Longevity and maternal productivity of F1 crossbred landrace sows managed in two different gestation systems

Livestock Production Science, 19 (1988) 499-510 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

499

Longevity and Maternal Productivity of F1 Crossbred Landrace Sows Managed in Two Different Gestation Systems STEVE B. JUNGST 1, DARYL L. KUHLERS' and JOE A. LITTLE 2

'Department of Animal and Dairy Sciences, Auburn University, AL 36849 (U.S.A.) 2Lower Coastal Plain Substation, P.O. Box 460, Camden, AL 36726 (U.S.A.) (Accepted 10 December 1987)

ABSTRACT Jungst, S.B., Kuhlers, D.L. and Little, J.A., 1988. Longevity and maternal productivity of F, crossbred Landrace sows managed in two different gestation systems. Livest. Prod. Sci., 19: 499-510. Longevity and maternal productivity of 83 Duroc-Landrace (DL), 86 Hampshire-Landrace (HL) and 87 Yorkshire-Landrace (YL) sows were evaluated. Half of the sows of each cross were penned by cross in pasture lots during gestation. The remaining sows were confined in individualsow gestation stalls. The 3 crosses of sows were bred in all possible combinations to 16 Duroc, 19 Hampshire and 19 Yorkshire boars. Litter sizes and weights at birth, 21 and 56 days were summed across 4 parities for each sow to form maternal productivity variables for each stage of production. The 256 sows farrowed 844 litters. A greater percentage of HL sows confined in gestation stalls completed 4 lactations than confined YL sows (88.0 vs 69.8%, P < 0.10). In the pasture gestation system, more total live pigs were produced at birth, 21 and 56 days in 4 parities by DL (40.0, 32.5, 30.9) and HL (38.2, 30.9, 30.2) sows, respectively, than by YL (31.1, 24.7,24.3) sows (P<0.10). In the pasture gestation system, DL (66.3, 168.9) and HL (56.5, 159.0) sows produced more kilograms of litter weight at birth (P < 0.10) and 21 days (P < 0.05 ), respectively, than YL (45.6, 124.8) sows. Confined HL (173.6) sows produced more kilograms of litter weight at 21 days in 4 parities than confined YL (143.1) sows (P < 0.10). Results from this study indicate that the breed of crossbred sows used in a production unit should be selected for the type of gestation system used on the farm.

INTRODUCTION Most recent swine cross-breeding research has been based primarily on mat e r n a l p r o d u c t i v i t y o f f i r s t - l i t t e r gilts a n d s e c o n d - l i t t e r s o w s ( H o l t m a n n et al., 1975; S c h n e i d e r , 1976, 1978; J o h n s o n et al., 1978; J o h n s o n , 1981). T h e m a x i m u m n u m b e r o f pigs f a r r o w e d a n d w e a n e d b y s o w s n o r m a l l y o c c u r s b e t w e e n the third and sixth parity. In most commercial pig production units, sows are k e p t f o r 4 o r m o r e p a r i t i e s b e f o r e c u l l i n g a n d r e p l a c e m e n t b y gilts. L o n g e v i t y

0301-6226/88/$03.50

© 1988 Elsevier Science Publishers B.V.

500 differences among crosses of sows are economically important to producers along with the total productivity of the sows in the herd. The objectives of this study were to evaluate, over 4 parities, longevity and total maternal productivity of Duroc-Landrace (DL), Hampshire-Landrace ( H L ) a n d YorkshireLandrace (YL) sows that were used in a pasture gestation system or were confined in individual-sow gestation stalls throughout the gestation period. MATERIALSAND METHODS Longevity and total maternal productivity of 83 DL, 86 HL and 87 YL sows were evaluated over 2 replicates. Included in the first replicate were 41 DL, 42 HL and 43 YL sows. The 126 sows were sired by 4 Duroc (D), 3 Hampshire (H) and 4 Yorkshire (Y) boars that were bred to 33 purebred Landrace females. The 42 DL, 44 HL and 44 YL sows in the second replicate were sired by 4 D, 4 H and 4 Y boars that were bred to 39 purebred Landrace gilts. The F1 cross-bred sows in the 2 replicates were sired by different D, H and Y boars. Each replicate consisted of 3 farrowing groups. Within each group were 14 sows of each of the 3 crosses. Half of the sows of each cross within each farrowing group were randomly assigned to be penned by cross in 0.41-ha bahia grass (Paspalum notatum) lots. The other half of the sows within a group were confined in 2.13 X 0.61-m individual gestation stalls. Sows within crosses were randomly assigned to be bred to D, H or Y boars with the restriction that approximately equal numbers were bred to each sire breed. Once a sow was assigned to a particular sire breed, she was always bred to a boar of that breed during the remainder of the study. This resulted in the production of 6 types of 3-breed crossbred litters and 3 types of backcross litters. For each parity, two 8-month-old boars of each sire breed were purchased from purebred breeders. The boars were used to breed 3 groups of sows within a replicate and were then replaced. The litters of pigs were sired by 16 D, 19 H and 19 Y boars. Extra H and Y boars were purchased to replace boars that died or sustained a permanent injury. During each 6-week breeding period, the confined sows were taken out of their gestation stalls for approximately half an hour each morning to be exposed to sexually mature boars to check for estrus. Sows found in estrus were bred to a boar of their designated sire breed. Boars were allowed to service a sow once in the morning and afternoon for as many days as she remained in estrus. After breeding, the sow was returned to her gestation stall until the next breeding attempt. Similar management practices were followed during the breeding period for the sows assigned to the pasture lot gestation system. Sows that did not express estrus during the 6-week breeding period or failed to conceive were culled. After the breeding period, conception failure was determined by visual observation. In order to maintain a contemporary group, each breeding period began on a pre-determined date and continued for 6 weeks.

