Sheep Extension Program
Montana Farm Flock Sheep Production Handbook Nutrition Part 2 — Section 6 of 7
By Rodney Kott, Extension Sheep Specialist, Animal & Range Sciences Department, Montana State University
The most productive ewe in any flock of sheep is neither too thin nor too fat. Although measurements of body composition on live animals are estimates, producers must utilize the best system available. Body weight alone is inadequate because of apparent differences in mature body size among different breeds and individuals within a particular breed. The use of both body weight and condition scores can help producers make important feed management decisions. Body condition scoring is a simple but useful procedure which can help producers make management decisions regarding the quality and quantity of feed needed to optimize performance.
Condition scoring is a system of describing or classifying breeding animals by differences in relative body fatness. It is a subjective scoring system but provides a fairly reliable assessment of body composition. In sheep, scores range between 1 and 5 with the lower-scoring ewes being the least fat and the highest-scoring ewes being the fattest. A ewe in average body condition would have a score of 3. Usually 90% of the ewes fall within the 2, 3 or 4 range and usually 70 to 80 percent of the animals will usually fall within a range of two condition scores.
Ewes in this body condition have no fatty tissue detectable between skin and bone. These ewes appear weak and unthrifty.
|2||Ewes in this body condition have only a slight amount of fatty tissue detectable between skin and bone. Spinous process are relatively prominent. These ewes appear thrifty but have only minimal fat reserves.|
|3||Ewes in this body condition have average flesh but do not have excess fat reserves. This condition score includes ewes in average body condition.|
|4||This condition score includes ewes that are moderately fat. Moderate fat deposits give sheep a smooth external appearance|
|5||Includes ewes that are extremely fat. Excess fat deposits can easily be seen in the brisket, flank and tail-head regions. These ewes have excess fat reserves to the point that productivity may be impaired.|
A sheep producer will find that body condition scoring is fairly easy and they will develop confidence in their ability relatively quickly. Condition scoring involves both visual and hands-on appraisal. Scoring is accomplished by using the hand to feel the fullness of muscling and fat cover over and around the vertebra in the loin region. While the ewe is standing in a level and a relaxed position the fingers and thumb are used to determine sharpness of the spine and transverse process behind the last rib and in front of the hip bone (loin area). In addition it may be helpful to determine the extent of fat covering over the fore ribs. After all factors have been evaluated an overall condition score is assigned. If a producer is unsure as to whether a ewe is a 2 or 3, a condition score of 2.5 should be used. As a general rule of thumb mature ewes vary 6 to 7 percent in body weight for each half unit change in body condition score. For example, a ewe in condition score of #3 weighing 150 pounds would weigh between 165 and 175 pounds if she were in condition score #4.
It may be impractical for large sheep producers to condition score all ewes; however, if a producer condition scored approximately 10-20% of the flock this would be adequate to get an estimate of the condition of his entire flock. Regular condition scoring and action on the results will ensure healthier ewes and more pounds of lamb and wool marketed per year.
Optimum feeding systems can vary from the intensive feeding of confined sheep, where they are entirely dependent on harvested feeds at one extreme, to the supplementation of flocks mainly dependent on range forage. An optimum feeding system consists of a planned nutritional regime that will result in an expected biological and economic response.
The nutritional status of the ewe at anytime during the year has an influence on productivity. Nutrition in the weeks just prior to and after breeding determine the number of lambs conceived. Nutrition during pregnancy determines the number of lambs born alive and lamb birth weights which are directly related to subsequent lamb survivability. Proper nutrition during lactation is critical for adequate milk production. After weaning, nutrition is important for replenishing body reserves, preparing the ewe for another production cycle.
Direct observation of a sheep’s nutrient needs has provided a comprehensive framework for the formation of optimum feeding strategies. However, rarely do these strategies involve meeting the ewes exact nutrient requirements at each stage of her reproductive cycle. Instead, for economic, practical and sound physiological reasons they involve periods where the nutrient intake exceeds requirements and other periods where nutrient consumption is below the requirements. Body composition at a given point in the production cycle may influence both production response at that point and response to varying levels of nutrition. The goal is to achieve a balance in body composition over the yearly reproductive cycle.
