Productivity of Polypay, Dorset and Polypay × Dorset ewes under two accelerated breeding systems

Small Ruminant Research, 3 (1990) 269-281 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

269

Productivity of Polypay, Dorset and Polypay × Dorset Ewes under Two Accelerated Breeding Systems M.H. FAHMY 1and D. LAVALLEE2

1Agriculture Canada, Research Station, LennoxviUe, Que., J I M 1Z3 (Canada) 2Ferme Eco de la VaUde, Ste-Sophie de M~gantic, Que. (Canada) (Accepted 11 May 1989)

ABSTRACT Fahmy, M.H. and Lavallde, D., 1990. Productivity of Polypay, Dorset and Polypay × Dorset ewes under two .accelerated breeding systems. Small Rumin. Res., 3: 269-281. Forty-one Dorset and 113 Polypay ewes were subjected to a system of three lambings in 2 years (3/2) followed by five lambings in 3 years (5/3), in which 22 Polypay×Dorset crossbred ewes were also involved. The objective was to evaluate yearly ewe productivity. Fertility of Polypay ewes averaged 85% compared to 94% for Dorsets and 100% for the cross. Numbers of lambs born for the three groups were 1.76, 1.40 and 1.47; and those weaned were 1.52, 1.09 and 0.88, respectively. Fertility of ewes under the 3/2 system was 98% compared to 79% for the 5/3 system. Numbers of lambings per year for Polypay and Dorset ewes were 1.55 and 1.50 under the 3/2 system; 1.54 and 1.57 under the 5/3 system, respectively. Numbers of lambs weaned per ewe per year was 2.53 and 1.79 for Polypay ewes under the 3/2 and 5/3 systems. The corresponding estimates for Dorsets were 1.61 and 1.60, respectively. At 100 days, Polypay ewes produced 86 and 61 kg of lambs, vchile Dorset ewes produced 54.6 and 54.2 kg under the 3/2 and 5/3 systems, respectively. It wa~ concluded that unless fertility in the 5/3 system is improved, the 5/3 system may not be anymore advantageous than the 3/2 system.

INTRODUCTION W i t h 5 m o n t h s of g e s t a t i o n a n d close to a m o n t h for u t e r i n e involution, a s y s t e m to b r e e d ewes to achieve two l a m b i n g s in one c a l e n d a r y e a r is t h e biological limit of t h e ewe. T h i s level of p r o d u c t i o n is s e l d o m a t t a i n e d in p r a c t i c e a n d is v e r y stressful for ewes w h i c h c a n achieve it. T h e s i t u a t i o n is also comp l i c a t e d b y t h e n a t u r a l a n e s t r o u s p e r i o d w h i c h in some breeds c a n e x t e n d for 8 m o n t h s , t h u s r e q u i r i n g s y n c h r o n i z a t i o n a n d o v u l a t i o n i n d u c t i o n with horm o n e s or t h e c o n t r o l o f light (Vesely a n d Swierstra, 1985; Rawlings et al., 1987). Studies o n l a m b i n g twice a y e a r h a v e generally m e t w i t h limited success

