Genetic parameters of the thick-to-thin albumen ratio and egg compositional traits in layer-type chickens

ABSTRACT

1. Generating a robust egg albumen is one of the major factors contributing to interior egg quality owing to its nutritive value and superior appearance. However, the genetic factors regulating the proportion of thick albumen are poorly understood.

2. In this study, 1330 eggs were collected from 450 Rhode Island White layers, aged 40 weeks, to measure egg compositional traits for three successive days. The restricted maximum likelihood method was applied to estimate genetic parameters for the thick-to-thin albumen ratio and other egg compositional traits. A univariate animal model was fitted to calculate heritability for each trait.

3. The heritabilities of egg weight, yolk weight, albumen height, Haugh units, percentages of yolk, thick albumen, thin albumen and the thick-to-thin albumen ratio were 0.32, 0.34, 0.28, 0.47, 0.61, 0.39, 0.31, and 0.45, respectively. The percentage of thick albumen was negatively correlated genetically with all traits, and percentage of thin albumen was negatively correlated genetically with all traits except for Haugh units. The thick-to-thin albumen ratio was positively correlated genetically with egg weight, albumen height and Haugh units, with correlations ranging from 0.21 to 0.54.

4. The results indicated that the percentage of thick albumen and the thick-to-thin albumen ratio were found to be moderately to highly heritable, and selection for the thick-to-thin albumen ratio could be conducive to the improvement of egg albumen quality.     

Genetic parameters for semen production traits in Swiss dairy bulls

Variance components (VC) were estimated for the semen production trait ejaculate volume, sperm concentration and sperm motility in the Swiss cattle breeds Brown Swiss (BS), Original Braunvieh (OB), Holstein (HO), Red‐Factor‐Carrier (RF), Red Holstein (RH), Swiss Fleckvieh (SF) and Simmental (SI). For this purpose, semen production traits from 2,617 bulls with 124,492 records were used. The data were collected in the years 2000–2012. The model for genetic parameter estimation across all breeds included the fixed effects age of bull at collection, year of collection, month of collection, number of collection per bull and day, interval between consecutive collections, semen collector, bull breed as well as a random additive genetic component and a permanent environmental effect. The same model without a fixed breed effect was used to estimate VC and repeatabilities separately for each of the breeds BS, HO, RH, SF and SI. Estimated heritabilities across all breeds were 0.42, 0.25 and 0.09 for ejaculate volume, sperm concentration and sperm motility, respectively. Different heritabilities were estimated for ejaculate volume (0.42; 0.45; 0.49; 0.40; 0.10), sperm concentration (0.34; 0.30; 0.20; 0.07; 0.23) and number of semen portions (0.18; 0.30; 0.04; 0.14; 0.04) in BS, HO, RH, SF and SI breed, respectively. The phenotypic and genetic correlations across all breeds between ejaculate volume and sperm concentration were negative (?0.28; ?0.56). The other correlations across all breeds were positive. The phenotypic and genetic correlations were 0.01 and 0.19 between sperm motility and ejaculate volume, respectively. Between sperm motility and sperm concentration, the phenotypic and genetic correlations were 0.20 and 0.36, respectively. The results are consistent with other analyses and show that genetic improvement through selection is possible in bull semen production traits.     

Genetic parameters for claw health and feet and leg conformation traits in Finnish Ayrshire cows

Genetic parameters for different claw disorders, overall claw health and feet and leg conformation traits were estimated for Finnish Ayrshire cows. The merged data set with records of claw health and feet and leg conformation traits consisted of 105 000 observations from 52 598 Finnish Ayrshire cows between 2000 and 2010. The binary claw health data and the linearly scored conformation data were analysed using an animal model and restricted maximum likelihood method by applying the statistical package ASReml. Binomial logistic models with mixed effects were used to estimate genetic parameters for sole haemorrhages, chronic laminitis, white‐line separation, sole ulcer, interdigital dermatitis, heel horn erosion, digital dermatitis, corkscrew claw and overall claw health. Estimated heritabilities for different claw disorders using a binomial logistic model ranged from 0.01 to 0.20. Estimated heritability for overall claw health using a binomial logistic model was 0.08. Estimated heritabilities for feet and leg conformation traits ranged from 0.07 to 0.39. The genetic correlations between claw health and feet and leg conformation traits ranged from ?0.40 to 0.42. All phenotypic correlations were close to zero. The moderate genetic correlation, together with higher heritability of feet and leg conformation traits, showed that RLSV (rear leg side view) is a useful indicator trait to be used together with claw trimming information to increase the accuracy of breeding values for claw health in genetic evaluation.     

