title: Effect of dietary protein level and rumen-protected amino acid supplementation on amino acid utilization for milk protein in lactating dairy cows.
abstract: This study investigated the effect of metabolizable protein (MP) supply and rumen-protected (RP) Lys and Met supplementation on productivity, nutrient digestibility, urinary N losses, apparent total-tract digestibility of dietary AA, and the efficiency of AA utilization for milk protein synthesis in dairy cows. The experiment was conducted with 8 ruminally cannulated Holstein cows in a replicated 4×4 Latin square design trial with 21-d periods. Treatments were (1) MP-adequate diet (AMP; MP balance of -24 g/d); (2) MP-deficient diet (DMP; MP balance of -281 g/d); (3) DMP supplemented with 100 g of RPLys/cow per day (estimated digestible Lys supply=24 g/d; DMPL; MP balance of -305g/d); and (4) DMPL supplemented with 24 g of RPMet/cow per day (estimated digestible Met supply=15 g/d; DMPLM; MP balance of -256g/d). Diet had no effect on total-tract nutrient digestibility, milk production, and milk composition, but the DMP diets decreased urinary N excretion and the ammonia emitting potential of manure. Plasma Met concentration was increased by DMPLM compared with AMP. Supplementation with RPLys had no effect on plasma Lys. Concentration of most AA in milk protein was increased or tended to be increased by DMPLM compared with DMPL. Except for the AA supplemented as RPAA (i.e., Met and Lys), apparent total-tract digestibility of all dietary AA was generally greater for the DMP diets and ranged from 33% (Arg, AMP diet) to 67% (Thr, DMPL diet). Apparent recovery of dietary AA in milk protein followed the same trends, being greater for the DMP diets than AMP and generally lower for Lys and Met with the RPAA-supplemented diets versus AMP and DMP. The RPAA were apparently not used for milk protein synthesis in the conditions of this experiment. The AA recoveries in milk protein varied from around 17% (Ala) to 70% (Pro). Milk protein recoveries of essential AA (EAA) were around 54% for the DMP diet and 49% for AMP. The estimated efficiency of utilization of digestible EAA for milk protein synthesis was generally greater for the DMP diets compared with AMP. In this trial, blood plasma Lys and Met were labeled by abomasal pulse-dose of 15N-Lys and 13C-Met (respectively). Analysis of the 15N-Lys and 13C-Met decay curves in plasma indicated trends for a faster extraction of Lys and Met from plasma for the MP-deficient diets, compared with AMP. Overall, this study confirmed conclusions from previous analyses that the efficiency of utilization of dietary EAA will increase with decreasing MP-AA supply.
authors.affiliation: Department of Animal Science, Pennsylvania State University, University Park 16802.
authors.forename: C
authors.initials: C
authors.lastname: Lee
authors.affiliation: Department of Animal Science, Pennsylvania State University, University Park 16802.
authors.forename: F
authors.initials: F
authors.lastname: Giallongo
authors.affiliation: Department of Animal Science, Pennsylvania State University, University Park 16802. Electronic address: anh13@psu.edu.
authors.forename: A N
authors.initials: AN
authors.lastname: Hristov
authors.affiliation: Dairy and Swine Research and Development Centre, Agriculture and Agri-Food Canada, Sherbrooke, QC, Canada J1M 0C8.
authors.forename: H
authors.initials: H
authors.lastname: Lapierre
authors.affiliation: Department of Animal Science, Pennsylvania State University, University Park 16802.
authors.forename: T W
authors.initials: TW
authors.lastname: Cassidy
authors.affiliation: Department of Animal Science, Pennsylvania State University, University Park 16802.
authors.forename: K S
authors.initials: KS
authors.lastname: Heyler
authors.affiliation: Department of Animal Science, Pennsylvania State University, University Park 16802.
authors.forename: G A
authors.initials: GA
authors.lastname: Varga
authors.affiliation: Evonik Industries AG, Hanau 63457, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Parys
mesh_terms: D000596:Amino Acids / Q000008:administration & dosage* / Q000378:metabolism*; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002417:Cattle / Q000378:metabolism*; D004032:Diet / Q000662:veterinary; D004044:Dietary Proteins / Q000008:administration & dosage* / Q000378:metabolism; D019587:Dietary Supplements; D004063:Digestion; D005260:Female; D007774:Lactation; D008239:Lysine / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism; D008715:Methionine / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism; D008892:Milk / Q000737:chemistry; D008894:Milk Proteins / Q000096:biosynthesis*; D012417:Rumen / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D004044:Dietary Proteins; D008894:Milk Proteins; D008715:Methionine; D008239:Lysine
keywords: amino acid utilization; dairy cow; dietary protein; rumen-protected lysine; rumen-protected methionine