Effects of crossbreeding and mutations at the αs1-CN gene in Ethiopian and crossbred goats on casein content, and coagulation properties of their milks. A short review

This short review presents the developments in genetic improvement of Ethiopian goat breeds and the impact of the crossbreeding programs on αs1-CN gene (CSN1S1). The influence of newly identified mutations on milk components and technological properties are considered. The indigenous Ethiopian goat breeds are low milk yielders with high percentage of milk organic component and thus with good technological properties. Crossbreeding programs were taken as an option to improve their genetic potential. The main objective of crossbreeding programs in Ethiopia were to increase milk yield and thus, to enhance protein consumption at household level. The success of crossbreeding programs was impaired due to high input requirements, incompatibility of the genotype with the farmers breeding objectives and the production system, owing mainly to less net benefit than expected from the crossbreeding. Evaluation of CSN1S1 gene revealed 36 mutations, which were not previously reported. Four of these mutations were detected in the exon region of CSN1S1: two synonymous (exons 4 and 12), one non-synonymous (exon 10) and a nonsense mutation (exon 15). The non-synonymous mutation was detected only in the indigenous goats and their crosses with exotic Boer goats. It involved amino acid exchange Gln77→Pro77. Goats carrying this mutation have higher αs1-CN, fat and protein content and good coagulation properties with exceptionally high gel strength. The nonsense mutation involved a transversion, at amino acid position Gln140, CAG→TAG giving rise to a premature stop codon. The mutation was found in three crossbred goats between the exotic Toggenburg buck and the local Arsi-Bale does. This mutation was not detected in any of the local goat breeds and therefore, we assume it originates from the exotic parent. The lesson is the need for careful evaluation of the exotic genes for milk quality in bucks chosen for crossbreeding programs, prior to introduction.