Search

International audience; Feed conversion ratio (FCR) is an important trait to target in breeding programs in order to improve fish farming sustainability and increase environmental efficiency. Due to the complexity of accurately measuring the individual feed consumption of fish, developing a selective breeding programme to improve FCR is a challenge. Using video-recordings of several consecutive meals in tilapia groups, we selected two divergent lines of Nile tilapia for high (FCR+) and low (FCR-) FCR at juvenile stage (12.2 g) combining BLUP and within family selection. After two generations, we observed a 12% realized difference in FCR between both divergent lines, indicating that the inclusion of FCR in a selective breeding programme can be efficient in practice. This divergence was in line with a realized heritability of 0.19 for FCR. The divergence in estimated breeding values of FCR between the two lines was reduced (3%) but still present. Another important result was that the realized genetic correlation between FCR and Daily Weight Gain (DWG) was highly negative (rg = -0.69 + 0.16), meaning that improving growth by selective breeding would also indirectly improve FCR in juvenile Nile tilapia, although direct selection for FCR would be more efficient than indirect selection through growth to improve FCR.

Nile tilapia is a key aquaculture species with one of the highest production volumes globally. Genetic improvement of feed efficiency via selective breeding is an important goal, and genomic selection may expedite this process. The aims of this study were to 1) dissect the genetic architecture of feed-efficiency traits in a Nile tilapia breeding population, 2) map the genomic regions associated with these traits and identify candidate genes, 3) evaluate the accuracy of breeding value prediction using genomic data, and 4) assess the impact of the genetic marker density on genomic prediction accuracies. Using an experimental video recording trial, feed conversion ratio (FCR), body weight gain (BWG), residual feed intake (RFI) and feed intake (FI) traits were recorded in 40 full-sibling families from the GIFT (Genetically Improved Farmed Tilapia) Nile tilapia breeding population. Fish were genotyped with a ThermoFisher Axiom 65 K Nile tilapia SNP array. Significant heritabilities, ranging from 0.12 to 0.22, were estimated for all the assessed traits using the genomic relationship matrix. A negative but favourable genetic correlation was found between BWG and the feed-efficiency related traits; −0.60 and −0.63 for FCR and RFI, respectively. While the genome-wide association analyses suggested a polygenic genetic architecture for all the measured traits, there were significant QTL identified for BWG and FI on chromosomes seven and five respectively. Candidate genes previously found to be associated with feed-efficiency traits were located in these QTL regions, including ntrk3a, ghrh and eif4e3. The accuracy of breeding value prediction using the genomic data was up to 34% higher than using pedigree records. A SNP density of approximately 5,000 SNPs was sufficient to achieve similar prediction accuracy as the full genotype data set. Our results highlight the potential of genomic selection to improve feed efficiency traits in Nile tilapia breeding programmes.

International audience; Given the strong effects of behavioural hierarchies on growth in many cultured species and the key role of feed efficiency in aquaculture economics, understanding the nature of the interaction of these variables is important for the sustainability of aquaculture. The relationship between agonistic behaviour, growth and feed efficiency in Nile tilapia, Oreochromis niloticus, was studied by rearing 120 fish in eight aquaria. Fish were video-recorded to estimate the occurrence of agonistic behaviour during a fasting and a refeeding period. Growth, feed intake and feed conversion efficiency (FCE - calculated as the inverse of feed conversion ratio (FCR)) were subsequently measured individually for each fish. Fish showed 58% less agonistic traits during the fasting period compared to the feeding period, but generally, an aggressive fish during the fasting period was also aggressive during the refeeding period. The nature of agonistic behaviours between individuals was used to assess the presence of hierarchical relationships between fish. There were dominance hierarchies established in each experimental aquarium that despite minor shifts were maintained throughout the experiment. Agonistic behaviours were strongly correlated with each other, the aggression Index (AI) and with hierarchy rank. PCA analysis of the agonistic behaviours summarising the behavioural information showed little or no correlation between agonistic behaviour, fish growth or FCE. FCE was correlated with body weight gain (BWG). These results suggest that agonistic interactions in juvenile Nile tilapia do not have a large impact on growth and feed conversion efficiency.

