Effect of Different Sperm Numbers on Fertility after Artificial Insemination of Foxes

Abstract

A total of 325 blue for vixens were inseminated with fresh semen from 50 silver fox males. Each ejaculutate was divided into 4 portions and diluted so as to contain 100, 60, 40, and 20 million sperm/ml. Vixens in groups 1,2,3 and 4 had been randomly assigned to their group at the time of insemination. The animals were inseminated once with either 100,60,40, or 20 million sperm. Vixens in groups 5 and 6 were selected by the technician after detecting signs of estrus during a physical examination. Animals judged to be at their optimal time for conception were assigned to group 5 and inseminated once with 20 million sperm. Animals considered to be early in their heat were assigned to group 6 and inseminated twice within 24 to 36 h with 20 million sperm per insemination dose. All inseminations were performed within 3 h of semen collection. A 1-ml total volume of extended semen was used for intrauterine deposition. In the random group inseminated once with 20 million sperm (group 4), both pregnancy rate and litter size were lower compared to the other random groups (groups 1,2, and 3), although the difference was not statistically significant. Among the vixens inseminated with 20 million sperm (group 4, 5, and 6) there was a significant difference in fertility between animals randomly selected and inseminaed once and those selected by the technician and inseminated twice (group 6). Our results suggest that for the crossbreeding of foxes 20 million sperm is the minimum insemination dose required for acceptable fertility with the present tecnique for sperm preservation and estrous determination.

Sammendrag

325 blårevtisper, fordelt på 6 forsøksgrupper, ble inseminert med fersk sæd fra 50 sølvrevhanner. Dyra i grupperne 1–4 ble inseminert med henholdsvis 100, 60, 40 og 20 millioner spermier. Dyra i gruppe 5 ble inseminert en gang med 20 millioner spermier etterat inseminøren kontrollerte rett inseminasjonstidspunkt ved palpasjon av cervix. Dyr i gruppe 6 ble inseminert 2 ganger med 24–36 timers mellomrom med 20 millioner spermier. Alle inseminasjoner ble utført innen 3 timer etter sæduttak. Inseminasjonsdosen var 1 ml og hvert ejakulat var mest mulig jevnt fodelt (split sample) mellom gruppene.

Resultatene viste at med nåværende teknikk for spermiehåndtering og brunskontroll, syns 20 millioner spermier pr. ml å være den minste inseminasjonsdose som gir akseptabel fruktbarhet ved artskrysning mellom blårevtispe og sølvrevhann.