Phenotypic correlations between feed efficiency, growth, and meat quality of slow-growing chickens.

1. Korat (KR) chicken is a new meat-type chicken breed established with the purpose of developing Small and Micro Community Enterprise Production. This slow-growing chicken has been recognised for its good texture and flavour, but its low feed efficiency is associated with high cost of production which can hamper the development of local production. This has highlighted the importance of studying the trade-off between feed efficiency and meat quality in KR chicken.2. This study investigated the phenotypic correlations between feed efficiency, growth performance, and meat quality in KR chicken. Individual body weight and feed intake were recorded weekly for 75 male KR chickens for the calculation of feed conversion ratio (FCR) and residual feed intake (RFI). The growth curve was modelled by Gompertz function and meat quality evaluated at 10 weeks of age, through the measurement of pH (pHu), water-holding capacity (WHC) and drip loss (DL) in breast and thigh muscle.3. Faster growth rate at young age appeared favourable, regarding feed efficiency, since a moderate negative correlation was found between FCR and initial growth rate. Chickens with a higher initial growth and maturation rates were characterised by lower water-holding capacity in meat. This was not associated with acidic meat, since a higher speed of growth (especially in the first weeks) was positively associated with final pH in breast meat. Relationships between RFI and meat quality traits appeared to be weak. While better FCR could be achieved by increased initial growth rate, this seemed to negatively impact water-holding capacity of the meat.4. RFI appeared as an interesting alternative as a compromise between FCR and meat quality.

Review: Towards the agroecological management of ruminants, pigs and poultry through the development of sustainable breeding programmes. II. Breeding strategies.

Agroecology uses ecological processes and local resources rather than chemical inputs to develop productive and resilient livestock and crop production systems. In this context, breeding innovations are necessary to obtain animals that are both productive and adapted to a broad range of local contexts and diversity of systems. Breeding strategies to promote agroecological systems are similar for different animal species. However, current practices differ regarding the breeding of ruminants, pigs and poultry. Ruminant breeding is still an open system where farmers continue to choose their own breeds and strategies. Conversely, pig and poultry breeding is more or less the exclusive domain of international breeding companies which supply farmers with hybrid animals. Innovations in breeding strategies must therefore be adapted to the different species. In developed countries, reorienting current breeding programmes seems to be more effective than developing programmes dedicated to agroecological systems that will struggle to be really effective because of the small size of the populations currently concerned by such systems. Particular attention needs to be paid to determining the respective usefulness of cross-breeding v. straight breeding strategies of well-adapted local breeds. While cross-breeding may offer some immediate benefits in terms of improving certain traits that enable the animals to adapt well to local environmental conditions, it may be difficult to sustain these benefits in the longer term and could also induce an important loss of genetic diversity if the initial pure-bred populations are no longer produced. As well as supporting the value of within-breed diversity, we must preserve between-breed diversity in order to maintain numerous options for adaptation to a variety of production environments and contexts. This may involve specific public policies to maintain and characterize local breeds (in terms of both phenotypes and genotypes), which could be used more effectively if they benefited from the scientific and technical resources currently available for more common breeds. Last but not least, public policies need to enable improved information concerning the genetic resources and breeding tools available for the agroecological management of livestock production systems, and facilitate its assimilation by farmers and farm technicians.

Review: Towards the agroecological management of ruminants, pigs and poultry through the development of sustainable breeding programmes: I-selection goals and criteria.

Agroecology uses natural processes and local resources rather than chemical inputs to ensure production while limiting the environmental footprint of livestock and crop production systems. Selecting to achieve a maximization of target production criteria has long proved detrimental to fitness traits. However, since the 1990s, developments in animal breeding have also focussed on animal robustness by balancing production and functional traits within overall breeding goals. We discuss here how an agroecological perspective should further shift breeding goals towards functional traits rather than production traits. Breeding for robustness aims to promote individual adaptive capacities by considering diverse selection criteria which include reproduction, animal health and welfare, and adaptation to rough feed resources, a warm climate or fluctuating environmental conditions. It requires the consideration of genotype×environment interactions in the prediction of breeding values. Animal performance must be evaluated in low-input systems in order to select those animals that are adapted to limiting conditions, including feed and water availability, climate variations and diseases. Finally, we argue that there is no single agroecological animal type, but animals with a variety of profiles that can meet the expectations of agroecology. The standardization of both animals and breeding conditions indeed appears contradictory to the agroecological paradigm that calls for an adaptation of animals to local opportunities and constraints in weakly artificialized systems tied to their physical environment.

