A total of 1178 cows from 28 farms [7 for category A (50+ dairy cows), 8 from category B (31 to 50 dairy cows, and 13 for category C (11 to 30 dairy cows)] was randomly selected from different areas of Chittagong, Bangladesh. A questionnaire was developed for data collection in relation to feeding. The milk production data was collected from the record book kept by the dairy farms from 2014 to 2015 by direct visiting the farm. The year was divided into three seasons, summer (March to June), the monsoon (July to September) and dry/winter (October to February) for conducting the study. The body weight of cows was determined by using Shaeffer’s formula as described by
Machila et al., (2008).The required metabolizable energy (ME) and crude protein (CP) for cows was calculated according to the method of
AOAC(1980) Feeding systems of this study was total mixed rations (TMR) type provided in confinement system of rearing. Farmers provided fresh chopped mixed grasses: German grass (
Echinochloapolystachya), Helencha (
Enhydrafluctuans) and Water hyacinth (
Eichhornacramipes) in addition to rice straw. During monsoon they cultivated plenty of German grasses, however, in the dry season they providedHelencha and Water hyacinth as green roughage and a more amount of rice straw. Along with green forages, they provided concentrate mixture consists of broken maize, broken rice, rice polish, wheat bran, mustard oil cake, till oil cake, lentil husk, mung (
Vignaradiata)husk, common salt and vitamin mineral premix. A few numbers of farmers rarely supplied the urea treated straw to their cows.
Feed and milk samples were collected monthly from selected farms. Feed samples were analyzed for moisture, CP, crude fiber, nitrogen free extract, ether extract in Poultry Research and Training Centre Laboratory of Chattogram Veterinary and Animal Sciences University (CVASU) as per
AOAC (1994). Milk samples were stored at 4°C until further analysis for fat, solids- non-fat, proteinby using Lactostar (model no. 3510, Funke Gerber, Germany). For each group, separate TMR samples were collected the day before the milk sampling and stored at -20°C until further analysis for proximate composition.
The level of MUN in this trial was determined by infrared spectrophotometry (Fos 120 Milko Scan, Fos Electric, Hillered. Denmark) for the analysis of ammonia and urea in biological fluids as reported by
Weatherburn (1967) and
Chaney and Marbach (1962), respectively, urea and modified indophenol with enzyme modification. method. For changes to this method, Milk was replaced with serum or plasma, incubation temperature and time and enzyme concentration were varied.
Reagents, solutions
Reagent 1 (A1): 50 g phenol and 0.25 g sodium nitroprusside were dissolved with deionized water in a volumetric flask and diluted to 1000 ml.
Reagent 2 (A2): 25 g sodium hydroxide and 40 ml sodium hypochlorite (5.25%) were put into a volumetric flask and diluted to 1000 ml with deionized water.
Enzyme solution: from the lyophilized urease enzyme preserved at+4°C (5 U/mg), 0.6 g was weighted and diluted to 100 ml (30 U/ml) with deionized water in volumetric flask.
Standard solution: From the dried urea in the drying chamber, 0.8576 g was taken into volumetric flask, dissolved with deionized water and diluted to 1000 ml (40 mg/dl). By taking varying amounts from the standard solution, solutions with varying nitrogen content were prepared.
Preparation of the standard curve
100 ml urease solutions was put into spectro cuvettes, standard solutions containing 10 ml increasing concentrations of urea were added, the mixture was shaken and kept 10 minutes at 40°C temperature. Later, the cuvettes were sealed and turned upside-down following the addition of 1 ml of A
1 and A
2. The preparation was kept 3 minutes at 55°C and the absorbance were read in spectrophotometer (Schimadzu UV 1240) against the blind sample that contained deionized water on 625 nm.
Preparation and analysis of milk
100 ml urease solution was put into spectro cuvettes, supplemented with 10 ml well mixed milk sample heated at 40°C, mixed and kept for 10 minutes at 40°C. 1 ml A
1 and 1 ml A
2 were added, then the cuvettes were sealed and turned upside-down. After keeping the preparations 3 minutes at 55°C, absorbance was read in the same way.
Data analysis
The observed data were calculated on the basis of the regression equation obtained through the standard solutions using the General Linear Model (GLM) of SAS (
SAS, 2009).