Being a predominantly grass-based system, many farmers calve cows down in spring to best utilise grass, matching peak grass growth with peak yield.

The six-week calving rate is often cited as a key performance indicator (KPI) on Irish Cattle Breeding Federation (ICBF) reports, particularly for dairy farmers.

Days in milk is a key driver of milk solids and where cows are routinely dried off before the Christmas break, late April- or May-calving cows will typically see a reduction in days of milk of 40 to 60 days or, to put it in to context, a May-calving cow will typically yield 100kg of milk solids less than a February calver.

Health risks

Cows being dried of in December with a dry period of three-plus months will be susceptible to more health risks.

A longer dry period leaves cows more prone to lay down fat, both in the udder (impeding milk yield potential) and body fat, leaving them more prone to calving difficulty, milk fever and displaced abomasums.

Removing the bull or stopping AI on 20 July will see all cows calved before 1 May (based on a 283-day gestation).

Where farmers are using continental or longer-gestation bulls, gestation length is likely to creep closer to 290 days, meaning breeding with these bulls would need to stop this week.

Switch sire

An option is to switch sire choice, either by using a shorter-gestation stock bull or a shorter-gestation AI bull.

Using longer-gestation bulls will also result in larger, harder calvings, which may result in an already late-calving cow being slow to come back into heat come breeding time.

Completing the above should help ensure that you haven’t an AI gun in one hand and a calving jack in the other come May 2023.

Farmers who do not typically dry off may choose to continue milking late calvers and ‘recycling’ them.

Again, the longer dry period leads to health issues and milk yield loss, and recycled cows generally have poor fertility and farmers will see them slip back in to the late-calving bracket the subsequent year.