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M.H. FAHMY AND D, LAVALLI~E

(Land and McClelland, 1971; Whiteman et al., 1972; Walton and Robertson, 1974; Duncan and Black, 1978). On the other hand, the traditional system of lambing once a year fails to capitalize on the full potential of the ewe. In present day intensive farming systems, the need for more lambs marketed to offset the higher cost of production makes one lambing per year less attractive economically, especially with breeds of low and average prolificacy. An alternative which has been successful is a system of three lambings in 2 years, with one lambing occurring during the anestrous period once every 2 years (Speedy and FitzSimons, 1977; Notter and Copenhaver, 1980; Dzakuma et al., 1982; Dyrmundsson, 1983; Rawlings et al., 1987). One of the draw-backs of this system, however, is that ewes which fail to conceive after a mating are rebred only 4 months later, which amounts to a considerable economic loss. Terrill and Lindahl (1975) developed the Morlam system, in which ewes are exposed continuously to rams except for short periods during lactation. Management of the animals under this system is rather complicated and hence the application has been very limited. A compromise system is to breed ewes as soon as they are diagnosed nonpregnant (usually after 2 months of mating) during prearranged mating periods. This system of five to six mating sessions per year can theoretically result in achieving five lambings in 3 years or 1.7 lambings per year, compared to 1.5 lambings per year in a system of three lambings in 2 years. Such a system capitalizes on the natural capacity of ewes without unduely over-stressing them. Other advantages are that lambs are born every 2 months and a continuous supply of market lambs can be expected; and since many matings are scheduled during the year, females are bred for the first time when ready regardless of the time of the year of their birth, hence age at first lambing can be reduced and the length of the reproductive life increased. The disadvantage of such system, however, is that it involves much work in planning and executing several breeding and lambing periods per year, and unless the flock is large, each period could involve only small number of ewes which may complicate the management. The CAMAL and STAR breeding systems developed at Cornell University (Hogue et al., 1980) were based on these principles. Alternative systems were suggested by Magee {1983). So far, only the published report of Iniguez et al. (1986) is available on the performance of sheep subjected to the Morlam and CAMAL systems. In order to succeed with accelerated systems such as the CAMAL, STAR, Morlam or similar systems, ewes should be of an extended breeding season type, so that one can keep to a minimum the need to apply artificial means for inducing ovulation. The objective of the present study is to report on the performance of Polypay and Dorset breeds of sheep subjected to two accelerated lambing systems, three lambings in 2 years and five lambings in 3 years. The data also provided results on the reproductive performance of the F1 cross between these two breeds.

POLYPAY, DORSET AND POLYPAY × DORSET EWES UNDER ACCELERATED BREEDING SYSTEMS

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MATERIALSAND METHODS This study was initiated in autumn 1981 and terminated in winter 1987 on a commercial sheep farm approximately 160 km east of Montreal (latitude 46°N, longitude 72°E).

Animals The aniraals used in this study were 30 Polypay ewes born in 1979, 1980 and 1981, imported as yearlings from the USDA Sheep Research Station in Idaho, and 1983 progeny born in Canada between 1982 and 1984. Forty-one Dorset ewes born between 1978 and 1982 were also used in addition to 22 crossbred Polypay × Dorset ewes born in 1982 and 1983.

Feeding management From beginning of May to end of October each year, ewes and rams were allowed to graze during the day, but were housed during the night. Ewes were grouped according to their reproductive cycle into pregnant, lactating or replacement ewes and placed in separate pastures. Lambs had access to a 17% crude protein ration consisting of barley, soya, bran and minerals ( 1.85 Mcal/ kg), and hay until 100 days of age. Pasture was supplemented daily with 1/2 kg whole barley for yearlings from 100 days until mating whereas ewes reaching the latter ,~tage of gestation received 1/4 kg, which was increased to 3/4 kg during lactation. Rams were also supplemented with 1/2 kg of the same grain mixture. From end of October to beginning of May the animals were housed continuously in a barn which maintained a comfortable temperature (8-10°C) during winter and was adequately ventilated during spring. Lambs up to 100 days of age were fed the grain mixture and hay ad libitum. Yearlings from 100 days of age to first mating were fed 1/2 kg whole barley per day in addition to hay ad libitum Ewes were flushed during the breeding season with 1/4 to 1/2 kg barley. The barley was changed to the concentrate mixture described earlier, 4 to 6 weeks before lambing. Lactating ewes received 1 kg of the concentrate mixture when raising twins and 1.5 to 2 kg when raising triplets. Rams were fed good quality hay and 1/2 kg of whole barley per day. Ewes and rams were yearly dewormed in November (Evomec, Merck Co.) if tests on feces showed infestation of more than 150 eggs (Ostertagia) per g. Lambs born on pasture in June and September were dewormed at weaning (50 days). Larabs born indoors during winter were only treated with an antihelmintic at the end of July on pasture. Lambs were given injections of vitamins A, D, E and selenium (Se) at birth, (1/4 cc AI), 1/4 cc E, Se), weaning (1/2 cc AD, 1/3 cc E, Se) and 100 days (1/2 cc AD, 1/2 cc E, Se). Two cc of vitamins A, D were injected into ewes at

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M.H.FAHMYANDD. LAVALLEE

the end of gestation and before spring mating, and into rams 2 months before spring mating.

