Review
Frequency of the proli®cacy gene in ¯ocks
of Indonesian thin tail sheep: a review
J.A. Roberts
Schultz Road, Witta, via Maleny 4552, Queensland, Australia
Accepted 15 November 1999
Abstract
Indonesian thin tail (ITT) sheep have a major proli®cacy gene (FecJF), the frequency of which is higher in the new born lambs, than in the remainder of the ¯ock when mating is random, because carrier ewes produce more progeny than do non carriers. The frequency of the gene may vary between ¯ocks, but remains relatively stable in ¯ocks with established husbandry procedures. The countermanding selection pressures maintaining the equilibrium value for the frequency ofFecJFare mainly those deriving from higher mortality rates of lambs in larger litters. Embryo survival is not signi®cantly different across the range of ovulation rates in ITT ewes, in contrast to observations in other proli®c breeds. Generation intervals and the incidences of metabolic and infectious diseases in ewes carrying larger litters can also affect the frequency ofFecJFin ¯ocks. In turn, each of the factors affecting the frequency ofFecJFis modulated by the level of nutrition and management in each ¯ock. The distribution of proli®cacy genotypes in the ewes of a standard ¯ock is calculated asFecJFFecJF/12;FecJFFecJ/44;
FecJFecJ/44 giving a frequency of 0.34 forFecJF. The frequency ofFecJFis then 0.43 in the lambs at birth, when their numbers have been ampli®ed in the carrier ewes. There are heavier metabolic demands on ewes carrying larger litters and the foetuses constitute a higher proportion of weight gain during pregnancy. Consequently, more of the lambs of carrier ewes are smaller and weaker at birth, and the reserves of the ewes for colostrum and milk production are depleted. When low lamb survival rates in larger litters are considered, the frequency ofFecJFfalls to 0.35 in the lambs at weaning in lean years and 0.38 in middling years. At a high level of husbandry, ewe weight gains during pregnancy and lamb survival rates improve substantially, and after 3 years, the frequency ofFecJFin the lambs at birth is estimated to have risen to 0.49; and 0.47 at weaning.#2000 Elsevier Science B.V. All rights reserved.
Keywords:Indonesian thin tail sheep; Proli®cacy; Gene frequency
1. Introduction
Indonesian thin tail (ITT) sheep are the predomi-nant breed in the province of West Java where they are well adapted to the hot humid environment. Tradi-tionally, they are maintained in family ¯ocks of about three ewes, many families relying on neighbours for a ram. They are housed at night in small elevated pens
with slatted ¯oors, and are provided with feed cut and carried from roadsides, woodland and fallow land. In some areas family ¯ocks are permanently housed, while in others they graze under supervision during part of the day. Small closely supervised ¯ocks appear to provide the conditions necessary to maintain genes for proli®cacy (Mason, 1980), and a proli®cacy gene with major effect (Bradford et al., 1986, 1991), occurs
in the ITT breed. On institutional farms, ewes are usually kept in group pens and nutrition and manage-ment vary widely. Like most proli®c breeds of sheep (Bindon et al., 1996), ITT sheep reach puberty early (Sutama et al., 1988), resume ovarian activity shortly after parturition (Sutama et al., 1988) and are non seasonal breeders (Fletcher and Putu, 1985). With this combination of traits, the breed produces meat ef®-ciently (Reese et al., 1990; Iniguez et al., 1991; Inounu et al., 1993), in spite of the small size of the ewes (17± 30 kg). The proli®cacy gene of ITT sheep is desig-natedFecJF, with the standard allele FecJ, (COG-NOSAG, 1989).
When mating is random, gene distributions of traits which do not affect reproduction remain relatively stable. However, for a proli®cacy gene, the frequency in the zygotes is determined by the frequency in the parental generation ampli®ed by the proli®cacy of the ewes. That is, a homozygous normal ITT ewe, which produces mainly single lambs, will contribute genes to one zygote, whereas a homozygous carrier, which produces mainly twins and triplets, Table 1, will contribute genes to more than two zygotes. In the absence of countermanding selection pressures, the frequency of the fecundity gene would increase with each generation. Nevertheless, distributions of litter sizes in institutional and village ¯ocks in West Java, Table 2, remain relatively stable. Bradford et al. (1986, 1996) have suggested that the proli®cacy gene is in all populations of ITT sheep at a frequency of 0.05±0.25. Factors which may modulate the frequency ofFecJFin ¯ocks of Indonesian sheep on institutional farms and in villages are assessed in this review, and distributions of genotypes and the corresponding frequencies of
FecJFunder different husbandry conditions, are
cal-culated. In addition, some of the characteristics of other proli®c breeds are compared with those of ITT sheep.
