1761
Milk fatty acid profile in cows fed red clover or alfalfa based diets differing in rumen-degradable protein supply
Polyphenol oxidase in red clover silage (RCS) has been shown to reduce lipolysis and consequently protect its constituent fatty acid (FA) against biohydrogenation by ruminal microorganisms. Fatty acid biohydrogenation could be further inhibited by reducing the supply of nitrogen to ruminal bacteria. To compare the effects of RCS and alfalfa silage (AS) fed in diets differing in rumen-degraded protein (RDP) supply on milk FA profile, 8 multiparous Holstein dairy cows (72 ± 17 DIM) were used in a replicated 4×4 Latin square design (21-d periods, 14-d adaptation). Four treatments were compared in a 2×2 factorial arrangement with AS or RCS fed in diets formulated to provide 85% (RDP85) or 100% (RDP100) of calculated RDP requirements. Untreated and heat-treated (AminoPlus®) soybean meals were used to adjust dietary RDP. No significant interaction of silage by RDP was observed on milk FA profile (P>0.05). As compared with AS, feeding RCS increased (P<0.01) c9c12c15-18:3 (6.89 vs. 4.26 mg/g fat) and c9c12-18:2 (18.64 vs. 16.50mg/g), but decreased (P<0.01) t11-18:1 (5.87 vs. 6.75 mg/g; P<0.01) and t11c15-18:2 (0.63 vs. 0.82 mg/g) concentrations in milk fat. As compared with AS, feeding RCS increased (P<0.03) milk fat content of iso 13:0 (0.23 vs. 0.21 mg/g), iso 14:0 (1.23 vs. 0.89 mg/g), iso 15:0 (1.46 vs. 1.22 mg/g), iso 16:0 (2.25 vs. 1.84 mg/g), iso 17:0 (1.90 vs. 1.77 mg/g), anteiso 15:0 (4.01 vs. 3.57 mg/g), and anteiso 17:0 (3.58 vs. 3.10 mg/g), but decreased (P<0.01) milk fat content of 11:0 (0.60 vs. 1.32 mg/g), 13:0 (0.98 vs. 1.83 mg/g), 15:0 (10.64 vs. 15.77 mg/g), 17:0 (4.99 vs. 5.87 mg/g), and c9-17:1 (1.65 vs. 2.05 mg/g). The supply of RDP had only minor effects on milk FA with higher concentrations (P<0.01) of iso 13:0, iso 15:0, and iso 17:0 observed with RDP100 (0.23, 1.41, 1.91 mg/g, respectively) as compared with RDP85 (0.21, 1.28, 1.76 mg/g, respectively). In conclusion, cows fed RCS as compared with those fed AS produced milk with greater concentrations of major forage FA (i.e. c9c12c15-18:3 and c9c12-18:2) and lower proportions of intermediates (i.e. t11-18:1 and t11c15-18:2) that are produced during the ruminal biohydrogenation of these FA. Variations in milk fat concentrations of odd and branched chain FA, which are known to be synthesized in the rumen by various microbial populations, may reflect the effect of forage legume species on ruminal fermentation.
Keywords:
Biohydrogenation, Odd and Branched Chain Fatty Acids, Polyphenol Oxidase