Semen backflow after insemination and its effect on fertilisation results in sows

The aim of the present study was to investigate the volume of and number of spermatozoa in semen backflow during and after insemination, and the effect of backflow on fertilisation results assessed at day 5 of pregnancy. Multiparous sows (n = 140) were artificially inseminated with either (1, 3 or 6) x 10(9) mixed spermatozoa from three boars in a constant volume of 80 ml. Backflow of semen was measured three times: during insemination (M1); during the first half hour after insemination (M2); and from 0.5 h until about 2.5 h after insemination (M3). Transrectal ultrasonography was performed at intervals of 4 h to determine the time of ovulation. Sows were sacrificed at 120 +/- 0.4 h after ovulation to assess the results of fertilisation. Every sow had some backflow and the variation in volume, and number of spermatozoa within the backflow was high. The average semen backflow within 2.5 h after insemination was 70 +/- 3.4% of the volume and 25 +/- 1.4% of the spermatozoa of the inseminated dosage. The concentration of the backflow (% of the inseminated dosage) decreased with time after insemination from 65% at M1 to 40% and 26% at M2 and M3, respectively. The correlations between volume and number of spermatozoa were high: r = 0.97, r = 0.73 and r = 0.81 in M1, M2 and M3, respectively. More than 5% of the inseminated spermatozoa in backflow during insemination affected fertilisation negatively in those sows inseminated with 1 x 10(9) spermatozoa (P < 0.05). Backflow after insemination had no effect on fertilisation results (P > 0.05). Timing of insemination relative to ovulation and oestrus were not related to backflow during or after insemination (P > 0.05). Of the sows which had backflow, those of parity 1 tended to have the highest proportion of sows with more than 5 ml backflow (47%; n = 8 of 17) compared with sows from parity 2 and higher (24%; n = 14 of 59) (P = 0.075). It was concluded that excessive backflow of semen during insemination had a negative effect on fertilisation results when sows where inseminated with only 1 x 10(9) spermatozoa. Causes of variation in backflow between sows were not clearly identifiable.