149
Cold Winter Climates
rates, mortality rates, and feed supplementation costs. Based on this data, Hughes concludes that the
commercial beef cows in northern USA cold winter climates delivering their 8
th
calf are less proitable to the herd than irst calving cows relative value of 0.75 vs.
0.81. At this point, the herd beneits from their removal and replacement with heifers. Consequently, a culling
policy based on removing 8.5 to 9 year old cows and after weaning the 7
th
calf would generate the highest return for the commercial herd.
During a herd development phase, where Australian cattle are imported to form the foundation of a specialist
beef herd development program, it would be advisable to retain all imported cattle until after they wean their
8
th
calf at least, or are required to be culled for health or welfare reasons. This rationale is based on recovering
the greatest return on the signiicant expense incurred in importing heifers, and the relatively small 7.5
diference in proitability between 8
th
calvers and irst calving heifers, in particular.
5.7. Heifers
Maximum breeding herd productivity is achieved when cows calve on or about the same date each
year, beginning at two years of age and ending when they leave the herd as aged culls. To help achieve this,
heifers must be managed to reach puberty at a young age, conceive soon after irst exposure to the bull, and
rebreed while lactating with their irst calf.
Management of breeding females begins at weaning. The ideal growth and body condition targets for female
weaners being retained for consideration as replacement breeders difers considerably from the ideal targets for
males and undesirable females during growth.
5.7.1. Selecting Replacement Breeders
Not all heifer calves born will go on to have a long and productive life as a breeder. Obvious factors such
as poor health, physical problems or stunted growth will eliminate some young heifers from contention for
selection as replacement breeders.
However, in a productive breeding enterprise it is common to have more young heifers on hand at irst
joining than required to replace culled breeders. In such circumstances, a selection process is required to
determine those heifers most likely to have greatest beneit to the breeding enterprise and should therefore
be retained.
Table 5.2. Efect of age, represented by the number of calves born to a cow, on the relative contribution to the proitability of the breeding herd. Source: Hughes, H. North
Dakota State University.
Number of calves born to the cow
Relative Value of Cow in the Herd
1 0.81
2 0.89
3 1.23
4 1.22
5 1.33
6 1.05
7 0.91
8 0.75
9 0.56
Older cows are of lower value
to the herd than younger cows
}
150
Beef Breeder MANUAL
The number of heifers required for mating each year largely depends upon whether the herd is building up
breeder numbers, or only replacing those breeders being culled. Herd build–up includes:
• Increasing total breeder numbers; or •
Undergoing a considerable genetic shift within a stable sized herd. This genetic shift may be changing from
one breed to another, or changing the genetic type within the resident breed e.g. to an earlier maturity
type or superior body structure and growth rate. In each of these situations, a greater number of
replacement heifers will be required each year than when only replacing culled adult breeders in a stable
sized herd. It is envisioned that most of the destination farms
for Australian heifers will be increasing their breeder numbers, so a selection process with this in mind is the
focus. While the process is known as ‘selecting replacement
breeders’, in practice it is often a case of selecting out the heifers not desired as replacement breeders, with
those remaining in the group considered suitable for joining. Identifying those individuals who do not meet
a minimum requirement in terms of their likelihood to become productive and proitable breeders is the
purpose of the selection process. Selection process must consider several aspects:
• Weight • Body condition score
• Body conformation • Health.
In general the older, heavier heifers at weaning have the greatest chance of going on to become fertile,
productive cows. Segregating out the smaller and younger heifers is therefore an important irst stage of
the selection process.
5.7.2. Targets for Heifer Development
