Review of the relationship between milk urea nitrogen and days in milk, parity, and monthly temperature mean in Iranian Holstein cows.
The objectives of this study were to determine the relationships between milk urea N and days in milk, parity, and season in Iranian Holstein cows. Twelve Iranian commercial dairy herds participated in a 13-mo study from December 1, 2008, to December 31, 2009. All cows were milked 3 times daily, housed in freestalls, and fed a total mixed ration twice a day. Mean milk urea N over the study period was 16.0mg/dL. Mean milk urea N, categorized by 30-d increments of days in milk, paralleled changes in milk values and followed a curvilinear shape. However, milk urea N concentration reached a maximum at the fifth month of days in milk, but milk production reached a maximum at the third month. The concentration of milk urea N was lower during the first 30 d in milk category compared with all other days in milk categories. Overall mean milk urea N concentration of Holstein cows in the third and greater lactations was lower than in the first or second lactation. Milk urea N was at its lowest level in December (13 mg/dL), increased in the spring and summer months, and reached a maximum in July (18.8 mg/dL). From that point, milk urea N concentration progressively diminished to the autumn-winter level. In this study, milk urea N concentration was positively correlated with monthly temperature mean and may be a reason for the lower reproductive performance during the summer months. It has been recommended that milk urea N concentration should be evaluated in association with parity, days in milk, and season (or month). These variables should be considered potential sources of misinterpretation when exploring the relationship between milk urea N and nutritional management or measures of performance.
Department of Animal Science, Campus of Agriculture and Natural Resources, University of Tehran, Karaj, Tehran, Iran 31587-77871. Electronic address: fatehif@ut.ac.ir.
F
F
Fatehi
Department of Animal Science, Campus of Agriculture and Natural Resources, University of Tehran, Karaj, Tehran, Iran 31587-77871.
A
A
Zali
Department of Animal Science, Shahriar Shahr-e-Qods Branch, Islamic Azad University, Tehran, Iran 37515-374.
M
M
Honarvar
Department of Animal Science, Campus of Agriculture and Natural Resources, University of Tehran, Karaj, Tehran, Iran 31587-77871.
M
M
Dehghan-Banadaky
Department of Animal, Dairy, and Veterinary Sciences, Utah State University, Logan 84322.
A J
AJ
Young
Department of Animal Science, Campus of Agriculture and Natural Resources, University of Tehran, Karaj, Tehran, Iran 31587-77871.
M
M
Ghiasvand
Department of Animal Science, Campus of Agriculture and Natural Resources, University of Tehran, Karaj, Tehran, Iran 31587-77871.
M
M
Eftekhari
D000818:Animals; D002417:Cattle; D005260:Female; D007492:Iran; D007774:Lactation / Q000502:physiology; D008892:Milk / Q000737:chemistry*; D009584:Nitrogen / Q000378:metabolism; D010298:Parity / Q000502:physiology*; D011247:Pregnancy; D012621:Seasons; D013696:Temperature; D013997:Time Factors; D014508:Urea / Q000032:analysis*
D014508:Urea; D009584:Nitrogen