Linear growth model analysis of factors affecting boar semen characteristics in Southern China

Nonsynonymous SNPs within C7H15orf39 and NOS2 are associated with boar semen quality

Spermatogenesis is the developmental process that produces spermatozoa. The aim of this study was to investigate the single nucleotide polymorphisms (SNPs) within C7H15orf39 and NOS2 genes and to determine the correlations between two SNPs and semen quality in Duroc boars (n = 604). The polymerase chain reaction-restriction fragment length polymorphisms (PCR-RFLP) method was used for genotyping the selected two nonsynonymous SNPs. The significant correlation was observed between two SNPs (rs80969873: g.58385473 G > A within C7H15orf39; rs325865291: g.44175445 G > A within NOS2) and semen traits in Duroc boars. This study indicates the SNPs in C7H15orf39 and NOS2 may be the potential molecular marker for improving the semen quality traits in Duroc boars.

Cluster analysis and potential influencing factors of boars with different fertility

The fertility of boars is intimately tied to the pig farm's economic benefits. This study aimed to rapidly categorize boars of different fertility and investigate the factors influencing the categorization using the production data in a large pig farm in northern China, including 11,163 semen collection records of Yorkshire boars (215), 11,163 breeding records and 8770 records of farrowing performance of Yorkshire sows (4505), as well as 4720 records of selection indices (sire line index and dam line index) for boars and sows (215 and 4505) between 2017 and 2020. The boar population was classified by two-step cluster analysis, followed by factor analysis to minimize the dimensionality of data variables and eliminate multicollinearity, and then using ordinal logistic regression model to investigate the risk variables impacting boar fertility categorization. Results showed that the two-step clustering divided the 215 boars into three subgroups: high-fertility (n = 61, 28.4%), medium-fertility (n = 127, 59.1%) and low-fertility (n = 27, 12.6%). The high-fertility boars were shown to be substantially greater than the medium-fertility or low-fertility boars (p < 0.05) in average total litter size, number of born alive, and number of healthy piglets of mated sows. Compared with low-fertility boars, the high-fertility boars were also significantly higher (p < 0.05) in the pregnancy rate and farrowing rate of mated sows. However, the three boar subgroups showed no difference (p > 0.05) in semen quality information (average sperm motility, average sperm density, and average sperm volume). Collinearity diagnosis indicated severe multicollinearity among the 20 data variables, which were reduced to 8 factor variables (factors 1-8) by factor analysis, and further collinearity diagnosis exhibited no multicollinearity among the 8 factor variables. Ordered logistic regression analysis revealed a significant and positive correlation (p < 0.05) of boar fertility with factor 2 (average total litter size, number of born alive, number of healthy piglets), factor 4 (average number of weak piglets and average weak piglet rate), factor 6 (sire line index of boars and dam line index of boars), factor 8 (pregnancy rate and farrowing rate), highlighting factor 2 as the most important factor influencing the classification of boar fertility. Our results indicate that the two-step cluster analysis can be used as a simple and effective method to screen boars with different fertility and that farm producers should pay attention to the recording of the reproductive performance of the mated sows due to its role as the risk factor for classification of boar fertility.

Effects of copper citrate on physiological-biochemical parameters of ejaculate of sire boars

