LIFETIME PRODUCTION OF 1/4 AND 1/2 FINNSHEEP EWES FROM RAMBOUILLET, TARGHEE AND COLUMBIA DAMS AS AFFECTED BY NATURAL ATTRITION ABSTRACT

LIFETIME PRODUCTION OF 1/4 AND 1/2 FINNSHEEP EWES FROM RAMBOUILLET, TARGHEE AND COLUMBIA DAMS AS AFFECTED BY NATURAL ATTRITION S. K. Ercanbrack and A. D. Knight 1 U.S. Department of Agriculture 2, Dubois, ID 83423 ABSTRACT Lifetime production of first-generation 1/4 and 1/2 Finnsheep crossbred ewes from Rambouillet (R), Targhee (T) and Columbia (C) dams was compared with that from randomly selected purebred R, T and C ewes. All 1,190 ewes, representing nine breed groups, were managed under range conditions and mated annually to Suffolk rams. Lifetime production was evaluated as the total lamb and total wool production per ewe from the time each entered the breeding flock at 7 mo of age through the period each remained in the flock (potentially seven producing years). Culling was for debilitating unsoundness only. The study was designed to determine the average lifetime production per breed group as affected by natural ewe attrition. Orphan-reared lambs were not included in lamb production nor were foster lambs, except those actually born in and reared by the groups. Differences among pooled breed groups (1/4 Finns, 1/2 Finns and purebreds) were not significant for average final age in the flock (5.1, 5.1 and 4.9 yr, respectively), but differences were significant (P <.01) for lifetime lamb and wool production. Average lifetime fleece weights of 1/4 and 1/2 Finn ewes were only 95 and 82% as high, respectively, as those of purebreds. However, 1/4 and 1/2 Finn ewes had 34 and 46%, respectively, higher numbers of lambs weaned (at 130 d) and 30 and 38% higher total weight of lamb weaned than purebreds. Considering the unit value of wool to be 2.5 times the unit live-weight value of lamb, and after adjusting for differences in value of wool grades, the net value of lifetime production from Finn crosses was about 15 and 17% higher, respectively, than that of purebreds. (Key Words: Sheep, Lifespan, Lamb Production, Wool Production, Finnish Landrace, Crossbreeding.) J. Anita. Sci. 1989. 67:3258-3265 Introduotion The impressive findings of Donald et al. (1968) in crossing the Finnish Landrace (Finnsheep) with local breeds of sheep in Great Britain to improve lamb production stimulated considerable interest in Finnsheep crosses in the U.S. Several investigators (Laster et al., 1972; Meyer and Bradford, 1The authors gratefully acknowledge the valuable technical assistance of T. R. Kellom in collecting and assembling the data 2ARS, U.S. Sheep Exp. Sta., Dubois, in cooperation with the Univ. of Idaho, Moscow 83843. Received November 21, 1988. Accepted April 26, 1989. 1973; Dickerson et al., 1975; Dickerson, I977; Hohenboken and Clark, 1981; Oltenacu and Boylan, 1981) studied production from Finnsheep crosses reared under pasture conditions, and Ercanbrack and Knight (1985) examined annual production of Finnsheep crosses through 7 yr of age under range conditions. Each of these investigations found that Finncrosses were superior for annual lamb production. A matter of concern arising from these findings was whether high annual production increased rates of ewe attrition and, hence, affected lifetime production. The notable advantage of Finncrosses in annual lamb production ultimately might be offset, on a lifetime basis, if attrition among high-producing Finncrosses greatly exceeded that of more moder- 3258

LIFETIME PRODUCTION OF TABLE 1. DISTRIBUTION OF CLASS NUMBERS FOR BREED GROUP AND BIRTH YEAR Cl~s~cafion No. Breed groups a F R 141 F T 149 FxC 144 1/4 F x 3/4 R 124 1/4 F x 3/4 T 152 1/4 F x 3/4 C 132 R 114 T 121 C 113 Birth year 1973 399 1974 381 1975 203 1976 207 ar = Rambouillet; T = Targhee; C = Columbia; F = Finnsheep. ately producing purebreds. Ercanbrack and Knight (1985) considered attrition effects on lifetime production by weighting average annual production of each age group within a breed group by the percentage (averaged over all breed groups) of surviving ewes for that age group and then totaling weighted annual production through age seven. They did not consider that attrition rates for each breed group might differ, as suggested above. Such differences would affect estimates of lifetime production per group. The objective of this study was to estimate the average lifetime production, per entering ewe, of Finnsheep crosses and purebred ewes and to determine whether these groups differed in natural attrition rates (culling was for unsoundness only). Lifetime production was evaluated as the total lamb and wool production per ewe from the time each entered the breeding flock at 7 mo of age through whatever period each actually remained in the flock (potentially seven producing years). Mate~alsandMethods Ewes included in this study were produced and managed under range conditions at the U.S. Sheep Experiment Station, Dubois, Idaho. Each year from 1973 through 1986, randomly selected purebred and all currently available (no