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.

Genome-wide association study for feed efficiency in collective cage-raised rabbits under full and restricted feeding.

Feed efficiency (FE) is one of the most economically and environmentally relevant traits in the animal production sector. The objective of this study was to gain knowledge about the genetic control of FE in rabbits. To this end, GWASs were conducted for individual growth under two feeding regimes (full feeding and restricted) and FE traits collected from cage groups, using 114 604 autosome SNPs segregating in 438 rabbits. Two different models were implemented: (1) an animal model with a linear regression on each SNP allele for growth trait; and (2) a two-trait animal model, jointly fitting the performance trait and each SNP allele content, for FE traits. This last modeling strategy is a new tool applied to GWAS and allows information to be considered from non-genotyped individuals whose contribution is relevant in the group average traits. A total of 189 SNPs in 17 chromosomal regions were declared to be significantly associated with any of the five analyzed traits at a chromosome-wide level. In 12 of these regions, 20 candidate genes were proposed to explain the variation of the analyzed traits, including genes such as FTO, NDUFAF6 and CEBPA previously associated with growth and FE traits in monogastric species. Candidate genes associated with behavioral patterns were also identified. Overall, our results can be considered as the foundation for future functional research to unravel the actual causal mutations regulating growth and FE in rabbits.

Genetic parameters of sow feed efficiency during lactation and its underlying traits in a Duroc population.

As a result of the genetic selection for prolificacy and the improvements in the environment and farms management, litter size has increased in the last few years so that energy requirements of the lactating sow are greater. In addition, selection for feed efficiency of growing pigs is also conducted in maternal lines, and this has led to a decrease in appetite and feed intake that is extended to the lactation period, so the females are not able to obtain the necessary energy and nutrients for milk production and they mobilize their energetic reserves. When this mobilization is excessive, reproductive and health problems occur which ends up in an early sow culling. In this context, it has been suggested to improve feed efficiency at lactation through genetic selection. The aim of this study is to know, in a Duroc population, the genetic determinism of sow feed efficiency during lactation and traits involved in its definition, as well as genetic and environmental associations between them. The studied traits are daily lactation feed intake (dLFI), daily sow weight balance (dSWB), backfat thickness balance (BFTB), daily litter weight gain (dLWG), sow residual feed intake (RFI) and sow restricted residual feed intake (RRFI) during lactation. Data corresponded to 851 parities from 581 Duroc sows. A Bayesian analysis was performed using Gibbs sampling. A four-trait repeatability animal model was implemented including the systematic factors of batch and parity order, the standardized covariates of sow weight (SWf) and litter weight (LWs) at farrowing for all traits and lactation length for BFTB. The posterior mean (posterior SD) of heritabilities were: 0.09 (0.03) for dLFI, 0.37 (0.07) for dSWB, 0.09 (0.03) for BFTB, 0.22 (0.05) for dLWG, 0.04 (0.02) for RFI and null for RRFI. The genetic correlation between dLFI and dSWB was high and positive (0.74 (0.11)) and null between dLFI and BFTB. Genetic correlation was favourable between RFI and dLFI and BFTB (0.71 (0.16) and -0.69 (0.18)), respectively. The other genetic correlations were not statistically different from zero. The phenotypic correlations were low and positive between dLFI and dSWB (0.27 (0.03), dSWB and BFTB (0.25 (0.04)), and between dLFI and dLWG (0.16 (0.03)). Therefore, in the population under study, the improvement of the lactation feed efficiency would be possible either using RFI, which would not have unfavourable correlated effects, or through an index including its component traits.

Indirect genetic effect model using feeding behaviour traits to define the degree of interaction between mates: an implementation in pigs growth rate.

