Aim: The study was to determine seasonal fluctuations and non-nutritional factors associated with bulk tank milk urea nitrogen (BTMUN).

Materials and Methods: A total of 58,364 BTM testing records were collected from 2364 farms in Central Thailand during September 2014-August 2015. Using square root BTMUN as the outcome, other milk components, farm effect, and sampling time were analyzed by univariable repeated measures linear regression, and significant variables were included in multivariable repeated measures linear regression.

Results: The average BTMUN (standard deviation) was 4.71 (±1.16) mmol/L. In the final model, BTM fat and protein percentages were associated with BTMUN as quadratic and cubic polynomials, respectively. BTM lactose percentage and the natural logarithm of somatic cell counts were negatively linearly associated with BTMUN. At the farm level, the BTM lactose association was negatively linear; herd BTMUN decreased following an increase of herd lactose average, and BTM lactose slopes were quite different among farms as well. Sampling time had the highest potency for the estimation of BTMUN over time, with lows and highs occurring in August and October, respectively. The variation in test level BTMUN was decreased by 18.6% compared to the null model, and 6% of the variance could be explained at the farm level.

Conclusion: The results clarify seasonal variation in BTMUN and the relationships among other BTM constituents and BTMUN, which may be useful for understanding how to manage lactating dairy cattle better to keep BTM constituents within normal ranges.

Keywords: bulk tank milk urea nitrogen, farm level, non-nutritional factor, Thailand.

1. Roy, B., Brahma, B., Ghosh, S., Pankaj, P.K. and Mandal, G. (2011) Evaluation of milk urea concentration as useful indicator for dairy herd management: A review, Asian. J. Anim. Vet. Adv, 6: 1-19. [Crossref]

2. Arunvipas, P., VanLeeuwen, J.A., Dohoo, I.R., Keefe, G.P., Burton, S.A. and Lissemore, K.D. (2008) Relationships among milk urea-nitrogen, dietary parameters, and fecal nitrogen in commercial dairy herds, Can. J. Vet. Res, 72: 449-453. [PubMed] [PMC]

3. Nourozi, M., Moussavi, A.H., Abazari, M. and Zadeh, M.R. (2010) Milk urea nitrogen and fertility in dairy farms, J. Anim. Vet. Adv, 9: 1519-1525. [Crossref]

4. Arunvipas, P., VanLeeuwen, J.A., Dohoo, I.R. and Keefe, G.P. (2003) Evaluation of the reliability and repeatability of automated milk urea nitrogen testing, Can. J. Vet. Res, 67: 60-63. [PubMed] [PMC]

5. Kohn, R. (2007) Use of milk or blood urea nitrogen to identify feed management inefficiencies and estimate nitrogen excretion by dairy cattle and other animals, Florida Rumin. Nutr. Symp, 1-14. [PubMed]

6. Rukkwamsuk, T., Rungruang, S., Choothesa, A. and Wensing, T. (2010) Performance of periparturient dairy cows fed either by alfalfa hay or peanut hay in total mixed ration: A field trial in Thailand, African J. Agric. Res, 5: 1430-1438.

7. Arunvipas, P., VanLeeuwen, J.A., Dohoo, I.R., Leger, G.P., Keefe, E.R., Burton, A.S. and Lissemore, K.D. (2007) Milk urea-nitrogen negatively affected first-service breeding success in commercial dairy cows in Prince Edward Island, Canada, Prev. Vet. Med, 82: 42-50. [Crossref] [PubMed]

8. Butler, W.R. (1998) Review: Effect of protein nutrition on ovarian and uterine physiology in dairy cattle, J. Dairy Sci, 81: 2533-2539. [Crossref]

9. Walsh, S.W., Williams, E.J. and Evans, A.C.O. (2011) A review of the causes of poor fertility in high milk producing dairy cows, Anim. Reprod. Sci, 123: 127-138. [Crossref] [PubMed]

10. Arunvipas, P., VanLeeuwen, J.A., Dohoo, I.R. and Keefe, G.P. (2004) Bulk tank milk urea nitrogen: seasonal patterns and relationship to individual cow milk urea nitrogen values, Can. J. Vet. Res, 68: 169-174. [PubMed] [PMC]

11. Jarassaeng, C., Aiumlamai, S., Wachirapakorn, C., Techakumphu, M., Noordhuizen, J.P.T.M., Beynen, A.C. and Suadsong, S. (2012) Risk factors of subclinical mastitis in small holder dairy cows in Khon Kaen province, Thai J. Vet. Med, 42: 143-151.

