USE OF HIGHLY PROLIFIC BREEDS AND CROSSBREEDING

S. Kukovics

INTRODUCTION

Ewe reproductive rates are not very high - under 100 percent - in most sheep breeding countries. The efficiency of the sheep industry together with the production of prime lamb needs to be improved. A great potential exists to increase sheep productivity and efficiency by increasing reproductive rate, largely through exploitation of genetic variation among breeds.

Profitability mainly depends on lamb production and various genetic and management methods exists to increase lamb output which depends on fertility, fecundity, lamb survival and number of lambings per lifetime.

To improve prime lamb yield per ewe per year the highly prolific breeds must be exploited. However, many researchers have shown (Watson and Elder, 1961;Purser and Young, 1964) that neonatal losses increase with incidence of twin lambs and with further increases in litter size losses may be even greater. Highly fertile and prolific sheep are presently available and the challenge is to exploit this potential commercially. Several management options are available for producers: annual lambing; different forms of frequent lambing; continuous lambing, etc.

Whatever system is chosen, the full potential of sheep will only be realized by good sheep managers who are able to:

-  meet the nutritional requirements of ewes bearing various litter sizes;

-  optimize conception rates, through ram and ewe management;

-  optimize lamb survival by management during pregnancy and lambing;

-  increase lamb output by increasing the frequency of Iambings; (Jelbart and Dawe, 1984).

The aim of this paper is to review highly prolific sheep breeds and their use in different crossbreeding programmes. Prolific sheep are characterized by high fertility and fecundity values. Both, but mainly the litter size, vary greatly between breeds, as well as with season, age and nutrition.

Some breeds, such as the Romanov, Finnish Landrace and Booroola Merino, have litter sizes well over 2.0, while the other merino breeds generally have litter sizes below 1.3.The most popular breeds used for prime lamb production, such as the Border Leicester and Dorset, have intermediate litter sizes. Breeds such as the Clun Forest and East Friesian also have high prolificacy and a litter size of around 2.0, mainly the latter breed, but this review will summarize the role of the Finn Landrace (together with the Swedish), Romanov and the Booroola Merino in different crossbreeding trials and programmes, because these breeds have the highest reproduction rate.

Research Centre of Animal Production and Nutrition, 2053 Herceghalom, Hungary.

PROLIFIC BREEDS

The Finnish Landrace

Finn sheep were the first to be discovered as a highly fertile breed and results were reviewed by Maijala and Oesterberg (1977). Average production traits of Finn sheep were summarized as:

Because of its production data Finn sheep are used from Europe to the USA and to New Zealand. Perhaps it is most popular in Europe, where it has its own particular role in sheep improvement trials in almost every country. Table 1 summarizes litter size data of Finn sheep and its crossbred progenies published by different authors. It can be seen that the Finnish Landrace, which has litter sizes of between 200–291 percent, increased the productivity of crossbred progeny of less fertile sheep.

In Czechoslovakia, in addition to the work on increasing prolificacy of Merinos, Czigaja, Improved Valashka and Improved Sumavka (Jakubecz, 1975; Jakubecz et al., 1978, 1979; Machacek and Jakubecz, 1981; Slana, 1981) wool production of crossbreds was also studied. No great difference was found in wool yields of Czigaja and Finn × Czigaja (2.98 and 2.76 kg greasy wool weight, respectively).

Several crossbreeding trials were carried out in the USSR using Finnish Landrace. Shatskii et al. (1978 a, b) and Musabaev (1983), reported very successful experiments on improving the lambing percentage of the breeds studied. Some other researchers have also studied meat production of crossbred progeny of Finn sheep (Table 2).As one can see, the data are quite different. Another conclusion that can be drawn from the results of using Finn sheep is that greasy wool weight decreased and the average fibre diameter increased when it was crossed with Caucasian Merino (Timashev, et al. 1976).

