Physiological and immunological aspects of feed restriction and its beneficial impacts in fattening rabbits' productivity-an updated review.

Two feed restriction (FR) regimens are utilized with weaned rabbits including a quantitative FR (amount-limited feed or time-restricted admission to feed) and a qualitative FR (modulation of diet content especially protein and energy). The use of post-weaning FR may help in preventing post-weaning digestive disorders, stimulating compensating growth, improving feed efficiency, and decreasing carcass fat content. Interestingly, FR may contribute to changing meat's chemical composition and its physical quality attributes by regulating the morphological and biochemical characteristics of muscle fibers. Also, FR could enhance the gastrointestinal tract development, its histomorphology, and improve feed digestibility and absorption. Furthermore, FR regimens are involved in establishing gut microbial balance and enhancing the host immunological response. It might be concluded that post-weaning FR is involved in influencing the physiological and immunological aspects of growing rabbits. It might be documented that light to mild FR (i.e., 80-90% AL), early (i.e., at the first 2 weeks post-weaning), and relatively short in duration (i.e., for 2-3 weeks) had no negative effects on live body weight, while severing FR reduced live body weight in comparison with ad libitum rabbits.

Ramifications of Heat Stress on Rabbit Production and Role of Nutraceuticals in Alleviating Its Negative Impacts: An Updated Review.

Heat stress has become a widespread concern worldwide, which is a major environmental stress that causes substantial economic loss in the rabbit industry. Compared to other agricultural animals, rabbits are more sensitive to heat stress as they have fewer sweat glands and a thicker coat of fur, increasing the heat dissipation complexity. Thus, heat stress hurts rabbits' productivity, meat quality, reproductive performance, antioxidative properties, immune responsiveness, intestinal histomorphology, and microbiome. Nutraceuticals include vitamins, minerals, antioxidants, organic acids, fatty acids, probiotics, prebiotics, synbiotics, enzymes, and medicinal plants due to the possible impacts on maintaining common biological situations, strengthening immune response, and preventing illness, which ultimately led to an increase in productivity. Nutraceuticals have recently attracted a lot of attention to alleviate the adverse impacts of heat stress in rabbit farms. The objective of the current review is to provide acquaintance with the recent findings about the impact of heat stress on rabbit productivity and the advantages of dietary supplementation of nutraceuticals in mitigating it.

Effect of genotype of growing rabbits on productive performance with special reference to residual feed intake at hot temperature.

OBJECTIVE: Better feed efficiency can be achieved by selecting rabbit genotypes with lower residual feed intake (RFI) under high ambient temperatures. METHODS: Two genotypes of rabbits (Jabali, Saudi local breed and imported, Spanish V-line) were used to derive RFI and to investigate the relationship between RFI and productive traits. In total, 250 animals (125 each) were housed in individual wire mesh cages in a semi-closed rabbitry. Growth performance, feed criteria, carcass evaluation, biochemical blood analysis, and immune responses were determined. RESULTS: Superiority in growth performance, feed efficiency, carcass characteristics, and cellular immunity was recorded in the Jabali breed compared to the V-line genotype. According to regression analysis, a significant effect of daily body weight gain was found, upon computing the expected feed intake in both genotypes. Moreover, mid-body weight0.75 had a significant effect only in the Jabali breed. Positive correlation coefficients between RFI and dry matter feed intake or feed conversion ratio were found. The same trend in this relationship between RFI and productive traits was observed in some cases for both genotypes. An opposite trend in correlations was observed in the studied genotypes for some traits. CONCLUSION: The results suggest that the relationship between RFI and productive traits must be taken into consideration in rabbit breeding programs under the prevailing environment. However, further studies are required to investigate the effect of rabbit genotype and environmental factors on computing RFI.

Using major genes to mitigate the deleterious effects of heat stress in poultry: an updated review.

