A focus on genetics is key to producing the best lamb as efficiently as possible, for New Zealand sheep farmer Donald Morrison, who supplies Sainsbury’s, Tesco and Marks & Spencer.

Southland sheep farmer Donald Morrison has doubled output without expanding land size since switching to the dual-purpose Growbulk breed.

Mr Morrison, who runs Rosedale Farm, Gore, is one of the first Kiwis to introduce terminal production genes into his maternal breed.

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He transitioned from Romney to Growbulk, a composite breed made up of Texel, Romney and Poll Dorset, after being picked by New Zealand’s AgResearch and farmer-owned industry organisation Meat and Wool New Zealand alongside three other farmers to evaluate Growbulks more than 16 years ago.

Initially, Mr Morrison admits he didn’t have high expectations the Growbulk would add value to his operation, after unsuccessfully trialling other cross breeds on his flock of 4,000 pure Romneys. However he says he was “blown away” by the results.

“Right from the start we were blown away by its lamb survival and growth rates,” admits Mr Morrison, who farms in partnership with his wife Brigette.

Growth rates and lamb survival improved by about 8% on the year and lamb carcasses are higher yielding, says Mr Morrison.

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“Everyone thought we were crazy and you shouldn’t put terminal influence into a maternal breed. But I knew in the future meat would become an important part of our business.”

His predictions were right, as meat sales now account for 85% of the business’ income and wool is just 15%.

The Morrisons now run 2,000 Growbulk stud ewes and another 2,000 Growbulk commercial ewes, plus 1,000 hoggets.

They produce 400 stud rams for private sale each year and slaughter lambs are sold for export.

Mr Morrison says the move has given them a competitive advantage because the breed offers the very best maternal and terminal traits all rolled into one, which has widened their customer base. It means they can still produce breeding sheep and fast-growing fat lambs from just one genetic pool.

“In 2000 we weaned 4,600 lambs and that’s grown to 7,060 lambs.

“The Growbulk has been a huge part of that success story. It has allowed us to grow the sheep operation when sheep were largely unprofitable and dairying was expanding,” explains Mr Morrison.

A big emphasis has been placed on performance recording to allow them to select genetically superior animals to mate and since 2000 their sheep improvement limited (SIL) base index has increased by NZD30 (£13).

These genetic gains have led to massive improvements in the performance of both flocks, with lambing percentages, lamb survival and growth rates progressing rapidly.

This has contributed to big boosts in production, with total lamb meat output growing from 113kg/ha to 275kg/ha.


Stud ewes are single sire mated to the top 1% of rams to ensure maximum genetic gain and this also prevents inbreeding.

Each year 20% of the worst performers are culled based on age, body condition, udders and mothering ability.

“Anything that doesn’t have good fertility we mate to sires carrying the Inverdale gene,” adds Mr Morrison.

High ram to ewe ratios of 1:125 are used in the stud flock to maximise genetic value.

Ram to ewe ratio is lower in the commercials at 1:100 ewes. Teasers are only used on the two-tooth ewes and hoggets.

“All the sheep on the farm are flushed for three weeks prior to mating on grain. This year it was really beneficial because ewes were really lean [because grass has been tight].”

Ewes are scanned between 70-100 days post-tupping and are separated according to litter size so they can be fed according to feed requirements.

Last year the ewes averaged 195% and the hoggets scanned 113%. “When we started with the Romneys we were scanning under 150%,” explains Mr Morrison.

Ewes spend the winter months being stripped grazed on fodder beet where they are fed to maintenance.

Before lambing they are set stocked on grass according to their scanning results, on target grazing covers of 1,500kg/ha DM. Triplets are stocked at four an acre, twins at five an acre, singles eight an acre and hoggets at six an acre.

Lambing starts with the draft ewes on 1 September, followed by the main flock on the 15 September and hoggets two weeks later.

Last year, ewe pregnancy rates were 154% and hoggets 90% – the highest to date although the target for these is 100%, says Mr Morrison.

Testament to their high fertility is the fact that 85% of the ewes lamb in the first cycle, says Mr Morrison.

He reckons lamb survival rates have increased by 50% due to a combination of better maternal behaviour, higher birth weights, better skin thickness and the influence of internal brown fat levels.

