Productivity of crosses based on prolific breeds of sheep

Productivity of crosses based on prolific breeds of sheep

379 Livestock Production Science, 4 (1977)379--392 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands PRODUCTIVITY OF...

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379

Livestock Production Science, 4 (1977)379--392 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

PRODUCTIVITY OF CROSSES BASED ON PROLIFIC BREEDS OF SHEEP S u m m a r y o f r e p o r t s p r e s e n t e d at t h e E.A.A.P. S t u d y M e e t i n g in Ziirich, 1 9 7 6

V/kCLAV JAKUBEC Research Institute for Animal Production, Prague-Uh~n~ves (Czechoslovakia)

(Received 19 April 1977)

ABSTRACT Jakubec, V., 1977. Productivity of crosses based on prolific breeds of sheep (Summarizing report). Livest. Prod. Sci., 4: 379--392. The results of main and short papers on the productivity of crosses between domestic and prolific breeds presented in Ziirich in 1976 have been summarized according to the important reproduction and production traits. Fertility, prolificacy, mortality rate, litter size born and weaned, ovulation rate, accelerated and out-of-season lambing, milk production, growth and carcass traits were analysed. More attention has been paid to the reproduction traits, because of their importance in crossbreeding with prolific breeds. For all analysed traits the amount of heterosis has been estimated from various information sources: midparent value, F1, F2, B1 (backcrosses), one of the parent breeds. The use of prolific breeds mostly leads to an improvement in the reproductive characters. The breed differences are decisive for all traits. The reproduction traits generally show higher heterosis effects than the production traits, but this statement cannot be held as a rule. For international comparisons in future the traits must be standardized.

INTRODUCTION In the j o i n t session o f the C o m m i s s i o n o n A n i m a l Genetics and the C o m m i s s i o n o n S h e e p and G o a t P r o d u c t i o n held d u r i n g the 2 7 t h A n n u a l Meeting o f the E u r o p e a n A s s o c i a t i o n for A n i m a l P r o d u c t i o n in Z f r i c h , 1976, f o u r m a i n papers and 24 s h o r t papers were presented. In view o f the great i n t e r n a t i o n a l interest in the s u b j e c t it was c o n s i d e r e d desirable t o publish the o v e r w h e l m i n g n u m b e r o f c o n t r i b u t i o n s in s o m e general reviews. T w o such reviews a p p e a r elsewhere in " L i v e s t o c k P r o d u c t i o n S c i e n c e " , viz. t h a t on. F i n n s h e e p b y Maijala and O s t e r b e r g {1977, this issue) p r e s e n t e d in Ziirich a n d s u p p l e m e n t e d with material f r o m relevant s h o r t papers, and t h a t b y R i c o r d e a u et al. ( 1 9 7 8 , in press) w h i c h c o n s t i t u t e s a review in itself, giving f o r the first t i m e a full a c c o u n t o f the F r e n c h I . N . R . A . results since 1 9 6 3 ( a l m o s t exclusively o n R o m a n o v ) . This p r e s e n t review integrates relevant results

380 presented in main and short papers in Ziirich on the productivity of crosses between domestic and prolific breeds in various countries. For completeness some French results must also be included in the review, even though they are an integral part of the paper by Ricordeau et al. (1976). The results obtained by various authors in different countries on the same or similar prolific breeds used for crossing with native breeds are summarized according to the main reproduction and production traits. The reproduction traits which have been analysed are fertility, prolificacy, mortality rate, and litter size weaned. The production traits are connected with quantitative and qualitative aspects of meat production and are: birth weight, weaning weight, daily gain, carcass weight, percentage of muscle, fat and bones, gigots, shoulder, carcass length, and length of legs. I am aware t h a t the results are never completely comparable since they have been obtained in different environments. The traits are influenced by the type of crossing, i.e. the proportion of the breeds used, the age of ewes, m e t h o d of lamb rearing (artificial, natural), frequency of lambing per year, etc. The results are therefore grouped according to the main factors. One of the most important hybridization parameters is heterosis. Only a few papers give us reliable information for estimating the a m o u n t of heterosis. We rarely find reciprocal crosses of the parent breeds. We can assume the equality of reciprocal parent crosses as a rule. The heterosis has been mainly estimated as the difference between the mid-parent value and the performance of the F~, and in a few cases as twice the difference between the F~ and F: or from other sources of information, e.g. on the basis of the F~, B~ backcross and one of the parent populations. REPRODUCTION TRAITS

