For the first trial in this study, the sperm rich phase of the ejaculates of three fertility proven boars was pooled and adjusted to the following five sperm concentrations: 5x10⁸, 1x10⁸, 1x10⁷, 5x10⁶, 1x10⁶ sperm in 0.5 ml Androhep^TM extender. Oestrus was induced hormonally in prepuberal gilts by the injection of PMSG and ovulation was induced by the injection of hCG 72 hours later. These animals were divided into three experimental groups. In the first group, surgical insemination was performed 32 hours after hCG application, in the second group, insemination was performed 38 hours after hCG application and in the third group, insemination was performed during or shortly after ovulation. In all cases, sperm were surgically introduced as close as possible to the uterotubal junction. Pregnancy, farrowing rate, litter size and birth weight were recorded.

The following results were obtained:

1. The pregnancy and farrowing rates were not affected by either the time of insemination or the sperm concentration as long as there was a minimum of 5x10⁶ sperm and a volume of 0.5 ml was used in each uterine horn. In the experimental group in which insemination was performed with only 1x10⁶ sperm per uterine horn, pregnancy and farrowing rates were similar to those achieved with higher sperm numbers when insemination was performed at the time of ovulation but were significantly reduced when insemination was performed 32 or 38 hours after hCG application.
2. Neither the mean number of the live born or stillborn piglets nor the mean weight of piglets was significantly different between the different experimental groups. The total number of piglets born in each group was also not statistically different from the mean of all groups.

To exclude carryover effects from the hormone injections used for induction of oestrus, the experiments were repeated using sows which were surgically inseminated after weaning. The inseminations were carried out using the same procedure used for the gilts except that the sows were inseminated 24 to 32 hours after the first sign of oestrus. In the experiments with sows, three different concentrations of sperm were used. 5x10⁸, 1x10⁸, 1x10⁷ sperm in 0.5 ml Androhep^TM extender.

In addition, two groups of sows were inseminated once intra cervically at 24 to 32 hours after the first signs of oestrus with 1x10⁹ and 3x10⁹ sperm and a volume of 80 ml Androhep^TM extender as controls. Animals which became pregnant were allowed to farrow normally. The pregnancy rate, farrowing rate and litter size were recorded.

The following results were obtained:

1. No significant differences were observed among the animals surgically inseminated with the three different sperm doses with respect to pregnancy or farrowing. There was also no significant difference between the results from these groups and the results obtained from the non-surgically inseminated control group.
2. Neither the mean number of the live born or stillborn piglets nor the mean weight of piglets was significantly different between the different surgically inseminated groups and the control groups. The total number of piglets born in each group was also not statistically different from the mean of all groups.

In the third trial, hormonally stimulated prepuberal gilts were inseminated 32 hours after hCG application with the same five sperm dosages used in the first trial with gilts using the same surgical procedure. Gilts were sacrificed 48 hours after insemination and embryos were recovered by flushing the oviduct and uterous with a PBS solution. The fertilization rate was determined by counting the total number of normal embryos. To verify the developmental competence of these embryos, they were cultured and evaluated in vitro over a five day period.

The following results were obtained:

1. The division rate did not differ among the groups as long as a minimum of 5x10⁶ sperm and a volume of 0.5 ml was used in each uterine horn. Using only 1x10⁶ sperm per uterine horn, the division rate was significantly lowered with respect to the groups with higher sperm dosage. This confirmed the results obtained in the first trial.
2. The embryos developed after five days in culture to morulae and blastocyst stages. The final developmental stage reached did not differ significantly between the groups. In the group with the lowest sperm concentration, the rate of division through the first four rounds of cell division was reduced and the blastocysts they produced did not hatch. One reason for this reduced developmental competence may be that uncompensable semen deficiencies became apparent due to the lack of sperm competition.
3. The mean number of nuclei per embryo ranged from 31.1 to 43.9 and did not differ between groups after five days of in vitro culture.

The conclusion of this work was that one can reduce the sperm dose through deep intrauterine insemination in both gilts and sows without reduction in the overall efficiency of fertilization so long as there is at least of 5x10⁶ sperm in gilts and 1x10⁷ sperm in sows in 0.5 ml of extender per uterine horn. Low dose fertilization is practical where sperm quality is high and the time point of ovulation can be accurately determined. The limiting technology, at this point, is the lack of a suitable device for non-surgical deep intrauterine insemination. Low dose insemination will be useful in situations where only low numbers of sperm are a available, for example when sexed sperm is used.

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