501 Sows remained in the same contemporary groups throughout the study. The sows, on average, were 358.1 + 1.8 days old when their first litters were farrowed. Since breeding for the second, third and fourth parities occurred on pre-determined dates and lasted for 6 weeks, the average age of the sows increased in each parity by 6 months. Thus, the females could have been bred at either their first or second post-weaning estrus. Throughout the breeding periods, sows were fed 2.72 kg day- 1of a 16% crude protein corn-soya-bean meal diet. Sows were dewormed by feeding dichlorvos at recommended levels just prior to the start of the breeding period. After the breeding period and until the sows were taken into the farrowing house, they were fed 1.81 kg d a y - 1 of a 12% crude protein corn and soya-bean meal-based diet containing 10% alfalfa meal. During December, January and February, the amount of feed fed to the gestating sows was increased to 2.72 kg day-1. Sows in the pasture gestation system had access to additional nutrients by grazing the bahia grass pastures, except during the winter months when the grass was dormant. Prior to entering the farrowing house at 110 days of gestation, the sows were dewormed by feeding dichlorvos and were vaccinated with an atrophic rhinitis bacterin. Farrowing occurred in 2 environmentally-controlled buildings. During lactation, the sows were fed 1.81 kg d a y - 1 of feed plus an additional 0.45 kg day- ~of feed for each pig in the litter. The lactation diet was 15% crude protein with corn, soya-bean meal and alfalfa meal as the basic ingredients. Pig birth weights were recorded within 24 h post-farrowing. Three days following farrowing, the pigs were given 1 ml of iron dextran intramuscularly in the hind leg. Each pig was vaccinated against atrophic rhinitis with a commercially available bacterin at 7 and 21 days of age. Pig weights were recorded at ~ 21 days and were estimated using the following formula when weights were not recorded at 21 days (Whatley and Quaife, 1937): Adjusted 21-day weight =

27 actual age ÷ 6

A commercially-available 18% crude protein creep feed was provided to the pigs beginning at ~ 3 days post-farrowing and until the pigs were 5 weeks old. For the next 5 weeks, the pigs were fed an 18% crude protein diet that was ground and mixed at the farm. In the first replicate, the pigs were weaned at ~ 42 days post-farrowing, while in the second replicate they were weaned at ~ 35 days of age. After weaning, the pigs were penned in elevated 2.13 × 1.52-m flatdecked nursery pens with woven wire floors, where they remained until they were ~ 10 weeks old. All pigs were weighed at ~ 56 days. Pig weights not recorded at 56 days were estimated using the following formula (Whatley and Quaife, 1937):

(

410

Adjusted 56-day weight-- actual weight × \actual a g e - 15.0/

502 Longevity was defined as the percentage of the sows completing 4 lactations. Sows that did not express estrus during the 6-week breeding period or failed to conceive were culled from the herd. Likewise, sows that sustained a permanent injury, such as a broken leg, were culled from the herd. Total maternal productivity of a sow for number of pigs born (alive plus stillborn) and number of pigs born alive were summed over 4 parities. Sows that died or were culled from the herd were credited with the total number of pigs produced during the time they were in the study and zero pigs produced during the remaining parities. Culling of sows did not occur based on previous performance. Total maternal productivity for litter sizes and weights at 21 and 56 days and for number of pigs marketed were calculated in a similar manner to litter size born and born alive. Total maternal productivity, in this study, was a function of differences in longevity, fertility, milking ability and pig survival rate. The reproductive data were analyzed with the following statistical model:

