To adjust breeding programs for local, commercial, and fancy breeds, and to implement molecular (marker-assisted) breeding, a proper comprehension of phenotypic and genotypic variation is a sine qua non for breeding progress in animal production. Here, we investigated an evolutionary subdivision of domestic chickens based on their phenotypic and genotypic variability using a wide sample of 49 different breeds/populations. These represent a significant proportion of the global chicken gene pool and all major purposes of breed use (according to their traditional classification model), with many of them being characterized by a synthetic genetic structure and notable admixture. We assessed their phenotypic variability in terms of body weight, body measurements, and egg production. From this, we proposed a phenotypic clustering model (PCM) including six evolutionary lineages of breed formation: egg-type, meat-type, dual purpose (egg-meat and meat-egg), game, fancy, and Bantam. Estimation of genotypic variability was carried out using the analysis of five SNPs, i.e., at the level of genomic variation at the NCAPG-LCORL locus. Based on these data, two generally similar genotypic clustering models (GCM1 and GCM2) were inferred that also had several overlaps with PCM. Further research for SNPs associated with economically important traits can be instrumental in marker-assisted breeding programs.

The expression of nine functional candidates for QT abdominal fat weight and relative abdominal fat content was investigated by real-time polymerase chain reaction (PCR) in the liver, adipose tissue, colon, muscle, pituitary gland and brain of broilers. The high mobility group AT-hook 1 (HMG1A) gene was up-regulated in liver with a ratio of means of 2.90 (P ≤ 0.01) in the «fatty» group (relative abdominal fat content 3.5 ± 0.18%, abdominal fat weight 35.4 ± 6.09 g) relative to the «lean» group (relative abdominal fat content 1.9 ± 0.56%, abdominal fat weight 19.2 ± 5.06 g). Expression of this gene was highly correlated with the relative abdominal fat content (0.70, P ≤ 0.01) and abdominal fat weight (0.70, P ≤ 0.01). The peroxisome proliferator-activated receptor gamma (PPARG) gene was also up-regulated in the liver with a ratio of means of 3.34 (P ≤ 0.01) in the «fatty» group relative to the «lean» group. Correlation of its expression was significant with both the relative abdominal fat content (0.55, P ≤ 0.05) and the abdominal fat weight (0.57, P ≤ 0.01). These data suggest that the HMG1A and PPARG genes were candidate genes for abdominal fat deposition in chickens. Searching of rSNPs in regulatory regions of the HMG1A and PPARG genes could provide a tool for gene-assisted selection.

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Milk is an integral and therefore complex structural element of mammalian nutrition. Therefore, it is simple to conclude that lactation, the process of producing milk, is as complex as the mammary gland, the organ responsible for this biochemical activity. Nutrition, genetics, epigenetics, disease pathogens, climatic conditions, and other environmental variables all impact breast productivity. In the last decade, the number of studies devoted to epigenetics has increased dramatically. Reports are increasingly describing the direct participation of microRNAs (miRNAs), small noncoding RNAs that regulate gene expression post-transcriptionally, in the regulation of mammary gland development and function. This paper presents a summary of the current state of knowledge about the roles of miRNAs in mammary gland development, health, and functions, particularly during lactation. The significance of miRNAs in signaling pathways, cellular proliferation, and the lipid metabolism in agricultural ruminants, which are crucial in light of their role in the nutrition of humans as consumers of dairy products, is discussed.