Revealing peculiarities of the course of physiological and biochemical processes in the formation of parameters of ejaculate allows effective correlation of biological completeness of spermatozoids based on the use of chelate compounds of limiting microelements, particularly copper. The study was focused on determining changes in processes of spermatogenesis during correction of mineral nutrition. In the experiment, we used adult boars of the same age, live weight and quality of ejaculates. They consumed copper citrate during the 45 day experiment in doses higher than the norm by 10% (1.5 mg per 1 kg of combined feed) and 20% (3 mg per 1 kg of combined feed) compared with the control. We determined difference in the effects of different doses of copper citrate on the formation of parameters of ejaculates in sire boars. Addition of the mineral additive to the feed in the doses 10% exceeding the norm promoted increase in the parameters of functional activity of spermatozoids – mobility and survival – on day 45 of the intake, which occurred against the background of acceleration of peroxidation processes (increase in the concentration of thiobarbituric acid of active compounds) and activation of the system of antioxidant protection – increase in the activity of superoxide dismutase and decrease in the level of catalase in the sperm. At the same time, we observed increase in the morphometric parameters of spermatozoids – general length, width, length and volume of the head. On day 30, sire boars that had been consuming copper citrate in the amounts 20% above the norm were observed to have increase in concentration of spermatozoids, their mobility and survivability, though a decrease was seen in the morphometric parameters of the gametes. Further intake of this element caused increase in the amount of abnormal forms of spermatozoids. Under the action of this additive, we determined increase in the amount of metabolites of lipid peroxidation – conjugated dienes and thiobarbituric acids of active compounds, and also weakening of the system of antioxidative protection – decrease in the content of reduced glutathione and accumulation of dehydroascorbic acid. Thus, the intake of copper citrate in the amounts of 10% above the norm facilitated morpho-functional parameters of spermatozoids by activating the system of antioxidant protection. It would be promising to conduct further research to determine the effects of copper citrate on the processes of activation and capacitation of spermatozoids and fertilization of oocytes in in vivo and in vitro conditions.

Retrospective analysis of commercial heterospermic and homospermic cooled boar semen: effect of the season, sample type and shipping temperature on sperm quality

We retrospectively analyzed data from heterospermic and homospermic boar semen for motility and morphology during a 2-year period. Homospermic doses were also evaluated for viability, acrosome integrity, DNA fragmentation, osmolality and pH. Additionally, we investigated the effect of temperature upon arrival and the agreement between viability and motility as evaluating tool. We observed lower (p < 0.05) total motility (TM) and normal sperm morphology within summer and fall. Conversely, lower (p < 0.05) progressive motility (PM) was found at the beginning and end of each year. Viability and acrosome integrity were reduced (p < 0.05) in summer months but not exclusively, suggesting that samples could be compromised by transport temperature. Sperm DNA fragmentation was <6% with a small variation. Medium osmolality and pH slightly changed (p < 0.05). Sperm count was not source of variation on sperm parameters. Sample temperature upon arrival correlated to PM and VSL (p < 0.05). While motility was reduced <12°C (p < 0.05). Homospermic doses were less affected by season and arrival temperature, having better parameters (p < 0.05) than contemporaneous heterospermic samples but influenced by genetic line (p < 0.05). We found a high agreement between viable acrosome-intact sperm and TM, especially when TM was ≥80%. Our data verify the improvement of sperm quality during time as sperm count/dose does not affected quality, but season effect persists regardless of ejaculate selection at the stud. Homospermic exhibited better parameters than heterospermic doses, seemingly being more resilient to temperature variations, suggesting that selection for sperm quality within boars selected by growth traits can improve product quality.

Establishment of a multilevel linear model to analyse the factors affecting piglet litter performance at birth

This study aimed to establish a feasible model for analysing factors affecting piglet litter performance at birth. Data of 61,984 litters were collected from 16 herds, and general linear model (GLM), multilevel Poisson regression model (MPM) and multilevel linear model (MLM) were established to compare their goodness of fit for these data. Influencing factors of piglet litter performance at birth were analysed using the established optimal model. Results showed the intraclass correlation coefficients of total born piglets (TBP), piglets born alive (PBA), low-birth-weight piglets (LBW), and average birth weight of piglets (ABW) reached 27.89%, 23.88%, 24.66% and 22.27%, respectively (p < .05). Akaike's information criterion and Bayesian information criterion in MLM of TBP, PBA, LBW and ABW were lower than those in GLM. Pearson residuals in MPM increased to nearly 1 after introduction of a discrete scale factor, and the p values in MPM were similar to those in MLM. Analyses of MLM indicated crossbred sows with good management supplemented with oregano essential oil and farrowing at warm season had higher TBA, PBA and ABW, but lower LBW than other sows (p < .05). In conclusion, MLM is superior to GLM and can replace MPM in analysing discrete data with hierarchical structure in pig production. More importantly, other potential influencing factors of litter performance at birth can be analysed using the established MLM in the future.