Nitter (1977) reported (from the Federal Republic of Germany) from his studies on the Würtenberg Merino and its crosses with Finn sheep, that the lambing rate, at the experimental and at the commercial flock levels, was 1.20 – 1.42and 0.83 – 1.33for purebreds; and 1.64 – 1.87and 1.30 – 2.12for crossbreds, respectively.

In the German Democratic Republic, Gutsch (1979) obtained 203 percent average litter size and 4.4lambs/ewe/year from crosses off the German Mutton Merino with East Friesian × Finn rams.

Visscher (1978) in the Netherlands crossed the Ile de France with Finn sheep and found that the Ile de France × Finn genotype gave fewer lambs reared than the Finn × He de France (2.21 and 2.54, respectively).

In Spain, Espejo Diaz et al. (1977) increased the body weight gain of Aragon sheep by crossing with Finn sheep. According to Latif (1980), Finn × Dorset ewes give the best maternal progeny for prime lamb production.

Crossing the Dala and Steiger breeds with Finnish Landrace in Norway, Steine (1980) found that ewes having 1/4 Finnish blood gave 0.18lambs more than the flock average; however their body weight and greasy wool weight was 0.10and 0.16kg less, respectively.

In their work on improving Irish Galway sheep Flanagan et al. (1979) produced new strains having 1/8 and 1/4 Finnish blood. O'Ferrall et al. (1975) carrying out cross-breeding trials with Galway, Border Leicester, Cheviot, Scottish Blackface and Finnish Landrace, concluded that the progenies of Finn sheep were samaller but they had the highest prolificacy.

In New Zealand, Meyer et al. (1978) crossed the Romney with Finn sheep to improve productivity.

More trials were carried out in the USA using Finn (F), Dorset (D) and Rambouillet (R) sheep. Thomas et al. (1975) studying the 1/4 F × 3/4 R, 1/4 F × 1/4D × 1/2 R and 1/4 F × 1/2 D × 1/4 R genotypes concluded that lambing percentage increased with decreasing R percentage, the lambing rate was higher by about 20 percent after mating in August than after May and June; greasy and clean wool weight declined with increasing D blood (4.6; 4.5; 3.9kg and 2.35; 2.25; 2.10kg, respectively). Examining 1/2 F × 1/2 R and 1/4 F × 3/4 R ewes Notter and Copenhaver (1980), found that ewes of 1/2 F blood bad 0.48 more lambs. Average litter size in January was 2.21, in April 2.46 and in September 1.84 and the differences were significant between them. Cochrain et al. (1984) established by studying 1/2 F × 1/2 D and 1/4 F × 3/4 D ewes that halfbreds gave 0.23 more lambs.

In Israel Amir et al.(1981) and Goot and Foote (1983) carried out experiments to improve the prolificacy of Awassi sheep. They managed to reach 1.45–2.14and 2.20 – 2.45 lambing percentage with Finnish Landrace x Awassi sheep, respectively.

The Swedish Landrace

Though this breed has somewhat less importance, its production values are quite close to those of Finn sheep. In 1956, the average litter size was 1.85 and in 1980 this number increased to 2.25. Weight of lamb (at the age of 120 days) per ewe increased by 25.7 kg between 1956 and 1980 (Brasch, 1981).There are two strains within the breed: Finn-Ull and Rya, the latter producing carpet wool. The Finn-Ull has a higher lambing percentage (2.61 versus 2.10) and weaning percentage (2.03 versus 1.57) but a lower birthweight (3.4versus 3.7kg) than the Rya strain (Nilsson, 1976). The Swedish Landrace (Finn-Ull type) is more important in Hungary than the Finn sheep because of its stronger body and ability to tolerate the drier weather.