Heritability of body surface temperature in hens estimated by infrared thermography at normal or hot temperatures and genetic correlations with egg and feather quality.

Exposure of laying hens to chronic heat stress results in loss of egg production. It should be possible to improve hen resilience to chronic heat stress by genetic selection but measuring their sensitivity through internal temperature is time consuming and is not very precise. In this study we used infrared thermography to measure the hen's capacity to dissipate heat, in a commercial line of laying hens subjected to cycles of neutral (N, 19.6°C) or high (H, 28.4°C) ambient temperatures. Mean body temperatures (BT) were estimated from 9355 infrared images of wing, comb and shank taken from 1200 hens. Genetic parameters were estimated separately for N and H temperatures. Correlations between BT and plumage condition were also investigated. Wing temperature had low heritability (0.00 to 0.09), consistent with the fact that wing temperature mainly reflects the environmental temperature and is not a zone of heat dissipation. The heritability of comb temperature was higher, from 0.15 to 0.19 in N and H conditions, respectively. Finally, the shank temperature provided the highest heritability estimates, with values of 0.20 to 0.22 in H and N conditions, respectively. Taken together, these results show that heat dissipation is partly under genetic control. Interestingly, the genetic correlation between plumage condition and shank and comb temperatures indicated that birds with poor condition plumage also had the possibility to dissipate heat through featherless areas. Genetic correlations of temperature measurements with egg quality showed that temperatures were correlated with egg width and weight, yolk brightness and yellowness and Haugh units only under H conditions. In contrast, shell colour was correlated with leg temperature only at thermo-neutrality.

Robustness to chronic heat stress in laying hens: a meta-analysis.

Chronic heat is a major stress factor in laying hens and many studies on the effect of heat stress have been published. It remains difficult, however, to draw general conclusions about the effect of chronic heat stress on performance and its relationship with genetic and environmental factors, as these studies have been done under varying experimental conditions and using various experimental designs. A meta-analysis enabled us to make a quantitative review of the results from 131 published papers. The relative effects of four factors (genotype, age, group size, and amplitude of temperature variation) and their interactions with temperature were analyzed for 13 traits. After pre-correcting the data for a random study effect, the best model for each trait was selected in a stepwise procedure based on its residual sum of squares. Shell strength, daily feed intake, egg mass, and hen-day egg production were found to be more sensitive to heat stress than the other traits as they dropped by 9.0 to 22.6% between thermo-neutrality (15 to 20°C) and heat stress (30 to 35°C) while yolk and albumen proportions or Haugh units showed nearly no variation with temperature (<1.2% between thermo-neutrality and heat stress). Many interactions (17) were found between temperature and one or more factors in the 13 traits studied here, which reinforces the interest of using a meta-analysis to summarize data from the literature. This study highlighted that the impact of heat stress in laying hens depends on the genotype, age, and group size, some of which have rarely been investigated.

Cyclic variations in incubation conditions induce adaptive responses to later heat exposure in chickens: a review.

Selection programs have enabled broiler chickens to gain muscle mass without similar enlargement of the cardiovascular and respiratory systems that are essential for thermoregulatory efficiency. Meat-type chickens cope with high ambient temperature by reducing feed intake and growth during chronic and moderate heat exposure. In case of acute heat exposure, a dramatic increase in morbidity and mortality can occur. In order to alleviate heat stress in the long term, research has recently focused on early thermal manipulation. Aimed at stimulation of long-term thermotolerance, the thermal manipulation of embryos is a method based on fine tuning of incubation conditions, taking into account the level and duration of increases in temperature and relative humidity during a critical period of embryogenesis. The consequences of thermal manipulation on the performance and meat quality of broiler chickens have been explored to ensure the potential application of this strategy. The physiological basis of the method is the induction of epigenetic and metabolic mechanisms that control body temperature in the long term. Early thermal manipulation can enhance poultry resistance to environmental changes without much effect on growth performance. This review presents the main strategies of early heat exposure and the physiological concepts on which these methods were based. The cellular mechanisms potentially underlying the adaptive response are discussed as well as the potential interest of thermal manipulation of embryos for poultry production.

