COMPARISON OF DIFFERENT PROCEDURES FOR LACTATION LENGTH
ADJUSTMENT OF MILK YIELD IN SAHIWAL CATTLE
I. R. Bajwa, M. S. Khan, M. A. Khan1 and K. Z. Gondal2
Department of Animal Breeding
and Genetics, University of Agriculture, Faisalabad, 1Livestock production Research
institute, Bahadarnagar, Okara, 2Department of Livestock Management,
University of Agriculture, Faisalabad-38040, Pakistan
Abstract
The purpose of the present study was to compare three procedures for lactation
length adjustment of milk yield. For this purpose, weekly milk yield records (n
= 2039) of Sahiwal cows were used. Multiplicative adjustments using simple
linear regression of milk yield on lactation length was the first procedure, in
the second procedure last recorded milk yield was used to predict milk yield of
unrecorded lactation, while the third procedure was similar to the second
procedure except that predictions included average daily milk yield of the
recorded lactation as well. The bias (the difference between actual and
predicted milk yield) was lowest in the third procedure. The standard deviation
of bias was 235 kg for milk yield adjusted by using last test day milk yield and
average daily milk yield of the known lactation as compared to milk yield
adjusted by linear regression i.e. 496 kg for lactation length of 56 days. The
standard deviation of bias decreased to 23 kg of milk for the milk yield
adjusted by using last test day milk yield and average daily milk yield of the
known lactation as compared to 66 kg for the milk yield adjusted by linear
regression towards the end of the lactation length. The correlation coefficient
between actual and predicted milk yield was 0.881 for the milk yield predicted
by using last test day yield and average daily milk yield of the known lactation
length as compared to 0.10 for milk yield predicted by linear regression for the
lactation length of 56 days. The correlation coefficient also increased with the
increase in lactation length. Lactation length adjustment of milk yield should
be done using last test day information along with average yield of the recorded
lactation.