Effect of CSN1S1 gene polymorphism and stage of lactation on milk yield and composition of extensively reared goats.

The effect of CSN1S1 genotype and lactation stage on milk yield and composition were investigated in 80 extensively reared goats. Milk yield was recorded in early, mid and late lactation and individual milk samples were collected to determine: fat, protein, lactose and casein content, pH, freezing point, somatic cell count (SCC) and total microbic mesophilic count (TMC). Relative casein composition and amino acid profile were quantified by HPLC. Fatty acid profile was measured by gas-chromatography. Genotype did not affect milk yield, while this trait was significantly affected by lactation stage (P < 0.01). CSN1S1 BB goats produced significantly higher protein and casein percentages (P < 0.05). αs1-casein (CN) was significantly higher in BB and AB goats than AF and BF, showing intermediate values in AA goats (P < 0.01). The protein percentage and the αs1 and αs2-CN fractions were not affected by lactation stage, while the casein content and the ß and κ-CN significantly increased throughout lactation (P < 0.01). C4 : 0 and C6 : 0 were not affected by genotype, while C8 : 0 and C10 : 0 were higher in the AA goats than BB; most of the long chain FA were higher in BB than AA goats. MUFA and PUFA increased in late lactation. In addition, BB goats showed higher essential amino acids, resulting in an optimal composition from the nutritional point of view, when compared with AA goats. The increase of MUFA, PUFA, essential and cis-FA in late lactation indicate that the lipid composition of goat's milk, with the progress of lactation, tends to improve its nutritional value.

Effects of different storage conditions, the farm and the stage of lactation on renneting parameters of goat milk investigated using the Formagraph method.

This study evaluated the effect of storage on renneting properties of goat milk investigated using the Formagraph method. Milk samples from 169 goats in three farms (F1, F2 and F3) were analysed during an entire lactation (45, 75, 105, 135 and 165 days in milking DIM), to obtain renneting parameters, both from fresh milk and after storage with Bronopol and freezing at -20°C and -80°C. As regards fresh milk, mean values of clotting time were between 12·51 (45 DIM) and 13·29 min (105 DIM and F2), the curd firming time between 1·77 (45 DIM) and 2·15 min (F1) and curd firmness between 42·09 (165 DIM) and 49·55 mm (45 DIM). No statistical difference was recorded after storage. After regression analysis, all prediction models showed significance value at P<0·001 with the highest R2 value for clotting time, 0·710 (fresh vs. frozen milk at -20°C), and the lowest for clot firmness, 0·281 (fresh vs. frozen milk at -80°C). Results demonstrated that assessment of goat milk coagulation properties using the Formagraph method is also achievable after freezing or Bronopol addition.