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,
1
Livestock production Research institute, Bahadarnagar, Okara, 2
Department 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.