Yijklmn =,tt+ Ri + Sij + Dk + (RD )ih + Bl + (DB )kt +Gin + (DG)h,, + Eijklmn where Yijkt,-,,~was the observed record of the nth sow of the kth cross, bred to t h e / t h sire breed, assigned to the mth gestation system and belonging to the jth sow farrowing group within the ith replicate; Ri is the effect of the ith replicate; Sii is the effect of the jth sow group nested within the ith replicate; Dk is the effect of the kth sow cross; (RD)~h is the interaction between the ith replicate and the kth sow cross; B~ is the effect of t h e / t h sire breed; (DB)k~ is the effect of the interaction between the kth sow cross and/th sire breed; Gm is the effect of the mth gestation system; (DG)~m is the effect of the interaction of the kth sow cross and the mth gestation system; Ei2ktmnis the random error term. The data were analyzed using the mixed model least-squares and maximumlikelihood computer program written by Harvey (1976). A Tukey's test was used to test differences among the 3 sire breeds and 3 dam breed combinations, as well as differences among the sow crosses within the 2 gestation systems (Gill, 1978). Longevity of the sows in the second, third and fourth parities were analyzed with the same statistical model as the reproductive data, except that the effects of sire breed and its interaction with sow cross were excluded because breed of sire of the litter was not believed to affect longevity of the sow. Sows that did not complete 4 lactations were classified according to the reason (dead, injury or failed to conceive). A chi-square statistic was calculated to determine if the sow crosses and classifications were independent (Gill, 1978) using the PROC FREQ procedure of S.A.S. (1982). RESULTS Distribution of the sows by cross and gestation system at the start of the study are presented in Table 1. The 256 sows in the study farrowed 10 178 pigs in 844 litters.

503 TABLE I Distribution of sows by breed and gestation system and percentage of sows remaining in herd after second, third and fourth parity Effect

Breed 2 DL HL YL Gestationsystem3 P GS Breedandgestationsystem DL, P HL, P YL, P DL, GS HL, GS YL, GS

No.

Parity

of sows 1

9~

3

4

83 86 87

89.1±3.3 92.9±3.2 87.5±3.2

85.6±3.8 de 91.7±3.8 d 77.2±3.8 e

78.4±4.5 de 86.9±4.4 d 70.2±4.4 e

128 128

87.6±2.6 92.1±2.6

83.8±3.1 85.8±3.1

80.6±3.6 76.4±3.6

41 43 44

90.2±4.7 90.7±4.5 81.8±4.5

90.3±5.5 f 88.3±5.3 ~ 72.8±5.3 g

85.3±6.3 85.8±6.2 70.6±6.1

42 43 43

88.1±4.6 95.1±4.5 93.2±4.5

81.0±5.4 95.0±5.3 81.6±5.3

71.4 ± 6.3fg 88.0 ± 6.2f 69.8 _ 6.2g

1 Number of sows that completed the first parity. 2 DL= Duroc-Landrace; HL=Hampshire-Landrace; YL=Yorkshire-Landrace. 3 p__ pasture lots; GS = individual-sow gestation stalls. de Least-squares means with different superscripts differ significantly (P < 0.05). fgLeast-squares means with different superscripts differ significantly (P<0.10). L e a s t - s q u a r e s m e a n s for t h e p e r c e n t a g e s of sows t h a t c o m p l e t e d second, t h i r d a n d f o u r t h p a r i t i e s are p r e s e n t e d in T a b l e I. L o n g e v i t y of D L , H L a n d Y L sows did n o t differ s i g n i f i c a n t l y a f t e r t h e s e c o n d p a r i t y w h e n a v e r a g e d o v e r gestat i o n s y s t e m s , b u t a f t e r t h e t h i r d a n d f o u r t h parities, a g r e a t e r p e r c e n t a g e of H L sows r e m a i n e d in t h e h e r d t h a n Y L sows ( P < 0.05 ). T h e p e r c e n t a g e of D L sows t h a t c o m p l e t e d t h i r d a n d f o u r t h p a r i t i e s was i n t e r m e d i a t e a n d n o t sign i f i c a n t l y d i f f e r e n t f r o m t h e o t h e r 2 crosses. A g r e a t e r p e r c e n t a g e o f D L sows in t h e p a s t u r e g e s t a t i o n s y s t e m c o m p l e t e d 3 p a r i t i e s t h a n Y L sows ( P < 0.10). L o n g e v i t y of H L sows in t h e p a s t u r e g e s t a t i o n s y s t e m did n o t differ f r o m D L or Y L sows a f t e r t h e t h i r d p a r i t y ( P > 0.10 ). A t t r i t i o n o f D L sows in t h e p a s t u r e s y s t e m b e t w e e n t h e t h i r d a n d f o u r t h p a r i t i e s was g r e a t e r t h a n for t h e o t h e r 2 sow crosses. A t t h e e n d of 4 p a r i t i e s , t h e l o n g e v i t y of t h e 3 crosses did n o t differ ( P > 0.10). L o n g e v i t y of t h e 3 crosses w h e n m a n a g e d in t h e c o n f i n e m e n t gest a t i o n s y s t e m was n o t d i f f e r e n t a f t e r t h e s e c o n d or t h i r d parity. A g r e a t e r p e r c e n t a g e of H L sows c o m p l e t e d 4 l a c t a t i o n s t h a n Y L sows ( P < 0 . 1 0 ) . T h e

