title: Supplementary concentrate type affects nitrogen excretion of grazing dairy cows.
abstract: These experiments were designed to investigate nutritional means of reducing urine N excretion by grazing cows. In experiment 1, 36 Holstein-Friesian cows averaging 92 d in milk were fed either 1 or 6 kg of a high protein concentrate or 6 kg of a low protein concentrate. Pasture dry matter (DM) intake was higher for cows fed 1 kg of high protein concentrate (15.4 +/- 0.62 kg/d) than for cows fed 6 kg of low protein concentrate (13.4 +/- 0.55) but not for cows fed 6 kg of high protein concentrate (13.9 +/- 0.96). The reduction in pasture intake per kg of concentrate DM ingested amounted to 0.35 and 0.47 kg of pasture DM for cows fed 6 kg of high protein and 6 kg of low protein concentrate, respectively. Milk yield and milk protein yield were higher for cows fed 6 kg of high protein concentrate than for cows fed 1 kg of high protein concentrate. Cows fed 6 kg of high protein concentrate had the highest levels of N intake, total N excretion, and urine N excretion. The proportion of N excreted in the urine was lowest for cows fed 6 kg of low protein concentrate. Milk N excretion as a proportion of ingested N was higher for cows fed 6 kg of low protein concentrate than for cows fed 6 kg of high protein concentrate but not for cows fed 1 kg of high protein concentrate. In experiment 2, 24 Holstein-Friesian cows averaging 211 d in milk were supplemented with 4 kg of rolled barley or 4.32 kg of NaOH-treated barley. Milk yield and milk protein yield tended to be higher for cows fed rolled barley than for cows fed NaOH-treated barley. There was no difference in N intake, fecal N excretion, urinary N excretion, or milk N output between diets. Milk urea N concentration was lower for cows fed rolled barley. Significant positive linear relationships were found between N intake and fecal N excretion, urine N excretion, and milk N excretion in experiment 1. In experiment 2, the relationships between N intake and fecal N excretion and urine N excretion were curvilinear, with urine N excretion increasing at a decreasing rate, and fecal N excretion increasing at an increasing rate, as N intake increased. The N excreted by dairy cows may be partitioned to fecal N if supplements based on high concentrations of fermentable organic matter and low concentrations of N are fed. Refinement of this nutritional strategy may allow reduced N excretion without reducing animal performance.
authors.affiliation: Department of Animal Husbandry and Production, Faculty of Veterinary Medicine, University College Dublin, Ireland. finbar.mulligan@ucd.ie
authors.forename: F J
authors.initials: FJ
authors.lastname: Mulligan
authors.forename: P
authors.initials: P
authors.lastname: Dillon
authors.forename: J J
authors.initials: JJ
authors.lastname: Callan
authors.forename: M
authors.initials: M
authors.lastname: Rath
authors.forename: F P
authors.initials: FP
authors.lastname: O'Mara
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D004032:Diet; D004044:Dietary Proteins / Q000008:administration & dosage*; D004435:Eating; D005243:Feces / Q000737:chemistry; D005260:Female; D001467:Hordeum; D007774:Lactation; D008892:Milk / Q000737:chemistry; D008894:Milk Proteins / Q000032:analysis; D009584:Nitrogen / Q000032:analysis / Q000378:metabolism* / Q000652:urine; D012972:Sodium Hydroxide / Q000494:pharmacology
chemical_list: D004044:Dietary Proteins; D008894:Milk Proteins; D012972:Sodium Hydroxide; D009584:Nitrogen