2. Modulation of the frequency ofFecJF
The frequency ofFecJFin ¯ocks is modulated by nutrition and husbandry practices which are re¯ected in ovulation rates, survival and growth of lambs in larger litters, generation intervals, and metabolic dis-eases of ewes carrying large litters.
2.1. Ovulation rate
High levels of supplementary feeding over several months increased ovulation rates. The diet was free access to freshly cut grass, plus concentrate, 10 MJ/kg dry matter and 15% crude protein, either ad lib., or 700 g/day, and was compared with a maintenance diet of the same ingredients. In the study of Henniawati and Fletcher (1986), the mean body weights of the supplemented 2 and 4 tooth ewes increased from 19.5 kg to 24.5 kg over 22 weeks and the mean ovulation rate increased to a maximum of 2.65 at the sixth oestus after the beginning of the feeding regime, compared with 1.69 at the maintenance level. Nevertheless, mean litter size was only 1.78 compared with 1.50 at the maintenance level. At the same level of supplementation young ewes had a mean ovulation rate of 2.1 and a litter size of 1.8 compared with control ewes with 1.6 and 1.5 respectively (Sutama et al., 1988). So with prolonged supplementation at a high level, there was a higher ovulation rate, lower embryo survival and a small increase in litter size.
Table 1
Frequency distributions of the litter sizes produced by ewes of each of the proli®cacy genotypes of ITT sheep under different husbandry regimes. Data from the RIAP ¯ock
Level of nutrition Genotype Frequency distributions of litter sizes (%) Reference
Single Twin Triplet Quadruplet Quintuplet Mean
Lean/middling 76 24 0 1.24 Inounu et al., 1993
F 24 56 20 0 1.95
FF 14 33 34 17 2 2.59
Good 85 15 0 1.15 Subandriyo and Inounu, 1994
F 13 59 27 0 2.14
Reese et al. (1990) provided energy supplementation up to 826 kcal ME/day to ewes grazing on a rubber plantation. Litter size at the highest level of supple-mentation was 1.49 compared with 1.26 at lower levels, in ITT sheep from Sumatra, which have a relatively low frequency of the proli®cacy gene. Lamb birth weights, survival rates and growth rates all improved. On the other hand, in the Research Institute for Animal Production (RIAP) ¯ock (Inounu et al., 1993), mean litter sizes produced by each of the proli®cacy genotypes during years of good nutrition (Subandriyo and Inounu, 1994), did not differ from those of the lean and middling years (Inounu et al., 1993), Table 2. Lower levels of supplementation, provided strategically, did not affect ovulation rates (Inounu et al., 1985; Chaniago et al., 1988).
If supplementation does increase litter sizes, and the three proli®cacy genotypes respond in proportion to
their ovulation rates, then the frequency of FecJF
would increase in lambs from supplemented ewes.
2.2. Conception rate and embryo survival
Conception rates, embryo survival rates and net rates of survival of ova in ITT ewes were high, and embryo survival rates did not differ signi®cantly over the range of litter sizes, Tables 3 and 4, and proli®cacy genotypes (Bradford et al., 1991). Nevertheless, the trend of decreasing embryo survival rates with increasing ovulation rates in ITT ewes, was similar to that of other proli®c breeds, Table 4, re¯ecting decreasing marginal response of uterine ef®ciency with increasing numbers of embryos (Meyer, 1985).
