12 Apr 2023
Emma Fishbourne
Job Title
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Oestrus synchronisation programmes can be very useful in cattle practice as they allow the use of fixed time AI (FTAI), eliminating the need for oestrus detection. They can also be used in embryo transfer programmes to prepare donors and recipients.
Synchronisation programmes use hormones over a period of time to enable AI on a known date and time.
Improvements in our understanding of the bovine oestrous cycle and follicular dynamics has led to improvements in synchronisation programmes. Traditionally, programmes were mainly used in heifers due to poorer conception rates, but are now used more widely in cows in both the dairy and beef sectors, facilitating more widespread use of AI.
Synchronisation can be achieved using prostaglandins to induce luteolysis of a corpus luteum (CL), gonadotrophin-releasing hormone to either ovulate a dominant follicle or recruit a new follicular wave, or progesterone in the form of a vaginal insert, which mimics the activity of a CL.
In high-producing dairy cows subjected to FTAI protocols, suboptimal concentrations of progesterone during the development of the ovulatory follicle appears to be a major impediment for fertility (Wiltbank et al, 2014).
Circulating concentration of progesterone is determined by a balance between production from the CL and metabolism by the liver determined by liver blood flow, which is increased in these animals. FTAI protocols increase progesterone by increasing the number of CL or supplementing with exogenous progesterone. Wiltbank et al (2014) reviewed the literature on progesterone and fertility, concluding that increasing progesterone before AI increased pregnancy per AI and reduced twinning.
Pregnancy risk per AI in various FTAI protocols in dairy cows ranges from 28.4% to 49.7% and in dairy heifers from 29% to 61.7% (Lindley et al, 2021). As a comparison, pregnancy rates to observed oestrus after first service in the late 1990s was 40% (Stevenson, 2005).
A recent study (Fricke and Wiltbank, 2022) reviewed seven randomised, controlled experiments that compared pregnancies per AI of cows inseminated after a detected oestrus to that of cows receiving FTAI after submission to presynch-ovsynch or double-ovsynch protocols, and concluded that the newest programmes gave more pregnancies per AI than cows served after a detected oestrus.
In a meta-analysis looking at progesterone supplementation in dairy cows during FTAI programmes, progesterone supplementation was found to increase pregnancy per AI and reduce the risk of pregnancy loss (Bisinotto et al, 2015).
McDougall (2010) concluded that inclusion of progesterone in the ovsynch-56 protocol resulted in earlier conception compared with ovsynch alone. In more recent studies, the addition of a second prostaglandin injection to the ovsynch and progesterone protocol in pasture-based dairy cows not detected in oestrus increased conception rates to first service, and the number of cows pregnant after the start of mating at three and six weeks (McDougall et al, 2021).
Heifers have different follicular wave physiology compared to cows, and so the ovsynch protocol is not recommended for them, as pregnancy rates tend to be lower compared to other protocols. McDougall et al (2013) evaluated three synchronisation protocols in pasture-based dairy heifers and concluded that the cosynch plus progesterone protocol resulted in the highest fertility.
An economic comparison of natural service and FTAI in dairy cattle in the US concluded that the advantage of FTAI depended on the cost to feed bulls, price of semen and the genetic merit of the semen being used.
In this study, using a voluntary waiting period of 80 days and a pregnancy rate (defined as the number of eligible cows that become pregnant in a 21-day period) of 18%, it was found that FTAI gave an advantage of US$37.87 (£31.15) over natural service (Lima et al, 2010). This, however, may not be the same in the UK due to higher drug costs.
AI in both beef and dairy herds presents a huge opportunity for improvement of a herd. In the UK, we can select for bull genetics based on estimated breeding values (EBVs) for beef or profitable lifetime index (£PLI) or calving indices for spring or autumn block calving herds for dairy cattle.
Beef EBVs provide information about carcase and maternal traits, and enable us to improve food conversion efficiency and weaning weights of calves per cow while selecting easy-calving sires. In all-year-round calving dairy herds, the £PLI is made up of several traits – each weighted by its relative economic performance – with milk production only accounting for a third, and two-thirds comprising of health, fertility, survival and efficiency traits. These indices and traits reflect demands from the industry and consumers, and aim to increase productivity and efficiency, and improve animal health and welfare.
