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Milk ability for cheese manufacturing depends on both animals utilization of dietary nutrients and genetic polymorphism of caseins. It is well known that strong alleles associated with high content of as1-casein increase cheese-making properties of goat milk, whereas there is little information about effect of genetic variants of κ-casein. The aim of this experiment was to investigate the effect of some composite as1-casein and κ-casein genotypes n changing feeding behavior at pasture and milk yield and properties of Girgentana goats. Forty goats were genotyped at as1, as2, b and κ-casein loci using specific PCR protocols at DNA level and IEF technique at milk protein level. Twelve goats, differing only for as1-casein and κ-casein genotype and averaging 136±5 days in milk and 38±6 kg of live weight, were selected and divided equally into 3 groups according to their genotypes: WA, with weak alleles (FF) for as1-casein and AIEF for κ-casein; SA, with strong alleles (AA) for s1-casein and AIEF for κ-casein; SB, with strong alleles (AA) for as1-casein and BIEF for κ-casein. No goats with weak alleles for as1-casein and BIEF for κ-casein were found. Over a 5 weeks period in spring, goats were allowed to graze daily an Italian ryegrass and berseem clover mixture, and supplied with 500g/d of barley. Measurements, sampling and analyses of individual milk and forage selected by goats were performed weekly. Forage intake of goats at pasture was assessed by n-alkane technique. Data were analysed by MIXED procedure of SAS 9.1.3, using a model with genotype as fixed effect and goat as random effect. The genotype did not influence the goats intake of DM (1180,1137, 1250 g/d DM for WA, SA, SB), net energy, crude protein and NDF, and milk yield (994, 1104, 1130 g/d for WA, SA, SD). Milk casein increased passing from WA to SA and SB genotypes (2.66, 2.93, 3.33%; P |
