ACTA VETERINARIA ET ZOOTECHNICA SINICA

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Lactation Curve Fittings of Wood’s Nonlinear Model for Milk Yield, Milk Fat, Milk Protein and Somatic Cell Score for Chinese Holstein in Southern China

MAO Yong-jiang, ZHANG Mei-rong, XU Zhao-jun, LIU Shan, ZHANG Ya-qin, CHEN Dan, WANG Xing-long, YANG Zhang-ping   

  1. (College of Animal Science and Technology, Yangzhou University, Yangzhou 225009, China)
  • Received:2011-11-29 Online:2012-12-26 Published:2012-12-26

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Abstract:

 This study aimed to reveal the variations of daily milk yield, milk fat percentage, milk protein percentage and somatic cell score (SCS), and to establish the prediction models for these parameters in the lactation period for Chinese Holstein in southern China. A 33194-test-day dairy herd complete data from 5 Chinese Holstein dairy farms were collected in the southern China from first lactation to third lactation between 2008 to 2010 and fitted to nonlinear curve of test-day milk yield, milk fat percentage, milk protein percentage and SCS with the Wood’s incomplete gamma function model. The curve of test-day milk yield for Chinese Holstein was the standard lactation curve, and the curves of milk fat percentage, milk protein percentage and SCS were the reversed standard lactation curve. The best fitness of the Wood’s model occurred for milk protein percentage and daily milk yield with the lowest residual mean square, then following for milk fat percentage. The poor model fitness (R2≤0.7) was observed for SCS which residual mean square was highest. Daily milk yield peak day was accompanied with occurrences of minimal milk protein and SCS in the estimated lactation model. The minimal milk fat percentage came at the latest time of 18th week to 21th week in lactation curve. The peak milk yield was 30.4 kg·d-1 for first-parity cows, but the persistence for maintaining high milk yield and low SCS were greater than those of second- and third- parity cows in the latter lactation period, and the maximal milk yields for second- and third-parity dairy cows were 35.9 and 36.2 kg·d-1, respectively. The persistence for keeping high milk fat percentage and milk protein percentage was greater for second-parity cows than those of first- and third-parity cows in the latter lactation period. The Wood’s incomplete gamma function model was appropriate to predict the variation for test-day milk yield, milk fat percentage, milk protein percentage, and was not appropriate for SCS for Chinese Holstein dairy cows in southern China.

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