Summary. A total of 256 beef heifers, in 2 experiments, was used to establish fertilization rate and subsequent embryo survival rates. Fertilization rate following a single artificial insemination was 90%. Pooled estimates of embryo survival showed high survival rates up to Day 8 (93%) but markedly reduced (P < 0·001) survival at Days 12 (56%), 16 (66%) and 42 (58%). It is suggested that most embryonic mortality occurs between Days 8 and 16.
M. G. Diskin and J. M. Sreenan
J. M. Sreenan and M. G. Diskin
Summary. Uni- and bilateral twin embryo distributions were effected by the transfer of one embryo on Day 7 to the ipsi- or contralateral uterine horn of previously inseminated heifers (123, Exp. 1) or cows (95, Exp. 2). The embryo transfers were surgical in Exp. 1 and non-surgical in Exp. 2. Transferred and native embryos were distinguished by breed. Embryo survival rate was measured in a proportion (N = 40) of the heifers at Day 53 of gestation and in the remainder of the heifers and all of the cows at term. In the heifers (Exp. 1) overall pregnancy rates of 76% and 75% were recorded after uni- and bilateral twin embryo distributions respectively. Twinning rates of 55% and 60% at Day 53 of gestation and 60% and 60% at term were recorded for uni- and bilateral distributions respectively. In the cows (Exp. 2) calving rates of 61% and 63% and twinning rates of 33% and 38% were recorded following uni- and bilateral twin embryo distributions respectively. When the data from both experiments were combined, overall embryo survival rates were similar for both twin embryo distributions although the ipsilateral transfer of an embryo reduced the survival rate of the native embryo. It is concluded that the confinement of two embryos in one uterine horn on or after Day 7 does not depress pregnancy, twinning or overall survival rate to term.
Keywords: embryo distribution; twinning; survival rates; cow
M. Grealy, M. G. Diskin and J. M. Sreenan
The protein content of cattle oocytes and preimplantation embryos produced in vivo, from the two-cell to the elongated blastocyst at day 16, was determined. From the oocyte to the expanded blastocyst stage (day 8), protein determination was carried out on zona pellucida-enclosed embryos. Protein content was measured by the Pierce Micro BCA protein assay. The mean protein content of oocytes was 0.126 μg, with no significant increase at the two-cell stage (0.132 μg). Protein content was higher at the morula stage (0.183 μg; P < 0.05) with a further increase at the expanded blastocyst stage (0.367 μg; P < 0.05). There was a 160-fold increase in protein content from the expanded blastocyst to the hatched day 13 stage. Spherical, ovoid and elongated blastocysts were collected on days 13 and 14. The mean protein content of day 13 (59.8 μg) and day 14 (92.4 μg) embryos was similar (P > 0.1), but the protein content of the elongated embryos was higher than that of ovoid or spherical embryos collected on the same day. Protein content of day 15 embryos (362.2 μg) was higher than that on day 14, with a further increase to 946.6 μg by day 16. The correlation between protein content and day of development contained both a linear and a quadratic component. Embryo length and width increased from day 13 (5.24 mm and 0.89 mm, respectively) to day 16 (51.6 mm and 1.82 mm, respectively). From day 13 to day 16, the protein content was correlated with both embryo length and width (r 2 = 0.89 and 0.51, respectively; P < 0.001) and was highly correlated (r 2 = 0.95) with the product of embryo length by width, indicating that protein content increases as a function of surface area.
