The response of goats to different starch/NDF ratios of concentrates on the milk chemical composition, fatty acid profile, casein fractions and rennet clotting properties

The partial substitution of corn grain (rich in starch) with agro-industrial by-products (rich in NDF) could be a good strategy to reduce ruminant dietary costs with no negative effects on milk properties. Thus, the present study aimed to investigate the effect of different starch/NDF ratios of concentrates, with fixed forage proportions, on the chemical composition and fatty acid profile as well as on the relative proportions of individual caseins and rennet clotting properties of goat's milk. For this purpose, sixteen crossbred dairy goats were divided into two homogeneous sub-groups based on their mean body weight and milk fat corrected yield. Each goat of each group was fed individually with alfalfa hay, wheat straw and concentrates. The two concentrates of the two dietary treatments were formulated to produce difference starch/NDF ratios, which were 1.2 and 0.3 for high starch (HS) and low starch (LS), respectively. The results showed no significant effect on milk chemical composition between the two dietary treatments. Moreover, the different starch/NDF ratios of the concentrates had no effect on the casein profile and coagulation properties of goat's milk. A significant reduction of κ- and αs2- casein percentages in the milk throughout the experimental period was found. Finally, the different starch/NDF ratios of the concentrates did not reveal remarkable differences in milk fatty acids except for the individual proportions of C4:0, C6:0, C18:0 and C18:2n:6t, which were significantly higher, while those of C14:1, C15:0, C16:1, C17:0, C17:1 and C20:3n-3 were significantly lower, in goats that were milk fed with the HS diet compared with those who consumed the LS. In conclusion, the 4 times decrease in the starch/NDF ratio of the concentrates without changing the forage/concentrate ratio of the goat's diet could reduce the feeding cost without causing any problems in the rennet clotting properties of milk and consequently in the milk industry.