VET VIBESEmbryo transfer
Is embryo transfer the right choice for your mare?
DR DOUG ENGLISH looks at some of the basics.A recipient mare should have had a previously healthy foal, be under 10 years old), and a proven good mother with a quiet, friendly disposition.
The first transfer of an equine embryo occurred in 1974. Embryo transfer in equines is seemingly simple and involves flushing a fertilised embryo from the donor mare while she is safely held in a crush.
The flushing fluid is collected and closely examined in a laboratory set up beside the crush, not just to find the embryo but also to determine its viability. Seven or eight days later, the recipient mare is put into the crush and the embryo, along with a small amount of the flushing fluid, is inserted into her uterine horn.
All procedures are performed through the cervix of both the donor and the recipient mare with no invasive surgery involved. In order for the procedures to be carried out efficiently and safely, a good, protected crush area is essential.
Frozen embryos
An embryo can be frozen to be inserted into the recipient mare at a later time. Such embryos can be transported long distances, thus removing the necessity for the recipient mare to be in the same location as the donor mare. Ideally, a frozen embryo should be around six days old, and the recipient mare needs to be at about the same stage in her ovulatory cycle (i.e. six days) or a few days later, when the embryo is implanted.
Success rate
Aside from any other consideration, in order for a healthy embryo to be recovered the donor mare must of course be fertile, and the stallion must have proven fertility in the breeding modality (e.g. live cover, artificial insemination) that has been chosen. When fertile mares and stallions are used, a viable embryo is recovered approximately seventy per cent of the time.
Synchronisation
If a freshly harvested embryo (rather than one that has been frozen) is being used, close attention to detail is critical in all stages of the process. Both mares must be synchronised in their oestrus cycles to ovulate at about the same time or within a few days of each other. In the recipient mare, ovulation is best a day or so later. While the donor mare should be as healthy as possible, it’s more critical to make a discerning choice regarding the recipient mare, whose health should be excellent. The size of the recipient mare is also important. She should be equal to, or bigger than the donor mare and stallion. A recipient mare should have had a previously healthy foal foals, be young (under 10 years old), be a proven good mother, and of a quiet, friendly disposition. A backup mare or mares is a good idea in case, by remote chance, two embryos are produced.
Hormone injections to stimulate hyperovulation (a multiple ovulation where both ovaries release an egg, or more than one egg is released by either ovary) have been tried but the results are inconsistent. The number of oocytes (egg cells) are generally low, unlike cattle where several viable embryos are often produced.
Pluses for embryo transfer
There are a variety of good reasons to consider an embryo transfer:
• The donor mare has reproductive problems due to poor uterine health, hormonal issues, poor placental development, or any other reason. Many such mares have a history of repeated abortions.
• A high performance mare can continue to compete and not be weighed down by carrying a foal.
• An elite mare can produce more than one foal in each breeding season.
• An older or an unhealthy mare does not have to bear the parasitism of a pregnancy which may further deplete her health.
• The risk of foaling problems in a valuable mare is eliminated.
• Embryos can be collected from mares too young to successfully carry a foal.
• Embryos can be collected from compatible endangered equid species and transferred to ordinary domestic mares.
Approximately 24 hours after fertilisation the embryo has two cells.
At approximately four days old, the embryo is now 16 cells.
The flushing fluid is examined in the laboratory to find the embryo and determine its viability.Regulations
Breed society rules are an important consideration. Restrictions may apply as to the number of foals that can be registered to each mare, or if embryo transfer is actually allowed at all.
There is an ongoing debate around this and rules are changing. In 2003, the American Quarter Horse Association removed all restrictions on the number of foals that could be registered to a particular mare in a single year, and since then the number of specialised breeding clinics has increased considerably.
Unlimited embryo transfer is allowed by the American Quarter Horse Association, the Arabian Horse Association, the American Paint Horse Association, and the Australian Stock Horse Association. However, DNA testing is required for most foals before they can be registered.
So far as Thoroughbreds go, there is no permission for embryo transfer, and only one registration per year is allowed for each mare in national Stud Books that come under the auspices of the Thoroughbred Stud Book. Further, all Thoroughbreds are DNA typed.
Weighing it up
There are a range of variables to consider – from health, practicality, and embryo viability, to the rules currently enforced by your Breed Society - before you opt for embryo transfer. But if the conditions are right, a healthy live foal might be the welcome result.
NUTRITIONGetting spring ready
Equine nutritionist LARISSA BILSTON explains what
to expect from springtime pastures and offers tips
on keeping your horse safe from potential risks.Days are getting longer and warmer, the soil is moist and spring grass growth has begun. For many, this is good news – plentiful grass means horses won’t need to be fed as much hay, and those who had trouble holding weight over winter will flourish.
But if your horse is an easy keeper, has a metabolic condition, or is prone to laminitis then the next couple of months require very careful management to maintain good health.
Spring also brings out bad or overly exuberant behaviour in some horses, often caused by excess calorie intake, high sugar intake and associated hindgut acidosis, mineral imbalance, changing levels of reproductive hormones and mycotoxin ingestion.
Weight gain & laminitis
Most pasture plants produce lush green growth during spring provided there is adequate rainfall. Horses consuming large volumes of these highly palatable pastures will gain weight and add to their fat stores. If your horse is overweight but not insulin resistant or dangerously obese, you may be able to achieve weight loss without removing them from pasture.
Obesity increases the likelihood of developing Equine Metabolic Syndrome (EMS), a condition that affects the body’s ability to use and store blood sugar, often leading to insulin resistance (IR). Note that some horses with Cushings also have IR.