Acceleration of global warming has emerged as one of the biggest environmental challenges facing poultry farming. In heat stressed flocks, massive mortality rates and substantial damage to productive performance (eggs and meat) are commonly noticed. Because birds do not have sweat glands, they cannot tolerate high temperatures, especially when combined with high humidity. Under this harsh environmental condition, the birds reduce their feed consumption to decline metabolic energy rate. At an ambient temperature of more than 26°C, the bird increases panting and reduces metabolic rate to get rid of the body's heat increment. There are many scenarios that can be followed to alleviate the adverse effects of heat stress. Management practices, nutritional modification, and/or feed additives are frequently used in poultry farms. However, introducing major genes such as naked neck (Na), frizzle (F), slow feathering (K), and dwarf (dw) could be adopted as a significant solution to improve productive performance in birds raised under high environmental temperatures. The birds carrying these mutations gain popularity owing to their ornamental appearance and highly productive performance at high temperatures. Moreover, utilizing dwarf gene in broiler breeders as a dam line improves adaptability, survivability, and hatchability in flocks kept in hot climates. At hatch, the sex-linked slow feathering mutation has been widely used for wing sexing in some egg-type breeds. The potential use of major genes as a breeding strategy to enhance heat tolerance in chickens has been extensively reviewed.

Effect of genotype and egg weight on hatchability properties and embryonic mortality pattern of native chicken populations.

Fertility and hatchability are 2 major parameters that highly influence the reproductive performance of chicken breeds. The objective of this study is to investigate how the genetic background of chickens affects the aspects of fertility, hatchability, and embryonic mortality pattern. Six different native chicken genotypes (black, black-barred, brown, gray, naked neck, and frizzle) kept under similar conditions were evaluated. A total of 1,645 fertile pedigreed eggs from all genetic groups were collected and incubated in forced draft setter. Fertility, hatchability, embryonic mortality, and hatched chick weight were determined. The data were subjected to a one-way analysis of variance with breed (genotype) as a fixed effect. Sire component of variance were used to compute heritability estimates for hatchability traits. The results showed that the fertility and hatchability of the eggs produced from the naked neck or frizzle genotypes exhibited higher values compared to the other genetic groups. An increase in the relative weight of hatched chicks was detected in hatching eggs weighing 44 g or higher. Therefore, attention should be given to the egg size produced by native chicken populations to achieve maximum hatchability performance. Multiple regression analysis revealed that the settable egg weight and the egg weight loss during incubation are the main factors affecting the relative weight of hatched chicks of all genotypes.

Effect of propolis supplementation and breed on growth performance, immunity, blood parameters and cecal microbiota in growing rabbits.

OBJECTIVE: The present study was conducted to investigate the potential effects of dietary supplemented propolis in two growing rabbit breeds on growth performance, immune response, blood parameters, carcass characteristics, and cecal microflora composition. METHODS: A total of 90 growing rabbits aged 6 weeks from two breeds (V-line and Jabali) were randomly allocated to 3 dietary propolis experimental treatments. The experimental treatments consisted of a 2×3 factorial arrangement with two rabbit breeds and three levels of dietary propolis supplementation (0, 250 mg/kg, and 500 mg/kg). Each sub-treatment has 15 rabbits. The experimental period lasted six weeks. RESULTS: There were no significant differences in growth performance and carcass characteristics due to propolis administration. Propolis supplementation at a high level significantly increased (linear; p<0.05) cellular-mediated immunity compared with the unsupplemented group. Furthermore, the rabbits receiving propolis exhibited a significant increase (linear and quadratic; p<0.03) in IgM immunoglobulins compared to the control. The current study provides further evidence that the dietary inclusion of propolis can significantly reduce pathogenic bacterial colonization in growing rabbits. The total count of microflora, E. coli, and Salmonella spp. was significantly lower (linear; p<0.01) in supplemented rabbit groups compared to the control group according to the microbiological analysis of cecal digesta. Based on breed effect, the results indicated that Jabali rabbits (local) performed better than V-line rabbits (foreign) in the majority of the studied traits. CONCLUSION: Dietary propolis is promising for further investigation into improving intestinal health and enhancing immunity in growing rabbits.