Genetic parameters for litter traits at different parities in purebred Landrace and Yorkshire pigs

Comparison of the multi‐trait animal model and the traditional repeatability model was carried out using data obtained from 6,424 Landrace and 20,835 Yorkshire sows farrowed from January 2000 to April 2018 in order to estimate genetic parameters for litter traits at different parities. Specifically, records of the total number born (TNB), number born alive (NBA), total number of mortality (MORT), number of stillborn (NSB) and number of mummified pigs (MUM) were used. Although results showed the heterogeneity of heritability for litter traits at different parities, the mean heritability estimates from the multi‐trait model were found to be higher than those of the repeatability model for all traits in both pig breeds. In terms of genetic correlation between parities, a slight difference in genetic control in the first parity was noted for TNB and NBA in Landrace and Yorkshire pigs. The correlation between the first parity and later parities ranged from 0.48 to 0.74 for TNB and NBA in both breeds. Moreover, genetic correlation between parities for MORT and NSB was observed to be high for parities higher than 2 in Yorkshire pigs. For MUM, genetic correlation between the first and other parities was generally low in both breeds, indicating that culling pigs on the basis of MUM at the first parity could probably be unreasonable. Overall, the results of this study suggest that the multi‐trait approach for litter size traits is useful for the accurate estimation of genetic parameters.     

Genetic parameters for the prediction of abdominal fat traits using blood biochemical indicators in broilers

1. Excessive deposition of body fat, especially abdominal fat, is detrimental in chickens and the prevention of excessive fat accumulation is an important problem. The aim of this study was to identify blood biochemical indicators that could be used as criteria to select lean Yellow-feathered chicken lines.

2. Levels of blood biochemical indicators in the fed and fasted states and the abdominal fat traits were measured in 332 Guangxi Yellow chickens. In the fed state, the genetic correlations (r_g) of triglycerides and very low density lipoprotein levels were positive for the abdominal fat traits (0.47 ≤ r_g ≤ 0.67), whereas total cholesterol, high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C) showed higher negative correlations with abdominal fat traits (–0.59 ≤ r_g ≤ ?0.33). Heritabilities of these blood biochemical parameters were high, varying from 0.26 to 0.60.

3. In the fasted state, HDL-C:LDL-C level was positively correlated with abdominal fat traits (0.35 ≤ r_g ≤ 0.38), but triglycerides, total cholesterol, HDL-C, LDL-C, total protein, albumin, aspartate transaminase, uric acid and creatinine levels were negatively correlated with abdominal fat traits (–0.79 ≤ r_g ≤ ?0.35). The heritabilities of these 10 blood biochemical parameters were high (0.22 ≤ h² ≤ 0.59).

4. In the fed state, optimal multiple regression models were constructed to predict abdominal fat traits by using triglycerides and LDL-C. In the fasted state, triglycerides, total cholesterol, HDL-C, LDL-C, total protein, albumin and uric acid could be used to predict abdominal fat content.

5. It was concluded that these models in both nutritional states could be used to predict abdominal fat content in Guangxi Yellow broiler chickens.     

Genetic parameters for growth traits in Mexican Nellore cattle

The aim of this study was to estimate genetic parameters for growth traits in Mexican Nellore cattle. A univariate animal model was used to estimate (co)variance components and genetic parameters. The traits evaluated were birth weight (BW), weaning weight (WW), and yearling weight (YW). Models used included the fixed effects of contemporary groups (herd, sex, year, and season of birth) and age of dam (linear and quadratic) as a covariate. They also included the animal, dam, and residual as random effects. Phenotypic means (SD) for BW, WW, and YW were 31.4 (1.6), 175 (32), and 333 (70) kg, respectively. Direct heritability, maternal heritability, and the genetic correlation between additive direct and maternal effects were 0.59, 0.17, and −0.90 for BW; 0.29, 0.17, and −0.90 for WW; and 0.24, 0.15, and −0.86 for YW, respectively. The results showed moderate direct and maternal heritabilities for the studied traits. The genetic correlations between direct and maternal effects were negative and high for all the traits indicating important tradeoffs between direct and maternal effects. There are significant possibilities for genetic progress for the growth traits studied if they are included in a breeding program considering these associations.     