Matings The mating periods lasted 45 days. Vasectomized rams with marking harnesses identified ewes in estrus which were then bred by fertile rams. The rams were moved to a separate barn away from the ewes 1 month before the breeding season to increase their libido. During the first 2 years of the study, the ewes were subjected to a system of three lambings in 2 years (3/2) and six mating periods were planned. Fig. 1 illustrates the mating schedule. The first mating was from 10 August to 25 September 1981; all ewes conceived and lambed. They were rebred from 5 April to 20 May (April), then from 20 October to 5 December (November) and from 5 June to 20 July (June) (solid line). Ewes which failed to conceive in April were mated again in August-September (August), then April-May and formed an auxiliary group (broken line). Ewes which failed to conceive after the June mating were rebred in August and formed another auxiliary group (dotted line). Pregnancy was diagnosed at 60 days after mating using an ultrasonic device (Scanopreg 738, Ithaco, Ithaca, NY). Ewes found non-pregnant were mated 2 months later. During the last 3 years of the study, ewes were switched to a system of 5

3 LAME]INGS IN 2 Y E A R S

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Fig. 1. Schedule of the matings throughout the 5 years of the study. Solid line represents the schedule for the main flock, broken lines represent the schedule of alternate groups for ewes which changed groups because they failed to conceive.

POLYPAY, DOR'~ET AND POLYPAY × DORSET EWES UNDER ACCELERATED BREEDING SYSTEMS

273

lambings in 3 years (5/3). Five mating periods were planned each year {January, April, June, August and November) according to the design shown in Fig. 1. Ewes which did not conceive were rebred immediately after being diagnosed non-pregnant. Mating of yearlings was done according to their date of birth when they were between 7 and 10 months of age.

Control of light Since the matings during April and June occurred during the anestrous period for Dorset (which extends from March to August according to Dufour (1974)) alad presumably also for Polypays, a simple form of control of light was practiced during these matings. The treatment lasted from 15 February to 10 May and from 15 April to 10 July for the two matings. Using dark shades on the barn windows, the animals {rams and ewes) were allowed only 5 h of light per day (from 8.00 to 13.00 h). This meant that ewes to be bred in April and June were permitted to graze only 5 h per day until they were successfully bred.

Management of lambs At birth, the lambs were identified, weighed and isolated in small pens with their dams for 2 to 3 days. Ewes and their litters were grouped according to number of lambs suckling, to facilitate feeding of ewes according to their nutritional requirements. Lambs were weaned at about 50 days of age, some were weaned at younger ages (35 days minimum). A week before weaning, the feeding of ewes with the concentrate mixture was stopped, and hay was reduced gradually each day. On weaning day, the ewes were deprived of water and were fed only sl:raw. The next day, ewes had access to water and limited amount of hay which, was increased gradually every day.

Traits studied Data collected were fertility, percent of ewes pregnant of total exposed (ewes which aborted were still designated as fertile), prolificacy, total number of lambs born and weaned, and litter weight at birth, 50 and 100 days. Lamb weights at 50 and 100 days were obtained from the Record of Performance program which adjust for age at weaning, sex, age of ewe and type of birth. In cases of multiple litters where weight records of one or more lambs were missing, the ~hole litter was excluded from the analysis. Average individual lamb weights at birth, 50 and 100 days were calculated (litter weight/litter size). Number of lambings per ewe per year was calculated for each ewe as 12 n~ t 2 - tl where n is the number of lambings, t2 is age of ewe at last lambing and tl is age at first lambing in months. Only ewes which completed three lambings under the 3/2 system and at least four under the 5/3 system were analysed. Fifteen Polypay and 9 Dorset ewes were excluded from the analysis of difference between systems because they died or were culled for different reasons

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M.H. FAHMYAND D. LAVALLI~E

(mostly non-related to reproduction) before they could contribute enough records to calculate number of lambings per year according to the criteria above. Available data on these 24 ewes were, however, included in the analyses for fertility and lambing. For animals born before 1981 the yearly production of lambs was calculated for ewes on the two systems separately (3/2 and 5/3), whereas for those born after 1981 only the yearly average on the 5/3 system could be calculated. For ewes born in 1984 most of the yearly averages were calculated on only four lambings. The crossbred ewes were disposed of before they completed four lambings, hence, yearly averages were not calculated. Statistical analyses Data on fertility and litter performance were analyzed using Harvey's procedure included in the SAS package (SAS, 1985). The following mixed model was applied: Yijklmn ----]2-}- bi + wij ~- ah + sl +tm + eijktmn

