Pregnancy Disorders (Metabolic)
in Transition Ewes
Table of Contents
- Transition Philosophy
- Common Difficulties with the Transition Prolific
- Ration Formulation and Management
- General Ration Recommendations
The "Transition Cow" is considered by many
nutritionists and academics to be the "Frontier of Dairy Nutrition".
This transition period is that of late pregnancy to very early lactation.
Often it is considered to be from 2-3 weeks pre-calving to 2-3 weeks post-calving.
Over this very short period the animal is forced to deal with radical
changes such as:
- final difficulties of gestation and intake restriction
- parturition itself
- onset of lactation
- intake and appetite fluctuations
- diet transitions (from a gestation diet to a lactation diet), and
- fluctuations in hormone levels.
The dairy cow transition philosophy can be applied to
the prolific ewe, as this period is certainly at the frontier of ewe flock
nutrition. There are many similarities to the transition dairy cow, except
timelines shift ahead 1 week-10 days. This puts the transition timeframe
in the prolific ewe 4 weeks pre-lambing to 2-3 weeks post-lambing. The
massive draw experienced in dairy cattle is very similar to that in the
ewe in late gestation. Protein and minerals are rapidly being pulled from
the ewe's system much like in the dairy cow, only here they are incorporated
into fetal tissue rather than milk solids. It is nonetheless deposition
of these nutrients outside of the "self".
Common Difficulties with the Transition Prolific
Pregnancy Toxemia - Ketosis in Sheep
"Pregnancy Disease" or "Pregnancy Toxemia"
are the sheep industry terminologies for the condition veterinarians,
academics and ruminant nutritionists know as ketosis. Another technical
term for it is acetonemia. It is characterized by the "sweet"
smelling breath of affected animals, and depressed feed intake. The 'sweet'
smelling breath is a result of elevated beta-hydroxy butyrate. This substance
is an artifact of inappropriate fatty acid metabolism (breakdown of fat)
by the liver. This is caused by the liver being unable to function properly
during the massive breakdown of body fat seen in prolific ewes attempting
to support fetal growth.
As with most disorders seen in dairy cattle immediately
after calving, ewes experience ketosis in the final weeks and days of
pregnancy. This is because the highest nutritional demand in sheep production
is in the ewe prior to lambing, as a result of rapid fetal growth. Generally,
it is the result of ewes entering late gestation in an over-fat condition
[body condition score (BCS) 3.5 or greater], and undernourishment of ewes
carrying litters. It is serious as it affects lamb health and survival,
as well as ewe survival and productivity.
Avoidance of the condition is the preferred alternative.
This can be achieved by following several principles.
Recognize that the late gestation period is the single most critical
period for ensuring appropriate nutrition. Formulate rations diligently,
taking into consideration forage quality and intake. Manage these
animals with the special attention they deserve.
Identify which ewes are likely to have higher lamb numbers at birth.
This can be accomplished based on previous performance, genetics or
ultrasound diagnosis. This will ensure that:
productive animals are managed accordingly. Consideration must be
made for the potentially reduced rumen volume and resulting intake
capacity, while ensuring a higher nutrient intake. Typically, this
means diet nutrient density will have to increase substantially in
less productive animals, i.e., ewes carrying singles or twins, can
be grouped and fed an appropriate ration.
Ensure that the BCS of ewes entering late gestation (3-5 weeks prior
to lambing) are in the ideal range of 3.0-3.5. BCS should remain in
this range, while increasing slightly, not exceeding 3.5.
A veterinarian may recommend the use of ionophores for the late gestation
ration. Work in dairy cattle indicates ketosis is reduced when an
ionophore is included in the ration.
Contact your veterinarian for a diagnosis and the treatment
protocols for pregnancy toxemia. Propylene glycol is a commonly recommended
treatment that can be administered according to manufacturer's recommendations.
Following treatment to restore normal metabolism, assess the affected
ewes' nutritional status and adjust the energy level of the diet. This
adjustment needs to consider moving to a new ration as quickly as possible,
while slowly enough to ensure proper metabolic and rumen transition.
High Maintenance (Genetic Interaction)
Many prolific ewes have more internal fat as opposed
to back fat relative to traditional breeds. In winter lambing systems
and where ewes are shorn, the reduced insulation and higher basal metabolism
of such animals requires higher maintenance energy allowance to prevent
exacerbating the above issues.
Be prepared to increase energy in prolific ewes by 5%-10% to compensate
for extreme cold conditions (e.g. outdoor housing in February with
little wind shelter).
The literature reports that energy use may be as much as 45% higher
in close shorn versus unshorn late gestation ewes. Keep this in mind
when shearing pre-lambing, as BCS may suffer rapidly.