Genetic parameters for residual energy intake and energy conversion efficiency in Nordic Red dairy cattle

Abstract

Our aim was to estimate the genetic parameters of residual energy intake (REI) and energy conversion efficiency (ECE), and their relationships with milk, feed intake and body weight (BW) and condition in Nordic Red dairy cattle with data from 400 animals. These data were analysed with repeatability and random regression models. The highest heritabilities for energy efficiency traits were obtained in the beginning and the end of the 30 week lactation period (0.21–0.40). The results suggest that the energy efficiencies in early- and mid-lactation periods are partially different traits. The genetic correlations of REI were moderate to high and positive with the other studied traits, and high and positive for ECE with milk, but moderate to low and negative with dry matter intake, BW and body condition score. Further improvements are still needed in modelling the energy efficiency traits of cows during lactation.     

Genetic parameter estimation for beef bull semen attributes

Improvements in bull reproductive performance are necessary to optimize the efficiency of cattle production. Female fertility has been enhanced through assisted reproductive technologies as well as genetic selection; however, improving beef bull fertility has been largely ignored. Phenotypes routinely collected at bull semen collection facilities are believed to affect fertility and provide the phenotypes necessary for a genetic evaluation. The first objective of this study was to determine the significant fixed effects for modeling beef bull fertility using data from bull semen collection facilities. The second objective was to estimate variance components, heritabilities, repeatabilities, and correlations between beef bull semen attributes. Beef bull fertility phenotypes including volume (VOL), concentration (CONC), number of spermatozoa (NSP), initial motility (IMot), post-thaw motility (PTMot), 3-h post-thaw motility (3HRPTMot), percentage of normal spermatozoa (%NORM), primary abnormalities (PRIM), and secondary abnormalities (SEC) were obtained from two bull semen collection facilities. A total of 1,819 Angus bulls with 50,624 collection records were analyzed. Of the fixed class and covariate effects tested, the significant class effects were collection location and collection day within year and the significant covariate effects included age at collection, days since previous collection, and cumulative comprehensive climate index (CCI). For this study, the CCI was calculated for a 75-d period including the 61-d spermatogenesis cycle and 14-d epididymal transit time. The 75 d prior to collection accounted for the environmental stress a bull may have experienced over the course of development of the spermatozoa, which was more significant than the CCI calculated for collection day or spermatogenesis start date. Pre-thaw beef bull semen traits had low heritability estimates of 0.11 ± 0.02 (VOL), 0.09 ± 0.02 (CONC), 0.08 ± 0.02 (NSP), and 0.12 ± 0.03 (IMot). Heritabilities of post-thaw beef bull semen attributes were more variable at 0.10 ± 0.02 (PTMot), 0.05 ± 0.04 (3HRPTMot), 0.10 ± 0.04 (%NORM), 0.03 ± 0.03 (PRIM), and 0.18 ± 0.04 (SEC). Correlations of breeding values for these traits with scrotal circumference (SC) expected progeny difference (EPD) are low. The low to moderate heritability estimates indicate that genetic improvement can be made in beef bull semen quality traits if new tools are developed to augment the scrotal circumference EPD that are currently available within the industry.     

Genetic analysis of growth,visual scores,height, and carcass traits in Nelore cattle

Covariance components were estimated for growth traits (BW, birth weight; WW, weaning weight; YW, yearling weight), visual scores (BQ, breed quality; CS, conformation; MS, muscling; NS, navel; PS, finishing precocity), hip height (HH), and carcass traits (BF, backfat thickness; LMA, longissimus muscle area) measured at yearling. Genetic gains were obtained and validation models on direct and maternal effects for BW and WW were fitted. Genetic correlations of growth traits with CS, PS, MS, and HH ranged from 0.20 ± 0.01 to 0.94 ± 0.01 and were positive and low with NS (0.11 ± 0.01 to 0.20 ± 0.01) and favorable with BQ (0.14 ± 0.02 to 0.37 ± 0.02). Null to moderate genetic correlations were obtained between growth and carcass traits. Genetic gains were positive and significant, except for BW. An increase of 0.76 and 0.72 kg is expected for BW and WW, respectively, per unit increase in estimated breeding value (EBV) for direct effect and an additional 0.74 and 1.43, respectively, kg per unit increase in EBV for the maternal effect. Monitoring genetic gains for HH and NS is relevant to maintain an adequate body size and a navel morphological correction, if necessary. Simultaneous selection for growth, morphological, and carcass traits in line with improve maternal performance is a feasible strategy to increase herd productivity.     

