Farmers Guardian, asks Mike Christie, vet at Lambert Leonard and May, how to get the most from flushing technologies.
Embryo collection in the cow is a skilled process undertaken by vets or highly skilled embryo transfer (ET) technicians.
Many farmers and breeders who flush donor cows or heifers may well be familiar with the technique and what it entails, but there are still plenty of new breeders keen to try the technology and increase the rate of genetic gain in their herd.
The flushing process starts with superovulation, where cows are given hormonal treatment to produce more eggs than normal in a cycle. Most cows will resume cyclic activity 20-30 days post-calving.
Cows require a reference heat to start the superovulation programme and this can be as early as 50 days post-calving.
DONOR cows should be examined by ultrasound before embarking on any embryo collection programme to make sure the uterus is clean, free of infection and cycling normally with no cysts.
Mr Christie says: “Ideally the donor cow should be rescanned a week after the reference heat to make sure there is a corpus luteum and no cystic structures.
“This is not always possible, but it can help reduce the poor responses seen in some superovulation programmes.
Some 20 per cent of flushes fail to yield viable embryos.”
Cows in poor body condition or with periparturient disease, such as LDA, retained foetal membranes or ketosis will struggle to be flushed early post-calving, he adds.
“Good dry cow management, an uneventful calving and good appetite after calving will help the uterus get back to its normal size and aid resumption of cyclic activity with healthy follicle populations.
“I find high iodine and selenium boluses in the dry period can help. The availability of ketone boluses from your vet can prove very important in preventing ketosis post-calving for high risk cows.
“If these cows are to be flushed, these boluses will have a beneficial effect on the follicle populations at 50-150 days post-calving, when embryo collections are most likely to be carried out.”
Always check with your vet if you wish to target these at risk cows as these boluses need to be administered three weeks prior to calving and are prescription-only medicines.
Mr Christie says: “I am not a nutritionist, but good consistent diets are key for donor cows.
“Try to avoid wet inconsistent forages and, where possible, carry out a forage and mineral analysis of your donor’s diet. They should not be losing too much condition.
“Donor cows should be on a consistent diet, with good energy density and mineral specification, and be achieving good dry matter intake at least five to six weeks prior to flushing to help the outcome of embryo collection.”
He advises avoiding major management changes, such as group and diet alterations, in the run-up to flushing, as this can induce stress and poor fertility performance.
Insemination is critical to the success of embryo collection, and the use of an experienced inseminator is vital, says Mr Christie.
“No semen in the correct place means no viable embryos on collection.
“Using sexed semen can be successful, preferably on maiden heifers, but generally these will yield fewer viable embryos per collection than conventional semen, as there are only two million sperm in a sexed straw versus 10-20m in conventional.”
Now all ET-born calves are required to be DNA tested, many breeders use a ‘cocktail’ of between two and four bulls over three inseminations in the programme, says Mr Christie.
“This can improve results, as there can be a bull or semen effect on the outcome of number of viable embryos.
“Typically we would hope to get five or six viable embryos from a cow and four to five from a maiden heifer on average.
“There are, of course, a spectrum of results, as donors will respond differently to each other when given the same FSH drugs.”
Breed can also have an impact on flushing success.
Mr Christie says: “It is well-recognised by ET practitioners Holsteins can yield less viable embryos compared to beef breeds.
A Swiss practitioner I met recently was getting on average more than 10 viable embryos from the Fleckvieh breed.”
The superovulation programme involves two daily injections (at least eight hours apart) for four consecutive days.
Mr Christie says: “Handling and storage of medicines is vital for success. I always recommend injections be given using 3.81cm (1.5in) 18-gauge needles to ensure a deep intramuscular injection.
“Keep any follicle superovulation hormone [FSH] in the fridge during the programme. Any left-over reconstituted FSH can be frozen immediately after the last injection and re-used at a later date.”
There are two different preparations of FSH available for superovulation, says Mr Christie.
“Responses to these can vary, so it is good to discuss with your ET practitioner prior to embarking on a programme, as changing the FSH and/or dose can influence the outcome of the result, especially if there is a history of a poor or over response on previous superovulation attempts.”
Good handing facilities for accurate injection administration should be available and the use of propylene glycol (150ml daily) during the superovulation programme can also be beneficial, adds Mr Christie.