Multivariate models for estimating jackass semen production and quality

The purpose of this study was to analyse the effects of season, age, gonad and accessory sex glands on semen characteristics of jackass and to construct multivariate regression models to predict semen quality. In autumn, spring and summer, semen characteristics of 30 sexually mature donkeys (1,014 ejaculations) were analysed to investigate the effect of seasons on semen quality, and gonad and accessory sex gland parameters of 12 jackasses were measured immediately after ejaculation by ultrasonography to investigate the effect of seasons on reproductive organ size. Semen (598 ejaculates), gonad and accessory sex gland parameters of 40 jackasses aged between 3 and 7 years were analysed in autumn to investigate the effects of age and reproductive organ size on semen quality and to construct multivariate models. To verify the accuracy of the models, semen (476 ejaculates), gonad and accessory sex gland parameters of 20 jackasses were measured from March to June. Results revealed that semen, gonad and accessory sex gland parameters were not affected by season and age. Progressive motility (PM) was positively correlated with long axis of the spermatic cord (LASC) and negatively correlated with percentages of sperm abnormality (PSA). Total sperm count (TSC) was positively correlated with testis circumferences (TC) and cross-sectional area of cauda epididymis (CSACE). TC, CSACE, LASC and PSA were included into multivariate models to predict PM, TSC and functional sperm count (FSC) in 20 jackasses (PM = 72.332 + 0.428 LASC - 0.441 PSA; TSC = -169.929 + 8.728 TC + 0.253 CSACE; FSC = -206.645 + 8.788 TC + 0.258 CSACE). The predicted and observed values corresponded well. In conclusion, the tested models can be used for predicting semen quality of donkey.

Logistic Regression Analysis Factors Affecting Sperm Motility and Abnormal Sperm Morphology in Boars

Simple Summary

Reduced sperm motility and morphological abnormalities have significant negative impacts on conception rates in sows and are important indexes of semen. The identification of factors that influence sperm motility and morphology will improve boar fertility in commercial herds. On the basis of analysis of 5042 ejaculates from 385 boars using a logistic regression model, we found that serum Cu excess, serum Fe deficiency, and Pb presence in seminal plasma were risk factors for poor semen quality in boars. More importantly, the presence of seminal plasma Pb had more serious effect on the probability of abnormal sperm morphology than serum Cu excess and serum Fe deficiency. In addition, Yorkshire and Landrace boars had higher sperm motility and lower abnormal sperm morphology than Duroc boars. The difference in serum and seminal plasma elements among boars with different semen qualities may become a guide for regulating these elements used in boar diet. The highly predictive values of serum Cu, Fe, and seminal plasma Pb could be used in the future as an additional tool in semen quality evaluation.

Abstract

Logistic regression models, including variables of boar breed, age, serum, and seminal plasma elements, were used to identify the influencing factors of sperm motility and morphology in this study. Sperm motility degree was classified as grade 0: ≤85% and grade 1: >85%. Abnormal sperm morphology was classified as grade 0: ≤10%, grade 1: 10–20%, and grade 2: >20%. Element concentration of 385 boars was detected by inductively coupled plasma mass spectrometry. Results showed that boars with serum Cu ≥ 2.5 mg/L had lower sperm motility (odds ratio (OR): 0.496; 95% confidence interval (CI): 0.285–0.864) and higher abnormal sperm morphology (OR: 2.003; 95% CI: 1.189–3.376) than those with serum Cu ≤ 2.0 mg/L. Boars with serum Fe ≥ 1.5 mg/L had lower abnormal sperm morphology than those with serum Fe ≤ 1.0 mg/L (OR: 0.463; 95% CI: 0.255–0.842). The presence of Pb in seminal plasma increased abnormal sperm morphology. The probability of abnormal sperm morphology >20% from boars with seminal plasma Pb increased with a range of 5.78–15.30% than that from boars without seminal plasma Pb among three breeds. In conclusion, serum Cu excess, serum Fe deficiency, and seminal plasma Pb are risk factors for poor semen quality in boars.

