Novel phenotypes of feeding and social behaviour and their relationship with individual rabbit growth and feed efficiency

Due to the lack of a recording system for individual consumption of group-housed rabbits, published studies about feeding behaviour are based on information recorded at the group- and not at the individual level and periods covering only a few days or, in some cases, only part of a day. Such information could be used to inform rabbit management systems but cannot be used for genetic selection. We aimed to generate and use information from a novel automated feeder for group-housed rabbits to identify new phenotypes for individual animals that could be incorporated into breeding programs to improve feed efficiency and social behaviour under different feeding regimens. At 39 d of age, rabbits from 15 batches were placed in cages and fed ad libitum to become used to the electronic feeder. From 42 to 58-59 d, one group of 1 086 rabbits was fed ad libitum (AL), while another group of 1 134 rabbits was fed on a restricted feeding schedule (R) by limiting the feeding time to the period between 1800 and 0600 h of the following day. We implemented a reliable multivariate method to remove anomalous feeding behaviour records. We then defined novel traits for feeding behaviour that apply to both types of feeding regimes, and for social behaviour that indicates an animal's rank within the cage hierarchy. We based these traits on feeder records and a biologically sound definition of a meal. Finally, we estimated the phenotypic correlations of those traits with growth and feed efficiency traits. Our findings demonstrate that variables about resource distribution among cage mates and an animal's priority for feed access were found to be good indicators of an animal's dominant or subordinate status within the cage. Based on results obtained in R animals (results were similar in AL animals), the most efficient animals were those that ate less frequently (phenotypic correlation with feed conversion ratio, rho = 0.6), and consumed smaller amounts per meal (rho = 0.7), spent less time at the feeder (rho = 0.4), and appeared to be subordinate, as they did not have priority access to the feeder (rho = -0.3), and had the smallest share of resources (range of rho = 0.2-0.6). We conclude that quantifying feeding and social behaviour traits can enhance the understanding of the mechanisms through which individuals exert their effects on the performance of their cage mates.

Dissecting total genetic variance into additive and dominance components of purebred and crossbred pig traits

The partition of the total genetic variance into its additive and non-additive components can differ from trait to trait, and between purebred and crossbred populations. A quantification of these genetic variance components will determine the extent to which it would be of interest to account for dominance in genomic evaluations or to establish mate allocation strategies along different populations and traits. This study aims at assessing the contribution of the additive and dominance genomic variances to the phenotype expression of several purebred Piétrain and crossbred (Piétrain × Large White) pig performances. A total of 636 purebred and 720 crossbred male piglets were phenotyped for 22 traits that can be classified into six groups of traits: growth rate and feed efficiency, carcass composition, meat quality, behaviour, boar taint and puberty. Additive and dominance variances estimated in univariate genotypic models, including additive and dominance genotypic effects, and a genomic inbreeding covariate allowed to retrieve the additive and dominance single nucleotide polymorphism variances for purebred and crossbred performances. These estimated variances were used, together with the allelic frequencies of the parental populations, to obtain additive and dominance variances in terms of genetic breeding values and dominance deviations. Estimates of the Piétrain and Large White allelic contributions to the crossbred variance were of about the same magnitude in all the traits. Estimates of additive genetic variances were similar regardless of the inclusion of dominance. Some traits showed relevant amount of dominance genetic variance with respect to phenotypic variance in both populations (i.e. growth rate 8%, feed conversion ratio 9% to 12%, backfat thickness 14% to 12%, purebreds-crossbreds). Other traits showed higher amount in crossbreds (i.e. ham cut 8% to 13%, loin 7% to 16%, pH semimembranosus 13% to 18%, pH longissimus dorsi 9% to 14%, androstenone 5% to 13% and estradiol 6% to 11%, purebreds-crossbreds). It was not encountered a clear common pattern of dominance expression between groups of analysed traits and between populations. These estimates give initial hints regarding which traits could benefit from accounting for dominance for example to improve genomic estimated breeding value accuracy in genetic evaluations or to boost the total genetic value of progeny by means of assortative mating.