Fertility (conception rate) This trait is expressed by the percentage of ewes lambing, which is given by the number of ewes lambed on 100 ewes mated (Table I). Only a few investigations permit us to estimate the heterosis effect. The French (Ricordeau et al., 1976) and Lebanese (Fox et al., 1976) results show heterosis in the conception rate from 0 to 5%. The other experiments do n o t allow the evaluation of heterosis. The conception rate in the crossbred ewe lambs in all cases was much higher than in the indigenous breeds. The difference in favour of the crossbreds was from 16 to 50.3%. As a rule, we can accept that the fertility of adult ewes is higher than t h a t of the ewe lambs. Crossbreds with various proportions of the Berrichon, Border Leicester, Cotentin and Romanov were compared in French trials (Ricordeau et al., 1976). The crossbreds with 50% Romanov had the highest fertility, followed by crossbreds with 25% Romanov. The lowest fertility was in combinations w i t h o u t Romanov. In Czechoslovak experiments (Jakubec et al., 1976) crossbreds between the M u t t o n Merino (MM) and East Friesian Milksheep or Finnsheep (F) had a lower fertility in the ewe lambs and a slightly higher fertility

381 in the adult ewes than the crossbreds with Romanovs (R). In crosses of Finn X Dorset Horn rams on indigenous dam breeds in the United Kingdom (Robinson et al., 1976) the fertility of their progeny was negligibly higher than in the progeny from matings between indigenous dam breeds and sire breeds. Spanish authors (Vails Ortiz et al., 1976) found the percentage of ovulation in ewe lambs at an age of 7--12 m o n t h s to be 100% in crossbreds Rasa Aragonesa (RA) X Romanov, 58% in Rasa Aragonesa X Finnsheep and 61% in Rasa Aragonesa. The percentage of ewe lambs in heat (first oestrus) was much lower in all cases than the percentage of first ovulation (RA X R -- 86%, RA X F -- 25%, RA -- 31%). There is a good correlation between the two traits. The conception rates at induced heat were not significantly affected by PMSG treatment (500 I.U.) (Robinson et al., 1976). We can conclude that using prolific breeds (Finnsheep, Romanov, East Friesian Milksheep) generally leads to an increase in the conception rate in the crossbreds.

Prolificacy The prolificacy is mostly expressed as lambs born (alive, dead and alive) or weaned per ewe joined (exposed to the ram at mating) or per ewe lambing. The data presented are often n o t directly comparable. Sometimes the lambs had been naturally reared and suckled by their mothers. In other investigations accelerated lambing programmes had been carried out.

Litter size born From Table II the superiority of the crossbred ewes with prolific breeds over the indigenous breeds is evident in ewe lambs and adult ewes. In crossbreds the litter size born is a result firstly of the difference between the native and prolific breeds and secondly of the heterosis. Heterosis ranges from very low values o f - - 9 to 0% (Hanrahan, 1976; Hanrahan and Quirke, 1976; Jakubec et al., 1976; Kallweit, 1976; Ricordeau et al., 1976), through low and medium values of 1.08--12.53% (Fox et al., 1976; Goot et al., 1976; Hartmann and Wassmuth, 1976; Kallweit, 1976; Ricordeau et al., 1976) to a high value 30.96% (Nitter, 1976). From different sources of information we can reach different results as is shown in the papers of Fox et al. (1976) and Hartmann and Wassmuth (1976). In some studies no differences in heterosis have been found in the adult ewes and ewe lambs (Goot et al., 1976; Jakubec et al., 1976). Crossbreds with Finn and Romanov show a higher lambing frequency per ewe and year than the local breeds (Nitter, 1975, 1976; Theriez et al., 1976) and are therefore suitable for accelerated lambing programmes.

