Are big cows better?

By Dr Harriet Bunning, AHDB Lead Genetics Expert.

How big is your ideal cow? In the show ring, big cows tend to do well. Their size makes them impressive to look at compared to smaller females and for those chasing higher growth rates, a herd of large cows will, on average, produce calves with heavier weaning weights. This is also important for breeders who sell young bulls as again, on average larger cows will produce bulls who have made a better size for the bull sales.

However the overall profitability of your farm is not just your income. Especially in the current climate of high costs of fertiliser, labour and feed, reducing input costs is a great way to increase your profit. Smaller cows need less feed and so can greatly reduce your input costs. Estimates suggest that for a 10 kg reduction in mature cow weight, her daily feed requirements drop by 150-250g of dry matter. This reduction in feed requirements has an impact when she is a cow, but also when she’s a heifer as her feed requirements for growth will also be reduced. So by keeping a herd of smaller cows, you also reduce you replacement costs.

As you might expect, smaller cows also have a smaller environmental impact. Feed production has an environmental impact and so if less feed is required, we produce fewer greenhouse gases. In addition to this, as a rule, cows which eat more tend to produce more enteric methane. This means that keeping smaller cows who eat less feed, reduces CO₂ produced during feed production, as well as enteric methane production from the cattle themselves. It’s estimated that for a 10kg reduction in mature cow weight, the environmental impact of that cow reduces by 8.8kg CO₂ equivalents. This is even greater during the heifer rearing period when the same 10kg reduction in mature cow weight would reduce the environmental impact of the growing heifer by 18.9 kg CO₂ equivalents. This reduction in environmental impact is becoming increasingly important across the industry and by keeping smaller cows, alongside the carbon sequestration of your grassland, you can reassure consumers of your beef that it is a green choice.

What does this mean for breeders? Can you maintain good growth rates using smaller cows? Although there is a trend that smaller cows produce calves with lower growth rates, this is not universally true. Through good breeding, we can select for cows which are not too large, who still produce calves who grow well. EBVs (estimated breeding values), which are a measure of the genetic merit of an animal for a specific trait, are a great tool to help identify which are the best breeding animals to produce these cows. They are especially useful when selecting a bull as they give you a good idea of the mature size of his daughters, which can be difficult by eye alone.

To produce these EBVs, we need good data. This highlights the importance of performance recording for breeders. Through Signet, you can record the weights of your calves, youngstock and importantly, your cows. This will enable the production of more accurate EBVs for your animals and help you breed your ideal sized cow.