Seasonal reproductive inefficiency is globally observed within the swine industry. Even when photoperiod and temperature are controlled, reductions in pregnancies and subsequent farrowing rates are noted. The most obvious contributor to this phenomenon is the young female. In all likelihood, we see greater effects of seasonality on the young dam as a result of her inherent nature to care for herself first and foremost before imparting energies into fostering a pregnancy. However, it has been coming to light that seasonality also has impacts on the male contribution; sperm. Therefore, we comprehensively investigated the basic knowledge of how the primary contributors (male and female) behave physiologically and at a molecular level during heat and cool events.
Semen quality from 12 boars was assessed using percent motile, percent viable, and sperm nuclear shape by Fourier Harmonic Analysis (FHA). Selection of boars for breeding was based upon the amount of nuclear shape change from June (spring collection) and August (summer collection), with 3 boars from the most absolute change and 3 from the least. Breedings took place during summer (August) and winter (January) periods. Gilts were single-time AI following a synchronization protocol using Matrix with semen from either cooled-extended (ExT), cryopreserved from June collection (FrZ spring), or cryopreserved from August collection (FrZ summer).
In order to gain insight into the molecular activity of the sperm itself, we evaluated the transcript activity of candidate genes from motile-rich sperm that had been previously identified as different between summer or winter collected semen and within the epigenetic methylcytosine pathway. Only two transcripts tended to be influenced by treatments. Relative expression of Lectin, Galactoside-Binding, Soluble, 3 (LGALS3) tended to be greater in motile-rich sperm from June collection versus August collection. LGALS3 is necessary for pre-mRNA splicing and is associated with serum testosterone levels in humans. Ribosomal protein L8, a component of the 60S ribosome subunit and involved in protein synthesis, tended to be less in cryopreserved semen from June in comparison to cryopreserved sperm from August or cooled-extended semen from June.
Fertility, as measured by conception rate at approximately 45 days post-insemination, tended to be influenced by the main effects tested. Semen from the boars with the most HA change tended to have reduced fertility rates in comparison to those with the least HA change. Fertility rates also tended to be less in those gilts bred with semen collected during the summer in contrast to spring or winter collections. And cryopreserved (FrZ) semen tended to yield reduced conception rates in comparison to cooled-extended (ExT) semen.
Influences on litter characteristics from pregnant gilts were less discernible by influence of treatments. Production characteristics including; litter size, fetal weights, placental weights, and placental efficiency were all affected by interaction of the main effects; breeding season, season of semen collection, semen storage, and Harmonic Amplitude (HA) change. Fertility rates tended to be less in gilts inseminated with semen collected during the summer and from boars with the greatest absolute HA change; however, these matings had the largest litter size. Furthermore, cryopreserved semen from August collection period appeared to yield smaller litter sizes. As expected, weights of fetuses were generally less from breedings with the largest litter sizes. Interestingly, fetuses derived from August breedings appeared to be heavier than those from January breedings. Evaluation of placental weights suggested most interactions were similar with the exception of those pregnancies generated using natural estrus detection and 2x insemination, in which placental weights were less. Using placental efficiency as a means of evaluating the uterine environment, it appears the double insemination treatment were somewhat less efficient.
The ultimate product of the male and female contribution is the piglet. To investigate the influence of seasonal parental contributions, the DNA methylation activity, which is an indicator of gene transcriptional activity and can be influenced by epigenetic factors (e.g. temperature, feedstuffs), was measured in fetal liver and placenta. The conversion of 5-methylcytosine to 5-hydroxymethylcytosine is positively associated with increased gene transcript activity. In the current study, we found that the ratio of 5-methylcytosine to 5-hydroxymethylcytosine was favorable for increased gene transcript activation in fetal livers from summer matings that used cooled-extended semen. Whilst the placental methylation ratio was more favorable for increased gene transcript activation from winter matings.
Although we could not control the unseasonably cool summer temperatures, we were able to detect differences in the semen by collection period as well as by breeding season. The use of FHA appears to have provided additional information, beyond current acceptable standards, for semen quality assessment. Nuclear head shape varied by season and storage conditions, and was associated with fertility, as a measure of absolute most or least change in HA from June to August collections, however, no single HA was able to predict fertility. Regardless of HA, expected fertility rates tended to be greater if semen was collected during the cooler seasons (spring or winter) or if cooled-extended (ExT) semen was used. Although litter traits were different, no concise pattern was clearly discernable by treatment; therefore, the use of single insemination was not a detrimental approach to generate pregnancies in the current study. Transcript activity of genes known to be influenced by season of semen collection, tended to be altered in two genes with affiliation to protein synthesis and ribosomal activity, both of which could greatly influence proper sperm viability and/or fertility. Furthermore, general assessment of genomic methylation activity from post-fertilization tissues suggested that epigenetics of season in which semen was collected and breeding season may influence gene activation. These data support that season, even in the absence of extreme heat, may have a deeper molecular influence on infertility within both male and female components. A larger study assessing sperm parameters including the use of Fourier Harmonic methods may provide a greater predictor of fertility that could override seasonal infertility in gilts. However, alterations to the piglet may still be incurred as a result of epigenetic actions upon semen and the uterine environment by season.
• The use of Fourier Harmonic Amplitude suggests that additional measurements can be made to evaluate semen for a more comprehensive prediction of fertility.
• Following two breeding trials with gilts, cryopreserved semen collected during cooler period (Spring) had greater fertility than cryopreserved semen collected during summer.
• Two motile-rich sperm gene transcripts were altered among semen either collected during Spring and Summer or stored as cooled-extended or cryopreserved.
• Methylation activity was different within fetal livers and placentas between winter and summer breeding seasons, which could result in altered gene activation during fetal development.
Dr. Lea A. Rempel
USDA, ARS, US Meat Animal Research Center