Digestible energy values of diets with different fat supplements when fed to lactating dairy cows.

A total collection digestion trial using high producing lactating cows (average milk yield = 40.7 kg/d) was conducted to measure the effect of different fat supplements on dietary digestible energy (DE) concentrations and to calculate the DE value of the supplements. A diet with no supplemental fat, 2 diets with 1.75 or 3.5% (dry basis) Ca salts of palm fatty acids (Ca-PFA), and 2 diets with 1.6 or 3.2% hydrogenated triacylglycerides from palm oil (HPO) were fed in a 5 x 5 Latin square experiment with 28-d periods. Concentrations of supplemental long-chain fatty acids in the diets were 1.7 and 3.4% for the 2 supplementation rates. Dry matter intake was reduced when cows were fed the high concentration of Ca-PFA, but cows fed Ca-PFA produced more milk than cows fed the control diet or diets with HPO. The type or amount of fat supplementation did not affect measures of rumen fermentation or in situ fiber digestibility. Digestibility of energy, dry matter, and organic matter were higher for diets with Ca-PFA than for diets with HPO, mainly because of increased fatty acid digestibility. The dietary concentration of DE was similar between the control diet and diets with HPO (2.97 Mcal/kg), but it increased as the concentration of Ca-PFA increased (3.04 and 3.16 Mcal/kg for low and high supplementation rates). The calculated DE concentrations of the supplements averaged 7.3 and 3.1 Mcal/kg for Ca-PFA and HPO. The 2001 National Research Council dairy model accurately estimated DE concentrations in all diets (<1% difference).