University of Wyoming, Laramie

Transcription

1 CROSSBRED EWES COMPARED WITH EWES OF PARENT BREEDS FOR WOOL AND LAMB PRODUCTION 1 3I. P. BOTKIN AND LEON PA!JLES University of Wyoming, Laramie ATING of black-faced rams to white- M faced, wool-type ewes has been commonly practiced for many years in the western range area. However. the crossbred ewe lambs have usually been sent to market along with wether lambs, and little or no information is available on the subsequent production of the~ crossbred lambs. According to Terrill (1958) it is generally recognized by sheepmen that crossbreeding results in increased fertility and growth rate of lambs. Sidwell et al. (1962, 1964) reported increased fertility, prolificacy, lamb livability, and lamb weights of two-, three-, or four-breed crosses as compared with purebred averages. but no data on wool production were included. Reports by Hultz et al. (1935) and Neale (1943) indicated that wool production of cross-bred ewes sired by Hampshire or Southdown rams was below that of either whitefaced range ewes or crossbred ewes sired by Lincoln, Romney or Corriedale rams. Lasley (1963) summarized the average increase in various traits realized from crossbreeding sheep. The purpose of the present study was to obtain further information on the productivity (combined wool and lamb production) of crossbred ewes compared with purebreds of parent breeds. Experimental Procedure Data have been accumulated for 7 years ( ) from the experimental flock of sheep at the Wyoming Substation at Sheridan. Before the start of the crossbreeding experiment, 20 Suffolk and 80 Corriedale ewes had been maintained at the station for use in pasture studies. All the Suffolks and half of the Corriedales have been continued as purebreds. The remaining Corriedales were mated to Suffolk rams for production of crossbred lambs and gradually were replaced by F~ crossbred ewes. To avoid confounding the effects of year and age of dam, the first 4 years were devoted to establishing an F~ l'ublished with approval of the Director, Wyoming Agricultural Experiment Station, as Journal Paper No crossbred group of ewes comparable in age to the purebred groups. For the last 6 years of the study, the flock has consisted of about 20 Suffolk, 40 Corriedale, ~md 40 FI crossbred ewes of comparable ages. Ewe lambs were included in breeding groups. Data reported are those obtained from 1959 through Originally the plan was to use a criss-cross breeding program, but a reduction in numbers led to the use of a modified criss-cross, or alternating back-cross program. When the Ft crossbred ewes reached breeding age, half were randomly mated to a Suffolk ram, the other half to a Corriedale ram. The following year groups were switched and mated to a ram of the opposite breed, i.e., each year breed of sire was alternated for these crossbred ewes. The breeding season began in early September each year with rams provided from the University flock at Laramie. One ram of each breed (Corriedale and Suffolk) was used each year. Rams were selected to avoid inbreeding. After approximately 50 days of breeding, all ewes were combined, and a "clean-up" ram (usually Hampshire) was left with the entire group for another 30 days. Lambs born after the first 50 days of the lambing period were not inchlded in the data reported. Just before lambing in January each year all ewes were shorn and individual fleece weights were recorded. Side samples of approximately 200 gm. from all fleeces were obtained at shearing and returned to Laramie for grade and shrinkage determinations. Also, thigh samples were taken from the Suffolk and Ft crossbred ewes, and these were returned to Laramie for scouring, after which they were scored for freedom from black fiber. About the middle of July each year, lambs were weighed, staple length was measured, and lambs were assigned a visual score for type, fleece uniformity, and fleece color (freedom from black fibers). Scores for all traits ranged from 1 through 10, with l0 as the ideal. From 1959 through 1963 approximately 25 lambs representing all breed groups were slaughtered each year for carcass ewfiuation. 1111

