Population genetic structure and milk production traits in Girgentana goat breed

Abstract

Abstract. The aim of this work was to evaluate the genetic status of the Girgentana goat, an endangered breed from Sicily (Italy), using microsatellite markers. Furthermore, as the main purpose of the Girgentana breed is milk production, quantitative milk traits were investigated, including fatty acid profile. Molecular data from CSN1S1, CSN2, CSN1S2, and CSN3 casein genes were also used to infer haplotypes. A total of 264 individuals were collected. Samples of Maltese (n = 41) and Derivata di Siria (n = 33) goat breeds were also used to understand the genetic relationship among breeds. Testday records for milk production were collected to determine daily milk yield, fat, protein, casein, lactose, and somatic cell count. Individual milk samples were also collected for fatty acid extraction. Wright's statistics, gene flow, Nei genetic distance, factorial correspondence analysis, and Bayesian assignment test showed the existence of genetic variability and differentiation among breeds. The AMOVA results indicated that 89.96% of the total variance was partitioned within populations. The Girgentana breed appears to have a subdivided population, and has not experienced a recent bottleneck. A high variability in milk yield was observed. Mean morning milk yield was 1448 AE 404 g, with 4.30 AE 0.87% and 3.72 AE 0.44% of fat and protein percentages, respectively. The average somatic cell count found in Girgentana goat milk was higher than the threshold of 1 500 000 cells/mL advised in Europe for fresh milk. Gross milk and fatty acid composition were similar to that reported in the literature for other local goat breeds.

The Girgentana Goat Breed: A Zootechnical Overview on Genetics, Nutrition and Dairy Production Aspects

“…Being highly polymorphic, microsatellites are very informative markers and have been extensively used in diversity studies. Recently, an investigation conducted on population genetic structure of Girgentana goat using microsatellite markers showed a moderate genetic variation and a complex genetic structure because its genome was shared among subpopulations, whereas recent bottleneck has not been detected in the Girgentana goat population (Mastrangelo et al 2017b). Similar results for this breed were also reported by Pariset et al (2006) and Mastrangelo et al (2013a).…”

“…The clotting ability of Girgentana milk is quite good, with a renneting time equal to 17.0 ± 3.1 min, a rate of curd formation of 2.0 ± 1.6 min and a curd firmness of 25.1 ± 7.7 millimetres (Todaro et al 2005). In milk of the Girgentana goat, the sum of short and medium chain fatty acids (FA) accounted on about 35 g/100 g of total FA respectively (Bonanno et al 2013b;Mastrangelo et al 2017b); these FA, which include caproic (C6:0), caprylic (C8:0), capric (C10:0) and lauric (C12:0) acids, are the most characteristic in goat milk and derived dairy products, being more abundant than in cow milk FA profile, and are associated with the characteristic flavours of cheeses and can also be used to detect admixtures of milk from different species (Park et al 2007). …”

“…The Girgentana goat was characterized by an interesting and wide variability in the casein cluster, with haplotypes rarely found in other breeds, containing the N allele at the CSN1S1 locus (Mastrangelo et al 2017b), which has been reported in a few breeds, such as Tunisian goats (Vacca et al 2009). It is well known that goat caseins are characterized by different expression levels due to strong, medium, weak or null alleles responsible for high, medium or low casein content in milk, depending on the casein fraction (Caroli et al 2006).…”

“…A descriptive statistics for milk production traits were recently reported in a study conducted on more than 300 individuals from different farms located in different areas of Sicily (Mastrangelo et al 2017b) (Table 14.1). The authors reported a high variability in milk yield, which varied from less than 1000 to *4500 g/goat per day.…”

“…It is well known that goat caseins are characterized by different expression levels due to strong, medium, weak or null alleles responsible for high, medium or low casein content in milk, depending on the casein fraction (Caroli et al 2006). Haplotype analysis of the casein genes allows for selection of goat genetic lines for milk production with 'particular' protein content (Sacchi et al 2005;Mastrangelo et al 2017b). The high frequency of haplotypes containing strong alleles at each casein gene indicates that selection for these variants should be an easy breeding objective to improve milk composition and cheese-making properties in the Girgentana breed (Mastrangelo et al 2017b).…”