selection) crossbred ewe lambs, representing nine breed groups (Table 1), were assigned to the study and exposed initially to breeding 1/4 AND 1/2 FINN EWES 3259 in November at 7 mo of age. Fewer ewe lambs were added in 1975 and 1976 than during the first 2 yr so that grazing resources would be available to accommodate ewes from all four age groups simultaneously. Ewes were retained in the flock (to the extent that natural aurition permitted) without culling, except for debilitating disease or injured udders, through 7 yr of production. Seven years was considered an appropriate representation of lifetime production, because it is unusual in range flocks to retain ewes older than 6 or 7 yr because of rigorous environmental conditions and declining ewe productivity. The crossbred ewes were produced by mating purebred Finnsheep or 1/2 Finnsheep rams to randomly selected purebred dams of the appropriate breed from the station flocks. Purebred ewes were obtained by random selection from among all purebred lambs weaned in the station flocks. Ewes were produced by 27 Finnsheep, 21 1/2 Finn-l/2 Rambouillet, 20 1/2 Finn-l/2 Targhee, 21 1/2 Finn-l/2 Columbia, 55 Rambouillet, 67 Targhee and 49 Columbia sires. Typically, different sires were used in each birth-year. Notable relationships among ewes were confined to half-sib relationships within breed groups. All ewes were flock-mated annually to Suffolk rams, a practice typical of commercial range-sheep operations producing slaughter lambs; lambs were born in April in sheds. Ewes with newborn lambs were placed in individual 1.2-m 2 pens within the lambing shed immediately after lambing and housed for only 1 or 2 d, normally. Then ewes and lambs were moved outside into lots (mixing pens) where they were accumulated into bands prior to going to the range at 15 to 20 d postlambing. Group feeding during this period was restricted to alfalfa pellets at a rate of about 3 kg/d per ewe. Extra lambs from litters of three or more were removed at birth so that no ewe was released from the lambing shed with more than two lambs. When available, ewes with sufficient milk, but having a single or no surviving lamb, were used as foster mothers for surplus lambs. However, to emulate circumstances that would occur in a flock consisting entirely of the same fraction of Finnsheep breeding, foster lambs were included in production only if they were reared in a breed group having the same fraction of Finnsheep breeding (i.e., 0, 1/4 or 1/2) as the group in which they were born.

3260 ERCANBRACK AND KNIGHT Under these circumstances, foster lambs constituted.6,.7 and 1.2% of the lambs bom to purebreds, 1/4 Finns and 1/2 Finns, respectively. Surplus lambs for which foster mothers were not available were reared artificially as orphans and were not included in their dams' production. Genetic mothers received only half-credit for number and weight of lambs reared by foster mothers, with the other half being given to the foster mother. See Ercanbrack and Knight (1985) for justification of this lamb credit policy and for a description of subsequent grazing and management procedures. Twelve annual performance traits were investigated in the initial study of these ewes (Ercanbrack and Knight, 1985). Additional individual traits observed for this aspect of the study were 1) final age at which the ewe remained in the flock (for ewes still in the flock when the study was terminated, final age was 7 yr); 2) lifetime total fleece weight; 3) lifetime total number of Iambs weaned and 4) lifetime total weight of Iambs weaned. A ewe was considered present in the flock for a particular production year if she was present for breeding in November prior to that year. Ewe fleece weights were obtained annually in late May, and numbers and weights of lambs weaned were determined in August at an average lamb age of 130 d. All traits were analyzed using least squares methods of analysis of variance (Harvey, 1975). The basic mathematical model included effects for breed/birth-year group and sires within breed/birth-year group because different sires (of ewes) were used for each birth-year and for each breed group. Because the sire components of variance were slightly negative for numbers and weight of lamb weaned in this mixed-model analysis, a fixed-model analysis based on breed group, birth-year and the interaction between them also was completed to see whether conclusions from tests of significance would be different under the two models. Estimates of fixed effects were similar for the two models. In evaluating total weight of lamb weaned, an analysis for each production year provided the basis for correcting annual lamb weaning weights for effects of age of lamb at weaning, sex and grazing band. Type of birth and rearing, breed group and age of darn also were included in the model so that estimates of all other effects (sex, etc.) would be unbiased by these effects. However, no corrections for the latter three effects were made, so that the relative merit of single or multiple