Pasture lambing prolific sheep
Biology and management of low-input lambing management in easy-care systems
Presented at the 2007
Joint annual meeting of the ADSA, PSA, AMPA, and ASAS
San Antonio, TX
July 8-12th 2007
Tamarack Lamb & Wool
31077 County hwy 61
Hinckley, MN 55037
Tamarack Lamb & Wool added the Booroola FecB gene to Dorset ewes in 1987 through selective crossbreeding, resulting in a lambing rate of 240 to 280% in ewes that carry the FecB gene. Previously a fall and winter lambing flock, the flock was moved to late spring pasture lambing to accommodate the growing numbers of sheep. The benefits of lambing on pasture included better milk production and greater newborn survival, lower labor, considerably lower input costs, and the ability to run much larger numbers of sheep limited only by the forage resources that could be fenced. Over the past 17 years, a system of managing a prolific flock has been developed and has been so successful that it has remained remarkably the same for nearly two decades. Tools used to manage pasture and animals include the use of drift lambing, set stocking after lambing, rotational grazing, livestock guard dogs for predator control, and the use of high energy tillable crops for fall finishing. Pasture lambing requires education of both sheep and shepherd. A new set of stock handling skills are required from the shepherd, and sheep can take several years to unlearn their barn lambing habits.
Like most Midwestern flocks, the sheep at Tamarack Lamb & wool were once managed indoors at lambing time, with the assumption that the additional care bestowed on sheep in the barn would improve lamb survival. Also like many Midwestern flock owners the author strived to maximize lambing rate, because the costs of such an intensive system required that the number of lambs weaned be over 180%. Tamarack Lamb & Wool added the Booroola FecB gene to Dorset ewes in 1987 through selective crossbreeding, resulting in a lambing rate of 240 to 280% in ewes that carry the FecB gene and an overall flock average of around 200% (including non booroola ewes) with a typical lamb mortality of 15%. Previously a fall and winter lambing flock, the flock was moved to late spring pasture lambing to maximize the results from AI and to accommodate the growing numbers of sheep. The result was the accidental discovery that ewes lambing on pasture had better milk production and greater newborn survival, required lower labor, and reduced input costs. Now free to run much larger numbers of sheep, the flock sized was limited only by the forage resources that could be fenced, rather than limited by how many sheep could fit into the barn. Preweaning lamb mortality has dropped to 3% to 6% in most years. The flock became profitable.
The Tamarack flock is located in East Central Minnesota. While sheep production is not a traditional activity in the area (Dairy farming once was but is rapidly disappearing) the area does support native and naturalized mixed prairie grasses and native white clover that make excellent sheep pastures.
MATERIALS AND METHODS
My first formal education on pasture lambing was through a grazing seminar organized by the author, held at Pine Technical College, Pine City, Minnesota and instructed by Don and Virginia Wilkinson of Scotts Valley Oregon in 1991. I also visited sheep producers in New Zealand to gain further knowledge about pasture lambing systems and forage management. The rest was trial and error refining the program so it fit my set of circumstances.
RESULTS AND DISCUSSION
Why choose pasture lambing?
Pasture lambing allows one person to manage considerably more sheep with minimal capital investment. While highly mechanized barn lambing systems can be highly labor efficient (Alderfer 1994), they require considerable investment in buildings and machinery not readily justified without other farm enterprises to help share the cost. The second major advantage to pasture lambing is the reduction of input costs. As much as $16 per ewe is required to manage a lambing ewe in an indoor lambing system to pay for purchased feed, bedding, labor, structure, interest, and fuel to haul feed in and manure out (McNally 1999). The third advantage to pasture lambing is that ewes lambing on pasture experience fewer problems with dystocia and lambs are less likely to acquire infectious diseases common to newborns such as pneumonia and Escherichia coli scours (Rook 2005).
