title: Effects of dietary nonprotein nitrogen on performance, digestibility, ruminal characteristics, and microbial efficiency in crossbred steers.
abstract: Two trials were conducted to evaluate the effects of dietary NPN levels on animal performance, diet digestibility, ruminal characteristics, and microbial efficiency. Experiment 1 was conducted with 24 Holstein x Nellore crossbred steers (350 +/- 20 kg of BW) distributed in 6 blocks to evaluate intake and digestibility of nutrients and performance. The diets consisted of 70% corn silage and 30% concentrate (DM basis) and were formulated to contain 12.5% CP (DM basis). Treatments consisted of 0, 15.5, 31, and 46.5% of dietary N as NPN. There were no treatment differences in the daily intakes of DM (P = 0.47), OM (P = 0.60), CP (P = 0.24), nonfiber carbohydrates (NFC; P = 0.74), or TDN (P = 0.63); however, NDF intake decreased linearly as NPN increased (P = 0.02). Additionally, no effects of NPN were observed on apparent total tract digestibility of DM (P = 0.50), OM (P = 0.53), NDF (P = 0.63), or NFC (P = 0.44). The apparent total tract digestibility of CP increased linearly (P = 0.01), but ADG (1.14 kg/d) was not influenced (P = 0.96) as NPN increased. In Exp. 2, 4 ruminally and abomasally cannulated steers (300 +/- 55 kg of BW) were fed the same diet used in Exp. 1 to evaluate the effects of NPN levels on intake and digestibility of nutrients, ruminal characteristics, and microbial efficiency. There were no differences in the daily intakes of DM (P = 0.22), OM (P = 0.17), CP (P = 0.31), NDF (P = 0.29), or TDN (P = 0.49). However, NFC intake increased linearly (P = 0.02), and there was a quadratic effect (P = 0.01) on intake of ether extract as NPN increased. Ruminal digestibility of CP increased linearly (P = 0.01) with the increase of dietary NPN. There were no differences (P >or= 0.28) in microbial protein synthesis and microbial efficiency among the treatments. The results of these trials suggest that dietary NPN levels (up to 46.5% of total N) can be fed to crossbred steers receiving corn silage-based diets without affecting their growth performance or ruminal protein synthesis.
authors.affiliation: Department of Animal Science, Universidade Federal de Viçosa, Viçosa, MG 36571, Brazil.
authors.forename: F H M
authors.initials: FH
authors.lastname: Chizzotti
authors.forename: O G
authors.initials: OG
authors.lastname: Pereira
authors.forename: L O
authors.initials: LO
authors.lastname: Tedeschi
authors.forename: S C
authors.initials: SC
authors.lastname: Valadares Filho
authors.forename: M L
authors.initials: ML
authors.lastname: Chizzotti
authors.forename: M I
authors.initials: MI
authors.lastname: Leão
authors.forename: D H
authors.initials: DH
authors.lastname: Pereira
mesh_terms: D000821:Animal Feed; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001426:Bacterial Proteins / Q000096:biosynthesis*; D002417:Cattle / Q000254:growth & development* / Q000378:metabolism; D004043:Dietary Fiber / Q000008:administration & dosage; D004044:Dietary Proteins / Q000008:administration & dosage; D004063:Digestion; D004305:Dose-Response Relationship, Drug; D002149:Energy Intake / Q000187:drug effects / Q000502:physiology; D005285:Fermentation; D008297:Male; D009584:Nitrogen / Q000008:administration & dosage* / Q000378:metabolism; D011897:Random Allocation; D012417:Rumen / Q000378:metabolism* / Q000382:microbiology
chemical_list: D001426:Bacterial Proteins; D004043:Dietary Fiber; D004044:Dietary Proteins; D009584:Nitrogen