The gastric isthmus from D+ and D- broiler lines divergently selected for digestion efficiency shows histological and morphological differences.

Previous results suggested that the gastric function plays a paramount role in digestive efficiency differences between D+ and D- broiler lines divergently selected for AMEn (more feed efficient and less feed efficient, respectively). In this paper we show an histological analysis of the gastric isthmus located between the proventriculus and the gizzard in the D+ and D- lines. Cross-sections were performed using a cryostat (Leica CM30505) and stained with a routine procedure using Mayer's Hematoxylin and Eosin Stain. The surface and shape of the constitutive gastric isthmus tissues were quantified using the image analysis software Image J. The lumen occupied 11% of the whole D- isthmus cross-sectional area against 24% for D+ (P < 0.01). The mucosa relative area (cm(2)/total cross-sectional area) was higher in D- than in D+ [47% (D-) and 39% (D+), P < 0.01]. It was significantly more oval and more folded on the lumen side in D- than in D+ chickens; the muscle layer (muscularis mucosae) of the mucosa was relatively more developed in D- than in D+ (16 and 11% of the section, respectively; P < 0.01). A relationship between these observations and increased gastric motility reported in D- compared with D+ is discussed.

Broiler lines divergently selected for digestive efficiency also differ in their susceptibility to colibacillosis.

Increasing feed efficiency of broiler chickens by selective breeding could lead to decreased feed cost and reduced environmental impact of poultry production. At INRA, two broiler chicken lines (D+/D-) were divergently selected for their digestive efficiency. Strong differences were shown between both lines for the anatomy and histology of the digestive tract, and for the intestinal microbiota composition. In the present study, we investigated whether this selection also had an effect on susceptibility to colibacillosis, which is one of the main causes of economic losses in poultry production. The broiler lines D+/D- were challenged with an avian pathogenic Escherichia coli strain. A first experiment was conducted to assess the 50% lethal dose by subcutaneous infection of hatchlings, whereas a second experiment reproduced colibacillosis by infecting air sacs of 23-day-old chicks. The 50% lethal dose was very low for both lines. However, the line with the higher digestive efficiency (D+) was the less susceptible to colibacillosis. This result is interesting for selection purposes and opens the way to integrative genetic studies of the interactions between digestion efficiency and resistance to colibacillosis.

Thermal manipulation of the embryo modifies the physiology and body composition of broiler chickens reared in floor pens without affecting breast meat processing quality.

Selection in broiler chickens has increased muscle mass without similar development of the cardiovascular and respiratory systems, resulting in limited ability to sustain high ambient temperatures. The aim of this study was to determine the long-lasting effects of heat manipulation of the embryo on the physiology, body temperature (Tb), growth rate and meat processing quality of broiler chickens reared in floor pens. Broiler chicken eggs were incubated in control conditions (37.8°C, 56% relative humidity; RH) or exposed to thermal manipulation (TM; 12 h/d, 39.5°C, 65% RH) from d 7 to 16 of embryogenesis. This study was planned in a pedigree design to identify possible heritable characters for further selection of broiler chickens to improve thermotolerance. Thermal manipulation did not affect hatchability but resulted in lower Tb at hatching and until d 28 post-hatch, with associated changes in plasma thyroid hormone concentrations. At d 34, chickens were exposed to a moderate heat challenge (5 h, 32°C). Greater O2 saturation and reduced CO2 partial pressure were observed (P < 0.05) in the venous blood of TM than in that of control chickens, suggesting long-term respiratory adaptation. At slaughter age, TM chickens were 1.4% lighter and exhibited 8% less relative abdominal fat pad than controls. Breast muscle yield was enhanced by TM, especially in females, but without significant change in breast meat characteristics (pH, color, drip loss). Plasma glucose/insulin balance was affected (P < 0.05) by thermal treatments. The heat challenge increased the heterophil/lymphocyte ratio in controls (P < 0.05) but not in TM birds, possibly reflecting a lower stress status in TM chickens. Interestingly, broiler chickens had moderate heritability estimates for the plasma triiodothyronine/thyroxine concentration ratio at d 28 and comb temperature during the heat challenge on d 34 (h(2) > 0.17). In conclusion, TM of the embryo modified the physiology of broilers in the long term as a possible adaptation for heat tolerance, without affecting breast meat quality. This study highlights the value of 2 new heritable characters involved in thermoregulation for further broiler selection.

