INFLUENCE OF PROTEIN AND HORMONE SUPPLEMENTATION ON IN-VITRO MATURATION AND FERTILIZATION OF DOMESTIC CAT EGGS

Immature eggs were recovered from freshly excised ovaries from domesti c cats, and initially 931 eggs with a compact cumulus and uniform cyto plasm were cultured in I of 15 treatments. Eagle's minimum essential m edium containing, glutamine and pyruvate was supplemented with 5% (v/v ) fetal calf serum (FCS), 4 mg bovine serum albumin (BSA) ml(-1) or 2 mg polyvinyl alcohol ml(-1) (PVA; non-protein control). Within each of these supplement groups, eggs were cultured with: no hormone; LH+FSH; LH+FSH+oestradiol; or LH+FSH+oestradiol+progesterone. After incubatio n for 52 h, eggs were inseminated with conspecific fresh spermatozoa, cultured and examined for stage of meiotic maturation and in vitro fer tilization (IVF). There were fewer (P < 0.05) eggs maturing to metapha se II in vitro in FCS compared with BSA or PVA, the last two treatment s producing similar (P < 0.05) results. Gonadotrophins in concert with oestradiol or oestradiol+progesterone improved the incidence of matur ation (P less than or equal to 0.01) compared with no added hormones. The incidence of fertilization and cleavage in vitro ranged from 5.2 t o 33.9% and varied (P < 0.05) with hormone subtreatment. Adding FSH+LH +oestradiol consistently increased the incidence of IVF approximately twofold compared with controls with no added hormones. Although it inh ibited the ability of eggs to reach metaphase II, FCS in the presence of gonadotrophins and oestradiol allowed > 60% of mature eggs to ferti lize in vitro (P < 0.05, compared with PVA and BSA). Inhibitory effect s on egg maturation were further evaluated by testing four FCS batches from three commercial sources against BSA. All FCS batches were clear ly inhibitory, as 60.7% of treated eggs arrested at the germinal vesic le stage (21.1% of BSA-treated eggs, P < 0.001). Dialysis of FCS elimi nated a significant proportion of the inhibition; 69 of 158 eggs (43.7 %) matured compared with 22 of 135 (16.3%) in complete or 23 of 160 (1 4.4%) in recombined serum. In summary, FCS appears to exert a paradoxi cal effect in this system, inhibiting maturation in vitro (apparently due to small molecular weight components), but promoting IVF of mature eggs if gonadotrophins and oestradiol are present. Although hormone s upplementation enhanced the ability of in vitro matured eggs to fertil ize and cleave, neither protein source nor the hormone treatments test ed here appear responsible for the consistently low incidence of ferti lization in cat eggs matured in vitro.