504 TABLE II Reasons for removal of the sows from the study Effect

Died I

Breed2 DL HL YL

6 3 10

4 4 7

8 4 9

Gestation system 3 P GS

124 7

4 11

9 12

4 3 5

0 2 2

2 1 6

2 0 5

4 2 5

6 3 3

Breed and gestation system DL, P HL, P YL, P DL, GS HL, GS YL, GS

Injury I

Failed to conceive1

1Number of sows that did not complete 4 parities for each classification. 2DL= Duroc-Landrace; HL = Hampshire-Landrace; YL = Yorkshire-Landrace. :~P= pasture gestation system; GS = individual-sow gestation stalls. 4X2=4.59; P<0.10. p e r c e n t a g e of D L sows in c o n f i n e m e n t c o m p l e t i n g 4 l a c t a t i o n s did n o t differ f r o m t h e o t h e r 2 crosses of sows ( P > 0 . 1 0 ) . Sows t h a t failed to c o m p l e t e 4 l a c t a t i o n s were classified by cross according to r e a s o n for r e m o v a l f r o m the h e r d ( T a b l e II). C h i - s q u a r e tests of cross combinations a n d removal classifications were not significant, which indicated t h a t the reasons for r e m o v a l f r o m the h e r d were n o t d e p e n d e n t on cross of sow. T h e a m o u n t of a t t r i t i o n in t h e h e r d due to death, p e r m a n e n t injury or failure of t h e sows to b e c o m e p r e g n a n t was d e p e n d e n t o n the t y p e of gestation s y s t e m ( P < 0.10). In t h e p a s t u r e g e s t a t i o n system, d e a t h was t h e major cause of sow loss, while failure to conceive a n d p e r m a n e n t injuries caused m o s t of the sow losses in c o n f i n e m e n t . Sire b r e e d l e a s t - s q u a r e s m e a n s for t h e litter size t r a i t s are p r e s e n t e d in T a b l e III a n d for the litter weight t r a i t s in T a b l e IV. Averaged across d a m breeds, sows b r e d to D b o a r s raised m o r e pigs to 21 ( P < 0.10) a n d 56 ( P < 0 . 0 5 ) days a n d m o r e pigs were m a r k e t e d f r o m t h e s e litters ( P < 0.05) over 4 parities t h a n f r o m litters out of sows b r e d to H boars. Since the 2 sire b r e e d s did not differ in t h e t o t a l n u m b e r of pigs sired or b o r n alive at b i r t h ( P > 0.10), these results indicate survivability of D - s i r e d pigs was greater t h a n for H - s i r e d pigs. Sur-

505 TABLE III Least-squares means of total numbers of pigs produced at birth, 21 and 56 days and number of pigs marketed in 4 parities Effect

