Apparent nutrient digestibility, nitrogen metabolism and microbial protein synthesis in sheep supplemented with different vegetable fats

Abstract

The objective of the present study was to delineate the effect of different vegetable lipid supplements on apparent nutrients digestibility, nitrogen (N) metabolism and microbial protein synthesis in sheep reared under intensive conditions. Three Latxa sheep were used in a 3 × 3 Latin square design, with three 21-day periods (14-day adaptation and a 7-day sample collection each period), and were fed barley straw plus a concentrate mixture supplemented with (1) prilled palm fat (PALM), (2) cold-pressed rapeseed cake (CPRC) or (3) cold-pressed sunflower cake (CPSC). Organic matter intake did not differ among dietary treatments (P = 0.246). No significant differences were found between PALM and CPRC for apparent nutrients digestibility (P > 0.05), (N) balance (P > 0.05) or microbial protein synthesis (P > 0.05). The CPSC diet did not affect (N) intake (P = 0.481) and faecal losses (P = 0.753), but increased urinary N excretion (P = 0.030), and decreased N retention (P = 0.034), compared with PALM. Daily microbial protein synthesis, expressed as mmol of microbial N/day, was reduced by 18% with CPSC, compared with PALM (P = 0.001). Decreased microbial (N) supply was mainly due to a decline in the amount of substrate available for microbial protein synthesis due to a lower organic matter digestibility in CPSC-fed sheep. Overall, substituting palm fat with cold-pressed rapeseed cake in a high-concentrate fattening diet of sheep did not alter feed digestibility, efficiency of N utilisation or microbial protein synthesis. In contrast, replacing palm fat with cold-pressed sunflower cake reduced organic matter digestibility, increased (N) urinary losses and reduced microbial protein supply to the host animal.