An alternative implementation of the animal model including indirect genetic effect (IGE) is presented considering pair-mate-specific interaction degrees to improve the performance of the model. Data consisted of average daily gain (ADG) records from 663 pigs kept in groups of 10 to 14 mates during the fattening period. Three types of models were used to fit ADG data: (i) animal model (AM); (ii) AM with classical IGE (AM-IGE); and (iii) AM fitting IGE with a specific degree of interaction between each pair of mates (AM-IGEi). Several feeding behavior phenotypes were used to define the pair-mate-specific degree of interaction in AM-IGEi: feeding rate (g/min), feeding frequency (min/day), the time between consecutive visits to the feeder (min/day), occupation time (min/day) and an index considering all these variables. All models included systematic effects batch, initial age (covariate), final age (covariate), number of pigs per pen (covariate), plus the random effect of the pen. Estimated posterior mean (posterior SD) of heritability was 0.47 (0.15) using AM. Including social genetic effects in the model, total heritable variance expressed as a proportion of total phenotypic variance (T 2) was 0.54 (0.29) using AM-IGE, whereas it ranged from 0.51 to 0.55 (0.12 to 0.14) with AM-IGEi, depending on the behavior trait used to define social interactions. These results confirm the contribution of IGEs to the total heritable variation of ADG. Moreover, important differences between models were observed in EBV rankings. The percentage of coincidence of top 10% animals between AM and AM-IGEi ranged from 0.44 to 0.89 and from 0.41to 0.68 between AM-IGE and AM-IGEi. Based on the goodness of fit and predictive ability, social models are preferred for the genetic evaluation of ADG. Among models including IGEs, when the pair-specific degree of interaction was defined using feeding behavior phenotypes we obtained an increase in the accuracy of genetic parameters estimates, the better goodness of fit and higher predictive ability. We conclude that feeding behavior variables can be used to measure the interaction between pen mates and to improve the performance of models including IGEs.

Sexually dimorphic tibia shape is linked to natural osteoarthritis in STR/Ort mice.

OBJECTIVES: Human osteoarthritis (OA) is detected only at late stages. Male STR/Ort mice develop knee OA spontaneously with known longitudinal trajectory, offering scope to identify OA predisposing factors. We exploit the lack of overt OA in female STR/Ort and in both sexes of parental, control CBA mice to explore whether early divergence in tibial bone mass or shape are linked to emergent OA. METHOD: We undertook detailed micro-CT comparisons of trabecular and cortical bone, multiple structural/architectural parameters and finite element modelling (FEM) of the tibia from male and female STR/Ort and CBA mice at 8-10 (pre-OA), 18-20 (OA onset) and 40 + weeks (advanced OA) of age. RESULTS: We found higher trabecular bone mass in female STR/Ort than in either OA-prone male STR/Ort or non-prone CBA mice. Cortical bone, as expected, showed greater cross-sectional area in male than female CBA, which surprisingly was reversed in STR/Ort mice. STR/Ort also exhibited higher cortical bone mass than CBA mice. Our analyses revealed similar tibial ellipticity, yet greater predicted resistance to torsion in male than female CBA mice. In contrast, male STR/Ort exhibited greater ellipticity than both female STR/Ort and CBA mice at specific cortical sites. Longitudinal analysis revealed greater tibia curvature and shape deviations in male STR/Ort mice that coincided with onset and were more pronounced in late OA. CONCLUSION: Generalised higher bone mass in STR/Ort mice is more marked in non OA-prone females, but pre-OA divergence in bone shape is restricted to male STR/Ort mice in which OA develops spontaneously.

Comparison of behaviour, performance and mortality in restricted and ad libitum-fed growing rabbits.

The objective of this study was to determine whether rabbits fed in a restricted regimen (75%) showed increased competition for feeding, drinking and use of specific areas of the cages as compared with those provided feed ad libitum. This evaluation was carried out by measuring their space utilisation in the cage, the incidence of agonistic behaviour and rates of mortality. In total, 504 rabbits between 31 and 66 days of age were used in this study. A total of 200 heavy-weight rabbits and 56 light-weight rabbits were randomly housed in 32 cages, each cage containing eight rabbits: 25 cages housing heavy rabbits and seven cages housing the light-weight ones. They were all fed ad libitum (AD). In addition, a total of 208 heavy-weight rabbits and 40 light-weight rabbits were randomly housed in 31 cages, each of them containing eight rabbits: 26 cages housing heavy weight rabbits and five cages housing light-weight ones. They were all fed a restricted diet (R) regimen. The restriction was calculated to be 75% of the feed consumed by the AD group. The total space available in the cage was 3252 cm(2), with a stocking density of 24.6 animals/m(2). Animals between 32 and 60 days of age from 20 different cages were observed nine times per week (morning or afternoon) by means of scan and focal sampling by one observer. During each period, cages were assessed for 5 min, registering every minute the position of all the animals in relation to Area A (feeder), Area B (central part) or Area C (back and drinker area). The incidence of agonistic behaviour such as displacement, biting and jumping on each other was also assessed. Performance variables such as daily gain and feed conversion ratio, in addition to general health status and mortality rates, were recorded for all rabbits. When the rabbits were under restricted feeding, the competition for feed and drink increased with clear signs of agonistic behaviour such as biting, displacement and animals jumping on top of each other. Although this competition was maintained during the entire growing period, the BW homogeneity between animals in the same cage was similar in both cases, suggesting that all animals could consume similar quantities of feed. The possible advantages of a restricted diet, such as better feed conversion ratio, were observed in this study only in the last few weeks of the growing period.

