title: Efficiency of lysine utilization by growing steers.
abstract: This study evaluated the efficiency of Lys utilization by growing steers. Five ruminally cannulated Holstein steers (165 ± 8 kg) housed in metabolism crates were used in a 6 × 6 Latin square design; data from a sixth steer was excluded due to erratic feed intake. All steers were limit fed (2.46 kg DM/d), twice daily, diets low in RUP (81% soybean hulls, 8% wheat straw, 6% cane molasses, and 5% vitamins and minerals). Treatments were 0, 3, 6, 9, 12, and 15 g/d of Lys continuously abomasally infused. To prevent AA other than Lys from limiting performance, a mixture providing all essential AA to excess was continuously abomasally infused. Additional continuous infusions included 10 g urea/d, 200 g acetic acid/d, 200 g propionic acid/d, and 50 g butyric acid/d to the rumen and 300 g glucose/d to the abomasum. These infusions provided adequate ruminal ammonia and increased energy supply without increasing microbial protein supply. Each 6-d period included 2 d for adaptation and 4 d for total fecal and urinary collections for measuring N balance. Blood was collected on d 6 (10 h after feeding). Diet OM digestibility was not altered ( ≥ 0.66) by treatment and averaged 73.7%. Urinary N excretion was decreased from 32.3 to 24.3 g/d by increasing Lys supplementation to 9 g/d, with no further reduction when more than 9 g/d of Lys was supplied (linear and quadratic, < 0.01). Changes in total urinary N excretion predominantly were due to changes in urinary urea N. Increasing Lys supply from 0 to 9 g/d increased N retention from 21.4 to 30.7 g/d, with no further increase beyond 9 g/d of Lys (linear and quadratic, < 0.01). Break-point analysis estimated maximal N retention at 9 g/d supplemental Lys. Over the linear response surface of 0 to 9 g/d Lys, the efficiency of Lys utilization for protein deposition was 40%. Plasma urea N tended to be linearly decreased ( = 0.06) by Lys supplementation in agreement with the reduction in urinary urea N excretion. Plasma concentrations of Lys linearly increased ( < 0.001), but Leu, Ser, Val, and Tyr ( ≤ 0.02) were linearly reduced by Lys supplementation, likely reflecting increased uptake for protein deposition. In our model, Lys supplementation promoted significant increases in N retention and was maximized at 9 g/d supplemental Lys with an efficiency of utilization of 40%.
authors.forename: E D
authors.initials: ED
authors.lastname: Batista
authors.forename: A H
authors.initials: AH
authors.lastname: Hussein
authors.forename: E
authors.initials: E
authors.lastname: Detmann
authors.forename: M D
authors.initials: MD
authors.lastname: Miesner
authors.forename: E C
authors.initials: EC
authors.lastname: Titgemeyer
mesh_terms: D000018:Abomasum / Q000378:metabolism; D000641:Ammonia / Q000378:metabolism; D000821:Animal Feed / Q000032:analysis*; D000818:Animals; D001806:Blood Urea Nitrogen; D002087:Butyrates / Q000378:metabolism; D002417:Cattle / Q000378:metabolism*; D004032:Diet / Q000662:veterinary; D019587:Dietary Supplements; D004734:Energy Metabolism; D005947:Glucose / Q000378:metabolism; D008239:Lysine / Q000378:metabolism*; D008297:Male; D008965:Molasses; D011422:Propionates / Q000378:metabolism; D013025:Glycine max / Q000378:metabolism; D014508:Urea / Q000097:blood
chemical_list: D002087:Butyrates; D011422:Propionates; D000641:Ammonia; D014508:Urea; D005947:Glucose; C029658:propionic acid; D008239:Lysine