Pasture lambing management systems
There are two lambing systems used in a pasture lambing program. Producers choose either to use drift lambing, or set stock lambing. Drift lambing is where the entire flock is managed as one drop bunch, and the farm is divided into many paddocks to allow moving the drop bunch every 1 to 3 days. During each day of lambing, the drop group is moved forward to a fresh pasture, and the ewes that have lambed during the last 1 to 3 days are left behind in the paddock they gave birth in. The ewes left behind are set stocked (remain in that paddock) for the next 30 to 50 days. Drift lambing requires a minimum of seven paddocks if ewes are moved every three days, to as many as 42 paddocks if ewes are moved twice per day. The number of ewes left behind and the decision to move, is based on when enough ewes have lambed to satisfy the stocking rate for the paddock. i.e. if a 10 acre paddock can supply enough grass to support 5 ewes to the acre for the next 30 days, then the drop bunch is moved when 50 ewes have lambed in that paddock. Paddock size should reflect the number of ewes expected to lamb in less than a 3 day period. In the example above, the flock would need to drop those 50 lambs in a one to three day period, or the paddock size would need to be changed so that the enough ewes will have lambed to reach the desired stocking rate in one to three days time. If the shepherd waits too long to move the drop bunch, ewes that have already lambed are much more likely to join the drop bunch and lambs will become separated from their dams. After 21 days of lambing, there should be sheep distributed throughout every paddock.
Set stock lambing is where the flock is distributed through out the farm just before lambing begins with a set number of ewes placed into each paddock based on the carrying capacity of each paddock. The ewes then remain in that paddock through lambing and throughout the first 30-50 days of lamb rearing.
Drift lambing offers the opportunity to better manage predator and weather related losses because the drop bunch can be relocated to more sheltered paddocks during storms, or predator deterrents can be concentrated where the most vulnerable lambs are. Drift lambing is also more suitable for flock owners who keep production records as all the new lambs will be located in one relatively small area. Drift lambing also provides a distinct advantage in that all the lambs in a given paddock are the same age, so there is less bumming from older lambs, who can sometimes learn to target a ewe giving birth and steal her colostrum before she has bonded to her own lambs.
Set stock lambing offers the very distinct advantage in that it is the lowest labor lambing system of all. Set stock lambing is more suitable for flighty sheep that do not tolerate people in close proximity, and because there is less sheep handling, is more suitable where unskilled labor is the only labor available. Granny behavior may be less problematic in a set stock system as there will be less congestion of lambing ewes. Grannies are ewes that are about to give birth, and go about stealing newborn lambs from other ewes.
Drift lambing does require a skillful shepherd who can quietly walk through the drop bunch without distressing the ewes that have lambed, and gently urging on the ewes that have not lambed. This person also needs to be experienced enough to be able to readily recognize a ewe that has lambed vs a ewe that has not lambed, solely by her appearance. Those who are relatively inexperienced are advised to paint the forehead of ewes that have lambed with an aerosol spray paint as they process the newborn lambs. Thus when the sheep are gathered up to move to the next paddock, one can make a quick search to see if any painted ewes have been accidentally gathered up.
Drifting is best done after the morning graze while the ewes are full, but before they lay down. At this time, the flock is usually distributed well through out the paddock, making it easier to avoid disturbing newly lambed ewes. Ewes that are full will not rush the gate which will help prevent dragging any lambed ewes, or newborn lambs with them.
newly lambed ewes and their lambs just after the morning drift
Lamb processing (tagging, docking tails, and castrating) is usually done on a daily basis in drift lambing within hours of birth, or done at the end of lambing in a set stock lambing system. The advantage of processing lambs during lambing, is that the tail will be healed before flies are a major problem. The advantage of processing lambs at a later date is simply one of labor management. By not processing lambs during lambing, one person can care for a greater number of lambing ewes.
Effect of management on bonding
Lambing management is all about managing for optimum ewe and lamb bonding at birth. The ewe will intially bond to the birthing spot where the amniotic fluid was spilled (Wilkinson 1991). The amount of time spent at the spot relates to the number born, but also other factors such as the available grass supply, her need for water, weather stresses such as wind or heat, biting insects, and disturbance by other animals including working dogs and humans. Bonding will be enhanced when lambing takes place during favorable weather (not too hot or too cold), on pastures with adequate forage supply so that she can procure all she needs to eat within 30 feet of her newborns, and where disturbance is kept to a minimum. It is also important that ewes are in good health and nutritional status. Ewes that are stressed from poor health or poor nutrition will have a lower desire to care for their lambs.
