Breeding replacements became a simple strategy that focused only on the most fertile cows at the front of the block to create a 12-week calving spread.
But as herds have successfully repeated their compact calving pattern, there has been a turnaround.
LIC farm consultant Piers Badnell reckons 50-75 percent of the spring-calving herds he works with are now back milk recording.
In part, this has been driven by milk buyers requiring tests for Johne’s control and cell count data for selective use of antibiotics at drying off.
The move has also been helped by the launch of more flexible services to suit grazing herds.
In addition, milk recording has now become a source of useful data.
Analysis finds the best performing animals in the herd to breed the next generation of heifers, and the focus has shifted somewhat to include both fertility and productivity.
Grass-based systems
Piers explains that productivity matters in a grass-based system because the limiting factor is how much grass can be grown.
This determines stocking rates and restricts herd size, unless grass yield can be improved, or more expensive purchased feed is brought onto the farm.
“If land area is the limiting factor, you need to find the most productive and efficient cows in your herd to breed from, because it is not profitable to buy in lots of feed,” he says.
However, cows also need to be weighed to calculate production efficiency, he points out.
Efficiency is expressed in kilograms of milk solids (MS) as a percentage of mature cow weight and worked out on an individual cow basis.
“This is about how much feed a cow converts into MS yield. The most efficient animal is 1:1 MS production to mature cow bodyweight.
“For instance, a mature cow giving 313kg MS, calving on day one of the block, will have brilliant fertility, but will not be a particularly efficient cow for her size.”
Piers adds that milk records can flag up how looks can be deceptive.
“A herd that looks uniform can have a range of cows with varying body depth and frame strength. One farm we worked with had an average mature liveweight of 543kg, but the range was 417kg to 736kg.
“So be aware that an ‘average’ always has a range,” he explains (see case study).
Sexed semen
As with any biological measure, whether it is height, weight or yield, he points out the results will always form a bell-shaped curve, so a range of values will be natural for every dairy herd.
“Over time, through breeding, it is possible to move the whole bell curve to the right by dropping the bottom cows out.”
Sexed semen is helping this process, with only the most efficient cows, in the first three weeks of calving (to ensure that heifers are as close in age as possible) bred to dairy sexed semen.
Equally fertile (yet lower-yielding) cows can be served with beef sires.
“It means you don’t have to serve so many animals, so you can be more selective and you may breed to dairy for three and a half weeks,” explains Piers.
“Herds culling because of TB or Johne’s control will slow production and genetic progress, which makes it even more important to serve the right cows as there is a smaller pool to select from.”
SOURCE: Farmers Weekly
