Inbred lines of mice derived from long-term growth selected lines: unique resources for mapping growth genes.

Lines of mice selected for many generations for high or low growth in several laboratories around the world have been collected, and from these, inbred lines are being developed by recurrent full-sib mating in Edinburgh. There are seven high selected lines and four low lines (each low line is from the same base population as one of the high lines), and the histories of each are summarized. Mean body weight of males at 70 days of age in the Edinburgh laboratory in the heaviest inbred line (77 g) is 4.8-fold higher than in the lightest line (16 g), and 1.9-fold higher than in the least extreme high line (41 g). Litter size, food intake, and fat content also differ substantially. These inbred extreme selected lines are a uniquely valuable resource for QTL or gene mapping, candidate gene identification, and elucidation of epistatic effects.

Cryopreservation of embryos as a means of germ plasm conservation in sheep.

Embryos were collected from 4 lines of Targhee sheep between 1986 and 1990. The lines were selected for preweaning growth rate (Lines DH and HW) or for multiple births (Line HT); Line C served as an unselected control group. Estrus was synchronized using fluorogestone acetate-impregnated vaginal pessaries, and ewes were superovulated with FSH. Embryos at the morula or blastocyst stage were surgically recovered from mature ewes at Days 5 to 6 and were frozen following morphological evaluation. The overall average number of freezable embryos per collection was 2.9, and did not differ significantly among years or among lines. Of the embryos collected between 1986 and 1988, 92 were transferred to 53 recipients in 1989, producing 53 lambs. Survival rates were 60.9 and 47.8%, respectively, for embryos evaluated as good and fair after thawing. Good-quality blastocysts yielded the highest survival rate (64.4%). Analyses indicated no significant effects of line, developmental stage or embryo evaluation on the incidence of lambing. It was concluded that embryos of morula or blastocyst stage can be successfully frozen for extended periods. The data on embryo yield and survival following cryopreservation were used to calculate numbers of donors needed to preserve and reconstitute a population of specified size.

Ram influence on ovarian and sexual activity in anestrous ewes: effects of isolation of ewes from rams before joining and date of ram introduction.

A 2-yr experiment was conducted to determine whether isolation of ewes from rams is necessary to achieve a high response to the ram effect and whether ewes respond as well in May as in June. The experiment was conducted at two locations, with the same four treatments at each location. The four treatments differed with respect to ewe proximity to rams before mating (isolated vs adjacent) and date of joining with novel breeding rams (May 15 vs June 15). The proximity treatment at one location was changed in the 2nd yr; teaser rams were joined with the ewes instead of being adjacent to them. Overall, 86% of the eligible ewes were judged to have responded to the ram effect. A period of isolation before mating did not increase response compared with ewes that remained adjacent to, or in contact with, rams (86 vs 85%). Response was greater (P less than .05) in June and in the 2nd yr (P = .05). A physiological response, different from that generally described, was identified. Ewes ovulated approximately 8 d (8.0 +/- .19 d) after joining with breeding rams. The subsequent ovulation, accompanied by estrus, occurred approximately 15 d later (15.3 +/- .29 d). Eighty-five percent (87/102) of the ewes sampled responded in this manner. However, 82% (31/38) of a sample of these ewes had at least one morphologically normal corpus luteum when examined by laparoscopy 4 d after joining. It seems that these corpora lutea were not completely functional with respect to progesterone production. The ram effect can be achieved without prior isolation of ewes from rams.(ABSTRACT TRUNCATED AT 250 WORDS)

Genetic and environmental effects on growth to 1 year and viability of lambs from a crossbreeding study of D'man and Sardi breeds.

Genetic effects were estimated for growth to 1 yr and viability to 90 d of 882 lambs from a diallel cross of Sardi (S), D'man (D), and D'man x Sardi (DS) male and female parents. Sardi direct genetic effects were significantly higher than those of D'man for weights at birth and up to 2 mo, but the difference decreased thereafter and was in favor of D'Man at 6 mo. Sardi maternal ability was better than that of D'man for weights at all ages. Estimates of individual heterosis were small and negative for weight at birth, weight at 1 mo, and lamb viability and positive for other body weights; the estimate was significant for 12-mo weight. Estimates of maternal heterosis were small and did not approach significance for any trait. Epistatic recombination effects were generally small, but negative for all traits and significantly so for viability to 30 d. In general, the results, combined with those on reproduction and total lamb production of ewes of these groups, reported elsewhere, indicate that a population produced by inter se mating of animals 50% D, 50% S breeding is expected to have higher total lamb production than either purebred.