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.

Lactating performance, water and feed consumption of rabbit does reared under a Mediterranean summer circadian cycle of temperature v. comfort temperature conditions.

The general aim of this research was to study the effect of high ambient temperature on the performance of does during lactation, specifically the following factors: average daily feed (ADFI) and water (ADWI) intakes, daily milk yield (DMY); milk composition: dry matter (DM), CP and gross energy (GE); doe BW (DW); individual kit weaning weight (IWW) and litter survival rate during lactation (SR). The study was undertaken comparing the performance of two groups of contemporary does reared under the same management, feeding regime and environmental conditions, except the environmental temperature and humidity. A total of 80 females were randomly allocated, at 60 days of age, into two identical and continuous rooms. In one room, the temperature was maintained permanently within the thermo-neutral zone (between 18°C to 22°C); thus, environmental conditions in this room were considered as comfort conditions. In the second room, the environmental temperature pattern simulated the daily temperature cycles that were characteristic of the summer in Mediterranean countries (24°C at 0800 h, increasing up to 29°C until 1100 h; maintenance at 29°C to 31°C for 4 h and decreasing to about 24°C to 26°C around 1700 h until 0800 h of the following day), which were considered as thermal stress conditions. Females followed a semi-intensive reproductive rhythm, first artificial insemination at 4.5 months of age, with subsequent 42-day reproductive cycles. Traits were recorded from a total of 138 lactations. Does were controlled up to the 5th lactation. Data were analyzed using linear and linear mixed models. High ambient temperature led to a lower ADFI (-9.4%), DW (-6.2%) and IWW (-8%), but it did not affect ADWI. No significant difference was found either for DMY, milk composition (DM, CP and GE) and SR during the lactation period. Heat stress was moderate, and does were able to adapt to it behaviorally by decreasing feed intake (to reduce heat production), but also live weight, allowing them to preserve milk yield and composition for assuring litter survival. On the other hand, water consumption could not be the main animal mechanism to overcome heat stress.

Absence of beneficial effects on rabbit sperm cell cryopreservation by several antioxidant agents.

The generation of reactive oxygen species associated with cryopreservation could be responsible for mammalian sperm damage and the limitable value of stored semen in artificial insemination. The aim of this study was to assess several antioxidant agents supplemented in a commercial freezing extender (Gent B®) in order to improve post-thaw rabbit sperm quality. Ejaculates of 26 New Zealand White rabbit bucks were collected, evaluated and frozen using a conventional protocol. Antioxidant agents were tested at different concentrations: bovine serum albumin (BSA; 5, 30 or 60 mg/ml), retinol (RO; 50, 100 or 200 µM) and retinyl (RI; 0.282 or 2.82 µg/ml). Per cent viability, morphological abnormalities and intact acrosomes were determined using eosin-nigrosin staining. Motility and progressivity were analyzed by computer-assisted sperm analysis (CASA). In general, all sperm quality parameters were negatively affected by the cryopreservation process, the largest effect seen was for total motility. The addition of antioxidant agents did not improve thaw sperm quality. Furthermore, for RI groups a significant decrease in sperm quality parameters was recorded. In conclusion, rabbit sperm quality is negatively affected by the cryopreservation process. To our knowledge this report is the first using these antioxidants to supplement rabbit freezing extender. BSA and RO at concentrations used in the study did not improve sperm quality parameters after thawing, whereas RI supplementation appeared to be toxic. More studies are required to find the appropriate antioxidants necessary and their most effective concentrations to improve rabbit post-thaw sperm quality.

Expected responses to different strategies of selection to increase heat tolerance assessed by changes in litter size in rabbit.

