Molecular regulation, breed differences and genes involved in stress control in farm animals.

Stress is a state of disturbed homeostasis evoking a multiplicity of somatic and mental adaptive reactions resulting from any of the 5 freedoms of animals being violated. Many environmental forces disrupt homeostasis in farm animals, such as extreme temperatures, poor nutrition, noise, hunger, and thirst. During stressful situations, neuronal circuits in the limbic system and prefrontal cortex are activated, which lead to the release of adrenalin and noradrenalin. The hormones released during stress are needed for adaptation to acute stress and are regulated by many genes. This review examined molecular regulation, breed differences, and genes involved in stress control in farm animals. Major molecular regulation of stress, such as oxidative, cytosolic heat shock, unfolded protein, and hypoxic responses, were discussed. The responses of various poultry, ruminant, and pig breeds to different stress types were also discussed. Gene expressions and polymorphisms in the neuroendocrine and neurotransmitter pathways were also elucidated. The information obtained from this review will help farmers mitigate stress in farm animals through appropriate breed and gene-assisted selection. Also, information obtained from this review will add to the field of stress genetics since stress is a serious welfare issue in farm animals.

Selection signatures in melanocortin-1 receptor gene of turkeys (Meleagris gallopavo) raised in hot humid tropics.

Feather colours are used by avian species for defense, adaptation and signaling. Melanocortin-1 receptor (MC1R) gene is one of the genes responsible for feather colour. This study identified selection signatures in MC1R gene of Nigerian indigenous turkeys (NIT) using British United turkeys (BUT) as control breed to investigate the evolutionary processes that have shaped NIT with various feather colours. Complete MC1R gene of 146 NIT (76 males and 70 females) and 32 BUT (18 males and 14 females) were sequenced. Transition/transversion and codon usage biases were predicted using MEGA v6 software. The selective force acting on the gene was predicted using HyPhy software. The FST values were estimated using Arlequin v3.5. The highest transition/transversion bias was predicted for white BUT (1.00) while the lowest was predicted for black NIT (0.50). Negative dN-dS values, indicative of purifying selection, were observed in MC1R gene of all the turkeys. The highest pairwise FST was observed between the MC1R gene of white BUT and black NIT while the least was observed between lavender NIT and white NIT. No recombination event was observed in black NIT and white BUT. The relative synonymous codon usage was the same among different colours for some codons. Presence of purifying selection in MC1R gene of all the turkeys with different feather colours confirms that the gene plays role in many biological processes such as feather colouration, behaviour, pain perception, immunity, growth and adaptation. The results also suggested that the genetic mechanisms generating different feather colours in turkeys are conserved.

Discriminant analysis of response to Newcastle disease and heat tolerance among chicken genotypes in hot humid tropical environment.

Newcastle disease and heat stress reduce the productivity of local chickens of Nigeria (LCN). This study compared the antibody response to Newcastle disease and heat tolerance among different LCN genotypes in hot humid tropics using multivariate discriminant analysis. A total of 299 birds were used for the study. Geometric mean titre against Newcastle disease before vaccination (GMTB), geometric mean titre against Newcastle disease after vaccination (GMTA), rectal temperature at week 4 (RT4), pulse rate at week 4 (PR4), respiratory rate at week 4 (RR4), heat stress index at week 4 (H4), rectal temperature at week 13 (RT13), pulse rate at week 13 (PR13), respiratory rate at week 13 (RR13) and heat stress index at week 13 (H13) were measured. All the traits were significantly (p < 0.05) affected by the genotype while sex differences were only observed in GMTB, GMTA and RR13. The stepwise discriminant analysis revealed RR4, PR13, RT13, H4, GMTA, GMTB, H13 and RT4 to be effective in differentiating the three chicken genotypes. Two canonical variables that accounted for 60.21% and 39.79% of the total variation were revealed. Linear discriminant functions for differentiation of the three chicken genotypes were also developed. 87.39% of normal feather, 76.58% of naked neck and 100% of frizzle feather chickens were correctly assigned into their genotypes. The longest Mahalanobis distance was observed between normal feather and frizzle feather chickens. The discriminant functions developed in this study could be used to differentiate the three genotypes of LCN using antibody response to Newcastle disease and heat tolerance.

Growth performance of Nigerian local chickens in crosses involving an exotic broiler breeder.

Six-hundred-and-seven-day-old chicks were generated from Nigerian local chickens consisting of three genotypes (Normal-feathered; Frizzled-feathered; Naked neck) and an exotic broiler breeder (Anak Titan) to evaluate growth performance for possible meat-type chicken development. Growth parameters measured were body weight, breast girth and keel length on weekly basis for 20 weeks. Effects of sire, dam and chick genotypes were significant (P<0.001) on growth traits. At week 20, chickens sired by the Anak Titan weighed 1,614.82 g followed by Normal-feathered local chickens with body weight of 1,211.32 g. Progenies of Anak Titan and Naked neck dams weighed 1,761.96 and 1,292.80 g at week 20, respectively. Among purebreds, Anak Titan weighed 35.05 g at day-old and had heaviest body weight of 2,360.29 g at 20 weeks compared to the three local strains. The average body weights for the crossbred, Normal-feathered × Anak Titan at day-old and week 20 were 36.39 and 1,577.63 g, respectively. This was followed by Anak Titan × Naked neck with 33.32 g at day-old and 1,514.14 g at week 20. Sex had significant effect (P<0.05) at weeks 16 and 20 with the males having higher mean values than their female counterparts. This study revealed that crosses involving Anak Titan sire × Naked neck dam had highest growth performance, and there was no strain differences among the growth performance of purebred Nigerian local chickens.