Strategies for Increasing the Number of Lambs Marketed per Ewe

Transcription

1 South Dakota State University Open PRAIRIE: Open Public Research Access Institutional Repository and Information Exchange South Dakota Sheep Field Day Proceedings and Research Reports, 1983 Animal Science Reports 1983 Strategies for Increasing the Number of Lambs Marketed per Ewe David L. Thomas University of Illinois Follow this and additional works at: Recommended Citation Thomas, David L., "Strategies for Increasing the Number of Lambs Marketed per Ewe" (1983). South Dakota Sheep Field Day Proceedings and Research Reports, Paper This Report is brought to you for free and open access by the Animal Science Reports at Open PRAIRIE: Open Public Research Access Institutional Repository and Information Exchange. It has been accepted for inclusion in South Dakota Sheep Field Day Proceedings and Research Reports, 1983 by an authorized administrator of Open PRAIRIE: Open Public Research Access Institutional Repository and Information Exchange. For more information, please contact

2 SHEEP DAY STRATEGIES FOR INCREASING THE NUMBER OF LAMBS MARKETED PER EWE David L. Thomas Assistant Pro fessor Department of Animal Science University of Illinois Urbana, Illi nois An obj ective of every commercial sheep producer should be to maximi ze the pounds of lamb ma rketed per ewe per year wi th the given feed, facility and monetary resources availab le. By increasing the pounds of lamb marketed per ewe, the relative fixed costs of maintaining a ewe are spread over mo re pounds of salable lamb and the efficiency of lamb meat production is imp roved and net income is increased. Since mo st producers market lambs at a constant weight, the maj or factor determining pounds of lamb marketed per ewe is the number of lamb s raised to market we ight per ewe. Presented in table 1 is the effect of different flock production levels on flock feed e fficiency. TABLE 1. EFFECT OF FLOCK PRODUCTION LEVEL ON FLOCK FEED EFFICIENCY a No. of lamb s markefied per ewe per year Lb of feed per lb of lamb c a Extrapolated from : Shelton Texas Agr Exp. Sta. Tech. Rep. 26. b Once-year lambing with lamb s marketed at 100 lb live we ight. c Includes pounds of feed fed to the entire flock (65% TDN). The two components that determine the number of lambs marketed are the number of lamb s born (prolificacy) and the survival of those lambs. This paper will attemp t to present several management strategies that can be used to improve these two maj or components. Due primar ily to a lack of professional expertise on the part of the author, the effect of a preventative health program on these components will no t be discussed. Sheep producers are well aware, however, that lamb losses due to abort.ion, pneumonia, enterotoxemia and other diseases can result in a signi f icant decrease in the number of lambs marke ted per ewe. Prepared for Sheep Day, June 9,

3 - 2 - Choice of Breed Tremendous variation exists between breeds for prolificacy. Table 2 presents the relative prolificacy of several breeds based on United States research results. TABLE 2. Breed RELATIVE BREED PROLIFICACY a Prolif icacy (Relative to Dorset) Finnsheep Suffolk Do rset Targhee North Country Chevio t Corriedale Hampshire Rambouillet Romney a Extrapolated from Dickerson and Glimp, 1975, J. Anim. Sci. 40 :397, and Clarke and Hohenboken (Unpublished). The prolificacy values given in table 2 are no t the actual number of lambs born but the number of lamb s born relative to the Dorset. As an example, the value of 174 for Finnsheep indicates that Finnsheep ewes are expected to give birth to 74% mo re lamb s than Dorset ewe s. Likewise, the value of 81 for Romney indicates that Romney ewes are expected to give birth to 19% fewer lamb s than Dorset ewes. It is quite evident from these data that the Finnsheep breed is far superior for prolif icacy to any other breed available in the United States. The easies t and fas test method of increasing flock prolificacy is to add some Finnsheep breeding to the ewe flock. Tab le 3 presents the proj ected ewe performance of Finnsheep crosses and the standard United States breeds. Information in the table summarizes research results from throughout the United States comparing many standard breeds with 1/4 and 1/2 Finnsheep ewes. In addition to increased prolificacy, it is also shown in table 3 tha t the addition of Finnsheep breeding to a ewe flock will increase the percentage of ewe lamb s that will ma te at 7 to 9 months of age and subsequently lamb at 12 to 14 mo nths of age. A high percentage Finnsheep flock (50% or more) may no t be desirable for all sheep operations. If feed, labor and management skills are no t available to properly care for a high percentage of twin and triplet born lambs, high lamb mo rtality and low lamb growth rate may result. In such a situation, the potential increase in pounds of lamb marke ted per ewe from the Finnsheep ewes It is difficult, however, to imagine very many sheep operations in which the infusion of one-fourth Finnsheep breeding into the ewe flock wo uld no t be beneficial. may no t be realized. 39