Genetic parameters for linear type traits in the Rendena dual‐purpose breed

The aim of the study was to estimate the genetic parameters for five composite traits and 20 individual type traits on 10 735 first‐parity Rendena dual‐purpose cows. Fixed effects included in the linear animal mixed models were herd‐year‐classifier, days in milk and age at first calving; the additive genetic effect of the animal was included as a random effect. Heritability estimates varied from 0.12 (feet) to 0.52 (stature). Genetic correlations between the individual body size traits were all ≥0.69; similar strong genetic correlations existed between traits describing similar morphological characteristics (e.g. mammary system, fleshiness). Many of the body size traits were negatively genetically correlated with animal fleshiness. Genetic trends showed that genetic merit for body size increased consistently over the last 10 years, while genetic merit for fleshiness declined. These results suggest that the characteristics of the dual‐purpose Rendena cattle are becoming more like specialized milk‐producing animals. Nonetheless, sufficient genetic variation exists to halt or reverse the deterioration in fleshiness.     

Analysis of testicular variables,semen motility and kinematics-derived indexes in boar using a CASA-Mot system

The present study aimed to evaluate differences in area, volume and testicular weight among groups related to breed and age of boar and establish associations between testicular parameters and seminal characteristics. Seminal quality has been studied using computer-assisted semen analysis (CASA) systems that reduce the subjectivity of kinematic parameters. Based on the data obtained through this system, sperm quality indexes and their derived parameters have been assessed to identify a better estimator for determining movement and velocity parameters. We also established indexes of velocity and sperm movement for boar semen. To this end, we evaluated 191 ejaculate samples from 63 boars. Differences related to the effects of season and age on quality boar semen were found (p ≤ .05) in the animal groups. Indexes were established for velocity and sperm movement based on CASA-Mot, and we proposed a sperm movement index (SMI) and sperm velocity index (SVI) with the CASA-Mot variables. Correlations were found (p < .05) among sperm indexes and CASA-Mot variables. Boar characteristics were found to be associated with some CASA-Mot variables, and the estimated SMI and SVI indexes predicted a greater variation in kinematic characteristics compared to the parameters evaluated separately using the CASA-Mot system.     

Estimation of genetic parameters for carcass grading traits,image analysis traits,and monounsaturated fatty acids in Japanese Black cattle from Hyogo Prefecture

Genetic parameters for carcass grading traits, image analysis traits, and monounsaturated fatty acid (MUFA) percentages were estimated in 29,942 Japanese Black cattle from Hyogo Prefecture. The analyzed traits included five carcass grading traits, two image analysis traits, fat area ratio and fineness index, and two MUFA traits, one measured in intermuscular fat using near-infrared spectroscopy (NIRS) and the other in intramuscular fat using gas chromatography (GC). The heritability estimates of image analysis traits and MUFA were moderate to high, ranging from 0.395 to 0.740, and it was considered that they could be improved simultaneously with carcass grading traits because no severe genetic antagonism was observed. Although the heritability of the NIRS-based intermuscular MUFA was slightly lower than that of the GC-based intramuscular MUFA, the genetic correlation between the two methods was as high as 0.804. These results indicate that the NIRS method can be used as an alternative evaluation procedure to predict MUFA in intramuscular fat in the longissimus muscle.     

Relationship between angioarchitecture of the testicular artery and spermiogram parameters in Egyptian buffalo bulls (bubalus bubalis)