Mihalka et al. (1982) carried out a repetitive crossbreeding experiment using Finn and Swedish sheep and Hungarian Merinos. Among the different crossbred genotypes the Merino female × Swedish male - F₁ proved the best under Hungarian conditions. This genotype is the maternal line of the so called J-AKI hybrid and the male line is the Suffolk breed. The lambing percentage per ewe per year in this genotype is 0.52 higher, and the litter size weaned about 0.37 higher than that of the Hungarian Merino (1.07and 0.93) though greasy wool weight is less by about 0.7kg/ewe (Table 3).

Because of the acclimatization problems of Finn sheep in Hungary another cross-breeding programme is going on at the Agricultural Combinat (Babolna) where the grand-parent population is a combination of Finn sheep and Romanov greater part) and Hungarian Merino (smaller part). These are crossed with Ile de France to produce the maternal line which is mated with Suffolk rams to give prime lambs for slaughter. Average litter size is around 1.8 – 2.0, birthweight between 2.2 – 3.0kg, and weaning percentage is 1.4 – 1.6.

The Romanov

This breed was discovered as a highly fertile sheep somewhat later than the Finn. However, Kovnerev (1969) reported that where nutrition and management were sufficient it could be bred every six months. In the USSR a great programme was built up on this breed with 15 units, with 5–5000 ewes in each and with 1.5 lambing per ewe year (V. Tosev, personal communication).

As can be seen in Tables 4 and 5 this breed has a litter size between 1.85–2.90 depending on place and nutrition as well as on other circumstances. Average birth weight is between 2.5and 3.0kg. Meat production capacity differs from place to place. From the data it appears that the use of this breed significantly increases the prolificacy of other breeds. In the USSR, Shatskii et al. (1976, 1978) stated in their experiments, that the use of the Romanov breed in crossings increases prolificacy and dressing percentage. Meat production of three crossbred was studied by Sallam (1978), Antonova (1979) and Erokhin et al.(1981) and they reported quite good results (Table 5).In the Trial of Timashev et al. (1976) the effect of using the Romanov breed gave less greasy wool weight and coarser wool when crossed with the Caucasian breed.

Czechoslovakian researchers (Jakubec 1975, Jakubec et al. 1978, 1979, Machacek and Jakubec, 1981) also improved the prolificacy of their breeds (Czigaja, Valashka and Sumava) but they reported some disadvantages regarding wool production.

In Spain many crossbreeding trials were carried out to improve the reproductive rate of local breeds. Sierra (1977, 1978, 1980) reported on several experiments. According to his data the Romanov × Aragon F₁ ewes produced 25–70 percent more lambs than pure Aragon sheep depending on the time of first matings. The litter size of F₁ ewes after autumn mating was 2.12, after the spring mating only 1.65, while the purebred Aragons had 1.39and 1.17, respectively. Sierra (1982) reported on a new Spanish synthetic sheep breed, which has 50 percent of blood from the Romanov and Aragon breeds. Its fertility is 86 percent and the litter size is 1.87and 2.13after the spring and autumn matings. Espejo et al. (1977, 1982) and Sierra (1983) gave reports on acceptable meat production data of Spanish Merino and Romanov crossbreds (Table 5).A hybrid programme is now operating in Spain, in which the first cross Aragon × Romanov ewes are mated with Ile de France rams to get first class lambs for slaughter (L. Lopez-Francos, personal communication).

In France the Romanov breed has been given great attention during the last ten years. According to the data of Ricordeau et al. (1976) the purebred Romanov produced 2.88 lambs per ewe and the best combination, Romanov × Cher Berrichon, had a litter size of 2.05 (Cotentin, Border Leicester, Cher Berrichon and Romanov were used in the trial. Ricordeau et al.(1977) reported that the C. Berrichon × Romanov F₁ and F₂ ewes had a 0.66 higher litter size than that of the purebred C. Berrichon ewes. The lambing rate of C. Berrichon × Romanov, 1/2 C. Berrichon × 1/4 Cotentin × T/4 Romanov and 1/2 C. Berrichon × 1/4 Border L. × 1/4 Romanov ewes exceeded that of purebred C. Berrichon ewes by 0.57, 0.30 and 0.36, respectively (Tchamitchian and Ricordeau, 1976).