Sward management is an important part of ewe and lamb bonding. When grass is too short (less than one inch), ewes are inclined to wander far from the birth site in search of feed, increasing the chance that multiple birth lambs will become scattered and lost. Sward height can also be too tall (greater than 8 inches) increasing the chance that a lamb that has wondered only a short distance from the dam might become lost. A lamb that is separated from the ewe for as little as two to four hours just after birth may be rejected by the dam. Ideally sward height should be between 2 to four inches. This height allows great visibility and optimum nutrition.
Post lambing management consists of set stocking ewes and newborn lambs for a period of 30 to 50 days. This is a very important part of management to enhance ewe and lamb bonding. Ewes manage lambs in one of two methods; they either take their lambs with them when out grazing, or plant the lambs at a rendezvous site and return to the site to suckle their lambs. Set stocking is particularly important to lamb survival with the ewes that rendezvous with the lamb. These lambs depend greatly on recognizing the rendezvous site to find their mother. If relocated, these rendezvous lambs may spend a lot of energy searching for the dam at the new location. This searching activity decreases the amount of time spent suckling and resting which in turn reduces lamb performance or can result in orphaning when lambs fail to relocate the dam in a 12-24 hour period. Mortality of newborn lambs can be increased when newborn lambs are relocated (Rook 2005).
At the end of the 30 to 50 days post lambing, ewes and lambs can be consolidated into a single large group to more effectively manage the forages. It is important that a paddock never be split, but that sheep are always consolidated by either merging paddocks together or by simply removing fencing where pastures were subdivided with temporary fencing. Splitting a paddock (i.e. removing just a portion of the ewes and lambs) is always risky because there can be a surprising amount of cross fostering going on, especially with drift lambing ewes.
Importance of good grazing management.
A good job of grass management prior to and during lambing will result in a dense vegetative sward that will provide a high level of nutrition to lactating ewes and their lambs. A poor job of grass management prior to and during lambing will result in a rank mature stand which will provide inadequate nutrition to lactating ewes and their lambs. To achieve a dense vegetative sward, it is important to keep adequate grazing pressure on the early spring flush of growth. There is typically a point in time (late May in Minnesota) where all pasture plants will strive to put out a seed head. If these plants are repeatedly bitten off during this stage, they will fail to put up the seed head and will continue to be in a more palatable vegetative state. So the goal is to make at least two rapid rotations through all the paddocks just prior to the start of lambing, and for sheep to have made one more complete circuit (with drift lambing) or be set stock such that they will be grazing the entire farm by the end of May or first week of June (in Minnesota). This time corresponds to approximately 3 to 6 weeks after the brush began to bud.
Lambing in late spring is usually complete in less than 21 days, which works nicely when trying to achieve forage management goals. The post lambing set stock period corresponds to the most rapid growth stage of pasture plants, a point where we would like to be simultaneously biting every plant to keep it vegetative, and which will provide a reliable and abundant forage supply for at least the first 30 days.
A high lambing rate provides no advantage if it is not followed with a high newborn lamb survival rate. Newborn lamb survival is the combination of healthy vigorous lambs, put together with an available milk supply in a favorable environment and a strong bond between dam and offspring.
Health, genetics, and nutritional status of the dam all play a roll in assuring the lamb will be healthy and the milk supply abundant and available. Conditions that favor bonding between ewe and lamb help assure the lamb will connect with the milk supply. Weather and predators are the two things we have the least control over, but they are not altogether uncontrollable and need to be kept in perspective. A bad day of cold wet weather can result in newborn lamb losses of up to 30- 50% for that day (Rook 2005). But not every day of lambing has a bad weather event. Over a 21 day lambing period, one day of bad weather with losses of 50% may represent only 3% of the total lamb crop for the season. Sheep breeds can vary significantly in the ability to survive cold wet weather as a newborn lamb. The author has observed one commercial flock that lambs born on the same day, a difference of lamb mortality of 50% vs 5% between lambs sired from two different sire breeds. Hardy, cold tolerant breeds should be chosen for pasture lambing systems. The Tamarack flock has used Dorset, Booroola Merino, Texel, Ile de France, and Finnsheep over the years. Finnsheep and Merino were found to be very vulnerable to cold wet weather as newborns. The Dorset was found to be moderately tolerant of cold wet weather, and the Ile de France and Texel were found to be the most tolerant to cold wet weather.
