Genetic studies on production and reproduction traits of crossbred dairy cattle
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Date
2008-05
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G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand)
Abstract
The data of 153 crossbred dairy cows progeny of 20 sires for the present study was recorded from the history sheets maintained at Instructional Dairy Farm of G. B. Pant. University of Ag. & Tech., Pantnagar. Among all the traits studied the period had significant effect on age at first calving and first lactation yield. However the season did not affect all these traits. The least square means for age at first calving, first lactation milk yield, first lactation period, first dry period., first service period, first gestation period, first peak yield, days to attain peak yield, first calving interval and herd life milk yield were found as 1134.02±16.53 days, 2523.95±53.46 liters, 318.20±3.09 days, 88.91±2.39 days, 100.60±2.38 days, 271.67±1.39 days, 12.69±0.25 liters, 42.62±1.37 days, 444.32±4.22 days and 11141.09±249.04 liters, respectively. The heritability values for corresponding traits were observed as 0.11±0.37, 0.55±0.308, 0.27±0.254, 0.79±0.209, 0.51±0.176, 0.17±0.232, 0.32±0.263, 0.81±0.347, 0.90±0.357 and 0.78±0.342, respectively. Magnitude of heritability indicated that these traits have sufficient additive genetic variance and could be improved through selection. First lactation milk yield had significant positive phenotypic correlation with first lactation peak yield and herd life milk yield while negative phenotypic correlation with first dry period. Herd life milk yield had significant positive phenotypic relationship with peak yield and calving interval. Positive phenotypic correlations between service period and lactation period, calving interval and service period, calving interval and lactation period were found significant. Age at first calving positively correlated with first lactation period, service period, dry period, peak yield, days to attain peak yield and herd life milk yield on genetic level. However, age at first calving negatively correlated with first lactation milk yield, gestation period and calving interval. First lactation milk yield had positive genetic correlations with all other traits except with first service period. First lactation period positively correlated on genetic level with first service period, days to attain peak yield, first calving interval and herd life milk yield but negatively correlated with first dry period, gestation and peak yield. The positive correlation was observed on phenotypic level between first lactation period, service period and first calving interval. First dry period had positive genetic association with service period, gestation period, peak yield, days to attain peak yield, first calving interval and herd life milk yield but on phenotypic level all these correlations were found non-significant. First service period had positive correlation with days to attain peak yield, first calving interval and herd life milk yield on genetic level but only first calving interval had significant positive correlation on phenotypic level. The first service period had negative correlation with first gestation period and peak yield but these relationships were not significant on phenotypic level. First gestation period had negative genetic correlations with other traits except first peak yield. First peak yield was negatively correlated on genetic level with days to attain peak yield, first calving interval and herd life milk yield. The R2 values considering the explanatory variables as age at first calving, first lactation period, first dry period, first service period, first gestation period, days to attain peak yield and first calving interval, separately, were found to be non-significant. It is concluded that the herd life milk yield can be predicted using first, second, third and fourth lactation milk yield or their combinations as an explanatory variable with sufficient accuracy.
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