bovine embryo transfer - xlvets · 2013-03-21 · bovine embryo transfer facts rf it takes four to...

Bovine Embryo Transfer

FACTS

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RRFF

It takes four to six months for the eggs in a cow's ovaries to grow to their ovulatory state. Managementof the cow during this period is critical in determining their ability to yield transferable embryos thatbecome established pregnancies. Later, it takes another six weeks for the embryo to implant into thedam. So again management during this period is critical. Six months before you plan to start your ET, itis wise to book a half hour session with your vet to talk over your plans

Some facts on fertility and bovineembryo transfer (ET):

About 20% of donors fail to yield any transferable embryos at all

The average yield of embryos is fiveper flush - but that can be made upof several ones and twos followedby a 12.

Perhaps ET results are mirroringnormal reproductive performance -conception rates of Holstein cowsare reported to be declining at thealarming rate of between 0.5 and 1per cent every year, although heiferconception rates seem to be holding.

Improving fertility and ET success Be warned there is no quick fix forimproving fertility and ET successrates, but paying detailed attention toall areas of cattle management willminimise those stresses mentionedabove.

It takes four to six months for theeggs in a cow's ovaries to grow totheir ovulatory state. Management ofthe cow during this period is critical indetermining their ability to yield transferable embryos that becomeestablished pregnancies. Later, ittakes another six weeks for theembryo to implant into the dam. Soagain management during this periodis critical.

Six months before you planto start your ET, it is wise tobook a half hour sessionwith your vet to talk overyour plans.

Obviously, nutritional management ofboth the donor and recipients arecrucial to the success of ET. A fulldietary and mineral analysis for thecattle concerned is recommended,not forgetting to look at the mineralspecification of any water suppliedfrom a bore hole.

For six weeks before and after flushing, management needs to bekept steady with no major changesduring this period. Ideally, the cow'sbody condition score should be 2 to2.5 and rising during this time.

Pre-ET testing for all diseases thatmight impact on results, plus vaccination if required means thatplanning must begin a long way inadvance. The list of diseases to lookfor is getting longer and includesBVD, leptospirosis, IBR, Johne's and neosporosis. Again your vet will be ideally placed to help adviseon the results.

Remember, both donors and recipients will need testing.

StressPoor fertility and reproductive performance can be attributed to stress. This can be caused by a number of factors:

Genetic stress through inbreeding and continual selection for productionimprovements

Production stress associated with higher and higher yields

Nutritional stress and the early lactation energy gap

Environmental stress

Disease stress with mastitis, lameness and infectious disease all havingmajor impacts on fertility

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XLVets Bovine Embryo Transfer RRFF

Flushing the donor cow

Flushing the donor cow should notbe done too soon after calving. Thecow needs to be away from her periodof maximum stress. Observation of a couple of standing heats with a normal inter-heat interval would be a good indication that reproductivecapacity is getting back on track.

Super-ovulation

Donor cows are normally super-ovulated mid-cycle with a four dayseries of injections. The vet shouldexamine the donor including a scanof the ovaries a few days beforethese injections start to check all iswell, and a good corpus luteum oryellow body is present on one of thedonors' ovaries.

This is normally done three daysbefore the super-ovulatory programme is due to begin. At thesame time, the cow's follicular wave is re-programmed by giving her asmall shot of gonadotrophin-releasing hormone to make sure there is nodominant follicle present at the timethe super-ovulatory injections start.

It is also useful for the number of follicular structures on the ovaries tobe counted at this point to predictpotential super-ovulatory response.

Usually about 80% of the folliclesseen on the ovaries at any time areactually on the way out, but 20%should be capable of joining thesuper-ovulatory wave.

Recipients

When flushing a cow for the first time, bearing in mind the costs involved, it isadvisable to prepare three recipients to ensure at least two are capable of receiving an embryo on the day. Often poor quality embryos are flushed and whilethey could not stand freezing they may have a chance if they are implanted fresh.The better quality embryos can be frozen for implantation on another day.

The next time the cow is flushed then line up as many recipients as there arefrozen embryos, so either way you know that all recipients will be implanted.

Cows that flush well once will flush well again, and those that do not will oftendisappoint again.

Fresh embryos should go into maidenheifers. After this, frozen embryos can beput into recipients seven days after anobserved natural heat. This may only bepossible if your ET operator is reasonablyclose. Mature cows are fine but wherepossible try and use younger ones withgood reproductive track records.

ET operators

There is probably little variation in theresults of established operators acrossthe country. Much bigger differenceswill be down to the on-farm factorsdescribed above. It is probably best touse the nearest operator, especially ifthey can offer to put your embryos inafter observed heats.

Pregnancy diagnosis

Pregnancy diagnosis should be leftlater than for normal pregnancies justto avoid the disappointment of latefoetal death. The foetus can be sexscanned between days 56 and 65 ofpregnancy as by then subsequentlosses should be minimal and it canbe useful to know whether a bull ora heifer ET calf is expected.

Reproduction and Fertility

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