Mortality rate The mortality rate is influenced by important non-genetic factors. It depends on the litter size, birth weight of lambs, milk production of the ewes, interval

F, 1]2MM, 1/2F F 2 1]2MM, 1/2F F~ 1/2A, 1/2F F~ 1/2A, 1/2CH 1/2(NC,SC,WM,SB,RS,SN ), 1/4BL, l [4F 1 ]2(NC,SC,WM,SB,RS,SN ), 1]2BL 1/2 (NC,SC,WM,SB,RS,SN), 1/4BL, 1/4F 1/ 2(NC,SC,WM,SB,RS,SN ), 1/2 (BL,CB,TW,BU,NC,S) F~ 1]2DH, 1/2F a F~ 1]2DH, 1/2F b F~ I[2DH, 1/2F c

Israel (Goot et al., 1976)

Lebanon (Fox et al., 1976)

Great Britain (Deeble and Barker, 1976)

{Robinson et al., 1976)

f

F~ 1/2HR, 1/2EF FI 1/2HR, 1/2F F~ 1/2HR, 1/2R

Hungary (Veress et al., 1976)

89.00 61.50

* The dam lines are in the first and the sire lines in the second position. a Once per year lambing. b Frequent breeding under artificial daylength conditions. c Frequent breeding under natural daylength conditions.

88.00 96.50 92.80

90.85

72.20

93.00 81.60

90.50

100.00

96.20

6O.00

90.00 90.00 86.00

91.00 91.00 87.10 87.10 87.10 87.10

77.47 77.47 77.47

Indigenous

95.00 94.00 75.00

91.60

64.00 64.00 33.00

86.20 96.80 87.00 99.00 98.00 95.30 83.10 89.20 93.70

72.60

81.00 80.00 81.00

76.00

33.80 84.10 56.50

F~ 1/2B, 1/2BL F~ 1/2B, 1/2R F~ 1/2B, 1/2CO F~ 1/2B, 1/2R F: 1/2B, 1/2R F~ 1/2B, 1/2R 1/2B, 1]4BL, 1/4CO 1/2B, 1/4BL, 1/4R 1/2B, 1[4CO, 1/4R

France (Ricordeau et al., 1976)

84.74 82.56 77.14

66.67 62.96 78.95

F~ 1/2MM, 1/2EF F~ 1/2MM, 1/2F F~ 1/2MM, 1/2R

Czechoslovakia (Jakubec et al., 1976)

40.00 40.00 40.00

Crossbred

Prolific

Crossbred Indigenous

Adult ewes

Ewe lambs

Type of crossbred*

Country and reference

Fertility

TABLE I

93.30

97.00 97.00

Prolific

00 t~

383

from birth to weaning, nutrition of ewes before lambing and during suckling, kind of lamb rearing (artificial or natural), diseases of ewes and lambs, etc. All these factors confuse the genetic basis of the character and the mortality rates differ from trial to trial. The mortality rates (Table III) are therefore in a range from 4% (Jakubec et al., 1976) to 52% (Veress et al., 1976). The heterosis lies between --111.04% (Kallweit, 1976) to 41.60% (Ricordeau et al., 1976). Litter size weaned

The litter size weaned is determined b y the litter size of lambs born alive and their mortality. Many non-genetic factors influence this trait in the same manner as the mortality. The litter size of lambs born is therefore the most important figure for the estimation of the genetic mechanism of prolificacy. The heterosis is within the range from --23.47% to 12.05% (Kallweit, 1976). Despite the higher losses in the ewes with a higher litter size, the crossbreds with prolific breeds have a higher litter size weaned than the native breeds. The relationship b e t w e e n the haemoglobin and potassium t y p e and litter size weaned in crossbreds b e t w e e n Finn rams and German Blackheaded Muttonsheep (GBM) has been analysed (Hartmann and Wassmuth, 1976). The gene frequency of H b A increased from 8.3% in GBM to 77.5% in crossbreds (F × GMB) F and the K h c o n t e n t from 20.4% to 78.7%, respectively. The results show a tendency towards a lower rearing capability in the H b A A ewes and a better development of the K' lambs.

B r e e d abbreviations used in the tables

Awassi Berrichon Bleu du Maine Bluefaced Leicester Border Leicester Cheviot Chios Colbred Cotentin Dorset Horn East Friesian Milksheep Fingalway Finnsheep Galway German Blackheaded Muttonsheep Hungarian Rambouillet Ile de France

A B BM BU BL C CH CB CO DH EF FG F G GB HR IF

Lacaune Leicester Limousine Local breed Merinoland Mutton Merino North Country Cheviot Radnor Swaledale Rasa Aragonesa R o m an o v Scottish Blackface Sennybridge Cheviot South Country Cheviot Suffolk Teeswater Texel Welsh Mountain