Estimation of genetic parameters and season effects for semen traits in three pig breeds of South China

The economic profitability of a boar station largely depends on semen quantity and quality traits. However, genetic analysis of semen traits has not yet been done in the boar population in China. In this study, we aimed to estimate genetic parameters for semen traits and the influence of seasons on these traits by using data of Duroc, Landrace and Yorkshire boars in South China. The following four semen traits were analysed: semen volume (ml; VOL), sperm concentration (10⁶ /ml; DEN), sperm motility (MOT) and percentage of abnormal sperm (ABN). Genetic parameters and season effects were estimated simultaneously for each breed by using a multiple-trait (4 × 4) repeatability animal model. The four traits had a moderate heritability with average estimates of 0.23, 0.28, 0.26 and 0.17 across the three breeds, respectively. The estimates of genetic correlations among four traits differed in the three breeds. In particular, in Yorkshire, the four traits were nearly genetically independent. The season of collecting semen had a significant impact on these four semen traits except ABN in Duroc (Bonferroni adjusted p < 0.05/6). The moderate heritabilities indicate the possibility of effective selection of boars for semen traits. Different genetic correlations for the three breeds suggest that the selection strategy for the four traits should be investigated separately for each breed. Some necessary actions should be taken to reduce the influence of seasons on semen traits.

Logistic regression analysis of the related factors in discarded semen of boars in Southern China

This study aimed to investigate factors affecting the discarded semen of boars. A total of 176,368 ejaculates of boars from nine AI centers were collected from January 2013 to May 2016 in Southern China. The criteria for determining whether their semen was abnormal included cytoplasmic droplets, coiling tail, sperm agglutination, impurity, poor motility, oligozoospermia, necrozoospermia, azoospermia, and hemospermia. The cause of discarded semen was evaluated with a Chi-square test, and the effects of housing type, breed, age at collection, season identified in the northern hemisphere, and age at herd entry of the discarded semen of boars were analyzed with a logistic regression model. Results indicated the proportion of the discarded semen (PDS) in the nine AI centers was 13.09%. Chi-square test showed the greatest PDS among all causes was found in semen discarded due to cytoplasmic droplets (31.60%), followed by impurity (25.96%), sperm agglutination (20.31%), coiling tail (17.72%), oligozoospermia (10.86%), and others (6.78%; P < 0.0001). Logistic regression analysis revealed the PDS was affected by all these five factors (P < 0.0001). The PDS of boars raised individually in stalls was greater than that of boars raised individually in pens (OR: 1.657; 95% CI: 1.607 to 1.709). The PDSs of Duroc boars (OR: 1.130; 95% CI: 1.093 to 1.167) and Yorkshire boars (OR: 1.432; 95% CI: 1.380 to 1.486) were greater than that of Landrace boars. The PDSs of adult boars (aged from 13 to 24 mo, from 25 to 36 mo, and more than 37 mo with OR: 0.800, 0.941, and 0.838, respectively; 95% CI: 0.771 to 0.831, 0.902 to 0.983, and 0.790 to 0.889, respectively) were lower than those of young boars (aged less than 12 mo). The PDSs of semen collected in summer (OR: 1.367; 95% CI: 1.314 to 1.422), autumn (OR: 1.185; 95% CI: 1.138 to 1.234), and winter (OR: 1.159; 95% CI: 1.115 to 1.206) were greater than those of semen obtained in spring. The PDSs of boars introduced at ages of 5-7 mo (OR: 1.432; 95% CI: 1.380 to 1.486) and 10-12 mo (OR: 1.432; 95% CI: 1.380 to 1.486) were greater than those of boars introduced at an age of 8 and 9 mo. In conclusion, logistic regression analysis reveals discarded semen is affected by housing type, breed, age at collection, season, and age at herd entry. More importantly, cytoplasmic droplets is the primary reason for discarding boar semen, and 8 months at herd entry is the most suitable age for boar introduction.