8 October 1999

Its costly to cull

cows too quickly

Fertility may be an

increasing concern as cow

yields rise, but as

researchers try to unravel

this mystery, culling cows

for failing to conceive is

proving costly.

Jessica Buss reports

BALANCE the cost of delayed breeding against the cost of culling to assess how long to continue trying to get cows in calf. It may be worth continuing to serve them until 300 days after calving, depending on yield.

That was the message from Reading Universitys Dick Esslemont, speaking at a recent BSAS conference, Fertility in the High Producing Dairy Cow, in Galway, Republic of Ireland.

"Fertility is now being seen as a problem with lower profit levels, and high yielding, high merit cows are being delivered to farms that are not used to managing them. Their lactation curves would be flat if they were delivered feed to promote that." This and other factors, such as semen storage on farms, needed to be reviewed to try and reduce the decline in cow fertility, he said..

Bull semen fertility could also be poor and semen companies were getting away with selling those sires, he added.

Other factors that may be reducing cow fertility could include having fewer man hours a day available, giving less time for jobs such as heat detection.

On average, UK herds only managed to serve half the eligible cows during a heat cycle, the best achieved 80-90%, which in New Zealand would be seen as low. Tools, such as tail-paint and progesterone testing are available to improve submission rates, but are not taken up on farm, he said.

Nationally, the calving interval is increasing by one day a year, according to NMR figures. It is now 397 days.

But when considering what it really costs to cull cows, reducing failure to conceive culls to 7% was more important than achieving a 365 day calving interval, said Dr Esslemont.

"Some producers are wasting cows by culling for failure to conceive at a cost of £600-£700 a time."

Recent Kingshay Farming Trust research found that failing to conceive culls accounted for 14% of an average herd each year.

He estimated the typical cost of culling at £575 for a 6000-litre cow and £681 for a 10,000-litre cow, taking into account the cost of a replacement and lower margin achieved by a heifer.

The cost of keeping a cow with a longer calving interval also needed to be calculated to assess how long to continue to serve her, but there were many variables. These included the shape of lactation curve, milk price, quota cost, level of feeding and delay in herd calving pattern. There were also possible benefits such as fewer calvings, reducing disease risk.

Dr Esslemont estimated that initially each day the start of pregnancy is delayed, beyond the ideal 85-day period from calving, cost about £1.70 a day for both a 6000 and 10,000-litre cow. But this increased to £3.55 and £3.20 a day, respectively, for a delay in the start of pregnancy of 145 to 175 days after calving (see table).

These figures suggest a break-even of 270 to 300 days after calving, he said. "That gives about 10 cycles to get a cow pregnant, otherwise you have the cull costs as well. If those 10 cycles meant 10 services it would be excellent." But in practice average submission rates meant only five were likely on an average farm.

Producers who calculated this information for their own herds could draw a graph to find out at what point a cow must be pregnant – when the cost of keeping her outweighed the loss through culling. They could then make decisions on culling on an economic basis rather than on calving interval, he said.

FERTILITYCULLS

&#8226 Reduce to 7%.

&#8226 Calculate delayed breeding cost.

&#8226 Improve submission rate.

Cost of delayed breeding (£/day)

6000 10,000

litre litre

cow cow

Days from calving

86-100 days 1.73 1.68

101-115 days 2.30 1.68

116-145 days 2.86 2.47

146-175 days 3.55 3.20

176-205 days 3.87

206-235 days 4.08