4 - 3 - TABLE 3. PROJECTED PERFORMANCE OF FINNSHEEP-CROSS EWES GIVEN THE PERFOP 1ANCE OF A STANDARD BREED a Lambs born Lamb 22 Lb lamb at % ewes per ewe % lamb week wt. 22 weeks per Cross lamb ing lambing survival (lb) ewe exposed Ewe lamb production 1/2 Finn x 1/2 Std /4 Finn x 3/4 td Standard breeds.so Ma ture ewe production 1/2 Finn x 1/2 Std /4 Finn x 3/4 Std Standard breeds a From : Thomas, Oregon State Univ. Ext. Serv. Spec. Rep. 575 :33. b Standard breeds were Suffolk, Targhee, Minnesota 100, Hampshire, Dorset, Rambouillet, Corriedale, Co lumbia, North Country Cheviot, and Romney. Differences among breeds for lamb survival have no t been well documented. However, many stud ies have shown that lambs containing Finnsheep breeding have higher survival rates than the standard breeds to wh ich they have been comp ared. U.S.D.A. researchers have also shown that Oxford-sired lambs have higher survival ra tes than either Suffolk- or ampshire-sired lambs. Season of Ma ting Season of mat ing is very important in determining the number of lambs born per ewe exposed. Mo st ewes have an annual period of anestrus that runs from April through July when they wi ll not exhibit heat. Some breeds, such as the Dorset, Rambouillet, Barbados and Finnsheep, tend to show greater estrus ac tivi ty during this period than other breeds. But even these breeds are less fertile during this period than at other times of the year. Most United States sheep producers expose their ewes for 40 to 60 days sometime during the period from August to December for the production of winter and spring lambs. Cho ice of breeding season during this period can affect size of subsequent lamb crop. Ovulation rates of crossbred Suffolk ewes during different months of the year in Oregon are presented in table 4. These data show that the maj ority of ewes come out of anestrus in August and that ovulation rate continues to increase each month thereafter until it peaks in November. By delaying ma ting until November, there is the potential for approximately 40 more lamb s born per 100 ewes over August mating and approximately 10 mo re lambs per 100 ewes over Septemb er ma ting. Although there is little published data on the effect of month of lamb ing on lamb survival, one could hypo thesize that lambs born in April from a November ma ting would have higher survival rates than lambs born in January from an August mating or in February from a September mating. Lamb dea ths due to exposure to inclement weather should be less in April than in Januaryand February-born lambs. 40

5 - 4 - TABLE 4. Month May June July Au gust September Oc tober November Decemb er MONTHLY OVULATION RATES OF AGED SUFFOLK-CROSS EWES a Ovulation rate (per ewe available) a Lamberson and Thomas J. Anim. Sci. 54 :533. There are, however, some disadvantages to later born lambs. Lambs born in April will no t reach marke t weight before the hot portion of summer and their gains will be reduced. They will reach market weight after the traditional peak in lamb prices. The potential advantages of marketing more lamb s from the November mating must be weighed against these disadvantages. In some specific localities in the United States, the normal mating One such area is the winter wheat producing areas of Kansas, Oklahoma and Texas. These areas have abundant forage of high quality in the form of winter wheat pasture available from October to March in mo st years. In order to use this feedstuff to its fullest, ewes are ma ted in May and June and lactate and raise their lambs on wheat pasture. Mo st of the lambs can be sold off wheat pasture at proper market weight with very little supplemental feed. Since the May-June mating season occurs at a time when most breeds are in anestrus, breeds with a short anestrus period must be used. Research at Oklahoma has shown that the Dorset x Rambouillet ewe performs very well under this management system. With May June ma ting, 80 to 85% of these ewes will lamb with a lamb ing rate of 1.40 to Attemp ts to improve the productivity of these fall-lambing flocks by incorporat ing 1/4 Finnsheep breeding has no t been successful ( table 5). season does no t occur during the August-December period. TABLE 5. PRODUCTIVITY OF 1/4 FINNSHEEP AND DORSET X RAMBOUILLET EWES WHEN LAMBING IN THE FALL IN OKLAHOMA a Breed Fertility (%) Prolif i cacy Pounds of lamb weaned per ewe exposed Dorset-Rambouillet 1/4 Finnsheep (3/4 Dorset) l a Thomas and Whiteman J. Anim. Sci. 48 :