The conception rates of F₁, F₂, F₃, and F₄, C. Berrichon × Romanov crossbreds were 86, 82, 97 and 99 percent respectively while the corresponding lambing rates were 1.67, 1.87, 1.98and 2.01, (Ricordear et al., 1982). The INRA 401 maternal line was produced from crossing the Romanov and the Cher Berrichon, work which was done by Tchamitchian et al. (1979) for INRA's crossbreeding programmes. In a comparison of Limousin and Limousin × Romanov F₁ ewes Marzin et al. (1979) found that litter size was 1.63and 2.25, birthweight 3.56 and 3.40 kg and mortality was 10.4and 12.8percent in the two genotypes, respectively. Though ewes lambed three times within two years, the lambs born per ewe per year were 2.15and 3.06 and weaning rate per ewe per year 1.92and 2.66, respectively.

In South Africa Faure et al. (1983) tried to improve the prolificacy of Karakul sheep. They produced crossbred sheep having 25, 50 and 75 percent Romanov blood and the litter size of these genotypes was 1.17, 1.74and 1.74respectively. The first genotype did not differ significantly from purebred Karakul.

In Hungary a programme led by Prof. Veress developed a so called “Fertile Merino” by crossing the Romanov breed with the Hungarian Merino. The aim of this programme was to produce a genotype of 1/4 Romanov × 3/4 Merino. This sheep population produced Merino-type wool with a 20 percent longer staple than the original Merino without any coloured fibres. These ewes had 20–30 percent more lambings per year (1.3 – 1.4) and 20–30 percent higher litter size (1.50–1.60) than the Merinos. In frequent lambings the ewes of this genotype give two or more lambs per ewe per year (Tables 6 and 7).In fattening the male lambs of the “Fertile Merino” breed daily growth rate was 294–307 g compared with 207–227 g in the females. That of the control Merinos was between 264–281 g and 194–200:g for the sexes, respectively. Wool production data of this breed are as follows: staple length 9–11 cm, greasy wool weight 4.8 – 5.2kg, yield 49 percent, fibre diameter 23–24 microns (only the greasy wool weight data are less favourable than those of the Merino). (Veress and Lovas, 1978; Veress, 1982).

The Booroola Merino

This is the most recently discovered fertile breed, which may have better prospects than the others. It has Merino wool and high prolificacy, having oestrus any time of the year as well as high fertility and fecundity and this quality is determined by only one major gene - “F” so called fertility gene (Davis et al., 1982). This breed was developed in Australia and nowadays is also bred in New Zealand. During the last few years many countries in South America and Europe have tried to obtain this valuable breed. Production data of the Booroola Merino and its crossbreds is summarised in Table 8. These reports have come from Australia and New Zealand.

In the experiment of Piper et al. (1979), studying Collinsville Merino, Medium non-Peppin Merino ewes and their crossbreds with Booroola, it was found that lambing rate was significantly higher but survival rate and clean wool weight was lower in the crossbreds.

In producing halfbred Booroola and 1/4 Booroola genotypes, using Collinsville and Muray Merino ewes, Beetson (1982) reported that the halfbreds gave 58 percent more lambs and weaned 33 percent more progenies than the control ewes.

Allison et al.(1982) carrying out crossbreeding experiments with Booroola × Merino and Booroola × N.Z. Romney accompanied by purebred controls found that crossbred ewes had an ovulation rate of 1.95–2.50, which was higher by 0.72 – 0.94 than that of purebreds. Lambing rate was 0.43 – 0.73 higher in the crossbreds.

Piper and Bindon (1982) found a litter size of 2.30 in Booroola ewes compared with 1.30for control Merino. The survival rate was higher in the control up to weaning. They established that the high prolificacy of Booroola ewes could result from the action of only one major gene or numerous very closely-linked minor genes. Robertson (1982) reported on a new strain of the Booroola breed which had a some-what lower litter size and weaning rate.