LA L LI LO ML MM NC RS RA R SB SN SC S TW T WM

F~ I/2B, I/2BL F~ I/2B, I/2R F I I/2B, I/2CO FI I/2B, I/2R F, 1/2R, 1/2B F, 1/2B, 1/2R F 2 1/2B, 1/2R F~ 1/2B, 1/2R 1/2B, 1/4BL, 1/4CO 1/2B, 1/4BL, 1/4R 1/2B, 1/4CO, 1/4R 1/2IF, 1/2R F~ 1/2LI, 1/2R F, 1/2GB, 1/2F F 2 1/2GB, 1/2F B~ 3/4GB, 1/4F B~ 1/4GB, 3/4F 1/2GB, 1/4F, 1/4EF 1/4GB, 3/8F, 3/8EF

F, F, F, F, F, F, F, 1/2ML, 1/2F B, 1/4ML, 3/4F

France (Ricordeau et al., 1976)

Germany (Hartmann and

(Kallweit, 1976)

(Nitter, 1976)

1976)

Wassmuth,

I/2GB, I/2T I/2T, I/2GB 1/2GB, I/2F I/2F, 1/2GB 1/2T, 1/2F 1/2F, 1/2T

F~ 1]2MM, 1/2EF F, 1/2MM, 1/2F F1 1]2MM, 1/2R

Czechoslovakia (Jakubec et al., 1976)

(Theriez et al., 1976)

Type of crossbred*

Country and reference

Prolificacy (litter size)

TABLE II

1.67 1.64 1.60 1.79 1.53 1.69

1.28 1.46 1.57

1.33 1.33 1.33 1.33 1.33 1.33

1.08 1.08 1.08 1.92 2.08

1.84 1.71

1.23 1.23

1.56 1.56 1.56 1.56 1.44 1.44

1.25 1.51 2.12 2.12 2.03 2.10

1.41

2.21

1.41

1.27 1.27 1.22 1.22 1.26 1.26 1.26 1.26 1.24 1.63

1.48 2.06 1.37 1.91 1.84 1.90 1.91 1.83 1.27 1.62 1.56 1.12 2.17

1.90

1.34 1.34 1.34

1.54 1.73 1.83

Crossbred Indigenous

Prolific

Crossbred

Indigenous

Adult ewes

Ewe lambs

1.44 1.44 2.38 2.38 2.38 2.38

2.41 2.41 2.62 2.62

2.18 2.33

Prolific

Qo

F~ 1/2G, l / 2 F

F~ I/2MM, 1/2F F 2 1/2MM, 1/2F F~ 1/2A, 1/2F F, 1/2A, 1/2CH F~ 1/2A, 1/2CH F 2 1/2A, 1/2CH 1/2(NC,SC,WM,SB,RS,SN), 1]4BL, 1/4F 1/2(NC,SC,WM,SB,RS,SN), I/2BL 1/2(NC,SC,WM,SB,RS,SN), 1/4BL,1/4F 1/2(NC,SC,WM,SB,RS,SN ), I/2(BL,CB,TW,BU,NC,S) F~ I/2DH, l / 2 F b F~ I/2DH, 1/2F c F~ I/2DH, l / 2 F d F~ I/2BL, 1/2C F~ 1/2SB, 1/2F F~ I/2SB, I / 2 E F

Ireland (Hanrahan, 1976; Hanrahan and Quirke, 1976}

Israel (Goot et al., 1976)

Lebanon (Fox et al., 1976)

Great Britain (Deeble and Barker, 1976)

(Robinson et al., 1976)

(Tempest et al., 1976)

1.65

0.72

2.08 2.38 2.06

2.22 2.28 2.56

1.83

0.94

1.61 1.64

1.68

1.03 0.91 0.91

1.42 1.19 1.07

0.70

1.00 1.00 0.90

1.40

1.42 1.42 1.42 1.20 1.20

1.70 1.60 1.30

1.85

0.80 0.80 0.30

2.00

1.87 1.62 1.56 1.64 1.39

0.95

1.20 1.10 1.00

1.77

* The dam lines are in the first and the sire lines in the second position. a Accelerated lambing programme with artificial lamb rearing. b Once per year lambin$ c Frequent breeding under artificial daylength conditions. d Frequent breeding under natural daylength conditions.

