IN-VITRO PRODUCED EMBRYOS AS A MEANS OF ACHIEVING PREGNANCY AND IMPROVING PRODUCTIVITY IN BEEF-COWS

The possibilities of using embryo transfer (ET) with in-vitro produced embryos as an alternative to artificial insemination (AI) for achievi ng pregnancy in commercial cattle, and improving the number and qualit y of calves produced were assessed using 157 multiparous, beef X dairy suckling cows (mainly Hereford X Friesian) in three autumn and three spring-calving herds in Scotland. Within each herd, cows were allocate d at random to (i) AI; or ET with in-vitro produced embryos, either (i i) singly (ET(s)), or (iii) in pairs (ET(t)) to establish pregnancy. I n-vitro produced embryos were derived from oocytes recovered from the ovaries of heifers with high-quality carcasses post slaughter. Semen f rom a single Simmental sire was used for in-vitro embryo production an d for AI across all herds. Following oestrous synchronization, AI cows were inseminated at 48 and 72 h after removal of the synchrony device . ET cotes that had a palpatable corpus luteum received either one ol two in-vitro produced embryos placed non-surgically in the ipsilateral uterine horn on day 7 after oestrous (oestrus = day 0). Pregnancy rat e, calving rate and calving difficulty were monitored for all cows. Ca lf performance was monitored on the farms of origin from birth to purc hase and thereafter at one finishing unit until slaughter. Animals wer e slaughtered at a prescribed level of body fatness and saleable meat yields determined. Cows that received one in-vitro produced embryo gav e birth to fewer calves than cows that were artificially inseminated o r received two embryos (P < 0.01). Gestation length was longer for cow s that gave birth to single ET calves (288 days; P < 0.01) than cows t hat gave birth to AI calves (285 days) or twin ET calves (284 days). S ingle ET calves were heaviest at birth (P < 0.01) and higher levels of assistance at calving were required for ET calves whether born as sin gles or twins. ET calves of both birth types grew more quickly (simila r to 1.00 kg/day; P < 0.05) and produced larger carcasses (297 kg; P < 0.01) with higher yields of saleable meat (220.7 kg; P < 0.01) than A I calves (0.92 kg/day; 281.7 kg; 206.3 kg respectively).