One of the best ways to determine how a ewe should be fed is by monitoring her changes in weight. Ideally, a ewe should lose 5 to 7 percent of her body weight during lactation, recover this during the post weaning period and then gain weight during gestation.
A sheep flock consists of ewes of different sizes, body conditions and different levels of production and therefore varying nutritional needs. Although it is impossible to treat each ewes needs separately, there are times that it is beneficial to divide the flock into groups of ewes having similar needs, feeding each group accordingly.
Flushing is the practice of increasing intake of ewes prior to and during mating. Its purpose is to increase the ovulation rate, and subsequently, the lambing rate. It can be accomplished by turning ewes onto a lush, high quality pasture just prior to breeding. If such pasture is not available, the same result can be obtained by supplementing the ewes regular diet with about .25 to .50 pound of grain or pellets per head, per day. Flushing usually begins about 2 weeks prior to joining with rams and continues for about 2 to 3 weeks into the breeding season, for a total flushing period of 4 to 6 weeks.
The response to flushing can be divided into two components, the static effect of increased body weight or body condition, not specifically related to the breeding season, and the dynamic effect which is specific to the breeding season.
As a general rule, each 10 pound increase in body weight increases lambing rates by about 5 to 6 percent. The dynamic flushing effect, on the other hand, is distinguishable from the live weight effect and is specific to the immediate pre-mating and mating periods. Ovulation rate appears to respond to short term increased nutrition within a specific, intermediate range of body condition. Although results vary greatly, most studies suggest that flushing will improve lambing rates by 10 to 20 percent in ewes with body condition scores of 3 or below. However, when ewes have body condition scores of 4 or higher, little additional benefit will be obtained by flushing.
Although it is not likely that all the benefits ascribed to flushing will be fully realized under all conditions, the general feeling persists that the practice will result in: 1) more eggs being shed and therefore higher lambing rates; 2) the ewes coming in heat more promptly; and 3) more certain and prompt conception — with lambs arriving in the early part of the lambing season.
Affect Of Body Condition And Flushing On Ovulation Rate.
Poor nutrition during pregnancy can lead to lamb deaths before, during and soon after lambing due to numerous complex interactions. Many of the lamb deaths that occur shortly after birth can be attributed to nutritional factors during pregnancy which influence placenta growth, fetal development and ewe mammary gland development. Quite often cold weather is blamed for lamb losses when in fact the major contributing factor was inadequate nutrition during pregnancy. Critical time periods for placental development, fetal growth and mammary gland development is between day 30 and day 90, after day 90 and after day 120 of pregnancy, respectively.
Early & Mid:
During pregnancy the ewe must be fed enough to meet her requirements for maintenance, fleece production, fetal and associated tissue development and growth if the ewe is not fully mature. Since fetal growth is minimal during the first 15 weeks of pregnancy the ewes nutrient requirements during this time are only slightly higher than they are for maintenance. There are however some important functions that occur during this period and thus nutrition cannot be ignored. During early gestation the embryo becomes attached to uterine walls (first 45 days of pregnancy). Extremes in nutrition (severe under or over feeding) during this period is detrimental to this process. A drastic reduction in nutrition during the first 45 days after conception can result in significant reductions in reproductive performance. Also the majority of placental development occurs during mid gestation (day 30 to 90 of pregnancy). Research suggests that if in good condition at conception, ewes can lose a little weight or condition during mid-gestation. However, excess weight loss will result in poor placental development, which will in turn result in lower fetal growth rates and reduced lamb survival rates. Good nutrition during late pregnancy is wasted if adequate placental development has not occurred.
The last six weeks of gestation is the most critical period in ewe nutrition. During this period approximately 70 percent of the fetal growth occurs. Poor nutrition during late pregnancy will cause lighter lambs at birth, uneven birth weights in twin and triplet born lambs, reduced wool follicle development and low energy reserves in the new born lamb. Lowered energy reserves in the newborn lamb will result in increased lamb losses especially in colder weather. Severe under nutrition will lead to pregnancy toxemia and possibly ewe death.