Genetic variability of metabolic characteristics in chickens selected for their ability to digest wheat.

Improving feed efficiency remains crucial for poultry production. Birds have previously been selected on their ability to digest their diet, as assessed by AMEn (Apparent ME corrected for 0 nitrogen). Such selection, for either a high (D+) or a low AMEn (D-), affects energy, nitrogen, lipid, and starch digestibility. The aim of this study was to establish whether selection on the digestive ability of birds modified metabolic traits. A total of 630 broiler chickens of the eighth generation of a divergent selection experiment on AMEn were used for this purpose. A balance trial was performed to determine energy, nitrogen, and phosphorus retention. Growth performance was recorded and body protein and lipid deposition assessed by breast and abdominal fat yields. Tibia development and mineralization were also studied and heat production was indirectly assessed through the measurement of body temperature during fasting and feeding. Phenotypic correlations estimated within line showed that an increased efficiency was associated to fatter birds and more solid bones in D- but not in D+ line, whereas increased consumption was associated with more solid bones in D+ but not in D- line. The heritability estimates for metabolic traits were relatively high, except for temperature traits (from 0.08 to 0.12), ranging from 0.28 to 0.56 for body composition, and from 0.38 to 0.77 for bone characteristics. Breast meat yield did not differ between the 2 lines whereas a slight increase in abdominal fat yield was observed in the high-digestion line (D+). The relative dry tibia weights and ash weights were greater in D+ birds (+6.56 and +8.06%, respectively) but the lengths and the diameters of the tibia were lower (-7.89 and -3.77%, respectively). Finally, AMEn was poorly correlated with almost all metabolic traits (ranging from -0.10 to 0.20), indicating that the ability of the animal to digest its diet is genetically independent of post-digestion metabolic traits.

Genetics of behavioural adaptation of livestock to farming conditions.

Behavioural adaptation of farm animals to environmental changes contributes to high levels of production under a wide range of farming conditions, from highly controlled indoor systems to harsh outdoor systems. The genetic variation in livestock behaviour is considerable. Animals and genotypes with a larger behavioural capacity for adaptation may cope more readily with varying farming conditions than those with a lower capacity for adaptation. This capacity should be exploited when the aim is to use a limited number of species extensively across the world. The genetics of behavioural traits is understood to some extent, but it is seldom accounted for in breeding programmes. This review summarizes the estimates of genetic parameters for behavioural traits in cattle, pigs, poultry and fish. On the basis of the major studies performed in the last two decades, we focus the review on traits of common interest in the four species. These concern the behavioural responses to both acute and chronic stressors in the physical environment (feed, temperature, etc.) and those in the social environment (other group members, progeny, humans). The genetic strategies used to improve the behavioural capacity for adaptation of animals differ between species. There is a greater emphasis on responses to acute environmental stress in fish and birds, and on responses to chronic social stress in mammals.

Reducing the environmental impact of poultry breeding by genetic selection.

Improving the sustainability of poultry production involves limiting its environmental impact and maintaining effectiveness. It has recently been shown that genetic selection on the ability of chickens to digest wheat at 23 d of age can decrease chicken excretion without decreasing BW at this age. The aim of this study was to check whether selection on digestibility modified excretion and growth performance over the whole production cycle. The 2 divergent lines selected for high (D+) and low (D-) apparent metabolizable energy corrected for 0 N balance (AMEn) values were compared with a reference line used at the beginning of the selection experiment (RL) to evaluate the potential excretion improvement that could be expected with such selection. These 3 lines were therefore compared for growth and excretion (raw and relative to feed intake, fresh and dry excreta weights, and moisture content of excreta) from 4 to 53 d. Between 4 and 7 d, 17 and 21 d, and 49 and 53 d, AMEn and N and P excretion rates were also compared between the 3 lines. Furthermore, body composition (breast meat and abdominal fat yields), bone breaking strength, and meat quality traits (lightness, redness, yellowness, and ultimate pH) were compared between lines at 53 d. Over the whole rearing period, D+ birds excreted significantly less fresh and dry excreta (-56 and -61%) than D- and RL birds (-6 and -26%). Similarly, N and P excretion rates of D+ birds were 13% to 30% less than those of D- birds and 12% to 19% less than RL birds, depending on age. These excretion differences may be related to the differential development of the gastrointestinal tract. Differences between lines were already present at 7 d for relative gizzard weight and the weight of the upper to the lower part of the gastrointestinal tract ratio. Anatomic differences were maximum at 23 d for all traits except for relative weight of the duodenum. At slaughter age, BW, breast and fat yields, and meat color did not differ between D+ and RL birds, but D- birds were fatter than D+ and RL birds. Finally, ultimate meat pH was 1% to 2% greater in RL birds than in the D+ and D- lines. In conclusion, this study showed that selection of chickens for AMEn is a possible way to reduce the environmental impact of production over the whole rearing period without a negative impact on growth, body composition, or meat quality.

