Stage-specific effect of growth hormone on developmental competence of bovine embryos produced in vitro

Abstract. Many efforts have been made to develop effective culture conditions for the production of bovine blastocysts. Growth hormone (GH) and glucose are known to affect in vitro embryo development. To improve in vitro culture conditions, the culture medium containing fetal calf serum (FCS) or bovine serum albumin (BSA) was supplemented with GH at various periods of development, and the effects of GH on the rate of development and the quality of the blastocysts were studied. Then, starting at the morula stage, the effect of glucose and GH on the rate of development was studied. In all experimental periods, FCS was more effective than BSA at improving the development rate and increasing the cell number of blasiocysts. Adding GH to the culture medium between 18 and 48 h after fertilization (1-8 cell stage embryo) did not affect either the rate of blastulation or the cell number regardless of the serum protein (FCS or BSA). From 48 to 120 h after fertilization (5-cell to morula stage) GH increased the cell number of the blastocysts in the presence of BSA, but not in the presence of FCS. From 120 to 192 h after fertilization (morula to blastocyst stage), GH improved the developmental rate and cell number in the presence of FCS, although there was no significant difference when BSA was used instead of FCS as the serum protein. When cows were implanted with blastocysts developed in the presence of GH from the morula stage, their pregnancy rate did not differ from that of the control. Increasing the glucose concentration in the medium from 1.5 mM to 3 mM starting at the morula stage (120 h after fertilization) slightly decreased the rate of development, but on the other hand, decreasing the glucose concentration to O mM did not affect either the rate of development or the cell number. Also, then GH had no effect on the developmental rate or the cell number in the absence of glucose. In conclusion, when the medium was supplemented with serum, GH improved embryo development from the morula stage, but an increased concentration of glucose decreased embryo development. Furthermore, GH did not improve the pregnancy rate of blastocysts developed in vitro.