F~ I/2HR, I / 2 E F F~ 1/2HR, 1/2F F~ 1/2HR, 1/2R

1/2F 1/2BM 1/2T 1/2F a 1/2BM a

Hungary (Veress et al., 1976)

I/2ML, 1/2ML, 1/2ML, 1/2ML, 1/2ML,

F, F~ F~ F, F~

(Nit~r, 1975)

1.77

2.50

e~ (3O cj~

F 1 1/2MM, 1/2EF F 1 1/2MM, 1/2F F 1 1/2MM, 1/2R

F l 1/2B, F l 1/2B, F l 1/2B, F, 1/2B, F 2 1/2B,

F~ I/2LI, I/2R

F, 1/2GB, 1/2F 1/2GB, 1/4F, 1/4EF

F, 1/2GB, 1/2T F~ 1/2T, 1/2GB F, 1/2GB, 1/2F F 1 1/2F, 1/2GB F 1 1/2T, 1/2F F 1 1/2F, 1/2T

F, 1/2ML, I / 2 F BI I/4ML, 3 / 4 F

Czechoslovakia (Jakubec et al., 1976)

France (Ricordeau et al.,1976)

(Theriez et al., 1976)

Germany (Hartmann and Wassmuth, 1976)

(Kallweit, 1976)

(Nitter, 1976)

1/2BL 1/2R 1/2CO 1/2R 1/2R

Type of crossbred*

Country and reference

Mortality rates

TABLE III

29.35 26.32

31.20 25.17 37.74 25.00 15.76 17.62

35.99 21.82

8.80

17.50 13.40 16.70 7.30 8.90

17.24 20.78 18.75

Crossbred

Prolific

Crossbred

Indigenous

Adult ewes

Ewe lambs

18.70 18.70

12.82 12.82 12.82 12.82 13.89 13.89

22.70 22.70

9.00

15.80 15.80

23.00 23.00 23.00

Indigenous

13.89 13.89 24.11 23.11 23.11 23.11

9.70 9.70

Prolific

Oo O~

1/2(NC,SC,WM,SB,RS,SN), 1/4BL, 1/4F 1/2(NC,SC,WM,SB,RS,SN), 1/2BL 1/2 (NC,SC,WM,SB,RS,SN), 1/4BL, 1/4F 1/2(NC,SC,WM,SB,RS,SN), 1/2 (BL,CB,TW,BU,NC,S)

F~ 1/2DH, 1/2F b

F 1 1/2BL, 1/2C F 1 1/2SB, 1/2F F 1 1/2SB, 1/2EF

Great Britain (Deeble and Barker, 1976)

(Robinson et al., 1976)

(Tempest et al., 1976)

22.88 18.41 19.25

27.27 23.92 23.68

11.50 21.00 13.10

8.03

21.06

10.57 21.54

52.00

33.69 28.40 28.21 7.32 12.23

24.72

* The dam lines are in the first and the sire lines in the second position. a Accelerated lambing programme with artificial lamb rearing. b Frequent breeding under natural daylength conditions.

F 1 1/2LO, 1/2CH F 1 1/2A, 1/2CH

Lebanon (Fox et al., 1976)

1

F~ 1/2HR, 1/2EF F~ 1/2HR, 1/2F F 1 1/2HR, 1/2R

Hungary (Veress et al., 1976}

1/2F 1/2BM 1/2T 1/2F a 1/2BM a

F 1 1/2ML, F~ 1/2ML, F1 1/2ML, F 1 1/2ML, F l 1/2ML,

(Nit~r, 1975)

3.60 16.19

31.69 31.69 31.69 8.33 8.33

18.00 18.00

03 {30 .-..]