birth and of each breed group would be reflected appropriately in the total weight of lamb weaned by each ewe. Inasmuch as this study was concerned with lifetime production as affected by attrition, it also was inappropriate to correct for age of dam, because ewes leaving the flock at younger ages, for example, would never produce at the level of older ewes. It was desirable to adjust for age of lamb at weaning because weaning dates varied as much as 9 d depending on weather and logistics. Further, genetic differences among breed groups in lambing dates, typically amounting to little more than 3 or 4 d, can be accommodated easily with negligible expense by slightly shifting breeding dates, with the result that lambs from different breed groups can be born at the same dates. Linear contrasts among effects of breed group were calculated (i.e., all purebreds vs 1/ 4 Finncrosses vs 1/2 Firmcrosses and Rambouillet Finncrosses vs Targhee Finncrosses vs Columbia Finncrosses). Bonferroni t-statistics (Gill, 1978) were used in testing differences. These tests of significance are not exact because of disproportionate numbers among classes and subclasses in the mixed-model analysis and because the distributions of the traits are moderately skewed (positively, except for age, which is skewed negatively). Results and Discussion Traditionally, crossbreeding in the Western range sheep industry has involved the crossing of a meat-type sire on whiteface range ewes. The result has been increased efficiency of meat production through fast-growing, crossbred market lambs. However, as emphasized by Dickerson (1970, 1978), one of the most effective methods of increasing the efficiency of meat production is to increase the number of lambs marketed per ewe per year. This concept has led to increased use of crossbred ewes presumably adapted to Western conditions to increase lamb production (Dickerson, 1977; Matthews et al., 1977; Clarke and Hohenboken, 1983; Ercanbrack and Knight, 1985). When planning a breeding program involving crossbred ewes, the difficulty of obtaining replacements always is a consideration. The difficulty becomes less important as

LIFETIME PRODUCTION OF 1/4 AND 1/2 FINN EWES 3261 TABLE 2. ANALYSIS OF VARIANCE, MEANS AND STANDARD DEVIATIONS FOR FINAL AGE AND LIFETIME PRODUCTION TRAITS Final Flcccc No. Wt!tern dt a age, yr vet, kg weaned weaned, kg Sires ignored Breed group Years Breed group x years Sires considered Breed/year group Sires within group Overall mean Residual standard deviations Sires ignored Sires considered F-ratios 8 1.12 4.26** 9.55** 7.48** 3.97 5.14"*.88 1.16 24 1.16 1.32 1.07 1.15 35 1.10 2.11"* 3.18"* 2.73** 284 1.09 1.39"*.96.97 5.06 20.0 4.81 170 2.04 10.0 3.24 116 2.02 9.6 3.26 117 adegrees of freedom for the residual mean squares were 1,154 and 870 for analyses with sires ignored and sires considered, respectively. **P <.01. the average number of years that ewes contribute to flock production increases. In any breeding program, it is prudent to consider that the annual cost per unit of product (Dickerson, 1970) typically is reduced both as female years in production increases and, more significantly, as total production per female increases. Increasing years in production can decrease only a fraction of the annual cost of production, that attributable to replacements; increasing total production per ewe (lamb plus wool in economic equivalents) decreases the entire cost per unit of product. An important question to be answered in the present study was whether or not the total value of lifetime production of Finncross ewes, which typically had superior annual lamb production but lower wool production, was higher than that of purebred ewes, which perhaps lived longer and thus might have compensated for more moderate annual lamb production. The F-ratios from both the fixed and the mixed-model analyses of variance, along with overall means and residual standard deviations, are shown in Table 2. Breed group differences were significant for all traits except final age in the flock. Year (birth-year) differences were significant only for fleece weight, and interactions between breed group and year were not significant for any trait. Sire differences within group were significant only for fleece weight. Interactions between level (fraction) of Finnsheep breeding (1/2, 1/4 or none) and the maternal breed (Rambouillet, Targhee or Columbia) of the ewes were evaluated by linear contrasts in the mixed-model analysis. None TABLE 3. LEAST SQUARE MEANS OF POOLED 1/2 FINNSHEEP, 1/4 FINNSHEEP AND PUREBRED BREED GROUPS FOR FINAL AGE AND LIFETIME PRODUCTION TRAITS Breed Final Fleece No, Wt.group age, yr wt, kg a weaned b weaned, kg c 1/2 Firm 5.12 17.9 5.52 191 1/4 Finn 5.11 20.8 5.04 179 Purebred 4.92 21.9 3.77 138 SE d.11.6.17 6 alinear response (b L = -2.01; P <.01) with purebred, 1/4 Finns and 1/2 Finns coded as 0, 1 and 2. bquadrafic response (b L =.88, bq -.39; P <.07). CQuadratic response (b L = 26.8, bq = -13.8; P <.07). dapproximatr standard errors.