D. G. Morris, M. G. McDermott, M. Grealy, M. G. Diskin, C. A. Morrison, P. J. Swift and J. M. Sreenan
The effects of immunizing cattle against either of two peptides from the amino terminal peptide (αN) of the α43-subunit of bovine inhibin on ovulation rate, gonadotrophin concentration and fertility were investigated. Two peptide sequences from the αN-subunit of bovine inhibin (P1N, bIα-(8-20) and P2N, bIα-(153-167)) were synthesized and conjugated to human serum albumin (HSA). Hereford-cross heifers (n = 5 per group) were given an initial injection of 3 mg of one of the peptide conjugates, followed by three booster injections (1.5 mg) at intervals of 11 weeks. Control heifers (n = 5) were injected with HSA only. Blood samples were taken once a week to measure antibody titre and every hour at about the time of the first oestrus and during the mid-luteal phase after the second booster injection, to measure FSH and LH concentrations. Ovulation rate was measured by ultrasonography. Gonadotrophin concentrations were analysed for four periods relative to the peak (time = 0 h) of the preovulatory LH surge as follows: pre-surge: −16 to −5 h; surge: −4 to 4 h; post-surge: 5 to 16 h and a period of 12 h during the mid-luteal (days 10–12) phase. Antibodies that bound to the individual peptides were generated and the ovulation rate increased (P < 0.05) in immunized heifers. Control heifers had one ovulation at all ovulatory cycles monitored. In group P1N, one heifer had two ovulations at each of the six cycles monitored, while another heifer had two ovulations at one cycle. Three heifers in group P2N had more than one ovulation; one heifer had a superovulation response on seven occasions and another heifer on three occasions while the third heifer had two ovulations at one cycle. The superovulation responses ranged from three to eight ovulations. There was no evidence of a significant correlation between peptide antibody titre, ovulation rate and FSH at any of the periods studied. After mating following the third booster injection, nine of the ten immunized and all five control heifers calved. One heifer from group P1N and two heifers from group P2N gave birth to twin calves. These data show that in cattle immunization against the αN-subunit of bovine inhibin significantly disrupts the mechanism(s) controlling ovulation rate but does not impair fertility.
D. G. Morris, M. G. McDermott, M. G. Diskin, C. A. Morrison, P. J. Swift and J. M. Sreenan
Three peptide sequences from the bovine inhibin α-subunit (P1: 18–30; P2: 63–72 and P3: 107–122) were synthesized and conjugated to human serum albumin (HSA). Hereford crossheifers (n = 5 per group) were injected with 3 mg of one of the peptide conjugates, followed by three booster injections at intervals of 11 weeks. Control heifers (n = 5) were injected with HSA only. Antibodies recognizing both the individual peptides and 32 kDa bovine inhibin were generated and ovulation rate was increased in peptide immunized heifers. In group P1, 1 of 5 heifers responded with an increased ovulation rate whereas in groups P2 and P3, 5 of 5 and 4 of 5 heifers, respectively, had an increased ovulation rate. In group P2, in the first oestrous cycle following booster injections 2 and 3, 4 of 5 and 3 of 5 heifers, respectively, responded with twin ovulations, whereas a fourth heifer had three ovulations following booster injection 3. After breeding following booster injection 3, 3 of 5 heifers in group P2 and 1 of 5 in group P3 gave birth to twin calves. This study demonstrates the potential of immunizing against synthetic peptide sequences of the α-subunit of bovine inhibin to increase ovulation and twinning rates in cattle.
C. McCaffrey, T. G. McEvoy, M. G. Diskin, F. C. Gwazdauskas, M. T. Kane and J. M. Sreenan
Summary. Bovine ova (n = 326) collected at the 1–4-cell stage were cultured in TCM199 + 10% foetal calf serum with or without oviducal cells. The bovine oviducal cells were collected and seeded either on the day of ovum recovery (BOC-0) or 3 days earlier (BOC-3). In Exp. 1, the effect of age of oviducal cells in co-culture on ovum development was examined. In the BOC-0 and BOC-3 treatments, respectively, 36/46 (78%) and 30/37 (81%) of ova developed to morulae or blastocysts, while no ova developed past the 8–16-cell stage in the absence of oviducal cells. In Exp. 2, the effect of age of oviducal cells and of physical contact between the oviducal cells and ova on ovum development was examined. In the BOC-0 and BOC-3 treatments, respectively, 29/42 (69%) and 23/43 (53%) of the ova developed to morulae or blastocysts, while 1/42 (2%) developed to the morula stage in the absence of oviducal cells. Physical separation of the ova using a microporous membrane inserted between the oviducal cells and the ova did not affect ovum development, with 26/42 (62%) and 22/42 (52%) of ova developing to morulae or blastocysts in the BOC-0 and BOC-3 treatments, respectively. A high proportion of the morulae and blastocysts in Exp. 1 (57/66, 86%) and Exp. 2 (67/100, 67%) were of quality grades 1 or 2, with mean nuclei counts of 85 for morulae and 111 for blastocysts. It is concluded that (i) oviducal cells, whether initially in suspension or as a near-confluent monolayer, can support the development of 1–4-cell ova to good quality blastocysts in a high proportion of cases and (ii) direct physical contact between ova and oviducal cells is not required to ensure a high rate of ovum development.
Keywords: cattle; embryo; co-culture; blastocysts