Ability of chicken spermatozoa to undergo acrosome reaction after liquid storage or cryopreservation.

The effects of in vitro storage on the sperm's ability to undergo the acrosome reaction (AR) have never been studied in avian species despite its major importance for reproduction management. The ability of chicken sperm to undergo the AR was measured after liquid storage at 4 °C and after cryopreservation, and its relationship with other semen quality parameters, including viability, mass motility and objective motility parameters measured by computer semen analyser (CASA) was analysed in two different flocks. The percentage of intact acrosome-reacting spermatozoa (IAR) was dramatically decreased by 48 h liquid storage (loss of 2/3 among the spermatozoa initially able to undergo the AR) whereas motility, viability and morphological integrity were reduced by 10-15%. By contrast, cryopreservation did not affect the induction of AR in flock 1 (29% IAR) whereas it was strongly affected in flock 2 (7% IAR). Motility parameters, viability and morphology were considerably altered by freezing in every case (more that 50% loss). Positive correlations were found between the percentage of intact acrosome-reacting spermatozoa and viability, mass motility and many objective motility parameters. Our results showed that the sperm's ability to undergo the AR was much more affected than other sperm functions after storage at 4 °C, while cryopreservation only had an effect in semen with the lowest initial quality. These results raise questions regarding the specific features of chicken sperm biology that must be taken into account in the treatment of semen.

Digestive tract measurements and histological adaptation in broiler lines divergently selected for digestive efficiency.

Two lines of broilers divergently selected for a high (D+) or a low (D-) AME(n) on a wheat-based diet were studied for morphological and histological characteristics of the digestive tract. A total of 630 birds of both lines were slaughtered after a 23-d feeding period. Digestive tract morphology and intestinal histology were investigated on a total of 24 birds to describe the consequences of divergent selection. Birds of the D+ line had 34% heavier gizzards (P < 0.001) and 22% heavier proventriculi than their D- counterparts. In contrast, intestines were 15 to 40% heavier in D- birds, mainly in the jejunum (P < 0.001) and ileum (P < 0.001). Intestinal segments were also longer (between 3 and 6%) in the D- birds. Intestinal villi were larger and longer in D- birds (P < 0.001), mainly in the jejunum (14 to 16%), and crypts were 10 to 15% deeper for the 3 intestinal segments in D- birds (P < 0.001). Muscle layers of the intestine were 17 to 24% thicker (P < 0.001) and goblet cells were 27 to 34% more numerous in the jejunum and ileum of D- birds (P = 0.027). This new characterization of the 2 lines shows that divergent selection based on AME(n) modified the morphology of the proventriculus and gizzard, suggesting greater activity of this compartment in D+ than in D- birds. Intestinal adaptation revealed by visceral organ weight and length and histological modifications in D- birds can be viewed as an attempt to compensate for the low functionality of the gastric area.

The European experience in poultry welfare--a decade ahead.