Despite weather and predator worries, pasture lambing does not necessarily come with a higher lamb mortality. The total losses inside a barn are as high if not higher than a pasture lambing operation. One study compared a drop lot lambing flock to three pasture lambing flocks (Rook 2005). The barn lambing flock had a lamb loss of 15% compared to losses of 5% to 11% for the pasture lambing flocks lambing during the same period. 15% lamb loss is close to the national average. Further examination of the data found that while the total losses to starvation and hypothermia were similar in both indoor and outdoor flocks, representing just over 50% of the total lamb losses, indoor flocks had more losses to stillbirth, dystocia, and pneumonia, while outdoor flocks had losses to predators and fly strike, but no losses to pneumonia, and fewer losses to dystocia . Further the Rook data suggests that the only real difference between lambing indoors and lambing in a barn, may be that the date of death is prolonged indoors. In a pasture lambing system, more lambs simply die within the first 24 hours, where as barn lambing flocks had higher mortality in days 1-3. This suggests that human intervention may not be as beneficial to keeping lamb mortality low as we had hoped.
As mentioned earlier, the crux of lamb survival is connecting a healthy vigorous lamb with the milk supply. Making that supply available hinges on maternal behavior that results in the ewe making the milk accessible to the lamb, good udder structure so that the lamb has no problem finding and grabbing the teat, and the genetics and nutrition to produce a good milk supply. Starvation of lambs from ewes with faulty udders or teats have accounted for approximately 55% of lamb mortality prior to weaning in a University of Wisconsin study lambing a flock of typical Midwestern ewes (Cadwallader 1983). Newborn lambs are unable to suckle over sized teats, or locate teats that were too low to the ground because the udder was pendulous. Desireable udder structure is where the floor of the udder is above the hocks, with teats pointing out at a 45 degree angle toward the ground, and a good medial suspensory ligament. Teats need to be small enough for newborn lambs to grasp easily.
an example of desirable udder structure
Weather related losses are controlled primarily by lambing late enough in the spring so that cold rain or sleet is less likely, but yet early enough so that extreme heat and flies are not yet a problem. An average air temperature of 50 degrees (and perhaps just as important, an average soil temperature of 50 degrees) seems to be conducive to good lamb survival with minimal problems (Rook 2005). For most of the Midwest, this time corresponds to 3 weeks after the brush has budded out, or corn planting time.
table 1 weather triage chart
Table 1 is a guide developed by the author used for deciding which lambs are at greatest risk during bad weather. This guide assumes low wind speed (<15 mph).
The lambs that are at the greatest risk of hypothermia, are those lambs that were born during the rain, or that did not get an opportunity to dry off before the rain began. Triplet born lambs are more vulnerable than twin and single born lambs. Once a lamb is dried off, it can resist hypothermia much better. Most lambs are also quite able to endure a one or two hour rain shower. Natural windbreaks are very beneficial to reducing losses to hypothermia. Farms with a woodlot can turn the drop flock into the woodlot during bouts of severe weather, or shelterbelts can be planted along fence rows to help provide shelter. Simply turning the drop bunch into a paddock on the lee side of a hill can help improve lamb survival. Where natural shelter is not available or is not adequate, some type of portable shelter can be used for high risk newborns. The author uses lambing teepees at Tamarack lamb & wool. They are 6’ x 6’ x 6’ pyramid shaped tents with no floor. The tent holds an amazing amount of body heat. Although rarely needed (once or twice per lambing), they easily earn the purchase price. We have one tent per 30-40 ewes lambing. Even something as simple as snow fencing, zig zagged through T posts can help provide some minimal shelter during stressful weather.
Because hypothermia/starvation represents more than ½ of the total losses in both indoor and outdoor systems, learning to recognize hypothermia and knowing how to treat hypothermic lambs is an important shepherding skill. Hypothermic/starving lambs are triaged with course of action determined by the age of the lamb and body temperature as per the flow chart on page 326 of The Veterinary Book for Sheep Farmers by David C. Henderson (Henderson 1990).