Trait 1 NB

NBA

N21

N56

NM

Sirebreed 2 D H Y

41.0±1.6 39.8±1.6 38.5±1.6

37.9±1.5 36.4±1.5 35.2±1.5

31.9±1.3 g 27.9±1.3 h 29.1±1.3 gh

31.4±1.3 e 26.8±1.3 f 28.1±1.2 ef

29.8±1.2 ~ 25.6±1.2 f 26.8±1.2 ~f

Dambreed 3 DL HL YL

40.8±1.6 41.4±1.6 37.1±1.6

37.4±1.6 ef 38.6±1.5 e 33.4±1.5 f

30.4±1.3 g 31.9±1.3 g 26.5±1.3 h

29.3±1.3 ef 31.1±1.2 e 25.9±1.2 f

28.1±1.2 ef 29.4±1.2 ° 24.8±1.2 f

Gestationsystem 4 P GS

39.8±1.3 39.7±1.3

36.5±1.3 36.5±1.3

29.4±1.0 29.8±1.0

28.5±1.0 29.0±1.0

27.3±1.0 27.5±1.0

Breedandgest~ionsystem DL, P HL, P YL, P

43.8±2.3 e 40.7±2.2 ~f 34.9±2.2 f

40.0±2.2 g 38.2±2.2 g 31.1±2.1 h

32.5±1.8 ~ 30.9±1.8 e 24.7±1.8 f

30.9±1.8 g 30.2±1.8 g 24.3±1.7 h

29.9±1.7 g 28.5±1.7 g 23.4±1.7 h

37.8±2.3 42.1±2.2 39.3±2.2

34.8±2.2 39.0±2.2 35.8±2.2

28.2±1.8 32.9±1.8 28.4±1.8

27.6±1.8 32.0±1.8 27.5±1.8

26.2±1.7 30.3±1.7 26.1±1.7

DL, GS HL, GS YL, GS

1NB = number of pigs born; NBA = number of pigs born alive; N21 = number of pigs at 21 days; N56 = number of pigs at 56 days; NM-- number of pigs marketed. 2D = Duroc; H = Hampshire; Y = Yorkshire. 3DL = Duroc-Landrace; HL = Hampshire-Landrace; YL = Yorkshire-Landrace. 4p = pasture gestation system; GS = individual-sow gestation stalls. e'fLeast-squares means with different superscripts differ significantly (P < 0.05). g'hLeast-squares means with different superscripts differ significantly (P < 0.10 ). v i v a l o f D - s i r e d p i g s w a s 9.4 a n d 10.0% g r e a t e r t h a n f o r H - s i r e d p i g s i n s t u d i e s r e p o r t e d b y J o h n s o n e t al. ( 1 9 7 8 ) a n d K u h l e r s e t al. ( 1982 ), r e s p e c t i v e l y . S o w s bred to Y boars did not differ from sows bred to D or H boars in terms of number of pigs produced in 4 parities. More total kilograms of litter weight at 56 d a y s w e r e p r o d u c e d w h e n s o w s w e r e b r e d t o D b o a r s c o m p a r e d w i t h w h e n s o w s w e r e b r e d t o H b o a r s ( P < 0.01 ). M o s t o f t h i s d i f f e r e n c e w a s b e c a u s e m o r e p i g s w e r e r a i s e d t o 56 d a y s w h e n s o w s w e r e b r e d t o D b o a r s i n s t e a d o f H b o a r s . HL sows farrowed more live pigs (P < 0.05) in 4 parities, raised more pigs to 21 ( P < 0 . 1 0 ) a n d 56 d a y s ( P < 0 . 0 5 ) a n d m o r e p i g s w e r e s o l d f r o m l i t t e r s o u t of HL sows than YL sows (P<0.05) ( T a b l e I I I ) . A t 21 d a y s , D L s o w s r a i s e d

506 TABLE IV Least-squares means of total kilograms of litter weight produced at birth, 21 and 56 days in 4 parities Effect

Trait d LBWT (kg)

L21WT (kg)

L56WT (kg)