6 - 5 - The poor productivity of the Finnsheep ewes was due to a lower percentage of ewes lambing of those exposed. In mo re northern environments, a high percentage of Finnsheep ewes has been shown to exhibit estrus during May and June. The Finnsheep, which was developed in a relatively cold environment, may be adversely affected by the hotter weather found in the Southwest in May and June. This examp le indicates the importance of using a breed that is well adapted to the management system and environment in which it is to produce. Crossbreed ing It is well documented tha t crossbred ewes give birth to and rear more lambs than the average of the purebred ewes that make up the cross. This crossbred advantage is known as heterosis. A summary of a large number of crossbreeding studies conducted throughout the wo rld shows that crossbred ewes will wean approximately 18% mo re pounds of lamb per ewe exposed than the average of purebred ewes that make up the cross (Nitter, 1978). The expected superiority of crossbred ewes over purebred ewes for fertility (conception rate), prolificacy, lamb survival and lamb weaning weight is 8.7, 3.2, 2.7 and 6. 3 %, respectively. In many cases (but no t all), the crossbred ewes will outperform the best purebred. This is the mo st desirable situation. If one of the purebreds used in the cross was mo re productive than the crossbred, the sheep producer would generally be better off using the superior purebred. In order to take advantage of increased performance due to heterosis, an organized crossbreeding program should be developed. In order to have maximum control over the genetic quality of replacement animals, some type of "rotational" system in which replacements are produced within the flock instead of purchased is probably preferable. Within Flock Selec t ion Selection for increased number of lamb s born is effective. Two long-term selection experiments, one conducted in New Zealand and the other in Au stralia, have shown that, if to tal selection effort is devoted to number of lambs born, the numb er of lamb s bo rn per 100 ewes exposed can he expected to increase by about two lambs per year (Turner, 1968 ; Clarke, 1972). A two-lamb increase per 100 ewes per year may seem small, but, if accumulated over a 10- year period, selected ewes will produce 20 more lambs per 100 ewes than unselected ewes. In addition, the selected ewes are expected to produce these 20 additional lamb s under the same conditions as the unselected ewes, so no additional inputs have been required--the 20 extra lambs are virtually free. When selecting for number of lamb s born, it is important no t to base selection to tally on individual lamb birth type. Selection progress will be faster if selection is based upon the lifetime production of an individual 's dam. This is illustrated by the following example : 42

7 - 6 - Two ewe lamb s (A and B) born in 1983 are available for selection. Lamb A is single born and lamb B is twin born. Their dams have the following lifetime lambing records. Wh ich ewe lamb should be selected? Lamb A's dam Lamb B's dam 1977 l No. of lamb s born each year In the above examp le, it is obvious that A's dam is genetically superior for number of lamb s born. In 1983, she probably produced the single lamb as a result of old age. B's dam, on the other hand, is genetically inferior and probably produced twin lamb s in 1983 because ewes no rmally produce more lambs from 3 to 6 years of age. Since one-half of the genetic make-up of each ewe lamb comes from its dam, ewe lamb A should be selected over ewe lamb B, even though A is a single and B is a twin. Selection on individual 's birth type is preferable over no selection at all but not over selection on dam's lifetime record. It 's generally felt that lamb survival from birth to market will show little response to selection. The heritability of this trait is near zero. Body Weight and Condition Score at Mat ing The positive effects on lambing rate of increased ewe body weight and condition score at mating have not been promo ted in the United States to the same extent as in the maj or sheep producing countries of the wo rld. Given the feed resources available on the farm, ewes should be at maximum body weight at mating and should have gained slowly but continuously from weaning to mating. Presented in figure 1 are data from New Zealand which illustrate the positive effects of increased ewe body weight at ma ting. The data presented in figure 1 indicate that, for every 10-pound increase in body weight at mating, 6% mo re lamb s will be born. The value of increased production of heavy ewes at mating must, of course, be evaluated against the costs of putting extra weight on the ewes. With current grain and lamb prices, a producer probably canno t afford to feed grain to ewes during the weaning to mating period in order to increase ma ting weight. The value of the increased number of lambs from the heavier ewes will no t cover the co st of the extra grain fed the ewes and rearing costs of the extra lambs. If, however, those weight gains can be obtained on pasture or low cost harvested forages, it would probably be economically feasible to put weight on ewes during the weaning to mating period : The increase in ewe body weight which takes place during the weaning to mating period is largely due to an increase in body fat. If a scale is no t available to monitor we ight change in ewes, a subj ective measure of "fatness" or condition of ewes can be made periodically. A change in condition over time should be related to a change in body weight. A series of condition scores have been developed that range from 1 to 5. The condition score is arrived at after feeling by hand the amount of fat cover over and around the vertebrae in the loin region. A condition score of l is assigned to a very thin ewe and 5 to a very fat ewe. It has been shown tha t each 1 / 2 unit of condition score is equivalent to 6 to 8 pounds of live weight. As mating condition score increases, number of lambs born also increases. 43

