Factores relacionados con nitrógeno ureico en leche de vacas lecheras

摘要

Milk urea nitrogen (MUN) is an indicator of dietary energy, protein and fiber balance in lactating cows. Some non-nutritional factors can also cause MUN variations. The objective of this study was to assess the effect of environmental and genetic factors on MUN levels and their relationship with fat and protein content in milk. A total of 32,837 milk samples from the afternoon milking of 4094 cows in 100 herds located in eight municipalities of northern Antioquia was used. The factors analyzed were parity, season and year of calving, municipality, farm, breed, days in milk, day of the week when the sample was taken, and percentage of fat and protein in milk. A generalized additive model was used. The average milk yield of the afternoon milking was 9.25 ± 3.73 L, with 3.76 ± 0.6% fat and 3.09 ± 0.31% protein. The mean MUN value was 18.5 ± 4.04 mg/dL. All fixed effects influenced the MUN (p 0.05). First-lactation cows showed higher MUN values (18.8 mg/dL) compared to other lactations. The MUN concentration reached its peak (19.1 mg/dL) in the second third of lactation (between 101 and 200 days of lactation). The MUN values were lower for Tuesdays, Wednesdays and Thursdays (8.6, 18.4 and 18.6 mg/dL, respectively) compared with Mondays and Fridays (19.0 mg/dL and 19.3 mg/dL, respectively). In conclusion, milk fat and protein as well as parity, season and year of calving, municipality, farm, breed, lactation stage, days in milk, and day of the week were related to MUN variations.