New research reveals what the optimum age at first calving is

There are many different opinions out there on what the age at first calving should or shouldn’t be. Although the optimum age at first calving to increase profitability – according to Teagasc – is 22-26 months of age.

To prove this, the Irish Cattle Breeding Federation’s (ICBF’s) Susan Moriarty recently completed a study on the optimum age at first calving.

The objective of her study was to investigate the relationship between age at first calving on milk production and survival in dairy heifers.

The study began in 2014 so that five lactations could be assessed. All the heifers involved came from spring-calving dairy herds and 90% of the herd had to calve between January and June.

Also, 305-day milk figures were used to compare like with like in milk production.

Four different age groups were assessed, which included:
  • Less than 22 months (but no younger than 20 months);
  • 22-26 months;
  • 27-32 months;
  • And greater than 32 months (but not over 40 months).

The total number of animals included in the study was 160,334. As there were only 950 animals in the under 22 months category, these were not used in the research.

The findings

Milk production

In the graph (below) you can see that the 27-32 month category surpassed the other two categories in parity one, three and five.

This, Susan said can be related to the fact they are older when first calved, therefore carrying more weight, thus having the ability to produce more milk.

Image source: ICBF

Whereas the greater than 32-month category did not surpass the 27-32 month category.

Likewise, she explained that this is because older heifers can develop fatty udders before they eventually calve down and this will impact their milk production for the rest of their lives resulting in suppressed yields.

National survival statistics

The 22-26 month category had the highest percentage of animals surviving to each parity.

For example, 30% of animals from the optimum age category survived to parity six, in comparison to 11% of the 27-32 month category.

Image source: ICBF

The graph (above) also shows a significant drop and a lower number of animals surviving in the two older age categories.

Production difference between the three

When survival and milk production are looked at together, there is a different outcome for which age category produces more.

The graph (below) shows that in parity one at 22-26 months, milk production is less than the other two categories.

However, what is most interesting, is that by the end of parity two the 22-26 month group surpassed the other two categories and by parity four and five it significantly surpassed both.

Image source: ICBF

In essence, first lactation milk was lower, but lifetime milk yield was significantly increased.

When Susan looked at it in terms of profitability; at the end of parity one, the 32-month category produced 240kg additional milk, 3kg additional fat and 6kg additional protein than the 22-26 month category.

However, at the end of parity 4, the 22-26 month category produced 862kg additional milk, 38kg additional fat and 33kg additional protein than the 32-month category.

She applied an average milk price of 30.5c/l to get the net value of production and a €0.04 milk yield penalty, €3.637/kg fat bonus and €6.183/kg protein bonus to get the total net outcome for each group.

She discovered that the difference in net outcome between the two was €307/cow. If this occurred in a 100 cow herd it would equate to a loss of €30,700 – by not calving heifers between 22-26 months.

The number of heifers calving at 22-26 months has increased, but there is a long way to go. In 2015, according to the ICBF, only 70% calved between 22-26 months.

To conclude, she said: “Minimising the number of replacements to rear, as well as only identifying the most reproductively efficient heifers, is essential to avoid unnecessary economic losses.

Sustainability is also improved as a lower age at first calving results in cows lasting longer in the herd, therefore reducing the replacement rate.

“Also, calving heifers earlier prevents additional unwanted methane than older calving heifers produce.”