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Growth of preimplantation embryos is influenced byThe cells of the mammalian preimplantation embryo (from the time of fertilization until the implantation of the blastocyst into the uterus) form the progenitor cells for all other cell lineages. The regulation of the growth and survival of the cells of the early embryo is, however, poorly understood. Mammalian preimplantation embryos develop in vitro with simple medium requirements and have no absolute requirement for exogenous vitamins, hormones, or growth factors. This contrasts with the absolute requirement of normal somatic cells for exogenous mitogens and survival factors. The continued mitoses of preimplantation embryo cells in the absence of exogenous growth factors implicates a role for endogenous, autocrine trophic factors, or the constitutive activation of signaling pathways in the early embryo. Several lines of evidence support a role for the former: (i) the rate of embryo development in vitro is density-dependent, with embryos growing in relatively small volumes (or in large groups) developing more successfully than those grown in large volumes (or individually) (1, 2); (ii) the synthesis by the preimplantation embryo of a number of growth factor ligands and their receptors (3-8); and (iii) the capacity of some exogenous growth factors to enhance embryo metabolism in vitro and to compensate for the adverse effects of culture in large medium volumes (1, 2, 9).Experimental partial deprivation of released autocrine trophic factors did not arrest the cell-cycle at given checkpoints (9). Rather, there was progressive loss of viability with increased cell death as embryos progressed past the 8-cell stage. This finding suggests that the autocrine factors may act as survival factors rather than classical growth factors (triggering progression through specific cell-cycle checkpoints). While several autocrine factors have been implicated, platelet-activating factor (PAF) 1 seems to be one of the first produced, being synthesized de novo by the embryo soon after fertilization (10, 11). Its actions are required by the mid-2-cell stage for normal rates of embryo survival (9).Despite this range of supportive data, there is limited direct evidence for the action of autocrine trophic factors in early embryo development. Transgenic and recombinant knock-out models have not generally been informative of the growth requirements of the early embryo prior to implantation. This may be due to extensive redundancy of regulatory pathways.

Fertility after insemination of cryopreserved boar semen is currently below that of fresh semen. In an attempt to improve the post-thaw motility and acrosome integrity of boar sperm, semen was frozen using an adapted Westendorf method in which the chicken egg yolk was replaced by either duck or quail egg yolk. The different composition of the yolk types, particularly the amount of cholesterol, fatty acids and phospholipids, were thought to potentially afford a greater level of protection to sperm against damage during freezing and thawing. Sperm frozen in medium containing chicken egg yolk displayed higher motility immediately after thawing, but there was no difference in the motility of sperm frozen with different types of egg yolk 3 or 6 h after thawing and maintenance at 37 degrees C. Sperm frozen in media containing chicken or duck egg yolk had a higher proportion of intact acrosomes immediately after thawing than sperm frozen in medium containing quail egg yolk, but 6 h after thawing and maintenance at 37 degrees C the sperm that had been frozen in medium containing chicken egg yolk had a higher proportion of intact acrosomes than the sperm frozen in media containing duck or quail egg yolk. Analysis of the composition of the different yolk types showed that the basic components of the yolks were similar, but the ratios of fatty acids and phospholipid classes differed. Duck egg yolk had more monounsaturated fatty acids (MUFA) than chicken egg yolk, which had more MUFA than quail egg yolk. Duck egg yolk contained more phosphotidylinositol (PI) than chicken or quail egg yolks and quail egg yolk contained more phosphotidylserine than either chicken or duck egg yolks. The differences in post-thaw motility and acrosome integrity of boar sperm when frozen in media containing the different types of egg yolk may be due to the variation in composition.

Epididymal spermatozoa were harvested from male alpacas and frozen after extension and cooling to 4 degrees C in citrate-, Tris- and lactose-based diluents (Experiment 1) and as pellets in 0.25- and 0.5-mL straws on either dry ice or over liquid nitrogen vapour (Experiment 2) to determine the effects diluents and packaging on their motility and acrosome integrity. In Experiment 1, sperm motility was higher after cooling to 4 degrees C and after freeze-thawing (0 but not 3 h post-thaw) for spermatozoa extended in the lactose- than the citrate- or Tris-based diluent (P < 0.05). Post-thaw acrosome integrity after cooling to 4 degrees C and post-thaw (0 h) was reduced for spermatozoa frozen in citrate- compared with lactose- or Tris-based diluents, but was similar for all groups 3 h after thawing. In Experiment 2, sperm motility immediately after thawing was higher for pellet freezing than for 0.25- or 0.5-mL straws on dry ice or liquid nitrogen vapour (P < 0.05), although by 3 h post-thaw motility was similar for pellets and straws (P > 0.05). Acrosome integrity was similar for all groups immediately after thawing and 3 h post-thaw. Cryopreservation of epididymal alpaca spermatozoa is feasible, with retained motility and acrosome integrity post-thaw. Freezing as pellets in a lactose-based diluent is recommended.

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