3262 ERCANBRACK AND KNIGHT 9.8 o 7 6 ',Cd Cr.5 4 9 2.3 2 1 0 1 2 3 4 5 6 PRODUCTION YEAR PUREBREDS ~ 1/4 FX ~ 1/2 FX Figure 1. Fraction of each original pooled purebred, 1/4 Finn and 1/2 Finn breed group remaining for rebreeding for each production year. were found to be significant (P >.10), indicating that differences among levels were independent of the maternal breed involved. Hohenboken and Clarke (1981) similarly found no significant interaction between breed of the ewe's sire (Cheviot, Dorset, Finnsheep, and Romney) and breed of the ewe's dam (Columbia and Suffolk) for cumulative lamb production or longevity of crossbred ewes mated to Hampshire rams. A supplementary fixed-model analysis, which included main classifications for level of Finnsheep breeding, maternal breed of ewe and birth-year and all interactions among them, was completed to evaluate significance of nonorthogonal polynomial regressions for level of Finnsheep breeding. This analysis substantiated findings from the mixed-model analysis that interactions between level of Finnsheep and maternal breed of ewe were not significant (P >.13) for any trait. It also revealed that effects of level (coded as 0, 1, and 2 for purebreds, 1/4 Finns and 1/2 Finns, respectively) were not significant (P >.35) for age, were significantly linear (P <.01) for fleece weight and were almost significant for quadratic regression (P <.07) for numbers and weight of lamb weaned. The curvilinear effect on numbers and weight of lamb weaned, contrary to what might be expected genetically, perhaps may be explained by the increasing pressure of environmental factors on lambs as number of Iambs per ewe increased. In the absence of information from reciprocal crosses and pure Finnsheep females or from second-generation crosses (F2 equivalents), little can be concluded about possible heterotic effects, which here are confounded with maternal and additive effects. Differences among pooled breed groups (1/ 2 Finns, 1/4 Finns and purebreds) were not statistically significant (P >.20) for average final age (Table 3). Figure 1 portrays the fraction of each original pooled breed group remaining for breeding at the beginning of each production year and reveals an almost linear attrition rate for each group to the end of the study. Annual attrition rates were -10.4, -9.1 and -10.7% for 1/2 Finns, 1/4 Finns and purebreds, respectively. Interestingly, the highest attrition rate occurred in the purebreds. Many differences were clearly significant (Table 3) for lifetime lamb and wool production. Average lifetime 1/4 and 1/2 Finn fleece weights per ewe were only 95 and 82% as high, respectively, as those of purebreds. In contrast, 1/4 and 1/2 Finn ewes had 34 and 3,6%, respectively, higher numbers of lambs weaned and 30 and 38% greater total weight weaned than purebreds. Similarly, Hohenboken and Clarke (1981) observed superior cumulative lamb production through 5 yr for

LIFETIME PRODUCTION OF 1/4 AND 1/2 FINN EWES 3263 TABLE 4. LEAST SQUARE MEANS OF POOLED 1/2 ADN 1/4 FINNCROSSES FOR FINAL AGE AND LIFETLME PRODUCTION BY MATERNAL BREED OF CROSS Maternal Final Fleece No. Wt breed age, yr wt, kg weaned weaned, kg Rambouillet 5.11 19.1 5.66 a 198 a Targhee 5.06 19.3 5.37 ab 189 ab Columbia 5.18 19.8 4.80 b 168 b SE c.14.7.21 7 a'bmeans without a common superscript differ (P <.05). CApproximate standard errors. crosses of Finnsheep and Dorset ewes compared with Cheviot- and Romney-sired crossbred ewes. They observed no differences in longevity among these crossbred ewe types under irrigated pasture conditions, but Finnsheep crosses ranked poorest under hill pasture conditions. In the current study, differences among pooled breed groups depended importantly on the fostering opportunities for lambs of Finnsheep cross ewes. When all foster lambs, regardless of where reared, were included, 1/4 and 1/2 Finns were approximately 44 and 71% higher in numbers of lambs and 38 and 59% higher in weight of lambs weaned, respectively, than purebreds. These figures are substantially higher than those above. Foster lambs not included in production because they were reared outside the group in which they were born constituted 3.6, 5.2 and 9.7% of those born to purebred, 