THE main focus of my two
previous articles on the two-day
pre-conference seminar at the
annual conference of the American
Association of Bovine
Practitioners, on “The replacement
heifer from birth to calving”, has
been the pre-ruminant calf. Now
we switch to post-weaning and
reproduction in the heifer.
Management of the dairy heifer
from weaning to calving is a hugely
neglected area
– how many
vets in the
UK have
regular input
into this on
their clients’
farms? I
know I don’t.
Rob Corbett discussed this key area
and ways to maximise growth at this
stage.
Once the calf is weaned it should
stay in its hutch (or UK equivalent) for
a week to monitor starter intake.
Ensure the calf eats 3-4kg of starter
daily, if it drops below 1kg then it
should be placed back on milk. The
calf should then be moved into a small
group, still on starter for a week. A
grower ration can then be introduced;
preferably 20% alfalfa hay and 80%
concentrate.
If alfalfa hay is not available, then
discussion with the nutritionist about
an alternative is advised, but fermented
forages should be avoided. Calves can
stay on a grower ration until five
months.
Adjust the ration
As the heifer matures, her ration has to
be adjusted according to her
requirements. In the UK, like many
dairy farms in the USA, grouping of
heifers is extremely difficult, with a
wide age range making ration
formulation difficult. The aim must be
to meet the nutrient requirements of
the youngest animal to get maximum
growth rates whilst monitoring older
animals in the group to make sure they
don’t become over-conditioned. The
most common cause of interfering
with growth rates and increasing
disease incidence is low protein diets.
Ultimately, discussion with the
nutritionist, use of highest quality
concentrates and use of available
forages on farm must be brought
together to maximise growth and
health.
Mike Overton discussed the
opportunities and challenges in dairy
replacement heifer reproductive
programmes. The focus so far had
been getting our heifer to this point
but if there is no focus on then getting her in calf, we have wasted a lot of
effort.
There are two big drivers for
achieving an earlier age at first calving:
1. Improved nutritional management
n efficiency and increased rate of gain;
n achievement of puberty and
adequate frame at an earlier age with
less disease and less variation.
2. Efficient reproductive management
n less variation around time of first
service;
n improved pregnancy
rates once breeding
starts;
n reduced reproductive
culls;
n an established limited
period of breeding.
Table 1 shows the
commonly promoted
“goals” for Holstein
heifers in the USA. The
average age at first
calving in the USA is 25
months. The major factors
driving this are: age at puberty; growth
patterns; management factors such as
voluntary waiting periods, pen
management and pregnancy diagnosis;
conception risk; oestrus detection and
breeding management –
synchronisation, timed AI or natural
service.
The opportunities for earlier heifer
rearing are reduced morbidity and
mortality, an earlier potential age at
first service and first calving and
enhanced milk production in future
lactations – research suggesting 800kg in first lactation and 450kg
in second lactation.
Critical
Early heifer growth and
development along with
efficient reproductive
management are critical for
reaching this goal. Without
proper early development,
breeding can’t begin early,
and without good heifer
reproduction then there is
a failure to capture the full
benefit of intensive rearing.
Figure 1 shows the
life-cycle of a heifer from
birth to calving. The
“breeding” window varies
significantly on farms in
both the USA and UK.
The use of AI and not
natural service in heifers
was encouraged. It was
emphasised what a great
tool it is to improve genetic
progress and reduce
dystocia.
Conception rate or “risk”, as Mike
Overton called it, is influenced by
several factors: oestrus detection
accuracy, technician, sire, animal – including age and breed,
days since last
insemination at PD,
semen – conventional v.
sexed, and season (e.g.
heat stress).
In basic AI
programmes oestrus
detection (insemination
rate) is often the largest
bottleneck to improving
reproductive efficiency.
Figure 2 shows
synchronisation in
heifers whilst Figure 3 is a suggested timed AI programme in
heifers.
The five-day CIDR Cosynch-72
has been developed to deal with the
issues of OvSynch in heifers. These
are that heifers have a faster rate of
follicular growth than cows, they are
more likely to have three (or even
four) wave follicular cycles, they are
less likely to ovulate a dominant
follicle in response to the first GnRH,
and they are at risk of premature
regression of the CL and expression
of oestrus compared with cows.
There are some
adjustments to the five-day
CIDR Cosynch-72
programme that achieve
comparable conception
rates; quoted at around 50%
pregnant at day 32, with
80% non-pregnant found in heat and re-bred by 25 days. Assuming
a 50% conception rate, this equates to
70% pregnant in two cycles.
The use of prostaglandin is much
more tightly regulated in the UK and
the cost of such a synchronisation
programme may seem unacceptably
high. What I learned, though, was the
American approach to heifer
reproduction is much more aggressive
than our own which is often: “turn
them in with the bull”.
Employing aggressive oestrus
detection plus aggressively re-enrolling
heifers that fail to conceive – which of
course requires regular routine vet
visits, means more pregnant heifers
weekly.
Heifer reproductive performance is
a larger economic opportunity than
many realise and is a key part to
getting the full benefit of intensive
heifer rearing programmes.
Acknowledgements
The author would like to thank both
Shepton Veterinary Group and Zoetis
Animal Health for co-sponsoring his
trip to the AABP Annual Conference.
