The terms “artificial” or “advanced” breeding are used to describe a variety of techniques which aim to advance genetic improvement and reproductive efficiency by selecting the best animals to breed from and optimising their use. In livestock, these techniques are not used to treat infertility but instead aim to speed up natural processes and are quite separate from technologies such as cloning and gene editing.

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Advanced breeding techniques also have a part to play in disease control, animal health and welfare, rare breed survival, efficient food production and on-farm safety as we will discuss later. In cattle and sheep, commercially available advanced breeding techniques include Artificial Insemination (AI), Embryo Transfer (ET) and In Vitro Production (IVP), but let’s review natural breeding first.

Natural breeding – key points

  • Sheep are seasonal breeders, reproductively cycling with the reducing day length of Autumn in the UK (with a few breed exceptions). 
  • One tup (ram) may be expected to mate between 40 and 80 ewes in a breeding season. Each pregnant ewe should give birth to between 1 and 3 lambs (usually!). 
  • Cattle may breed at any time of the year although in the UK we often work around Spring or Autumn calving periods for beef herds. 
  • One bull may be expected to mate around 35 cows per breeding season depending on various factors such as bull age, area of ground to cover, number of weeks run with cows etc. Most cows will produce a single calf per year.
  • Pregnancy is most likely to result from animals mated close to ovulation (when the egg is released from the ovary). During natural breeding this occurs through a combination of natural heat detection by the tup/bull (detecting when the female is most fertile), and because multiple matings usually occur during the fertile period.
  • Genetic gains are fairly slow with natural breeding so moving a herd/flock towards increased efficiency or towards a preferred type, can take years or even decades. Using a beef herd as an example, the single calf born to one particularly good cow bred naturally this year, will only join the breeding herd in another 2-3 years’ time. That is assuming the calf was female, stayed healthy and accident free, and is suitable for breeding. 
  • In most herds and flocks, replacement females are kept for breeding but this means that related breeding males i.e. the stock bull/tup, cannot continue to be used across their offspring in 2 years’ time, so an additional, unrelated bull or tup must be bought. 

Artificial Insemination (AI)

Artificial insemination has been used in UK cattle since the 1930’s and involves collecting semen from a male and placing it directly into the uterus of a fertile female, hopefully resulting in a pregnancy. In cattle, this semen is placed non-surgically, via a thin tube passed through the vagina and cervix. In sheep in the UK, insemination is usually carried out using surgical laparoscopy (better known as keyhole surgery) as this gives better pregnancy rates. This is a quick process, carried out under anaesthetic, however it is more invasive than the non-surgical technique in cattle. 

Semen collection and analysis

Semen is usually collected by having a teaser female present, that is a fertile, cycling ewe/cow that is in heat i.e. sexually receptive. This encourages the bull or tup to mate but, with a little timely intervention, he can be redirected so that semen is collected into a specifically designed chamber. The semen is then evaluated under the microscope, diluted and (unless being used freshly) frozen in straws or pellets. One collection can yield in excess of 200 straws from a bull and up to 50 doses from a tup (ram).

Sometimes, tup (and even bull) semen is collected by electroejaculation, using rectal electrodes to stimulate the spinal nerve reflex. However, with modern understandings of animal welfare this is increasingly uncommon and is usually reserved for situations where normal collection options are for some reason impossible.

Insemination

Beef cows and sheep that are to be inseminated are often synchronised first, allowing AI to be carried out when across a whole group at the optimum time during the reproductive cycle. Most commonly this is achieved using a hormone releasing device placed into the vagina for around a week. The subsequent removal of this hormone source results in ovulation occurring within a fairly predictable timeframe thereafter.

AI can be used in groups of synchronised dairy cattle too, but the technique is commonly used here based on detection of natural heats (i.e. not synchronised), inseminating individual animals rather than groups. Technologies such as milk progesterone testing are available to aid the stockperson or AI technician with heat detection but this is still a labour intensive process requiring round the clock observation and attention to detail. 