The potential role of feed restriction on productivity, carcass composition, meat quality, and muscle fibre properties of growing rabbits: A review.

After weaning rabbits, two post-weaning feed restriction (FR) programs are used: a quantitative FR (quantity of feed-limited or time-limited access to feed) or a qualitative FR (modification of diet composition in particularly protein, energy or fibre). Application of post-weaning FR has potential to control post-weaning digestive disorders, and early lower growth rates may be compensated for by later compensatory growth. FR strategies also have potential to enhance feed conversion ratio and reduce carcass fatness. FR may also influence meat chemical composition and physical quality characteristics via controlling the morphological and biochemical properties of muscle fibres. The purpose of this review was to shed light on recent findings regarding benefits of FR on productive performance, carcass characteristics, meat quality characteristics, and muscle fibre properties in growing rabbits.

Influence of strain and flock age on geometrical and mechanical attributes of eggs produced from Japanese quail birds.

We investigated how the geometrical and mechanical properties of eggshell of Japanese quail are affected by strain and flock age. Two strains of quail (white and gray) were used in the current experiment. The results showed that there was no significant difference for all geometric measurements due to strain effect. Eggs produced from the older birds showed significantly higher (P < 0.01) values compared with younger age for all studied traits. Eggs produced from quails at 22 weeks had a significantly (P < 0.01) darker yolk color than that of the younger age. Superiority in shell thickness, shell weight, and breaking force was detected in eggs of gray quails compared with white quails. On the other hand, the eggs from white quails had significantly higher values for static stiffness and Young's modulus as compared with those of gray counterparts. A significant decrease (P < 0.01) was found for fracture toughness and Young's modulus in eggs of aged birds. A significant negative relationship was found between the breaking force and both static stiffness and Young's modulus. A significant positive relationship was observed between breaking force and both shell thickness and shell percentage. The phenotypic correlation between eggshell breaking force and toughness was relatively high.

Effect of Silver Nanoparticle Administration on Productive Performance, Blood Parameters, Antioxidative Status, and Silver Residues in Growing Rabbits under Hot Climate.

The influence of subcutaneous injections of silver nanoparticles (AgNPs) on rabbit performance, hematological and biochemical parameters of blood, antioxidant status, and the residues of silver in meat and blood in two breeds (New Zealand White (NZW) and Jabali) of rabbits growing under high ambient temperature was evaluated. A total of 90 six-week-old rabbits (45 NZW and 45 Jabali) were randomly distributed into three equal treatment groups (control, 0.5 mg, and 1.0 mg AgNPs/kg body weight). The treated rabbits were injected twice a week for four consecutive weeks. The results revealed that AgNPs administration had no significant effect on average daily gain (ADG), feed intake, and feed conversion ratio (FCR). The NZW breed surpassed the Jabali breed in growth performance traits, carcass weight, dressing percentage, and cuts of mid parts and hind cuts. Administration of AgNPs had a significant effect on hematocrit (HCT) and platelet (PLT) values. Rabbits injected with AgNPs at a dose of 0.5 mg showed a lower plasma concentration of total cholesterol and triglycerides than that of control rabbits. The NZW breed had significantly low platelet, total cholesterol, and triglyceride values. Rabbits injected with 0.5 mg/kg BW had the lowest total antioxidant capacity and highest malondialdehyde (MDA) and glutathione peroxidase. The Ag residues were higher in blood than those in meat in treated rabbits. The local breed (Jabali) had significantly lower residues than the imported one (NZW) either in meat or in blood. However, the amount of accumulated silver in blood plasma and meat increased with increasing dose.

Assessment of Residual Feed Intake and Its Relevant Measurements in Two Varieties of Japanese Quails (Coturnixcoturnix japonica) under High Environmental Temperature.

