title: Dietary cation-anion difference and dietary protein effects on performance and acid-base status of dairy cows in early lactation.
abstract: Our objective was to examine the effects of dietary cation-anion difference (DCAD) with different concentrations of dietary crude protein (CP) on performance and acid-base status in early lactation cows. Six lactating Holstein cows averaging 44 d in milk were used in a 6 x 6 Latin square design with a 2 x 3 factorial arrangement of treatments: DCAD of -3, 22, or 47 milliequivalents (Na + K - Cl - S)/100 g of dry matter (DM), and 16 or 19% CP on a DM basis. Linear increases with DCAD occurred in DM intake, milk fat percentage, 4% fat-corrected milk production, milk true protein, milk lactose, and milk solids-not-fat. Milk production itself was unaffected by DCAD. Jugular venous blood pH, base excess and HCO3(-) concentration, and urine pH increased, but jugular venous blood Cl- concentration, urine titratable acidity, and net acid excretion decreased linearly with increasing DCAD. An elevated ratio of coccygeal venous plasma essential AA to nonessential AA with increasing DCAD indicated that N metabolism in the rumen was affected, probably resulting in more microbial protein flowing to the small intestine. Cows fed 16% CP had lower urea N in milk than cows fed 19% CP; the same was true for urea N in coccygeal venous plasma and urine. Dry matter intake, milk production, milk composition, and acid-base status did not differ between the 16 and 19% CP treatments. It was concluded that DCAD affected DM intake and performance of dairy cows in early lactation. Feeding 16% dietary CP to cows in early lactation, compared with 19% CP, maintained lactation performance while reducing urea N excretion in milk and urine.
authors.affiliation: Department of Animal Sciences, University of Illinois, Urbana 61801, USA. whu@udel.edu
authors.forename: W
authors.initials: W
authors.lastname: Hu
authors.forename: M R
authors.initials: MR
authors.lastname: Murphy
authors.forename: P D
authors.initials: PD
authors.lastname: Constable
authors.forename: E
authors.initials: E
authors.lastname: Block
mesh_terms: D000136:Acid-Base Equilibrium / Q000502:physiology*; D000596:Amino Acids / Q000032:analysis; D000821:Animal Feed / Q000032:analysis; D000818:Animals; D000838:Anions / Q000008:administration & dosage / Q000097:blood; D001835:Body Weight; D002412:Cations / Q000008:administration & dosage / Q000097:blood; D002417:Cattle / Q000378:metabolism*; D003404:Creatinine / Q000097:blood; D004032:Diet / Q000662:veterinary*; D004044:Dietary Proteins / Q000494:pharmacology*; D004435:Eating / Q000502:physiology; D005260:Female; D006863:Hydrogen-Ion Concentration; D007774:Lactation / Q000502:physiology*; D016018:Least-Squares Analysis; D008892:Milk / Q000737:chemistry; D008903:Minerals / Q000097:blood; D009584:Nitrogen / Q000032:analysis / Q000378:metabolism; D011897:Random Allocation; D014556:Urine / Q000737:chemistry
chemical_list: D000596:Amino Acids; D000838:Anions; D002412:Cations; D004044:Dietary Proteins; D008903:Minerals; D003404:Creatinine; D009584:Nitrogen