Ovulation rate and pre- and postimplantation survival in mice with a major gene for rapid postweaning gain.

Differences in ovulation rate, embryo survival, litter size, and fertility are presented for four lines of mice that have been selected for growth or are homozygous for a recessive gene (hg) imparting rapid postweaning gain. Two of the lines were hg/hg, one in a growth-neutral and one in a growth-selected background. The remaining two were Hg/Hg (the corresponding normal, dominant allele with no effect on postweaning gain) in the same two backgrounds. Average ovulation rates ranged from 10.9 to 17.1 eggs shed, and litter sizes ranged from 8.6 to 14.0. In the growth-selected background, the hg allele reduced the number of ovulations, implantation, and litter size by nearly three compared with the Hg/Hg controls. The impact of the hg allele in the growth-neutral background was not significant. When males of a different line selected for high litter size were mated to females of the four stocks, more than two additional eggs, implants, and pups were recorded, compared with results of mating to males of the same line as the female.

Growth hormone and insulin-like growth factor-I measurements in high growth (hg) mice.

Effects of a recessive gene causing high growth (hg) were studied on two major components of the growth axis in mice. Plasma and pituitary levels of growth hormone and plasma levels of insulin-like growth factor I (IGF-I) were measured in three lines homozygous for hg, each compared with a control line of alike genetic background but wild type for the hg locus (Hg). Line Gh (hghg) and line GH (HgHg) are from a line which had undergone long-term selection for high postweaning weight gain; line Ch (hghg) and line CH (HgHg) were extracted from the second backcross of Gh to C57BL/6J; line L54 (hghg) was from the sixth backcross to C57BL/6J (B6) (HgHg). Pituitary GH levels and plasma IGF-I levels were measured in both sexes at 3, 4.5, 6 and 9 wk of age. Plasma growth hormone was measured in 8- to 12-wk-old males at hourly intervals from 08.00 to 17.00. Body weight in lines homozygous for hg at 6 and 9 wk of age was 10-30% greater than in control lines. The ontogeny of this increased growth depended on genetic background. Pituitary growth hormone content was 52% lower in the two hghg lines measured (lines Ch and Gh) than in control lines at 4.5, 6 and 9 wk. Plasma growth hormone levels were also much lower in hg mice, with values only 20-30% of those in their respective controls. hg lines showed consistently low plasma growth hormone levels throughout the 9 hr sampling period, while control lines expressed the characteristic pulsatile hormone secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth performance and plasma insulin-like growth factor I concentrations in sheep selected for high weaning weight.

A study was undertaken to determine the effect of selection for high weaning weight on concentrations of plasma insulin-like growth factor I (IGF-I) in sheep and to evaluate the usefulness of measuring IGF-I as an aid in identification of genotypes with a higher growth potential. Lambs from two lines selected for high 120-d weight (HW and DH) and an unselected control (C) were weighed and blood samples collected monthly from birth to weaning (4 mo. of age). A clear differentiation in size occurred after 1 mo of age between lines, between sexes, and between singles and twins. At weaning, selected lines were 3.8 and 5.0 kg heavier than controls. Plasma IGF-I concentrations were 1.5 to 2 times higher (P less than .001) in males than in females after 1 mo of age. There were no significant differences in IGF-I concentration between lines or types of birth. However, line DH and single lambs on average had higher concentrations of IGF-I. Within sex and type of birth correlations between IGF-I concentrations at 0, 1, 2, 3, and 4 mo and 4-mo BW ranged from -.16 to .49 in the three lines, and most were not significant. Coefficients of variation for IGF-I concentrations (36 to 50%) were two to three times higher than those for BW (11 to 15%). Due to the high variability of IGF-I measurements, the low correlations between IGF-I concentration and BW, and the small differences in IGF-I between control and selected lines, measurement of plasma IGF-I is unlikely to be an effective aid to selection for growth rate in sheep.

Inheritance of litter size and its components in crosses between the D'man and Sardi breeds of sheep.