Three hundred and ten 12-week-old laying Japanese quails (Coturnixcoturnix japonica) from gray and white varieties (155 each) were randomly selected from the initial population and kept in individual battery cages. The measurements of growth and egg production were determined to derive residual feed intake (RFI). The relationship between RFI and egg quality, blood parameters, and carcass characteristics was also determined. The results indicated that the gray quails had significantly higher egg mass and lower broken eggs compared to the white quails. A significant increase of eggshell strength and shell percentage was found in eggs produced from gray quails compared to their white counterparts, although their shell thickness means weresimilar. The results of multiple regression analysis clearly identified a significant effect of metabolic body weight and egg mass for the computation of expected feed intake, rather than body weight gain, in both varieties of Japanese quails. A strong positive correlation between RFI and feed intake in both gray and white quail varieties was found. The same trend was also observed for feed conversion ratio (FCR). Therefore, including RFI in the selection criteria of Japanese quails in order to improve FCR under high environmental temperature is highly recommended.

Genetic diversity of Saudi native chicken breeds segregating for naked neck and frizzle genes using microsatellite markers.

OBJECTIVE: Recently, there has been an increasing interest in conservation of native genetic resources of chicken on a worldwide basis. Most of the native chicken breeds are threatened by extinction or crossing with ecotypes. METHODS: Six Saudi native chicken breeds including black naked neck, brown frizzled, black, black barred, brown and gray were used in the current study. The aim of the current study was to evaluate genetic diversity, relationship and population structure of Saudi native chicken breeds based on 20 microsatellite markers. RESULTS: A total of 172 alleles were detected in Saudi native chicken breeds across all 20 microsatellite loci. The mean number of alleles per breed ranged from 4.35 in gray breed to 5.45 in normally feathered black with an average of 8.6 alleles. All breeds were characterized by a high degree of genetic diversity, with the lowest heterozygosity found in the brown breed (72%) and the greatest in the frizzled and black barred populations (78%). Higher estimate of expected heterozygosity (0.68) was found in both black breeds (normal and naked neck) compared to the other chicken populations. All studied breeds showed no inbreeding within breed (negative inbreeding coefficient [FIS]). The phylogenetic relationships of chickens were examined using neighbor-joining trees constructed at the level of breeds and individual samples. The neighbor-joining tree constructed at breed level revealed three main clusters, with naked neck and gray breeds in one cluster, and brown and frizzled in the second cluster leaving black barred in a separate one. CONCLUSION: It could be concluded that the genetic information derived from the current study can be used as a guide for genetic improvement and conservation in further breeding programs. Our findings indicate that the Saudi native chicken populations have a rich genetic diversity and show a high polymorphism.

Effect of probiotic supplementation and genotype on growth performance, carcass traits, hematological parameters and immunity of growing rabbits under hot environmental conditions.

The effect of dietary inclusion of probiotics and genetic groups on rabbit performance under hot environmental conditions was studied. A total of 80 rabbits aged 8 weeks were distributed into a completely randomized design in a 4 × 3 factorial arrangement, including four genetic groups and three concentrations of dietary probiotic (0, 200 and 400 g/t feed). The utilized probiotic contained 4 × 109  colony-forming units/g of Bacillus subtilis. Jabali local breed (J), imported Spanish V-line (V) and their crossbreds (»J¾V and ¾J»V) were included in the current study. Final weight and body weight gain were not significantly affected by dietary probiotic levels or genetic group. The feed conversion ratio was better for purebreds than that of crossbreds. A significant improvement in percentage of dressed carcass, mid and hind parts was recorded for rabbits fed a diet containing 400 g probiotic/t feed compared with those fed a basal diet or low probiotic level. Probiotic supplementation had a significant decrease in serum cholesterol. Rabbits given 400 g probiotic/t feed had higher hemoglobin, red blood cells and platelets. Adding 400 g probiotic/t feed to rabbit's diet significantly (P ≤ 0.05) improved cell-mediated immunity compared to the other treatments 48 h post-injection.