Thus, on the basis of the available data, conception rate and embryo survival will not have signi®cant effects on the frequency of FecJF in the progeny of
Table 2
Distributions of litter sizes in institutional ¯ocks of ITT sheep. There would be overlap in the data bases used to compile the results from the RIAP ¯ock
Parity Frequency distributions of litter sizes (%) Founding Location Reference
Single Twin Triplet Quadruplet Quintuplet Sextuplet Mean stock
Institutional farms
First 57 33 11 0 1.54 Garut RIAP Bradford et al., 1986
Second 40 35 14 12 0 2.00
Latter 32 24 18 21 3 1 2.47
41 31 20 7 1 1.96 Garut RIAP Inounu et al., 1984
41 38 16 9 1 2.06 Garut RIAP Bradford et al., 1989
43 41 13 3 1.76 Garut RIAP Iniguez and
Gunawan, 1990
45 38 14 3 1.71 Garut RIAP Inounu et al., 1993
40 39 17 4 1.86 Garut RIAP Subandriyo and
Inounu, 1994
31 38 24 7 2.07 Not stated Bogor BPPH, 1955a
48 35 13 4 1.73 Not stated Bogor IPB, 1977a
41 37 20 2 1 1.86 Garut Ciawi Obst et al., 1980
55 34 11 1 1.58 Bogor Ciawi Obst et al., 1980
49 38 11 2 1.66 Garut Margawati Atmadilaga, 1992
56 36 7 1 1.53 N. Sumatra N. Sumatra Iniguez et al., 1991
Villages
Single Twin Triplet and above
29 50 21 1.97 West Java Inounu et al., 1984
38 44 17 1.77 West Java Subandriyo, 1986
68 28 4 1.36 West Java Means of data from
Mason, 1980
71 26 3 1.32 Sumatra Verwilghen
et al., 1992
ITT sheep; but would reduce the frequencies in other proli®c breeds.
2.3. Survival from birth to weaning
In the study of Obst et al. (1982), 31% of lambs died. Of those lambs, 32% were stillborn, 5% died at birth and 49% between birth and 3 days, and 60% of the total deaths were from litters of triplets and above. About 40% of the total deaths were attributed to lambs being small, weak or immature, and 11% to mis-mothering. Inounu et al. (1993) found that stillbirths constituted 52% of mortality to weaning.
Survival from birth to weaning is directly related to the weights of individual lambs at birth, and there is a strong inverse relationship between survival to wean-ing, and litter size, Table 5. Larger litters comprise a larger proportion of ewe weight gain during gestation than do singles (Inounu et al., 1993), Table 6, so after parturition ewes with larger litters have lower body reserves and are less able to provide colostrum and milk for the small lambs in those litters. This leads to
lower survival rates of lambs to weaning, Table 7, and lower litter weights at weaning, Table 6.
Moreover, the low survival rates in larger litters are exacerbated when the level of nutrition is low, Tables 6 and 7.
The quality and quantity of milk produced by ITT ewes is in the low range of sheep breeds (Sutama et al., 1988), but the requirement of the small lambs is also low. Level of nutrition and litter size affected weight changes of ewes, Table 6, and milk production, but not milk composition (Sitorus et al., 1985b). During 12 weeks from lambing, average milk production was 26 kg on a low level of nutrition and 31 kg on a higher level (Sitorus et al., 1985b), similarly 25 and 37 kg respectively (Sutama et al., 1988), and an average of 30 kg (Atmadilaga, 1958). Milk production was higher during the second lactation on both levels of nutrition (Sutama et al., 1988). Suckling of twins increased milk production by 28% on a low level of nutrition and 5% on a high level. Maximum produc-tion occurred 3±4 weeks after lambing (Atmadilaga, 1958; Sitorus et al., 1985b; Sutama et al., 1988).
