RECIPIENT SELECTION

The selection of recipient cows is nearly as important to the success of an embryo transfer program as the selection of donor cows.  The recipient will have a profound effects on several aspects including conception rate, calving success, calf performance and cost.  

 

Recipient size

Each recipient cow must be of sufficient size and conformation to reduce the chances of calving difficulty upon delivery of a term calf.  Upon initial selection of a group of recipients one usually must choose the best prospect by eyeballing them.  It is essential to develop a feel for recipient frame size, weight, age and general "quality" upon this initial inspection.  Recipient size should approximate that of the donor animal if possible to reduce the chances of dystocia due to calf / recipient size mis-match.  A person should select the best and healthiest recipient, even if a premium price is involved.  It is silly to go to the expense to flush a donor, get a pregnancy and then on delivery loose the calf due to dystocia or inability of the recipient to otherwise rear her calf.

 

Some of the factors that should be considered are:

General size and condition

It is very difficult to say exactly what height and/or weight a recipient should be.   We have not established a minimum height, frame score or weight for the recipients.  We expect to select the best cows available, based on size and productivity for use as recipients for the embryos. 

 

Body condition scoring

Post partum cows that are to be used as recipients should calve with a body condition score of at least 5 and maintain a score of at least 4 at breeding time in order to achieve adequate success in estrus synchronization and conception.

 

Pelvic size

Pelvic measurements may be taken on recipients, especially if heifers are used, in order to eliminate those that will require excess traction or cesarean section to deliver a healthy calf.  The cross sectional area and shape of the pelvis in a heifer (or cow) and the size and shape of the calf at birth are equally important factors relating to calving ease.  Typically a 2 year old Angus heifer (20 to 24 months of age) will have a pelvic diameter of 275 sq. cm. at calving time.  An Angus cow will usually have a pelvic area of at least 325 sq. cm.  Typically a 2 year old Holstein heifer (24 to 28 months of age) will have a pelvic diameter of 300 sq. cm. at calving time.  A Holstein cow will usually have a pelvic area of at least 350 sq. cm.  If a projected minimum pelvic area of 270 sq. cm. at calving time is used as a selection criteria, it should be possible to limit severe calving difficulties for average size calves (71 to 90 pounds).  Formulas are available to project the pelvic area at calving time when the actual measurements are obtained prior to breeding.

           

Calving management:

It must be anticipated that some calving difficulties will occur when these cows deliver their embryo calves.  The calving crew should not hesitate to assist the recipients in delivering their calves and be ready to perform a cesarean section if the need arises.  Under no circumstances should extremely difficult vaginal extractions with the use of a calf puller be allowed.  After serious dystocia the recipient may or may not be able to raise the calf.  If not, the calf should be raised on milk replacer as a dairy calf would be raised.  The better the selection process is in selecting recipients of adequate size and health the less difficulty there will be in calving and raising of embryo calves.

 

Since it should be anticipated that some dystocia will occur, full‑time monitoring of the recipients should be available at calving time.  When embryos are transferred into a group of cows with estrus cycles that are synchronized, the period during which calving occurs is also synchronized. This enhances the herd manager and the crew’s ability to closely watch the calving cows on a rotating 24 hour basis.  In addition, any cows that exceed their calculated calving date by more than 2 days may be induced to calve using corticosteroid and prostaglandin.  This will prevent the calf from growing any larger in‑utero prior to delivery.  With these techniques, most calving from a round of embryo transfers will occur within a 7 to 10 day period and can be highly supervised and attended.

 

Milking ability

The recipient must have adequate ability to produce milk for the ET calf.  This is determined by assessing the udder of the lactating cow and the body condition and development of calves that are currently nursing a prospective recipient candidate.  If heifers are to be used as recipients it is more difficult to assess her future ability to produce milk.  The heifers own performance at weaning time could be used as a measure of her genetic ability to produce milk.

 

Recipient's reproductive status 

Once "good looking" young cows have been selected as candidates to be recipients the next step is to put them through a chute and make the final selection of the animals based on a physical exam.  Further testing subsequent to the physical exam may disqualify the animal as a recipient, but usually these are laboratory tests and results will be pending for a week or more.

 

Each recipient must pass a physical exam of all organ systems and the reproductive tract to assure general health and sound reproductive status.  Not to be ignored is an examination of the udder for mastitis or evidence of poor milk producing capacity.

 

Recipient processing

Prior to synchronization of estrus for embryo transfer the recipients should receive all vaccinations and parasite treatments.  Thirty or more days is considered a safe interval for processing prior to the estrus that will be used for the embryo transfer.