Sire breeda D H Y

56.4 ± 2.3 56.0 _+2.3 52.4 ___2.3

162.7 +_6.6 147.6 _+6.6 147.8 ± 6.6

466.7 _+18.4e 381.0 _+18.4f 421.3 _+18.3ef

Dam breedb DL HL YL

60.7_+ 2.3g 56.7 +_2.3g 47.4_+ 2.2 h

157.8_+ 6.7g 166.3_+ 6.6g 134.0_+ 6.5h

442.0_+ 18.6g 448.0_+ 18.2g 379.0_+ 18.1h

Gestation systemc P GS

56.1 + 1.9 53.7 _+1.9

150.9 _+5.4 154.5 _+5.4

416.2 _+15.0 429.8 ___15.0

Breed and gestation system DL, P HL, P YL, P

66.3 _+3.3g 56.5_+ 3.2g 45.6_+ 3.2h

168.9 +_9.5g 159.0_+ 9.3g 124.8_+ 9.2h

465.4 _+26.4g 427.1 + 25.8g~ 356.0 + 25.5h

55.0 + 3.2 56.5 +_3.2 49.2 +_3.2

146.7 + 9.4 ij 173.6 + 9.3 i 143.1 _+9.3j

418.5 + 26.1 468.9 + 25.8 402.1 + 25.8

DL, GS HL, GS YL, GS

"D = Duroc; H = Hampshire; Y = Yorkshire. bDL = Duroc-Landrace; HL = Hampshire-Landrace; YL = Yorkshire-Landrace. cp = pasture gestation system; GS = individual-sowgestation stalls. OLBWT = litter birth weight; L2 l W T = litter 21-day weight; L56WT = litter 56-day weight. e'fLeast-squares means with different superscripts differ significantly (P < 0.01 ). g'hLeast-squares means with different superscripts differ significantly (P<0.05). iJLeast-squares means with different superscripts differ significantly (P<0.10). m o r e pigs i n 4 p a r i t i e s t h a n Y L sows ( P < 0 . 1 0 ) , b u t d i d n o t d i f f e r f r o m H L or Y L sows a t t h e o t h e r s t a g e s o f p r o d u c t i o n . W h e n t h e 3 sow c r o s s e s w e r e c o m p a r e d w i t h i n t h e p a s t u r e g e s t a t i o n s y s t e m , D L sows f a r r o w e d m o r e p i g s (live a n d s t i l l b o r n ) t h a n Y L sows ( P < 0 . 0 5 ) , w i t h t h e H L b e i n g i n t e r m e d i a t e a n d n o t s i g n i f i c a n t l y d i f f e r e n t f r o m t h e 2 o t h e r sow c r o s s e s . I n 4 p a r i t i e s , D L a n d H L sows i n t h e p a s t u r e g e s t a t i o n s y s t e m f a r r o w e d m o r e live p i g s ( P < 0 . 1 0 ) , r a i s e d m o r e p i g s t o 21 ( P < 0 . 0 5 ) a n d 56 d a y s ( P < 0 . 1 0 ) a n d m o r e p i g s w e r e s o l d ( P < 0 . 1 0 ) f r o m t h e s e sow c r o s s e s t h a n f r o m l i t t e r s o u t o f Y L sows. T h e 3 sow c r o s s e s d i d n o t d i f f e r for a n y o f t h e l i t t e r size t r a i t s w h e n t h e sows w e r e c o n f i n e d i n g e s t a t i o n s t a l l s ( P > 0.10 ).

507 Least-squares means for total kilograms of litter weight produced at birth, 21 and 56 days are presented in Table IV. In 4 parities, DL and HL sows produced more litter weight at the 3 ages than YL sows (P < 0.05). When the sow crosses were compared within the pasture gestation system, DL and HL sows produced more litter weight at birth and 21 days than YL sows (P < 0.05 ). At 56 days, DL sows in the pasture gestation system produced more litter weight than YL sows in the pasture gestation system (P < 0.05 ). The HL sows did not differ from the other crosses for this trait. The sows in the confinement gestation system did not differ in terms of the total litter weight produced in 4 parities, except at 21 days, when HL sows produced more litter weight than confined YL sows (P<0.10). The confined DL sows did not differ from the other 2 sow crosses at 21 days (P > 0.10). For litter weight at birth and 21 days, the sow crosses did not rank the same in the 2 gestation systems. In both gestation systems, YL sows ranked third while DL and HL sows changed rank between the 2 gestation systems. The DL sows produced the most litter weight of the 3 breeds when the sows were in the pasture gestation system, but the HL sows ranked first in the confinement gestation system. DISCUSSION Unlike other crossbreeding studies, this study allowed evaluation of longevity and total productivity of crossbred Landrace sows through 4 parities. Most other crossbreeding studies only evaluated the productivity of first-litter gilts and perhaps second-litter sows. Dagorn and Aumaitre (1979) studied the productivity of 106 242 sows in 5118 commercial herds. Sows within these herds on average weaned 4.2 litters before culling occurred. Longevity of sows within a herd has economic importance, especially when costs of producing or purchasing replacement gilts and the lower productivity of gilts are taken into account. The total number of pigs produced over 4 parities by sows accounts for differences in longevity, fertility, milking ability and pig survival rate. This method may be a better way of expressing reproductive ability than the more common method of the number of pigs produced per sow per year. Differences in longevity in the herd and total productivity of the crosses could not be attributed to age of the sow when her first litter was farrowed. Regression coefficients of longevity and also total productivity at birth, 21 and 56 days on age of the sow were not significantly different from zero. Ages at breeding or farrowing are significantly correlated with first-parity litter size (Korkman, 1947; Omtvedt et al., 1965 ), but do not have a significant effect on total productivity over 4 parities. Longevity of DL, HL or YL sows did not differ significantly through the second parity. However, after the third and fourth parities, a significantly greater percentage of HL sows remained in the herd compared to YL sows. There is other experimental evidence of differences in longevity of different