Up to the 2000s, dairy genetic selection programmes selected predominantly for milk yield – often at the expense of fertility and health – but by starting to include traits such as longevity, calving interval and health, we have started to reverse some of these trends. Work is ongoing to identify fertility traits that have easily measured phenotypes or genomic markers that can be incorporated into breeding programmes (Crowe et al, 2018).
Using AI enables herds to select sires that would not be available or affordable if relying on natural service. Other benefits of AI include improved biosecurity and safety, as no need exists to have a bull present on the farm, reducing risks to staff handling bulls, avoiding any disease risks associated with buying animals in and reducing costs incurred from purchasing a bull and keeping it.
Bull fertility is also closely monitored at semen collection for AI, so no need exists for bull breeding soundness examinations or concerns of reduced fertility from an injured or ill bull.
AI also allows selection of different bulls for replacement heifers or for commercial beef production, and allows farms to use sex-sorted semen and select which animals they want to breed replacements from. This means genetic gain can be faster, as heifers can be selected to breed the next generation of heifer calves.
Reproductive efficiency is a key driver for profitability for both dairy (Esslemont and Kossaibati, 2002; Hudson, 2011) and beef enterprises (Lamb and Mercandante, 2016), and crucial for the sustainability of the cattle industry. Estimated financial losses due to poor fertility are as much as £100 per cow per year in a typical UK dairy herd (Hudson, 2011).
The aim in dairy enterprises is to achieve high 21-day pregnancy rates to reduce calving intervals and increase days in milk, while beef and block calving dairy enterprises need optimal calving intervals and heifers to calve down promptly in the block. The main reason cited for involuntary culling in Holstein-Friesian dairy cows is poor fertility – 27.4%, quoted in a study by Chiumia et al (2013), is similar to other studies.
For a cow to get pregnant using AI without synchronisation programmes, it must be detected to be in oestrus and inseminated, and it has to conceive.
Several factors affect the expression of oestrus, including surfaces of the floors, the presence of any feet or leg problems, housing arrangements and herd mate status. But the single biggest factor affecting oestrus detection is the person monitoring for oestrus behaviour.
Oestrus detection, usually measured as submission rate, is time-consuming and ideally must be carried out five times a day, with between 30% and 70% of cows in oestrus identified (Diskin and Sreenan, 2000). In dairy practice, it is widely accepted that the modern cow displays less overt signs of oestrus behaviour and for a reduced period of time, making accurate oestrus detection difficult. Oestrus detection with beef cattle out at grass is also problematic.
Using FTAI eliminates the requirement for oestrus detection and means that an animal at least has the opportunity to get pregnant, as enrolled cows will get submitted for service. This is very useful in herds with low submission rates, and facilitates optimal timing of insemination relative to ovulation to maximise the chances of a cow conceiving.
If an animal doesn’t conceive to first service then these animals can be monitored for returns and are more likely to be detected, as other animals will be in oestrus.
In beef herds, the advantage of FTAI is that it can make managing the herd easier with less handling required; for block calving herds (beef and dairy), it facilitates tighter calving patterns, which may make management and feeding easier.
In block calving systems, heifers can be synchronised to calve down at the start of the block and to calve by 24 months – this ensures they have the maximum time to get back in calf and stay in the herd, as well as breeding heifer replacements from them.
The success of FTAI protocols are affected by diet, breed composition, body condition, postpartum interval, climate and geographical location (Lamb et al, 2010). In beef cattle, a single unit increase in body conditions score (BCS) from poor BCS to adequate BCS gave a 23% increase in the proportion of cows pregnant to FTAI (Lamb et al, 2001).
The same study also showed that pregnancy rates were greater for cows calved more than 50 days before the onset of the breeding season. Others have also concluded that nutrition probably has the greatest influence on the success or failure of a synchronisation programme (Penny, 1998).
Not only must cows be in optimal body condition, but heifers must be of adequate bodyweight and age at commencement of breeding, with breeding occurring at a minimum of 55% of their mature bodyweight. This should ensure they have reached puberty and begun cycling.