Response on litter size (LS) to selection based on EBV of the own trait and several indexes including EBV of 1 or more parameters of a reaction norm model (RNM) was evaluated by simulation. The RNM described animal's performance under different environmental temperatures assuming that this has an animal-specific effect on LS beyond an animal-specific temperature threshold (i.e., it had 3 parameters: intercept [Int], slope [Slp], and threshold [Thr]). Litter size data were generated assuming this model under 2 environmental conditions (comfort [CC] and comfort-to-heat [CtHC]). Variance components for Int, Slp, Thr, and LS were taken from literature. The initial base population consisted of 125 females and 25 males. Ten generations of selection were conducted keeping constant the population size. Eight different selection criteria were considered, depending on both the evaluation model and the index combining EBV for 1 or more parameters of the RNM. In 1 case selection was based on EBV of the own trait predicted by using a repeatability animal model. In the other 7 cases the genetic evaluation was conducted using the same model as that used in the simulation. For each scenario 25 replicates were conducted and response to selection was assessed within replicate as the difference between generations in the average of trait. Results indicate that, under the studied conditions and for the used genetic parameters, selection based on the observed trait seems to have the same effect as selection based on some index, including EBV of the RNM parameters. In addition, response to selection could be greater under CtHC rather than CC. Animals selected exclusively for EBV of the Slp and Thr are not expected to have good performance under CC. Under CtHC, selection for LS has a major response on those parameters, whereas response on Int was very small. Under CC, response to selection on LS is mainly determined by a change in Int, whereas Slp does not change and Thr slightly increases. Selection based on EBV of Slp, Thr, or on an index including both seems to have the same effect on the trait and it was doubly effective in modifying the shape of the RNM under CtHC than under CC. Selection based on EBV of Thr and Slp does not seem to lead to any response in LS. Selection based on EBV of Int seems to have no effect on the trait or on animal's tolerance to heat under CtHC, but it would lead to a positive response in LS under CC.

Feasibility of selection for male contribution to embryo survival as a way of improving male reproductive performance and semen quality in rabbits.

The objective of this research was assess the male contribution to the number of implanted embryos (IE) and embryo survival (ES) estimated as the rate of variance due to male genetic and permanent environmental effects regarding total variance. In prolific species, the number of embryos and ES at early stages of gestation could be considered as fertility measurements because it indicates the number and rate of fertilized ova which are able to initiate the embryo development. Analyzed traits were ovulation rate (OR) estimated as the number of corpora lutea in both ovaries, IE estimated as the number of implantation sites, and ES calculated as IE/OR. A total of 1477 records from 900 females were used to analyze OR, whereas 1081 records from 855 females and 201 males were used to analyze IE and ES. The number of animals in the pedigree was 1107. The model included the systematic effects of year-season, parity order, lactation, and the random effects of additive genetics and permanent environmental effects due to the female (for OR) or both sexes (for IE and ES). Gibbs sampling was used to estimate posterior distributions of model parameters. The heritabilities of the male contribution to IE and ES were low (0.05 [0.01, 0.10] and 0.07 [0.02, 0.12]) but these estimates are probably biased downward since laparoscopy was only performed on those does that were pregnant at d 12 of gestation, instead of on all mated does. The genetic correlations between all analyzed traits and also between male and female genetic components of IE and ES were inaccurate, and it was not possible to draw any conclusion about them. The proportion of variation due to the male nonadditive genetic plus permanent environmental effects for IE and ES was almost negligible (0.027 [0.001, 0.058] and 0.031 [0.002, 0.068] for IE and ES, respectively), being the repeatability for male contribution on IE and ES around 8 and 10%, respectively.

Use of infrared thermography to assess the influence of high environmental temperature on rabbits.

The aim of this work was to ascertain if infrared thermography (IRT) can be used on rabbits to assess differences in surface body temperature when they are subjected to two different environmental temperatures outside the comfort zone. Rabbits housed in room A were maintained at a temperature of below 30°C and rabbits in room B at a temperature of above 32°C for a year. Faeces were collected six times during the year to assess stress by means of faecal cortisol metabolites (FCM). The assessment of IRT was carried out to assess maximum and minimum temperatures on the eyes, nose and ears. FCM concentration was higher in room B than A, to confirm that stress conditions were higher in room B. Significant differences in IRT were found between the animals housed in both rooms. It was observed that it was more difficult for animals from room B to maintain a regular heat loss. Although all the body zones used to assess temperature with IRT gave statistical differences, the correlations found between the eyes, nose and ears were moderate, suggesting that they were giving different information. In addition, differences up to 3.36°C were found in the eye temperature of rabbits housed in the same room, with a clear effect of their position in relation to extractors and heating equipments. Therefore, IRT could be a good tool to assess heat stress in animals housed on typical rabbit farm buildings, giving a measure of how the animal is perceiving a combination of humidity, temperature and ventilation. Some face areas were better for analysing images. Minimum temperature on eyes and temperatures on nose are suggested to assess heat losses and critical areas of the farm for heat stress in rabbits.