Data on ovulation rate, litter size and embryo survival of 364 Sardi (S), D'man (D), S x DS, DS x S, S x D, D X S (F1), F2, D x DS and DS x D ewes mated for first and second lambing to F1 rams were analyzed. Breed group, birth group and season had significant effects on ovulation rate and litter size but not on embryo survival. D'man ewes had the highest ovulation rate (2.79) and litter size (2.00), with an essentially linear increase in each of these variables with percentage of D'man inheritance in the ewe (b = .017 +/- .001 CL and .009 +/- .001 lambs born). Embryo survival was influenced only by the number of ova shed. D'man direct genetic effects were higher (P less than .01) than those of Sardi for ovulation rate (+1.78) and litter size (+1.08) but did not differ for embryo survival (-.07). Maternal effects differed little for any of the three traits. Individual heterosis estimates were negative and significant for ovulation rate but not significant for litter size and embryo survival. Maternal heterosis and epistatic recombination effects were small and not significant for any trait.

Genetic effects on ewe productivity of crossing D'man and Sardi breeds of sheep.

Data from 364 ewes of Sardi (S), D'man (D), S x DS, DS x S, S x D, D x S (F1), F2, D x DS and DS x D breed groups mated to F1 rams were analyzed for fertility, number of lambs born alive, litter size at weaning, litter weight at weaning per ewe joined and mean lamb weight at 60 d. Each ewe was exposed in two seasons and had one or two lambings. Effects of breed group were significant for all traits. The highest number of lambs born alive and litter size at weaning were recorded in D'man (1.84 and 1.45, respectively) and D x DS (1.81 and 1.43, respectively). F1 ewes (S x D and D x S) had the highest fertility (.94) and litter weight at weaning per ewe exposed (13.8 kg). Mean lamb weight at 60 d was highest for S x DS and Sardi ewes (13.4 kg and 13.2 kg). D'man additive effects were positive and significant for number of lambs born alive, litter size at weaning and litter weight at weaning per ewe joined; were significant but negative for mean lamb weight at 60 d; and were not significant, although positive, for fertility. Significant individual heterosis was found for fertility, litter weight weaned and mean lamb weight at 60 d. Maternal heterosis and direct epistatic recombination effects were small for all traits.

Evaluation of production and reproduction of sheep, goat and alpaca genotypes in the Small Ruminant Collaborative Research Support Program.

Research has been conducted as part of the Small Ruminant Collaborative Research Support Program (SR-CRSP) on evaluation of genetic resources and methods of effecting genetic improvement of small ruminants in the participating countries. In Kenya, the focus has been on development of a dual-purpose goat for milk and meat production in farming areas, utilizing two locally adapted breeds, Galla and East African, and two imported dairy breeds, Anglo-Nubian and Toggenburg, into a single stock. That research now has reached the stage of field testing. In Morocco, the performance of a highly prolific breed of sheep, the D'Man, and of a less prolific but larger breed, commonly raised under extensive management, the Sardi, and of their F1, F2 and backcross progeny has been evaluated for several reproduction and growth traits. Prolificacy of the D'Man was transmitted additively, but there was favorable heterosis for age at puberty, fertility and growth rate, resulting in substantial heterosis in total performance. In Indonesia, a high degree of variability in prolificacy in sheep appears to be due to segregation of a gene with large effect on ovulation rate, similar in some respects to the Booroola gene. In Peru, work has involved evaluation of effectiveness of current selection programs and estimation of phenotypic and genetic parameters, in unimproved and improved types of sheep, with a limited amount of work also on alpacas. Fiber production is the principal economic trait in alpacas. There also has been work on evaluation of hair sheep in Brazil, Kenya and Indonesia.

Reduced male reproductive capacity in mice with high genetic potential for post-weaning growth.

Male reproductive capacity was examined in 5 lines of mice which differed markedly in mature body weight (30-73 g) due to selection for growth and/or substitution of the high growth gene (hg). Testes weight ranged from 0.75-0.77% of body weight in control lines to 0.33% in the largest mice which had the hg gene in a growth selected background. Both selection for growth and the hg gene in a control background reduced absolute testes size (0.200 and 0.207 g vs 0.236 and 0.228 g in control lines) as well as relative testes size although body weight was increased by at least 50%. Although the combination of growth background and hg gene reduced sperm production per g testis compared to the outbred control, the primary cause of reduced sperm production per mouse in lines containing either the growth background or the hg gene alone was reduced absolute testes size. At 24, but not at 11, weeks of age, the hg gene reduced sperm motility. In these lines, high genetic potential for post-weaning growth was associated with decreased male reproductive capacity.