Prediction of complex traits: Conciliating genetics and statistics

This review focuses on methods used to predict complex traits. Main characteristics of prediction approaches are given: the deterministic or stochastic nature of prediction, the objects of prediction, the sources of information and the main statistical methods. Sources of information discussed are the traditional genealogies and phenotypes, nucleotide sequences, expression data and epigenetics marks. Statistical methods are presented as successive degrees of generalization from the definition of the conditional expectation as the prediction rule, to best linear unbiased prediction, then Bayesian and, recently, machine learning methods, including meta-methods. We highlight the contributions of Daniel Gianola to this methodological evolution.

Daily exposure to summer temperatures affects the motile subpopulation structure of epididymal sperm cells but not male fertility in an in vivo rabbit model

High temperatures have negative effects on sperm quality leading to temporary or permanent sterility. The aim of the study was to assess the effect of long exposure to summer circadian heat stress cycles on sperm parameters and the motile subpopulation structure of epididymal sperm cells from rabbit bucks. Twelve White New Zealand rabbit bucks were exposed to a daily constant temperature of the thermoneutral zone (from 18 °C to 22 °C; control group) or exposed to a summer circadian heat stress cycles (30 °C, 3 h/day; heat stress group). Spermatozoa were flushed from the epididymis and assessed for sperm quality parameters at recovery. Sperm total motility and progressivity were negatively affected by high temperatures (P < 0.05), as were also specific motility parameters (curvilinear velocity, linear velocity, mean velocity, straightness coefficient, linearity coefficient, wobble coefficient, and frequency of head displacement; P < 0.05, but not the mean amplitude of lateral head displacement). Heat stress significantly increased the percentage of less-motile sperm subpopulations, although the percentage of the high-motile subpopulation was maintained, which is consistent with the fact that no effect was detected on fertility rates. However, prolificacy was reduced in females submitted to heat stress when inseminated by control bucks. In conclusion, our results suggest that environmental high temperatures are linked to changes in the proportion of motile sperm subpopulations of the epididymis, although fertility is still preserved despite the detrimental effects of heat stress. On the other hand, prolificacy seems to be affected by the negative effects of high temperatures, especially by altering female reproduction.

Model averaging for genome-enabled prediction with reproducing kernel Hilbert spaces: a case study with pig litter size and wheat yield

Predictive ability of yet-to-be observed litter size (pig) grain yield (wheat) records of several reproducing kernel Hilbert spaces (RKHS) regression models combining different number of Gaussian or t kernels was evaluated. Predictive performance was assessed as the average (over 50 replicates) predictive correlation in the testing set. Predictions from these models were combined using three different types of model averaging: (i) mean of predicted phenotypes obtained in each model, (ii) weighted average using mean squared error as weight or (iii) using the marginal likelihood as weight. (ii) and (iii) were obtained in a validation set with 5% of the data. Phenotypes consisted of 2598, 1604 and 1879 average litter size records from three commercial pig lines and wheat grain yield of 599 lines evaluated in four macro-environments. SNPs from the PorcineSNP60 BeadChip and 1447 DArT markers were used as predictors for the pig and wheat data analyses, respectively. Gaussian and univariate t kernels led to same predictive performance. Multikernel RKHS regression models overcame shortcomings of single kernel models (increasing the predictive correlation of RKHS models by 0.05 where 3 Gaussian or t kernels were fitted in the RKHS models simultaneously). None of the proposed averaging strategies improved the predictive correlations attained with single models using multiple kernel fitting.

Using the product threshold model for estimating separately the effect of temperature on male and female fertility

