Recipients should be large-framed, healthy, mature young buffaloes in good body condition. A minimum of two normal cycles should ideally have been recorded before use whether they will be synchronized with prostaglandins or selected from a pool of cycling animals. It has been common in embryo transfer programmes to overlook the quality of the recipients. Recipients and their maintenance represent the greatest single cost of running a commercial bovine embryo transfer programme. Culls from a breeding programme, animals in poor condition and early post-partum animals do not make suitable recipients. Recipients should not be fat and should preferably be gaining 0.1–0.2 kg per day. They should be vaccinated against the common abortion diseases.
Permanent (double) identification of each animal, meticulous record keeping, accurate heat detection, ample handling and quarantine facilities are all absolute essentials of reliable recipient management. Pregnancy rates are highest when the oestrous cycles of the donor and the recipients are synchronized within 36 hours, whereby the recipient comes in oestrus from 24 hours before until 12 hours after the donor.
The availability of synchronous recipients can be achieved in two ways: (1) a large pool of cycling females, which limits the number of donors and time when they can be collected: 5 percent of the herd will be in heat on any given day; (2) a relatively small number of recipients can be synchronized with prostaglandin F2 alpha (PGF2 alpha) or its analogues to exhibit heat the same day or just ahead of the donor. Animals with a palpable corpus luteum are injected with 25 mg PGF2 alpha or 0.5 mg PG-analogue IM and may be expected to come into oestrus in two to four days with a peak on the third day. Alternatively, all recipients may be injected with prostaglandins regardless of the presence or absence of a corpus luteum. A second injection is then given 11 days later, and again oestrus will peak on the third day after the second injection. The recipients that did not respond to the first injection, because they were in the first five days of the oestrous cycle, respond the second time as they are then in the mid-to-late luteal phase, while the recipients that did respond are in the early-to-mid luteal phase at the time of the second prostaglandin injection. (Effectiveness of synchronization with prostaglandins in cattle ranges from 60 to 85 percent. Recent work at the University of Florida indicates that the percentage of cattle exhibiting oestrus can be significantly improved by giving a second injection of PGF2alpha 12–24 hours after the first. In addition to increasing the percentage responding positively, this treatment scheme also achieves closer synchrony of oestrus in the animals that respond.)
The average buffalo donor yields two to three transferable embryos. Therefore, four recipients per donor is a reasonable number to prepare. When recipients are palpated for corpora lutea, about 12 are palpated in order to identify six definitely with corpora lutea on their ovaries. When six are injected with prostaglandins, four on average will be suitably synchronized with the donor. Recipients must be injected with prostaglandins one day earlier than the donor. Following prior gonadotrophin treatment, the donor comes into oestrus 48 hours after the prostaglandins, while the recipients that did not receive any gonadotrophin treatment will come into oestrus 72 hours after prostaglandin treatment.
Not all donors will respond to the superovulatory treatment. For optimal efficiency, two to four donors should be superovulated at the same time to permit the sharing of the prepared recipients and avoid the expensive failure encountered too frequently when only one donor is prepared at a time.