Measurements of metabolic rate in rats: a comparison of techniques.

Two different open-circuit techniques of measuring metabolic rate were examined in rats at rest and during exercise. With one technique ambient air was drawn through a tightly fitting mask that was secured to the rat's head, whereas with the other technique the rat was placed into and ambient air was drawn through a Plexiglas box. Two series of experiments were performed. In series I, two groups were studied that consisted of rats that had received myocardial infarctions produced by coronary arterial ligations and rats that had received sham operations. In this series of experiments O2 uptake (VO2) and CO2 production (VCO2) were measured at rest, during four levels of submaximal exercise, and during maximal treadmill exercise in the same group of rats by use of both techniques in random order. VO2, VCO2, and the calculated respiratory exchange ratio (R) were similar at rest, during the highest level of submaximal exercise (20% grade, 37 m/min), and during maximal exercise; however, VO2 and VCO2 were significantly lower with the metabolic box technique compared with the mask technique during the three lowest work loads (5% grade, 19 m/min; 10% grade, 24 m/min; and 15% grade, 31 m/min). These differences appeared to be associated with a change in gait produced when the mask was worn. In series II, the arterial blood gas and acid-base responses to both submaximal and maximal exercise were measured using both techniques in a group of instrumented rats that had a catheter placed into the right carotid artery.(ABSTRACT TRUNCATED AT 250 WORDS)

Release of prostaglandin F-2 alpha and the timing of events associated with luteolysis in ewes with oestrous cycles of different lengths.

Ewes (N = 32) were bled every 2 h from 5 days before expected oestrus until the end of oestrus. Plasma concentrations were determined for progesterone to monitor luteal activity and for the prostaglandin F-2 alpha (PGF-2 alpha) metabolites, 15-keto-13,14-dihydro-PGF-2 alpha and 11-ketotetranor-PGF to determine uterine synthesis and release of PGF-2 alpha. Most of the variation in cycle length was associated with the time of onset of luteolysis, the timing of events after luteolysis being constant and not related to cycle length. The time of occurrence of the first PGF-2 alpha pulse and the interval between this pulse and the start of luteolysis were the two main determinants responsible for oestrous cycle length. Several PGF-2 alpha pulses with interpulse intervals of 15.9 h occurred before the onset of functional luteolysis compared with 7.7 h for pulses associated with luteolysis. The numbers of PGF-2 alpha pulses and interpulse intervals were similar for oestrous cycles of different lengths. While a gradual decline in progesterone concentrations was observed before functional luteolysis in the ewes with longer cycles, this did not appear to be an integral part of the stimulus which initiates the pulse frequency of PGF-2 alpha required for luteolysis. We therefore suggest that differences in oestrous cycle length in the ewe are determined by the time of the onset of PGF-2 alpha pulsatile release, and especially by the time of increased pulse frequency.

Modification of prostaglandin F-2 alpha synthesis and release in the ewe during the initial establishment of pregnancy.