The stud progeny is weighed at birth, dam and sire details are recorded alongside the ewes’ maternal ability. Thereafter weight gains are recorded at weaning and every 50 days up until 200 days.

Each year the top 500 ram lambs from the stud flock and 300 commercial rams are ultrasound scanned in February.

“From the results we select the best 420 to retain through the winter and the top 20% are sold for breeding between NZD1,000 (£430) and NZD1,500 (£645).

“We scan at the end of summer because it is relevant to commercial farmers as it reflects when they are selling lambs,” says Mr Morrison, who adds they are targeting a score of 18mm-plus.

Donald Morrison

Commercial lambs

The presence of the naturally occurring loin-muscling gene marker LoinMax, which adds 10% more meat to the loin area, and the double muscling marker MyoMax, which adds up to 14% more meat to the rump area, within the Growbulk breed, has led to improved growth rates.

Overall growth has been lifted by 40%, from 14kg deadweight to 19kg deadweight and kill dates have been brought forward one month, resulting in lambs being sold by Christmas. This means ewes can be given priority grazing for tupping to get them into the best condition possible.

Because lambs are early maturing Mr Morrison says they have had more success from breeding hoggets, which has contributed to an overall lift in meat output.

“We tried breeding from Romneys but it was unsuccessful. When we first started mating hoggets we got 80% from the Growbulks compared to 20% from the Romneys.

“They are earlier maturing and achieve a higher weight in the autumn. Plus the Poll Dorset is a highly fertile sheep,” believes Mr Morrison.

Fat lambs from the commercial flock are sold to the co-operative Alliance Group, the world’s largest exporter of sheepmeat, of which Mr Morrison is a director. A large percentage of the lambs from Rosedale are destined for the shelves of Sainsbury’s, Tesco and M&S.

Last year they averaged NZD90 (£39) a head at 18kg deadweight and premiums of NZD6-NZD7 (£2.50-£3) are paid to higher meat-yielding carcasses.

“We are yielding around 60% which is adding another NZD7 [£3] to our lamb price. It doesn’t sound a lot but when you’re selling 5,500 a year it soon adds up,” he adds.

More recently they have been using a 5K SNP DNA chip to identify the highest value ram lambs for sale from their commercial flock. The heaviest commercial ram lambs are left entire at tailing and they then choose the best 250 for DNA analysis from a pool of about 900. The DNA analysis identifies rams with the MyoMax, LoinMax and Inverdale prolificacy gene marker.

“Now up to 85% of the sheep have the MyoMax and LoinMax gene marker when we DNA test them,” explains Mr Morrison.

Body condition score

Mr Morrison believes a big part of their success is as a result of improvements in ewe body condition and they are involved in the development of an EBV for ewe body condition score which will be available later this year.

At mating and weaning ewes are given a body condition score and all lamb weaning weights are recorded.

“Ewe body condition score has the biggest influence on total production. It has a huge effect on lamb survival and growth rates pre and post weaning.

“We want a 65kg ewe that will be 3.5 plus at mating and will wean its own bodyweight and have the same condition score after weaning. That to us is the most efficient animal.”

As a management tool the ewes are shorn twice a year, in December and May. “It gives you a more accurate picture of ewe condition. With 12 month shearing there was part of the summer where the ewes had too much wool and it was limiting growth because their appetite wasn’t as stimulated.

“My total drive for efficiency is kilogrammes of lamb liveweight in relation to ewe bodyweight but within that I want to maintain a good fleece because it is still an important drive of overall profit.”

Wool weights are recorded when ewes and rams are two-tooths and across the flocks they are harvesting about 7kg of wool an animal each year, at a value of NZD40 (£17).


Despite the massive leaps in performance, Mr Morrison’s passion for genetics means he is still on a quest to do even better.

This spring Rosedale has their first crop of Merino Growbulk lambs on the ground as the result of a partnership between themselves and Nine Mile Merino.

It is a project that flock manager Tim Labeth is very excited about.

“The commercial demand for Merino has grown five-fold in New Zealand. The aim is to produce a half-bred ewe with superior meat traits and a finer wool option.”

Mr Morrison adds: “If we don’t keep doing things better everyone else will catch up and I love the challenge of it.

“To me it is the really exciting thing about farming.”