title: Bulk tank milk urea nitrogen: seasonal patterns and relationship to individual cow milk urea nitrogen values.
abstract: The objectives of this study were: 1) to determine if bulk tank milk urea nitrogen (BTMUN) and whole herd weighted average of the individual cow MUN levels (WHMUN) were equivalent measurements of herd MUN status; and 2) to determine the seasonal variation in BTMUN concentrations in Prince Edward Island (PEI) dairy herds. For BTMUN-WHMUN correlation testing, bulk tank milk samples from 176 herds were tested for MUN once every 1 to 2 wk between September 1999 and August 2002, as part of routine BTM testing for milk components. During this 3-year period, all herds had all milking cows tested for MUN once a month at the same lab. The WHMUN levels (weighted for milk production) were calculated for each month, and were compared to BTMUN levels using a concordance correlation coefficient (CCC) and a graphic procedure. Tests were only compared if they occurred on the same date, producing a final dataset of 669 comparisons. The BTMUN had good (but not perfect) correlation with WHMUN (CCC = 0.91). This high reliability extended to both the pasture and non-pasture seasons, various milk sampling protocols, and all herd sizes seen in PEI. For evaluating the seasonal variation of BTMUN, the 3 y worth of data (24 803 observations) were divided into 15 seasonal categories, 5 seasons per year (early, mid, and late pasture, and early and late stable). Using linear mixed modelling, significantly (P < 0.05) higher BTMUN values were found during the mid and late pasture seasons of 2000, likely because the precipitation was unusually high during this period, enhancing pasture growth.
authors.affiliation: Department of Health Management, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, Prince Edward Island. parunvipas@upei.ca
authors.forename: P
authors.initials: P
authors.lastname: Arunvipas
authors.forename: J A
authors.initials: JA
authors.lastname: VanLeeuwen
authors.forename: I R
authors.initials: IR
authors.lastname: Dohoo
authors.forename: G P
authors.initials: GP
authors.lastname: Keefe
mesh_terms: D000818:Animals; D002417:Cattle; D003612:Dairying; D005260:Female; D007774:Lactation / Q000502:physiology*; D008892:Milk / Q000737:chemistry*; D009584:Nitrogen / Q000032:analysis*; D011325:Prince Edward Island; D012621:Seasons; D014508:Urea / Q000032:analysis*
chemical_list: D014508:Urea; D009584:Nitrogen