Does your feed budgeting take variation in gestation length into account?
Traditionally, the cow’s standard 282 day gestation length has been used as the basis for predicting daily feed requirements post-calving and into mating – but there are significant fish-hooks to consider.
Take random acts of nature, for example.
“Setting up a feed plan strictly on a 282-day theory isn’t really workable and doesn’t reflect the realities,” says LIC’s Greg Hamill, genetics business manager.
When he was farming, Greg said he always began supplying the factory before his official planned start of calving date. In his observation, little had changed since that time.
“For many farmers, sending milk to the factory earlier than they anticipate happens year-in, year-out. That’s because 95% of calves are born in a window that ranges between -9 days or +9 days of the expected arrival date. In other words, say you’ve synchronised 100 heifers and their due date is 20 July. About 95 of those heifers will calve between 11 and 29 of July. Five could be expected to calve outside this window, some may be earlier, some later. Farmers are pragmatists, so they’ll be aware that simply calculating 282 days from mating isn’t going to cut it for proper feed budgeting these days.”
While it was true MINDA’s Expected Calving Reports were previously dependent on the national average 282-day gestation length to calculate a cow’s calving date (based on her mating date), this was no longer the case, Greg said.
Sire gestation length was incorporated into MINDA a few years ago, reflecting the individual bulls’ expected gestation length. More progress came last year, when cows’ individual gestation breeding values were added to the mix.
“With MINDA’s recent refinements, farmers aren’t relying on the 282-day national gestation length average – they’re dealing with information specific to their set of cows, together with the bulls those cows have been mated to. In short, MINDA reports are now reflecting case-by-case situation at the specific farm, or herd, level.”
Best practice among high-performing farmers was to coincide feed budgets with their herd’s Expected Calving Reports (available in MINDA).
Farmers now had the ability to better-predict what portion of cows were likely to calve before planned start of calving, allowing for more-precise feed budgeting.
Precise feed budgeting was particularly important for increasing numbers of farmers who were transitioning their cows from winter crops back to grass.
Interestingly, goalposts on a separate front were also shifting, albeit ever so slightly. On average, gestation length for the national herd has moved from 282 days to 281. This was perhaps largely explained by the influence of LIC’s top bulls, Greg said.
Among a handful of other important traits, many of LIC’s sires were carefully selected for shorter gestation breeding values, and their progeny continued to flow into the gene pool of the national dairy herd.
Currently, the team Breeding Value (BV) gestation length of LIC’s Premier Sires ranged between -2 to -5 days (individual sires range between -9 days and +4 days). Half a bull’s BV is expressed in the BV of his offspring.
“This is good news for farmers,” Greg said. “Every additional day a farmer gets in milk is more money in the pocket. The more days a cow is in milk, the more profitable she is.”
In general, farmers could expect to continue to supply the factory before their planned start of calving, but fewer surprises could be anticipated, and the risk of being ‘caught short’ would be reduced.
The more-aligned feed planning was to expected calvings, the better the season could be ‘set-up’ to capitalise on spring growth, weight gain, peak season, and better reproductive results.
Are my cows calving earlier each year?
Whether cows are calving earlier each year is not entirely dependent on gestation length, but when the planned start of calving (PSC) is. PSC dates have been getting earlier in the majority of regions over the last 15 years. See Figure 1.
Sire breeding values for gestation length are becoming slightly more negative over time.
Famers might consider the average gestation length BV of the bulls used over their own herd: If cows with negative gestation length breeding values are mated successfully to bulls with negative gestation length breeding values, the resulting heifers will also have negative gestation length breeding values. Slowly, the gestation length breeding value of herd is likely to become more negative, leading to shorter gestation lengths.
This shorter gestation length can be advantageous as it gives cows more time to recover from calving before mating starts, but it does mean that farmers need to ensure adequate feed is available on the milking platform for the early-calvers.