Pugliano, Mariagiulia (2024) Study of Genes Involved in Milk Production in Livestock Species. [Tesi di dottorato]

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Abstract

The main objective of this thesis was to genetically characterize populations of animals of zootechnical interest in central-southern Italy, focusing on genes associated with milk production and resistance to livestock diseases, in particular technical ones such as mastitis. Using the candidate gene approach, three native Lazio goat breeds (Capestrina, Grigia Ciociara and Bianca Monticellana) were analyzed at the calcium-sensitive casein loci (CSN1S1, CSN2, CSN1S2), the Bagnolese sheep at the DIGAT1 locus, the MBL2 gene in the Italian Mediterranean Buffalo and in the Comisana sheep, with the aim of characterizing them and subsequently associating them with production parameters and disease/health status. The choice of TGA (Autochthonous Genetic Types) and/or of breeds that contribute to the identity of a territory (Italian Mediterranean Buffalo), as well as the loci to be analyzed, is motivated by the intention to search for the peculiarities of the breeds that allow them to be distinguished from those with a high diffusion rate, to be able to plan their mating in order to avoid the loss of typical genetic variants, to define the productions to which they are more predisposed and to implement appropriate valorization plans. The results of these studies have not only allowed us to present new, more accurate screening methods for certain loci (CSN2 and DGAT1) but have also provided important information on the characteristics of the breeds and species analysed at these loci. In particular, molecular analyses of calcium-sensitive caseins have revealed a discrete genetic variability for the CSN1S1 locus in native goat populations of the Lazio region, in which four alleles (αs1-Cn A*, B*, F and N) have been identified, highlighting the almost complete absence of alleles associated with an intermediate or absent content of this protein in milk. When the three genetic types were grouped together, a high frequency of alleles associated with low (CSN1S1F) and high (CSN1S1A*, B*) αs1-casein content in milk was observed. Finally, the association with production parameters showed that animals with the A*A* genotype appear to be more productive than other genotypes in terms of fat and protein in milk, whereas animals with the FF genotype tend to produce milk with lower protein, casein and solids-non-fat content. Molecular analysis of the DGAT1 gene revealed a high frequency of the C allele (0.5655) at the g.5553 (C>T) locus, whereas the C allele predominated at the g.8539C>T locus. All animals tested for milk had a monomorphic genotype at g.8539C>T of the DGAT1 gene, i.e. CC. Regarding the genotype at g.5553C>T, significant differences were observed between the genotypes in terms of percentage fat and protein yield. In particular, animals with the CT genotype had a higher percentage of fat produced per milking than those with the CC and TT genotypes (p < 0.01). Similar results were found for protein yield percentage, with CT individuals being more productive than CC individuals (p < 0.01). The characterization of the MBL2 gene in the Italian Mediterranean Buffalo showed that this gene is particularly polymorphic in this species, in fact 33 SNPs were found compared to the reference sequence, of which some (6689061 T>C, 6689062 G>A, 6689080 T>A, 6689100 G>A, 6690721 G>T, 6690757 C>A, 6690949 C>T, 6691003 T>C, 6691397 A>G) were statistically associated with SCC (p<0.05). Finally, regarding the MBL2 gene in sheep, the characterization of exon 1 revealed the presence of three alleles: A1, C and D. The A1 variant is, in our opinion, a derivation of the A allele previously found in other sheep breeds. The A1 allele is responsible for an amino acid substitution in the corresponding translated sequence. Furthermore, variant A1 was the most frequent in the analyzed population (0.416). Interestingly, the A1C genotype was found to be present only in mastitis-free (healthy) animals, suggesting a possible relation between this genotype and the absence of mastitis; this hypothesis could explain the statistical significance observed in the analysis of the association between the A1C genotype and low SCC compared to the A1A1 and DD genotypes. In this context, these studies make an important contribution to the genetic understanding of Italian livestock breeds and to the promotion of sustainable livestock production, with practical implications for genetic selection and livestock health management.

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