MODELLING OF BEST FIT LACTATION CURVE IN CROSSBRED CATTLE OF KERALA
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Date
2018
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COLLEGE OF VETERINARY AND ANIMAL SCIENCES-MANNUTHY,THRISSUR
Abstract
The main objectives of the present study was modelling of best fit lactation
curve in crossbred cattle of Kerala by using monthly test day milk yields (MTDMYs).
For developing lactation curve models, data of 936 crossbred cattle sired by 188 bulls
spread over a period of 16 years (2002-2017) in seven different field centers of
ICAR-Field Progeny Testing Scheme, Kerala were used. Least squares means for ten
monthly test days starting from 20th day of calving at 30 days interval and first
lactation milk yield (FLMY) were 10.35±0.15, 10.71±0.14, 10.25±0.14, 9.73±0.13,
9.11±0.13, 8.44±0.13, 7.80±0.12, 7.03±0.0.11, 6.16±0.12, 5.41±0.13 and
2510.71±30.49 kg, respectively. Period of calving and batches of sires had significant
effect on some of the MTDMYs and FLMY. Season of calving had significant effect
only on first MTDMY. Genetic group, sources of sires and age at first calving had
non-significant effect on MTDMY and FLMY. Heritability estimates ranged from
0.004±0.107 in 9th MTDMY to 0.531±0.136 in 4th MTDMY. Lactation curves using
different MTDMY were modelled with Inverse Polynomial Function (IPF), Mixed
Log Function (MLF), Parabolic Exponential Function (PEF), Wilmink function
(WIF) and Woods function (WOF). Among these, Wilmink Function showed best
fitness of good criteria. WIF had maximum R2 (86.45%), low RMSE (0.009949 kg),
minimum AIC (-58059.79) and minimum BIC (-9656.57) values. Stepwise backward
multiple regression method was used to predict FLMY using different combination of
MTDMYs. Prediction equation with 3 variables viz. MTDMY-1, MTDMY-2 and
MTDMY-5 was found to predict of FLMY with 84.08 per cent accuracy. Lactation
curve parameters were validated with 60 crossbred cattle of a different herd. The
average deviations of predicted FLMY of IPF, MLF, PEF and WOF from actual
FLMY were significantly different. For animals with initial MTDY more than 11
liters, prediction with WOF was effective as it was not significantly different from
observed value. Wilmink function is adjudged as the most effective function in
predicting MTDMYs and FLMY of crossbred cattle of Kerala