Effects of Neutral Detergent Fiber from Rice Straw on Blood Metabolites and Productivity of Dairy Cows in the Tropics

This study aimed to assess the effects of neutral detergent fiber (NDF) from rice straw on blood metabolites and productivity of dairy cows in the tropics. Eight Holstein ${\times}$ indigenous (75-87.5% Holstein) were randomly allocated to dietary treatments according to a double $4{\times}4$ Latin square design. Contents of roughage NDF from rice straw were 12.8, 14.8, 16.8 and 18.8% dry matter (DM) and concentrate NDF content was 10.2% DM, so that levels of dietary NDF were 23, 25, 27 and 29% DM. Dietary treatments were isonitrogenous and isocaloric diets. The average maximum and minimum temperature humidity index during the experimental period were 85.6 and 76.9, respectively. Plasma glucose (p<0.05), dry matter intake and 4% fat corrected milk (p<0.01) decreased with increasing contents of roughage NDF from rice straw, while rectal temperature, serum urea, cortisol, low density lipoprotein-cholesterol (p<0.05), serum total protein and ${\beta}$-hydroxybutyrate (p<0.01) increased. Serum triglyceride, total cholesterol and high density lipoprotein-cholesterol were not affected (p>0.05). Decreased rectal temperature and concentrations of serum cortisol were associated with decreasing levels of ${\beta}$-hydroxybutyrate and serum urea, but with increased concentrations of plasma glucose, DMI and 4% fat corrected milk indicating that lactating cows fed lower fiber diets were in lower oxidative stress. Therefore higher intake and metabolic efficiency in dairy cows fed diets lower in roughage NDF from rice straw would be of an advantage in productive systems under tropical conditions.