In vitro produced embryos as a means of achieving pregnancy and improving productivity in beef cows

Abstract

AbstractThe possibilities of using embryo transfer (ET) with in-vitro produced embryos as an alternative to artificial insemination (Al) for achieving pregnancy in commercial cattle, and improving the number and quality of calves produced were assessed using 157 multiparous, beefX. dairy suckling cows (mainly Hereford × Friesian) in three autumn and three spring-calving herds in Scotland. Within each herd, cows were allocated at random to (i) Al; or ET with in-vitro produced embryos, either (ii) singly (ET(s)), or (Hi) in pairs (ET(t)) to establish pregnancy. In-vitro produced embryos were derived from oocytes recovered from the ovaries of heifers with high-quality carcasses post slaughter. Semen from a single Simmental sire was used for in-vitro embryo -production and for Al across all herds. Following oestrous synchronization, Al cows were inseminated at 48 and 72 h after removal of the synchrony device. ET cows that had a palpatable corpus luteum received either one or two in-vitro produced embryos placed non-surgically in the ipsilateral uterine horn on day 7 after oestrous (oestrus = day 0). Pregnancy rate, calving rate and calving difficulty were monitored for all cows. Calf performance was monitored on the farms of origin from birth to purchase and thereafter at one finishing unit until slaughter. Animals were slaughtered at a prescribed level of body fatness and saleable meat yields determined.Cows that received one in-vitro produced embryo gave birth to fewer calves than cows that were artificially inseminated or received two embryos (P < 0·01). Gestation length was longer for cows that gave birth to single ET calves (288 days; P < 0·01) than cows that gave birth to Al calves (285 days) or twin ET calves (284 days). Single ET calves were heaviest at birth (P < 0·01) and higher levels of assistance at calving were required for ET calves whether born as singles or twins. ET calves of both birth types grew more quickly (<1·00 kg/day; P<0·05) and produced larger carcasses (297 kg; P < 0·01) with higher yields of saleable meat (2207 kg; P < 0·01) than Al calves (0·92 kg/day; 281·7 kg; 206·3 kg respectively).