title: Influence of rumen protein degradability and supplementation frequency on performance and nitrogen use in ruminants consuming low-quality forage: cow performance and efficiency of nitrogen use in wethers.
abstract: Two studies were conducted to determine the influence of CP degradability and supplementation frequency (SF) on ruminant performance and N efficiency. Treatments included an unsupplemented control (CON) and degradable intake protein (DIP; 82% of CP) or undegradable intake protein (UIP; 60% of CP) provided daily, every 3 d, or every 6 d. Seven wethers (36+/-1 kg BW) were used in the digestibility study with DIP and UIP treatments formulated to meet CP requirements. Eighty-four Angus x Hereford cows (512+/-42 kg BW) in the last third of gestation were used for the performance study. The DIP treatments were calculated to provide 100% of the DIP requirement and UIP treatments were provided on an isonitrogenous basis compared with DIP. Basal diets consisted of low-quality (5% CP) meadow hay. Forage DMI and N intake by lambs decreased (P < 0.05) linearly as SF decreased. Additionally, DMI, OM intake, N retention, N digestibility, and digested N retained were greater (P < 0.01) for supplemented wethers than for controls with no difference due to crude protein degradability. Nitrogen balance, DMI, and OM intake decreased linearly (P < 0.05) as SF decreased. Plasma urea (PU; mM) was measured over a 6-d period and supplemented lambs had increased (P < 0.01) PU compared with CON. Plasma urea linearly decreased (P < 0.01) as SF decreased. Pre- and postcalving (within 14 d and 24 h of calving, respectively) cow weight and body condition score change were more positive (P < 0.05) for supplemented groups than for controls. Results suggest CP supplements consisting of 20 to 60% UIP can be effectively used by ruminants consuming low-quality forage without adversely affecting N efficiency and animal performance, even when provided as infrequently as once every 6 d.
authors.affiliation: Eastern Oregon Agriculture Research Center, Oregon State University, Burns 97720, USA. dave.bohnert@orst.edu
authors.forename: D W
authors.initials: DW
authors.lastname: Bohnert
authors.forename: C S
authors.initials: CS
authors.lastname: Schauer
authors.forename: T
authors.initials: T
authors.lastname: DelCurto
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D004044:Dietary Proteins / Q000378:metabolism*; D019587:Dietary Supplements; D004063:Digestion; D005260:Female; D008297:Male; D009584:Nitrogen / Q000032:analysis / Q000378:metabolism*; D009751:Nutritional Requirements; D011247:Pregnancy; D011897:Random Allocation; D012417:Rumen / Q000378:metabolism*; D012756:Sheep / Q000378:metabolism*
chemical_list: D004044:Dietary Proteins; D009584:Nitrogen