Embryo Transfer (ET)

Commercial ET became available in the UK during the 1980’s. An embryo transfer donor female is treated with hormones similar to that of a synchronisation programme but is given an additional treatment to create the release of several eggs from the ovary at the same time. This is usually followed by artificial insemination which aims to create several fertilised embryos within the donor animal. A few days later, embryos are collected from the uterus of the donor by a process known as flushing. Each embryo can then be assessed and graded under the microscope, and thereafter implanted into recipient females, effectively creating surrogate pregnancies. 

As with AI, embryo recipients are often synchronised, enabling a group to be implanted at the same time, when pregnancy is most likely to succeed, but embryos can also be stored, then transferred on an individual basis.

In vitro production (IVP)

To my knowledge, this technique is only commercially available in cattle in the UK at the moment although one part of the process, IVF (in vitro fertilisation), is available in sheep. IVP is similar to embryo transfer, however eggs are collected from the donor animal before insemination rather than after. Insemination then takes place in the lab (in-vitro), meaning that individual eggs from one collection may be inseminated using semen from different males. After insemination, the fertilised eggs are matured in the lab until they are ready for implantation into recipient (surrogate) females. 

Why Use Artificial Breeding Techniques?

It would be fair to say that while all this sounds like pretty amazing science, it could also be viewed as a lot of cost, hassle and unnecessary medical intervention. So why use advanced breeding techniques at all?

  • A compact calving/lambing period can be created by synchronising breeding females.  This can help on farms of all sizes to optimise use of resources e.g. housing, feed and labour. 
  • Synchronisation also results in more even batches of youngstock to manage which is advantageous again in efficient housing, feeding, labour,  healthcare (e.g. vaccination and worming), weaning and at sale time. Avoiding a large spread of ages within youngstock groups also helps to reduce the incidence of many diseases such as pneumonia and scour.
  • An early breeding season in sheep as a result of synchronisation and AI gives early born lambs that can be weaned and sold earlier too, giving some competitive advantages.
  • Access to superior genetics is perhaps the most commonly considered advantage of AI and ET, as both give stock keepers access to a global market, as well as to genetics of previous years. Semen and embryos can be used freshly after collection but can also be frozen, stored, transported around the world, thawed – sometimes decades later – and then implanted. AI gives that access to male genetics but with ET, female genetics can also be brought in.
  • Multiple sires can be used across one breeding female group in the same year using AI, allowing the best matches to be made of male and female genetics. Most farms would not have the resources to run so many different female groups and multiple tups/bulls to achieve this naturally, and similarly it is unlikely to find one male that will suit all the breeding herd/flock. 
  • Future breeding choices may be informed by experimenting with multiple breeds/genetics across the herd or flock using AI first, allowing informed choices to be made if/when buying in males.
  • Rare breeds can benefit hugely from advanced breeding techniques, moving semen and embryos around the world to maximise the use of a very small genetic pool. Additionally, genetic lines can be protected through semen or embryo storage, in case of individual accident/illness or flock/herd disease outbreak.
  • Disease risk can be lowered using AI and ET as the live animal is not brought onto farm and the health status of the donor animals can be assured. For example, buying animals from a high-risk TB area may be unadvisable to most, but moving semen or embryos removes the risk. Care must be taken with this however as some diseases may be transferred even in frozen embryos so careful screening is essential.
  • Disease outbreaks involving venereal (sexually transmitted) diseases such as campylobacter can occur, and AI can be a significant management tool in affected herds. 
  • Injury or illness affecting breeding males in the run up to mating can be disastrous. After illness, sperm production can take 6 weeks or more to return to normal, delaying mating and reducing overall pregnancy rates.
  • Number of offspring per breeding animal in one year is much increased using advanced breeding techniques, allowing for rapid genetic improvement within a herd. 
  • Whilst costs incurred using advanced breeding techniques may be more up front and visible (vet visits, medicines, AI/ET charges, semen costs etc), this must be weighed against the costs of purchasing and keeping breeding males including year-round housing/grazing, feeding, vaccinating, foot trimming, healthcare and depreciation in value. Currently this bull cost is estimated at approximately £32 per cow per year (based on average values of £6K purchase price per bull, lasting 4 years in the herd and serving 35 cows per year), so natural service is probably more expensive than many consider.
  • Bull numbers may be reduced, by using AI. Assuming a reasonable conception rate of 60% to one fixed time insemination in synchronised beef cows, a farm previously running 3 bulls could potentially reduce only 1 bull. Furthermore, this bull could last many more years on the same farm if only calves born to AI pregnancies (i.e. not his offspring) are kept for breeding.
  • Safety can be improved for all those working on farm, by reducing the number or need for bulls. Bulls are not always the easiest to handle, especially on smaller holdings that may have more limited housing and handling facilities. Small holdings may choose not to keep a bull at all in fact, and instead use AI across the entire herd.
  • EBV’s (estimated breeding values) are available for most commercially available bull semen, meaning selection can be made for ease of calving or low calf birth weight but with good calf growth rates. This can reduce the need for interventions such as assisted calvings or caesarean sections, protecting animal welfare.
  • EBV’s can also guide genetic gains, for example a farm producing calves for meat production may select semen from a bull whose offspring are expected to have greater muscle depth, or a dairy farm may select a bull with higher milk production EBV’s.
  • EBV’s are available for some tups too, indicating values such as litter size, mature weight and maternal ability (related to milk production)
  • Sexed semen is available. Collected semen can be screened to differentiate between sperm carrying X or Y chromosomes. Individual sperm carrying the undesired chromosome can then be removed from the sample, leaving a higher chance of the pregnancy producing offspring of the desired sex. This “sexed semen” is particularly used in the dairy industry, where male dairy bred calves have little to no value, but it can also be advantageous for small herds looking to increase breeding female numbers rapidly or for breeders looking to produce specific male genetics.