12. Arunvipas, P., Dohoo, I.R., VanLeeuwen, J.A. and Keefe, G.P. (2003) The effect of non-nutritional factors on milk urea nitrogen levels in dairy cows in Prince Edward Island, Canada, Prev. Vet. Med, 59: 83-93. [Crossref]

13. Cao, Z., Huang, W., Wang, T., Wang, Y.Y., Wen, W., Ma, M. and Li, S. (2010) Effects of parity, days in milk, milk production and milk components on milk urea nitrogen in Chinese holstein, J. Anim. Vet. Adv, 9: 688-695. [Crossref]

14. Dohoo, I., Martin, W. and Stryhn, H. (2009) Veterinary Epidemiologic Research, 2nd edition. AVC Inc., Prince Edward Island.

15. Sakhong, D. (2013) Raw milk quality in lower northeastern region of Thailand during 2006-2010, Thai-NIAH eJournal, 8(2): 75-85.

16. Yeamkong, S. Koonawootrittriron, S., Elzo, M.A. and Suwanasopee, T. (2010) Factors affecting composition of Milk Producing by Members of a Private Collecting Milk Center in Central Thailand, in: 46th Kasetsart University Annual Conference: Animals and Veterinary Medicine, 162-169.

17. Chiba, S., Chiba, H. and Yagi, M.A. (2005) Guide for silage making and utilization in the tropical regions. Available from: http://jlta.lin.gr.jp/report/detail_oversea_pdf/kaigai_m039.pdf. Last accessed on 04-01-2018.

18. National Research Council (2001) Nutrient Requirements of Dairy Cattle. 7th edition. Washington: National Academies Press.

19. Tangjitwattanachai, N. (2013) Bulk tank somatic cell count and bacteria standard plate count from bovine milk in northeastern region of Thailand, J. Agric. Sci, 44: 391-394.

20. National Bureau of Agricultural Commodity and Food Standards (2005) Thai agricultural standard: raw cow milk. Thailand.

21. Wongnen, N. (2007) Feed supplementation of dairy cattle with UMMB in the northeastern region of Thailand. Feed Supplementation Blocks: Urea-molasses Multinutrient Blocks: Simple and Effective Feed Supplement Technology for Ruminant Agriculture. Available from: http://www.fao.org/3/a-a0242e.pdf. Last accessed on 03-01-2018.

22. Henao-Velasquez, A.F., Munera-Bedoya, O.D., Herrera, A.C., Agudelo-Trujillo, J.H. and Ceron-Mu-oz, M.F. (2014) Lactose and milk urea nitrogen: Fluctuations during lactation in Holstein cows, Rev. Bras. Zootec, 43: 479-484. [Crossref]

23. Grande, P.A., Dos Santos, G.T., Ribeiro, H., Damasceno, J.C., Alcalde, C.R., Barbosa, O.R., Horst, J.A. and Dos Santos, F.S. (2009) Monitoring the nutritional and reproductive state of dairy cows through the presence of urea in milk, Brazilian Arch. Biol. Technol, 52: 249-258. [Crossref]

24. Nousiainen, J., Shingfield, K.J. and Huhtanen, P. (2004) Evaluation of milk urea nitrogen as a diagnostic of protein feeding, J. Dairy Sci, 87: 386-398. [Crossref]

25. Chumpawadee, S., Chantiratikul, A., Rattanaphun, V., Prasert, C. and Koobkaew, K. (2009) Effects of dietary crude protein levels on nutrient digestibility, ruminal fermentation and growth rate in Thai-indigenous yearling heifers, J. Anim. Vet. Adv, 8: 1131-1136.

26. Kanjanapruthipong, J. and Buatong, N. (2002) Effects of rumen undegradable protein and minerals proteinate on early lactation performance and ovarian functions of dairy cows in the tropics, Asian-Australasian J. Anim. Sci, 15: 806-811. [Crossref]

27. Miglior, F., Sewalem, A., Jamrozik, J., Lefebvre, D.M. and Moore, R.K. (2006) Analysis of milk urea nitrogen and lactose and their effect on longevity in Canadian dairy cattle, J. Dairy Sci, 89: 4886-4894. [Crossref]

28. Garcia-Mu-iza, J.G., Lopez-Villalobosb, N., Burkeb, J.L., Sandbrokc, T. and Vazquez-Pelaez, C.G. (2013) Spatial-time correlation between milk urea with milk components and somatic cell score of bulk milk samples from farms supplying milk for cheese and milk powder manufacturing. Proc. New Zeal. Soc. Anim. Prod., 73: 108-113.

29. Yoon, J.T., Lee, J.H., Kim, C.K., Chung, Y.C. and Kim, C.H. (2004) Effects of milk production, season, parity and lactation period on variations of milk urea nitrogen concentration and milk components of Holstein dairy cows, Asian-Australasian J. Anim. Sci, 17: 479-484. [Crossref]

30. Rajala-Schultz, P.J. and Saville, W.J.A. (2003) Sources of variation in milk urea nitrogen in Ohio dairy herds, J. Dairy Sci, 86: 1653-1661. [Crossref]

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