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Once-a-day Milking (OAD) is the practice of milking cows once during a 24 hour period. Most NZ Dairy farmers milk twice-a-day (TAD), although the numbers milking OAD is increasing. The OAD milking regime may be used exclusively as the overall farming system, or strategically for part of the herd or for shorter periods during the season.

For the past 10 years LIC has operated an OAD index, with calculations largely aligned to the-then small amount of OAD herd performance data to the much larger twice-a-day (TAD) data sets. The upshot of the maths was a set of predictions for OAD breeding values.

In June 2015 the above method at LIC was overhauled. After considerable consultation with the OAD community, LIC identified non-negotiable functional OAD traits that were essential to reducing wastage in OAD regimes.

The new index (released March 2016) has a strong correlation to Breeding Worth (BW) but also combines the non-negotiable OAD functional traits. It reflects what farmers have told us is required in a desirable OAD cow:

  • Capacity
  • Strong udder support
  • Good front teat placement
  • Fast milking speed
  • Less emphasis on residual survival and fertility because these factors were less of an issue than in TAD herds

The new OAD selection index (OADSI) to be strongly correlated to BW, because at the end of the day BW is an outstanding predictor of productive efficiency. However, with the added pressure of only extracting milk once a day, OAD cows need to last.

The following weightings for OADSI were settled on:


When the breeding values (BVs) of these traits are calculated for bulls (or cows) it re-ranks some animals noticeably. However, the range of numbers is similar to BW: To make the number distinctly different, we simply add 1000 to the OADSI to avoid any possible misunderstanding of the two numbers.


Udder support, front teat placement, milking speed, and body capacity are critical success factors in an OAD cow; these traits acknowledge the key differences, and challenges, between OAD and TAD herds. The four traits ultimately dictate survival of a cow in an OAD herd and require a weighting within the new desired gains OAD Selection Index – and potentially in place of the Residual Survival weighting within BW.

On the flipside, fertility – which has a current weighting of 15% in BW – is much less of an issue to an OAD farmer (with the regime going a long way to drive fertility improvement on farm).

The weighting for the somatic cell count (SCC) trait has been an interesting discussion point. There is a common, misunderstood, perception that SCC can be an issue particular to OAD milking. Unfortunately, this opinion frequently comes from TAD farmers who have negative experiences brought about from putting their herd onto OAD late in a dry season (when there appears to be few other options); this can result in a bulk count doubling and running into the grading zone.

The majority of the OAD farmers admit they must be vigilant with mastitis, treating and culling appropriately. However, if best practice is observed, bulk counts are kept under good control. A statistic that supports this, and really blows me away, is that the average SCC for OAD farmers (supplying milk to Fonterra) is actually lower than TAD counterparts across the season.

The decision to convert a farm system to OAD is not as simple as ‘just not getting the girls in tonight’. The breeding of the best cows to perform on OAD is a long game. Many will convert extremely well, but some don’t, and some won’t last.

The new OADSI will be a valuable tool in driving the rate of genetic gain in OAD herds as a result of driving down herd wastage. For the most up to date OADSI values, see your country Sire team.

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