Submitted to: National Pork Board Web Site <www.porkboard.org>
Publication Type: Research Technical Update
Publication Acceptance Date: 3/28/2016
Publication Date: 4/18/2016
Citation: Rempel, L.A., Miles, J.R., Parrish, J. 2016. Evaluation of contributions to seasonal reproductive inefficiency; NPB #14-052. National Pork Board. Available: http://research.pork.org/FileLibrary/ResearchDocuments/14-052-REMPEL-final%20rpt.pdf.
Interpretive Summary: 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
Technical Abstract: The objective of the current study was to evaluate quality of semen collected from June (spring), August (summer), or January (winter) and either stored and used as cooled-extended (ExT) or cryopreserved (FrZ) for breeding gilts in summer (August) or winter (January). Semen quality evaluation included: % motile, % viable sperm, and Fourier Harmonic Analysis (FHA) of sperm nuclear shape resulting in harmonic amplitudes 0–5 (HA0-5). Six boars were selected for breeding by least- and most-absolute nuclear shape change between June and August collections. Gilts were artificially inseminated 1x following synchronization in August or January with one of three semen types (August ExT or January ExT, August FrZ, and June FrZ). An additional control group of females (CC) was artificially inseminated following natural heat detection and 2x insemination with ExT semen. Fertility rates tended (P = 0.10) to be greater in gilts inseminated with 1) least HA change semen, 2) semen collected in cooler months (i.e. spring or winter), or 3) if semen was cooled-extended (ExT) versus cryopreserved (FrZ). Largest litters (P = 0.05) were observed in CC females bred with semen having most HA change whilst smallest litters were in gilts bred with least HA change, and August FrZ semen at the August breeding event (P = 0.05). Fetal weights and placental weights were significant (P < 0.05) by semen collection time x semen storage x HA change x breeding season. Relative ribosomal protein L8 transcript from motile-rich sperm tended (P = 0.0521) to be increased in samples collected in June and cryopreserved in comparison to June collected, cooled-extended or August collected, cryopreserved. Relative lectin, galactoside-binding, soluble, 3 transcript tended (P = 0.0551) to be greater from June collected sperm in contrast to August collected sperm. Methylation (5-methylcytosine; 5mC) and hydroxymethylation (5-hydroxymethylcytosine; 5hmC) activity in fetal liver and placenta was measured to estimate gene transcription activity as influenced by epigenetic factors. Fetal livers tended (P = 0.0863) to have a reduced 5mC:5hmC when derived from FrZ semen in comparison to ExT semen (12.0 ± 2.70 and 18.6 ± 2.61, respectively) or summer breedings versus winter breedings (10.1 ± 2.63 and 20.4 ± 3.03, respectively). In contrast, placentas derived from summer breedings had greater 5mC:5hmC versus winter breedings (4.7 ± 0.70 and 1.2 ± 0.74, respectively). The findings in the current study support the occurrence of factors contributing to seasonal infertility even in the absence of extreme heat. Of great interest, male and female components may contribute to epigenetic actions influencing piglet gene transcription.