1/4 Finn and 1/2 Finn ewes, respectively. However, after offsetting these figures with numbers of foster lambs born outside of a group but fostered by the group (but also not included), the net results were a 3.2% gain in number of lambs for purebreds and net losses of 1.6 and 7.7% for 1/4 and 1/2 Finns, respectively. Hence, much of the potential difference among the groups in lamb production is lost if fostering opportunities do not exist. Differences among crosses of Finnsheep associated with the maternal breed (Rambouillet, Targhee or Columbia) of the crosses were examined, also. Results presented in Table 4 indicate no statistically significant differences among pooled 1/4 and 1/2 Finncrosses having different maternal breeds for either final age or fleece weight. However, Rambouillet crosses were 18% higher (P <.05) in both number and weight of lambs weaned than Columbia crosses. Other differences were not significant. Note that Columbia crosses had slightly higher final ages and fleece weights and lower total number and weight of lambs weaned than others. Assuming the unit value of wool (based on wool incentive values) to be 2.5 times the unit live-weight value of lamb and ignoring differences in unit value of purebred and Finncross wools, net values of lifetime production (Table 5) for 1/4 and 1/2 Finnsheep crosses were about 20 and 22% higher, respectively, than that of purebreds. However, it is inappropriate to ignore potential effects of Finncrossing on market value of wool. Drummond et al. (1980, 1982) examined wool characteristics from the identical breeds and crosses discussed herein. They found, on the basis of fiber diameter determination (rapid comparator method), that crossing with Finnsheep had the effect of TABLE 5. RELATIVE VALUE OF TOTAL LIFETIME PRODUCTION BY POOLED BREED GROUP Breed group Lifetime production a Relative value 1/2 Finn 236 (225) 1.22 (1.17) 1/4 Finn 231 (222) 1.20 (1.15) Purebred 193 1.(30 alncludes total production of lamb and wool in kilograms with kilograms of wool weighted at 2.5 times that of lamb. Figures in parentheses reflect results if value of 1/2 Finn wool was discounted 25% and 1/4 Finn wool was discounted 18% because of coarser wool grades.

3264 ERCANBRACK AND KNIGHT changing Rambouillet and Targhee wool grades (in spinning counts) from 64 to 60 in 1/ 4 Finns and to 58 in 1/2 Finns. Spinning counts of Columbia wools were less affected, dropping from 58 to 56 in both 1/4 and 1/2 Finns. All spinning counts were within the apparel wool classification. Staple lengths were increased by crossing Finnsheep with Rambouillet and Targhee. They concluded that Finnsheep crossing had no influence on the production (yield) of wool top or the quality of yarn when wools of similar grades were compared. But in consideration of the above effects on wool grade, we discounted the value of wool from 1/4 and 1/2 Finnsheep crosses by 18 and 25%, respectively. These discounts were determined after calculating the average price (clean wool basis) paid for wools of various spinning counts over the period 1978 to 1986 (ASPC, 1988). They are based on grade changes for Rambouillet and Targhee crosses and therefore are somewhat excessive for Columbia crosses. Also, these discounts are slightly excessive because they do not account for the typically higher clean-wool yield of the coarser wools. After these discounts were applied, net values of production for 1/4 and 1/ 2 Finns were still 15 and 17% higher, respectively, than those for purebreds. Saoud and Hohenboken (1984) found a correlation of.93 between lifetime lamb production (based on four or five producing years) and lifetime net revenue (wool income excluded). Their correlation was.95 between lifetime gross income from lamb production and net revenue. The correlations likely would have been lower, however, had wool income been included in net revenue. Despite their high annual rates of lamb production, attrition among the Finncrosses over the 7-yr period was no more serious than that among purebreds; they remained in the flock to slightly, but not significantly, older average ages than the purebreds. Hence, replacement costs for the Finnsheep crosses, prices being equal, would be about the