508 crosses of sows. Drewry (1980) reported that 82.9% of Duroc-Yorkshire sows completed 4 parities while only 76.2% of Hampshire-Yorkshire and 64.7% of Landrace-Yorkshire sows completed 4 parities. In the study completed by Dagorn and Aumaitre ( 1979 ), through 4 parities, Landrace sows had the greatest culling percentage. Large White sows had the lowest culling percentage and F1 Large W h i t e - L a n d r a c e sows were intermediate to the 2 purebreeds. The Duroc and Hampshire breeds have been generally selected to perform in non-confinement production systems. This previous selection history may explain why longevity of sows that were half Duroc or Hampshire was greater than the longevity of YL sows in this study and the Drewry (1980) study. Interactions between sow cross and gestation system were significant for total productivity at birth and 21 days. These results are interpreted to mean a producer should select the breed of crossbred sow for the type of gestation facilities at the farm. On farms with a pasture gestation system, the producer should consider using either D L or H L crossbred sows and should not use YL sows, but with a confinement gestation system, results from this study are interpreted to mean DL, H L or YL sows would perform equally well. In the pasture gestation system, YL sows produced 2.7-4.7 fewer pigs than when confined in gestation stalls. These differences occurred even though longevity of YL sows in the 2 gestation systems did not differ significantly after the second, third or fourth parity. Apparently, YL sows cannot handle being kept outside during gestation. DL sows tended to produce more pigs when kept in the pasture gestation system than when confined. A greater percentage of DL sows in the pasture gestation system completed the fourth parity than when confined. H L sows tended to perform equally well in both gestation systems. The previous selection history of the Duroc and Yorkshire breeds may have had an important effect on the ability of the DL and YL sows to perform better in one gestation system than the other.

REFERENCES Dagorn, J. and Aumaitre, A., 1979. Sow culling: reasons for and effect on productivity. Livest. Prod. Sci., 6: 167-177. Drewry, K., 1980. Sow productivity traits of crossbred sows.J. Anim. Sci., 50: 242-248. Gill, J.L., 1978. Design and Analysis of Experiments in the Animal and Medical Sciences. Iowa State University Press, Ames, IA, 410 pp. Harvey, W.R., 1976. User's Guide for LSML76. Ohio State University, Columbus, OH, 78 pp. Holtmann, W.B., Fahmy, M.H., McIntyre, T.M. and Moxley, J.E., 1975. Evaluation of female reproductive performance of 28 one-way crosses produced from eight breeds of swine. Anim. Prod., 21: 199-207. Johnson, R.K., 1981. Crossbreedingin swine: experimental results. J. Anim. Sci., 51: 906-923. Johnson, R.K., Omtvedt, I.T. and Waiters, L.E., 1978. Comparison of productivity and performance for two-breed and three-breed crosses in swine. J. Anim. Sci., 46: 69-82.

509 Korkman, N., 1947. Causes of variation in the size and weight of litters from sows. Acta Agric. Suec., 2" 253-310. Kuhlers, D.L., Jungst, S.B., Edwards, R.L. and Little, J.A., 1982. Comparisons of specific crosses from Duroc-Landrace, Spot-Landrace and Hampshire-Landrace sows. J. Anita. Sci., 55: 236242. Omtvedt, I.T., Stanislaw, C.M. and Whatley, J.A., 1965. Relationship of gestation length, age and weight at breeding and gestation gain to sow productivity at farrowing. J. Anita. Sci., 24: 531535. S.A.S., 1982. S.A.S. User's Guide: Statistics. Statistical Analysis System Institute, Inc., Cary, NC, 584 pp. Schneider, J.F., 1976. Heterosis, combining abilities and maternal ability estimated for singlecrosses among four breeds of swine. M.S. Thesis, Iowa State University, Ames, IA. Schneider, J.F., 1978. Individual and maternal heterosis estimated from single crosses and backcrosses of swine. Ph.D. Dissertation, Iowa State University, Ames, IA. Whatley, J.A. and Quaife, E.L., 1937. Adjusting weights of pigs to a standard age of 56 days. Proc. Am. Soc. Anim. Prod., 1937, pp. 126-130.

