Maataloustieteellinen A ikakauskirja Vol. 60: 585—590, 1988 The Cambridge sheep its exploitation for increased efficiency of lamb production J.B. OWEN and I. AP DEWI University of Wales, Bangor, School of Agricultural & Forest Sciences, Deiniol Road, Bangor, Gwynedd, LLS7 2UW, England Abstract. The Cambridge breed has been developed since 1964, based on a foundation group of 54 ewes representing 11 breeds mated initially to seven Finnsheep rams. Data presented show that a high litter size (LS) has been established (mean 2.8 in 3 year old ewes) by a policy of selection coupled with minimising generation interval. Observations on ovulation rate (OR) show a large range (1 —13) and are consistent with an hypothesis that OR is influenced by a major gene effect superimposed on a basal level of about 2.5 ova. The gene appears to increase ovulation by about two ova per copy and to have a frequency approaching 0.3 in the Bangor University flock. Data on the relationship of LS at birth and of lambs weaned per ewe are presented which indicate that under ideal conditions the optima for OR and LS at birth cannot exceed 5 and 3.5 respectively for mature ewes. The practical utilisation of the breed as a dam-line sire of crossbred ewes show that the Cambridge crossbreds are more precocious, more prolific, have slower growing lambs with carcasses of similar qualityto the corresponding Border Leicester crosses. Overall superiority in efficiency of feed utilisation is about 20 Vo. Methods of genotyping sheep and utilising the major gene in practice are discussed. Index words: Cambridge, Finnsheep, ovulation rate, litter size, major gene, precocity, feed efficiency Introduction The Cambridge (C) breed was established in 1964 at Cambridge University by screening British breeds for ewes with high litter sizes (LS). The foundation flock of 54 ewes includ- ed a total of 11 breeds although the majority were Clun Forest (34 ewes), Llanwenog (6 ewes) and Lleyn (3 ewes). The seven founda- tion sires were Finnsheep (F). By initial back- crossing to the foundation ewes the genetic contribution of F was reduced to 20—25 %. Selection in the initial stage was primarily based on LS at birth and the generation length was minimised by confining matings to sires of 7 months old and to dams mainly up to 2 years old. From 1969 the foundation flock was part- 585 JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND https://www.c-info.fi/en/info/?token=dvv0fuL1-DLiVCFk.BJtl5qinI5Yo8rSoYLvJTw.V9e2XH3c3Q4hyiRrY_RKXjAvPtpFku-faNK4-8jqvOAX4RC3OG0GHeBW9UGrOpARGjOyqw3XpQj4IY4BS2mxVHHZyFdPFxbiYdpBUBll1qJ4XUdJNHgTRd5OOOs_BMk3_HheQQTEJyHWEy9zXZ3YL_hVcx7CdvUv78X3jg0rKziVRbJ5tj8 ly disseminated to a small group of cooperat- ing breeders (10—12 members). In 1983 the Cambridge Sheep Society was formally estab- lished and in September 1985 the first of the Society’s annual sales was held at Malvern, England. Since 1975 selection criteria have been wi- dened to include, in addition to LS, an em- phasis on milking ability and meat quality related to the needs of theEuropean Market. The paper describes the performance of pure C stock, evidence for the genetic basis of the prolificacy achieved and the transmis- sion of prolificacy to maximise lamb produc- tion efficiency in crossbred ewes kept under commercial conditions. These findings are discussed in relation to the strategy for future deployment of prolific sheep genotypes. Material and methods Performance ofpure bred C: The results are based on the performance achieved in the flock kept at the University of Wales, Ban- gor, using methods described previously (6). Ovulation rates (OR) were recorded from Oc- tober 1983 using the endoscope technique (2). Performance of crossbredewes: A contem- porary comparison of crossbred ewe types was carried out in the period 1980—1985 as described by Owen & Whitaker (7). These included comparisons of crossbred ewes sired from Welsh Mountain dams by C or Border Leicester rams. In these experiments the crossbred ewes were mated mainly to Suffolk (S) rams. In addition, some preliminary investigation was carried out into the effect of the mating Table 1. Lambs born per ewe lambing in the Bangor flock 1983—1987. Age of ewe No of ewes Lambs born per ewe 1.62241 2.4932 2.81423 3.01394 + ram (C vs. S) on ovum survival when mated to Welsh Mountain ewes. This study involved a total of 136 ewes for which OR and lamb- ing performance was recorded. Results and discussion The basis of prolificacy in the Cambridge breed Table 1 summarises the prolificacy of C ewes in the Bangor flock in the years 1983—1988. The values for ewes of 4 years old and over are biassed because of the sub- stantial rate