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HERD FERT I L I TY
WORKING
TOGETHER
FOR A HEALTHIER FUTURE...
15
LIVESTOCK MATTERS
Worse still, it is estimated that around 40%
of heats are silent. ‘So immediately, that’s
adding another 21 days until the cow may
be served again,‘ says Owen. ‘Cows may
show heat again 21 days later if the next
follicle produced is of better quality. Or
they may not.‘
‘The main driver for oestrus activity is the
hormone oestrogen, and levels of this
are determined by the quality of the
developing follicle.
‘Poor follicles tend to result in a corpus
luteum which produces sub-optimal levels
of progesterone thus reducing the quality
of the next follicular wave. This circle of
sub-oestrus continues until the stress factors
are reduced, for instance, the cow comes
out of negative energy balance, the diet
improves, her lameness is resolved, or the
weather improves, etc.
‘Further exacerbating this issue, is that the
high metabolic rate of high yielding cows
also means that oestrogen gets broken
down very quickly. Hence this is another
reason why a cow might only express
oestrus for a short time, or not at all.
‘One way of stimulating oestrus behaviour
and making heat detection easier, is to
increase the cow’s progesterone levels.
‘This allows an appropriate pulsatile
release of LH leading to a healthy follicular
wave resulting in a follicle producing
good levels of oestrogen and promoting
oestrus activity. This can be done using an
intra-vaginal device to release a controlled
flow of progesterone for a period of
seven to nine days.‘
Quality issues
When cows are presented for PD-ing and
luteal cysts are found, then vets can
administer a prostaglandin-based product
which will cause the corpus luteum to regress
so that the cow can return to cycling again,
and exhibit a normal oestrus, 2-5 days later.
Owen explains: ‘Although this creates a
heat, if the corpus luteum has not been
producing adequate progesterone - as is
often the case in anoestrus or cystic cows -
and so is not good quality, then the knock-on
effect is a follicle of poorer quality, and
consequent release of a poorer quality egg.
‘The animal may have a heat but not
conceive, or the pregnancy may not be
maintained - known as late embryonic death
- resulting in a return to oestrus often 24-35
days post service.
‘So on some farms, with some cows, the
use of progesterone and synchronisation
programmes will be a faster route to a full
term pregnancy.‘
The diagram below outlines some of the key
factors affecting pregnancy rate, and the
factors that have an impact on them.
The inter-related factors affecting fertility (pregnancy rate)
Fixed Time AI
Submission rate
Egg quality
+
=
Stress factors
Heat detection
LH hormone
FSH hormone
Progesterone
Pregnancy rate
Conception rate
AI technique
and timing
Corpus Luteum quality
Heat/Oestrus
Oestrogen
Follicle quality
Fixed Time AI
Owen explains: ‘When non-bulling or
non-pregnant cows are presented to me on
a routine visit, the desired outcome of any
treatment I administer should ultimately be the
creation of a pregnancy in as many of these
animals as possible - ie a high pregnancy
rate post-treatment.
‘To improve pregnancy rate the aim is to
have submission rates as close to 100% as
possible combined with ensuring a healthy
follicle is produced in each case, allowing
higher conception rates. High submission rates
are best achieved when routine intervention
results in a fixed time AI, so that 100% of
treated cows are served.
‘Synchronisation of oestrus in healthy cycling
cows with normal follicular dynamics is
relatively straightforward and one common
treatment is the ov-sync protocol which will
yield good conception rates when
appropriately used.
‘However, many cows presented as
non-bullers to vets will have some form of
stress-related disturbance to their ovarian
cycle. This may result in poor quality egg
production following ov-sync treatment and
this will reduce conception rates in this type
of patient.
‘So a preferred treatment protocol in those
instances involves the combination of a
progesterone releasing device in combination
with an ov-sync type protocol. By improving
the progesterone status in these ‘broken’ cows,
a healthier follicle develops resulting
in improved conception rates.
Intra-vaginal device with progesterone