Milk production and composition in two Mediterranean goat breeds based on the alpha s1 casein locus (CSN1S1) genotype

The objective of this study was to investigate the effect of three genotypes at αs1-casein locus in Girgentana (G) and Derivata di Siria (DS) goats fed ad libitum on milk yield and composition. 27 unrelated Girgentana goats and 27 unrelated Derivata di Siria goats were selected according to their CSN1S1 genotype as follows: 9 goats homozygous (AA) for strong allele, 9 goats homozygous (FF) for weak allele and 9 goats heterozygous (AF) for each breed. The goats were uniformely characterised by strong alleles at CSNS2 and CSN2 loci. All the animals were housed in individual pens and goats received the same diet (5.8 MJ NEl/kg DM; 15.2% CP) ad libitum consisted of a pelleted feed including 65% of alfalfa hay. The experimental period consisted of 15d for adaptation and 8d for data and samples collection. Milk samples were analysed for protein and fat by an infrared method. The nitrogen fractions and urea content were measured by FIL-IDF methods and differential pH meter, respectively. In each goat breed, data were analysed by ANOVA procedure for repeated measures. Milk production was significantly affected by αs1-casein genotype in G (P<0.05) and DS (P<0.046) breeds. In particular, DS AA goats produced more than AF and FF goats (1273.5, 1030.6 and 980.1 g/d; P<0.05). The same effect was observed in G breed: milk production in AA genotype was higher, compared to AF and FF (respectively: 1550, 1200 and 1050 g/d; P<0.05). Protein, casein and urea content were affected by genotype in both breeds. In G AA goats, the highest content of protein, casein (3.79, 2.98%) and the lowest urea content (32.14 mg/dL) were found (P<0.05). The same trend was observed in DS AA goats: the highest content of protein, casein (4.01, 2.80% ) and the lowest urea content (36.21 mg/dL) were detected (P<0.05). No effect of genotype was found on fat content.