EFFECTS OF HERD, SEASON AND DAYS IN MILK IN MILK UREA NITROGEN OF CROSSBRED DAIRY COWS IN SYLHET

Abstract

The study included 724 crossbred cows (Local × Holstein Friesian) from nine dairy farms of Sylhet district from July 2013 to June 2014 to determine the effect of herd, season, lactation stage and days in milk on milk urea nitrogen and the effect of milk production and composition on milk urea nitrogen. According to the season, milk samples were divided into two groups: wet season (June - October) and dry season (November - February). Days in milk (DIM) were grouped into two lactation stages: Lactation 1 (˂100 days in milk) and Lactation 2 (˃100 days in milk). Milk urea nitrogen was grouped into five categories by the increments of 5 mg/dl, started with those less than 10 mg/dl and finishing with concentration greater than 25 mg/dl. The daily milk yield was 6.78 kg ranged from 2.00 to 18.00 kg. The mean MUN concentration was 14.58 mg/dl. Mean values for milk fat and protein contents were 3.74 % and 3.72 %. The highest content of MU (16.37 mg/dl) was found in herd 2 and the second highest estimation of MU content were in herd 1, 3 and 6 (15.58, 15.51 and 15.12 mg/dl, respectively). In the district of Sylhet, the lowest MU content was estimated in herd 4, 5, 7 and 8 (13.59, 13.48, 13.16 and 13.60 mg/dl, respectively). Difference of MUN concentration was not significant between the dry and wet season. The MUN concentrations were 14.82 mg/dl and 14.90 mg/dl in dry and wet season respectively. The concentration of MUN in Lactation 1 was 13.61 mg/dl and in Lactation 2 was 16.26 mg/dl. The same inverse relation was not observed between MUN categories and milk fat percentage. Milk fat (%) were 3.56, 3.77, 3.64, 4.15 and 3.66 when MUN concentration were ≤10.00, 10.01-15.00, 15.01-20.00, 20.01-25.00 and ≥24.01 mg/dl respectively. Daily milk yield did not increase with the increase of MUN concentration. Milk yield were 6.37, 7.21, 6.23, 7.31 and 7.00 Kg/d while MUN concentration were ≤10.00, 10.01-15.00, 15.01-20.00, 20.01-25.00 and ≥25.01 mg/dl. It may be concluded that herd category and lactation stage influence the milk urea nitrogen concentration of crossbred dairy cow in the Sylhet district.