THREE things are out to get young lambs; birth difficulties, starvation and exposure to the elements.
As every sheep producer knows, picking up dead lambs after a nasty cold snap is a distressing job.- AT A GLANCE
- Who: Ralph Behrendt
- What: lamb survival
- Why: reducing death by exposure
- Where: Hamilton
- Report: KATE DOWLER
However, hope is at hand to minimise the third risk, death by exposure.
An Evergraze trial near Hamilton is using perennial hedge rows in pasture to cut down wind chill and lift twin-lamb survival rates by about 40 per cent.
The trial has been running at the Department of Primary Industries' Evergraze site for four seasons with Merino and Coopworth ewes mated to terminal sires.
Trial leader Ralph Behrendt said various forms of shelter belts could be used to reduce wind speed and chilling.
The study has shown that where shelter is limited, productivity can be boosted by pregnancy-scanning ewes and placing twinning ewes in sheltered paddocks, with good feed, before lambing.
Dr Behrendt said any type of stalky, perennial grasses could be used to form a hedge.
"Any type of grass that is stalky and produces a tussock is suitable, such as phalaris or tall fescues," he said.
The Evergraze trial was set out with strips of rows one to 1.2 metres wide and spaced eight to 10 metres apart.
The bays in between these rows were sown to perennial ryegrass and sub clovers, to supply high-quality feed for ewes during lambing.
Previous research has shown that for every one metre of hedge height, there was an area of 10 metres that benefited from reduced wind speed.
"Our research has shown that windspeed next to the hedge is reduced to 1 per cent of the open area," Dr Behrendt said.
Scientists have calculated a chill index that indicates the degree of risk to lamb survival, based on a combination of factors, such as wind speed, rainfall during the past 24 hours and temperature.
Once this index exceeds 1000, lamb mortalities increase.
Dr Behrendt said the hedge rows decreases the wind chill index by 10-15 per cent compared with open paddocks.
"In general, at an average lamb birth weight, we saw lamb survival rates increased to 90 per cent in the areas sheltered by hedge rows, compared with 69 per cent in the open areas," he said.
For the single lambs, the shelter area survival percentage was 82 per cent; compared with 78 per cent in open areas.
For twins, 87 per cent survived in the sheltered areas, compared with a base figure of 76 per cent, while in triplets, those in shelter achieved a 96 per cent survival rate, compared with just 50 per cent in open areas.
Dr Behrendt said the benefits to individual farmer depended on current survival rates and management.
"The benefits are more apparent for twins, rather than singles," he said.
The level of decreased lamb mortalities seen in the experiment could result a $5/ewe benefit every year.
"At this rate, when you consider the cost of establishment, within three years, the producer should be breaking even," Dr Behrendt said.
The hedge rows could last for about 10 years. The trial compared Merino and Coopworth ewes, mated to terminal sires.
Dr Behrendt said both breeding systems benefited equally from the shelter belts. Both breeds had a 40 per cent reduction in mortalities for twins.
"Lamb survival is a key issue for the industry and at Wagga Wagga in NSW another Evergraze site has done a similar trial looking at shrubs instead of tall grasses," he said.
"It doesn't really matter what you use, as long as it is able to provide a good protection."
At the Hamilton trial site lambing ewes were put in the small hedgerow paddocks a few days before lambing and taken out when lambs were about three days old.
"Lambs are most susceptible to exposure in the first three days of life," Dr Behrendt said.
The rows were best sown in a north-south direction, to prove shelter from the cold winds and after lambing the pasture could be cut for hay.
"We also graze the site in about March to take off the grass-seed heads and control excess growth," he said.
"But you do have to be careful and make sure the plants are not over-grazed. These hedges work best for winter-early spring lambing when the coldest weather is about."