Animals under environmental thermal stress conditions have reduced fertility due to impairment of some mechanisms involved in their reproductive performance that are different in males and females. As a consequence, the most sensitive periods of time and the magnitude of effect of temperature on fertility can differ between sexes. The objective of this study was to estimate separately the effect of temperature in different periods around the insemination time on male and on female fertility by using the product threshold model. This model assumes that an observed reproduction outcome is the result of the product of 2 unobserved variables corresponding to the unobserved fertilities of the 2 individuals involved in the mating. A total of 7,625 AI records from rabbits belonging to a line selected for growth rate and indoor daily temperature records were used. The average maximum daily temperature and the proportion of days in which the maximum temperature was greater than 25°C were used as temperature descriptors. These descriptors were calculated for several periods around the day of AI. In the case of males, 4 periods of time covered different stages of the spermatogenesis, the transit through the epididymus of the sperm, and the day of AI. For females, 5 periods of time covered the phases of preovulatory follicular maturation including day of AI and ovulation, fertilization and peri-implantational stage of the embryos, embryonic and early fetal periods of gestation, and finally, late gestation until birth. The effect of the different temperature descriptors was estimated in the corresponding male and female liabilities in a set of threshold product models. The temperature of the day of AI seems to be the most relevant temperature descriptor affecting male fertility because greater temperature records on the day of AI caused a decrease in male fertility (-6% in male fertility rate with respect to thermoneutrality). Departures from the thermal zone in temperature descriptors covering several periods before AI until early gestation had a negative effect on female fertility, with the pre- and peri-implantational period of the embryos being especially sensitive (from -5 to -6% in female fertility rate with respect to thermoneutrality). The latest period of gestation was unaffected by the temperature. Overall, magnitude and persistency of the temperatures reached in the conditions of this study do not seem to be great enough to have a large effect on male and female rabbit fertility.

The number of dysfunctional telomeres in a cell: one amplifies; more than one translocate

Chromosomal instability is increasingly appreciated as a key component of tumorigenesis in humans. A combination of abnormal telomere shortening and cell-cycle checkpoint deficiency has been proposed as the initial lesions causing destabilizing chromatin bridges in proliferative cells. We examined the participation of the different types of end-to-end fusions in generating instable karyotypes in non-transformed human breast epithelial cells. We concluded that short dysfunctional telomeres represent an initiating substrate for post-replicative rejoining of sister chromatids and are likely to make an important contribution to the formation of chromosomal rearrangements and the amplification of chromosome arm segments in breast epithelial cells. We propose that there is a chronological order in the participation of the different types of end-to-end fusions in the generation of chromosomal instability. Thus, intrachromosomal post-replicative joining would proceed mainly in the early stages after overcoming growth arrest, when telomere dysfunction is limited and affects only one chromosome end in a cell. The absence of a second substrate for end joining will conduct the cell with the uncapped chromosome to replicate its DNA and fuse the uncapped sister chromatids after replication. Later, since telomeres shorten progressively with each DNA replication round, the uncapping will affect many more chromosome ends, and fusions between the uncapped ends from different chromosomes will be produced. While the fusion of sister chromatids will produce chromosome segment amplification and terminal deletions in the daughter cells, interchromosomal fusion will produce unbalanced rearrangements other than chromosome segment amplifications.

Radiation-induced chromosome breaks in ataxia-telangiectasia cells remain open

PURPOSE

To determine if broken chromosome-end healing mechanisms through the addition of new telomeric sequences exist in cells having difficulties in rejoining the ends of broken chromosomes.

MATERIALS AND METHODS

A full-colour painting protocol of all human chromosomes by FISH was combined with a telomeric and centromeric labelling using PNA probes to characterize the rejoining pattern and telomere status of radiation-induced chromosome breaks in ataxia-telangiectasia (A-T) and normal lymphoblastoid cell lines.

RESULTS

It was first established that the cell lines used for chromosome healing analysis were chromosomally stable. FISH analysis provided evidence that the frequency of deleted chromosomes, apparently unrejoined, was much higher in A-T than in normal cells, as expected by the role of ATM in cell-cycle control, as well as in DNA repair. In spite of their high frequency, broken chromosome ends in A-T cells do not seem to act as substrates for telomerase since additional terminal telomere sequences (more than the 92 expected pairs) indicative of chromosome healing were never observed. Broken chromosome ends in A-T cells remained open.

CONCLUSION

The disability of cells to rejoin broken chromosome ends does not lead to the healing of DSBs by the acquisition of new telomeric sequences.

A new assay to asses aneuploidy in human-hamster embryos

Fluorescent in situ hybridization using three chromosome-specific centromeric human DNA probes was used to analyze the aneuploidy frequency in human-hamster two-cell embryos. With these techniques first mitotic division errors due to the effects of physical or chemical agents on human spermatozoa, such as non-disjunction and anaphase lag, can be easily detected. In control samples the estimated frequency of non-disjunction and anaphase lag was 3.4%. This assay can also detect premeiotic or meiotic errors. We estimated the same frequency (3.4%) for disomy, whereas monosomy was not found.