Table 3
Conception rates and survival of embryos to lambing, for ewes producing different numbers of corpora lutea. Most ewes were served once when oestrus was ®rst detected. Data of Javanese and Semarang strains of ITT sheep in Bradford et al. (1986)
Number of corpora lutea
1 2 3 4±5 All
Number of ewes mated 79 79 29 14 201
Number of ewes lambed 57 65 19 12 153
Fertility (%) 72 82 66 71 76
Embryo survival/ewe lambing (%) 100 92 89 80 91
Net survival of ova (%) 72 75 59 57 69
Table 4
Distributions of the mean litter sizes, and survival rates, which correspond to each ovulation rate in lambing ewes of some proli®c breeds
Mean litter sizes (embryo survival %) at different ovulation rates Reference
Breed Ovulation rate
2 3 4 55
ITTa 1.83 (92%) 2.68 (89%) 3.30 (80%)b Bradford et al., 1986 Romanov 1.90 (95%) 2.61 (87%) 3.17 (79%) 3.58 (72%) Ricordeau et al., 1990 Finn, sheep 1.72 (86%) 2.24 (75%) 2.63 (66%) 2.90 (42%) Ricordeau et al., 1990 D'man 1.80 (90%) 2.33 (78%) 2.83 (71%) 2.44 (46%) Lahlou-Kassi and Marie, 1985 Icelandic 1.76 (88%) 2.25 (75%) 2.48 (62%) 2.50 (50%) Eythorsdottir et al., 1991
Survival of lambs, particularly those in larger litters, is dependent on the levels of nutrition and manage-ment in a ¯ock. In turn, low survival rates of the small lambs in large litters is the major pressure counter-manding ampli®cation of the frequency ofFecJFin the zygotes of proli®c ewes. The survival rates of lambs in larger litters, would increase from the commencement of better husbandry in a ¯ock, and continue to improve over a full reproductive cycle. Survival of lambs is inversely related to litter size regardless of the level of husbandry, Table 7, so the frequency ofFecJFin the ¯ock would continue to rise as more large litters were produced and more lambs survived. Ultimately, a new equilibrium will be established between the distribu-tion of litter sizes and lamb survival at the new level of husbandry. At very high levels of nutrition, the increased incidence of metabolic diseases in ewes (Obst et al., 1980, 1982; Fletcher et al., 1982; Aitkin,
1996) would reduce the increase in the frequency of
FecJF. Lambs in larger litters have lower survival rates in all proli®c breeds of sheep (Aitkin, 1996).
2.4. Breeding life of ewes
Age, weight and parity are generally inseparable in the data available; but they have important effects on ovulation rates and litter sizes, which were higher in older, heavier, multiparous ewes. Mean ovulation rates increased from 1.43 to 2.93 for ewe body weights from 17.1 to 29.6 kg (Bradford et al., 1986). Mean numbers of lambs per litter increased from 1.54 for primipara ewes to 2.47 for third and later parities (Bradford et al., 1986), Table 2. Ewes carrying the proli®cacy gene would be differentially affected to the extent that average life span is reduced by the metabolic and infectious diseases to which ewes with larger litters are
Table 5
Survival rates of individual ITT lambs from birth to weaning at 90 days, in relation to birth weight and litter size. Data from Chaniago et al. (1988)a
Survival rates (%) of individual lambs by birth weights and litter sizes
Litter size <1.0 kg 1.0±1.4 kg 1.5±1.9 kg 2.0±2.4 kg >2.4 kg All birth weights
Single 0 (2) 75 (4) 86 (14) 89 (26) 88 (24) 85
Twin 25 (4) 43 (28) 70 (46) 79 (33) 89 (9) 66
Triplet 0 (12) 21 (24) 60 (10) 0 (2) ± (0) 27
Quadruplet 0 (2) 0 (4) 0 (2) ± (0) ± (0) 0
All litter sizes 5 33 69 84 88 63
a( )
Number of lambs per class.
Table 6
Weight gains of ewes during gestation, and weaning weights of litters, related to the proli®cacy genotypes and litter sizes in the RIAP ¯ock of ITT sheep, in years with different levels of husbandry
Level of Lambs in Prolificacy genotype Litter size at birth Reference husbandry litter
FF F Single Twin Triplet Quadruplet
Ewe weight gain during gestation (kg)
Lean 0.5 1.1 1.4 1.8 0.7 0.3 ÿ0.9 Inounu et al., 1993
Middling 1.8 2.3 2.9 3.2 2.2 1.1 1.1
Good 3.8 4.0 3.8 5.2 2.8 2.4 7.9
Weaning weight of litter (kg)
Lean 6.7 7.4 7.7 7.7 7.6 6.1 5.3 Inounu et al., 1993
Middling 12.2 11.9 10.9 10.5 12.3 13.1 11.9
Good One 13.7 12.7 14.2 Subandriyo and Inounu, 1994
Two 20.2 19.0 23.0 13.8 19.9 20.3a Three/four 22.8 18.2
more prone (Aitkin, 1996). In the Ciawi ¯ocks with a continuous high level of nutrition, 11% of breeding ewes in one ¯ock died per lambing interval (Obst et al., 1980), the main causes being vaginal prolapse and pregnancy toxaemia (Obst et al., 1982), and dystocia (Fletcher et al., 1982). In the same ¯ock, the mortality of ewes was halved when strategic supplementation replaced continuous high level feeding (Chaniago et al., 1988).