2 1112 BOTKIN AND PAULES These were selected from the largest lambs of market weight and as nearly the same size as possible regardless of age. A least squares analysis was used to estimate the effect of breed, as well as of measurable environmental factors for data on lambs at weaning time. Intrayear analysis of variance was used to measure breed differences in fleece data obtained at shearing and in carcass data from the lambs that were slaughtered. Duncan's (1955) multiple range test was used to determine significance of difference between means for each group of data. Results and Discussion Lamb Production. A summary of lamb production for the various groups is shown in table 1. Lambing percents were rather low, because ewe lambs were included in breeding groups, and late lambs sired by "clean-up" rams were not counted; also death loss of both lambs and ewes is reflected in lambing percent. However, this is a realistic measure of actual production. Year, age, sex, type of birth and age of dam all significantly affected weaning weight, and all except sex significantly influenced type score. Yearly variation in weaning weight is shown in figure 1. Wether lambs were 1.4 kg. heavier than ewe lambs; singles and twins raised as singles were 6.2 kg. and 4 kg., respectively, heavier than twin lambs. Regression of weight on age at weaning was 0.17 kg./day. For weaning weight the ranking in descending order of age of dam was 5, 4, 3, 2, 6 and 1 years. Only a few lambs were included that were raised by yearling ewes. About half of the ewe lambs were bred, but most of these were bred to "clean-up" rams. Suffolk ewes were below all other groups in lamb production, even though Suffolk lambs averaged heaviest in weaning weight. The low lambing percent for Suffolk ewes was due to a higher percent of dry ewes than for other groups and also to greater loss at birth. The lambing percent of Suffolk ewes in this study was lower than that of Suffolk ewes in the flock at Laramie, but ewe lambs have not been included in the breeding flock at Laramie. The temperature at Laramie. too. is lower during the breeding season than that at Sheridan. Crossbred ewes had a higher average lambing percent and were higher in kilograms of lamb raised per ewe bred than either parent breed, indicating a definite heterotic effect. Lambing percent for F~ crossbred ewes was 122% of the average of the parent breeds, a greater advantage than that indicated by Lasley (1963). Corriedale ewes mated to Suffolk rams produced more and heavier lambs than did the Corriedale ewes mated to Corriedale rams. This agrees with the findings of Sidwell et al. (1962). For average weaning weight the ranking in descending 'order was Suffolk, backcross to Suffolk or to Corriedale, F~ and Corriedale. Corriedale lambs were significantly lighter than lambs in all other groups, but differences between Suffolk, backcross and F1 crossbred lambs were not significant. Except for 1 year, F1 crossbred lamb weaning weights were between Suffolks and Corriedales; on the average they were closer to the Suffolks. This represents an advantage of above the average of the parent breeds, not quite as great an advantage as that cited by Lasley (1963). Type scores of Corriedale lambs were significantly below those of the other groups. Type scores were probably influenced by size and condition of the lambs. For further comparison of lambs, a summary of carcass measurements is shown in table 2. Considering carcass quality from the standpoint of grade, carcass yield of wholesale cuts and meatiness (loin-eye area and leg area), the backcross lambs and Suffolk lambs ranked higher than Corriedale and F~ crossbred lambs. The F1 crossbreds, which were scored for type about as high as Suffolk or TABLE 1. LAMB PRODUCTION FOR VARIOUS BREEDS AND CROSSES Breed of Ewes Lambs Av. type Wt. of lamb Ewes raising Lambs raised per Av. weaning score of raised per Dam Sire bred lambs a raised a ewe bred wt. b lambs b ewe bred no. no. no. no. kg. kg. Corriedale Cnrriedale ~0.47 e e 32.6 Corriedale Suffolk ~0.60 a a 39.3 F1 crossbred Corriedale I ~0.60 a 7.2~0.11 a 40.8 F1 crossbred Suffolk ,0~0.66 a 7.3+O.13 a 38.4 Suffolk Suffolk I ~0.74 a 7.2 a 26.9 a Lambs born after April 1 each vear are not included. u Year, age, sex, type oi birth and age of dam were held.constant. Type score ranged from 1 to 10, with 10 as the ideal. e, a Means in the same column bearing different superscript letters differ significantly (P(.05).

3 EWE PRODUCTIVITY 1113 Legend: ~D r- ID Suffolk sire, Suffolk dam... Suffolk sire, F1 Crossbred dam -- Corriedale sire, F1 Crossbred dam... Suffolk sire, Corriedale dam Corriedale sire, Corriedale dam,/', "\-7/ ", ' V 1! \ /,'\ I I k~ / k Year Figure 1. Average weaning weights, of different groups by year. backcross lambs, ranked low and about equal to Corriedales in carcass quality. In general lambs from groups that weighed heavier also produced more desirable carcasses. Lambs that were slaughtered were not random samples from their respective: breeding groups; thus, caution must be used in drawing conclusions from carcass data. Wool Production. Data on wool include fleece weight, grade and shrinkage for the three groups of ewes, as well as staple length, uniformity score and color score taken at weaning for all five groups of lambs. These data are presented in table 3. In addition, fleece weights are shown by year in figure 2. Data obtained at shearing were not from the same sheep as data obtained at weaning, though some overlapping occurred as ewe lambs were added to the flock as replacements. Year differences were significant for all fleece traits except grade and shrinkage. Staple length was significantly greater for singles and twins raised as singles than for twin