388 Ovulation rate Analyses of among breed variation with respect to litter size have indicated that ovulation rate accounts for m o s t of the differences in litter size. This conclusion has been supported b y egg-transfer studies in which two or more fertilized eggs were transferred to various recipient breeds, and b y successful selection for litter size which led to an increase in ovulation rate. It is therefore logical to select for increased ovulation rate in order to increase litter size. It has been suggested (Ricordeau et al., 1976) that the additive gene action for the ovulation rate is responsible. The results are not discussed here in detail since an English version of this paper (Ricordeau et al., 1978) will appear elsewhere in "Livestock Production Science". The e m b r y o mortality is lower in the FI than in the parental breeds when the basis of calculation is the ewes exposed for mating. This indicates the existence of heterosis, even though no differences have been found b e t w e e n the F1 and F2. A comparison of F1 (Galway X Finnsheep) and the mid-parent values (Hanrahan, 1976) showed that there was no heterosis for litter size b u t significant negative heterosis for ovulation rate. The repeatability of ovulation rate was high in breeds with a high litter size and low in breeds with a small litter si~e. The heritability of ovulation rate was much lower than the repeat~ ability, b u t they are parallel, and suggest the existence of considerable additive genetic variation for ovulation rate. The repeatability estimates for litter size are substantially lower than for ovulation rate. Egg-transfer studies with Galway have shown that this breed does n o t differ from the Finn-sheep in ability to gestate two or three fertilized eggs (Hanrahan and Quirke, 1976). Breed differences in litter size are n o t associated with differences in uterine capacity. The number of eggs transferred is the only significant source of litter size. Spanish authors (Vails Ortiz et al., 1976) found an ovulation rate of 1.06 in the Rasa Aragonesa. The crossbreds Rasa Aragonesa X Romanov had a higher ovulation rate (1.73) than Rasa Aragonesa X Finnsheep (1.60). Accelerated and out-of-season lambing From all the papers presented it is evident that the crossbreds of indigenous breeds with prolific breeds have a better out, of-season sexual activity than the local breeds. These crossbreds have a higher prolificacy when they are synchronised with induced heat. An accelerated lambing system is used in the exploitation of prolific breeds for purebreeding or for crossing with native breeds (Jakubec et al., 1976; Nitter, 1975, 1976; Ricordeau et al., 1976; Robinson et al., 1976). Robinson et al. (1976) subjected Finn X Dorset Horn ewes to frequent breeding under artificial and natural daylength conditions and they found that the ewes would breed under natural daylength conditions if the artificial daylength regime was replaced by 400 I.U. PMSG at progestagen withdrawal. The German results (Nitter, 1975, 1976) showed a significant economic superiority of Merinoland X Finnsheep crossbred ewes if an accelerated lambing programme and early weaning techniques are applied.

389

Milk production There are two aspects of milk production. On the one hand milk is a source of cheese production and on the other hand it is a trait of mothering ability. Both aspects are important for France, Mediterranean countries and some eastern European countries, and the latter aspect is important for fat lamb producing countries. The milk production can also be measured indirect. iy by the growth rate of lambs during the early stages of life when they are primarily suckled by the ewes. The estimation of milk production using lamb growth is possible when all ewes are mated to the same sire breed, b u t only if specific combining ability is assumed absent. Very extensive investigations on milk production in sheep have been done in France (Ricordeau et al., 1976). The estimates of heterosis are very uncertain over a wide range. On the basis of the comparison of the F~ and F2 crosses of Berrichon × R o m a n o v (Ricordeau et al., 1976), the heterosis in the daffy gains of lambs remains within 3.65% (10--30 days) and 42.50% (0--42 days). The directly measured milk production for 0--42 days shows a heterosis of 5.63%. A very high heterosis in milk production during the first 100 days after weaning, a b o u t 50%, was found (Fox et al., 1976) in crossbreds between the Chios breed and a local breed or the Awassi breed. A very low heterosis (3.88%) was found in crossbreds between Merinoland and Finnsheep (Nitter, 1976). We can conclude that the heterosis generally fluctuates within a wide range from 3.65% to 50.67%. In Ireland (Hanrahan and Quirke, 1976) the Finnsheep had a significantly lower milk production than the native Galway breed or the Fingalway sheep. The production per unit metabolic size of the Finnsheep equals that of the Galway breed. The milk production has been estimated on the basis of growth rate from birth to 8 weeks. GROWTH

AND CARCASS TRAITS

The growth and carcass traits are determined by various measurements. The most important are the birth weight, weaning or slaughter weight, the daily gain from birth to weaning or slaughter, litter weight, feed efficiency, carcass weight, percentage of muscle, fat, bones, gigots, shoulder, carcass length, length of legs, ring value, index G/F, etc. The comparison o f the results of the presented papers is very difficult. Besides various breeds and comparisons under different environmental conditions, the growth and carcass traits have n o t been standardized in Europe. The weights of lambs have been determined during various stages of their life and the intervals for testing the growth rate differed greatly, i.e. from 40 days to 6 months. The female crossbreds between the domestic and prolific breeds are mainly produced for their improved reproduction traits. The ram lambs are a byp r o d u c t which can have a very important influence on the whole system of m u t t o n lamb production. Heterosis is of secondary importance and for various growth traits lies b e t w e e n - - 8 . 4 1 % (Kallweit, 1976) and 43.5%

