10 May 2021
Phil Elkins
Job Title
Bovine fertility continues to be a mainstay of farm animal vet-farmer interaction – and rightly so, as it has such a large influence on farm output.
Over the past 10 years, we seem to have started to buck the trend of worsening fertility associated with increased production. According to the annual National Milk Records (NMR) survey of 500 Holstein/Friesian herds, the past 10 years has seen a reduction of mean calving interval of 24 days, driven by a conception rate increase from 32% to 35% and a submission rate increase from 27% to 40%1.
A prerequisite to successful fertility control, in particular in higher-yielding herds, is successful transition cow management. By improving the control of infectious and metabolic disease around calving, farmers and their advisors can maximise the proportion of cows returning to normal cyclicity with high chances of conception and implantation at an appropriate time.
An approach to successful transition management has been previously covered in this publication2. This article will concentrate on the management of issues once they occur.
The most common fertility issue presented to clinicians is that of a non-cycler cow – or, to be more correct, a cow with no detected oestrus. These represent a potential significant loss of production, income and frustration for farmers.
Subjectively, the author has seen greater uptake of synchronisation programmes within the fertility control plan for dairy herds. This is equally true of block calving and year‑round calving herds.
It is worth reminding ourselves of the aims of breeding programmes within different management systems:
Year‑round calving: maximise the proportion of cows conceiving a viable pregnancy at the optimal time to produce maximum value of milk and calves for this, and subsequent, lactation.
Block calving: maximise the proportion of cows conceiving within a defined time period, with a large financial benefit towards a left skew within the block.
A number of individual and farm factors define that “sweet spot” for the optimum time for an animal to conceive, including milk yield, milk persistency, target replacement rate (as influenced by genetic progress, net return on a sale, and youngstock capacity and performance), transition disease incidence, calf value and many others.
However, it is fair to say in almost all cases, assuming the right cows are selected, treatment for no visible oestrus is financially rewarding.
Two main types of treatment exist for non-cyclers – those that aim to synchronise or advance the onset of oestrus, and those that aim to synchronise ovulation.
This is an important distinction as oestrus is the physical manifestation of hormonal changes within the cow that do not always correlate exactly with ovarian function – if they did, we would never see a non‑cycling cow with a corpus luteum (CL).
The success of oestrus synchronisation programmes relies on detection of oestrus, which is improving across the national herd, but is still only 40% within the NMR cohort. These programmes are also being used within a subset of cows already preselected as non‑cyclers for showing poor or no oestrus. Therefore, it is rarely a sound decision to use an oestrus synchronisation programme, such as a single injection, or even two injections of prostaglandins.
It is the author’s experience that submission rates following a single injection of prostaglandin is about 60%, with a similar rate following the second injection. This equates to 84% submission rate at best.
Compare this with an ovulation synchronisation programme, which, by its very nature, aims to optimise insemination timing relative to synchronisation and, therefore, should have a 100% submission rate.
Assuming the national average conception rate of 35% is achieved for ovulation synchronisation programmes, to achieve the same number of pregnancies, an oestrus synchronisation programme must achieve a conception rate of 42%, which is improbable.
Once the premise that we should be prioritising ovulation synchronisation programmes is accepted, the next questions are which one and how.
In the treatment of non‑cycler cows, two protocols are widely accepted – Ovsynch, and Ovsynch plus progesterone device. A meta‑analysis of the effect of adding a progesterone device into the Ovsynch programme showed a 14% increase in pregnancies per AI at 32 days for cows with no CL at the initiation of synchronisation (P<0.01). Where a CL was present at initiation, the results are less marked, with a 3% increase, which is not statistically significant3.
Therefore, the addition of a progesterone device to the Ovsynch programme is warranted in the absence of a CL at initiation, and potentially beneficial in all cows.
Incomplete luteal regression is a common issue within Ovsynch programmes, reducing pregnancies per AI by 66% in those affected cows4. One strategy to reduce the impact of this is to introduce a second injection of prostaglandin at day eight while maintaining all other timings. This increases the luteal regression and pregnancies per AI by 14% (P<0.05) and, as such, should form part of the synchronisation programme5.
While prolonged lactation due to poor fertility is associated with over‑conditioning in late lactation – leading to increased risk of poor hepatic function, dystocia, transition disease and then future fertility, sometimes referred to as “fat cow syndrome” – the decision on a suitable approach to improving fertility in early lactation is often a balance between perceived costs and outcomes.
Dynamic modelling with a range of inputs can be used to demonstrate the likely cost-benefit of different approaches. Two slightly different studies have compared approaches.
The first looked at economic returns on oestrus detection only, a Presynch‑Ovsynch programme using two injections of prostaglandin prior to an Ovsynch programme for fixed time AI and Presynch‑Ovsych, but with oestrus detection and appropriate AI to the prostaglandin injections.
This study found that for all levels of oestrus detection sensitivity and specificity, and synchronisation compliance, a combination of fixed time AI and oestrus detection proved the most financially rewarding. However, this benefit was diminished in favour of oestrus detection, where oestrus detection rates are greater than 60% with a 95% accuracy, and in favour of fixed time AI only where compliance with protocols is 95%6.
The second study compared returns from two programmes – one based entirely on fixed time AI and one incorporating oestrus detection.
This study found that for variations in all parameters, fixed time AI programmes are more rewarding in terms of both net value and fertility parameters if the conception rate to oestrus detection is 25% or less. When the conception rate is 30% and oestrus detection is 60%, the outputs are comparable. Where the conception rate is 35% or higher, adding oestrus detection into the programme is beneficial7.
Combining these two studies shows that wider use of synchronisation programmes for first service is likely to be beneficial – both in terms of fertility output and financial return – in all situations other than where accurate heat detection identifies more than 60% of eligible cows in heat with at least 30% conception rate.
Similarly, unless conception rate to detected oestrus is poor (lower than 25%), incorporating heat detection into fixed time programmes is beneficial.
Cystic ovarian disease is a less common occurrence for dairy practitioners, yet a potentially frustrating one when it happens.
Precious little research has been carried out into the treatment of cystic ovarian disease in the past 10 years, with one study showing gonadotropin‑releasing hormone analogues giving the best response for follicular cysts, and prostaglandins for luteal cysts8.
Within the profession globally, a trend appears to exist for ignoring the cyst and treating the cow with a programme based purely on the absence or presence of luteal tissue. This is an approach endorsed and followed by the author.
Endometritis – or, more accurately, purulent vaginal disease – is a common and frequently underdiagnosed condition affecting many cows post‑calving. Over the years some quite contradictory information has been available regarding the role of prostaglandins or intrauterine antibiosis in the therapy and recovery from endometritis, and ongoing fertility. Both approaches are ultimately justifiable.
One recent study, however, looked at extending the duration of antibiosis beyond the “clinical” cure usually achieved with a single infusion. A second infusion of antibiotics 14 days subsequent to the initial treatment at diagnosis was shown to increase conception rate at first AI from 28% to 38.8%9. As much as this would increase antibiotic usage on farm, this is justified given the significant increase in treatment response.
This article has given a whistle‑stop review of recent research, which, in the light of current UK dairy vet practices, could be incorporated into fertility control programmes to increase fertility performance and then financial returns for our clients.