More importantly, the cause of hypothermia/starvation should be determined and long term solution implemented. Solutions may include providing more shelter in pastures, or may require culling of ewes with milk production problems.
A short term solution for ewes with an inadequate milk supply, is to set up a milk creep for triplet lambs that require supplementary milk. Lambs must be caught and carried to the creep at least four times to teach them to suckle from the bucket before they learn to use it on their own. The milk creep should be set up where the flock lays down to rest. This is a preferred alternative to orphaning the lamb as lambs that remain with the dam will consume ½ as much milk replacer, will learn to graze from the dam, and will be nearly equal in size to twin reared lambs at weaning. Orphan lambs reared in the barn will not learn to graze and will require separate treatment through out the first 6 months.
a lamb milk creep set up, training a lamb to use the milk pail
A long term solution is to select for more milk production. When the booroola gene was first added to the Tamarack flock, only 1 out of 3 ewes had enough milk to rear triplets. Initially ewes were selected for rearing ability by total raw litter weight. Later maternal weaning weight (mwwt) estimated breeding values (EBV) through Lamb Plan were used in a selection index. According Lambplan data, significant progress was attained once we began using rams with maternal weaning weight EBVs. Now nearly every ewe in the Tamarack flock giving birth to triplets has enough milk to rear all three, and a few ewes can even raise quads. Eliminating ovine progressive pneumonia from the flock is also an important step to assuring sufficient milk supply for large litters. The Tamarack flock underwent testing and culling between 1987 and 1991, with the last positive test in 1991.
genetic selection and freedom from OPP lead to ewes that can rear triplets
Forming good ewe/lamb bonds at birth are crucial to assure the lamb continues to have access to that milk supply. Although most shepherds hold the ewe accountable for the bonding process it is important to point out that the lamb plays a significant role. Some lambs have a propensity to wander from the ewe, or are very lively and will not stay within the vicinity of the ewe. This problem becomes life threatening when the ewe has several lambs to contend with. Some sires produce a higher proportion of wandering lambs, and therefore the sire can provide a significant impact on the success of ewe and lamb bonding. Blackfaced sire breeds have been noted by some producers, as siring a higher proportion of wandering lambs as compared to whitefaced sire breeds Bartlet et al. noted that blackfaced sired lambs were more likely to be depredated on than whitefaced sired lambs, which could be that the lambs were more available if they wandered further from the dam. A quick fix for wandering lambs is to tether newborns together for 24 hours by hobbling one front leg to the front leg of a litter mate (Collins 1966). For triplets be sure to hobble the entire set together.
lambs inclined to stray apart are tethered for 24 hours
One common complication of lambing on pasture is what I call the lambing party, where several ewes have lambed together at once and are mothering any and all of the lambs. Lambing parties suggest too little structure or natural shelter in the paddock to spread ewes out, weather or insects that cause ewes to congregate, or simply too much congestion (drop bunch too large). Generally ewes that have lambed together are fairly willing to mother any and all of the lambs. It is best to assign each ewe to a set of lambs and separate them by removing them to another paddock, or putting them on the other side of a fence, bush etc. so that they do not re unite with the other lambs for most of the first day. Lambing parties are more common when ewes are not experienced at lambing outdoors.
lambing parties may be common in the first few years of pasture lambing, or, may be a symptom of too little structure, shade etc in the pasture
The Tamarack flock has been using the Number of Lambs Weaned (NLW) estimated breeding value (EBV) to help improve maternal rearing ability. This trait has helped reduced the % pre weaning lamb mortality from 15% down to as low as 3%*, but has done so in some surprising ways. It appears lambs are less vulnerable to newborn diseases such as joint ill and e coli scours. This could be due to improved quantity or quality of colostrum intake. However the benefit seems to pass on via sires sold into other flocks, that is to say, it appears the lamb is hardier. Further study is required to better understand which traits are changing in response to selection on the NLW EBV.