390

(Hartmann and Wassmuth, 1976). Most common are medium values of 10--20% (Hartmann and Wassmuth, 1976; Kallweit, 1976). Lebanese results (Fox et al., 1976) show a heterosis o f 2.44% for feed conversion efficiency. Carcass traits in contributions from France (Ricordeau et al., 1976), Germany (Nitter, 1975), Lebanon (Fox et al., 1976) and Spain (Espejo Diaz et al., 1976; Vails Ortiz et al., 1976) have been analysed. The slaughter and carcass weights differed in individual experiments. The heterosis (Fox et al., 1976; Popp et al., 1976) in almost all traits is very low, in the range from --9% to 7% (percentage of muscle, bones, gigots, shoulder carcass length, length of legs). Only the fat percentage shows a heterosis of 12--23% (Popp et al., 1976). The breed differences for the growth and carcass traits are more important than the heterosis. REFERENCES The following 17 papers were presented in the joint session of the Commission on Animal Genetics and the Commission on Sheep and Goat Production at the 27th Annual Meeting of the E.A.A.P. in Ziirich, 1976. (All papers are mimeographed.) Deeble, F.K. and Barker, J.D., 1976. Finnish Landrace × Border Leicester Rams as sires of crossbred ewes. 5 pp. Espejo Dfaz, M., Mora Seco de Herrera, M. et Garcia Barreto, L., 1976. Croissance et valeur bouch~re des produits issus de croisement entre b~liers de races prolifiques et brebis locales Espagnoles. 4 pp. Fox, C.W., Choueiri, E. and Chabaan, R., 1976. The results of crossbreeding between Chios and the local fat-tail Awassi. 9 pp. Goot, H., Folman, Y., Benjamin, R.W. and Drori, D., 1976. Finn-Mutton Merino and Finn-Awassi crosses in the semi-arid zone of Israel. 8 pp. Hanrahan, J.P., 1976. Repeatability of ovulation rate and its relationship with litter size in four sheep breeds. 8 pp. Hanrahan, J.P. and Quirke, J.F., 1976. An egg-transfer study of embryo survival and maternal performance in Finn, Galway and Fingalway sheep. 8 pp. Hartmann, W. und Wassmuth, R., 1976. Fruchtbarkeit, Aufzuchtleistung und Wachstum yon Schafen unterschiedlichen F'innanteils unter Beriicksichtigung der Haemoglobinund Blutkaliumtypen. 5 pp. Jakubec, V., Kr~i~ek, J. and Slan~, O., 1976. The fertility of prolific breeds (Finnsheep, Romanov Sheep, East Friesian Milksheep) and their crosses with Mutton Merino. 10 pp. Kallweit, E., 1976. Steigerung der Fruchtbarkeit durch Gebrauchskreuzungen mit Finnschafen. 6 pp. Nitter, G., 1976. Improvement of reproduction performance by introducing Finnish Landrace genes into Merinolandschaf (Wiirttemberg-Merino). 11 pp. Popp, Th., Terzis, P. und Wassmuth, R., 1976. Ergebnisse der Zerlegung yon L~immerschlachtkSrpern mit verschiedenen Anteilen Finnischer Landrasse. 7 pp. Ricordeau, G., Tchamitchian, L., Thimonier, J., Flamant, J.C. et Theriez, M., 1976. Performance de reproduction et d'~levage des brebis Romanov, Finnoises et crois~es: premier bilan des r~sultats obtenus en France dans les troupeaux expArimentanx de I'INRA et dans quelques troupeaux d'~tude. 25 pp.

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Robinson, J.J., Fraser, C., Gill, J.C. and McHattie, I., 1976. Productivity of Finnish Landrace × Dorset Horn ewes. 8 pp. Tempest, W.M., Boaz, T.C. and Jones, R., 1976. The productivity and efficiency of Border Leicester × Cheviot, Finn × Blackface and East Friesland × Blackface prolific crossbred ewes for lamb and carcass meat production in England. 22 pp. Theriez, M., Tissiar, M., Molenat, G., Brelurut, A., Brun, J.P. et Dacheux, P., 1976. Productivit~ compar4e de deux troupeaux de brebis Limousines et Romanov × Limousines en conduite intensive. 7 pp. Vails Ortiz, M., Cognie, Y., Valdemoro, M.D. et Hallauer, J., 1976. Le croisement Romanov et Finnois sur la Rasa Aragonesa: r~sultats pr~liminaires sur l'engraissement et la reproduction. 6 pp. Veress, L., Stosz, J. and Lovas, L., 1976. Model experiments for developing sheep populations. I. Increase o f prolificacy per lambing. 9 pp.

