Milk yield and reproductive efficiency
are crucial to profitable dairying.
Although, genetic improvement in the
last few decades has led to substantial
increases in milk yield/cow, fertility and
reproductive health have declined
(Dematawewa and Berger, 1998).
In a pasture-based system, a 365 day
calving interval is crucial for optimum
profit. Hence the need to increase milk
yield by improving persistence of
lactation rather than peak lactation
which puts increased stress on the
cows at the time when they should be
rebreeding. Peak milk yield,
persistency and lactation length are
the key components of the lactation
profile. Dairy cows with high peak
yields are more prone to metabolic
and physiological disorders (Terkeli et
al 1999). Although estimated breeding
values (EBV) in dairy cows in Australia
incorporates indices of economic
value, such as survival and milking
speed, the impact of the current breeding approach and management
on the shape of the lactation profile is
not clear.
Mathematical functions such as those
previously used to describe a series of
milk test day records (Wood, 1967,
Wilmink, 1987), have the advantage of
minimizing random variation while
simultaneously summarising the
lactation profile into biologically
interpretable parameters