Farm animal welfare is a major issue in Europe, which resulted in regulations and development of research dedicated to animal welfare, especially on standard poultry production, which is often considered as resulting in very poor welfare. The effect of selection is also often questioned. Indeed, capacities of adaptation have been very little considered during the first years of commercial selection and thus have been reduced. Nowadays, a much greater importance is given to welfare-related traits and genomic selection should alleviate the need for their measurements in the short-term. However, the choice of the fittest selection criteria is still to be made. Because behavioral traits are highly dependent on environment, general reactivity may be more efficient. For example, selection against undesirable behavior such as feather pecking has been proven to be efficient, but selection for reduced mortality rates in collective cages proved to be preferable. Most often, selection should not exacerbate extreme values, which are most often detrimental, as in the case of social motivation, which, when increased to too large of an extent, results in increased aggressivity. Moreover, a general propensity will not result in overall improvement; for example, reducing fearfulness has positive effects but does not modify response to social stress. Detrimental effects on other traits may also be observed: although genetic resistance to diseases should increase animal welfare, it may also result in increased frequency of silent carriers and in turn to human transmission. Indeed, an optimum must be found. Studying lines selected for or against these traits will be of great help to choose the best strategy of selection. Another and longer term concern should be on links with other production traits but also on sustainability, which will probably be of greater importance in the coming years.

Mapping QTL for growth and shank traits in chickens divergently selected for high or low body weight.

An F(2) population (695 individuals) was established from broiler chickens divergently selected for either high (HG) or low (LG) growth, and used to localize QTL for developmental changes in body weight (BW), shank length (SL9) and shank diameter (SD9) at 9 weeks. QTL mapping revealed three genome-wide QTL on chromosomes (GGA) 2, 4 and 26 and three suggestive QTL on GGA 1, 3 and 5. Most of the BW QTL individually explained 2-5% of the phenotypic variance. The BW QTL on GGA2 explained about 7% of BW from 3 to 7 weeks of age, while that on GGA4 explained 15% of BW from 5 to 9 weeks. The BW QTL on GGA2 and GGA4 could be associated with early and late growth respectively. The GGA4 QTL also had the largest effect on SL9 and SD9 and explained 7% and 10% of their phenotypic variances respectively. However, when SL9 and SD9 were corrected with BW9, a shank length percent QTL was identified on GGA2. We identified novel QTL and also confirmed previously identified loci in other chicken populations. As the foundation population was established from commercial broiler strains, it is possible that QTL identified in this study could still be segregating in commercial strains.

Effects of diet particle size on digestive parameters in D+ and D- genetic chicken lines selected for divergent digestion efficiency.

The aim of this experiment was to compare the D(+) and D(-) chicken lines genetically selected for divergent digestion efficiency by testing the effects of diet particle size on growth performances, digestion efficiencies, and digestive organ weights in both lines. A 2 x 3 factorial arrangement of treatments was used to test the D(+) and D(-) lines (sixth generation) and 3 diets, namely a pelleted standard corn diet (S), a pelleted hull diet (H) made by diluting S diet with 7% coarse cereal hulls, and a coarse corn diet (C) identical to the S diet, distributed as 30% coarsely crushed corn mixed with the 70% pelleted remaining part. Experimental diets were fed from 7 to 26 d of age. Combining results from all diets obtained at 26 d of age, D(+) birds showed 9% heavier (P < 0.0001) gizzard and 10% lighter (P < 0.0001) small intestine than D(-) birds. The AME(n) and digestibilities of lipids, protein, and starch measured at 3 wk of age were, on average, 3.5, 5.6, 5.8, and 0.5% higher (P < 0.0002) in D(+) than in D(-) birds, respectively. Significant (P

Predictors of success of semen cryopreservation in chickens.

Semen cryopreservation is very important for the ex situ management of genetic diversity in birds but it is rarely used. This is partly because of the highly variable success rates, and this emphasizes the need for predictors of semen freezability. This study evaluated the ability of semen quality tests to predict the success rates of semen cryopreservation in chickens and the relationships between each test. Individual variations of in vitro quality tests of semen were compared to the fertility obtained with fresh and cryopreserved semen. The in vitro semen quality tests represented viability, integrity, motility (percentage of viable and morphologically normal cells (PVN); mass motility (MMOT) and different motion parameters including percentage of motile spermatozoa (PMOT)) and biophysical tests (OSM, resistance to osmotic stress; membrane fluidity (FLUID)). Different in vitro tests were significantly correlated between each other for fresh (MMOT, PVN and FLUID, many criteria of objective motility) and cryopreserved semen (MMOT, different objective motility parameters, PVN). Fertility was significantly correlated with PVN for fresh semen and PVN and different objective motility criteria for cryopreserved semen. Membrane fluidity, followed by PVN, PMOT and MMOT, measured on fresh semen samples was positively correlated with fertility obtained with cryopreserved semen. The combination of the first three tests explained 85% of the variability of fertility observed with cryopreserved semen. In conclusion, we showed that different in vitro tests of semen quality are of predictive value for the success rate of semen cryopreservation in the chicken, the most accurate being membrane fluidity.