where Y refers to single observation; ~t, overall mean; b, breed of ewe within year of birth; w, ewe within b subclasses (error 1); a, effect of age of ewe; s, effect of season of mating-lambing; t, mating system (3/2 or 5/4) and e, experimental error. The effect b was then separated into its components, breed of ewe, year of birth and their interaction using the sum squares obtained from all possible orthogonal comparisons. The interactions b × s and b × t were included in preliminary models, but their effect was not significant and they were excluded from the final model. Effect of mating system was excluded from the model used to analyse the data at 50 and 100 days of age. Data on the number of lambing per ewe per year were analyzed using a simple model which included effects of year of birth and breed. Ewe productivity under different systems was calculated from fertility, litter size and number of lambings per year for each year of birth of ewes, then pooled across year of birth (weighted by the number of ewes in each class). Data of ewes born between 1979 and 1982 (Polypay and Dorset) and those born in 1983 and 1984 (Polypay and F1) were analyzed separately using the same model. RESULTS AND DISCUSSION

Fertility in Polypay ewes averaged 85% (ranged between 83 and 94% for different years of birth), 9% lower than in Dorset ewes and 12% lower than in the Polypay × Dorset crossbred ewes (Table 1). On the other hand, Polypay ewes exceeded Dorset and crossbred ewes in prolificacy at birth and at weaning. Polypay ewes weaned 1.5 lambs per litter compared to 1.1 for Dorset (P < 0.01 ). The corresponding difference between Polypay and crossbred ewes was 0.5 lambs (P < 0.05 ). Over a 3-year period, Hulet et al. (1984) reported an average fertility of 89% for Polypay ewe lambs mated at 7 to 8 months of age,

POLYPAY, DORS ET AND POLYPAY × DORSET EWES UNDER ACCELERATED BREEDING SYSTEMS

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TABLE1 Least squares means for Polypay, Dorset a n d Polypay × Dorset cross

No. of ewes No. of records Fertility (ewes lambing/ewes m a t e d ) Total n u m b e r of lambs b o r n / e w e lambing L a m b s born alive/ewe lambing Mortality al; b i r t h (%) Lambs weaned/ewe lambing Pre-weaning loss (%) Litter b i r t h weight (kg) No. of records at 50 days L a m b 50 days weight (kg) Litter 50 days weight (kg) No. of records at 100 days Lamb 100 days weight (kg) Litter 100 days weight (kg) N u m b e r of larabings per ewe per year No. of ewes on 3 / 2 system Average No. of ewes on 5 / 3 system Average

Weighted means over years of b i r t h (1979-1982)

Weighted means over years of b i r t h (1983-1984)

Polypay

Dorset

Polypay

Cross

60 460 0.85 1.76 a

41 174 0.94 1.405

53 292 0.88 1.63

22 50 1.00 1.47

1.64 a 7.3 1.52 a 7.9 6.55 a 179 20.5 38.6 a 158 34.2 54.5 a

1.30 b 7.1 1.095 16.1 5.52 b 51 20.1 33.9 b 29 33.9 41.95

1.44 13.2 1.38 a 4.3 5.74 185 20.2 28.2 52 34.9 46.4

1.27 13.9 0.885 30.7 4.90 30 20.3 26.6 4 33.6 51.4

27 1.55 40 1.54

27 1.50 13 1.57

40 1.45

-

a'bMeans followed by different letters were significantly different P < 0.05.

compared to 91% for Finnsheep × Rambouillet and 62% for Dorset × Targhee crosses, which were the foundation stock used to develop the Polypay. Mortality at birth and to weaning was high in lambs from crossbred ewes (14 and 31%, respectively) and may be the result of their younger age at lambing. Polypay ewes showed an 8% lower preweaning mortality than Dorset ewes (8 vs. 16% ). As a result of their larger litters, Polypay ewes produced heavier litters at birth, 50 and 100 days than Dorset (P < 0.05). The weight of individual lambs was similar, however, in the three genetic groups (Table 1 ). Hulet et al. (1984) showed that the 22% preweaning lamb mortality in Polypay was the lowest among the breeds they studied. It was, however, much higher compared to the 7.9 and 4.3% estimates found in the present study.