of selection for prolificacy in these ewes. Since the autumn of 1983, data have been recorded for OR although the data do not necessarily include information for each age group in each year. Table 2 gives a frequency distribution for OR according to age. These observations, with the unusually high range of values and the within age CV of over 0.5, are suggestive of the presence of a gene with a major effect, segregating in this population. Similar observations have been reported for the Booroola Merino (8). The values for the repeatability of OR with- Table 2. Frequency distribution for ovulation rate (no of corpora lutea) according to ewe age. 1983—1987 Ewe age at lambing Ovulation rate 1 2 3 4 + 1 22 9 5 3 2 48 36 23 24 3 33 43 43 34 4 14 25 24 42 5 14 9 7 27 6 2 10 11 7 3 6 3 8 1 2 6 9 1 3 10 1 11 - 1 12 13 No of ewes 134 131 120 153 Mean O.R. 2.7 3.2 3.7 4.1 586 in ewe between years are also much higher than would normally be expected (2). The data for OR in this flock can be classified into three classes (or clusters), each relatively uniform within themselves and differing substantially in mean value (Table 3). Assuming that the three classes correspond to the genotypes CC, Cc & cc (C being the ’Cambridge prolificacy’ gene and c its allele) the results suggest that the gene is present in this flock at a frequen- cy of approximately 0.3. Prolificacy in C can be explained on the ba- sis of a basal OR of about 2.5 upon which is superimposed a further additive increment of approximately 2 ova per copy of a major gene. Another interesting facet of the observa- tions in the high level of ovum survival (OS) indicated by the data as shown in Figure 1 as compared to other breeds of high prolificacy (1). This high level of OS needs confirmation in controlled comparisons under similar con- ditions. The data as they stand do not indi- cate any obvious relationship between this en- hanced level of OS and the presence of the major gene since it appears throughout the range of OR studied. Limited preliminary data (Figure 2) do not support the hypothesis that OS is influenced by ram breed as noted by Meyer (5) in his ob- servations on different breeds. Optimum prolificacy The study of this unusual sheep population with a range of observed OR values from 1—l3 has afforded an opportunity for the first time to address in detail the important problem of where the range of optima for OR and LS in sheep are likely to lie. The involve- ment at Bangor with studies of Welsh Moun- tain Sheep and collaborative studies of Awassi sheep under semi-arid ranges (3) has clearly emphasised that the appropriate economic op- tima for conditions with severe constraints are an OR and LS of one. In contrast, Figure 3 shows the range of values for the number of lambs reared (to 50 days) per ewe in relation to OR and to LS in C under good lowland husbandry conditions. These indicate that the economic optima for OR and LS are unlikely to exceed 5 and 3.5 respectively for mature ewes. Performance of Cambridge crossbred ewes Early comparisons of C as a dam-line sire of crossbred ewes indicated that C crossbred ewes gave birth to 14 % more lambs and Table 3. Ovulation rates for two and three year old ewes classified into three genotype classes observed in the peri- od 1983—1987. Age of Classification Presumed No of Mean Coefficient ewe criterion genotype ewes ovulation of rate variation 3 I—3 cc 71 2.5 0.25 4—6 Cc 41 4.7 0.18 7—12 CC 8 8.5 0.21 2 I—3 cc 88 2.4 0.28 4—6 Cc 36 4.4 0.14 7—12 CC 7 7.1 0.05 587 Fig. I. Preliminary data on ovum survival in relation to ovulation rate. reared 6 % more at weaning than Border Lei- cester sired crossbreds although the latter crossbreds gave lambs that were 4 % heavier at 18 weeks old (4). The more recent compar- ison based on crossbred ewes born in the peri- od 1980—83 have the results shown in Table 4. These results indicate that C crossbreds are earlier in reproductive maturity and produce at least 20 % more lambs per ewe lambing. The weight and quality of the final lamb (as judged by UK Meat and Livestock Commis- sion grading) was similar for the C and Bord- er Leicester crossbred. The C crossbred ewe was however 7 % lighter in mating weight and reared lambs 22 % lighter at 56 days of age. Overall, taking estimated feed intake into ac- count, it was calculated that the C crossbred ewes were approximately 20 % more efficient in terms of lamb production per unit of feed intake. Strategy for the future deployment of prolific sheep genotypes The foregoing observations suggest that in practice the optimum exploitation of geno- types like the C, that may carry a gene with a major effect on OR, is to produce commer- cial