Behavioural and physiological fear responses in ducks: genetic cross effects.

Mule duck, a cross between a Muscovy drake and a Pekin female, is reported by the farmers to frequently express fear behaviours, such as man avoidance. The genetic basis of fear responses in mule ducks was therefore investigated in this study. According to a previous experiment, the dominant effect of Pekin genotype was hypothesised; however, due to the absence of birds from the reciprocal cross, a superiority of the Pekin in additive effect could not be distinguished from a direct maternal additive effect. In order to clarify this, ducks from the mule genotype, the two parental genotypes (Pekin and Muscovy) and the reciprocal intercross (hinny) underwent a set of physiological and individual behavioural tests of fear. Both parental genotypes were highly fearful but exhibited responses of different patterns: Pekin ducks manifested a higher locomotor activity, whereas the Muscovy ducks showed a higher avoidance to man. Hybrids expressed higher panic responses and specific fear of man than the two parent breeds. Both hybrids expressed similar patterns and the maternal effects were not significant. Significant heterosis effects were found for most of the behavioural responses, in agreement with the fact that higher fear responses were expressed by the hybrids compared to the parental genotypes. A significant heterosis effect was also found for basal adrenal activity; hybrids having higher basal level than parental genotypes. Maximum capacity of adrenal response appeared to be determined by direct additive effects with a superiority of the Pekin genotype.

Effects of xylanase and antibiotic supplementations on the nutritional utilisation of a wheat diet in growing chicks from genetic D+ and D- lines selected for divergent digestion efficiency.

The experiment consisted of a 2 × 2 × 2 factorial design testing the two D+ and D- chicken lines selected for divergent digestion efficiency (fifth selection generation), xylanase (with or without) and ampicillin and collistin (with or without) supplementations. From 8 to 22 days, 144 chickens (18 birds per treatment) were fed a diet containing 55% wheat from a high-viscosity cultivar (Rialto). Effects of treatments were evaluated on individual growth performance (8 to 19 days), digestibilities of lipids and dry matter, dietary energy value (apparent metabolisable energy corrected to zero-nitrogen retention (AMEn)), digestive organ and breast sizes, and intestinal bile acids at 3 weeks of age. Individual variabilities were much lower in D+ than in D- birds for feed : gain ratios, digestibilities and AMEn values. In all cases, feed : gain ratios were lower in the D+ than in the D- line (P < 0.001), and D+ birds showed 22% to 86% higher values than in D- birds (P < 0.001) for digestibilities and AMEn. In D- birds, antibiotics but not xylanase supplementation had significant effects on lipid digestibility (P < 0.01) and AMEn (P < 0.05), whereas both supplements improved these parameters in D+ birds (P < 0.001 for both additives on lipids digestibility, P < 0.05 for xylanase and P < 0.01 for antibiotics on AMEn). Relative weights of gizzard and proventriculus, and gizzard : intestine weight ratio were higher in D+ than in D- birds, while relative weight of intestine was increased in D- birds compared with D+ birds. Antibiotics reduced intestine relative weight in D+ (P < 0.001) and D- (P < 0.01) lines. AMEn variations were efficiently predicted by the gizzard : intestine weight ratio. In conclusion, antibiotics were very efficient for improving growth performance, AMEn and digestibility values in both chicken lines. Xylanase was less efficient than antibiotics. Because of their low individual variabilities, D+ birds were much more efficient than D- ones for the detection of significant effects induced by xylanase supplementation. Differences between lines in feed : gain ratio, digestibilities and AMEn were reduced when xylanase and antibiotics were added together. Effects of xylanase supplementation and animal genetics on lipid digestibility could not be entirely explained in terms of intestinal bile acids. Other factors should be involved, especially for the lipid digestibility difference induced by animal genetics. The gizzard : intestine weight ratio was an efficient parameter for predicting AMEn variations due to animal genetics and additives.