Sources of individual variation to heat tolerance in a rabbit line.

The objective of the present study was to quantify the extent of the interaction between temperature and animal-specific effects on prolificacy and average weaning weight in rabbit does and to assess to what extent this interaction has a genetic determination. For this purpose, 18,491 total born (TB) records from 5,929 Caldes does, as well as 16,868 weaned kits (NW) and average weaning weight (AvgWW) records from 5,353 does of the same line were used. Four models were considered, ranging from the simplest, which assumed no effect of temperature on the traits studied, to the most complex, which allowed for different slopes of response and thresholds for heat tolerance for each animal. Deviance information criteria (DIC) were adopted as model choice criteria. The model postulating that each animal is subjected to a linear change in its performance when the temperature reaches a certain animal-specific threshold was preferred for all the considered traits. This interaction has the greatest effect for AvgWW; the ratio between the variance associated to the intercept and the total variance declined from 29.1% at 19°C to 19.4% at 25°C. This decline results from the increase in the variation associated with the interaction of the individual effects with temperature and also from the covariance between this interaction term and the intercepts. An important part of this interaction has a genetic origin, particularly for AvgWW and NW, for which the estimated heritability increased from 0.11 to 0.24 and 0.06 to 0.10, respectively, from 19 to 25°C. Similarly, it was found that the proportion of the total variance for the individual effects involved in the interaction with temperature which have a genetic origin is high for all the traits, around one-half for the variation on the linear changes in the performance and more than one-third for the variation on the onsets for heat stress. However, the error associated with these estimates is large and results must be considered with caution. Thus, in conclusion the extent of the interaction between individual variation and in farm temperature seems to be important and has a genetic origin. Nevertheless, the accuracy of the estimated genetic parameters is low.

Effect of heat intensity and persistency on prolificacy and preweaning kit growth at different stages of the rabbit production cycle.

The aim of this research was to assess the effect of temperature intensity and variation both throughout the day and between days within different periods of the reproductive cycle and the lactation of the rabbit. This information would help in establishing optimal patterns of environmental temperature control in rabbitries. The traits analyzed were total number of kits born (TB), number of kits alive at weaning (NW), and average individual weight at weaning (AvgWW). For each trait, several mixed models were fitted to the data, differing only in the number and type of temperature descriptors included in the vector of fixed effects. Those descriptors were the average daily mean, maximum, and range of temperatures (AvgTmean, AvgTmax, and AvgRg, respectively) and the CV of daily mean temperature (CVTmean). All were calculated for periods in which important physiological processes related to the studied traits occur. High environmental temperature was found to have a detrimental effect on prolificacy and preweaning growth of the kits. When the average daily mean reached 20°C, it produced a linear decay of TB of around 0.1 kit/°C. The most sensitive period for TB could cover from spermatogenesis to embryo implantation. However, the high correlation between descriptors calculated for different periods makes it difficult to assign an effect to each specific period and therefore to the specific physiological process occurring in that period. The effect on NW was smaller and quadratic, with an optimum value between 18°C and 21°C. Weaning weight was the most strongly affected trait similar to NW. It also showed a quadratic response to AvgTmean, with an optimum value in the same temperature interval as NW and a strong decline in weaning weight with temperatures higher than 21°C (-14 g/°C). There were no differences on the effect of heat at different stages of lactation on NW and AvgWW. The impact of high environmental temperatures on prolificacy is alleviated if a drop in temperature is produced during the day. Thus, the effect of AvgRg was relevant and positive for TB and NW. However, it had a quadratic negative effect for AvgWW at late lactation. The temperature variation between days within a period has a positive effect on TB and AvgWW but a negative effect on NW when it is produced at middle lactation, whereas there is no effect at other stages of lactation.

Genetic correlation between growth and female and male contributions to fertility in rabbit.

