Diurnal Variations in Milk Yield and Milk Constituents During Entire Lactation in Mithun (Bos frontalis)

摘要

The studis aimed to investigate the diurnal variation in milk yield and composition during an entire lactation period and assess the relationship between seasonal variation in pasture quality and milk yield along with composition in 11 mithun (Bos frontalis) cows. Milk yield recording and milk sample collection were done at weekly interval. Milk samples were analyzed for the concentrations of major constituents. Representative fodder samples from the grazing area were collected during the experimental period and subjected to proximate analysis. Throughout the lactation, the range of daily milk yield (kg) in morning (0.90±0.03 to 0.61 ±0.03) was found to be significantly (P<0.01) greater compare to evening (0.56±0.02 to 0.37±0.03). In contrast, the total solid (TS, %), fat (%), total protein (TP, %), casein (%), non-protein nitrogen (NPN, %) and milk urea (MU, mg/dl) were found significantly (P<0.01) greater in evening milk (23.88±0.44 to 22.36±0.29, 10.35±0.49 to 8.07±0.19,7.22±0.15 to 6.66±0.12,5.08±0.12 to 4.76±0.06,0.49±0.02 to 0.46±0.03 and 48.11+2.71 to 40.53±1.18 respectively) as compare to morning milk (21.43±0.41 to 19.57±0.18,10.17±0.42 to 7.39±0.19,6.37±0.11 to 5.98±0.10,4.29±0.13 to 4.04±0.06,0.39±0.01 to 0.36±0.01 and 39.87±2.16 to 33.16± 0.91 respectively). The peak milk yield (kg/d) was observed on the second (1.01 0.10) and first (0.60 0.05) fortnight respectively, followed by a gradual declining trend. The fortnightly trend of all the milk constituents was found nearly similar for morning and afternoon milk. In the entire lactation, concentrations of all the milk constituents except lactose and ash were found significantly (P<0.01) greater in afternoon milk. No significant relationship between pasture quality and milk yield and composition was observed except that milk NPN content was positively (P<0.05) correlated with pasture CP content. In conclusion, lesser milk yield and greater concentration of major milk constituents in mithun might be attributed to the unique genetic makeup of this species. A substantial diurnal variation in milk yield and concentration of major milk constituents was observed throughout the lactation. The nutritional influence on the seasonal variations in milk yield and composition in grazing mithun was difficult to assess based on the data of pasture quality.