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Passion pays, at home and away (Sept 23)

One Cornwall-based producer’s passion for Guernsey genetics is key to the success of his family’s dairy business, as well as other herds across the world. We spoke to him to find out more.


You can take a cow from Zennor anywhere, but you can’t bring a cow from anywhere to Zennor. That’s a wise quote from David Mann’s grandfather Arthur who, alongside David’s great grandfather Henry, was instrumental in establishing the Trewey pedigree Guernsey herd, based at St Ives in Cornwall, back in 1943.

Now, 80 years on, David and his wife Katie, his parents Harry and Caroline, and four children Anebelle, Henrietta, Gregory and Suzannah, run the 180-cow herd, on the 202-hectare unit.

Guernseys, historically, have thrived in conditions here on the north west coast of Cornwall and it’s said that the area’s black-and-white herds developed from a Guernsey British Friesian cross many generations ago. “It’s extremely exposed here,” says David. “Our farm stretches from 46 metres to 216 metres above sea level. Growing maize is a non-starter. We’d need 6.5 tonnes per hectare to make it pay and we just couldn’t achieve that here.”

Home-grown forage

But the herd does well on home-grown forages, which comprise mainly grass, plus three hectares of swedes and some kale for winter grazing. This year 14-hectares of home-grown crimped spring-grown barley has been added to the mix.

Around 50% of the herd’s average yield, which currently stands at 6,100kg of milk at 4.9% butterfat and 3.6% protein, is produced from home-grown forage, and cows graze for about 10 months of the year. Cows are fed concentrate in the parlour, according to yield, at an average rate of 0.25kg/litre. David wants to reduce this figure by improving feed efficiency, through better forage quality or breeding a more feed efficient cow. The herd is milked twice a day through a Boumatic 16:32 parlour, which was installed in 2010, and milk is sold to Arla.

David says he’s eyed up some tempting milk prices from smaller buyers from time to time, but he’s happy with the security and prices offered by Arla, and he uses data from schemes, such as Arla Climate Check and Arlagården, to support his management and ensure the highest farm assurance levels are met.

“It includes soil sampling, which we’d do anyway but it’s a good discipline. We also carry out routine lameness scoring and health tests, including Johne’sdisease screening using the milk sample twice a year, and tag-and-test for BVD. We vaccinate heifers prior to breeding at 15 months old, and cows prior to serving. “The fertiliser cost savings, reduced waste of inputs, and healthier cows offer many benefits. So the testing and screening pays dividends,” he adds.

Health management

A preventative approach is taken when it comes to herd-health management and this includes a monthly vet visit. All calves are vaccinated against pneumonia, for example, even though male calves leave the farm at eight weeks old.

“It’s all about reducing the risk to other calves. We want our stock to stay as healthy as possible and an outbreak of pneumonia in young heifer calves could set them all back.”

Similarly, cows with any level of Johne’s infection calve separately and these calves are removed from the dam and fed pre-stored colostrum from Johne’s-free cows. These cows, even if infection rates are low, will be bred to a beef bull.

“We control what we can,” explains David. “The whole team adheres to strict protocols, which are followed in the calf shed by David’s mother Caroline and one other member of the milking staff.

“We always have two people in the parlour at milking so we can give each cow the attention she needs. This includes full pre-milking preparation, including predipping. The average 12-month rolling somatic cell count sits between 160,000 and 180,000 cells/ml.

Breeding programme

David’s father Harry also works full time on the farm and they employ one relief milker and a tractor driver. The children all help out too, when time allows. Attention to detail in daily routines permeates through to the herd’s longer-term breeding management. Around 50 heifers are bred each year and heats are synchronised with a PRID programme in groups of 25, two weeks apart, to avoid calving them all together.

“This works well and we’re achieving 70% success to first service and more than 80% conception to first and second service,” says David.

The best heifers and cows calving in the first six weeks of the autumn block are bred to sexed semen, and then a beef bull is used. “We do our best to minimise dairy bull calf production,” says David. “And we breed highquality stock for our own herd and for selling. Stock sales are a key part of the business, including the sale of Trewey bulls, including one bull to Ireland in 2022. “We’ve sold surplus cows to several well-known Guernsey herds in 2022 and to a Derbyshire-based producer-processor who wanted Guernsey milk to offer their customers alongside the farm’s Ayrshire milk.”

Particularly exciting for the family this year has been the sale of 10 in-calf heifers to a Sheik in Oman for a newly established Guernsey herd – the Guernsey being his breed of choice because of the high A2 and omega content in the milk. “I was apprehensive about them travelling that far, but I checked their transport and accommodation and it was five star, so I’d nothing to worry about.”

The herd comprises 50 cows classified EX and 58 classified VG, and another of their cows has recently been classified EX95 – one of few Guernseys in the country to achieve this accolade. And their well established Juno cow family has plenty of trophies to its name, including the English Guernsey Cattle Society’s North American trophy for the highest classified cow family.

Trewey Junos Beau is one of the herd’s most recent home-bred bulls to go into AI. “He has daughters in herds throughout the world that have done well and we had some owners visit us as part of the World Guernsey Tour in June,” adds David. “They were delighted to see the bull’s roots.”

He says that having quite a few bulls go into AI and leaving their mark on many Guernsey herds is a double-edged sword. “It’s rewarding, but it doesn’t help us to broaden the genetic base of our herd. So, from time to time, we buy in new bloodlines from leading cow families.”

Breed development

Broadening the gene pool is one of the key challenges for the Guernsey which, like other minor breeds, has been hampered by bovine TB restrictions. “One of the main issues is that bulls born on a farm under bTB restrictions can’t go into AI despite not being affected,” explains David.

A member of the Guernsey Society’s ‘Future of the Breed’ committee, David is seeing the merits of genomics in helping to identify the best genetics, and the society has funded genomic tests for 500 cows so it can rank and breed from the best and then test the daughters. This will hopefully allow the breed to progress.

Looking forward: breeding is building a herd fit for the future

As for the Mann’s herd, David plans to genomically test all heifers this year so they can identify their best more accurately. “Genomics is a significant investment, but we hope it will help to build our future,” he says. “We want to make sure we breed a strong grazing cow that can produce good yields from a forage diet, and one with good conformation to support longevity.”

He favours the English Guernsey, having tried imported semen from US bulls many years ago. “The US-sire daughters were taller and frailer – it was like having two herds of cows. The genetics are good, but they don’t suit our system.”

Cow tracks

Instead his focus is on breeding and managing cattle to maximise the farm’s resources. “We grow plenty of grass but it can dry up in summer, so we calve two thirds of cows between early September and Christmas.

“Cows are usually outdoors until late November and, after about two months indoors, they’re back out in February. We’ve a good network of tracks across our grazing land so we can do this.”

Good grazers: Guernsey herd is out for 10 months each year

Even during the housing period, cows may go out to graze if there’s a decent dry spell of weather midwinter. “I like to see cows outdoors and in the fresh air, and it’s good for cow health and welfare.

“We’ll also put them onto the kale for two or three hours a day from October onwards, if conditions are suitable. This takes the pressure off silage stocks. Our three or four hectares of kale saves about half a tonne of silage per cow.”

Cows are back out to full-time grazing in early February and supplemented with silage until grass growth takes off. The herd rotates through one- or two-hectare fields every two to three days, and they are only supplemented with silage through summer if grass growth slows.

“We took on more land in 2018 and that allowed us to add another 20 cows, but I am reluctant to expand the herd further at the moment due to impending slurry regulations and labour availability,” says David. “It’s important that we have time to enjoy our cows, family life, a bit of showing, and the pleasure of welcoming groups to see our herd and the farm.”

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