Skip to main content Accessibility help

An analysis of the relationship between plasma urea and ammonia concentration in dairy cattle fed a consistent diet over a 100-day period

  • Richard A Laven (a1), D Claire Wathes (a2), Kevin E Lawrence (a1) and Rex J Scaramuzzi (a2)


Measurement of plasma urea concentration is often used to identify a risk of dietary nitrogen-associated infertility. However, the use of plasma urea concentration in this way relies on it being an effective predictor for other potential toxic products associated with nitrogen metabolism (such as plasma or uterine ammonia). Recent research has shown that dietary nitrogen-associated infertility can be produced by diets which elevate plasma ammonia concentration without markedly increasing plasma urea concentration. Thus for cattle on different diets plasma urea concentration cannot be used to predict plasma ammonia concentration. This study evaluated whether plasma urea concentration could be used to predict plasma ammonia concentration in cattle kept on consistent diets. Data were analysed from a study where 42 cattle had been fed a control diet or the control diet plus 250 g urea per cow per day and had had weekly measurements of post-prandial plasma urea and ammonia concentrations. This analysis found that over a 100-d period, plasma urea concentration was relatively constant and unaffected by time while plasma ammonia concentration was significantly more variable, being affected by time since the study started, and whether cows began the study in the first or second group. Correlation between plasma ammonia and urea was limited; plasma urea concentration explained only 3·8% of the variation in plasma ammonia concentration. These data suggest that, even in cows on consistent diets, plasma urea concentration is not a good predictor of plasma ammonia, and that a simple urea threshold may not accurately identify the risk of dietary nitrogen-associated infertility.


Corresponding author

*For correspondence; e-mail:


Hide All
AFRC 1993 Energy and Protein Requirements of Ruminants. An advisory manual prepared by the AFRC Technical Committee on Response to Nutrients. Wallingford, UK: CAB International
Butler, WR, Calaman, JJ & Beam, SW 1996 Plasma and milk urea nitrogen in relation to pregnancy rate in lactating cattle. Journal of Animal Science 74 858865
Dawuda, PM, Scaramuzzi, RJ, Leese, HJ, Hall, CJ, Peters, AR, Drew, SB & Wathes, DC 2002 Effect of timing of urea feeding on the yield and quality of embryos in lactating dairy cows. Theriogenology 58 14431455
Diggle, PJ 1988 An approach to the analysis of Repeated Measurements. Biometrics 44 959971
Hamlett, A, Ryan, I, Serrano-Trespalacios, P & Wolfinger, R 2003 Mixed models for assessing correlation in the presence of replication. Journal of the Air and Waste Management Association 53 442450
Kassirer, JP 1971 Clinical evaluation of kidney function-tubular function. New England Journal of Medicine 285 499502
Kenny, DA, Boland, MP, Diskin, MG & Sreenan, JM 2001 Effect of pasture crude protein and fermentable energy supplementation on blood metabolite and progesterone concentrations and on embryo survival in heifers. Animal Science 73 501511
Kenward, MG & Roger, JH 1997 Small sample inference for fixed effects from restricted maximum likelihood. Biometrics 53 983997
Laven, RA & Drew, SB 1999 Dietary protein and the reproductive performance of cows. Veterinary Record 145 687695
Laven, RA, Biggadike, HJ & Allison, RD 2002 The effect of pasture nitrate concentration and concentrate intake after turnout on embryo growth and viability in the lactating dairy cow. Reproduction in Domestic Animals 37 111115
Laven, RA, Dawuda, PM, Scaramuzzi, RJ, Wathes, DC, Biggadike, HJ & Peters, AR 2004 The effect of feeding diets high in quickly degradable nitrogen on lactating Holstein dairy cows. Animal Reproduction Science 84 4152
Laven, RA, Scaramuzzi, RJ, Wathes, DC, Peters, AR & Parkinson, TJ 2007 Recent research on the effects of excess dietary nitrogen on the fertility of dairy cows. Veterinary Record 160 359362.
Littell, RC, Henry, PR & Ammerman, CB 1998 Statistical analysis of repeated measures data using SAS procedures. Journal of Animal Science 76 12161231
Littell, RC, Pendergast, J & Natarajan, R 2000 Modelling covariance structure in the analysis of repeated measures data. Statistics in Medicine 19 17931819
Mondzac, A, Ehrlich, GE & Seegmiller, JE 1965 An enzymatic determination of ammonia in biological fluids. Journal of Laboratory and Clinical Medicine 66 526
Ocon, OM & Hansen, PJ 2003 Disruption of bovine oocytes and preimplantation embryos by urea and acidic pH. Journal of Dairy Science 86 11941200
Ordonez, A, Parkinson, TJ, Matthew, C, Holmes, CW, Miller, RD, Lopez-Villalobos, N, Burke, J & Brookes, I 2007 Effects of application in spring of urea fertiliser on aspects of reproductive performance of pasture-fed dairy cows. New Zealand Veterinary Journal 55 6976
Rhoads, ML, Rhoads, RP, Gilbert, RO, Toole, R & Butler, WR 2006 Detrimental effects of high plasma urea nitrogen levels on viability of embryos from lactating dairy cows. Animal Reproduction Science 91 110
Roy, A 2006 Estimating correlation coefficient between two variables with repeated observations using mixed effects model. Biometrical Journal 48 286301
SAS Institute 1989 SAS/Stat User's Guide, V, 4th Edn. SAS Institute Inc., Cary, NC, USA
Sinclair, KD, Kuran, M, Gebbie, FE, Webb, R & McEvoy, TG 2000 Nitrogen metabolism and fertility in cattle, II. Development of oocytes recovered from heifers offered diets differing in their rate of nitrogen release in the rumen. Journal of Animal Science 78 26702680
Sinclair, KD, Sinclair, LA & Robinson, JJ 2000 Nitrogen metabolism and fertility in cattle, I. Adaptive changes in intake and metabolism to diets differing in their rate of energy and nitrogen release in the rumen. Journal of Animal Science 78 26592669
Singer, JD 1998 Using SAS PROC MIXED to fit multilevel models, hierarchical models, and individual growth models. Journal of Educational and Behavioral Statistics 23 323355
Spilke, J, Piepho, HP & Hu, X 2005 Analysis of unbalanced data by mixed linear models using the MIXED procedure of the SAS system. Journal of Agronomy and Crop Science 191 4754
Talke, H & Schubert, GE 1965 Enzyme determination of urea in blood serum by the Warburg optical test. Klinische Wochenschrift 43 174175
Visek, WJ 1984 Ammonia, its effects on biological systems, metabolic hormones, and reproduction. Journal of Dairy Science 67 481498
Zimmerman, CA, Rakes, AH, Jaquette, RD, Hopkins, BA & Croom, WJ 1991 Effects of protein level and forage source on milk production and composition in early lactation dairy cows. Journal of Dairy Science 74 980990



Full text views

Total number of HTML views: 0
Total number of PDF views: 0 *
Loading metrics...

Abstract views

Total abstract views: 0 *
Loading metrics...

* Views captured on Cambridge Core between <date>. This data will be updated every 24 hours.

Usage data cannot currently be displayed