A Bayesian bivariate Linear-Threshold Animal Model was implemented to determine the genetic correlation between fertility (F), defined as success or failure to conceive, and average daily gain (ADG) in a rabbit line selected for ADG. A total of 27 234 records of F from 7895 females and 1293 males, and 114 135 records of ADG were used for the analysis. The pedigree included 114 485 animals. The model used for ADG included the systematic effects of year-season, parity order and number of kids born alive, the animal additive effect, the maternal and paternal permanent environmental effects, the common litter permanent environmental effect and the residual. The model for the liability of F included the systematic effects of year-season and physiological status of the female, the female and male additive genetic effects, the female and male permanent environmental effects and the residual, which was divided into a permanent environmental effect related to the common litter effect for ADG, and an independent term. The estimated heritabilities were 0.15 for ADG and 0.07 and 0.04 for the female and male contributions to F, respectively. Male and female contributions to F had a positive genetic correlation (0.34). The genetic correlation between ADG and the female component of F was low to moderate and negative (-0.31), whereas it was null for the male contribution to F. Thus, it is expected that only the female contribution to reproductive performance may be impaired by selection for ADG in rabbit lines.

Genetic basis of semen traits and their relationship with growth rate in rabbits.

This work aims to estimate the genetic parameters of seminal and production traits in a paternal line of rabbits selected for ADG during the fattening period. The considered traits were male libido (Lib) defined as successful mounting of an artificial vagina; presence of urine (Ur) and calcium carbonate deposits (Ca) in the ejaculate; semen pH; individual sperm motility (IM); the suitability for AI of the ejaculate (Sui), which involves the subjective combination of several quality traits; the average ejaculate volume (Vol); sperm concentration (Conc); and the average sperm production per ejaculate (Prod = Vol × Conc). The genetic relationship between all of these traits with ADG is also provided. Male libido and seminal data came either from routine evaluations of the ejaculates in an AI center or from 2 experiments in which bucks from the same population were used. Two consecutive ejaculates per male and per week were collected, leaving 7 d within weekly collections. A linear tri-trait model was used to analyze Conc, Vol, and ADG, whereas linear and threshold-linear 2-trait models were used to analyze male libido and the remaining seminal traits with ADG. A Bayesian approach was adopted for inference. Approximately 38% of ejaculates were rejected for AI primarily due to low IM scores. Variables related to the quality of the ejaculate (Ur, Ca, pH, IM, Sui) and Lib were found to be lowly heritable (h(2) ranged from 0.04 to 0.11), but repeatable. This indicates performance of bucks for seminal quality traits and libido in AI centers would be more strongly affected by management practices rather than genetic selection. Semen production traits exhibited moderate values of h(2) (0.22, 0.27, and 0.23 for Conc, Vol, and Prod, respectively), suggesting the possibility of effective selection for these traits. A moderate to high negative genetic correlation (r(g); posterior mean; highest posterior density at 95%, HPD(95%)) was estimated between Conc and Vol (-0.53, HPD(95%) = -0.76, -0.27). The ADG was estimated to have an h(2) of 0.16, to have a low, positive r(g) with Conc (0.21, HPD(95%) = -0.03, 0.48), to have a low, negative r(g) with Vol (-0.19, HPD(95%) = -0.47, 0.08), and to be genetically uncorrelated with all remaining traits analyzed. Therefore, selection for increasing ADG in paternal lines is expected to have no detrimental effects on Ur, Ca, pH, IM, Sui, and Lib and little to no effect on Conc, Vol, and Prod.

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.

Different ways to model biological relationships between fertility and pH of the semen in rabbits.