Effect of breeding system Table 1 shows number of lambings per year for Polypay and Dorset ewes subjected to two accelerated lambing systems. Both breeds succeeded in at-

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taining 1.5 lambings per year expected under the 3/2 system. The theoretically expected rate is seldom achieved in practice since some ewes fail to conceive and require rebreeding. For example, Fahmy (1989) reported 1.34 lambings per year for Romanov sheep under a 3/2 system. In the present study, the ewes were exposed less than 8 months apart when the transition 3/2 and 5/3 systems was underway in 1983. Many ewes conceived in less than an 8 months interval, hence the better than expected results observed with the 3/2 system. Polypay ewes exposed to the 5/3 system averaged 1.51 litters per year, lower than the 1.7 expected in theory. Dorset ewes produced 1.57 litters, however, this average was based on relatively few ewes. Twenty (74%) Polypay and 19 (70%) Dorset ewes succeeded in producing a litter at least every 8 months under the 3/2 system (Table 2 ). To conform to a 5/3 system, a ewe should produce a litter each at least 7.2 months. Nine (11%) Polypay and 1 (8%) Dorset ewe succeeded in attaining that level. Each missed mating period increased the cycle by 2 to 3 months. Twenty-four % of Polypay and 38% of Dorset ewes missed one, while 31 and 38% of the ewes missed two mating periods, respectively. Of the 80 Polypay ewes under the 5/ 3 system, 53 (66%) produced a litter every 8 months or better, compared to 11 out of 13 (85%) for the Dorset ewes (Table 2). On the other hand 15 Polypay ewes (19%) failed to respond to this system of accelerated lambing. Ewes under the 3/2 system showed significantly higher fertility than those under the 5/3 system (97.8 vs. 79.4). However, differences in litter traits were generally small and non-significant. It must be recalled that the two systems were tested one after the other; thus contemporary comparisons were not possible, since effect of system was confounded with other environmental effects. Also the two systems were applied for ewes born in 1979, 1980, and 1981, for ewes born in 1982, 1983 and 1984 only the 5/3 system was applied. Accordingly, all calTABLE 2 Distribution of Polypay and Dorset ewes according to the number of lambings per year on two accelerated lambing systems Lambing system Breed (lambings/year)

No of litters per year ( corresponding lambing interval in months ) <1.20 (>10)

1.21-1.32 (9-9.1)

3/2

Polypay 1 (3.7) 1 2 (7.4) Dorset 4 (14.8) 1 (3.7)

5/3

Polypay 6 (7.5) Dorset -

1Percentage of total.

9 (11.2) -

Total number

1.33-1.44 1.45-1.56 1.57-1.68 (9.1-8.3) (8.3-7.7) (7.7-7.1) 4 (14.8) 3 (11.1)

1 (3.7) 4 (14.8)

12 (15.0) 25 (31.2) 2 (15.4) 5 (38.4)

15 (55.6) 10 (37.0)

>1.69 (<7.1) 4 (14.8) 27 5 (18.5) 27

19 (23.8) 9 (11.2) 80 5 (38.4) 1 (7.7) 13

POLYPAY, DORSET AND POLYPAY × DORSET EWES UNDER ACCELERATED BREEDING SYSTEMS

277

culations o:a the merit of the two systems should be considered with these limitations in mind. Numbers of lambs born and weaned per ewe per year under the 3/2 system (fertility×litter size X number of lambings per year) were 2.77 and 2.53 for Polypay and 1.95 and 1.61 for Dorset. Under the 5/3 system, they were 2.11 and 1.79 fo:r Polypay and 1.82 and 1.60 for Dorset. At 100 days post lambing, Polypay produced 86.5 and 61.2 kg of lambs per ewe per year under the 3/2 and 5/3 systems, respectively. Corresponding values for Dorset were 54.6 and 54.2 kg, respectively. Higher performance under the 3/2 systems was a direct result of higher fertility since litter size and number of lambings per year were similar in the two systems. It can be stated, however, that both Polypay and Dorset sheep responded satisfactorily to accelerated lambing systems. In the present study, ewes which failed to conceive repeatedly were not culled in order to evaluate the system. In practice such ewes are usually culled. It is thus possible, by this kind of selection to maintain a flock well adapted to an intensive system. Ewe productivity increased as the mating system became more intensive. Hulet et al. (1984) showed that Polypay mature ewes under the twice a year lambing system produced 2.11 lambs at birth and 1.70 at weaning compared to 1.83 and 1.49 for those on a once a year lambing system. A difference of 9 more kg weaned favored the accelerated system. Iniguez et al. (1986) compared the Morlam and CAMAL systems and reported 1.28 and 1.21 lambings per year, respectively, which are lower than what is expected theoretically. Vesely and Swierstra (1985) reported productivity (kg of lambs marketed per ewe) of 243 kg for ewe.,~bred once a year, 241 for those under the 3/2 system and normal daylight b~,t 266 kg for those subjected to a light regime. Differences were nonsignificant. Other studies involving the 3/2 system include Speedy and FitzSimons (1977) in which the annual productivity was 2.13 for Finnsheep × Dorset and 1.67 lambs for Border Leicester and that of Dyrmundsson (1983) in which 2.58 lambs born per ewe per year were reported. Studies involving more intensive systems (Magee, 1983 ) showed that Dorset and Finnsheep ewes subjected to the Magee system (a modification of the STAR system) lambed every 7.2 months (1.67 lambings/year). At that rate, an average yearly lambing of 250 and 535% per 100 ewes was achieved for the two breeds, respectively. In a later study, Magee (1986) reported results from Dorset ewes over 3 years on the STAR system (5/3). Average lambing interval varied from 7.4 to 8.1 months, depending on the month of lambing and the corresponding adjusted annual lambing was 239 and 220% per 100 ewes.

