title: Effects of dairy cow diet forage proportion on duodenal nutrient supply and urinary purine derivative excretion.
abstract: Four mature Holstein-Friesian dairy cows were used in a 4 x 4 Latin square change-over design experiment made up of four 4-wk periods to investigate the relationship between microbial protein flow to the duodenum and excretion of purine derivatives (PD) in the urine. Four dietary treatments based on ad libitum access to ryegrass silage were offered, with a standard dairy concentrate included at different forage:concentrate (F:C) ratios, calculated on a dry matter basis: 80:20, 65:35, 50:50, and 35:65. Feed intakes increased as the proportion of concentrate in the diet increased, despite a concurrent decrease in silage intake. Increased feed intake led to increased nutrient flow to the duodenum. Milk yields increased as the diet F:C ratio decreased, with cows offered the 35:65 diet yielding nearly 8 kg/d more milk than cows offered the 80:20 diet; the concentrations of milk fat decreased and milk protein increased with a decreasing F:C ratio. Purine derivative excretion in the urine increased with an increasing proportion of concentrate in the diet, and there was a strong linear relationship between total PD excretion (allantoin and uric acid) and microbial N flow to the duodenum: microbial N (g/d) = 19.9 + 0.689 x total PD (mmol/d); R = 0.887. This strengthens the case for using PD excretion as a noninvasive marker of microbial protein flow from the rumen in dairy cows.
authors.affiliation: Institute of Grassland and Environmental Research, Plas Gogerddan, Aberystwyth, SY23 3EB, UK. jon.moorby@bbsrc.ac.uk
authors.forename: J M
authors.initials: JM
authors.lastname: Moorby
authors.forename: R J
authors.initials: RJ
authors.lastname: Dewhurst
authors.forename: R T
authors.initials: RT
authors.lastname: Evans
authors.forename: J L
authors.initials: JL
authors.lastname: Danelón
mesh_terms: D000821:Animal Feed / Q000032:analysis; D000818:Animals; D001426:Bacterial Proteins / Q000378:metabolism; D002417:Cattle / Q000378:metabolism* / Q000502:physiology; D003404:Creatinine / Q000652:urine; D003612:Dairying / Q000379:methods; D004032:Diet / Q000662:veterinary*; D004063:Digestion / Q000502:physiology; D004386:Duodenum / Q000378:metabolism*; D004435:Eating / Q000502:physiology; D005260:Female; D005285:Fermentation / Q000502:physiology; D007774:Lactation / Q000502:physiology; D008892:Milk / Q000737:chemistry / Q000502:physiology; D009584:Nitrogen / Q000032:analysis / Q000378:metabolism; D011687:Purines / Q000652:urine*; D012417:Rumen / Q000737:chemistry / Q000378:metabolism; D013997:Time Factors
chemical_list: D001426:Bacterial Proteins; D011687:Purines; D003404:Creatinine; D009584:Nitrogen