2.5. Generation intervals
ITT ewe lambs attained puberty when their body weights averaged 17±18 kg, so the slower growing lambs reared in larger litters, were up to 80 days older when they produced their ®rst litters (Sutama et al., 1988). Similarly ewe lambs on high and low levels of nutrition, reaching puberty at similar body weights, were 221 days old on the high level, and 297 days on a low level (Sutama et al., 1988).
ITT ewes on a higher level of nutrition conceived about 60 days after lambing and those on a lower level about 14 days later (Sutama et al., 1988). Lambing
intervals were directly related to the postpartum body condition of the ewes (Sutama, 1992), and so were prolonged by about 9 days for ewes with previous larger litters (Sitorus et al., 1985a).
Low nutrition of lambs, and the draining effects on ewes bearing large litters, would increase generation intervals for carriers of the proli®cacy gene, with the main effect being on the time taken for ewe lambs to reach puberty. There would be minor, long term selection against carriers ofFecJF.
2.6. Husbandry procedures
The management procedures which can improve survival of ITT lambs are seldom recorded. At Ciawi, ewes were joined continuously with rams except for 2 weeks after parturition when ewes were in individual pens with their lambs. Dystocia cases were assisted, pregnancy toxaemia was treated and weak lambs were assisted to suckle (Obst et al., 1982). Nevertheless, there was a husbandry problem in that ¯ock because no quadruplets survived over a number of years, Table 7 (Obst et al., 1982; Chaniago et al., 1988). Ewes and
Table 7
Survival rates of individual ITT lambs to weaning related to proli®cacy genotypes of the ewes, and litter sizes, in the RIAP and Ciawi ¯ocks of ITT sheep during years with different levels of husbandry. A village ¯ock is included for comparison
Level of Lambs Survival rates (%) Location Reference
husbandry in litter
Genotype Litter size
FF F Single Twin Triplet Quadruplet
Instutional farms
Lean 41 58 74 81 55 30 21 Cicadas Inounu et al., 1993
Middling 59 75 89 91 78 52 35 Cicadas
Good 88 80 90 94 84 83 73 Bogor Inounu et al., 1993
Good One 90 93 93
Two 88 84 97 93 86 65a Bogor Subandriyo and
Inounu, 1994 Three and
above
71 60
High nutrition/mixed management
94 73 46 0 Ciawi Obst et al., 1982
Strategic supplementation/ unknown management
85 66 27 0 Ciawi Chaniago et al., 1988
Levels of supplementation/ good management
92 77 67 55 Sumatra Iniguez et al., 1991
Village
Unknown nutrition/ management
97 88 70 Village Inounu et al., 1993
lambs need space, time and quiet to promote mother-ing and bondmother-ing (Gatenby et al., 1994; Poindron et al., 1996). Most mature ITT ewes lambed within 30 min, and licked the newborn lamb. Lambs stood within 30 min and ewes encouraged them to suckle by nuz-zling the rump. There were no differences between lambs from single and multiple births (Sutama and Inounu, 1993; Gatenby et al., 1994). Assisting weak lambs to suckle, hand feeding and fostering can improve survival of weak lambs if suitable carers are available (Tiesnamurti, 1992a,b). Some village families supplement weak lambs with milk substitutes (Bell and Inounu, 1982), but fostering and hand rear-ing are rare on institutional farms. Self weanrear-ing of lambs from large litters at about 5 weeks probably occurs (Sutama et al., 1988), as it does in other proli®c breeds (Poindron et al., 1996). Again, the fre-quency ofFecJFis raised when lambs in larger litters survive.
