Current Status and Perspectives of Artificial Insemination in Pigs

Artificial insemination (AI) of pigs has grown exponentially as reproductive technology with more than a dozen of the top pig producers of the world inseminating >95% of the females in production schemes, at either nucleus or multiplication herds. Above 98% of AIs still concern liquid semen, often inseminated just within a day or maximum two from collected and extended, and most often using cervical deposition. Despite this conservative scenario, developments are ongoing. Some relate to the development of new extenders and temperatures of conservation, intending avoidance of the interval 16-20°C towards more convenient cooling temperatures of 5°C. Others focus on diminishing sperm numbers per AI-dose, so that differences in fertility can be determined between boars (often close to a billion sperm per dose). As well, new methods for intrauterine-AI are devised (trans-cervical, deep-intrauterine, double-intrauterine) to deposit low-to-very-low sperm numbers and thus accommodate for further use of selected sperm, either by robustness (colloid-separation) or chromosomal sex, freshor frozen-thawed. As re-emergent issues in pig-AI we see the use of alginate-encapsulated sperm for single AI with liquid semen per estrus, as well as reintegration of autologous seminal plasma (or some selected components) to washed sperm to facilitate sperm survival over time and to be crucial signaling to the female. Use of frozen-thawed semen is gaining terrain with the use of selected ejaculate sub-populations, or addition of exogenous chemicals (prostaglandins, oxytocin) or, of new strategies for the accurate induction of ovulation (GnRH agonists) and of single fixed-time AIs. Clouds are still blurring further development. Focused selection of females for ovulation rate and uterine capacity has led to large and heterogeneouslitters (often yielding high piglet mortality/weakness). Males, selected using such criteria, have only shown modest increases in sperm production and minor positive changes in sperm quality. Male-to-male variation is still a problem to solve, including our incapacity to properly diagnose fertility levels of boars with an apparent similar semen picture; these males still could yield different fertility after conventional AI. New developments in sperm transcriptomics for semen (sperm and seminal plasma) are, however, encouraging and are discussed alongside my critical views of the state-of-the-art in porcine AI.