Porcine Field Fertility with Two Different Insemination Doses and the Effect of Sperm Morphology K Alm 1 , OAT Peltoniemi 1 , E Koskinen 2 and M Andersson 1 1 Department of Clinical Veterinary Sciences, Faculty of Veterinary Medicine, University of Helsinki, Saarentaus, Finland; 2 Department of Animal Science, University of Helsinki, Finland Contents In swine artificial insemination, several dose regimens are applied, ranging from 1.5 · 10 9 to 6.0 · 10 9 spermatozoa per intra-cervical insemination dose. A lower sperm dose is more profitable for artificial insemination centres and offers a more effective use of superior boars. To evaluate fertility, 50 boars were used for a total of 10 773 homospermic first insemina- tions at a dose of 2 billion spermatozoa. In addition, 96 boars were used at a dose of 3 billion spermatozoa for 34 789 homospermic first inseminations. Fertility was determined by a 60-day non-return rate (NR%) of first inseminations. Litter size was registered by total number of piglets born separately in primiparous and multiparous farrowings. On average, a sow was inseminated 1.5 times. A significant decrease was observed in all three fertility parameters (NR%, litter size of both primiparous and multiparous farrowings) with a dose of 2 billion spermatozoa compared with a dose of 3 billion spermatozoa. The NR% was 75.8% and 84.0% (p < 0.001), the mean litter size of primiparous farrowings 10.1 and 10.7 (p < 0.001) and the mean litter size of multiparous farrowings 11.7 and 12.1 (p < 0.001) for 2 and 3 billion spermatozoa/ dose, respectively. The proportion of normal spermatozoa in the sperm morphology analysis correlated significantly with NR% in both insemination regimens: p < 0.001, r ¼ 0.604 and p < 0.05, r ¼ 0.223 for 2 and 3 billion spermatozoa/dose, respectively. These results confirm that quantity can at least partly compensate for poor sperm quality. When the boars with <70% normal spermatozoa in the morphology evalua- tion were excluded from the data there were no correlation between the sperm morphology and NR%. However, the difference between the NR% and litter size remained statistically significant (p < 0.001) in favour for the bigger insemination dose. In conclusion, a decrease in sperm dose from 3 to 2 billion spermatozoa on commercial farms will severely decrease prolificacy at least under field conditions, where a sow is inseminated an average of 1.5 times/heat, and the semen is typically used within 3 days after collection. We recommend that under commercial circumstances the homo- spermic semen doses contain no <3 billion spermatozoa/dose. Introduction In swine artificial insemination (AI) several dose regi- mens are applied, ranging from 1.5 · 10 9 to 6.0 · 10 9 spermatozoa per intra-cervical insemination dose (Colenbrander et al. 1993; Martin Rillo et al. 1996; Althouse 1997a,c). A lower sperm dose is more profit- able for AI-centres and makes more effective use of superior boars. A decrease in sperm dose from 3 to 2 billion spermatozoa increases the number of doses produced by 50% at almost the same total cost. However, when decreasing the insemination dose the effect of semen quality becomes more important and otherwise compensable morphological deficiencies can no longer be overcome (Althouse 1997a–c; Johnson 1997; Althouse et al. 1998; Saacke et al. 2000). This leads to decreased fertility rates and litter sizes (Althouse 1997a). Because fertility and prolificacy are of funda- mental economic importance for farmers, we compared non-return rate (NR%) and litter size when 2 vs 3 billion spermatozoa/insemination dose were used for commercial homospermic insemination. Our aims were to study the effect of total sperm count in the AI dose on NR% and litter size, and to evaluate the effect of sperm morphology on fertility and prolif- icacy in pigs in both dose regimes separately. Materials and Methods Animals and inseminations A total of 146 AI boars used for individual insemina- tions were included in this study. Boars were of Finnish Landrace (n ¼ 76) and Yorkshire (n ¼ 70) breeds. The age of the boars ranged from 9 to 40 months when the 1 year lasting study period begun. The age and breed matched boars were randomly divided into two groups (A and B), with inseminations of 2 billion (50 boars) and 3 billion spermatozoa/dose (96 boars), respectively. The inseminations in this study were performed evenly during 1 year (September 2000 – August 2001). Semen was collected with a gloved hand technique once a week. Only grossly normal looking ejaculates with total volume >1 dl were accepted for further evaluation and processing. Fresh ejaculates with a progressive motility ‡60% and total amount of ‡30 bil- lion spermatozoa were accepted. The density of ejac- ulates was measured with a photometer (Novaspec II, Pharmacia LKB Biotechnology, Uppsala, Sweden), and semen was extended with MR-A (Kubus, Madrid, Spain) to obtain 2 · 10 9 (group A) or 3 · 10 9 (group B) spermatozoa per insemination dose. The average number of spermatozoa/AI dose was regularly con- trolled also in a haemocytometer (Bu¨rker counting chamber; VWR International, Haasrode, Belgium). Sperm morphology Semen smears of all boars were prepared in May 2001 when the age of the boars ranged from 11 to 48 months (average 24 months). The smears were air-dried and sent to our laboratory, where they were fixed and stained by the Giemsa staining method according to Watson (1975); 100 spermatozoa/smear were examined, and classification of sperm morphology was carried out as Reprod Dom Anim 41, 210–213 (2006); doi: 10.1111/j.1439-0531.2005.00670.x ISSN 0936-6768 Ó 2006 The Authors. Journal compilation Ó 2006 Blackwell Verlag