embryos then implant into the uterine wall of the recipient. Of course, the recipient ewe ova are not fertilised and therefore fail to implant. It is best if the recipient ewes are non-maiden robust healthy ewes that have been fed appropriately for pregnancy.
The recipient ewes then carry the embryo/foetus/lamb to term, give birth naturally and raise the lamb as their own. On average, six lambs are obtained with each flush but more can be obtained. Occasionally, over 40 can be obtained. It is unusual to get less than three. After flushing, the donor ewes can be returned to the paddock, run normally with a ram and give birth to their own lamb naturally. The technique in sheep employs the same technology and methods used in IVF in people.
The obvious advantage of ET is that large numbers of superior-quality sheep are produced quickly. On average, six lambs can be produced from one ewe in 5 months. With natural breeding, this would take at least 5 years. Cost is a factor. If six lambs are produced, each lamb costs approximately $400. If the value of the sheep produced exceeds this, then the procedure can be financially justified.
Personally, Coolibah Persian Sheep Stud has been able to get up to 24 lambs in 6 months from one ewe. This was the case in our dilute tricolour ewe Coolibah Pearl. Half of these lambs were blue and this single flush essentially established this colour of Persians in Australia. One of these embryos is our well-known ram Coolibah Berwick (pictured). 24 embryos represent more than twice a good breeding ewe’s entire life-time lamb output –and all obtained in under 6 months.
Embryo transfer is a widely practiced veterinary procedure. It does, however, provoke strong comments from some hobby breeders.
One post on Facebook several years ago stated “There is no need to put your ewes through expensive painful vet procedures just to boost your "hobby" flock numbers as some breeders do”. The post went onto say that the practice is cruel, that sheep should be cherished and not used as breeding machines, and that quality not quantity is the aim so upgrading is a better technique.
Embryo Transfer is a standard veterinary practice that is not regarded as cruel by the RSPCA or the Australian Veterinary Association. It is important to remember that embryo transfer in sheep and IVF in people use similar methods and techniques. Obviously, IVF is not regarded as “cruel” in people. It is important to remember also that, if not for ET, then many of the genetics in Australia today would not be present. The statement “quality not quantity” makes no sense when talking about upgrading. Exactly the opposite is achieved as larger numbers of poorer quality genetic animals are produced. Breeders can choose for themselves what methods work best for them. Often an integrated approach is the answer.