Considerations with Artificial Breeding

With all the possibilities that artificial breeding techniques bring, we must be careful not to be blinded to the potential implications of manipulating nature. Yes, there is incredible potential for rapid genetic gains to be made but it would also be easy to reproduce hereditary defects just as quickly. 

Animal welfare may be improved by using semen from easy calving bulls to minimise interventions, but the opposite effect may occur if choosing the wrong bull when looking to make rapid gains in calf muscle depth for example. This can happen with natural breeding too of course, but using different AI semen next year may be a lot easier than purchasing a better bull. 

Welfare must also be protected in terms of the medical interventions required to carry out advanced breeding techniques. In the UK, Organic producers may use AI but are prohibited from administering hormone treatments to manipulate breeding cycles, and from using embryo transfer. 

Non-surgical AI to an observed heat may be as close to natural as artificial breeding can be, but in sheep in particular, pregnancy rates can be significantly higher using surgical AI after synchronisation. Surgical egg or embryo collection, AI or embryo implantation is not to be undertaken lightly especially, as this does not directly enhance the health or welfare of the individual undergoing the procedure. For this reason, these techniques are not permitted in Scandinavian countries at all, so a non-surgical AI to natural heat is the only technique used there and studies are ongoing to determine if/how comparable pregnancy rates can be achieved with this less invasive technique.

Artificial breeding techniques conclusion

Advanced breeding techniques can open a global market and significantly improve or preserve livestock genetics, increase production efficiency and improve safety, without the need for live animal movements and the disease and welfare risks associated. Animal health and welfare can benefit significantly in some circumstances, but it is our responsibility as stock keepers and vets to employ these techniques thoughtfully and carefully, with animal health and welfare remaining a priority. 

If you think advanced breeding techniques may be beneficial on your holding, speak to your vet now to discuss the possibilities. Remember also that good animal health and management are the foundation for success with any breeding approach, natural or artificial, and your vet is ideally placed to advise on all aspects of this too.

Further reading