Ultrasound scanning for fetal number is a tool that some producers might find useful. Prior to lambing ewes can be sorted by fetal number so that ewes pregnant with triplets can be separated from the twin group, and so that single bearing ewes can be placed on the paddocks with the poorest feed or highest predator risk (as triplets are more vulnerable to depredation). If ewes are sorted by fetal number, it is easier to provide assistance, such as a milk creep, or to lamb the triplet group in the most sheltered pastures to reduce weather related losses. By separating the triplet drop group, it is also possible to supplement the triplet rearing ewes. One to one and a half pounds of a corn distillers based supplement fed daily for the first 30 days, can increase litter weight by as much as 15 pounds.
Predators, once an important reason to lamb indoors, are now manageable through the use of livestock guarding dogs and electrified fencing. These two tools were not available back in the 1950’s when indoor lambing first became fashionable. Both tools are largely responsible for the growing trend of lambing on pasture today. The specific details as to how to manage predators with fencing and livestock guarding dogs is a subject unto itself for another time. For now it is important just to mention that Tamarack Lamb & wool uses two livestock guard dogs per location to help prevent depredation of newborn lambs.
Pasture lambing can lower lambing time input costs by as much as $16 per ewe and increase the number of ewes lambed per employee. Highly prolific flocks are normally managed intensively indoors with the idea that lamb mortality is lower when lambs are sheltered in the barn. However, both producer experience and data from the University of Michigan suggest that lamb losses are as high if not higher indoors, and that each system presents its own unique causes of mortality.
Access to the milk supply and a good ewe/lamb bond are critical to lamb survival. Bonding is enhanced when the environment is conducive such as favorable lambing weather, adequate but not excessive forage growth, and minimal congestion in the paddock. Udder and teat structure are critical as is a good milk supply and nurturing maternal behavior. Predators were once an important reason to lamb indoors, are now manageable through the use of livestock guarding dogs and electrified fencing.
Converting the flock to pasture lambing will require some time as the sheep and shepherd adapt to the new system. One can expect a higher culling rate for the first three years as sheep that are not suitable for pasture lambing are culled from the flock. The learning curve for the sheep to learn the system is about three years. The learning curve for the shepherd will also take a few years as the shepherd learns to let go of some beliefs and learns new skills.
*reduction of lamb mortality is multifactorial and includes the benefit from pasture lambing, hybrid vigor from cross breeding, and selection using number of lambs weaned (NLW) EBV.
- Alderfer, Rich 1994. Minnesota Sheep Producer Labor Project. University of Minnesota/WCES – Morris
- Bartlett, Ben. J. Rook, D. Bonine, Terminal Sires on White Faced Ewes Michigan State University, College of Veterinary Medicine PDF http://cvm.msu.edu/Extension/docs/index.htm
- Cadwallader, T. 1983. Early summer pasture lambing. Proc. Spooner Sheep Day, Cooperative Extension Service, Univ. of Wisconsin-Extension, Madison. 42-44.
- Collins, Spelman B. 1966. Profitable Sheep. Spellman B. Collins, 274 Hathway Street, San Luis Obispo, California 93401. pp 130.
- Henderson, David C. 1990. The Veterinary Book for Sheep Farmers. Farming Press Books, 4 Friars Courtyard, 30-32 Princes street, Ipswich IP1 1RJ, United Kingdom. pp 326.
- McNally, Janet W. 1999. Presentation to the Minnesota Wolf Roundtable. MN Dept of Natural Resources.
- J. S. Rook, D.V.M., M. Kopcha D.V.M., M.S., & B. Bartlett, D.V.M. Pasture Lambing – A Viable Alternative for Sheep Producers? MSU Extension & Agricultural Experiment Station, Michigan State University, College of Veterinary Medicine
PDF http://cvm.msu.edu/Extension/docs/index.htm also presented at Rice Lake Wisconsin 2005.
- Wilkinson, Don 1991. Grazing and Pasture Management Workshop for Beef, Dairy, and Sheep Producers. Pine Technical College Lamb & Wool Program, Pine City, MN.
|All day rain + 65 degrees F||No worries|
|All day rain + 55 degrees F||Newborn triplets at risk|
|All day rain + 45 degrees F||All lambs under 24 hrs at risk|
|All day rain + 35 degrees F||All lambs under 3 days old at risk|
Table 1 guide for determining weather related risk to newborns
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