Are "cull" cows worthy of valuable supplements?

By Kevin Wilson

Now that we have the cows into winter mode, it is a good time to reflect on the season past and plan for the season ahead. Often we make decisions with minimal information during a busy day. So now that you have a bit of time to ponder, while the cows have a holiday, think about the question I have just posed.

The answer to this is not always straightforward and will depend on pasture cover, supplements on hand, milk production, milk payment and setting up for the following season. Milk production response to supplements will depend on how hungry the cow is. In situations where cows would be underfed if not supplemented (i.e. residuals less than 1600kgDM/ha), milk solids responses are consistently 6g to 8g MS/MJ ME fed. With good quality silage, this means you would expect about 75gMS/kg supplement, or $0.53/kgDM.

This also raises the debate about when to ‘offload’ empty and cull cows; are we better to milk them to the end or use that feed to set up cows for the following season? This question is not simply a cost benefit analysis on the supplement (in table below), but also a question of whether that supplement would benefit the business through increasing body condition score (BCS) of the main herd for the following season. If it is assumed we need a margin over feed costs of $2 per cow/day to cover variable costs, and declining value of cull cows, then we would need to produce over 1.4kgMS/ cow/day before there was a true monetary benefit from feeding silage to culls/empties at $7.00 pay out.


Dairy diary


Based on the table above, there can be monetary gain from milking culls/empties provided you are utilising pasture and supplements offered, and that milk production is at a sufficient level. However, there can be significant indirect benefits from culling these animals early (start of April). Studies from New Zealand and overseas consistently show that BCS has an important role in influencing cow reproduction, with BCS at calving being the most important BCS measure relating to fertility. Therefore, autumn and winter management of your herd will have a strong influence on seasonal production and fertility. John Roche of DairyNZ published that milk yield increases linearly with increasing calving BCS up to BCS 5. This would suggest that farmers need to focus on improving average BCS at dry off to help meet industry target BCS at calving. Cows calving at less than BCS 5 will also have an extended postpartum anoestrus period, reduced potential number of breeding events, reduced milk production and increased vet and artificial insemination costs.

In conclusion, as indicated, we can make gains from feeding supplements to cull cows during the autumn period, provided we do the basics well and are aware of the associated cost/benefit, but this should not occur at the expense of capturing the full indirect benefits for the following season.