4 1114 BOTKIN AND PAULES TABLE 2. MEANS AND STANDARD ERRORS FOR CARCASS TRAITS BY BREED GROUP Breed Group Backcross Backcross F1 to to Item Corriedale crossbred Cerriedale Suffolk Suffolk No. of lambs slaughtered Carcass wt., kg _0.49 Carcass grade e u Fat depth over Ioin, ram. 2.8~0 30 a b e a 1.8 "T-0.46d Carcass leg width, cm a, b a a,b 20.6 b 20.6_~-0-27b Loin-eye area, sq. cm '~ b ~ I ~ Leg area, sq. cm a a '~,b 103.1~+1.68 b,e e \~, holesale breast wt., kg , I3 a. b 3. 1 ~0. 18 b 3. 7 ~0. 18 a a _0. 13 a, b Wholesale shoulder wt., kg. 3.9~0.10 ~L b ~ ~, e 4.2~0.10a' e Wholesale rack wt., kg a, b a ~ 1. 5 ~0.06 ~, b a, Wholesale loin wt., kg. 1 6_0.08 a i b a a a Wholesale leg wt., kg a 4.7_0.18 a b b 5.6~_0.14 b a, b, e, a Means on the same line bearing different superscript letters differ significantly (P<.05). e Grade of 9zHigh Good, 10zLow Choice. lambs, but type of birth had no significant effect on uniformity or color score. Fleeces of ewe lambs measured significantly longer (2.5 ram.) than fleeces on wether lambs, but fleeces on wethers were scored significantly higher for uniformity. Color score was not influenced by sex. Age of lamb had a significant influence on color score, but not on uniformity score. The regression of staple length on age at weaning was 0.23 mm./day. For fleece traits Corriedales were highest, Suffolks lowest, and crossbreds intermediate. The only exception was shrinkage; F~ crossbred fleeces shrank slightly more than either Suffolk or Corriedale fleeces. However, all shrinkages were extremely low, since ewes were shorn during January when grease content is normally low. Regardlesss of year-toyear fluctuations in fleece weights, the differences between groups were consistent (figure 2). Hultz etal. (1935) also found that crossbred ewes resulting from mating white-faced ewes to rams of mutton breeds sheared lighter fleeces than straightbred white-faced ewes, although Suffolk crosses were not included in their fleece studies. Quantity and quality of wool were in direct agreement, Corriedale fleeces were heaviest, longest stapled and free from contamination with black fibers. Corriedale fleeces were also softer to the touch and did not have the harshness noticed in fleeces from Suffolk and F1 crossbred ewes, even though grades were the same in all three groups. For staple length, uniformity score and color score at weaning the ranking in descending order was Corriedale, backcross to Corriedale, F1 crossbred, backcross to Suffolk and Suffolk. The average staple length of F1 crossbreds was 101.8% of the average for the parent breeds. This is not as high as the 130% cited by Lasley (1963). However, in this study staple length was measured on lambs at weaning time and did not necessarily represent measured staple length of shorn wool. Productivity. In order to give proportion: ate emphasis to lamb and wool, productivity as used here is the value of products per head per year. This was based on the number of ewes in the flock at breeding time in the fall. Productivity was calculated as follows: kilograms of lamb raised per ewe bred at kilograms of wool per ewe at $1.36/kg. Production for lamb and wool is taken from tables 1 and 3, respectively. Lamb price was an average of Denver market quotations during July of the 6 years of the TABLE 3. SUMMARY OF WOOL PRODUCTION FOR VARIOUS BREEDS AND CROSSES Fleece data for ewes Av. Av. color Fleece data for lambs at weaning Breed of Av. spin- score on Av. shrink- ning scoured Av. Av. Av. Sire Dam fleece wt. age a count a samples staple length uniformity scoreg color scoreg kg. % ram. Corriedale Corriedale b b 7.0 -I-0. 12b 10.0~--- O.00b Corriedale Suffolk 3.56~0.06 e b e e 8.5+0"20e FI crossbred Corriedale ~ 1-09d e 9-I+0.19a Ft crossbred Suffolk e a "17e Suffolk SuUolk i/gg;c6/6g* 36~i 56 ~e 34.2~0.81 f 5.8~0.13 d f a Determinations were made from scoured side samples. b, e, d, e, f Means in the same column bearing different superscript letters differ significantly (P~.05). gscore ranged from 1 to 10, with 10 as the ideal.

