Pregnancy Disorders (Metabolic) in Transition Ewes
|Last Reviewed:||11 February 2010|
|Written by:||Christoph Wand - Beef Cattle, Sheep and Goat Nutritionist/OMAFRA|
Table of Contents
- Transition Philosophy
- Common Difficulties with the Transition Prolific Ewe
- 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 Ewe
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 prolific ewes.
- 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 acidosis risk.
- 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
|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)||70%-75% TDN|
|15%-17% protein||16% protein|
|0.8% calcium, 0.3% phosphorus||0.75% calcium, 0.3% phosphorus|
|100 IU Vit E, 0.2 ppm Selenium (Se)/day||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.
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