Effects of αs1-casein and k- casein genotypes on nutrient intake and milk production in Girgentana goats: a further investigation

The influence of polymorphism at αs1-casein locus (CSN1S1) on goat milk properties is adequately known, whereas the knowl- edge is limited on the effects of κ-casein gene variants (CSN3), C-093 and the association between variants of CSN1S1 and CSN3 Milking technique in jenny: effects on milk production genes. This study aimed to investigate the effect of some CSN1S1-CSN3 composite genotypes (CG) on feed intake and milk production of 95 Girgentana goats from 6 experiments (551 Rossella Di Palo, Diana Neri, Barbara Ariota, Rosanna Serafini, observations). Goats, genotyped using specific PCR protocols at DNA level and IEF technique at milk protein level, were equal at αs2-casein and β-casein loci, and belonged to one of 6 CG derived from the association of strong (A) and weak (F) alleles for αs1-casein with A-IEF and B-IEF for κ-casein: AA-A (23 Corresponding author: dipalo@unina.it goats), AA-AB (7goats), AA-B (8 goats), AF-A (31 goats), AF-AB - (18 goats), FF-A (8 goats). Data were analysed using a model for repeated observations. No CG effect emerged for dry matter, crude protein, NDF and net energy intake, and milk yield of goats. However, CG affected milk casein content (P<0.001), which was the highest in AA-B genotype (3.25%), and the lowest in FF-A genotype (2.64%). Thus, FF-A goats showed the lowest efficiency of dietary N utilization for milk casein synthesis (118 C-096 g casein N/kg N intake), which was lower by more 50 g/kg than those of other genotypes (P>0.001). In goats with A-IEF for κ- Prediction of coagulating and noncoagulating milk samples using mid-infrared spectroscopy casein, the strong A allele at CSN1S1 loci was associated to an increasing (P>0.05) in milk clotting parameters (clotting time, r: 11.0, 11.9, 13.5 min; curd firming time, k20: 1.69, 1.93, 2.38 min; curd firmness, a30: 34.7, 42.2, 44.0 mm, for FF-A, AF-A, AA-A. Moreover, in AA goats for αs1-casein, κ-casein alleles referred to B-IEF were responsible of a decreasing trend (P>0.05) in clotting time and curd firming time, and a further increase (P>0.01) in curd firmness (r: 13.5, 11.8, 10.3 min; k20: 2.38, 1.53, 1.50 min; a30: 44.0, 48.6, 51.6 mm, for AA-A, AA-AB, AA-B). The strong alleles (A) at CSN1S1 and B-IEF at CSN3 seem to improve synergistically casein synthesis and curd consistency (a30), whereas they show an opposite effect on curd formation rate (r and k20).