8 ,, "'"' -"',_,Ir,,"', TWIN BEARING, 30,..., z, w, u I a: I J I' I,,, 10 "'" o......_ LIVE \\"E IGHT AT MAT ING Figure 1. Effect of live weight at ma ting on percentage of barren ewe s and twin bearing ewes. (From Coop, I. E Oregon State University, Department of Animal Science 1). Even though ewes with ma ting condition scores of 4 and 5 tend to give birth to mo re lamb s than ewes with lower condition scores, it is generally uneconomical to get them this fat. An optimum condition score for ma ting would be 3 to 3 1/2 in most situations. Well in advance of mating, ewes should be condition scored and those with low scores (1 to 2 1/2) should be fed additional energy to bring them up to the desired 3 o 3 1/2 score at ma ting. Flushing Flushing is the management practice of providing increased nutrients to the ewe immediately prior to mating. Flushing results in an increase in ovulation rate which leads to an increase in number of lambs born. Flushing can be expected to increase number of lambs born per ewe by 5 to 20%. The flushing ration should provide about 50% more energy than the preflushing ration and should be fed for 2 weeks prior to and the first 17 days of the ma ting season. Light ewes in poor body condition are mo re responsive to flushing than heavy ewes in good body condition. This is no t to say that ewes should be taken down in body weight prior to being flushed. If this is done, lamb production will suffer due to the negative effect of low body weight at ma ting on numb er of lambs born that wa s discussed previously. Ewes that have been increasing in body weight from weaning to flushing and are at a 3 to 44

9 - 8 - ewes which have lost weight and are at a 1 1/2 to 2 condition score wh en flushed. upon the length of this separation, death of the lamb through starvation or a poor ma ternal-young bond may result. 3 1/2 condition score when flushed will generally produce more lambs than the The wisdom of the old-time practice of allowing ewe s to get down to poor condition and then bringing them up just prior to breeding is questionable. Lamb ing Management If the sheepman has done his job properly, he should be rewarded with a large lamb crop. Survival of a high percentage of these lambs will help assure a profitable enterprise. The vast maj ority of lamb deaths from birth to market occur during the first few weeks of life. Ewe milk replacers, artificial rearing systems, new grafting techniques, the stomach tube and selenium- fortified salt are a few of the recent innovations that have reduced early lamb mo rtality. Research is currently underway at the University of Illinois to study ewe behavior at lamb ing with the hope of applying what 's learned to reducing early lamb mortality. Most sheep producers shed lamb. Pregnant ewes are penned together and generally lamb in this pen. They are then moved with their lambs to a smaller pen where they remain for 1 to 2 days before being placed with other ewes and their lambs. Just prior to the lambing process, ewes tend to seek isolation from other pregnant ewes. If the ewe is unable to have this isolation, if she gives birth to mul tiple lambs or if there is a "mo therly" ewe that would like the ewe 's lambs, there is a relatively high probability that a lamb will become separated from its mo ther. Depending In order to provide isolation for lambing ewes and to prevent separation of a ewe from her lambs, a lamb ing "cubicle" has been designed by University of Illinois researchers for placement in a pen of pregnant ewes. The cubicles are constructed of panels and are 6 feet square and 3 feet high with a 2-foot opening to allow sheep free access. Across the bot tom of the opening is a 10-inch threshold that the ewe must step over when entering or leaving the cubicle. Percentage of ma ture ewes lambing in the cubicles has been 26%, 42% and 46% in three trials conducted wi th over 400 ewes (Gonyou and Stookey, 1983). Cub icle usage by nonlambing ewes was minimal. Use of cubicles appears to be an effective way of preventing separation of newborn lambs from their dam and reducing interference by other ewes. Accelerated Lamb ing Mo st of the previous discussion has been directed toward once-per-year lambing. However, with a 5-month gestation length in the ewe, it is theoretically possible to lamb more than once per year. The accelerated system that is most of ten used is the 8-month lambing interval or lambing three times in 2 years. A prerequisite for success with this type of system is the use of breeds that have a short anestrous period. Results from an accelerated lamb ing program at Purdue University are presented in table 6. The Purdue results were obtained wi th no hormone or light treatments to induce or synchronize estrus 45

