Seven interesting facts about gestation length
With calving well underway, farmers will be noticing the actual arrival date of their calves compared to the expected arrival date.
While many will be arriving on or close to their due dates, some may be quite a few days either side of when they were expected. This could have a lot to do with the gestation length breeding values (BV) of the animals you used for mating.
Here are seven interesting facts about gestation length from a recent study of 58,000 animals (Donkersloot, 2014):
1. Gestation length is highly heritable
It explains about 52% of the genetic variation in birth date for calves.
That’s why we’ve been able to target it successfully at LIC and why we report the figure for farmers to use if this is a priority for them.
2. There is a natural distribution around expected due date
95% of calves will be born within ±9 days of their expected calving date. This applies to both normal and shorter gestation length sires, although sires selected on gestation length may have a slightly tighter calving pattern around due date.
Practically this means if 100 heifers are expected to calve on 20 March, 95 of them should calve between 11 and 29 March. The other five heifers are expected to calve outside of this window.
3. Calf gender influences gestation length
Heifer calves are born about one day earlier than bull calves. Averages in the study were:
• 282.7 days for bull calves
• 281.2 days for heifer calves
4. Twins are born about six days earlier than singletons
5. Age effects gestation length
Gestation length is about one day shorter for first-calvers than second-calving cows.
6. Different breeds have different gestation lengths
On average for NZ genetics, crossbreds have the shortest gestation length and Jerseys the longest. In 2016, the New Zealand average gestation length breeding value (BV) of herd tested cows of various breeds was:
• -1.3 days for Friesian cows
• -1.5 days for Kiwicross cows
• -0.9 days for Jersey cows
7. Gestation length is getting shorter
The gestation length of New Zealand’s genetic base cow – the average of 21,585 cows born in the year 2005 – was 281 days. By July 2016, the average gestation length of all herd-tested cows in New Zealand was 1.3 days shorter.
Cows and bulls with negative gestation length BV pass these onto their calves. Over time, this will result in a shorter gestation length across your herd. This gives you more days in milk, and your cows more time to recover before mating starts.
There are a couple of short gestation length (SGL) options that can help deliver these benefits to your herd:
SGL + Breeding Worth
Reduce gestation length and get offspring with high genetic merit that you can keep as replacements and breed from. For example, promising new bull Tirohanga Take Note has a gestation length BV of -10.6 days as well as great breeding worth.
A cost effective way to get cows in-calf late in mating and reduce gestation length down to 9 days. These beef bulls breed white-faced offspring that you can easily identify in the herd.
Contact your LIC representative for more information on gestation length.