Effect of season of mating All ewe~,~which were mated in February conceived, while only 83% of those mated in April and September had litters (Table 3). Differences in fertility

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TABLE 3

Least squares means of the traits studied according to season of mating - - lambing Season of mating - - lambing SeptemberNo. of records

Fertility Total litter size Litter size alive Mortality at birth ( % ) Litter size weaned Preweaning mortality ( % ) Litter birth weight (kg) No. of records (50 days)

Litter 50 days weight (kg) L a m b 50 days weight (kg) No. of records (100 days)

Litter 100 days weight (kg) Lamb 100 days weight (kg)

AprilSeptember

DecemberApril

June-

January

November

FebruaryJune

163 0.83 1.66 1.51 9.0 1.36 9.9 6.53 32 32.3 b

140 0.83 1.51 1.48 2.0 1.34 9.4 5.04 26 31.6 b

151 0.94 1.72 1.61 6.4 1.40 13.0 6.79 61 41.5 a

109 0.96 1.61 1.50 6.8 1.31 12.7 6.16 64 35.5 b

71 1.01 1.54 1.43 7.1 1.32 7.7 6.03 32 34.8 b

20.7

19.2

20.9

21.0

20.4

53 53.4

39 46.1

49 46.6

25 55.9

21 43.6

36.5 ab

32.6 b

30.8 b

39.5 a

33.3 b

a'bMeans followed by different letters were significantly different P < 0.05.

between the different seasons were, however, non significant. Little differences among season of mating were also observed for litter size at birth and weaning, litter weight at birth and at 100 days. Litters born in April, the result of December matings, were significantly heavier than those born in other seasons, but the difference disappeared at_100 days. The small effect of season of mating in the present study agrees with findings of KSnig (1981) working on German Mutton Merino ewes mated in JanuaryFebruary, September-October aiad May-June. In most other studies on accelerated lambing, season of mating was the most influencing factor on fertility and prolificacy. Hulet et al. (1984) reported 100% fertility of Polypay ewes in autumn, 79% in winter and only 52% in summer. As a result of the low fertility in summer, the average numbers of lambs born and weaned per Polypay ewe exposed were 0.79 and 0.62 compared to 1.43 and 1.10 lambs for those lambing in winter, respectively. Dzakuma et al. (1982) working on crosses with Dorset, Finnsheep and Rambouillet mated in winter, autumn and summer over two cycles of the 3/2 system, showed that fertility and litter size (47.8% and 1.35 lambs) were lower

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TABLE 4 Analysis of variance for Polypay and Dorset ewes born between 1979 and 1982 Traits

Mean squares for sources of variation Breed

Year Breed)< of year of birth birth

Ewes/ Ageof Season Mating Remainder breed ewe of system (error 1) mating

d.f. 1 3 3 93 Fertility 0.05 0.04 0.33 0.13 Totalnumber oflambsborn 14.3"* 0.2 1.4" 0.4 L a m b s b o r n alive 14.4"* 0.1 2.1" 0.6 Lambs weaned 14.6"* 0 3.7** 0.7 Litter birth weight (kg) 98** 2 19" 7 Litter 50 days weight (kg) 1493" 39 392 263 Litter 100 days weight (kg) 2151" 45 1480" 482

