High replacement rates can damage a herd's bottom line

Published 5 April 10

Most dairy farmers are fully aware of the importance of achieving a low herd replacement rate, yet often fail to address this properly when making breeding decisions. Now, two sets of research throw new light on its financial value and highlight the tools to be used to breed a long-living cow.

The difference between a good and a bad replacement rate can mean as much as £20,000 to a typical 150 head dairy herd, yet many farmers are failing to use tools at their disposal to produce longer lasting cows.

This figure, derived from work undertaken by Kingshay, reflects all of the input costs incurred when rearing a heifer, which - for a typical herd calving at two and a half years - amounts to £1,192 per head (see table 1).

Multiply this up by different replacement rates and it's clear that a herd with a high replacement rate of 30 percent, is spending almost £40,000 on bringing new heifers into the herd, compared with a herd replacing at 15 percent, whose replacement costs are around £20,000.

These figures will be even higher if heifers are purchased rather than reared (which also comes with the added danger of bringing disease into the herd), and the cost will increase further still as age at first calving goes up.

There are many things which can be done to reduce the cost of replacement according to Kathryn Buckland, farm services manager with Kingshay, who says that a key focus of management attention should be on age at first calving.

"Reducing the age at first calving to two years reduces the cost of rearing a heifer to £982," says Miss Buckland, "while increasing the age to three years will raise the rearing cost to £1,247."

This inevitably means there's a longer payback period as age at first calving goes up, which - for Kingshay-costed herds - works out at 2.4, 2.9 and 3.1 lactations respectively for two, two and a half and three year calving heifers.

Once in the milking herd, there's a whole raft of actions which can be taken to prolong the cow's life, ranging from regular foot trimming and mobility scoring to spotting cows bulling and getting them in calf.

"In a lot of the best herds, it's not one thing that makes the difference but lots of small things that come together and constitute good management practice," says Miss Buckland. "And we have noticed through our herd health survey that a number of producers with a high culling rate have low vet and med costs and will tend to cull, with less focus on preventative actions.

"These are the herds with the fire fighting approach, compared to those with the higher vet and med costs, who invest in preventative treatment, often vaccinate for a range of diseases and have a lower culling rate."

But in reality, the process of achieving a low replacement rate should begin before conception, and Miss Buckland believes that breeding the right kind of cow can have a significant impact on lifespan.

Breeding specialist Marco Winters, from DairyCo breeding+ concurs, and says there are many features of the cow which have become associated with longevity.

"Most farmers would agree that there are some traits which tend to improve longevity although they may argue over whether that's a well attached udder, a low cell count, good feet and legs, a robust frame or an ability to get in calf," he says.

But with modern breeding tools, the answer to this conundrum is presented on a plate, as an easy-to-use genetic index that takes the guesswork away.

"We have been publishing Lifespan indexes for Holstein bulls since the late '90s, and these are calculated for proven bulls from actual daughter survival," say Mr Winters. (See Lifespan index box.)

"So, rather than second guess how long a bull's daughters are likely to live by considering other traits, it makes far more sense to look at the trait itself, if you are trying to improve the longevity of you herd.

"Breeders often think that if they select on type, they will also get longevity, but this is not necessarily true; it only gives you part of the picture, and the Lifespan index itself is a far more powerful tool if you want to breed a long-living cow.

"In a nutshell, type indexes tell you about the structure of the cow and Lifespan index tells you how long she is expected to last.

"Of course, as with any genetic index, it's the average across all daughters that's being predicted, which means there will inevitably be exceptions which stray from this norm."

However, in spite of the industry's growing confidence in Lifespan indexes, it is probably true to say that they haven't captured the farmer's imagination in quite the same way as the other health and fitness indexes such as SCC or, more recently, Fertility index.

"This is probably because there's a more immediate or obvious financial penalty from failing to breed for, say, SCC or Fertility index, whereas Lifespan index may seem nebulous, only of long-term interest, and not immediately associated with a significant financial gain," says Mr Winters.

"But the work at Kingshay highlights how wrong this argument is and just how much money can be added to a business's bottom line by breeding long-life cows."

And although Mr Winters accepts that herdlife and replacement rates are strongly influenced by management, he explains how work recently undertaken by DairyCo breeding+ highlights the importance of breeding in terms of actual daughter survival on British farms.

Graph one clearly illustrates this point, showing that the highest Lifespan index bulls have a much stronger performance in average daughter survival, with almost 40 percent reaching their fifth lactation, while for the worst LS bulls, only around 20 percent reach the same stage.

"It's clear from the graph that the impact of the good Lifespan index bulls really begins to be felt later on in life," says Mr Winters. "This may not sound surprising, and when we looked at average herd performance it clearly suggests that it is only those cows with the good lifespan traits that are able to survive and escape 'involuntary' culling in the early lactations due, for example, to high somatic cell count or infertility.

"A closer analysis of the same dataset gave some indication of the sort of cows that were leaving the herd at the different stages," continues Mr Winters. "Clearly many different reasons come into play, but when we focus on the most prominent genetic factors it shows that those culled in lactation one tend to be bred by bulls with the lowest milk PTAs [Predicted Transmitting Abilities]; those leaving in lactation two represented a group with poorer SCC indexes and those leaving as third calvers were, on average, worse for fertility.

"However, those that survived into their fifth lactations and potentially beyond, were, on average, daughters of bulls with notably better indexes for Lifespan of course, but also the other fitness traits of SCC, Fertility and maternal Calving Ease. And the one index which very consistently went up within the groups of increasing age was Profitable Lifetime Index [PLI]."

This is good news for an industry which is increasingly adopting PLI as its primary selection criterion, but begs the question of whether breeders should stick to breeding for PLI alone or select on their choice of its individual components.

"We'd always recommend that PLI is used as a primary screening tool," says Mr Winters, "but a herd with a particular problem may do well to also focus on one of its components.

"This could be Lifespan for a herd wishing to improve replacement rates, or other health and fitness traits such as cell counts, feet and legs, or udders, which together make up 55 percent of the overall PLI figure. But it's always important to remember that it's not difficult to make genetic progress by concentrating on any one of these areas, but too much emphasis on one trait will almost always be at the expense of others.

"Production will always be among the main commercial drivers, but if it is not selected for as part of a balanced breeding strategy which ensures longer herdlife, lower cell counts and better overall health and fitness, that production will come at too great a cost to the cow and to the bottom line."

Table 1: Replacement costs for a typical 150 cow herd at four replacement rates

Herd size





Replacement rate %





Cull cow cost
(per head)





Heifer rearing cost
(per head)





Replacement cost
(per cow)





Total cost






The Lifespan index (LS)

A bull's Lifespan index is expressed on a scale of around -0.5 to +0.5 and provides an indication of the number of extra lactations his daughters, on average, are predicted to survive. In other words, daughters of a bull with a +0.5 LS are expected to live half a lactation longer than daughters of a bull whose LS index is zero. Similarly, the +0.5 bull's daughters should live a whole lactation longer than daughters of a bull whose LS index is -0.5.

LS indexes are calculated from actual daughter survival when that information is available. When it is not - as in the case of young bulls - information on type (feet, legs and udder), cell count and family is used to make the best possible predictions of lifespan. The choice of traits used in this prediction is based on extensive research using many years of cow records which have indicated which traits are most strongly related to survival.

The article was originally produced for Dairy Farmer, April 2010.