By far the most common cause of pasture associated laminitis is a spike in blood insulin levels. This is triggered by eating grass, hay or hard feeds high in sugar and starch. During spring and autumn, pastures are naturally high in plant carbohydrates (sugars or starches), putting insulin resistant horses at high risk for laminitis.
When sugar levels increase suddenly, or the horse gorges on lush pasture, digestive upsets can occur as sugars that aren’t absorbed in the small intestine overflow into the hindgut where they are fermented by gut microbes. This produces more and different organic acids to those produced by fibre fermentation, which can cause gut pain, diarrhea, hindgut acidosis and dysbiosis (a change in the microbial population) any of which can affect behaviour and may lead to colic or laminitis.
Managing dietary ethanol-soluble carbohydrates (ESC) and starch is important for laminitis-prone horses even when they are not overweight. And if they’re insulin resistant due to EMS or Cushings then you need to be even more vigilant.
Obese horses, those with active laminitis and all horses with IR should avoid pastures with ryegrass and clover and usually need to be removed from all pasture during spring and autumn, or anytime that pasture plants are stressed. Grass can become stressed during drought or waterlogging, frost, herbicide application or severe nutrient depletion. Use yards or laneway systems without any grass, especially very short grass plants or runners and feed a controlled amount of ‘safe forage’ with salt and a concentrated mineral balancer.
Courtesy of FarmalogicTo encourage non-lame horses to move more, position multiple hay nets at opposite ends of the area to water. Laneway systems, especially those that create a loop, are particularly effective at encouraging exercise.
It is important to restrict intake to 1.25 to 1.5 per cent of bodyweight which equates to around 7kg of hay for a 500kg horse or 3.5kg for a 250kg pony. ‘Safe’ hay for IR horses and for weight loss is low in sugar and starch levels. Ideally, choose hay which has been analysed and has a combined ESC + starch value of less than 10 per cent.
Although you can’t pick a suitable forage just by looking at it, the safest forages are rapidly growing, mid-length leafy grasses of native species or lower sugar introduced grasses. Avoid pastures or hay made from high production grasses such as clover and ryegrass and do not feed cereal (oaten, wheaten) hay or chaff. Limit lucerne hay to no more than 30 per cent of total daily intake. Do not give access to very short pastures (e.g. mowed or over-grazed) or grass carrying filled seed heads.
Courtesy of FarmalogicThe levels of starch and sugar become more concentrated later in the day as the sugars from photosynthesis accumulate. Stressed plants also accumulate carbohydrate as they experience slower growth. Although some plant species are more likely to be lower in starch and sugars, these levels change throughout the day, from day to day, week to week and across the season.
If carbohydrate levels of hay are unknown, soak in warm water for 30 minutes or cold water for 60 minutes to remove soluble sugars. Drain and discard soak water before feeding. Remove and discard any uneaten hay at least every 12 hours to avoid mycotoxin contamination. Soaking hay can reduce water soluble carbohydrates by 30 per cent but also removes some minerals, which need to be replaced with a quality, concentrated mineral balancer.
Provide a mineral supplement to top up and balance the levels in your horse's pasture. An overweight horse needs roughage, salt and minerals, but don’t feel that you have to give a ‘laminitis safe’ hard feed which, although low in sugar, is nevertheless adding calories that an overweight horse does not need. A handful of damp lucerne chaff, beet pulp or copra to act as a carrier for salt and a mineral balancer is all that’s required during weight loss.
Planting safer pastures
Successful long-term management of metabolic and easy-keeper horses can be improved by replanting with horse friendly lower sugar/starch pasture varieties:
In temperate zones
Choose a mix of slower growing, higher fibre, lower nutrient varieties such as Cocksfoot, Browntop Bentgrass, Yorkshire Fog, Crested Dogtail, or Prairie Grass. A good variety of Australian native grass seeds are now available but these plants aren’t always as resilient under hooved animals and heavy grazing as the introduced species. Look for Wallaby Grass, Native Wheatgrass, Native Bluegrass and Weeping Grass as these are amongst the best suited to grazing.
In tropical zones
Many tropical pasture grasses contain high levels of oxalates which bring their own challenges with managing horse calcium levels to avoid bighead disease. Rhodes is considered low oxalate, with under 5g oxalate/kg DM (dry matter), whilst Teff is considered moderate oxalate, falling in the 5-10g oxalate/kg DM range. High oxalate grasses such as setaria, buffel, para or signal grass contain 15-75g oxalate/kg DM.
Rhodes Grass is a high producing, low oxalate C4 grass preferred for planting horse friendly pastures in the tropics and subtropics, with Bluegrass, Native Wheatgrass, Mitchell Grass, Kangaroo and Wallaby Grass also well suited.
Macromineral balance
During spring and autumn, rapidly growing, heavily fertilised or stressed grass may become high in potassium and nitrate and low in sodium, which can have a dramatic effect on electrolyte balance and metabolism in horses, potentially leading to colic, grass-affected behaviour, grass tetany or grass staggers.Manage overweight (but not IR) horses by:
• Removing excess calories from the diet by cutting hard feeds back to just a token amount to carry the necessary mineral supplements.
• Limiting the quantity of grass consumed with a grazing muzzle or by dividing the paddock into strips or small sections with moveable electric tape. Do not regraze sections until growth is at least 15cm high. If using a grazing muzzle, keep it on at least 90% of the time the horse is at pasture, to prevent compensatory gorging while muzzle is removed. (A horse can eat a full day's worth of food in just four hours!).
If your horse does not lose weight with these measures, lock your horse off pasture to give total control of the entire intake.