Only a few rams are required for breeding and the remainder must be culled, so, if the best ram lambs are kept they will probably have been singles, and there will have been selection reducing the frequency of
FecJF. Weight was the main selection criterion for rams and ewes for the ¯ocks of village families (Bell and Inounu, 1982).
2.7. Frequencies of FecJFand distributions of litter sizes
The reported distributions of litter sizes in the RIAP ¯ock from 1981 to 1989 are relatively consistent, Table 2, probably because ¯uctuations in the level of husbandry were random at Cicadas, where there were lean years (1982, 1985, 1986, 1988) and mid-dling years (1981, 1983, 1984, 1987, 1989), (Bradford et al., 1991; Inounu et al., 1993). The frequency of
FecJF would be around that corresponding to the average level of husbandry over the period, being buffered as the maiden ewes from each lambing, entered a ¯ock containing older ewes reared under differing husbandry regimes. In 1990, the ¯ock was moved to Bogor and the husbandry was good from 1991 to 1993 (Inounu et al., 1993; Subandriyo and Inounu, 1994). Ewe weight gains during gestation, survival rates of individual lambs to weaning, and litter weaning weights, are presented as indicators of the respective levels of husbandry, Tables 6 and 7.
The distribution of litter sizes at birth in a ¯ock, re¯ects the distribution of proli®cacy genotypes of the ewes, as each genotype produces a distribution of litter sizes, Table 1. Empirically, each of the distributions of litter sizes in ¯ocks, Table 2, approximates the dis-tribution of litter sizes which would result from a Hardy Weinberg distribution of proli®cacy genotypes in the breeders, Table 8. The reason for this relation-ship will be discussed when survival rates of lambs in different litter sizes are considered below. The dis-tribution of litter sizes in the RIAP ¯ock during lean and middling husbandry periods (Inounu et al., 1993), Table 2, approximates that for a frequency of 0.35 for the proli®cacy gene, Table 8. At that frequency of the proli®cacy gene, the distribution of litter sizes for each genotype, Table 1, can be transposed to provide the distribution of proli®cacy genotypes for each litter size, Table 9. Application of those values to the observed distribution of litter sizes from Inounu et al. (1993), Table 2, gives the actual distribution of proli®cacy genotypes in the ewes asFecJFFecJF/12;
FecJFFecJ/44; FecJFecJ/44, compared with the Hardy Weinberg approximation of FecJFFecJF/12;
FecJFFecJ/46; FecJFecJ/42. The actual distribu-tion of genotypes in the ewes is then used to calculate the number of lambs of each genotype in each litter size, being the product of the frequency of the
proli-Table 8
Approximate frequency distributions of litter sizes, at different frequencies of the proli®cacy gene in ITT ewes, based on a Hardy Weinberg distribution of the gene as discussed in the text. The distributions of litter sizes reported by Inounu et al. (1993) for each proli®cacy genotype, have been used in the calculation
Frequency distributions (%) of litter sizes
Frequency ofF
Single Twin Triplet Quadruplet Quintuplet
®cacy genotype of the ewe, by the litter size, by the frequency of that litter size in the appropriate proli-®cacy genotype, Table 1 (Inounu et al., 1993). The sums of the values gives the distribution of proli®cacy genotypes in the progeny at birth asFecJFFecJF/18;
FecJFFecJ/50;FecJFecJ/32, and the frequency of
FecJF as 0.43. In all cases, it is assumed that the distribution of proli®cacy genotypes of rams is the same as that of ewes.