Pregnant (N = 10) and non-pregnant (N = 10) ewes were bled every 2 h from Days 12 to 17 after oestrus (oestrus = Day 0). Plasma concentrations of progesterone, 15-keto-13,14-dihydro-PGF-2 alpha and 11-ketotetranor-PGF metabolites were determined in all samples. The number of PGF-2 alpha pulses in non-pregnant ewes was 8.2 +/- 0.4 (mean +/- s.e.m.) with an interpulse interval of 10.7 +/- 0.7 h. Two or 3 pulses of low frequency (interpulse interval = 13.4 +/- 1.6 h) occurred in most non-pregnant ewes before the onset of luteolysis; the interpulse interval then decreased to 7.9 +/- 0.4 h for the 6.0 +/- 0.3 pulses temporally associated with luteolysis. In contrast, the number of PGF-2 alpha pulses in pregnant ewes was lower (2.5 +/- 0.7, 0-8) and the interpulse intervals longer (18.9 +/- 6.1 h). Most pulses occurred on Days 14 and 15 in the pregnant and non-pregnant ewes. The mean concentrations of both PGF-2 alpha metabolites in non-pregnant ewes were highest on Day 15 while basal levels of both metabolites remained constant at all times. In pregnant ewes, the mean concentrations of both metabolites were highest on Day 14; basal concentrations of both metabolites were also highest on Day 14. The mean concentrations of 15-keto-13,14-dihydro-PGF-2 alpha were higher in pregnant than in non-pregnant ewes on Days 13 and 14 (P less than 0.05) and higher in non-pregnant than pregnant ewes on Day 15 (P less than 0.05). The basal concentrations of the 15-keto metabolite were higher in pregnant than non-pregnant ewes at Days 13, 14, 15, 16 and 17 (P less than 0.05). Both the mean and the basal concentrations of 11-ketotetranor-PGF metabolites were higher in pregnant than in non-pregnant ewes on Day 14 (P less than 0.05). It is concluded that uterine production of PGF-2 alpha peaks at Days 14-15 after oestrus in pregnant and non-pregnant ewes. Patterns of release differ, however, in that non-pregnant ewes have a pulsatile PGF-2 alpha pattern superimposed on a constant baseline, while pregnant ewes have an increasing basal secretory pattern which is more nearly continuous, i.e. not pulsatile in form. Modification of pulsatile PGF-2 alpha synthesis and release is therefore a key aspect of prolongation of luteal function at the beginning of pregnancy in the ewe.

Glycogen concentrations and endurance capacity of rats with chronic heart failure.

The endurance capacities of rats with myocardial infarctions (MI) and of rats having undergone sham operations (SHAM) were tested during a submaximal exercise regimen that consisted of swimming to exhaustion. During this test, a decrement in the endurance capacity of the MI rat was demonstrated as the SHAM rat swam 25% longer than the MI rat (65 +/- 4 vs. 52 +/- 4 min). Glycogen concentrations were measured in the liver and the white gastrocnemius, plantaris, and soleus muscles of SHAM and MI rats that were randomly divided into four subgroups, which consisted of resting control, swim to exhaustion, swim to exhaustion + 24 h recovery, and swim to exhaustion + 24 h recovery + a second swim to exhaustion. The results demonstrated that the glycogen concentrations found in the liver, white gastrocnemius, plantaris, and soleus muscles of the SHAM and MI rats belonging to the resting control groups were similar. After swimming to exhaustion the glycogen concentrations in these tissues were significantly reduced compared with those found in the resting control groups of rats, and after 24 h of recovery the glycogen concentrations in these tissues were again similar to those found in the resting control groups of rats. Since the magnitude of the glycogen depletion in the liver and the white gastrocnemius, plantaris, and soleus muscles was similar in the SHAM and MI rats and because the SHAM rats consistently swam for longer periods of time in each of the experimental groups, it would be logical to assume that the rates of glycogen utilization for the various tissues may have been greater in the MI rat during exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Organ and skeletal growth in mice with a major gene for rapid postweaning growth.

Growth of liver, heart, kidney and femur in mice with a major gene for rapid postweaning growth (hg/hg, line Ch) was compared to that of their normal controls (Hg/-, line CH). Male mice of both lines were sacrificed at 7 day intervals from 21 to 56 days of age. By day 56 mice of line Ch weighed 40.1 g and individuals of line CH weighed 30.2 g. At sacrifice, individuals were weighed, the naso-anal length and tail length measured and the liver, heart and kidney were removed and weighed. The left femur was also removed and its length measured. Significant differences between lines were detected for all traits observed when examined on an uncorrected basis. This significance disappeared when organ weights were adjusted by body weight at sacrifice through covariance analysis. Similarly, there was no significant in femur length across lines when bone lengths were adjusted for naso-anal length. Only differences in tail length remained significant after adjustment for body length. These results suggest that the impact of the hg allele is of a fundamental and general nature, with little impact on specific tissues or functions of growth.

Natural and induced ovulation rate in prolific and non-prolific breeds of sheep in Ireland, Morocco and New Zealand.