The current study aimed to investigate the effect of testicular artery angioarchitecture on the spermiogram parameters in Egyptian Buffalo bulls. Eight adult buffalo bulls aged between 2 and 8 years were used for semen evaluation. For anatomical studies, the masculine gonads were collected after slaughtering 30 adult bulls and prepared for injection by different masses (Urographine^®, Latex and Epoxy) through the testicular artery. The mass activity of the ejaculate was assessed immediately after collection. The sperm motility in fresh bull ejaculate was more than 80%. The overall mean percentage of sperm abnormalities was <18%. The recorded sperm abnormalities were mostly secondary one including distal protoplasmic droplet, fragmented tail, detached head, detached galea capitis and bent tail. The highest percentage of sperm viability was recorded just after sperm collection (alive > 85%). The results revealed that testicular artery can be divided into three parts (abdominal, funicular and marginal parts) along its course. The coils of the funicular part forming a cone-like structure with its base fixed to the head of the testis. Two epididymal branches to the head and tail of epididymis emanate from the funicular part which continues as pars marginalis on the lateral surface of testis before its division into the lateral and medial testicular arteries on approaching the tail extremity of the testis. The increase in the length of the testicular artery with increase in the size of the testes played a great role in the degree of complexity of the architectural vascular patterns. The degree of complexity is affected by the number of coils formed by the vessel. The increase in the convolutions of the vessel will reduce the speed of blood flow to the gonads. Thus in turn will enabling the thermoregulatory mechanism to work more efficiently and will affect the semen value.     

Estimation of genetic parameters and genome scan for 15 semen characteristics traits of Holstein bulls

A QTL detection experiment was performed in French dairy cattle to search for QTL related to male fertility. Ten families, involving a total of 515 bulls, were phenotyped for ejaculated volume and sperm concentration, number of spermatozoa, motility, velocity, percentage of motile spermatozoa after thawing and abnormal spermatozoa. A set of 148 microsatellite markers were used to realize a genome scan. First, genetic parameters were estimated for all traits. Semen production traits were found to have moderate heritabilities (from 0.15 to 0.30) while some of the semen quality traits such as motility had high heritabilities (close to 0.60). Genetic correlations among traits showed negative relationships between volume and concentration and between volume and most quality traits such as motility or abnormal sperm while correlations between concentration and these traits were rather favourable. Percentages of abnormal sperm were negatively related to quality traits, especially with motility and velocity of spermatozoa. Three QTL related to abnormal sperm frequencies were significant at p < 0.01. In total, 11 QTL (p < 0.05) were detected. However, the number of QTL detected was within the range of expected false positives. Because of the lack of power to find QTL in this design further analyses are required to confirm these QTL.     

Genetic parameters of pelt character,feed efficiency and size traits in Finnish blue fox (Vulpes lagopus)

Pelt character traits (size, quality, colour clarity, darkness) are important economic traits in blue fox breeding. Better feed efficiency (FE) is another economically important and new breeding goal for fur animals. The purpose of this study was to determine the correlations between pelt character traits, FE and size traits and to estimate genetic parameters for pelt character traits. Pelt size (pSI_cm) had a high positive genetic correlation with animal grading size (gSI), final body weight (BW_Fin), body length and daily gain (DG), and a moderate correlation with body condition score (BCS). Animal body length and BCS (describing fatness) were considered as genetically different traits. Genetic correlations between pelt quality and size traits were estimated without precision and did not differ from zero, but colour clarity (pCL) had a low antagonistic genetic correlation with FE. Pelt size and DG had a favourable genetic correlation with FE but a fairly high unfavourable genetic correlation with dry matter feed intake. The current emphasis on selection for larger animal and pelt size improves FE indirectly, but selection for larger pelt size favours fast‐growing and fat individuals and simultaneously increases feed intake. The detected genetic connections between FE, size, feed intake and pCL should be taken into account in the Finnish blue fox breeding programme.     

Genetic parameters in Finnish blue fox population: Pelt character and live animal grading traits

Abstract

Finnish blue fox farmers breed for increased litter size and pelt size, and improved fur quality. Some farmers select pelt size and fur quality indirectly using live animal evaluations (grading traits). In order to be able to define breeding goals properly, heritabilities and genetic correlations were estimated for size traits and fur quality traits. There were four pelt character traits (pelt size, pelt colour darkness, pelt colour clarity and pelt quality) measured on dried skins, and six grading traits (animal size, grading colour darkness, grading colour clarity, underfur density, guard hair coverage and grading quality). The data included 54,680 animals born during the years 1987–2002, originating from seven farms. The heritabilities were high for pelt colour darkness and grading colour darkness, moderate for pelt size and low for other traits. In general, heritability of a pelt character trait was higher than its corresponding grading trait. Genetic correlations within the pelt character traits were low (～0.11) and within the grading traits mainly moderate or high (～0.44). There was high genetic correlation between pelt darkness and grading darkness, pelt quality and grading density, pelt size and animal size; between pelt quality and grading quality and between pelt colour darkness and grading guard hair coverage. This suggests that selection of pelt character traits via grading traits in most cases is relatively effective.     

