The replacement index, and particularly the benefits of five-star cows, has been a topic of debate in recent weeks with the re-opening of the Beef Data and Genomics Programme (BDGP).

At a recent beef breeding information evening, held in Carnew Mart, Teagasc’s Noirin McHugh highlighted some of the benefits of using five-star cows over one-star cows.

She explained: “The replacement index is a selection tool that a lot of farmers are using to breed heifers”.

To make clear the differences in performance between five-star and one-star cows to the farmers in attendance, she discussed the findings of research work carried out by Teagasc and the ICBF.

“We looked at 46 spring-calving commercial herds that had good information already feeding into ICBF through HerdPlus.

“The 46 herds were enrolled in a weight and recording initiative that was a joint programme between the ICBF and Teagasc.

We wanted to compare the cow’s replacement index value to the performance of the cow and the calf she produced.

Under the study, the performance of a number of traits was examined. These included fertility, survival and production traits and the star rating of each heifer was collected from the point of first mating.

This, McHugh said, mirrored that action of farmers going out to select heifers based on their star ratings from marts or from within their own herd.

In total, the study looked at the performance of 6,000 heifers, with the star rating of each heifer gathered at the point of breeding.

Calving age and interval

McHugh discussed the key differences found in the performance of five-star and one-star cows.

“The first trait we examined was age of first calving and we found that the five-star heifers calved down almost 40 days earlier than the one-star group, even though they were managed under similar conditions.

“We then looked at calving interval and there was actually no difference between the five-star and one-star groups,” she added.

But, she said, this was likely down to the management of each individual herd and it clashes with findings from the Better Beef Farms programme.

“When we looked at the calving interval on the Better Beef Farms, we found that five-star cows had a 10-day shorter calving interval than one-star cows,” she added.


The study also looked at how many of these heifers survived within the herd to produce a calf the following spring.

“We found that 8% more of the five-star cows lasted that extra year – they were giving the farmers that additional calf.

“In the case of a 50-cow herd, that’s an extra four cows that wouldn’t have to be culled at the end of the season.

There is a massive financial benefit for farmers if they can select five-star cows because they are lasting longer within the herd.

“We also saw that they were surviving longer, that obviously meant that they were having more calves over their lifetime.

“In terms of the five-star cows, they were producing 3.8 calves on average over their lifetime, whereas their one-star counterparts where back at 3.5.

“A number of these cows are still alive and we will find that the number of calves that these cows produce will increase as we follow them over the next couple of years,” she said.

In addition, the study found that five-star cows were lighter.

“They were actually 50kg lighter on average than the one-star cows. This is beneficial from a maintenance point of view.

Even though the five-star cows are lighter, they are still producing a lot more product for you – in terms of the weaning weight of their calves.

“The one-star cows were only weaning 37% of their live weight, whereas the five-star were up at 45%.

“Again they (five-star cows) are much more efficient animals, it’s not costing you as much to feed her and she is producing a much better weanling for you,” the Teagasc researcher added.

Calf traits

McHugh also discussed the differences in performance between the progeny of five-star and one-star cows.

The progeny from five-star cows were 42kg heavier at weaning. This is a massive benefit straightaway. You have a weanling that’s 312kg versus one that’s back at approximately 270kg.

“A lot of that additional weight gain has been driven from milk, so it’s free extra production,” she said.

The Teagasc researcher added that there was very little difference in the age of slaughter between progeny of five-star and one-star cows.

“They were all slaughtered at about 20 months-of-age, but there was a 10kg difference in carcass weight between the progeny of five-star and one-star cows.

“The progeny of the five-star cows yielded a superior carcass; we were getting an extra 10kg of carcass of the progeny produced from five-star cows,” she added.


McHugh also discussed the mortality rates (28-day mortality rate) and what impact the cows’ star rating had on this important trait.

“There was less mortality, up to 28 days, in the progeny of five-star cows. There were 4% fewer dead calves.

“In a 50-cow herd, that would be an extra two live calves on the ground from a five-star herd compared to a one-star herd.

“A lot of this was probably coming because less cows needed assistance at the point of calving – they had lower calving difficulties,” she said.