Five mid-lactation multicatheterized Jersey cows were used in a 4 × 4 Latin square design to investigate whether the increase in milk N yield associated with diets rich in starch versus fiber could originate from changes in the splanchnic AA metabolism and if these changes depended upon the dietary crude protein (CP) content. Four isoenergetic diets were formulated to provide 2 different carbohydrate compositions [diets rich in starch (350 g of starch and 310 g of neutral detergent fiber/kg of dry matter) versus rich in fiber (45 g of starch and 460 g of neutral detergent fiber/kg of dry matter)] crossed by 2 different CP contents (12.0 vs. 16.5% CP). At the end of each treatment period, 6 hourly blood samples were collected from the portal and hepatic veins as well as the mesenteric artery to determine net nutrient fluxes across the portal drained viscera (PDV), liver, and total splanchnic tissues. Dry matter and calculated energy intake as well as total absorbed energy were similar across treatments. However, the net portal appearance (NPA) of acetate, total volatile fatty acids, and β-hydroxybutyrate were higher with diets rich in fiber versus starch, whereas that of oxygen, glucose, butyrate, and insulin were lower. Concomitant to these changes, the percentage of N intake recovered as total AA (TAA) in the portal vein was lower for diets rich in fiber versus starch (42.3 vs. 51.4%, respectively), without, however, any difference observed in the NPA of the main AA used as energy fuels by the PDV (Glu, Gln, and Asp). Despite a higher NPA of TAA with starch versus fiber diets, no differences in the net hepatic flux of TAA, essential and nonessential AA were observed, resulting in a higher (+22%) net splanchnic release of AA and, hence, a greater (+7%) milk N yield. The net hepatic flux and hepatic fractional removal of none of the individual AA was affected as the main carbohydrate changed from fiber to starch, except for Gly and Lys, which were higher for the latter. After correcting for differences in NPA of TAA, the net hepatic uptake of TAA tended to be lower with starch versus fiber diets. The higher transfer of N from feed to milk with diets rich in starch is not the consequence of a direct sparing AA effect of glucogenic diets but rather the result of lower energy requirements by the PDV along with a higher microbial N flow to the duodenum. A better AA use by peripheral tissues with starch versus fiber diets was also hypothesized but more studies are warranted to clarify this issue.

Selenium deficiency is widely described in livestock from the Arabian Peninsula, notably in the camel, and selenium supplementation is based on cattle or horse requirements, usually with sodium selenite product. In order to test the effect of organic Se supplementation vs inorganic Se, 24 pregnant camels were subjected to 3 treatment groups starting one month before delivery (control without Se, non-organic bolus, organic Se). Blood, milk and feces samples were collected from one month before delivery to 3 months of lactation. At delivery, the organic group had a significant higher Se concentration (P < 0.01) in serum (8.21± 1.38 lg/100 mL) and in colostrum (7.27 ±2.89 lg/100 mL) than in inorganic group (3.90 ±0.68 and 3.72 ±0.71, respectively) and than in control group (5.45 ± 2.38 and 2.70 ± 0.66, respectively). In calf serum, the Se concentration was significantly higher (P < 0.001) in the two supplemented groups (6.32 ± 2.81 and 5.99 ± 3.31 lg/100 mL in organic and inorganic groups, respectively) than in control (3.42 ±1.41 lg/100 mL). The Se in mother serum decreased after parturition but was highly correlated to Se serum in calf and to Se fecal excretion. Se in milk was lower than in colostrum in all groups (P < 0.01). Treatments had no significant effect on somatic cell count. This study revealed that organic supplementation in camel appeared more efficient. (Resume d'auteur)

