Semirefined glycerin as an alternative energy source on intake, digestibility and milk production of lactating cows

This study aimed to evaluate the effect of dietary glycerin levels on feed intake, nutrient digestibility, milk yield and composition, nitrogen balance, microbial production, and eating behavior in confined lactating cows. Eight crossbred cows (Holstein × Zebu) were used, with an average of 90 ± 10 days in milk, milk production of 21.3 ± 0.47 kg/day, and body weight of 570 ± 51 kg. The cows were assigned to two 4×4 Latin squares with the following treatments: Control (G0), no glycerin inclusion; G6, 6% glycerin inclusion in the total dietary dry matter (DM); G12, 12% glycerin inclusion; and G18, 18% glycerin inclusion. Glycerin inclusion linearly decreased DM intake (p<0.001), crude protein (CP) intake (p=0.004), and neutral detergent fiber (NDF) intake (p<0.001). On the other hand, the digestibility coefficients of DM (p=0.001), CP (p=0.007), non-fiber carbohydrates (NFC) (p<0.001), and total digestible nutrients (TDN) (p=0.013) increased linearly. Milk yield (P=0.046) and 3.5% fat-corrected milk (FCM) (p=0.013) decreased linearly. Despite increasing the digestibility of nutrients, the inclusion of glycerin in diets for feedlot dairy cows resulted in a significant reduction in dry matter intake, which compromised total energy intake and, consequently, milk production. Thus, although it is a promising co-product due to its availability and energy value, semi-refined glycerin, in the proportions tested, was not viable as an energy substitute in diets of lactating cows, requiring caution not to compromise productive performance.