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Reversing the growing size of dairy cows

Andy Rutter is a dairy farmer, since he took over the performance of his 380-head Holstein herd, he has been choosing animals based on their size.

Rutter worked for the genetics company Genus for 20 years, running its EU breeding programme, before moving back to the Cheshire Clayhanger Hall Farm in northwestern England four years ago. He says he doesn’t understand why farmers keep choosing cows that are bigger.

“It seems like every time we have an accident, it involves a big cow. She does the splits, gets stuck, and has a displaced abomasum. This is especially true if you have to pull out a big calf and are left with a big hole. It’s very clear in the cows that are taller and heavier.

“We were told that breeding cows for their size would make them weak in the herd. But we’ve found the exact opposite: smaller cows are definitely more confident on concrete and show bulling more strongly.”
Getting cows smaller

In order to reduce cow size, breeders have had to pay close attention to the available breeding indexes. Positive stature is the most obvious trait to avoid, so the farm would rarely use a bull with a stature score of more than zero.

But because breed averages are calculated every year for genetic evaluations, Rutter thinks it’s easy to lose track of how big a bull’s daughters will be: “A rolling base is great for giving accurate, up-to-date information, but it hides everything that’s happened before. If you added up all of the changes in height, it would be scary. It means that a slightly negative stature bull today would have been positive last year and strongly positive six years ago.

He uses indexes to find bulls that are most likely to pass on good feed conversion efficiency to their daughters. He also uses other indexes to find cows that are best for the environment, rewarding those that are expected to produce the least greenhouse gas emissions over their lifetimes for each kilogramme of solids-corrected milk they produce.

“We like how well they use their feed and how much milk solids they produce. We always want to choose bulls with high fat and protein percentages, even though we don’t get paid for them under our current milk contract. We need to make sure the cows have what it takes to produce more milk solids, though.

All of this is shown in the Rutters’ own herd, which sells an average of 10,600 kg of milk each year with 4.2% fat and 3.2% protein. This is on top of a 33% pregnancy rate, which is much higher than the national average, and a 372-day gap between births.

“Everywhere I go, farmers tell me they don’t want bigger cows, but all the genetic trends show that’s what they’re breeding…”

Cows getting bigger

Marco Winters, who is in charge of animal genetics at the Agriculture and Horticulture Development Board (AHDB), said that cows have been getting bigger since the mid-1980s, and there are no signs that this will change. Winters thinks this is important because the average UK farmer now has to feed and care for the same amount of weight as 10 extra cows because animals are bigger than they were 30 years ago.

This trend has happened at the same time that milk production has gone up a lot, but Winters thinks that with the precision of modern breeding tools, there’s no reason why production can’t go up without making cows bigger and taller. But if dairy farmers don’t do something to stop this trend, it will cost even more to run the average Holstein in the UK.

“Everywhere I go, farmers tell me they don’t want bigger cows, but all the genetic trends show that’s what they’re breeding,” said Winters, even though national breeding indexes have a negative weighting for bodyweight.

Graphs show that the average weight of a cow in 2021 is 30 kg more than the average weight of a cow in 1991. This extra weight means that the average 200-head UK herd is feeding the equivalent of almost 10 extra cows every day.

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