Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/3/2012
Publication Date: 1/4/2013
Publication URL: http://handle.nal.usda.gov/10113/56326
Citation: Boyd, J.A., West, J.W., Bernard, J.K. 2013. Effects of feeding different amounts of supplemental glycerol on ruminal environment and digestibility of lactating dairy cows. Journal of Dairy Science. 96:470-476. Interpretive Summary: Glycerol can be used to replace corn in a dairy cow's diet, but feeding glycerol to dairy cattle has been cost prohibitive because of its value in other fields. However, feeding glycerol became more feasible when it became a byproduct of biodiesel production. A study was conducted to evaluate the effects of increasing amounts of dietary glycerol on rumen environment, blood metabolites, and nutrient digestibility. Results indicated that the inclusion of dietary glycerol in the ration of high producing dairy cows may reduce intake, and alter milk yield and composition because of changes in ruminal fermentation. This trial was one step in determining optimal inclusion rates for glycerol in dairy cattle diets.
Technical Abstract: A study was conducted to evaluate the effects of increasing amounts of dietary glycerol on rumen environment, blood metabolites, and nutrient digestibility. Six rumen cannulated Holstein cows averaging 56 ± 18 DIM and 38.0 ± 8.2 kg/d of milk were used in the study. Experimental design was a replicated 3 x 3 Latin square with a 3wk adjustment period followed by a 1wk collection period. Diets were corn silage based and balanced to be iso-caloric and iso-nitrogenous. Treatments were 0 g/d glycerol (control, C), 200 g/d glycerol (G2), and 400 g/d glycerol (G4). During the collection weeks, DMI was higher for C (24.2 kg/d) compared with G2 (23.0) and G4 (23.0). Milk yield was higher for C and G2 in comparison to G4; 37.8, 37.2, and 35.8 kg/d, respectively. Milk fat percentage and yield were lower for G2 and G4 compared with C. Milk protein percentage was lower for C and G2 compared to G4; 2.76, 2.75, and 2.81%, respectively. No differences were observed in ruminal pH and ammonia (mean 6.06 and 11.19 mg/dl). Nutrient digestion and blood glucose were not different among treatments but a trend for lower plasma urea N was observed for G4 (20.5 mg/dl) versus C and G2 (21.7 and 21.8 mg/dl). The acetate: propionate ratio was reduced with the inclusion of glycerol: 2.7, 2.5, and 2.3 for C, G2, and G4 respectively. Results of this trial suggest that feeding increasing amounts of glycerol results in changes in milk yield and composition primarily because of changes in ruminal fermentation, but yield of energy-corrected milk is similar for cows fed 0 to 400 g/d of supplemental glycerol.