Abstract:The objective of this experiment was to examine the effect of Subacute Ruminal Acidosis (SARA) on milk fatty acid (FA) profiles with emphasis on odd-chain and branched-chain FA. Sixteen multiparous Holstein dairy cows (618±35 kg of body weight, 221±32 days in milk) were used in a randomized complete-block design. During week 1, all cows received a high-forage diet (90% chopped grass hay, 5% grain mix, 5% protein supplement, dry-basis; HF). During weeks 2 through 4, cows either continued receiving the HF diet or received a low-fiber diet (38% chopped grass hay, 57% grain mix, 5% protein supplement, dry-basis; LF). Milk yield and dry matter intake were recorded daily, milk samples were collected twice weekly and ruminal pH was continuously recorded during the last 48 h of each week. Statistical analysis was conducted on weekly measuring Proc Mixed of SAS accounting for repeated measurement. The model included the fixed effects of diet, week, their interaction and block. Helmert contrasts were used to describe the difference between treatments over time. The dietary treatment induced a significant difference over time between treatments (diet by week 1 Vs. average week 2, 3 and 4; p<0.05). The treatment reduced (p<0.05) milk fat concentration (g100g −1 ) of branched-chain FA (including 14:0 iso, 15:0 iso, 15:0 anteiso, 16:0 iso and 17:0 iso), 18:0, trans-11 18:1,cis-9, trans-11 conjugated linoleic acid (CLA), 18:3 n-3, 20:0, cis-11 20:1, 20:4 n-3,22:0 and 24:0. The treatment increased (p<0.05) milk fat concentration (g100g −1 ) of odd-chain FA (including 11:0 and 13:0), 12:0, 13:0 antiso, cis-9 14:1, cis-12 18:1, cis-13 18:1, trans-6-8 18:1, trans-10 18:1 and trans-12 18:1. The treatment also increased (p<0.05) the concentration of cis-9, cis-12 18:2; trans-9, cis-11 CLA; trans-10, cis-12 CLA; and 20:4n-6. The results indicate that SARA is associated with a shift in odd-chain and branched-chain FA, which can be utilized to diagnose a cow with SARA.
