AgResearch scientist Dr David Stevens says foetal aging might not give an exact birth date, but provides a good indication that is useful for planning and management.
AgResearch scientist Dr David Stevens said ram harnesses were a labour intensive method of determining which cycle ewes were mated, especially as ewe flocks had increased in size and farmers were often using more than one breed of ram.
Foetal aging involved taking a closer look at the foetus of lambs, calves or fawns at pregnancy scanning and using key growth indicators to estimate their age.
“The scanner is looking at how old the foetus is; that doesn’t necessarily determine gestation length.”
In deer, nutrition would accelerate or slow the development of the foetus, while sheep and cattle gestation lengths were less sensitive to feed, he said.
Foetal aging was more commonly used in dairying, but Stevens said sheep and deer farmers were starting to use the practice more extensively. In beef farming, it depended on the size of the operation.
“If they’re getting up to 1000 cows then certainly knowing when those calves are going to be born becomes quite important in your feed budget.”
When pregnancy scanning first became available it was not widely used because farmers could not see the benefits.
“We scanned for multiples, then triplets. It’s just another refinement of that process.
“There are definitely benefits in making sure they’re feeding animals at the right time.”
Foetal aging could indicate the spread of lambing, calving or fawning, so farmers would have some idea of how many new-borns would be on the ground at various times. Having that information could then help them work out what happened at mating to spread lambing out so far, so that could be avoided next season, or why it was so nicely condensed and how they could achieve that again.
AgResearch scientist Dr Geoff Asher is project leader for the deer industry venison supply systems programme. He said that between 30 and 70 days the rate of development in the deer foetus was fairly standard.
To age the foetus, the scanner looked at size, head shape, whether a heartbeat could be seen and development of limbs and bones. This could be used to calculate conception date and estimate when calving may occur.
Similar principles applied in other species and accuracy was usually plus or minus five days.
Veterinarian Ivan Holloway, of Vetlife Oamaru, works mainly with dairy cows, but said foetal aging was becoming more popular with other farmers who might want less specific information than dairy farmers.
For example, a beef farmer might want foetal aging information so they could sell their late cows or know which ones were likely to calve at the end of calving.
Holloway could usually pregnancy scan 200 dairy cows an hour. Foetal aging would reduce that to 100 at the most.