Lamb Fetal Growth
Lamb birth weight is a major factor affecting lamb mortality. Birth weights vary from 3.5 to 20 lbs. Although these differences are associated with breed, dams age and litter size, they are highly dependent on ewe nutrition and in particular energy intake during the last month of pregnancy. Inadequate energy intake during this period will result in lowered birth weights which in turn is a major factor affecting lamb mortality. There may be as high as a 12 percent increase in lamb mortality for every 2 pound decrease in lamb birth weight. On the other hand, excessive levels of feeding may result in lambs with increased birth weights leading to lambing difficulties.
Birth Weight & Lamb Mortality
Ewes in late pregnancy require 50 percent more feed if bearing a single lamb and about 75 percent more feed if bearing a twin lamb, than they do earlier in gestation. If the ewe is fed a high-roughage diet, she will usually not be able to consume enough to supply her requirements for energy. When on high-roughage diets it is generally advisable to supplement the ration with .5 to 1 pound of grain during the last 3 to 4 weeks of pregnancy. In situations where large numbers of multiple births are expected, it is desirable to begin graining ewes as early as six weeks prior to lambing. All changes in grain feeding should be gradual.
During this period there is a limit to the extent to which body fat reserves can be utilized, as excessive mobilization of fat results in pregnancy toxemia. Pregnancy toxemia (pregnancy disease, twin lamb disease or ketosis) is a result of improperly-fed ewes in late pregnancy. Affected ewes are most often carrying multiple lambs.
After lambing, the feed allowance of the ewe should be increased according to her needs. A ewe will usually reach maximum milk production by two to three weeks after parturition. Milk production generally declines fairly rapidly thereafter. Assuming the ewe has the capacity to produce milk, she will produce at this level only if challenged by the lambs nursing her. Since single lambs normally are not able to consume all of the ewe's milk, the ewe will adjust her milk production downward to the level the lamb is consuming. Ewes nursing multiple lambs will produce 20 to 40 percent more milk than those nursing singles and thus have greater nutritional requirements. For maximum rate and efficiency of lamb gains, it is desirable to separate ewes with multiple lambs from ewes with singles and feed each according to their nutritional needs.
In the first month after lambing the lambs growth is primarily dependent upon milk production. Milk is critical in the first 3 to 4 weeks of the lamb’s life and in this period the correlation between milk intake and live weight gain is approximately .90. Lambs receiving inadequate amounts of milk can compensate to some degree by increasing their consumption of feed. However, because of the differences between the digestibility of milk and feed, dry matter intake of feed must increase by about 3 to 5 units to compensate for each unit decrease in milk consumption.
A ewe suckling two lambs growing at .6 pounds per day is as productive as a dairy cow yielding 65 pounds of milk per day. To prevent loss of her body tissue, daily intakes of over 7.2 Mcal. of metabolizable energy (three times maintenance) are required. In practice this cannot be achieved. As in high producing dairy cows, it is impossible to feed a high producing ewe enough feed to prevent body weight loss during early lactation. Fortunately early lactation is a period in which body fat can safely be used to meet some of the high energy demands of lactation. During this period a loss in body condition score of 1.0 is quit acceptable, provided she was in proper body condition at lambing (3.5+). However, the ewe must have sufficient reserves of body fat to mobilize and use for milk production.
Fat can only be used efficiently for milk synthesis if the ewe is absorbing adequate amounts of amino acids from her diet. Thus, protein intake is critical during this period if maximum milk production is to be achieved in high milk producing ewes. Thus protein as well as energy is critical in a ewe’s diet during early lactation.
Late (last 4-6 weeks lactation):
Although some ewes continue producing a good supply of milk throughout the nursing period, milk production in most ewes declines fairly rapidly after two to three weeks and is of minor importance after 8 to 10 weeks. Milk production during late lactation is relatively low and nutrient needs are substantially lower than they were during early lactation. Also by this time, ewes are usually on lush spring grass which will be adequate in most cases.
This is a time of rest for the ewes. It is the period of time that the ewe’s body condition can be adjusted so they are in appropriate body condition at breeding.