Lambing and lactation

Page last updated: Monday, 17 December 2018 - 11:14am

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The first 48 hours of a lamb’s life are critical – around 90% of lamb mortality from birth to weaning occurs within this period. It is also a critical period of time for the ewe. She is at risk during birth, has her highest demand for food and is vulnerable to sudden changes in diet and conditions.

Lambing success is very dependent on the condition of the ewe coming into lambing and the conditions at lambing including feed on offer, shelter and predator control.

The survival of single and twin born lambs is mostly affected by birth weight, which in turn is influenced by the ewe’s condition over pregnancy with late pregnancy being the most important phase. Lamb birth weight can be an indicator of energy reserves of the lamb and its exposure risk to hyperthermia or dystocia.

Table 1 The major causes of lamb death within 48 hours of being born. (The range includes results from four studies)

Cause of neo-natal lamb death

Percentage (%)

Starvation/mis-mothering/exposure

27-58

Difficult birth

18-33

Infection

4-5

Predation

2-7

Unidentified

2-12

Pre–natal (pregnancy)

1-3

Ewe and lambing management at lambing

The key requirements for good lamb survival are:

  • good lamb birth weights
  • maternal bonding
  • good lactation and colostrum
  • protection from wind chill.

The ideal birth weight for lambs is between four and six kilograms (kg) and this is influenced by the nutrition of the ewe in pregnancy. Having ewes in condition score 3.0 at lambing ensures that survival and production are at high levels.

Twin lambs are much more sensitive to changes in ewe condition score and twinning ewes should be given higher priority when feed supply is limited. Higher condition score of the twinning ewe at lambing (condition score 4.0 compared to condition score 3.0) can mean an increase in lamb survival of more than 10%.

On-farm case studies of lamb survival show that 15–20% more lambs survive when born to ewes of condition score 3.0-3.5, compared with ewes of condition score 2.0-2.5.

Any individual ewe whose condition score is less than 2.0 prior to lambing should be managed separately and have increased access to good feed. Twinning ewes are more likely to be in danger than single bearing ewes, with at least 2–3% higher mortalities for the same condition score.

Ewes in condition score over 4.0 (particularly single ewes in a good year) may be at increased risk of having lambing difficulties (dystocia).

Table 2 Management targets for lambing ewes. Note: pasture targets are in kilograms of dry matter per hectare (kg DM/ha)
Ewes

Condition score target

Pasture target

(kg DM/ha green feed on offer)

single ewes

3.0 1500

twinning ewes

3.0+ 1800+

Ewe mortality can be a serious issue when condition score falls below 2.0 during late pregnancy or at lambing.

Maternal bonding and lamb survival

Poor nutrition and low condition score have detrimental effects on ewe and lamb behaviour, contributing to increased lamb mortality. Ideally the ewe and lambs should remain at the birth site for at least six hours; twelve hours being optimal.

If feed on offer is low the ewe is more likely to move off the birth site to look for food. Ewes in poor condition at lambing will also be more likely to search for more food, leaving the lamb or lambs behind prior to suckling. Poor nutrition is likely to impact on the ewe’s maternal response to groom the lamb and ensure suckling takes place.

A Merino ewe with her new born lamb.

Weather impacts on lamb survival

Weather has the greatest impact on twin born lambs as they have smaller liveweight per surface area. Wind chill is also important and cold and wet conditions are worse than cold conditions without rain.

Evergraze experiments found that twin lamb survival increased by 15% when lambs were given shelter; twin lamb survival at the average birth weight increased from 76% in the open areas to 87% in the sheltered areas.

Milk supply and colostrum

It is critical that lambs receive colostrum during the first 24 hours of life in order to ensure adequate absorption of colostral antibodies. Antibodies are large protein molecules that can cross the intestinal wall and enter the blood stream of the lamb only during the first 24 to 36 hours of life. Absorption of these antibodies is most efficient during the first few hours after birth.

Ewe colostrum can vary in quantity as well as viscousness. Ewes in good condition will produce good levels of fluid colostrum. Those in poor condition may produce colostrum that is thick and difficult for the newborn to suckle.

Improving lactation

Ewes in good condition during lactation produce more milk, which means larger lambs with higher survival and growth rates through to weaning. Feed on offer (FOO) during lactation is the driving factor.

Ewes in good condition will use fat reserves and pasture to provide high lactation levels, and will therefore tend to lose condition over lactation.

Daily milk production peaks at two to three weeks and 40–50% milk is produced in the first four weeks of lactation. Competition for feed between ewes and lambs begins about four to six weeks after lambing commenced. By 12-15 weeks of lactation milk production has almost completely ceased and the ewe is competing fully for feed with the lambs.

If supplementation is required then it is important to provide good levels of roughage in the diet, even low quality barley straw, as well as high quality grain.

Table 3 Management targets for lactation
Ewes

Condition score target

Pasture target

(kg DM/ha green FOO)

single ewes

2.7-3.0 2000

twinning ewes

2.7-3.0 2500+

Lambs eat pasture from around two weeks old and the lamb’s rumen is fully capable of digesting pasture by three weeks of age. However, lambs weaned before six weeks are likely to suffer as they can’t make up for the lost milk by suddenly increasing pasture intake. Lambs can increase pasture intake a little if milk intake declines but lambs under eight weeks are likely to grow better on their mother than if weaned.

Single lambs consume more milk and can grow around 80 grams (g)/day faster than twin lambs in early lactation and 35g/day faster than twins in late lactation. This occurs even if twin ewes are grazing high FOO pastures. Although ewes produce more milk for twins, these lambs get around 68% and 59% of the milk intake of single lambs in peak and late lactation respectively.

Imprint feed lambs

Imprint feeding of lambs with ewes before weaning will reduce the time required to train lambs to eat grain. At least four to six feedings of grain are recommended over a two to four week period so that lambs recognise the feeder and remember it.