DESCRIBING THE LACTATION CURVE OF DAIRY CATTLE WITH MULTIPHASIC FUNCTION

Abstract

An experiment to describe pattern of lactation curve using Multiphasic Function
(MF) has been conducted. The MF is based on a sum of logistic functions:
where Y, is milk yield at time t (days in rn.ilk), n is the number of lactation phases,
tanh is hyperbolic tangent and for each phase i: parameter a; is half asymptotic total
yield (liter), bi is rate of yield relative to a; (days'1) , aibi is maximum (peak) yield
and c, is time of peak yield (days). In this study, the monophasic and diphasic
function of MP was applied to adjust the pattern of lactation curve of Holstein cows
in UPT Baturraden, Central Java. The milk yield data came from 236 first three
lactations of 126 cows that had completed lactation and the data were collected
weekly, beginning with day 5 after calving until day 301. Mean rnilkyield was used
to estimate parameters of lactation curve. These parameters were fitted to the mean
observed data. Goodness-of-fit was checked on two criteria proposed: 1) Adjusted
coefficient of determination (Adj-R2), and 2) Akaike’s infonnation criterion (AIC).
Results showed that milk yield a day averaged about 10.4 liter with 2.79 standard
deviation. Adj-R2 both for monophasic and diphasic functions were 0.9798. AIC
for monophasic function was -68.2245 while diphasic function -74.2246, which
indicated that diphasic function revealed slightly better fit to mean milk yield data
compared with monophasic function. Estimates for maximum yield was about 2.7
and about 7.9 liter for first phase and second phase, respectively. Time of peak yield
was about 43 days for first phase and 180 days for second phase.