same over the years as those for purebreds. The differences among 1/2 Finns, 1/4 Finns and purebreds in total production were not significantly affected by the year (birth-year) in which the ewes entered the breeding flock. They also were not affected by the maternal breed (RambouiUet, Targhee or Columbia) of ewe from which the crosses were derived; Finnsheep crosses clearly were superior in lamb production and inferior in wool production regardless of the maternal breed. Differences among Rambouillet, Targhee and Columbia crossed with Finnsheep were negligible for final age and fleece weight, but Rambouillet-Finnsheep crosses were superior to crosses of Columbia-Finnsheep in number and weight of lamb weaned. Implications The net value of lifetime production for both 1/2 and 1/4 Finnsheep crosses was substantially higher than that of purebreds, even after considering differences in quantity and quality of wool produced. The net value for 1/2 Finnsheep crosses was only slightly higher than that for 1/4 Finnsheep crosses when opportunities for fostering extra lambs were limited. Much of the potential contribution of 1/2 Finnsheep to lamb production can be lost unless sufficient foster mothers are available or environmental circumstances permit dams to rear triplet lambs. Yet, recent pilot trials at this station revealed that as many as 60% of selected ewes turned on the range with triplet lambs reared them to weaning. Perhaps we are not fully exploiting the capabilities of 1/2 Finnsheep ewes by arbitxarily limiting dams to two lambs. Literature Cited ASPC. 1988. U. S. Sheep Industry Market Situation Report 87/88. American Sheep Producers Council, Inc. Denver, CO. Clarke, S. E. and W. D. Hohenboken. 1983. Estimation of repeatability, heritability and breed differences for lamb production. J. Anita. Sci. 56:309. Dickerson, G. 1970. Efficiency of animal production-molding the biological components. J. Anita. Sci. 30:849. Dickerson, G. E. 1977. Crossbreeding evaluation of Finnsheep and some U.S. breeds for market lamb production. North Central Regional Pubt. 246. Dickerson, G. E. 1978. Animal size and efficiency: basic concepts. Anim. Prod. 27:367. Dickerson, G. E., H. A. Glimp and K. E. Gregory. 1975. Genetic resources for efficient meat production in sheep: Preweaning viability and growth of Finnsheep and domestic crossbred Iambs. J. Anita. Sci. 41:43. Donald, H. P., J. L. Reed and W. S. Russell. 1968. A comparative trial of crossbred ewes by Finnish Landrace and other sires. Anim. Prod. 10:413. Drummond, J., R. A. O'Counell and D. A. Price. 1980. Processing characteristics of Finn-cross wool. J. Anita. Sci. 50:405. Drummond, J,, R. A. O'Connell and K. L, Colman. 1982. The effects of age and Firmsheep breeding on wool properties and Im~cessing characteristics. J. Anita. Sci. 54:8.

LIFETIME PRODUCTION OF 1/4 AND 1/2 FINN EWES 3265 Ercanbrack, S. K. and A. D. Knight. 1985. Lifetime (seven years) production of 1/4 and 1/2 Finnish Landrace ewes from Rambouillet, Targhee and Columbia dams under range conditions. J. Anim. Sci. 61:66. Gill, J. L. 1978. Design and Analysis of Experiments in Animal and Medical Sciences. Vol. 1. pp 176-177. The Iowa State Univ. Press, Ames. Harvey, W. R. 1975. Least-squares analysis of data with unequal subclass numbers. Publ. H-4. ARS, USDA, Washington, DC. Hohenboken, W. D. and S. E. Clarke. 1981. Genetic, environmental and interaction effects on lamb survival, cumulative lamb production and longevity of crossbred ewes. J. Anita. Sci. 53:966. Laster, D. B., H. A. Glimp and G. E. Dickerson. 1972. Factors affecting reproduction in ewe lambs. J. Anita. Sci. 35:79. Matthews, D. H., M. A. Madsen, J. A. Bennett and W. C. Foote. 1977. Lamb production of Targhee and Suffolk- Targhee range ewes. J. Anim. Sci. 44:172. Meyer, H. H. and G. E. Bradford. 1973. Reproduction in Targhee and Finnish Laodrace x Targhee ewes. J. Anita Sci. 36:847. Oltenacu, E.A.B. and W. J. Boylan. 1981. Productivity of purebred and crossbred Finnsheep. I. Reproductive traits of ewes and lamb survival. L Anita. Sci. 52:989. Saoud, N. B. and W. D. Hohenboken. 1984. Genetic, environmental and interaction effects on lifetime production efficiency of crossbred ewes. J. Anita. Sci. 59:594.