Survival rates from birth to weaning, Table 7, are a consequence of litter size, not of the proli®cacy gene carrier status of the dam per se, so litter size distribu-tions have been calculated for each genotype and the appropriate survival rate has been applied to each litter size at each of the levels of husbandry. The frequency of FecJF in the progeny at weaning in a lean year reduces to 0.35 with a genotype distribution FecJ F-FecJF/12; FecJFFecJ/46; FecJFecJ/42, and in a middling year to a frequency ofFecJFof 0.40 with a genotype distributionFecJFFecJF/15;FecJFFecJ/50;
FecJFecJ/35. So with the additional losses asso-ciated with carrier ewes and their progeny discussed above, the frequency ofFecJFwould be maintained in the ¯ock at a value of about 0.35. Clearly at these levels of husbandry, survival of lambs from birth to weaning is the major selection force countermanding the ampli®cation of theFecJFgene in carrier ewes. Consequently, in a ¯ock in which the frequency of
FecJF is at the equilibrium level for the prevailing level of husbandry, the effects on the frequency of
FecJFof ampl®cation of genotypes at conception, and of mortality rates of lambs in larger litters from birth to weaning, will be opposite, and approximately equal. So the distribution of litter sizes in the ewes will
approximate that for a Hardy Weinberg distribution of the genotypes of the ewes.
Application of the survival rates of lambs from birth to weaning for the ®rst of the good years in 1991 (Inounu et al., 1993), Table 7, yields a distribution of proli®cacy genotypes at weaning of FecJFFecJF/17;
FecJFFecJ/49; FecJFecJ/34, and a frequency of 0.42 forFecJF. Subandriyo and Inounu (1994) studied the ¯ock during the good years 1991±93. It is apparent from the improved growth and survival rates, Tables 6 and 7 that nutrition was much better then, but there is no information on management changes which might also have contributed. The frequency distribution of proli®cacy genotypes calculated above for the good year 1991, from the results of Inounu et al. (1993), can be applied to the observed litter size distribution in the ¯ock from 1991±93, Table 2, and the frequency dis-tributions of litter sizes for each genotype in the good years Subandriyo and Inounu (1994), Table 1, to calculate the distribution of genotypes in the progeny at birth. The values areFecJFFecJF/21; FecJFFecJ/ 56; FecJFecJ/23 giving a frequency of 0.49 for
FecJF. When the lamb survival rates from birth to weaning in those years are applied, Table 7 (Suban-driyo and Inounu, 1994), the distribution of genotypes in the weaners becomesFecJFFecJF/20;FecJFFecJ/ 54;FecJFecJ/26 and a frequency of 0.47 forFecJF. So if the higher level of husbandry is maintained, and there is no planned selection againstFecJF, it would be expected that the frequency in the RIAP ¯ock will continue to rise for some time.
2.8. ITT sheep in villages
Levels of nutrition and management vary between and within villages (Knipscheer and Soedjana, 1982; van Eye et al., 1984; Inounu et al., 1984; Tiesnamurti et al., 1984). Mason (1980) lists nine student surveys of litter sizes in villages in West Java. One result is unrealistic with 75% twins, and the others give mean
s.d. values of singles 6816, twins 2814, triplets 44 and 0.1 quintuplets. Two of the results could have indicated that theFecJFgene was not in the sample, and no village gave values as high as those on institu-tional farms. An estimate of the average frequency of
FecJF in the villages, from Table 8, would be 0.1, indicating a low level of husbandry. Nevertheless, there are villages where husbandry is good
(Tiesna-Table 9
Calculated frequency distributions (%) of each of the proli®cacy genotypes of ITT sheep in each litter size, on the basis of a frequency of 0.35 for the gene, as discussed in the text. Data transposed from Inounu et al. (1993)
Frequency distributions of genotypes (%)
murti et al., 1984), survival of lambs from birth to weaning can be better than on instutional farms, Table 7 (Inounu et al., 1993), and there is a high proportion of larger litters, Table 2 (Inounu et al., 1984; Suban-driyo, 1986). There are other factors which may in¯uence the results of village studies. Whereas record keeping can be reliable on institutional farms where a responsible person can check the animals daily, in villages, data may be collected intermittently by an outsider who can only obtain that information which can be recalled by those who are willing to cooperate. Moreover, culturally, villagers may provide informa-tion which they believe will please a guest, and village people may have different perceptions, such as farm-ers generally not counting lambs which die within 3 days of birth (Bell and Inounu, 1982).
3. Comparisons with other proli®c breeds
As described above, the frequency of the proli®cacy gene in ITT sheep is, in the main, an equilibrium between the amplifying effect of the higher ovulation rates of carrier ewes, balanced by lower survival rates of the smaller lambs from litters with multiple lambs. The equilibrium point is set by the level of husbandry in the ¯ock which affects survival rates of lambs, and perhaps litter sizes. A similar equilibrium might be expected when proli®cacy is controlled by many genes. In that case the frequencies of minor proli®cacy genes would be in equilibrium with the survival rates of lambs in larger litters, the equilibrium level being modulated by the level of husbandry.