4 4 1 0.20 0.27 1.34"* 1.0" 0.7 0.5 1.0 0.4 0.6 0.8 0.6 0.2 82** 47** 66 502* 385 582 -

4961 0.13 0.37 0.50 0.52 4 205 436

*'**Significanl: P < 0.05 and P < 0.01, respectively. 1For litter 50- and 100-day weights, d.f. for remainder were 145 and 104, respectively.

after sumraer than after autumn (90.6% and 1.80) and winter (91.8% and 1.61 ) lambings. Rawlings et al. (1987) found fertility of ewes under a 3/2 system was affected by season of mating, 93% for January, 81% for September and 64% for May. Stellflug and Nett (1988) working on Polypay ewes mated between January and April or April and June, reported lambing percentages of 24 and 6% for the two seasons, respectively. To overcome low summer fertility, light and/or hormonal treatments are often used. Vesely and Swierstra (1985) showed that conception rate for May breeding was 16% in ewes bred naturally and 88% for those subjected to light treatment. Fertility in the study of Stellflug and Nett (1988) was 24% for ewes mated naturally between January and April, 45% for those subjected to an extended light treatment and 54% for ewes under extended light treatment and injected with melatonin. Effects Of year of birth and age of ewe Year of birth of the ewe had no effect on the traits studied, while age of ewe had a significant effect on number of lambs born and weaned, and litter weight at birth (Table 4). CONCLUSIONS

Almost all research published on intensive management has shown that different systems resulted in increased productivity of sheep compared to the traditional once a year lambing. Rawlings et al. (1987) estimated an increase of 37% for the 3/2 system, while Hulet et al. (1984) reported a 15% increase

280

M.H. FAHMY AND D. LAVALLI~E

for lambing twice a year over lambing only once. The important questions to ask are: (1) to what extent is the increase in productivity offsetting increase in labor and management cost and is it economically advantageous? and (2) what system should a breeder apply to maximize profits? Studies on lambing twice a year have shown limited success and involved intensive management (early weaning, synchronization of estrus, etc). Less intensive systems such as STAR, CAMAL and Magee also involve intensive management and from the few reports available on these systems any advantage over a less intensive system such as 3/2 is questionable. The 3/2 system was found by m a n y researchers to provide a reasonable economic advantage while requiring a minimal increase in management. Analysis of Spanish farms practicing different intensive systems (Valls Ortiz, 1983) showed t h a t no real advantage is gained by applying a system more intensive t h a n 3/2. Studies comparing different systems under similar conditions and with similar breeds of sheep are scarce, and further studies are needed before recommendations can be made to sheep breeders. ACKNOWLEDGEMENTS This research was supported by a grant from Agriculture Canada. The authors acknowledge the contribution of V. Lavall~e, C. Corriveau, P. Bilodeau, L. Charette and L. Boisvert. They also wish to t h a n k Dr. G.L. Roy for his comments and suggestions. Lennoxville Station Contribution No: 279.

REFERENCES Dufour,J.J., 1974. The duration of the breedingseason of four breeds of sheep. Can. J. Anim. Sci., 54: 389-392. Duncan, J.G.S. and Black, W.J.M., 1978. A twice yearly lambing system using Finnish Landrace × Dorset horn ewes. Anim. Prod., 26: 301-308. Dyrmundsson, O.R., 1983. Accelerated breeding - a possibility in Icelandic sheep. Acta Agric. Scand., 33: 17-19. Dzakuma, J.M., Stritzke, D.J. and Whiteman, J.V., 1982. Fertility and prolificacyof crossbred ewes under two cyclesof acceleratedlambing. J. Anim. Sci., 54: 213-220. Fahmy, M.H., 1989. Reproductiveperformance,growth and woolproduction of Romanovsheep in Canada. Small Rumin. Res., 2: 253-264. Hogue, D.E., Magee,B.H. and Travis, H.F., 1980. Acceleratedlambing schemes. Anim. Sci. Mimeo. CornellUniv., Ithaca, NY, Series, No. 47, 11 pp. Hulet, C.V.,Ercanbrack, S.K. and Knight, A.D., 1984. Developmentof the polypaybreed of sheep. J. Anim. Sci., 58: 15-24. Iniguez,L.C.,Quaas, R.L.and Van Vleck,L.D., 1986.Lambingperformanceof Morlamand Dorset ewes under acceleratedlambingsystems.J. Anim. Sci., 63: 1769-1778. Ktinig,K.H., 1981.The realisationofeight-monthlambingintervalby regulatingday length.Proc. 32nd Annu. Meet. European Ass. Anim. Prod. No. S 3.9, 7 pp.

