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Effect of semen storage on the number of spermatozoa in the perivitelline layer of laid turkey eggs

A progressive decline in fertility over the course of egg production may be observed when turkey hens are inseminated weekly with semen stored for 24 h. In vitro storage of spermatozoa before insemination results in lower fertilization, possibly because fewer spermatozoa survive selection and storage in the hen's sperm storage tubules in vivo; alternatively, stored spermatozoa may be as capable of reaching the egg as are fresh spermatozoa, but unable to penetrate and fertilize the egg normally. The objective of this study was to determine whether this decline in fertility is a result of fewer spermatozoa reaching the egg after insemination with spermatozoa stored in vitro. Hens were inseminated weekly over the first 12 weeks of egg production with either fresh semen (n = 30 hens) or semen stored for 24 h (n = 30 hens). A total of 301 eggs was evaluated by determining the density distribution of spermatozoa embedded in the outer perivitelline layer. For the 12 weeks of egg production, the fertility of hens inseminated with fresh semen remained greater than 94%. Conversely, the percentage fertility of eggs from hens inseminated with stored semen in weeks 1–3 was greater than 94% but thereafter fertility averaged 86%. There was no difference in hatchability of fertile eggs between the two treatments over all weeks combined, and weekly throughout the study (P > 0.05). The mean number of spermatozoa in the perivitelline layer was higher (P < 0.001) when hens were inseminated with fresh (12.1 ± 1.3 spermatozoa per 5.5 mm² membrane) versus stored semen (2.5 ± 0.3 spermatozoa per 5.5 mm² membrane) over all weeks combined, and weekly throughout the study (P < 0.05). As a result of storage for 24 h, fewer spermatozoa are stored in the sperm storage tubules and, consequently, fewer spermatozoa are present at the site of fertilization, thus contributing to the depressed fertility.