The nutritional quality of poultry excreta in replacement of maize offal was evaluated in 16 growing West African Dwarf (WAD) goats (eight females and eight males about eight months of age) with an average liveweight of 6.5 kg. The goats were allotted to four different diets containing 0% (T1, control treatment), 10% (T2), 20% (T3) and 30% (T4) poultry excreta in maize offal based diets. Each animal was fed its assigned diet ad libitum for 120 days. Feed intake, daily weight gain, feed conversion ratio and fat efficiency ratio were generally higher (p < 0.05) in diets including poultry excreta. The feed cost per kilogram, cost per kilogram of weight gain and cost of production were generally lower (P 0.05). The leg, loin, rank, lean, shoulder, brisket cuts, fat and bone generally improved (p < 0.05) with the inclusion of poultry excreta in the diets. The bone:lean meat ratio increased similarly (p > 0.05) in all treatments, except in T3 where it was slightly higher. It is concluded that WAD goats could be sustained on poultry excreta as a component of formulated diets for increased performances in weight gain, feed conversion ratio, carcass yield, and increased economic benefits to farmers.

Many environmental impacts can be attributed to fish farming and there is a need to explore new ways of reducing environmental impacts, such as fish genetic improvement. The environmental consequences of genetic improvement in thermal growth coefficient (TGC) and in feed conversion ratio (FCR) were investigated, therefore, in an African catfish farm in Recirculating Aquaculture System. A Life Cycle Assessment study was conducted and combined with a bioeconomic model of genetic response. Results show that environmental consequences of genetic improvement in TGC and FCR are different among impact categories, depending on their main contributors and on the factor limiting production at farm level. Genetic improvement of FCR always leads to lower environmental impacts while improving TGC decreases environmental impacts only when density was the limiting factor. Those results are important for the future development of selective breeding programs in fish farming taking into account environmental impacts.

absent

Session : Génétique et qualité; Residual feed intake (RFI) is a selection criterion alternative to feed:gain ratio to improve feed efficiency, and thus to reduce production costs and the negative environmental impacts of pig production. Several studies based on RFI selection experiments have indicated that low RFI is associated with lower body fat content and decreased meat quality; these differences might arise from tissue metabolic reorientations for the storage and use of nutrients. To gain insights intothe molecular mechanisms underlying these differences, gene expression profiles in liver, skeletal muscle and subcutaneous adipose tissue were examined in16pigs(115 kg) from lines divergently selected for RFI. Transcriptomics analyses using a commercial microarray (Agilent‐026440 Sus scrofa Oligo Microarray v2, 44K) revealed large differences between high and low RFI pigs in the three tissues examined. The number of oligonucleotides found to be differentially expressed (P< 0.01) between lines was much higher in muscle (1013) than in liver (809) and adipose tissue (657). Gene functional classification indicated that pigs selected for low RFI generally exhibited a higher expression level of genes known to be involved in mRNA translation in liver and muscle, and of genes associated with mitochondrial energy metabolism in adipose tissue. In contrast, the expression of genes linked to aminoacid catabolism in liver was lower in low RFI than in high RFI pigs. These suggested differences in amino acid synthesis and protein catabolism may beinvolved in the differences in body composition observed between the two RFI lines.

International audience; 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.

International audience

Genetic parameters of feed efficiency and growth traits were estimated in two selected rabbit lines after 6 generations of selection. The ConsR line was selected for residual feed intake (RFI) under ad libitum feeding. The AlimR line was selected for average daily gain (ADG from 30 to 63 days) under restricted feeding corresponding to 80 % of ad libitum feed intake of control animals. Estimates of heritability of ADG and FCR (feed conversion ratio) were higher in the AlimR line than in the ConsR line, while estimates of heritability of weight at 30 and 63 days-old were similar between lines. Heritability of ADG (0.25), the selection criterion of the AlimR line, was higher than RFI (0.15), the selection criterion of the ConsR line. Estimates of heritability and genetic correlations between weaning weight, weight at 63 days, ADG and FCR are also presented for each line.

