Insemination before and after the onset of heat in sows

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Abstract
Counts were made before and after fixation of the numbers of fertilised and unfertilised ova recovered from 3 mated sows, 7 unmated sows and from 34 sows inseminated at varying times before and after the onset of heat.The percentages of fertilised ova for sows inseminated the day before heat (day — 1) on the first day of heat (day 0) the second day of heat (day 1) and the third day of heat (day 2) are respectively for unfixed and fixed ova: 7·1 and 9·8, day – 1 ; 55·9 and 68·8, day 0; 63·4 and 98·2, day 1; 20·1 and 15·2, day 2. No fertilised ova were recorded from unmated sows; the percentages for mated sows were 94·3 and 95·5.It is concluded that failure of fertilisation is likely to be the greatest source of loss of fertility in inseminations made before heat and late in heat.Most ova from sows inseminated on day — 1 and from sows inseminated in day 2 had no spermatozoa on the zona pellucida. A few ova from sows inseminated on day 2 had very large numbers of spermatozoa present.It is suggested that failure of the spermatozoa to reach the site of fertilisation rather than their loss of fertilising capacity is likely to be the cause of the low fertility of early inseminations.