Waxy corn as a replacement for dent corn for lactating dairy cows

Waxy and dent corn starch differences were compared in diets of early lactating dairy cows. Thirty multiparous Holsteins averaging 568 +/- 76 kg body weight (BW) and 50 +/- 24 d in lactation were randomly assigned at two locations to three treatments to evaluate: (1) the extent to which replacing dent corn in the diet with recently developed waxy hybrids affects milk yield and composition; and (2) to document changes in the concentration of blood and ruminal metabolites of dairy cattle fed waxy corn compared to dent corn. A 3 X 3 Latin square design was used to test the treatments: control, (100% dent corn in grain mix), dent + waxy (50% dent and 50% waxy corn in grain mix), and waxy corn (100% in grain mix). Total mixed rations (TMR) formulated to be isonitrogenous at 17.2% crude protein and isocaloric at 1.72 Meal net energy for lactation per kg of DM, were fed twice daily to individual cows in Calan gates (North Dakota State University Dairy Research Center) or in tie stalls (University of Minnesota, Crookston Dairy Research Center) for 15 weeks. Rumen, blood and milk samples were collected during the fifth week of each period. Ruminal acetate, isobutyrate, isovalerate and total volatile fatty acid (VFA) concentrations were lower (P < 0.05) when waxy corn was added to the diet. Serum urea nitrogen and milk fat percentage were decreased (P < 0.05) in rations where the grain concentrate was comprised of waxy corn. Blood glucose and insulin concentrations were unchanged (P > 0.05) by treatment. There was no difference in milk yield or total milk solids indicating similar lactational performance among treatments using waxy and dent corn. (C) 1998 Elsevier Science B.V.