5 EWE PRODUCTIVITY 1115 Legend: Corriedale ewes... F 1 Crossbred ewes Suffolk ewes 5 3 ", *~ 2 "~ ~'~ Year Figure 2. Average yearly fleece weights for three groups of ewes. study, and wool price is converted from 62~/lb. (the national incentive level). No attempt was made to adjust prices according to quality either for lambs or wool. Productivity for the various breeding groups is shown in table 4. For productivity as for separate traits, there is evidence of heterosis, since F1 crossbred ewes produced at a higher level than the average of the two parent breeds. When all Corriedale ewes are included (regardless of breed of ram to which they were mated) in determining the parental average, produc- tivity for F1 crossbred ewes is 122.5% of that for the average of parent breeds. If only siraightbred Corrieda!es are included, this becomes 128% of the parental average. In spite of this advantage for F1 crossbreds, the group with highest production was that in which Corriedale ewes were mated to Suffolk rams. This system of mating takes advantage of the wool-producing ability of Corriedale ewes, as well as the increased vigor and growth rate of crossbred lambs. This is a mating system commonly used in commercial production, not specifically with Suf- TABLE 4. PRODUCTIVITY OF EWES BY BREEDING GROUP Lamb raised Value of lamb and Breeding group per ewe bred Wool per ewe wool per head per year a Corriedale ewes mated to Suffolk rams F1 crossbred ewes mated to Corriedale rams F1 crossbred ewes mated to Suffolk rams Corriedale ewes mated to Corriedale rams Suffolk ewes mated to Suffolk rams a Lambs evaluated at 44r wool at $1.36/kg. kg. kg. $

6 1116 BOTKIN AND PAULES folk and Corriedale, but mating white-faced, wool-type ewes to black-faced rams. An obvious disadvantage of this mating system is that there is little or no opportunity for selection of ewes. Part of the flock would have to be mated to white-faced rams, and nearly all ewe lambs kept as replacements, or replacements would have to be purchased. A management system in which the top producers are selected and mated to high-producing rams for producing replacement lambs would enable an operator to make improvement over a period of years, but would reduce the production potential of the remaining ewes that are producing the marketable lambs. None of the mating systems used in this study allows for maximum production and maximum selection potential at the same time. Perhaps the inclusion of one or more additional breeds in a rotational cross-breeding system would permit further increases in production without encountering such difficulties. Sidwell et al. (1962, 1964) have indicated that three-breed crosses outproduce two-breed crosses and that four-breed crosses produce more than three-breed crosses, with regard to number and weight of lambs. Since range sheepmen derive a greater portion of their income from wool sales than do those in other regions, the combined wool and lamb production is of utmost importance. Further information is needed concerning wool production when more breeds are used in crossbreeding programs. Summary and Conclusions Data have been reported from a study covering 6 years comparing crossbred and purebred ewes for wool and lamb production. Weaning weights, although variable from year to year, were lowest for straightbred Corriedale lambs and highest for Suffolk lambs. F1 crossbred lambs were intermediate but above the average of the parent breeds, and backcross lambs form crossbred ewes were consistently, though not significantly, heavier than F1 crossbred lambs. Lambing percents were highest for crossbred ewes and lowest for Suffolk ewes. Corriedale ewes mated to Suffolk rams produced more and heavier lambs than did Corriedale ewes mated to Corriedale rams. Corriedale ewes produced heavier and more desirable fleeces than did the crossbred or Suffolk ewes. Suffolks were lowest both in quantity and quality of wool produced. These groups were in the same order for staple length, uniformity of grade, and color (freedom from black fibers) measured or scored at weaning time. In productivity Corriedale ewes mated to Suffolk rams ranked first, while Fz crossbred ewes mated to Corriedale or Suffolk rams ranked second and third, respectively. Straightbred Corriedales were fourth, and straightbred Suffolks were below all other groups. Literature Cited Duncan, D. B Multiple range and multiple F tests. Biometrics 11:1. Hultz, F. S., J. A. Gorman and S. S. Wheeler Crossbreeding with Western ewes. Wyo. Agr. Exp. Sta. Bul Lasley, John F Genetics of Livestock Improvement. Prentice-Hall, Inc., Englewood Cliffs, New Jersey. Neale, P. E Production of wool and lamb from different types of ewes and breeds of rams. N. Mex. Agr. Exp. Sta. Bul Sidwell, George M., Dale O. Everson and Clair E. Terrill Fertility, prolificacy and lamb livability of some pure breeds and their crosses. J. Animal Sci. 21:875. Sidwell, George M., Dale O. Everson and Clair E. Terrill Lamb weights in some pure breeds and crosses. J. Animal Sci. 23:105. Terrill, Clair E Fifty years of progress in sheep breeding. J. Animal Sci. 17:944.