Of the proli®cacy genes with large effect in sheep, none are known to be alleles, the Booroola gene is linked to markers from a region of the human chro-mosome 4q (Montgomery et al., 1993), the Inverdale gene of Romney sheep is on the X chromosome (Fahmy and Davis, 1996) and the locations of the Thoka gene of Icelandic sheep, the Olkuska gene and
FecJFof ITT sheep are not known. Ovulation rates are a more direct measure of the effects of a proli®cacy gene than are litter sizes, which are affected by embryo wastage, which varies between breeds, Table 4. Breeds and synthetics into which a major proli®cacy gene has been incorporated recently (Booroola, Cam-bridge and Belclare), tend to have wide ranges (1±14) of ovulation rates (Bindon et al., 1996), whereas those
proli®c breeds which have evolved in small ¯ocks in traditional societies, Romanov (Ricordeau et al., 1990), D'man (Lahlou-Kassi and Marie, 1985), ITT (Bradford et al., 1986) and Icelandic (Eythorsdottir et al., 1991), regardless of whether proli®cacy is the product of one or many genes, have compact ranges (1±7) of ovulation rates, which may have evolved with proli®cacy. Nevertheless, all of the proli®c breeds have litter size ranges from 1 to7, probably re¯ect-ing the common constraint of uterine ef®ciency (Meyer, 1985). Ovulation rates and litter sizes of different major proli®cacy genes are best compared when the frequencies of the genes are known, or like genotypes are available. Piper and Bindon (1996) have selected for the proli®cacy gene within their Booroola ¯ock until the vast majority are homozygous carriers. In the RIAP ¯ock of ITT sheep the ewes have been retrospectively separated into genotypes on the basis of their lifetime breeding records (Bradford et al., 1991; Inounu et al., 1993; Subandriyo and Inounu, 1994). The mean litter sizes of the homozygous carriers are comparable, Booroola 2.59 (Piper and Bindon, 1996) and ITT 2.83 (Bradford et al., 1991). However, there is a large difference between the corresponding ovulation rates, Booroola 5.65 and ITT 2.92, which re¯ects the means and variances of ovulation rates discussed above.
4. Other small ruminants on Java
5. Utility of ITT sheep
In a hot humid environment, ITT sheep are highly productive (Reese et al., 1990; Iniguez et al., 1991; Inounu et al., 1993). In a managed production pro-gram, it would be necessary to select the appropriate mix of proli®cacy genotypes to optimise production on the available feed (Bradford et al., 1991). Given the lability of the frequency ofFecJF, the equilibrium mix of genotypes will respond to the level of husbandry provided. If that mix is not that which is desired, then the frequency could be maintained at a different level by using rams of an appropriate carrier status. All breeds in which a major gene for proli®cacy is seg-regating have the problem of rearing the large litters produced by homozygous carrier ewes, and it unlikely that a solution can be found in any realistic intensive production system in a developing country. If a breed is required for production of meat in a semi-intensive system in the humid tropics, the ITT sheep offer adaptation to hot wet climates, proli®cacy, 1.8 lamb-ings per year and parasite resistance. Resistance of ITT sheep against gastrointestinal nematodes is com-parable with that of other resistant breeds (Romjali et al., 1997), but there are still situations where chemical control is bene®cial (Handayani and Gatenby, 1988). ITT sheep have very high resistance against Fasciola gigantica (Roberts et al., 1997a), possibly controlled by a major gene (Roberts et al., 1997b), which may be unique.
Acknowledgements
Opportunities to work for several years with Indonesian colleagues in livestock industries on
ADAB, CIDA and ACIAR projects are greatly appre-ciated.
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Distributions of litter sizes in institutional ¯ocks of Javanese fat tail sheep and Javanese goats
Breed/species Parity Frequency distributions of litter sizes (%) Mean Founding Reference
Single Twin Triplet Quadruplet litter size stock
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