19 September 1997


Which is the most profitable month to calve your cows? In an exclusive report, John Burns and Sue Rider reveal that seasonality payments still fail to cover the cost of producing milk in summer, and that spring calving is the most profitable option provided grass management is excellent

CALVING cows in spring is still the most profitable route to milk production, provided grassland management is excellent.

That is the result of a detailed modelling exercise prepared exclusively for farmers weekly by independent, Dorset-based agricultural consultants John Easterbrooke and Partners.

The analysis suggests that seasonality payments for summer milk are insufficient to cover the extra cost of producing milk in these months. It reveals that calving mainly in May – even though that month attracts the largest seasonality deduction – is still the most profitable option because use of grazed grass is maximised.

"Our study shows that the advice of New Zealand consultants to calve in spring is correct, whether it is a grassy farm or not," says report author, John Easterbrooke. "But what it has highlighted is the importance of managing that grass, especially when it is plentiful in April, May, and June, to an extremely high standard, with no wastage."

If dairy farmers can do that, then it would seem sensible for some producers to switch to spring calving, focusing on May as the main month, Mr Easterbrooke adds. But in his experience few farmers have the ability to use grass efficiently in spring.

"My main concern is that farmers wont secure 90% efficiency of grass use in spring, management skills are just not good enough. It is far easier to achieve that level of efficiency – convert 90% of energy fed into milk – in autumn because it is easier to manage silage and concentrates," he says.

His study is based on Milk Marques pricing schedules. He reasons that it does not make much difference who the buyer is, since the variations in method of payment are not great, except for the buyer who pays month-by-month on a level basis.

"If this is the case maintaining output in the difficult months of July and August could be a major issue."

The report also assumes a herd of 100 cows kept on 51ha (125 acres) grass, and with forage production as either poor or good. "Site class poor is Brighton beach at 1000ft with no rain; very good is grade two land in a 35in rainfall area at 200-300ft above sea level," he says.

MAFF defines grassland sites in five categories, from poor to very good, on the basis of soil-available water capacity and rainfall in the growing season – April to September inclusive. Poor receives less than 300mm (12in) rain with a soil-available water capacity of less than 100mm (4in); good, 300-400mm (12-16in) rain with soil available water capacity at more than 150mm (6in); very good, more than 400mm (16in) rain, and more than 150mm soil available water capacity.

Herd calving is assumed to take place in May and September, or spring and autumn, respectively, with 60% of cows calving in that month, the rest 20% before and 20% after. Energy from forage is determined via the site class calculation at 250kg/ha (200 units/acre) of nitrogen a year. Concentrate needed is calculated by the difference between the forage ME produced and the total ME needed, assuming 25GJ a head a year for maintenance and 5.2MJ/litre for production.

The analysis reveals that for herds averaging 6000 litres, those that calve in spring out-perform autumn calving herds by about £30 a cow at a constant efficiency of grass use of 90%, that is 90% of grass energy generated by fertiliser use is converted into milk (table 1).

The same trend is apparent for herds averaging 6500 litres, where spring calving out-performs autumn calving by about £30 a cow a year (table 2).

But if efficiency of grass use in the spring calving herd drops to 70%, then it will only be as profitable as the autumn calving herd managed at 90% grass use, maintains Mr Easterbrooke.

When both herds use grass at only 70% efficiency, however, then the superiority of the spring calving herd re-emerges.

Season of calving

Herds averaging 6500 litres show the same results in terms of efficiency and season of calving as the lower yielding herds. Further-more, herd performance does not appear to be affected by whether calving is in autumn or spring, he says.

What is shown, therefore, is that, at present Milk Marque prices, spring calving appears to be more profitable than autumn calving, if efficiency of grass use is comparable.

"But unless the efficiency of grass use by spring calving herds is of a high order, then autumn calving continues to be the best option." It is easier to achieve 90% efficiency when cows are on winter diets because it is easier to ration silage and concentrates than grazed grass, says Mr Easterbrooke.

But he cautions that his report takes no account of the high cost of switching calving pattern and the time it takes.

"It is one thing to say this is what you should do and quite another to cash flow the consequences of doing the same when, according to these calculations, there does not appear to be more than £30 a cow in favour of spring calving."

John Easterbrooke… calving in spring still most profitable option provided farmers have the ability to manage grass to a high standard.


&#8226 Seasonality payments for summer milk insufficient.

&#8226 Spring calving £30 a cow a year advantage over winter.

&#8226 Grassland management skills must be excellent.

&#8226 Consider high cost of switching calving pattern.

Notes to tables


1. 100-cow herd on 51ha (125 acres)

2. Milk Yield6000 and 6500 litres

3. Calving Pattern60% main month

20% either side

4. 25% Replacement Rate

5. Calving Patternbeforemain monthafter



6. Milk Price Calculation based on Milk Marque prices @ 1-8-07

Standard litre4.1% Fat

3.3% Prot.

  @ p/% BF2.28

   p/% Prot.3.84

Therefore standard litre value

4.1 @ 2.289.348

3.3 @ 3.8412.672


+ Hygienic Bactosan0-50+.200



+ Seasonality Jan – March-22.420






September+ .5022.920

Oct – March-22.420

7. UME Needed GJ/cow

a. for 6000 litres Maintenance 25.0

6000 @ 5.3 MJ 31.8


b. for 6500 litres GJ/cowMaintenance 25.00

6500 @ 5.3 MJ 34.45


8. UME from Forage @ 200 units N

Site Basicon@@@

ClassUME/acre1.25 acres70%80%90%



Very good46.958.6341.0446.9052.77

9. Efficiency

say 90% where mostly grazing

i.e. calving monthsMarch, April, May

80% where 50/50January, February, June, July, August

70% where mostly silageSeptember, October, November, December

10. Concentrates

Assume 85% DM @ 13.5 ME

Therefore 1t is equivalent to 11.475 units ME

and cost £130/t

Table 1: Calving pattern (6000 litres/cow)

Site ClassAutumn calving (Sept, Oct, Nov)Spring calving (March, Apr, May)


iencylitreMDFiencylitreMDF*iencylitreMDFiencylitre MDF



Very Good70%.231149.890%.061282.490%.061311.670%.231179.0

Table 2: Calving pattern (6500 litres/cow)

Site ClassAutumn calving (Sept, Oct, Nov)Spring calving (March, Apr, May)


iencylitreMDFiencylitreMDF*iencylitre MDFiencylitreMDF

Poor 70%.491028.090%.401102.090%.401133.670%.491059.6


Very good70%.251230.790%.091363.390%.091394.970%.251262.3

MDF"Margin due to Forage"