The effects of the number of oocytes and the volume of maturation medium in bovine in vitro embryo production

Abstract

For in vitro embryo production following ovum-pick-up groups with different number of oocytes and volume of medium may be required to maintain an individualized production of each cow. Bovine oocytes were randomly allocated in a 3x3 factorial design in order to evaluate the effect of number of oocytes (5, 10 and 20) and maturation medium volume ratios (1:1, 1:5 and 1:10 oocyte/μl) on embryo production. After 2224h maturation in TCM-199, in vitro fertilization was performed in FERT-TALP medium, for 18-22h. Groups of 20 presumptive zygotes were cultured in 200μl of SOF medium for eight days. There was no effect of interaction between number of oocytes and volume of maturation medium (P>0.05) on embryo development. Cleavage rates were not affected either by number of oocytes nor by volume of medium (P>0.05). Blastocyst rates on D7 (19, 26 and 28%; D0=day of fertilization) and D9 (23, 33 and 33%) were lower (P 0.05) for ratios 1:1, 1:5 and 1:10 oocytes/μl, respectively. Hatching rate with a 1:1 volume ratio (26%) was lower (P<0.05) than that obtained with a 1:5 volume ratio (44%). Maturation in larger groups increases embryo production. The volume of maturation medium does not influence the blastocyst production, however a low oocyte/μl medium ratio reduces the hatching rate.