RESUME Jungst, S.B., Kuhlers, D.L. et Little, J.A., 1988. Long~vit~ et productivit~ de truies F1 crois~es Landrace conduites dans deux syst~mes de gestation diff~rents. Livest. Prod. Sci., 19:499-510 (en anglais ). La long~vit~ et la productivit~ de 83 truies Duroc-Landrace (DL), 86 Hampshire-Landrace (HL) et 87 Yorkshire-Landrace (YL) ont ~t~ ~valu~es. Pour chaque croisement, la moiti~ des truies ~tait plac~e sur une parcelle de p~turage. Les femelles restantes ~taient mises en claustration dans des loges individuelles de gestation. Les truies des trois croisements ~taient saillies suivant toutes les combinaisons possibles avec 16 verrats Duroc, 19 Hampshire et 19 Yorkshire. Les tailles et poids de port~e h la naissance, 21 et 56 jours pour les quatre port~es de chaque truie ~taient additionn~s pour former des variables de productivit~ correspondant h chaque stade de production. Les 256 truies ont produit 844 potties. En claustration, une proportion plus importante de truies HL que de YL a effectu~ quatre lactations (88.0% contre 69.8%, P < 0.10). Dans le syst~me de gestation sur p~turage, il y avait davantage de porcelets ~ la naissance, 21 et 56 jours sur rensemble des quatres port~es produites par les truies DL (respectivement 40.0, 32.5, 30.9) et HL (38.2, 30.9, 30.2) que par les YL {31.1, 24.7, 24.3) ( P < 0.10). Dans ce m~me syst~me, il y avait davantage de kg de porcelets produits ~ la naissance et ~ 21 jours par les truies DL (66.3, 168.9) et HL (56.5, 159.0) (respectivement, P < 0.10 et P < 0.05) que par les truies YL (45.6, 124.8). En claustration, les truies HL produisaient plus de kg de porcelets ~ 21 jours au cours des quatre port~es que les YL (173.6 vs. 143.1, P<0.10). Les r~sultats de cette ~tude indiquent que le type g~n~tique des truies utilis~es dans un ~levage pourrait ~tre choisi en fonction du syst~me de gestation utilis~. KURZFASSUNG Jungst, S.B., Kuhlers, D.L. and Little, J.A., 1988. Langlebigkeit und maternale Produktivit~it von Landrasse-Einfachkreuzungssauen in zwei verschiedenen Abferkelsystemen. Livest. Prod. Sci., 19:499-510 (auf englisch). Die Langlebigkeit und maternale Produktivit~it von 83 Duroc × Landrasse (DL), 86 Hampshire X Landrasse (HL) und 87 Yorkshire X Landrasse (YL) Sauen wurde verglichen. Eine

510 H~ilfte der Sauen jeder Kreuzung wurde w~ihrend des Abferkelns auf der Weide gehalten, die andere H/~lfte in befestigten individuellen Abferkelst/illen. Die drei Sauen-Kreuzungen wurden in allen mSglichen Kombinationen mit 16 Duroc-, 19 Hampshire- und 19 Yorkshire-Ebern angepaart. Die WurfgrSt~en und -gewichte bei der Geburt, bei 21 und 56 Tagen wurden ffir jede Sau fiber 4 Abferkelungen aufsummiert und bildeten das Ma/~ fffirihre maternale Produktivitiit in jedem Produktionsstadium. Die 256 Sauen erbrachten 844 Wfirfe. Ein grSi~erer Teil der HL-Sauen in befestigten Abferkelst~illen schaffte 4 Laktationen mehr als die gleich gehaltenen YL-Sauen (88.0% gegen 69.8%, P<0.10). Im Weideabferkelsystem produzierten DL- {40.0, 32.5, 30.9) und HL- {38.2, 30.9, 30.2 ) Sauen mehr lebende Ferkel bei der Geburt bei 21 und 56 Tagen fiber 4 Abferkelungen als YL-Sauen (31.1, 24.7, 24.3). Im Weidesystem produzierten DL- (66.3, 168.9) und HL- (56.5, 159.0) Sauen grS£ere Wurf-, Geburts- und Absatzgewichte als YL-Sauen (45.6, 124.8). In befestigten Abferkelst~illen produzierten HL-Sauen (173.6) mehr Wurfgewicht bei 21 Tagen fiber 4 Abferkelungen als YL-Sauen (143.1 ). Die Ergebnisse dieser Studie zeigen, da£ der richtige Kreuzungssauentyp ffir die Produktion in Abh~ingigkeit von dem vorgesehenen Abferkelsystem ausgewiihlt werden sollte.