Effects of the number of sperm and site of uterine semen deposition on conception rate and the number of embryos in weaned sows receiving a single fixed-time insemination.

Reducing the number of sperm needed to produce a litter with artificial insemination (AI) allows greater use of higher genetic merit boars. Induced ovulation with single fixed-time artificial insemination (SFTAI), combined with intrauterine (IUI) or deep uterine insemination (DUI), could improve fertility with low numbers of sperm. The objectives of the study were to determine the fertility effects of sperm numbers and the site of insemination. At weaning (0 h), sows (n = 534) were assigned by parity and estrus induction method (equine chorionic gonadotropin [eCG] or Control) to receive 1,200 × 106 sperm by IUI; 600, 300, or 150 × 106 sperm by IUI or DUI; or 75 × 106 sperm by DUI. At 80 h postweaning, sows received OvuGel and 26 h later a SFTAI using pooled semen. Sows were exposed to boars once daily and ultrasound was performed to determine follicle size and time of ovulation. Following SFTAI, sows were slaughtered 27 d after AI to determine pregnancy and litter traits. Data were analyzed using different models to test for effects of estrus induction, interaction of three levels of sperm (600 to 150) with two levels for site (IUI vs. DUI), and the overall effects of AI method (eight treatments). There was no effect (P > 0.05) of estrus induction on estrus (93%) within 5 d of weaning or on follicle size (6.1 mm) at OvuGel, but wean-to-estrus interval (3.8 vs. 4.0 d) was slightly reduced (P < 0.01) as was AI-to-ovulation interval (15.9 vs. 17.0 h, P = 0.04) for eCG and Control, respectively. There was no effect (P > 0.05) of estrus induction on pregnancy rate (78.6%), number of corpora lutea (CL; 21.7), or number of viable embryos (12.2). There was no effect of number of sperm or site of insemination and no interaction (P > 0.05) on pregnancy rate (range: 80.9% to 70.5%), but AI occurring after ovulation reduced the pregnancy rate (P < 0.02). The total number of embryos (range: 16.5 to 10.3) was not affected by estrus induction, number of sperm, or site of insemination (P > 0.05), but was influenced by AI treatment (P < 0.01). Treatments with a higher number of sperm (1,200 and 600) had more embryos compared with those with a lower number of sperm (300 to 75). The numbers of embryos also increased with the number of CL (P < 0.0001). These results suggest that the lower number of sperm affects litter size more than the pregnancy status. Acceptable fertility can be achieved with low numbers of sperm when using a SFTAI and uterine deposition, but AI-to-ovulation interval and ovulation rate influence final fecundity.

Effect of sorting boar spermatozoa by sex chromosomes on oviduct cell binding.

This study examined the hypothesis that flow sorting sperm by sex chromosomes affects oviduct cell binding which would influence formation of the sperm reservoir in the oviduct. The sperm-rich fraction from boars (n = 5) was collected, sperm were stained with Hoechst 33342 and sorted. Sperm were sorted based on the presence of either an X or Y chromosome and placed into the following treatments: 1) sperm selected for the Y chromosome, 2) selected for the X, 3) an equal mixture of sorted X and Y, and 4) a control of non-sorted sperm from the same collection. Samples were tested for oviduct cell binding within 12 h of sorting. Additionally, sperm were analyzed for motility characteristics, acrosome status, and binding to the two oviduct glycan motifs that bind porcine sperm, biantennary 6-sialylated N-acetyllactosamine on a mannose core (bi-SiaLN) and sulfated LeX trisaccharide (suLeX). The disaccharide found within both glycan motifs, N-acetyllactosamine (LacNAc), was used as a control. Sperm binding to oviduct cells was reduced by more than half in the three sorted samples when compared to the control sperm that were not sorted. The percentage of sperm that were motile 24 h after sorting was also decreased significantly in each of the sorted sample groups when compared to the unsorted control. In contrast, sorting did not decrease the percentage of sperm that bound purified soluble glycans or the location on sperm to which they bound. There was also no difference in sperm acrosome status among the four groups. In summary, sorting reduced sperm binding to the complex matrix around oviductal cell aggregates but sperm binding to purified soluble oviduct glycans was not affected. The requirement for higher affinity and motility to bind glycans immobilized on oviduct cells may explain this difference. The reduction in sperm fertility observed following sex-sorting may be explained partially by a reduced or altered ability to bind to the oviduct epithelium.

Scrotal insulation and sperm production in the boar.

Seasonal infertility is a limiting factor in boar fertility, and is increasingly important as climate changes. Spermatogenesis in the boar produces 256 spermatozoa per type A1 spermatogonium, but the process is inefficient such that only 10-30% of these potential spermatozoa are actually produced. Heat further impacts spermatogenesis by reducing the number of specific germ cells produced while increasing the fraction of abnormal sperm. Early studies used whole-animal exposure to simulate seasonal exposure to heat under production settings, but this approach is associated with many confounding factors that make assessment of the mechanisms of heat-induced damage to spermatogenesis difficult. Scrotal insulation provides a better model to investigate the mechanisms and potential mitigation strategies of heat-induce damage. For example, scrotal insulation helped identify a link between short-term heat stress and damage to meiotic germ cells. This outcome is likely due to changes in the integrity of the blood-testis barrier, which induce apoptosis, autophagy and DNA damage in the germ cells. Further understanding how heat damages spermatogenesis, and whether or not this can be repaired, are crucial to mitigating heat effects on boars in production settings.