Effect of increased dietary sugar on dairy cow performance as influenced by diet nutrient components and level of milk production

Interactions among diet nutrient parameters can influence dairy cattle response to added dietary sugar. With the objective to evaluate the effect of dietary sugar, 2 data sets with dietary information and production responses were compiled from published research that tested the effect of additional dietary sugar on dairy cattle performance. The first data set included 24 scientific papers (97 observations) with dietary forage NDF content ranging from 14.61 to 38.48% of diet DM. To evaluate the effect of dietary sugar in diets with a more narrow range in dietary forage NDF (17.37 to 29.51% of diet DM), the second data set omitted 3 of the scientific papers in the first data set, resulting in 85 observations. Mixed model linear regression analysis included treatment category [control, 1.5-3%, 3-5%, vs. 5-7% added dietary sugar (% of diet DM)], DIM category within treatment, control milk yield category within treatment, and several continuous nutrient variables. In cows producing >33 kg of milk/d, added dietary sugar had a greater response (2.14 kg of 3.5% FCM/d; P < 0.0001) than in cows producing <33 kg of milk (0.77 kg of 3.5% FCM/d). Additional dietary sugar did not affect milk fat or protein percentage (P > 0.15). Nutrient variables with a positive effect on 3.5% FCM yield included added starch and protein B2 (insoluble in boiling neutral detergent but soluble in boiling acid detergent solution). Nonlinear statistical analysis predicted the optimal total dietary sugar to be 6.75% of diet DM. To optimize 3.5% FCM yield response when feeding additional dietary sugars, a low to moderate starch diet should be fed (22 to 27% of diet DM) in combination with a moderate to high soluble fiber content (6.0 to 8.5% of diet DM).