An international meeting held in Canada has yielded some intriguing insights into the application and further development of artificial insemination (AI) for pigs in North America. While demonstrating that the use of AI is now widespread, it also reported on research into the selection of boars for semen production.

Dr Robert Knox, University of Illinois, USA, reported to the 6th International Conference on Boar Semen Preservation that the USA now has 20 000 boars at 119 AI studs. By his estimate, the usage of AI is at about 80% for the 6 million sows in US herds. This level of uptake rises to 90% for herds with more than 500 sows each.

Between January and March 2007, he carried out a confidential electronic survey in which a multiple-choice questionnaire asking 65 questions was sent to AI stations nationally. Replies received from 44 boar studs representing 10 000 boars indicated that 48% of the stations were in the size category of 101-250 boars. Some 91% of the responding centres said they housed their boars in stalls. Most (70%) used housing with fully slatted floors. Another 26% had partial slats. The accommodation facilities at 74% of studs included evaporative cooling systems.

Barn staff averaged 16-25 hours per week in duties related to the collecting of semen. In 86% of cases the collection method was manual with double gloves. Only 19% of replies said AI doses prepared at the station did not contain pooled semen. Pooling with semen from 4-6 boars was practised by 49% of those answering the questionnaire.

At 90% of studs, the volume of the ejaculate was determined by its weight and 60% of semen assessments were by photocolorimeter. The survey found 28% of stations using a computer-assisted or CASA technique to assess the semen. Discard rates were in the 1-5% range for ejaculates at 45% of studs, with motility the reason behind 90% of decisions to discard. Samples for checking were generally kept for 5-7 days; this applied at 77% of the centres, whereas only 19% suggested that they retained samples for 3-4 days.

A question on the sperm concentration per dose produced an almost even balance of replies between aiming for 2-3 billion (47%) and 3-4 billion (44%). Half of the responses came from sites that extended with the Androhep diluent. Another 28% used X-cell. Nearly two-thirds (63%) of the doses supplied to herds went out packaged in tubes, compared with 39% in flat packs.

Looking at boars

A wide variation was described for boar replacement rates, from as low as 20% per year up to 70%. Turnover to achieve genetic improvement provided the main cause for the culling. The next most common cause was a problem with semen quality.

John Sonderman, Danbred North America, discussed his experience of analysing 1000 boars at 3 different studs using the proprietary CASA system called Spermvision to perform the semen assessments. Data for three years had been examined to look at breed differences in training, heat stress and the discarding of semen samples. A training success rate of 99.2% for hybrid boars compared with 98.2% for Durocs and 93.3% for Large Whites. As far as heat stress was concerned, a comparison of boars exposed to 29°C for more than 10 days found that purebred lines (Large White, Landrace and Duroc) had twice as much discarded semen as from a hybrid.

To what extent is extended semen likely to be contaminated by bacteria? Some clues came in a one-year study outlined by Gary Althouse, University of Pennsylvania, USA. According to this American survey, bacterial contamination was present in 31% of the samples examined, although the majority of the positives had only a single isolate. A marked seasonal difference could be detected, as might be expected. In this instance, however, the results were somewhat surprising by finding the highest contamination in the autumn/fall period. Another surprise was the discovery of a high 86% rate of resistance to gentamicin, the most commonly used antibiotic in semen extenders.

Dr Billy Flowers, North Carolina State University, USA, presented a pair of interesting trials, the first of which looked at subsequent semen production in relation to the boar's growth during the age phases 0-3 weeks and 8-12 weeks. Not surprisingly, the faster growing young boars were the top performers at producing semen. The second trial checked varying concentrations between 1-9 billion sperm per dose. The results showed that 7% of the boars had excellent semen quality even at a concentration of only 1 x 109. What is more, the vast majority of these superior boars were the sons of just 2 sires indicating a strong genetic link to semen quality. Attendees at the Canadian meeting debated a possible need to re-think selection indices for male lines by including some weighting on semen quality, which Dr Flowers suggested might be related seminal plasma protein profiles.

Dr George Foxcroft, University of Alberta, Canada, told the conference that the predictors of usable semen used in most commercial boar studs provided a very conservative estimate of the relative fertility of individual boars. A reliance on relatively high sperm concentrations and the use of pooled semen also tended to mask the effect of sub-fertile boars.

In his view, we must become more accurate in identifying sub-fertile AI sires in a practical way because of the need to achieve ever-higher genetic quality and reduced sperm numbers per dose. In-vitro fertilisation (IVF) has a high correlation to fertility and litter size, he commented, but it is expensive, time-consuming and not practicable at commercial studs. Nevertheless, investigations of the correlation between IVF and analyses of extended semen (in a simple BTS extender) after 4, 7 and 10 days of storage have found the viability at 10 days to be a very good indicator of future boar fertility. This laboratory test could be performed while the young boars were still in quarantine, as a routine screening mechanism.

Projects on frozen semen

The technology of frozen/thawed semen has been around for several decades, but its use until now has been limited by mediocre results that were not commercially viable. Its advantages from a biosecurity point of view and for global gene transfer are obvious. For this reason, a tremendous number of research projects are ongoing around the world in an attempt to overcome the problems caused by the freezing process such as a capacitation-like effect that results in reduced longevity.

Rudolf Grossfeld, the animal breeding institute at Mariensee, Germany, suggested a better selection of candidate boars for freezing protocols and the use of ultrasound to inseminate the frozen/thawed semen during the brief 4-hour window of ovulation. He also reported attempts at improving the thawing solution by the addition of an antioxidant. Adding BHT, the enzyme catalase and vitamin E seemed to reduce the sperm damage by reactive oxygen species (ROS).

Roy Kirkwood, Michigan State University, USA, has tried adding seminal plasma to the thawing solution since this is known to enhance the fertility. After first attempts at 10% inclusion proved unsuccessful, the work currently tries rates of 30-50%. The approach used by Janice Bailey, Université Laval, Canada, is to reinforce the sperm cell membrane to resist cold shock during freezing. Preliminary results with chlolesterol loaded cyclodextrins have been highly encouraging.

AI procedures continued to be investigated around the world. Work over many years by the veterinary school at the University of Murcia, Spain, was described by Dr J.M.Vazquez as having pioneered the idea of deep intrauterine insemination in an attempt to lower sperm concentrations and hence achieve a better and more widespread utilisation of higher-quality boars. The Murcia team now has developed a technique of intra-oviductal laproscopic insemination. This has been applied using sex-sorted semen and also frozen/thawed semen.

It is possible to perform the operation on 4 sows per hour, said the conference report. The oviduct is grasped and 100cc of semen solution are injected. The first site of injection was the utero-tubular junction, where fertilisation rates of 55% were achieved. A second trial involved injecting the semen into the ampulla and this gave up to 79% fertilisation with a concentration of just 600 000 sperm per dose.

The specialists assembled in Canada also considered the sow. Among presentations we noted in this area, Stig Einarsson, University of Uppsala, Sweden, discussed whether the trend to group gestation could bring problems in re-breeding. The grouping together of loose-housed sows after weaning involves a period of stressful confrontation, he commented, which coincides with many important reproductive events such as the onset of oestrus, insemination, ovulation and early semen transport. Re-grouping gives rise to elevated cortisol levels until the rank order is established. Depending on group size this may take up to 7 days. In a series of studies, re-grouping was simulated through repeated injections of ACTH in the pre-oestrus period. Sows in the simulated stress group took 3 days longer until their onset of oestrus. The standing reflex was shorter. Moreover, although ovulation occurred at the same time as in the control group, significantly fewer embryos were present 48 hours after the sow had ovulated.