 
Welcome to our first newsletter in which we background and bring
you up to date information about the Feed Efficiency Trial funded
by MeatNZ.
In most beef cattle production systems, researchers have established
that 65-85% of total feed intake is required by the breeding cow
herd and that half of that total feed intake is required just to
maintain cow liveweight. Despite its economic importance farmers
in New Zealand do not usually assess the cost of feed for their
farming operation. The complimentary roles of beef cattle on sheep
farms complicates the economic assessment of efficiency in New Zealand’s
mixed livestock farming systems.
There are a number of ways of expressing and measuring feed efficiency
in beef cattle. Recent Australian, USA and UK research has concentrated
on net feed intake (NFI) or residual feed intake as a measure of
feed efficiency. Net Feed Intake is defined as, the difference between
what an animal eats and what they are expected to eat for its weight
and gain when calculations are made from known energy requirements
(i.e. the factorial approach). For a given liveweight gain, some
animals will eat more than expected, and some less than expected
– these latter ones are more efficient in terms of Net Feed
Intake.
The usual measure of feed efficiency, feed conversion ratio (FCR),
is defined as feed intake divided by liveweight gain. This measure
has the disadvantage that it links closely with liveweight gain
and hence mature size. Selection for FCR would rapidly increase
mature weight. With Net Feed Intake, more efficient cattle can be
theoretically found within any desired cattle weight range, and
selection for improved NFI will not increase mature size.
If genetic improvement for net feed efficiency is undertaken in
New Zealand then it will generate profit when steers are finished
for slaughter sooner or at heavier liveweights when slaughtered
at the same time, however, greater gains may come from the improvement
in NFI when it is applied to beef breeding cows.
Selection for improved NFI needs to be assessed in conjunction
with improvement in liveweight gain (for example 600 day weight
EBV) and maternal traits (for example 200 day milk EBV).
The aim of the Massey University trial is to evaluate selection
for Net Feed Intake (NFI) under New Zealand pasture fed conditions.
At the same time we are comparing selection for high and low 600
day liveweight EBV and 200 day milk EBV. The trial allows us to
make an estimation of the value of using high EBV bulls (i.e. top
10% trait leaders) over commercial cows and then recording the performance
of steer and heifer progeny under normal farming conditions.
As most of you are aware we had a delay in obtaining the high and
low NFI semen from Australia which resulted in the 2000 matings
being just semen from the high and low 600 day and 200 day milk
EBV bulls. The 2001 matings contain link bulls from the 2000 mating
plus the high and low NFI bulls.
All the steers and heifers were transferred from the four industry
farms to Massey University in April/May. The steers arrived at an
average liveweight of 255 kg and the heifers weighed 244 kg. The
steers have been split into two - one group to be finished at 20
months and the other at 30 months of age.
The heifers are being run together and are being monitored for
onset of puberty with tailpainting and weekly blood sampling to
assess progesterone levels, an indication of when first oestrus
occurs. The first feed intake measurements were made in late June.
The graph below outlines target liveweight gains. Future newsletters
will supply further background information e.g. the likely benefits
of selection for NFI, and preliminary results from the trial.
Contact Information
Steve Morris
Institute
of Veterinary, Animal & Biomedical Sciences (IVABS)
College of Sciences (Mail Code 411)
Massey University
Private Bag 11-222
Palmerston North
Phone: 06 350 5329
Fax: 06 350 5616
Email: S.T.Morris@massey.ac.nz
Date added: 16 September 2002
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