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Land, R.B. and McClelland, J.H., 1971. The performance of Finn-Dorset sheep allowed to mate four times in two years. Anim. Prod., 13: 637-641. Magee, B., 1983. New directions for accelerated lambing. Cornell University, Ithaca, NY (mimeo.), 8 pp. Magee, B., 1986. Variation of the STAR accelerated lambing system. Cornell University, NY (mimeo, ), 8 pp. Notter, D.R. and Copenhaver, J.S., 1980. Performance of Finnish Landrace crossbred ewes under accelerated lambing. 1. Fertility, prolificacy and ewe productivity. J. Anim. Sci., 51:1033-1042. Rawlings, N.C., Jeffcoate, I.A. and Howell, W.E., 1987. Response of purebred and crossbred ewes to intensif:ied management. J. Anim. Sci., 65: 651-657. SAS, 1985. U~,~ers'guide, Statistics. Statistical Analytical Inst., Cary, NC. Speedy, A.W, and FitzSimons, J., 1977. The reproductive performance of Finnish Landrace × Dor'.set Horn and Border Leicester × Scottish Blackface ewes mated three times in 2 years. Anita. Prod., 24: 189-196. Stellflug, J.N. and Nett, T.M., 1988. Influence of exogenous melatonin and altered day length on reproductive performance of Polypay ewes. Theriogenology, 29: 535-543. Terrill, C.E. and Lindahl, I.I., 1975. Development of Morlam sheep for year-around lambing. J. Anim. Sci., 41:259 (Abstr.). Valls Ortiz, 1V[., 1983. Frequent lambing of sheep flocks in Spain: Productivity and management consequences. Livest. Prod. Sci., 10: 49-58. Vesely, J.A. mad Swierstra, E.E., 1985. Year-round breeding of crossbred Dorset or Finnish Landrace ewes using a synthetic light regimen. J. Anim. Sci., 61: 329-336. Walton, P. and Robertson, H.A., 1974. Reproductive performance of Finnish Landrace ewes mated twice year:[y. Can. J. Anim. Sci., 54: 35-40. Whiteman, J.V., Zollinger, W.A., Thrift, F.A. and Gould, M.B., 1972. Post partum mating performance of ewes involved in a twice-yearly lambing program. J. Anim. Sci., 35: 836-842. RI~SUMI~ Fahmy, M.H. et Lavallde, D., 1990. Productivitd des brebis Polypay, Dorset et Polypay×Dorset selon deux :~yst~mes de reproduction acc~ldr$s. Des brebis :Polypay et Dorset ont dtd soumises ~ un syst~me de 3 agnelages sur 2 ans, (3/2) suivi par un syst~me de 5 agnelages sur 3 ans (5/3). Des crois~es Polypay-Dorset ont aussi gtg utilisdes dans le 5/3. L'objectif ~tait d'dvaluer la productivitd annuelle des brebis. La fertilit~ des brebis Polypay dtait de 85% comparativement ~ 94% pour les Dorset et 100% pour les crois~es. Le nombre d'agneaux nds pour les trois groupes dtait respectivement 1,76, 1,40 et 1,47, les agneaux sevr~s 1,52, 1,09 et 0,88. La fertilitd des brebis du syst~me 3/2 ~tait 98% comparativement ~ 79% pour le syst~me 5/3. :be nombre d'agnelages par annie pour les Polypay et Dorset ~tait de 1,55 et 1,50 pour le syst~me 3/2 et 1,54 et 1,57 pour le syst~me 5/3 respectivement. Le nombre d'agneaux sevr~s par brebis Polypay par annde ~tait 2,53 et 1,79 pour les syst~mes 3/2 et 5/3 respectivement; en comparaison, les !Dorset en obtenaient 1,61 et 1,60 respectivement, h 100 jours les brebis Polypay ont produit 86 et 61 kg d'agneaux alors que les Dorset en ont produit 54,6 et 54,2 kg sous les syst~mes 3/2 et 5/3 re~pectivement. Lorsque les deux syst~mes sont compards, il n'y a aucun avantage utiliser le sys'~me 5/3 ~ moins d'am~liorer la fertilitY.