Low BCS is a major predisposing factor to several transition
problems. Thin ewes may be slow to cycle (show estrus) when compared to
moderate or average BCS ewes in accelerated/out-of-season breeding systems.
The high level of grain required to achieve the ideal
energy balance increases the risk of acidosis. When grain levels approach
50% of the diet, and rumen volume is reduced due to fetal space requirements,
the relative mass of grain compared to rumen volume is amplified and increases
- Use more caution with these animals than any other group!
- Reduce size of individual grain feedings and feed more frequently
(as per Sheep Ration Formulation Program guidelines [OMAF, Version 2.0.1)]
- no more than 30% of DM as grain in 2 feedings.
- 40% - 3 times per day
- 50% - 4 times per day
- 55% - 5 times per day
- Caution: Grain processing makes starch more quickly available!
- Total Mixed Rations (TMR) would be ideal.
Milk Fever (Pre-lambing)
Milk fever has appeared in a few cases with more productive
ewes. However in ewes, the condition appears pre-lambing as fetal bone
deposition is rapidly occurring. This rivals the magnitude of calcium
(Ca) mobilization in the early lactation dairy cow. In the cow, it is
now accepted that excessive potassium (K) levels are a risk factor. Timothy
and alfalfa hays especially are commonly high in K, particularly where
these forages have been heavily fertilized with potash. Avoid high K feeds
in gestation. Other hay species do have lower K levels.
Poor Colostrum Quality/Quantity
It has been clearly demonstrated in other ruminant species
that insufficient protein, energy and Vitamin E intakes all negatively
impact on colostrum quality and quantity. Additionally, colostrum has
extremely high levels of vitamins A and D, both drawn from the ewe's body.
Ensure diets are balanced and intake is adequate, and
monitor and record poor colostrum events.
Ration Formulation and Management
Note the similarities between the 2 rations shown in
Table 1. The requirements for the lactating animal are
in fact about 30% higher than in the gestating ewe. However, due to the
rumen restrictions of ewes carrying litters, the intake could be lower
in gestating ewes by 20%-30%. As a result, as long as the lambing due
dates are similar for a management group (within 2 weeks), those prolific
ewes can be fed similar amounts of grain whether they have lambed or not.
Also, females may still be growing after their first lambing. For practicality,
these animals can be managed as having a fetal count one higher than actual.
In the same spirit, animals in the last three weeks that are in thin body
condition should be fed as having one extra fetus per half BCS under 3.
For example, the growing ewe diagnosed by ultrasound as having 2 fetuses,
that is approaching her second lambing at BCS 2.5, will be fed as though
she carries 4.
General Ration Recommendations
Crude protein (CP) alone is not a good indicator of forage
quality. For example, an excellent grass hay or pasture may have a CP
of 18%-20%, while alfalfa of comparable maturity and therefore energy
may have a CP of 25%-28%.
The prolific ewe is a highly specialized animal that
is dependent on proper management to be productive and healthy. Ewes in
the transition period around lambing are the group for whom proper management
is most critical for immediate and long-term performance of the ewe herself
and her lambs. This period extends from 4 weeks pre-lambing until 2-3
weeks after the ewe has lambed. The critical points to remember are:
- prolific breeds may not be as winter hardy as other breeds
- provide additional feed for recently shorn ewes
- feed forages high in digestibility to ensure adequate intake and nutrition
- practice frequent and small concentrate feedings
- monitor feed intake and behaviour
- provide adequate energy [TDN or net energy (NE)], protein, Ca, P,
Vitamin E and selenium
- use a ruminally undegradable protein ("bypass protein")
source, avoiding excess CP
- feed essentially the same diet pre- and post-lambing
- avoid forages with excessive potassium (K) levels
- manage prolific transition ewes similarly to today's elite dairy cows
Tablel 1. Approximate Ration
Requirements for Late Gestation Ewes (fed per head per day in the last
3-4 weeks of gestation)
Pre-Lambing (Gestation) Rations
Post-Lambing (Lactation) Rations
ad lib good forage (1st cut)
ad lib 2nd cut hay
680 g (1.5 lbs.) or more grain/day
750 g (1.65 lbs.) or more grain/day*
70%-75% Total Digestible Nutrients (TDN)
0.8% calcium, 0.3% phosphorus
0.75% calcium, 0.3% phosphorus
100 IU Vit E, 0.2 ppm Selenium
100 IU Vit E, 0.2 ppm Se/day
* unless a BCS/milk yield drop is ok
Assuming ewes gestating and subsequently suckling three
or more lambs. Complete and accurate ration formulation should be undertaken
using the Sheep Ration Formulation Program version 2.0.1.