Clients also need to ensure they have safe handling facilities – especially if handling beef animals out at pasture or heifers that might be away from the main farm. Good AI experience and technique is also required to avoid fatigue when serving lots of animals in a short space of time – especially if synchronising large groups – and major changes to management, such as mixing groups, should also be avoided.
Synchronisation programmes can either be used immediately a cow becomes eligible for breeding post-calving or used if a cow is not inseminated by some time defined after calving, but not as soon as it is eligible for breeding.
Research by Higgins et al (2013) explored the clinical and ethical beliefs of dairy practitioners, and their prescribing practices for hormones to manage dairy cow fertility.
The study considered hormones prescribed to adult lactating cows with no reproductive pathology and two ways of using them: oestrus induction and synchronisation programmes for FTAI.
This study found that more than 80% of practitioners agreed that hormones improve fertility and farm business profitability, but over a five-year period, practitioners felt if farmers tackled management issues contributing to poor oestrus expression, these outcomes would both improve (more than 80%) – potentially with a less favourable outcome for veterinary practice profitability, but with an improvement in genetic selection for fertility and overall cow welfare.
More than 90% of practitioners felt that hormone use was acceptable provided sufficient time had been allowed to elapse, during which the cows were observed for natural oestrus.
Conversely, 69% and 48% of practitioners felt that on farms making no effort to address underlying management issues, long-term use of hormones at the start of breeding for timed AI or for inducing oestrus, respectively, was unacceptable.
In the UK, the word “hormone” in the context of food production can have negative connotations to the public.
A study conducted in Germany found that the majority of people perceived reproductive technologies negatively. In total, 65% of people in the study perceived the use of hormones to increase fertility negatively and 53% viewed the use of sexed semen negatively. These figures are likely to be much higher today, as this study was conducted in 2012 (Pieper et al, 2016).
Clearly, a lot of benefits exist to using synchronisation programmes, and with careful planning, good results can be achieved with oestrus synchronisation and FTAI in both dairy and beef cattle.
However, given consumers’ concerns and increasing awareness, along with concerns from practitioners, perhaps we should ensure that hormones are only used in cattle without reproductive pathology once sufficient time has elapsed, with time allocated for natural observed oestrus. The exception may be block calving herds, where a need exists to front-load the block with heifers and beef herds out at pasture.
Vets need to help clients maximise the reproductive performance of their herds and further improve our understanding about the factors that affect fertility at the herd management level; for example, nutrition and individual cow factors, such as disease events and genetics.
Research has shown that both clinical and subclinical mastitis reduce reproductive performance, and that the effect can be exerted over a period of time (Hudson et al, 2012).
At an individual cow level, lameness zero to 28 days after insemination has been shown to reduce the odds of a re-insemination by 20%, as it affects the return to service oestrus detection (Remnant et al, 2019). Lameness has also been shown to shorten the period when herd mates attempt to mount lame cows and lower the intensity of oestrus expression (Walker et al, 2010).
Work by McNally et al (2014) classified cows as having negative energy balance, clinical lameness, uterine infection, anovulatory anoestrus, high somatic cell counts or as healthy, and showed that both anoestrus and healthy dairy cows were good responders to progesterone-based protocols in both oestrus response and conception rates.
They concluded that cows with more disease or physiological problems were not ideal candidates for synchronisation; therefore, vets should consider this when synchronising cows and make clients aware of the reduced response in this group of animals.
Various technologies can be used to aid oestrus detection, including tail paint, pressure-activated heat mounts, pedometers and vasectomised bulls with chin-ball marking harness, and if vets can help clients tackle management issues contributing to poor oestrus expression, they can become less reliant on synchronisation programmes.
Some programmes will still be required as discussed, and it is important consumers are educated to understand some of the breeding technologies routinely used, as they can make marked improvements for cattle health and welfare, and have an environmental impact with improved feed conversion efficiencies.
Vets need to help their clients to identify and tackle factors that affect fertility, and ensure that any oestrus synchronisation programme selected is suited to the cattle on that farm.