Other references Maijala, K. and ()sterberg, S., 1977. Productivity of pure Finnsheep in Finland and abroad. Livest. Prod. Sci., 4: 355--377. Nitter, G., 1975. Results of a crossbreeding experiment with sheep for different systems of fat lamb production. (a) Reproductive traits. (b) Growth and carcass traits. Livest. Prod. Sci., 2: 167--177, 179--190. Ricordeau, G., Tchamitchian, L., Thimonier, J., Flamant, J.C. and Theriez, M., 1978. Reproductive and maternal performances in Romanov, Finnish and crossbred ewes. First survey of results obtained in France in the experimental flocks of I.N.R.A. Livest. Prod. Sci., 5 (iapress). ~

RESUME Jakubec, V., 1977. Productivit~ des animaux issus du croisement avec les races ovines prolifiques (Rapport de synth~se des contributions pr~sent~es ~ la r~union F.E.Z. de Z~irich, 1976). Livest. Prod. Sc~, 4 : 3 7 9 - - 3 9 2 (en anglais). On a r6sum~ les r~sultats des principaux caract~res de reproduction et de production des animaux issus du croisement entre les races ovines locales et les races tr~s prolifiques d'apr~s les communications et les rapports pr~sent~s ~ Zurich (1976). On a analys~ la fertilitY, la prolificit~, le taux de mortalitY, la taille de la port~e ~ la naissance, le taux d'ovulation, l'aptitude aux agnelages frequents ou hors saison, la production laiti~re, la croissance et la qualit~ des carcasses. On a accord~ plus d 'at t en t i o n aux caract~res de reproduction ~ cause de leur importance pour les animaux crois~s. Pour tous les caract~res analys~s on a estim~ le degr~ d'h~t~rosis ~ partir de diff~rentes sources d'information. L'utilisation des races prolifiques conduit essentiellement ~ une amelioration des caract~res de reproduction. Les differences entre les races sont d~terminantes pour t o u sl es caract~res. Les caract~res de reproduction m o n t r e n t des effets d'h~t~rosis plus ~lev~s que ceux de production, mais cela ne peut pas ~tre consid~r~ c o m m e une loi. Pour effectuer des comparaisons internationales ~ l'avenir, il faudra normaliser les mesures.

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KURZFASSUNG Jakubec, V., 1977. Leistung von Kreuzungstieren auf der Basis yon fruchtbaren Schafrassen (Zusammenfassender Bericht). Livest. Prod. Sci., 4 : 3 7 9 - - 3 9 2 (in Englisch). Ergebnisse der Haupt- und Kurzreferate fiber die Leistung yon Kreuzungstieren zwischen einheimischen und fruchtbaren Rassen, die in Ziirich 1976 vorgetragen wurden, sind mit Riicksicht auf die wichtigsten Reproduktions- und Produktionsmerkmale zusammen gefasst worden. Analysiert wurden: Befruchtung, Fruchtbarkeit, Mortalit~it, Anzahl geborener und aufgezogener L~mmer, Ovulationsrate, 5fteres und saisonunabh~ingiges Lammen, Milchproduktion, Mastleistung und SchlachtkSrperwert. Eine erhShte Aufmerksamkeit wurde den einzelnen Reproduktionsmerkmalen mit Riicksicht auf deren Wichtigkeit bei der Kreuzung mit fruchtbaren Rassen gewidmet. Bei allen analysierten Merkmalen wurde die Heterosis auf Grund verschiedener Informationsquellen gesch~itzt: Mittelwert der Eltern, F1, F2, B ! (Riickkreuzungen), eine der Elternrassen. Die Ausnutzung yon fruchtbaren Schafen fiihrt iiberwiegend zur ErhShung der Reproduktionsmerkmale. Ftir alle Merkmale sind rassenbedingte Unterschiede entscheidend. Die Reproduktionsmerkmale weisen im Durchschnitt hShere Heterosiseffekte als die Produktionsmerkmale auf. Diese Feststellung kann aber nicht immer als Regel gelten. Fiir internationale Vergleiche miissen in Z u k u n f t die einzelnen Merkmale standardisiert werden.