The result of contract matings, the calves which were born within weeks of each other, have been collected at about a week old to be reared together on a farm
in Waikato.
The sires and dams of half the calves have high-fertility genetic traits and the other half are low fertility. DNA testing will be used to confirm parentage.
All the calves are Friesian because the breed has the largest genetic variation
for fertility in New Zealand so extreme high and low-fertility traits can be
studied.
The seven-year programme, The Pillars of a Sustainable Dairy System, will also look at lifetime productivity and is jointly funded by DairyNZ and the Ministry of Business, Innovation and Employment with aligned funding from AgResearch.
Numerous experts from other research institutions and industry organisations are involved in the DairyNZ-led programme including Peter Amer from Dunedin-based AbacusBio who said the work would show how robust the current animal evaluation model for fertility was and hopefully improve it.
“The fertility traits used in NZ’s animal evaluation model have a very low heritability. Less than 5% of variation can be explained by genetics compared to milk production traits at 25%,” Amer said.
“But that could be because all the national information we have on the fertility of dairy cows in NZ is only the submission dates and calving dates.
“There is so much other noise going on that we really don’t know what is happening, such as when is the cow cycling, is the heat strong enough for the farmer to detect, did conception happen and the embryo failed to develop or did the cow abort later on?
“They all are factors in whether and when a calf is born but we don’t know which ones are causing the high or low-fertility traits we see in the animal evaluation model.”
Nicola Dennis of AbacusBio said no one knew why daughters of some bulls were not reaching higher six-week in-calf rates, or why empty rates were so high, compared with the daughters of other bulls.
“The biology of fertility in a dairy cow is really opaque and by biology we mean the length of time for a cow to start cycling, whether the mating happens when there is a high-quality oocyte (egg) present, whether fertilisation happens, whether the embryo develops.”
She said farmers were often left guessing why their cows didn’t get in-calf and although good management practices, such as correct body condition scores for mating, were well-known, there were other factors that possibly could be improved on.
“If we can enhance the animal evaluation model for fertility then we can breed cows that are easier to farm. That’s the idea behind this study.”
Farmers won’t see results from this part of the study for several years because the calves born this spring will not be mated for the first time until next year and it will be the second mating that will be intensively looked at. However, some of the research is already changing the way scientists are thinking about fertility.
About 1200 cows on four Fonterra-owned farms in the North Island were flushed last year as part of the study to understand when conception fails and work is underway to repeat it this year in the September-October mating period.
The work is being led by AgResearch senior scientist Debbie Berg, of Hamilton, with support from the DairyNZ research team and embryo flushing specialists.
Cows last spring were flushed at either day eight or day 16 after being inseminated to assess whether conception had occurred.
“We were surprised to see that there was more chance of conception failure in the first week than in the second week,” Berg said.
“We thought it would be the second week when there were the most failures as there is a lot more happening with the biological process of conception.”
Many of the eggs flushed at day eight did not even appear to be fertilised, she said.
“These were tested further to see if they contained more than one type of DNA (one from the dam and one from the sire) which told us which ones had been fertilised. At day 16 scientists looked for a range of things such as appropriate growth for the age of the embryo, growth of the future placenta and whether there was any degradation of the developing embryo which would mean it was no longer viable.”
Berg said the findings could be a positive as early conception failure, rather than later failure, gave the cow more time to recover and cycle again.
“They may also inform future management strategies around how and when farmers could intervene to improve reproduction performance which would mean more days in-milk,” she said.
“We still don’t know why the pregnancy is failing but we needed to know the when before we can start finding out the why.”
AgResearch science team leader Sara Edwards, of Dunedin, said a study of this size had never been done anywhere in the world to her knowledge.
“Not with this many cows being flushed. It’s a first.
“We’ve known pregnancies are failing early on and now that we are starting to know when they are failing we can start looking at possible management practices to lessen the amount of failure so farmers can increase their six-week in-calf rate.”
The six-week target
Year-round management practices were needed to get a high percentage of cows in-calf in the first six weeks of mating, LIC reproductive solutions adviser Amy Frampton of Rangiora said at a seminar at SIDE at Lincoln in June.
“It’s not just about those six weeks of mating. It is about everything happening to your animals from heifer management, herd nutrition, genetics, cow health, the previous year’s calving spread as well as heat detection and dealing with non-cycling cows at mating time.”
The six-week in-calf rate, two cow oestrus cycles, is used as a marker of fertility instead of the empty rate because it’s more easily compared across herds since it isn’t affected by culling or the duration of mating. It is measured using figures from early pregnancy scanning that shows the accurate age of the foetus.
Developed by InCalf Australia, the New Zealand target of 78% in-calf in the first six weeks of mating has been set using information from the LIC Monitoring Fertility Project and is the average performance of the top quartile of farmers in the project study from 1998 to 2000.
In 2013 the national average six-week in-calf rate was 66% with little variation across regions, herd size, or system type.
Frampton said it was important for farmers to aim for a high six-week in-calf rate.
“It’s an important key performance indicator just like average milksolids per cow, farm working expenses, and peak milk stats.
“Analysis from the National Herd Fertility Study showed the top 25% of farms on the six-week in-calf rate got 15 more additional days in peak milk than the bottom 25% of farms.”
She said farmers needed to identify what was holding back their six-week in-calf rate.
“The areas we see most commonly onfarm having the biggest impact are body condition score, nutrition, heat detection and heifer management.
“But whatever is the problem, farmers need to critique and review what they are doing. Top performers are doing the basics consistently well.”
The top six-week in-calf rate herds had short returns (2-17 days) averaging at 18%, heat detection efficiency at 90%, herd submission rate at 86% for the first three weeks of AI, heifer submission rates at 87% in the first three weeks of AI and a six-week in-calf rate of first calvers of 76%.
For more information go to www.6weeks.co.nz
