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Fertility trumps milk potential

Breeding programmes for next year's spring calving begin this month. The primary focus is compact calving, centred on milk production -- primarily from grazed grass.

The question of what criteria to use when choosing bulls can be a heated one. One of the most divisive issues is the ever increasing weighting given to the ICBF's fertility index in a bull or cow's EBI. This is often derided by owners of high production herds as being unnecessarily harsh on animals that have otherwise good production potential.

However, when I contacted Dr Donagh Berry, of Teagasc, he was adamant that the fertility index deserved the weighting it received. In addition, he believes that the index is as important for the high production farmer as the low input operator.

There is a psycological block that farmers have to overcome in thinking about this. For years, they have been told that the aim was to increase genetic merit for milk production.

This was all well and good in the days of cheap meal, high milk prices and poorly developed grazing systems.

In modern grass-based milk production systems, where the primary focus is milk production from grazed grass with minimal input of supplements, it is often not economical to fed a cow enough simply so that fulfills her genetic potential to produce milk.

There are other reasons why chasing higher milk volumes doesn't add up these days. Payment systems have evolved to the point that they reward the farmer more for the solids in their milk than the actual litres that they are selling.

However, picking the best bulls in a dairy herd to increase solids yield can only be determined by examining the HerdPlus reports.

This overcomes a scenario where a bull that is say +10kg for kilos of fat and protein is a good choice for a herd whose average genetic merit in the HerdPlus report is +5kg, but a retrograde step for a herd that already has a genetic index for milk solids of +12kg.

A third reason for placing less emphasis on the extra milk that a bull's index has is the fact that fertility will actually have a bigger impact on the amount of efficient litres your herd produces than milk volumes.

This is the point in this conversation that high production herd-owners often begin to see red.

But the fact is that cows that go in-calf quickly calve earlier and end up producing more milk from low-cost grass.

The ability to pull back calving dates can only be achieved if a herd has good genetic merit for fertility.

We are already seeing progress in this regard with a large increase in the number of calves registered in the early weeks of the calving season this year. It will result not only in cheaper milk but also longer lactations.

Another under-utilised genetic merit statistic to increase milk yield profitably is gestation length of the bull. Shorter gestation-length bulls, assuming they have respectable figures for the other key traits, can quickly provide extra days in milk and therefore greater milk yields.

This oft-forgotten trait is especially relevant for beef bulls used later in the breeding programme. These later calving cows have a limited opportunity to successfully establish pregnancy in a grass-based milk production system. The smaller calves that these types of bulls tend to throw will minimise calving difficulty and help the womb heal quicker post calving. This will enhance the window of opportunity to establish pregnancy.

So short-gestation bulls have the potential to not only increase the days in milk, but also reduce calving to pregnancy intervals.

However, there is a draw-back. Shorter gestation bulls have been associated with a higher incidence of dead calves at birth. But this increased perinatal mortality is accounted for in the EBI calculations to help counteract this.

The final reason why fertility counts so much is that cow survival is intricately dependent it. Mature cows will produce around 25pc more than a first lactation cow.

Assuming an average heifer yield of 5,000kg, average cow milk yield can be increased by 63kg per cow by reducing replacement rate from 25pc to 20pc, without any other genetic gain. This equates to an extra cow in a 100-cow herd.

So think twice when choosing a bull based on his superior milk production figures. Half the bulls on the ICBF active bull list have higher genetic merits for milk production than the average of +116kg for the Irish dairy herd. But that doesn't mean that they all deserve to be used.

The EBI is designed to take the guess work out of this huge selection for you, without having to be an expert on genetics.

Even though fertility now seems to be improving nationally, it is still far from optimum.

Reverting to the old practice of selecting aggressively for milk production without taking account of fertility traits reduce profitability in grass-based milk production systems.

Dr Dan Ryan is a breeding management consultant and can be contacted at www.cows365.ie

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