Coopworth Technical Bulletin 3

Management to maximise lamb production from prolific ewes

Introduction

Bulletin 1 addressed winter/early spring feeding of ewes and bulletin 2, feeding and managing the ewe flock from weaning to mating. Together, these first two bulletins summarised the feeding of the ewe flock throughout the year.

This bulletin goes into more depth on managing and feeding prolific ewes and their lambs in late pregnancy and through to weaning.

Too often we hear fanners using the phrase "one good lamb is better than two or three small ones", being used as an excuse for low reproductive rates in their systems. This implies that twins and triplets must be small - this is not necessarily so. Coopworths have the potential to have high lambing percentages and the maternal ability to rear very good multiples. The application of knowledge about feeding requirements of prolific ewes and lambs, and the use of techniques like ultrasound, enable many farmers to successfully rear twins and triplets to heavy weaning weights.

This bulletin addresses three key areas.

(I) Feeding and management of ewes in late pregnancy

(ii) Lambing management

(iii) Growth of lambs to weaning

(I) Feeding In late pregnancy

Correct feeding of single vs multiple bearing ewes in late pregnancy is very important for the following reasons:

• correct feeding levels of twin and triplet bearing ewes will increase lamb birth weights which in turn increases lamb survival and increases weaning weight of lambs

• correct feeding of single bearing ewes will reduce the incidence of dystocia caused by large singles, which in turn increases survival rates.

The trick is in ultrasound scanning: get a reliable scanner to ultrasound the ewes at about day 70-80 of pregnancy, and to separate the single and multiple carrying ewes from about day 100 (or a little later). They should be fed at levels indicated in the following table (reproduced from bulletin 1).

Pasture requirement: height of pasture (cm) post-grazing for mating (0 days) to early lactation for ewes carrying and rearing 0, 1,2 and 3 lambs

No. Lambs

0-100 days pregnancy

100 days • 125 days

125 days-term

First 4 weeks lactation

 

 

Pasture Req.

Pasture Height

Pasture Req.

Pasture Height

Pasture Req.

Pasture Height

Pasture Req.

Pasture Height

0

1.1

2

1.1

2

1.1

2

1.1

2

1

1.1

2

1.3

2.5

1.5

3

2.6

6

2

1.1

2

1.5

3

1.7

4

2.9

6

3

1.1

2

1.6

3

2.1

5

3.0

7

Table Key

Pasture requirement to maintain ewe body condition - kg Dry Matter/day/ewe (+ lambs)

Pasture height • cm after grazing. Assume ewe has bodyweight 60 kg (in non-pregnant state).

In New Zealand, about 20% of all lambs born are dead within 48 hours of birth. There are a large number of causes, but birth weight is important. As a rule of thumb, death rates increase in lambs weighing more than 5 kg (due to dystocia which causes ewe losses) and in lambs weighing less than about 3.5 kg (due to exposure). The target should be 4.5-5 kg. This is a good size for lambs - it is optimum for survival and also affects weaning weight (for every 1 kg difference in birth weight, there is about a 2 kg difference in weaning weight).

Twin bearing ewes need to be fed well to meet this target, but single bearing ewes are often restricted to quite low pasture heights to reduce lamb size.

(II) Lambing management

The aim is to optimise lamb survival and to initiate ewe lactation and lamb growth with minimum labour input. Coopworth ewes are bred for easy care characteristics - intervention at lambing should be minimised to just those ewes needing assistance (these should be identified and culled after weaning).

Generally, the choice is to set stock high fertility ewes over lambing. Lambing mobs are set up about seven days prior to the start of a lambing Interval using crayon marks to identify expected lambing Intervals (see bulletin 1)

(a) Stock densities

Multiple bearing ewes should be stocked at 10-15 ewes/hectare (depending on feed levels), so they have sufficient area to find a lambing site which they will tend to occupy for about 24 hours after lambing - the bonding process is critical to assist lamb survival.

Single bearing ewes can be stocked at higher densities because the process of lambing and bonding is shorter (six hours).

(b) Feeding levels

Multiple bearing ewes should be on feed of high quality and quantity (4-5 cm height). If pastures are too long, in damp conditions new born lambs may develop various illnesses and survival is reduced. (Some specialist ryegrass crops can be dangerous in this regard as lambing paddocks.) Single bearing ewes can be fed much shorter pastures (2-3 cm}.

(c) Minerals

In many areas selenium is naturally deficient In soils and historically this causes lamb deaths soon after birth, from white muscle disease. This problem is overcome by including selenium in topdressing mixtures or by drenching ewes.

(d) Shelter

Smaller lambs are more susceptible to heat loss (leading to hypothermia, exposure and death) than larger lambs. Multiple bearing ewes should lamb in the best-sheltered paddocks.

(Ill) Growth of lambs to weaning

Feed requirements of a ewe plus twins is higher than a ewe plus single. Unless the multiple rearing ewe is fed differentially, her lambs will be lighter at weaning and she herself will be lighter than the single-rearing ewe. Some farmers are weaning twins and singles at the same weight as singles through using ultrasound and differentially feeding their multiple and single bearing ewes before and after lambing.

(a) Milk production from twin vs single bearing ewes

The stimulus of having more lambs suckling causes twin bearing ewes (at the same pasture as singles) to produce more milk, but not twice the amount of milk. Therefore, each twin lamb receives less milk than a single lamb if they are in the same paddock. Pasture supply tends to be scarce, particularly in early lactation, and this further reduces milk production which affects multiple-born lambs more severely.

(b) Feeding levels

The answer is to allocate more feed to the multiple than the single suckling ewes. This can be done by scanning and lambing in different mobs, or by separating twinning ewes at lambing (not recommended as this practice is labour intensive and disruptive).

Ideally pasture height for multiple-bearing ewes should be at least 5 cm, while singles will grow at about the same rate at pasture height about 2-3 cm.

(c) Target growth rates to weaning

Attaining heavy weaning weights is important - heavier lambs are nearer target selling weights and are easier to grow to target two-tooth mating weights, and more feed can be allocated to ewes and rising two-tooths.

In Canterbury the average weaning weight (several breeds) is about 25 kg at 12 weeks. These lambs have grown say 20 kg (from 5 to 25kg) in 84 days, giving a growth rate of about 240g/day.

If growth rate is 300g/day (and many Coopworth flocks achieve this) at 12 weeks they will average 30 kg. This is a target growth rate for many intensive farms.

Productive sheep need better management


Lynda Clark

Publicity Officer Coopworth Society

If you require further information, please contact the Technical Secretary, Chris Logan, P.O Box 169. Lincoln University, Canterbury.