crossbred ewes heterozygous for this gene. Such a ewe would have the advantage of pos- sessing prolificacy at a rate likely to be near the economic optimum under good husban- dry conditions whilst at the same time exhibit- ing low (or normal) variability ofLS (as meas- ured in terms of CV in the region of 0.3). The main problem arises in securing a sup- ply of crossing rams proven homozygous for the C gene. This could be done by establish- ing flocks where the prolificacy gene is fixed at the locus in question or by developing a practical diagnostic technique for early genotyping of the male. The first alternative would obviously be helped by the availability of the diagnostic technique. Table 5 summarises the observed OR for 8 month old daughters of C sires measured in 1985 and 1987. These results suggest that even against the background of a ewe flock with a C gene frequency of about 0.3 it should be possible to make some useful preliminary as- sessment of the genotype of a ram when his daughters are 8 months old and he himself is Fig. 2. Comparison of Cambridge and Suffolk in terms of the ovum survival of ewes to whom they were mated 588 Table 4. Comparative lambing performance of crossbred ewes sired by Border Leicester and Cambridge rams (see Owen & Whitaker, 1987). Crossbred ewe sire breed Border Leicester Cambridge Ewe weight at mating 100 93 Ewes lambing at lyr 100 128 Lambs born per ewe lambing at lyr old 100 138 Lambs reared to 56d per ewe lambing at lyr old 100 151 Lambs born per ewe lambing at 2 & 3yrs old 100 113 Lambs reared to 56d per ewe lambing at 2 & 3yr old 100 115 Mean age at slaughter (all lambs) 100 115 Mean weight at slaughter (all lambs) 100 97 Efficiency of lamb production (lamb production estimated feed intake) 100 120 Table 5. Ovulation rate data for the progeny of rams measured as 8 month old females. Sire n Mean Range Sire n Mean Range 4023 3 1.3 I—2 6002 4 2.8 2—4 4029 1 1.0 * 6062 6 2.7 2—3 4062 8 2.9 I—s 6078 12 2.4 I—4 4106 5 3.2 I—s 6097 7 3.3 I—7 4114 7 2.3 2—3 6107 6 2.2 I—3 4117 10 3.1 o—s 6161 8 2.9 I—s 4129 5 3.0 I—s 6166 8 2.1 I—4 4136 3 2.0 2—2 6187 2 3.5 2—5 4165 6 2.5 I—s 6191 7 2.7 2—4 4184 7 2.3 2—3 6321 4 4.5 3—7 4194 5 2.6 I—4 6351 6 3.2 I—s 4275 4 1.5 I—2 589 Fig. 3. Lambs surviving to 50 days in relation to ovulation rate and litter size at birth. 21 months. Because of the high repeatability of OR it is possible to discriminate usefully between females of differing genotypes on the basis of their own OR even at the age of 8 months. A sub flock of C has already been estab- lished at Bangor based on rams progeny test- ed on the basis of their 8 month old female progeny mated to small groupsof ewes of high (7 + ) OR. If this method proves successful then such subflocks can be developed by breeders as one way of supplying a possible future demand for rams homozygous for the C gene. A more direct possibility for detecting geno- type at an early age is to apply the techniques of molecular biology. Work in progress at Bangor has the aim of enabling genotype with respect to the C gene to be determined from tissue (e.g. blood) taken from young lambs of either sex. Such a technique would allow the rapid exploitation of prolificacy genes in sheep to increase efficiency of lamb production. References 1. Hanrahan, J.P. (1987). Genetic variation in ovula- tion rate in sheep. In New Techniques in Sheep Production edited by I.M.F. Marai & J.B. Owen, PP 37—46, Butterworths, London. 2. Hanrahan, J.P. and Owen, J.B. (1985). Variation and repeatabilityof ovulation rate of Cambridge ewes. Anim. Prod. 40, 529 (ABS). 3. Kassem, R., 1987. Reproduction in the Awassi ewe under semi arid conditions. PhD thesis. Univ. of Wales. 4. Mann, T.S.L., Smith, C., King, J.W.8., Nicholson, D. & Sales, D.I. (1984). Comparison of crossbred ewes from five crossing sire breeds. Anim. Prod. 39, 241—249. 5. Meyer, H.H. (1985). Breed differences in ovulation rate and uterine efficiency and their contribution to fecundity. In: ’Genetics of Reproduction in Sheep’ (Eds. R.B. Land & D.W. Robinson), Butterworths, London: 185—191. 6. Owen, J.B. Crees, S.R.E., Williams, J.C. & Davies, D.A.R., 1986. Prolificacy and 50-day lamb weight of ewes in the Cambridge sheep breed. Anim. Prod. 42: 355—363. 7. Owen, J.B. & Whitaker, C.J. (1987). A comparison of cross-bred ewes raised from Welsh Mountain dams by three sire breeds; Cambridge, Border Leicester and Lleyn. J. Agric. Sci. 109, 159—164. 8. Piper, L.R., Bindon, B.M. & Davies, G.H. (1985). The single gene inheritance of the high litter size of the Booroola Merino. In: Genetics ofreproduction in sheep (Eds. R.B. Land & D.W. Robinson), But- terworths, London: 115—126. 590