Net Volatile Fatty Acid Absorption in Nonlactating Holstein Cows

Abstract

Net absorption of volatile fatty acids was measured in 4 nonlactating Holstein cows fed orchardgrass-clover silage ad lib and 50 g trace mineralized salt daily. Cows ranged in age from 2-4 yr and in body wt from 326-525 kg. Portal blood flow and volatile fatty acid concentrations of portal and arterial plasma were determined at 30 min (3 cows) or 90 min (1 cow) intervals for .apprx. 12 h. Mean portal blood flow was 836 l/h. Mean volatile fatty acid concentrations of portal plasma and differences of portal-arterial concentrations were (mM) as follows: acetate 2.00, 0.67; propionate 0.264, 0.228; isobutyrate 0.022, 0.017; n-butyrate 0.057, 0.038; 2-methylbutyrate 0.017, 0.014; 3-methylbutyrate 0.007, 0.005; and n-valerate 0.012, 0.008. Mean net volatile fatty acid absorption was 682 mmol/h. Acetate and propionate accounted for 91% of net volatile fatty acid absorption on a molar basis and 85% on an energy basis. Net energy absorbed as volatile fatty acid was 5.43 Mcal/cow per day, which was .apprx. 35% of calculated metabolizable energy intake. Portal blood flow was maximal 1.5 h postfeeding, and net volatile fatty acid absorption was maximal 2.5 h postfeeding.