Ovulation rate, in mixed-age groups of prolific and non-prolific ewe breed types, after administration of a range of doses of PMSG (0, 375, 750 and 1500 i.u.) during the follicular phase of the oestrous cycle, were compared in Ireland, Morocco and New Zealand. The ewes in Ireland and Morocco were from the Finnish Landrace and Galway, and D'Man and Timhadite breeds, respectively. In New Zealand Booroola Merino x Romney ewes which had been previously identified as heterozygous carriers (F+) of the Booroola high fecundity gene and purebred Romneys were used to represent the prolific and non-prolific genotypes respectively; in addition a group of Booroola Merino x Romney non-carriers (++) of the major gene were also included for comparison. Ovulation rate at the oestrus which preceded stimulation with PMSG was also measured in all animals. In all 3 locations the ewes of the prolific genotype had a greater ovulation rate after PMSG stimulation than did the non-prolific controls. However, this association between prolificacy and response to PMSG was removed when ovulation rate after PMSG was transformed by dividing by the ovulation rate observed before PMSG administration. Despite the differences in the genetic basis of their high prolificacy the pattern of response to PMSG over the range of dosages used was similar in Finnish Landrace, D'Man and Booroola Merino x Romney (F+) ewes and all breeds had means of about 10 ovulations in response to 1500 i.u. PMSG. Amongst the non-prolific breeds, the Timhadite was the most responsive to PMSG although it had the lowest natural ovulation rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Feed efficiency, growth rates, body composition, milk production and milk composition of Targhee sheep selected for increased weaning weight.

Lactation and growth of three contemporary lines of grade Targhee sheep developed from the same genetic base were characterized by three experiments performed over a period of 2 yr. Two lines (HW and DH) had been selected for 120-d weaning weights for 24 yr prior to beginning these experiments. A third line (C) was a randomly selected control. Year I experiment contrasted 10 DH with 7 C ram lambs fed to 58 kg. Year II experiments utilized 9 C, 14 DH and 10 HW ram lambs and 11 ewes suckling twins from each line. All Year II ram lambs were born and weaned as twins, then fed to 50 kg. Mature DH and HW ewes were heavier (P less than .05) than C ewes (65.2 and 68.8 vs 54.9 kg), and the DH and HW lambs grew faster than C lambs both before (P less than .05) and after weaning (P less than .05). While both DH and HW lambs drank more milk (2,419 and 2,368 vs 2,059 g X d-1 X pair-1; P less than .10) only HW ewes showed a trend towards greater potential milk production than controls (HW = 2,774 vs C = 2,155 g X d-1 X ewe-1 P less than .12). The HW lambs tended to be leaner than C lambs (P less than .05), but DH lambs did not differ from either line. Lambs from DH and HW lines required less post-weaning feed (121.9 and 129.3 vs 152.0 kg P less than .05) and exhibited 17 and 16% greater weight per day of age at 50 kg than controls (P less than .05). The DH line displayed lower feed: gain ratios than controls in both post-weaning trials (6.68 vs 7.30 to 58 kg; 5.83 vs 6.24 at 50 kg; P = .06).

Lambing date and lamb production of spring-mated Rambouillet, Dorset and Finnsheep ewes and their F1 crosses.

The reproductive performance of 255 Rambouillet (R), Dorset (D), Finnsheep (F) and F1 ewes born in 1978-1979 (group I) and 1979-1980 (group II) and managed in a semiconfinement fall/winter lambing system was evaluated through 4 yr of age of all ewes and through 5 yr for a portion of group I ewes. Ewes were with rams from approximately May 1 to late September each year, with a 2-wk break late in July/early August. Traits considered were fertility (ewes lambed/ewes exposed), lambing date, litter size, lamb survivial and 70-d lamb weights. Breeds and crossbred groups differed significantly in lambing date, with DR crossbred ewes earliest and F ewes latest. Repeatabilities for groups I and II were .31 and .22, .24 and .24 and .11 and .07 for lambing date, fertility and litter size, respectively. There was no significant heterosis in lambing date, although DR ewes in both groups I and II were superior to (D + R)/2, by about 1 wk on average. There was significant positive heterosis for fertility and traits of which fertility is a component in FR ewes in group I, but none in group II. The FD ewes showed negative heterosis for litter size, -.23 (P less than .05) for group I and -.09 for group II. The results indicate: F and FD ewes are not well adapted to the Mediterranean climate where this experiment was conducted; there is little, if any, useful heterosis in crosses among these three breeds for lambing date or other reproduction traits and RD and R ewes are most suitable of the groups tested, while late onset of the breeding season limits the usefulness of even 50% Finnsheep ewes for an autumn lambing system in this environment.