Absence of chromosomal instability in spermatozoa of men affected by testicular cancer

Testicular germ cell cancer affects mainly young men. It is the most frequent type of cancer in 20-35 year old men. Since cancer treatment using antineoplasic drugs and ionizing radiation has a negative effect on the function of the gonads, testicular cancer patients are offered the opportunity to cryopreserve their semen samples before the beginning of therapy. For this reason it would be of interest to know whether there is chromosome instability in their spermatozoa prior to any treatment. Using the interspecific human-hamster fertilization system, we have analysed a total of 340 chromosome complements from spermatozoa of control donors and 320 chromosome complements from testicular cancer patients. There were no significant differences in the frequencies of chromosomal aberrations between controls and cancer patients (9.7 and 10.3% respectively; P = 0.4921). Our results indicate that spermatozoa from untreated testicular cancer patients do not show an increased chromosomal instability as compared to control donors.

Hamster origin of metaphases with multiple chromosome rearrangements in first cleavage human-hamster embryos

Laboratories using the human sperm-hamster egg fertilization system to analyse sperm chromosomes obtain, sporadically, metaphases with multiple aberrations. Due to the high number of aberrations, these metaphases cannot be fully karyotyped. In some of them, one or several human chromosomes can be identified, guaranteeing the human origin of the whole metaphase. However, in others, none of the chromosomes can be recognized as human. This latter type of grossly rearranged metaphases is characterized by complex chromatid exchanges, multifragmented chromosomes and pulverized chromosome material. Using fluorescent in-situ hybridization techniques (FISH) with either human or hamster genomic DNA probes, we examined the origin of this second type of metaphase with multiple chromatid exchanges and fragmented chromosomes. Our study demonstrates that all of them hybridize with hamster genomic DNA probes and not with human DNA, proving their hamster origin. Since some of these metaphases seem to be diploid, we suggest that they may arise from hamster eggs that have failed to complete meiosis and have not extruded the second polar body.

Dose-response relationship for the induction of chromosomal abnormalities in gamma-irradiated human spermatozoa

The cytogenetic effects of in vitro irradiation on human spermatozoa have been studied by the interspecific in vitro fertilization system between human sperm and hamster oocytes. Semen samples from three healthy men were irradiated at doses of 0.00, 0.10, 0.25, 0.50, 1.00, 2.00, and 4.00 Gy. A total of 340 chromosome complements derived from non-irradiated human spermatozoa and 987 complements from irradiated spermatozoa were analyzed after sequential uniform stain-G banding. Both the frequency of spermatozoa with structural chromosome abnormalities, and the incidence of such abnormalities per cell, showed strong dose-effect relationships that were best expressed by linear-quadratic equations: Y = 0.06413(+/-0.00475) + 0.1982(+/-0.00833)D - 0.00763(+/-0.00204)D2 and Y = 0.07385(+/-0.00838) + 0.23329(+/-0.03124)D + 0.02317(+/-0.00955)D2, respectively. When analyzing separately unrejoined and rejoined structural abnormalities, we found that the incidence of unrejoined lesions was four times higher than the incidence of rejoined anomalies. The induction of unrejoined abnormalities showed a linear, dose-dependent increase, whereas the incidence of rejoined abnormalities showed a quadratic, dose-dependent increase. The distribution of radiation-induced breakpoints was also analyzed. Breakpoints were found to be randomly distributed among chromosomes, but a clustering of breakpoints in G-negative bands was found: 71.5% of breakpoints were located in G-negative bands, and 28.5% in G-positive bands.