Genetic parameter estimates for semen production traits and growth rate of a paternal rabbit line

Variance components of sperm production traits (volume in ml, V; concentration in ×10⁶ sperm/ml, CN; sperm production in ×10⁶ sperm, PROD) were estimated in a paternal line of rabbit selected for 25 generations based on daily weight gain (DG, g/day) between 28 and 63 days of age. Features of the marginal posterior distributions for ratios of genetic variance, variance owing to non‐additive plus environmental permanent male effects and variance owing to common litter of birth effects with respect to phenotypic variance are reported. The correlations between sperm production traits and the selection criteria were also estimated. Three sets of two‐trait analyses were performed, involving 12908 records of DG, 2329 ejaculates corresponding to 412 bucks and 14700 animals in pedigree file. The heritabilities (h²) of the semen traits were 0.13 ± 0.05, 0.08 ± 0.04 and 0.07 ± 0.03 for V, CN and PROD, respectively. The permanent environmental effects were lower than the corresponding values of h² and varied between 0.06 and 0.11. A favourable and moderate genetic correlation was observed between V and DG (0.36 ± 0.34; p > 0: 0.83), together with a non‐favourable and moderate correlation between permanent environmental effects owing to common litter of birth for both traits (?0.35 ± 0.35; p < 0: 0.85). On the other hand, the correlation between male permanent environmental effects for semen traits and DG was moderate and non‐favourable (?0.51 ± 0.29 with p < 0: 0.95 for DG‐CN, and ?0.31 ± 0.37 with p < 0: 0.79 for DG‐PROD).     

Genetic parameter estimation for long endurance trials in the Uruguayan Criollo horse

The aim of this study was to estimate the genetic parameters of performance in a 750‐km, 15‐day ride in Criollo horses. Heritability (h²) and maternal lineage effects (mt²) were obtained for rank, a relative placing measure of performance. Additive genetic and maternal lineage (rmt) correlations among five medium‐to‐high intensity phase ranks (pRK) and final rank (RK) were also estimated. Individual records from 1,236 Criollo horses from 1979 to 2012 were used. A multivariate threshold animal model was applied to the pRK and RK. Heritability was moderate to low (0.156–0.275). Estimates of mt² were consistently low (0.04–0.06). Additive genetic correlations between individual pRK and RK were high (0.801–0.924), and the genetic correlations between individual pRKs ranged from 0.763 to 0.847. The pRK heritabilities revealed that some phases were explained by a greater additive component, whereas others showed stronger genetic relationships with RK. Thus, not all pRK may be considered as similar measures of performance in competition.     

Genetic parameter estimates for prenatal and postnatal mortality in Nellore cattle

The aim of this study was to estimate genetic parameters for prenatal (PRE) and postnatal (POS) mortality in Nellore cattle. A total of 13 141 (PRE) and 17 818 (POS) records from Nellore females were used. PRE and POS were recorded using binary scale scores: a score of ‘1’ was given to calves that were born alive (PRE) and those that were alive at weaning (POS), and a score of ‘0’ was given to calves that were not alive at or around birth (PRE), as well as to those weighed at birth but not at weaning (POS). The relationship matrix included 698 sires, 107 paternal grandsires and 69 maternal grandsires. Data were analysed using Bayesian inference and a sire–maternal grandsire threshold model, including contemporary groups as random effects, and the classes of dam age at the beginning of mating season (for PRE), and dam age at calving and birthweight (linear covariable) (for POS), as fixed effects. For both traits, the covariance between direct and maternal effects (r_D,M) was estimated (r_D,M≠ 0) or fixed at zero (r_D,M = 0). PRE and POS rates were 3.00 and 4.04%, respectively. Estimates of direct and maternal heritability were 0.07 and 0.17, respectively, for PRE, and 0.02 and 0.07, respectively, for POS, assuming r_D,M = 0. For r_D,M ≠ 0, these estimates were 0.07 and 0.12, respectively, for PRE, and 0.03 and 0.07, respectively, for POS. The correlation estimates between direct and maternal effects were ?0.71 (PRE) and ?0.33 (POS). PRE and POS show low genetic variability, indicating that these traits probably suffer major environmental influences. Additionally, our study shows that the maternal genetic component affects preweaning calf mortality twice as much (or more) as the direct genetic component. A large number of offspring per sire is necessary in progeny tests to genetically decrease calf mortality.     

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.