Genetic evaluation of first lactation traits and lactation curve models used for predicting part milk yields in crossbred cattle
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Date
2021-07
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G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand)
Abstract
The present investigation was undertaken utilising the records of 529 daughters of 79 sires spread over a period of 30 years from 1990 to 2019 in crossbred cattle maintained at Instructional Dairy Farm of G.B. Pant University of Agriculture and Technology, Pantnagar to study the effects of genetic and non-genetic factors, inheritance pattern of different economic traits, to compare the sire using LSM method and to compare the efficacy of different curve models utilising monthly milk yields. The least squares method (LSM) along their standard errors of age at first calving (AFC), first service period (FSP), first dry period (FDP), first calving interval (FCI), first lactation period (FLP), first lactation milk yield (FLMY), first lactation 305 days milk yield (FL305DMY), first lactation peak yield (FLPY) and first lactation days to attain peak yield (FLDAPY) were estimated as 1170.62±31.50 days, 263.94±3.40 days, 115.90±19.84 days, 513.00±22.60 days, 397.25±9.19 days, 3584.92±118.42 kg, 2854.26±59.61 kg, 14.18±0.27 kg and 35.08±0.87 days, respectively. The significant effect of sire was found on AFC, FLMY, FL305DMY and FLPY. In contrast, nonsignificant effect of genetic group was found on all the first lactation traits except FLDAPY. The non-significant effect of season was found on all the first lactation traits except FLDAPY. The significant effect of period was found on AFC, FLP, FL305DMY and FLDAPY. The heritability estimates for first lactation traits AFC, FCI, FLP, FLMY, FL305DMY, FLPY and FLDAPY 0.184 ± 0.04, 0.08 ± 0.02, 0.039 ± 0.02, 0.12 ± 0.03, 0.114 ± 0.03, 0.194 ± 0.04 and 0.015 ± 0.02. The positive genetic correlations indicated that selection for higher first lactation milk yield, higher first lactation 305 days milk yield and higher first lactation peak yield can be used as a selection criteria for the genetic improvement in the herd. The estimation of breeding value of sires and ranking them on the basis of estimated breeding values by LSM method may be done for selection and utilization of sires in herd improvement programme. The relative efficiency of four lactation curve models viz. parabolic exponential, inverse polynomial, gamma type function and mixed log function were compared. Inverse polynomial function described the highest coefficient of determination for monthly milk yields (R2 = 97.1%) with least value of root mean squares error (RMSE) and absolute mean deviation (AMD) suggesting inverse polynomial function to be the best fitted curve for explaining the first lactation curve by utilising the records of monthly milk yields.