Ovulating in synchrony

Smart technology has its role in the quest for improved in-calf rates and so do staff, says Waikato clinical veterinarian Scott McDougall, of the animal health research organisation Cognosco. By Elaine Fisher.

“Never underestimate the value of well-trained, motivated human beings when it comes to understanding when cows are cycling.”

Scott McDougall acknowledges that with increasing herd sizes, staffing issues and new entrants to the industry, there is huge pressure on senior people on farms to get cows in calf, which is where technology which helps save labour and provides useful information comes into play.

However, there is no silver bullet, and no one solution to improving in-calf rates across all New Zealand farms as the factors which influence cow conception are complex and variable.

“There are opportunities from improving in-calf rates. Currently about one quarter of New Zealand dairy herds achieve a six-week in-calf rate of 73% but among the other three-quarters of the herds, there is room for improvement.”

The 2019-2020 national average six week in-calf rate was 67.8% up from 67.5% the previous year, but still well below the industry target of 78%.

“One of the best tools to help identify why six-week in-calf rates are not as high as they should be is DairyNZ’s InCalf programme which guides farmers through herd management in a structured way to ensure nothing is missed.

“It can be overwhelming if empty rates are high, and farmers feel they don’t know where to start. That’s where the InCalf process and talking to a vet or farm adviser they trust can help work through the issues.

“It requires taking a hard look and doing an honest appraisal of herd management. Acknowledge the areas where you are doing a great job, but the best bang for the buck will be focusing on those areas which are not going so well.”

Synchrony programmes are an important tool, but Scott says synchronisation in and of itself is generally not the solution to poor reproduction outcomes, if for example the heifers are poorly grown, there is poor nutrition or other animal health issues.

“It is not a band aid but is one of the tools farmers have to improve performance.”

Research into synchronisation of beef and dairy herds has been going on for the last 70 years with the result that today there is far better understanding of cow physiology, hormone levels and how ovaries, the uterus and brain interact.

That knowledge, along with advances in diagnostic techniques, has led to incremental gains from treatment programmes over time.

“In the past 20 years our basic understanding of how follicle waves work has also improved. We now know that every 10 days or so a new group of follicles form on an ovary with one becoming the dominant follicle which at the end of the cycle will go on to ovulate.”

When a cow ovulates, the site of ovulation develops a structure known as a corpus hemorrhagicum, which within four to seven days develops into a corpus luteum (CL), a mass of cells that forms in an ovary and is responsible for the production of the hormone progesterone during pregnancy. The role of the corpus luteum can influence whether or not the embryo survives.

“In a synchronisation programme we need to control the follicle waves, so the modern programmes are built around understanding how the hormone system, follicles and corpus luteum work. Using natural hormones to mimic the normal oestrus cycle of a cow allows us to predict when she will ovulate and the best time to inseminate.”

Gonadotropin-releasing hormone, or GnRH, is a key hormone used in synchrony programmes. It is a hormone made in a part of the cow’s brain that acts to release more luteinizing hormone (LH) and follicle-stimulating hormone (FSH) vital for successful follicular development and ovulation

in the ovary. Another key hormone is prostaglandin F2 alpha which removes the corpus luteum (“luteolysis”) allowing the dominant follicle to develop through to ovulation.

While synchronisation works on about 85% of cows, 10 to 15% fail to undergo luteolysis and hence fail to ovulate at the end of the programme. To address this Scott says the recommendation has been to increase the dose or give two treatments of prostaglandin one day apart.

“The latter strategy is a biologically better way to go and achieves a better response but does mean an extra yarding and cost, but leads to a 5% increase in conception rate and a 4% increase in six-week in-calf rate, so it is worth the effort.”

Modern synchronisation programmes mean that now it is possible to know precisely when a cow will ovulate and based on that, make decisions when to inseminate without relying on oestrous detection. “This works well in beef and dairy cows, even those which are not cycling.”

Scott says other research is highlighting the impact of genetics in reproductive performance.

“The Irish and Scandinavian industries, and more recently New Zealand, have put increased emphasis on reproduction in the breeding objectives with resultant improvements in in-calf rates.”

DairyNZ has carried out research into Fertility Breeding Value (BV) to identify new traits. The work centred on a unique herd of 550 heifers with high (+5%) and low (-5%) Fertility BV. Their fertility and other traits were studied during rearing (2015-17) and their first (2017-18) and second (2018-19) lactations.

A key finding was that animals that reach puberty at a younger age and at a lighter body weight were more fertile. A much larger DairyNZ study validating the results of that study is underway with Cognosco and other groups involved in assessing the long-term effects of age of puberty on fertility.

“Over time more precise measurements earlier in animals’ lives should improve the ability to select animals with high fertility which will bring long term positive benefits for the industry.”