Have you ever considered the cost of a pregnancy when making your mating decisions? It’s easy to focus on the tangible costs like what you get paid at the other end for a surplus calf but that’s only half the story.

Our team has collated the costs associated with calves of high and low birth weights and the results might surprise you.

Table 1: Cost of a calf by calf birthweight

Pregnancy energy requirements:
80 kgME required to produce 1 kgMS
26kg calf energy requirement* = 1,407kgME, 1,407/80 = 17.59kgMS @ $7/kgMS = $123 in forgone production, VS
43kg calf energy requirement* = 2,322kgME, 2,322/80 = 29.03kgMS @ $7/kgMS = $203 in forgone production
(*Source: Journal of Dairy Science, Requirements for zero energy balance of non lactating, pregnant dairy cows. Mandok, Kay, Greenwood, Edwards & Roche)
Calf rearing:
26kg calf x 4 litres/day, 43kg calf x 6 litres/day @53c per litre/milk
Cow losses:
1 cow lost per 200 higher birthweight calves born, $1,400 value
Higher empty rate:
2% higher empty rate, $600 salvage value vs $1,400 pregnancy value
Lower six week in-calf rate:
2% decrease in 6 week in-calf rate at $4/percent decrease (source DairyNZ In-Calf book)

Pregnancy energy cost

When it comes to the process of getting a live calf on the ground most of the “cost” comes down to the energy required by the cow to grow the calf over the gestation period. A higher birth weight calf will have a higher pregnancy energy requirement than a calf of lower birth weight. A higher birth weight calf will also have a greater volume of embryonic solids which are energy expensive and completely valueless.

The cost of the extra energy associated with a higher birth weight calf can come in two forms – either as the cost of extra feed or at the cost of sacrificed production.

For example a cow carrying a higher birth weight calf will require extra feed over the dry period to achieve the same body condition score gains as a like animal carrying a lower birth weight calf.

Alternatively, a cow carrying a higher birth weight calf will need to be dried off sooner than a like animal carrying a lower birth weight calf to allow the same body condition score gain over the dry period, due to more energy going into growing the calf and less going into conditioning the cow.

For the purpose of these calculations we’ve assumed that production is sacrificed but which scenario applies to your business will depend on your management. 

Calving difficulty

Higher birthweights are generally linked to a higher likelihood of calving difficulty. Use of higher birthweight sires is more likely to incur cow losses, calving damage and have associated impact on fertility and empty rates.

Recommendations

When it comes to creating a pregnancy and getting a calf on the ground much time can be spent weighing up tangible costs like the price of an AB straw, or the cost of calf milk replacer. But ironically, it’s pregnancy energy requirement that presents the greatest cost in creating a calf.

This is directly influenced by the birth weight of the calf. The bottom line is that larger calves take more energy to grow and therefore have a higher pregnancy energy cost.

So when you’re weighing up what to mate your cows to this season it’s important that you’re comparing apples with apples when it comes to the returns you get from surplus offspring. Consider lower birth weight sires to reduce your costs in getting cows in-milk.