10 - 9 - On an 8-month lambing interval, ewes lamb 1 1/2 times per year. If production at each lamb ing on the accelerated program is equal to that obtained on the once-per-year program, lamb production per year should be increased by 50%. The Purdue data indicate that Rambouillet ewes are better adapted to accelerated lamb ing programs than Columb ia ewes. However, even the 35% improvement for Columb ia ewes over a once-per-year lamb ing program is probably high enough to make such a program economically sound. TABLE 6. AVERAGE PRODUCTIVITY PER EWE PER YEAR FOR EIGHT YEARS AND 12 LACTATIONS a Item Breed Rambouillet Columb ia Lambs born/ewe exposed Lamb s raised/ewe exposed Percent improvement in lambs raised over once-per-year lamb ing a Outhouse Purdue Univ. Agr. Exp. Sta. Bul. No. 49. Conclusion An attemp t has been made to discuss in a relatively brief manner some of the available technologies that can be utilized to increase the number of lambs ma rketed per ewe per year. The topics discussed are no t the only ones that impact on this measure of performance. The effects of ewe and lamb health programs are no ticeably absent. By combining the technologies available to the United States sheep industry, how many lamb s is it possible to market per ewe per year? At a recent symposium, it was stated that a goal of 365 pounds of lamb marketed per ewe per year should be set for attainment in the near future using intens ive sheep production systems. This translates into about 3.32 lambs marketed at an average weight of 110 pounds from each ewe per year. Currently, United States production is less than 1 lamb marketed per ewe per year. The goal would seem to be impo ssible to reach. Wrong! The goal has been attained. A flock of Finn x Dorset ewes ma ted to Suffolk rams on an accelerated ambing program and utilizing many of the technologies mentioned in this paper is currently weaning 3.40 lamb s per ewe exposed per year. Thi s flock is ma intained at the Rowe tt Research Institute at Aberdeen, Sco t land. A detailed description of the management of this flock was presented at a recent United States symposium (Robinson, 1981). The management system used is an excellent example of the integration of known technologies to develop an efficient production system. 46

11 It is not advocated that all sheep enterprises should be striving for 3.4 lambs per ewe per year, but the point is that the techno logy is currently available to dramatically improve production above current levels. Literature Cited Clarke, J. N Current levels of performance in the Ruakura fertility flock of Romney sheep. Proc. New Zealand Soc. Anim. Prod. 32 :99. Coop, I. E The nu tritional requirements of the grazing ewe. Summary of Reports : Western Oregon Sheep Conferences and Meetings, Oregon State University. Dickerson, G. E. and H. A. Glimp Breed and age effects on lamb production of ewes. J. Anim. Sci. 40:397. Gonyou, H. W. and J. M. Stookey Use of lambing cubicles and the behavior of ewes at par turition. J. Anim. Sci. 56 : 787. Lamberson, W. R. and D. L. Thomas Effects of season and breed of sire on incidence of estrus and ovulation rate in sheep. J. Anim. Sci. 54 :533. Nit ter, G Breed utilization for meat production in sheep. Anim. Breeding Ab str. 46 :131. Outhouse, J. B Ewe productivity on accelerated lamb ing programs. Purdue Univ. Agr. Exp. Sta. Bul. No. 49. Robinson, J. J Improving ewe productivity. Proc. Nat ional Sheep Confinement Symposium, St. Louis, University of Illinois ( in press). Shelton, M Some factors affecting efficiency of lamb production. Texas Agr. Exp. Sta. Tech. Rep. 26. Thomas, D. L. States The Finnish Landrace breed of sheep in the United Oregon State Univ. Ext. Ser. Spec. Rep. 575 :33. Thomas, D. L. and J. V. Whiteman Effects of substituting Finnsheep and Dorset breeding for Rambouillet breeding. II. Productivity of falllambing ewes. J. Anim. Sci. 48 :265. Turner, Helen Newton The effect of selection on lambing rates. Proc. Symp. Physiol. Reprod. in Sheep. Sheep Industry Development Program, Denver, p