CH'ang et al. (1982) stated that Booroola Merinos had a 70 percent higher ovulation rate and 50 percent bigger litter sizes than Merinos as well as a 25 percent higher lambing rate than that of N.Z. Romney ewes.

The Hyfer synthetic breed was developed in Australia (Hall et al., 1982) using Booroola × Dorset and Booroola × Dorset × Trangie Fertility Merino genotypes. Ovulation rates of adult ewes were between 2.11 – 2.80 in different lines. Due to segregation at the F-gene locus Booroola crosses can fall into one of three groups: Homozygous (FF) and heterozygous (F+) carriers as well as non-carrier (++) (Davis et al., 1984; Kelly et al., 1984, Owens et al., 1984; Owens, 1984). They found in their experiments that the “FF” genotypes had 0.8 – 1.02and the “F+” genotypes 0.4 – 0.6higher ovulation rates and weaning percentage than the non-carriers. Also, the non-carriers had 0.2 – 0.4kg more greasy wool weight and 3.0 – 5.0kg higher body weight than the “F+” and “FF” genotypes, respectively.

Some preliminary results of slaughtered Booroola crossbreds were published by Geenty (1981, 1982).

In Hungary two crossbreeding programmes are presently going on based on the Booroola breed. The most recent is connected with the Oviscoop Sheep Production System in which Booroola rams are mated with Hungarian Merino ewes selected for a high twinning rate and the F₁ female progenies will be crossed with the rams of USA Suffolk or German Blackheaded mutton breeds. The older programme is led by Prof. Veress, who started crossing Hungarian Merino ewes of several cooperative farms with Booroola rams in 1980. According to his results the crossbred progenies of Booroola rams have 6–10 percent smaller body weight than Merinos (2–4 kg). Their greasy wool weight was less by 0.2 – 1.2kg, though the staple length was 1.0–2.0cm longer.

Unfortunately, the Booroola crossbred progenies have not produced the prolificacy results expected from the literature. After the first two lambings of 400 first cross ewes the fertility rates were found to be between 62–92 and lambing percentage 100–150 percent. After checking the origin of the Booroola rams the results can be explained; there was only one purebred and 6 Booroola (75 percent) crossbred rams in the programme, and four of them were non-carriers (++).

In fact the use of the Booroola breed in crossbreeding could lead to a completely new situation: due to the “F” gene one may not speak of 1/4, 1/2 or 3/4 (or more) Booroola blood in crossbred progenies, but only of homozygous (FF) and heterozygous (F+) carriers as well as non-carriers (++).

CONCLUSION

In summary, collecting experiences from crossbreeding experiments using highly fertile sheep breeds, one can conclude that it is not too difficult to obtain higher prolificacy in first cross progeny. A major problem still remains: how to rear these extra lambs.

In the use of high fecundity breeds to improve the number of lambs reared per ewe per year, the chances of survival to weaning will be increased if birthweight can be controlled through efficient management and satisfactory nutrition. To achieve this and to reduce lamb losses, intensive lambing systems are necessary.

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TABLE 1. Litter size of Finnish Landrace and its crossbreds

TABLE 2. Meat production traits of sheep crossed with Finnish Landrace according to USSR authors

TABLE 3. Lifetime production of Hungarian Merino and J-AKI hybrid ewes (Mihalka et al., 1982)

TABLE 4. Litter size of Romanov and its crossbreds

TABLE 5. Some meat production data of the Romanov and its crossbreds

TABLE 6. Productivity of Merino × Romanov F₁ ewes on different farms in Hungary ⁺

⁺ Based on Veress and Lavas (1978) and Veress (1980, 1982).

TABLE 7. Production data of Merino and Fertile Merino ewes in their first two Iambings ⁺

⁺ (Veress, personal communication, 1985)

TABLE 8. Prolificacy of the Booroola Merino and its crossbreds