International audience; The effect of feeding nutritionally different diets in sequential or loose-mix systems on the performance of laying hen was investigated from 16 to 46 wk of age. Equal proportions of whole wheat grain and protein-mineral concentrate (balancer diet) were fed either alternatively (sequential) or together (loose-mix) to ISA Brown hens. The control was fed a complete layer diet conventionally. Each treatment was allocated 16 cages and each cage contained 5 birds. Light was provided 16 h daily (0400 to 2000 h). Feed offered was controlled (121 g/bird per d) and distributed twice (4 and 11 h after lights-on). In the sequential treatment, only wheat was fed at first distribution, followed by balancer diet at the second distribution. In loose-mix, the 2 rations were mixed and fed together during the 2 distributions. Leftover feed was always removed before the next distribution. Sequential feeding reduced total feed intake when compared with loose-mix and control. It had lower wheat (-9 g/bird per d) but higher balancer (+1.7 g/bird per d) intakes than loose-mix. Egg production, egg mass, and egg weight were similar among treatments. This led to an improvement in efficiency of feed utilization in sequential compared with loose-mix and control (10 and 5%, respectively). Birds fed sequentially had lower calculated ME (kcal/bird per d) intake than those fed in loose-mix and control. Calculated CP (g/bird per d) intake was reduced in sequential compared with loose-mix and control. Sequentially fed hens were lighter in BW. However, they had heavier gizzard, pancreas, and liver. Similar liver lipid was observed among treatments. Liver glycogen was higher in loose-mix than the 2 other treatments. It was concluded that feeding whole wheat and balancer diet, sequentially or loosely mixed, had no negative effect on performance in laying hens. Thus, the 2 systems are alternative to conventional feeding. The increased efficiency of feed utilization in sequential feeding is an added advantage compared with loose-mix and thus could be employed in situations where it is practicable.

The Arabian camel (Camelus dromedarius) is well suited to the desert environment due to its remarkable physiological and metabolic adaptation. Nutrients requirements of the camel are not well defined, particularly that of trace elements. Selenium supplementation is often recommended to treat conditions attributed to Se deficiency such as cardiomyopathy. This paper reports the results of four experiments carried out using pregnant, non-pregnant, young and adult female camels. The commercial source of Se (i.e. sodium selenite) was used to provide supplementary levels between 0 to 16 mg of Se/day. The concentration of Se in serum and the activity of erythrocytes glutathione peroxidase (GSH-Px) were measured. The Se concentration in serum of camels increased linearly with increased Se supplementation levels from 0 to 4 mg/day, then plateau when levels further increased to a maximum of 16 mg/day. The average Se concentration (expressed as ng/ml) ranged between 100 and 500. Similar trend was observed for the GSH-Px activity. The results suggest a maximum tolerable dose of 8 mg/day and the recommended dose between 2 and 4 mg/day.

Les performances de ponte et d'efficacité alimentaire de la race Mandarah d'origine égyptienne, ont été comparées chez des poules en cages individuelles à deux températures constantes (21°C et 31°C) de l'entrée en ponte à l'âge de 47 semaines. La race Mandarah apparaît modérément affectée par la chaleur pour l'ensemble des critères (respectivement -10 et -6 % pour la masse d'oeufs et le poids moyen des oeufs).

Des animaux metis Zebu Brahman X Zebu Malgache de 16 mois environ et des metis Zebu Malgache X Frison (ou Normand) de 6 a 7 mois environ ont ete nourris intensivement. Les resultats des croissances des indices de consommation et les caracteristiques de carcasses sont donnes. Comparativement a des Zebus Malgaches de meme âge, nourris de facon comparable, des gains importants sont obtenus sur tous les plans. Le croisement Brahman, realisable en elevage extensif, parait tres recommande. (Resume d'auteur)