Farm Tech
In The Paddock
Seasonal sheep flock management tips May 2002
Shearing crossbreds in mid-pregnancy Considerable animal welfare
and production benefits
Key points
- Thousands of lambs die soon after birth each year
- By increasing the birth weights of twins and triplets, losses can
be greatly reduced
- Shearing crossbred ewes in mid-pregnancy (around day 70) can increase
the birth weights of their lambs by around 0.4 kg and their weaning
weights by around 1.0 kg
- The birth weight response does not appear to occur in ewes which are
very light (<50 kg) or very heavy (>70 kg). Nor does it occur
in those with very low (<1–1.5) or very high (>4) condition
scores.
- Ewes produce about 0.2 kg more wool a year if they are mid-pregnancy
shorn
- To protect winter-shorn ewes from exposure, they should be shorn (depending
on the region) with genuine winter combs, winter combs with lifters,
or blades
- They also must have good shelter and adequate feed after shearing
Each year, in New Zealand, more than 15 per cent of lambs die before
weaning. Most of them die within a few days of birth. This is a huge waste
of a potentially valuable resource.
Losses are highest in very light lambs, with starvation and exposure
the most common causes. A significant number of small weak lambs also
die from dystocia.
At a birth weight of 2.1 kg, the mortality rate is about 13 per cent.
Mortality declines by more than 1 per cent for every 200 grams extra lamb
birth weight until 4.1 kg, when it drops to around 2 per cent.
Once birth weights reach 5.1 kg, death rates due to starvation and exposure
drop away to almost zero.
In recent years, sheep farmers have made increased use of high fecundity
genes. This, combined with better pre-mating feeding, has led to a dramatic
increase in the number of twins and triplets, as well as the national
lambing percentage.
Because individual birth weights tend to fall as litter sizes increase,
this increase in multiple births could lead to more deaths of small lambs
at, or soon after, birth.
A solution
Shearing ewes in mid-pregnancy can increase lamb birth weights, especially
in multiple-bearing ewes. This results in an improvement in lamb survival
and in due course, farm lamb production.
Indeed, mid-pregnancy shearing has been proven to have significant animal
welfare benefits. Many lambs are saved from an early death, as are ewes
which might otherwise have become cast during lambing.
Ewe losses from dystocia are also reduced, if shearing is accompanied
by scanning and differential (reduced) feeding of single-bearing ewes.
There are many farm production benefits: farmers have more lambs to draft,
or from which to select replacements; fleece weights and quality improve;
and lamb weaning and drafting weights are increased.
Recent trials at Whatawhata and Massey University have examined various
aspects of this.
A 2-year trial at Whatawhata found that shearing in early to mid-pregnancy
increased the birth weight of singles by 0.2 kg in one year and the birth
weight of twins by 0.2 kg in both years.
The Massey trials found responses of up to 1.0 kg in combined birth weight
of twins, with an average of 0.4 kg, and in singles up to 0.8 kg. They
also showed that the response was greatest when ewes were in lighter condition
(<CS 3) in early pregnancy and lamb birth weights were likely to be
low.
A large field trial at Massey with more than 1000 twins showed that mid-pregnancy
shearing of ewes increased lamb survival by 3 per cent. In other trials
at both Riverside and Tuapaka, twins tended to have 34 per cent
higher survival rates.
In some trials, singles had higher losses, due to increased birth weight
and dystocia. These losses can be reduced by differential (reduced) feeding
of single-bearing ewes following scanning.
The increase in foetal growth is not due to increased feed intake following
shearing. Invermay trials showed that ewes used their own body fat to
support the increased foetal growth. Shorn ewes had 15 per cent less body
fat at day 140 of pregnancy than unshorn ewes.
The birth weight response does not appear to occur in ewes which are
very light (<50 kg) or very heavy (>70 kg). Nor does it occur in
those with very low (<1–1.5) or very high (>4) condition scores.
By weaning or slaughter, the birth weight advantages resulting from mid-pregnancy
shearing are generally magnified. For example, the average weaning weight
in the Massey trials was 0.9 kg for twins (cf 0.4 kg for birth weight)
and in the Whatawhata trials by 11.4 kg in both singles and twins
(cf 0.2 kg for birth weight).
In addition, there are wool production and quality benefits. Ewes shorn
in mid-pregnancy produce 0.2 kg more wool each year. Also, their wool
has better colour and fewer cotts.
Timing of shearing and management
The best lamb birth weight response is likely to be when ewes are shorn
between days 50 and 100 of pregnancy, with the optimum time being around
day 70. This means pregnancy scanning can be done at the same time.
Scanning enables the ewes to be split into dry, single and multiple mobs
for differential feeding during the latter stages of pregnancy.
Preferential feeding of multiples leads to improved ewe condition, early
colostrum production, better milk yields and faster lamb growth. Reduced
feeding in the singles mob reduces the risk of birth difficulties which
could otherwise be a problem in these ewes.
Ewes shorn during winter need to be protected from exposure. Depending
on the region, genuine winter combs, winter combs plus lifters, and blades
will leave sufficient wool to protect ewes from all except the worst weather.
After shearing, they should be put in sheltered paddocks with adequate
feed. Shelter is essential to prevent cold stress, especially if the weather
is bad. Wind and rain accentuate heat loss and in extreme conditions can
cause death due to hypothermia.
More information
Morris, S.T. etal., 2002. Mid-pregnancy shearing
a technique to improve lamb birthweight and survival. Final WoolPro
Report.
Your local farm consultant or veterinarian will also be able to help.
Alternatively, contact your local WoolPro extension specialist:
Northern North Island: Sally
Hobson tel 07-823 3321 or 025-924 751
Hawkes Bay/East Coast: Lew
Willougby tel 06-835 1888 or 025-434 417
Southern North Island: Richard
Gavigan tel 06-376 0006 or 025-499 851
Nelson/Marlborough/Canterbury: Alan
Marshall tel 03-343 7913 025 329 399
South Canterbury: Julia
Mackenzie, tel 03-680 6782 or 025-782 353
Otago: Robert
Pattison, tel 03-489 9021 or 025-323 094
Southland: Aaron
Meikle, tel 03-203 9071 or 025-846 377
|