This work aimed to study the relationship between pH of the semen and fertility (Fert, defined as the success or failure of conception), which is of special interest because pH of the semen can be considered a global marker of the expression of some seminal quality traits. Different methods used to model the relationship between Fert and pH are presented here: 1) ignoring genetic and environmental correlations and including pH either as a covariate or as a cross-classified effect on fertility, 2) a bivariate mixed model, and 3) recursive bivariate mixed models. A total of 653 pH records and 6,365 Fert records after AI were used. Crossbreed does from 2 maternal lines were artificially inseminated with buck semen from a paternal line in a commercial environment. A negative, and almost linear, effect of pH on Fert was detected. The posterior median of pH and Fert heritabilities, and the highest posterior density interval at 95% (in parentheses) were approximately 0.18 (0.05, 0.29) and approximately 0.10 (0.02, 0.20) across all the models, respectively. Genetic correlations between traits were negative, but the highest posterior density interval at 95% included zero [i.e., -0.31 (-0.91, 0.33) in the bivariate mixed model and -0.17 (-0.99, 0.48) and -0.44 (-0.99, 0.10) in the recursive bivariate mixed models including pH as a covariate or as a cross-classified effect, respectively]. All models predicted Fert data reasonably well (i.e., 76 and 62% correct predictions for success and failure, respectively). No differences in the prediction of the EBV for male fertility were encountered between models, showing a good concordance in the animals ranked by their EBV (the correlation between EBV in all models was close to 1). Thus, no differences in results were obtained considering, or not considering, genetic and environmental correlations between pH and Fert and assuming, or not assuming, recursiveness between each trait. This is because the magnitude of the effect of pH on Fert was not large enough; therefore, the same results were obtained even though the models were of different complexity.

Product versus additive model for studying artificial insemination results in several livestock populations.

Two models can be used for studying binary results of AI. The additive threshold model proposes an underlying variable as summing the environmental and genetic effects from the 2 individuals involved in the mating, and the product threshold model assumes that the conditional probability of AI success is the product of the probabilities of success of 2 unobserved binary phenotypes (one is the male fertility; the other is the female fertility). The purpose of this paper is to compare the predictive ability of the product and the additive threshold models for studying AI results and to compare results obtained with the 2 models in 3 different species: cattle, sheep, and rabbits. Results showed that the predictive ability of the product model is similar to the additive model in sheep and rabbits but worst in cattle (percentage of wrong prediction = 42, 27, and 35% in the additive model; 43, 28, and 47% in the product model in sheep, rabbits, and cattle, respectively). Even when the 2 models have similar performance, they differed in their EBV (for instance, Pearson correlation between EBV predicted with the 2 models = 0.46 in sheep for male fertility). The product model can determine which sex is responsible for an AI failure. In sheep, the female was the responsible in 94% of the cases and male in 2% of them; in rabbits, the female was the responsible in 54% of the cases and the male in 39% of them. Different estimates of probabilities for male and female fertility success obtained with the product model in the 3 species suggest that male and female fertilities behave differently depending on the species and the uniqueness of the data sets. Although product model seems to provide additional information in the fertility process, further research is needed to understand the worst performance of the product model in cattle.

Interaction of genotype × artificial insemination conditions for male effect on fertility and prolificacy.

Failures in fertilization or embryogenesis have been shown to be partly the result of poor semen quality. When AI is practiced, fertilization rate depends on the number and quality of spermatozoa in the insemination dose around the time of application. Individual variation in the male effect on fertility (success or failure to conceive; Fert) and prolificacy (total number of kids born per litter; TB) could also depend on these factors, and it could be better observed under limited conditions of AI, such as decreased sperm concentration, small or null preselection of ejaculates for any semen quality trait, or a long storage period of the AI doses. The aim of this research was to determine if an interaction existed between male genotype and the AI conditions for male effects on Fert and TB after AI was performed under different conditions. Fertility and TB were assumed to be different traits and were analyzed in 2 sets of independent analyses. In the first step, the different conditions were determined uniquely by the sperm dosage. Artificial insemination was performed at 10 and 40 × 10(6) spermatozoa/mL. In the second step, the different conditions were determined by all the factors involved in the AI process as a whole (conditions and duration of the storage period of the dose, genetic type of the female, and environmental conditions on the farm). Data from AI from the former experiment were analyzed with data from AI performed under different conditions. Threshold and linear 2-trait models were assumed for Fert and TB, respectively. The sperm dosage had a clear effect on Fert and TB, which favored the greater dosage (+0.13% and +1.25 kids born, respectively). Prolificacy was more sensitive to sperm reduction than was fertility. Male heritabilities for Fert were 0.09 for both sperm dosages, and were 0.08 and 0.06 for male TB with a smaller and larger sperm dosage, respectively. No genotype × sperm dosage interaction was found. Therefore, the same response to selection to improve male Fert and TB could be achieved at any sperm concentration. However, an interaction between male genotype and the AI conditions as a whole seemed to exist, indicating that the AI conditions for selection for Fert and TB could be modified to maximize genetic progress. Consequently, the optimization of a breeding program for male Fert and TB under a given set of semen utilization conditions is achievable.