Chromosome aberrations in human spermatozoa treated with Ca2+ ionophore A23187

Incorporation of A23187 ionophore into the human-hamster fertilization system clearly improves the ability of human spermatozoa to penetrate zona-free hamster oocytes. Thus, an increasing number of laboratories working in human sperm cytogenetics have substituted classical incubation with Biggers-Whitten-Whittingham (BWW) medium plus human serum albumin (HSA) by pretreatment of spermatozoa with calcium ionophore A23187 which directly induces the acrosome reaction in spermatozoa. However, there have been no formal studies on the effects of this ionophore pretreatment. To determine whether calcium ionophore could affect the cytogenetic characteristics of human spermatozoa we compared A23187-treated spermatozoa with controls (only incubated with BWW + HSA) by analysing a total of 447 sperm chromosome complements from two normal donors. Our results show that there are no statistical differences in the frequency and the types of human sperm chromosomal abnormalities between the two methods of sperm treatment. Thus, ionophore A23187 seems not to affect the cytogenetic characteristics of human spermatozoa, and the results of laboratories using either sperm capacitation in BWW + HSA or acrosome reaction by calcium ionophore can be compared.

Analysis of radiation-induced micronuclei in two-cell human-hamster embryos using telomeric and centromeric FISH probes

Simultaneous, fluorescent in situ hybridization using a centromeric human alpha satellite DNA probe and a telomeric DNA probe was used to analyze the chromosome content of micronuclei induced in two-cell human-hamster embryos by in vitro gamma-ray irradiation of human spermatozoa. In unirradiated samples, about 26% of micronuclei were centromere positive, indicating that both structural chromosome aberrations and numerical changes are involved in the spontaneous production of micronuclei. After exposure of spermatozoa to radiation, a significant increase in the number of micronuclei was found. About 77% of induced micronuclei contained only telomeric signals suggesting that they originated from acentric fragments. However, both centromere-positive and centromere-negative micronuclei increased with radiation dose. These results are consistent with the well known clastogenic effect of ionizing radiation and with its weak aneugenic effect.

Isochromosome 14q in childhood acute lymphoblastic leukemia

We report a case of childhood acute lymphoblastic leukemia (ALL) with an isochromosome 14q as the sole abnormality. A review of the literature revealed that isochromosome 14 has not been previously reported in ALL. The prognostic significance of this abnormality is compared with that of other hematologic disorders with trisomy 14.

Induction of micronuclei in human sperm-hamster egg hybrids at the two-cell stage after in vitro gamma-irradiation of human spermatozoa

The efficiency of the micronucleus test to assess radiation-induced chromosomal damage in human spermatozoa has been investigated. Micronuclei were scored in human sperm-hamster egg hybrids at the two-cell stage, after exposure of human spermatozoa to in vitro gamma-rays at doses of 0.00, 0.10, 0.25, 0.50, 1.00, 2.00, and 4.00 Gy. The relationship between the yield of micronuclei per two-cell stage as well as the percentage of two-cell stages with micronuclei and the different doses of irradiation were fitted to linear equations. To evaluate whether scoring micronuclei is useful for the quantification of chromosomal damage occurring in human spermatozoa, induced micronuclei at the different doses of sperm irradiation were compared to the induction of breaks and fragments in sperm-derived chromosomes. After interspecific fertilization of zona-free hamster oocytes by irradiated spermatozoa, a total of 699 fertilized eggs at the two-cell stage and a total of 387 sperm-derived complements were analyzed. The incidence of fertilized eggs with micronuclei at the two-cell stage coincided well with the incidence of sperm-derived chromosome breaks and fragments (e.g., 8.9% vs. 6.7% in the 0.25 Gy group and 52.8% vs. 58.6% in the 4.00 Gy group). A similar correlation was found between the number of micronuclei per two-cell stage and the number of breaks and fragments per sperm complement (0.09 vs. 0.07 in the 0.25 Gy group and 0.71 vs. 0.81 in the 4.00 Gy group). The results show that this test system can be used for the quantification of spontaneous or induced chromosomal damage in human spermatozoa.

Human origin of micronuclei in human x hamster two-cell embryos

Using fluorescence in situ hybridization techniques with either human or hamster genomic DNA probes, we studied the origin of micronuclei in two-cell hybrid embryos obtained from hamster oocytes and gamma-irradiated human spermatozoa. Our study demonstrates that over 99% of micronuclei hybridize with human DNA probes and not with hamster DNA, revealing their human origin. Thus, the micronucleus test represents a good method to evaluate genetic damage in human germ cells, since it is simpler and faster than sperm chromosome studies.