OPTIMISING COW MATURE WEIGHT –

HOW HEAVY IS
TOO HEAVY?

Research by AbacusBio International on behalf of AHDB, QMS and HCC has used industry data to create a model of UK beef production systems, which shows how increases in mature size affect traits such as carcase size and cow maintenance requirements, and how these changes affect cost and revenue on farm.

Suckler cows in the UK have been increasing in size over time. Heavier cows provide extra value to the farm by producing heavier offspring, and by having a higher cull cow value. However, they also cost more to keep on farm, and so we must strike a balance on cow mature weight.

The AbacusBio International team compared the cost of producing cows with a mature weight of 651kg compared to those with a mature weight of 751kg. The results (Table 1) showed that heavier

cows benefit the modelled farm through higher cull cow revenue, and by producing offspring with higher carcase revenue and quality. However, heavier cows have higher costs in terms of maintenance feed and replacements, and they also suffer from a decrease in fertility, potentially producing less offspring in their breeding lifetime. Heavier cows also require more land than lighter cows, resulting in a reduced stocking density on farm. Once you combine all of these factors, the cost of production is higher for heavier breeding females and therefore profitability is worse. 

Having taken all of these effects into account and applying the model across a range of cow mature weights, the team found that the optimum mature weight for a breeding female is between 680 and 685kg. Beef producers who feed primarily home-grown feedstuffs may be able to keep breeding females of up to 700kg to optimise their profits, as the cost of producing home-grown feed is lower than the cost of buying feed in. 

Table 1: Herd margin over feed for different cow mature weights (based on a 100 cow herd). The margin over feed is the net revenue when feed is the only cost that varies. In this model, all other costs remain the same.

AnimalMature Weight   
651KG751KG
CostRevenueCostRevenue
Maintenance Feed£11,771£21,655
Cull Cow£10,924£13,144
Replacement Growth£10,620£16,588
Heifer Carcase Value£15,834£28,906£18,278£34,292
Steer Carcase Value£24,522£42,920£29,296£46,175
Bull Carcase Value£5,465$8,120£6,602£9,948
Total£68,213£90,872£92,420£103,561
Margin Over Feed*£22,658£11,140

Simmental cow mature weight trends

As mentioned on page 80, and can be seen in Figure 1, the genetic trend for mature weight has been increasing by over 1kg per year. The average EBV for mature cow weight for animals born in 2000 was 46.9kg, rising to 66.7kg for animals born in 2018.

Looking at the phenotypic trend for mature cow weight over time using Breedplan data is difficult due to the low level of mature weight recording in the breed. However, we have been able to get an estimate of Simmental mature cow size over time by analysing cull cow data from the slaughter records that are shared by abattoirs for use in the AHDB national beef evaluations. The estimates are based on multiplying the cow carcase weight by the industry average killing out percentage.

Figure 2 shows the distribution of cow mature weights for cows born in 2000 vs 2013 that were slaughtered between 5 and 10 years of age. In this 13 year period, the estimated average mature cow weight has increased by 56kg, from an average of 631kg back in 2000, to an average of 687kg in 2013.

Assuming that this dataset is a representative sample of the UK Simmental herd, this would suggest that in 2013, over 50% of mature cows weighed more than the optimum 685kg, and as the genetic potential for larger mature cow weight increases, the percentage of mature Simmental cows over the optimum mature weight is likely to be higher than 50% today. The profitability of the national herd is therefore lower than it could be.

To increase herd profitability, there is a strong argument of the importance that this trend for heavier cows is reversed. As mature weight is a heritable trait, we can use genetic improvement techniques to help take aim at the current trend.

Steps to optimise mature cow weight

  1. Where available, make use of selection indexes that have penalties applied to breeding female mature weight EBVs; this controls the increase in mature weight, associated with selection for early growth
  2. Weigh breeding females regularly and compare this to the weight of the calf they produce at weaning. It is aimed that a cow should produce 45% of her weight at weaning. Sign up for performance recording so that the data can be shared with Breedplan and used in genetic evaluation.
  3. Don’t retain heifers from your biggest cows in the herd, mature weight is heritable. 
  4. Buy sires where it is possible to assess the size/weight of the breeding females, and gather more intelligence about the genetic merit of the males for growth, mature weight and other genetic merit estimates
  5. Communicate with commercial farmers to understand the needs in the context of breeding female mature weight, with an understanding that bigger is not always better.