Selection for net feed efficiency in beef cattle - a viable prospect
on pasture ?
(reprinted from a New Zealand Angus newsletter)
Paul Charteris
Institute of Veterinary, Animal
and Biomedical Sciences
Massey University
An economic objective of beef cattle breeding programmes is to maximise
profit from available resources. An alternative (yet related) biological
objective is to maximise feed conversion efficiency, assessed as
the weight of saleable beef per unit feed intake (or its inverse,
the amount feed required to produce a unit of saleable beef). As
yet we do not have Estimated Breeding Values (EBVs) available for
improved feed conversion efficiency, in fact do we actually need
them?
It has been suggested by many researchers that since the cost of
feed represents a major expense for most beef cattle production
systems, any improvement in feed conversion efficiency would lead
to major decreases in costs, thus increasing profitability at the
same level of output. However New Zealand's pasture based production
systems are characterised by a pattern of feed supply that varies
in terms of quantity and quality both within and between years.
Thus the cost of feed in mid-winter may be several times higher
than during Spring flush where feed is in surplus.
Selection for improved feed conversion efficiency in beef cattle
is not an easy task, a few of the challenges we are presented with
include:
- Individual animal feed intake is extremely difficult to measure.
Electronic tagging and the use of electronic feeders provide one
way to assess feed intake in cattle, however the cost of equipment
and staff time are usually considerable.
- Sires ranked on the basis of their EBVs for feed conversion
efficiency on a grain-based diet may not rank in the same order
when fed a pasture-based diet. This re-ranking, if large enough,
may result in some bulls being selected on the basis of high feed
conversion efficiency EBVs on grain-based diets but having poor
progeny performance on pasture diets.
- An indicator trait of feed conversion efficiency could be selected
for if the trait has a high heritability and a strong genetic
correlation with feed conversion efficiency. Ideally, such indicator
traits should be easily measured and be able to describe a large
portion of variation in feed conversion efficiency. Currently,
no single indicator trait meets all of these requirements.
- Little research has been undertaken to determine if differences
between feed conversion efficiency EBVs of bulls translates to
differences in feed conversion efficiency of the steer or heifer
progeny.
Deriving EBVs for feed conversion efficiency is extremely expensive
and only likely to be limited to a small number of young sires.
Current Australian research has focused on deriving EBVs for net
feed efficiency (nFE). It is possible to predict the amount of feed
each bull will need to eat given his live weight and rate of liveweight
gain. The difference between what the bull actually eats and what
he is predicted to eat is termed residual feed intake. Net feed
efficiency EBVs are derived from the difference between actual feed
intake and residual feed intake. A bull who ate less than predicted
to achieve a given rate of liveweight gain would be more likely
to be a trait leader for nFE EBV.
A desirable outcome from this research would be to deliver an EBV
capable of ranking candidate sires on the efficiency with which
they can convert feed to saleable beef.
From New Zealand's perspective, net feed efficiency EBVs may provide
some benefit to improve feed conversion efficiency of beef cattle.
Further work is required to determine if such EBVs will benefit
New Zealand's beef cattle industry. If it appears such EBVs would
be beneficial, considerable research will be required to derive
such EBVs for New Zealand conditions rather than adopt overseas
techniques. Such research will need to rank sires and their progeny
on pasture-based systems and evaluate how changes in feed conversion
efficiency affect other economically-important traits such as female
fertility.
An alternative strategy may be to encourage selection for lean
growth rate among our terminal sire breeds (after accounted for
changes in traits such as calving ease) then encourage greater use
of these terminal sire breeds. Such a strategy of mating a large
sire breed and a smaller dam breed essentially improves feed conversion
efficiency on a whole-farm basis. Other non-genetic changes which
can enhance feed conversion efficiency include matching appropriate
breed-types to particular farming environments (better suiting horses
to courses) and timing of key operations such as planned start of
calving.
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