Some Factors Affecting Litter Size in Pigs

Some Factors Affecting Litter Size in PigsAuthor(s): Patricia McGloughlinSource: Irish Journal of Agricultural Research, Vol. 15, No. 1 (Apr., 1976), pp. 141-145Published by: TEAGASC-Agriculture and Food Development AuthorityStable URL: http://www.jstor.org/stable/25555811 .

Accessed: 14/06/2014 00:13

Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at .http://www.jstor.org/page/info/about/policies/terms.jsp

.JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range ofcontent in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new formsof scholarship. For more information about JSTOR, please contact [email protected].

.

TEAGASC-Agriculture and Food Development Authority is collaborating with JSTOR to digitize, preserve andextend access to Irish Journal of Agricultural Research.

http://www.jstor.org

This content downloaded from 185.2.32.49 on Sat, 14 Jun 2014 00:13:28 AMAll use subject to JSTOR Terms and Conditions

http://www.jstor.org/action/showPublisher?publisherCode=teagasc

http://www.jstor.org/stable/25555811?origin=JSTOR-pdf

http://www.jstor.org/page/info/about/policies/terms.jsp


COMMUNICATIONS TO THE EDITOR 141

SOME FACTORS AFFECTING LITTER SIZE IN PIGS

Abstract: Field records of 1248 litters sired by 50 boars on 178 commercial farms were used to study some of the factors affecting litter size, at birth and weaning, which averaged 11.2 ?2.7 and 9.7 ?2.4 respectively. Litter parity had a significant effect on litter size, which was not influenced by year/ season, individual sire, type of service or breed of sire.

Introduction: The number of piglets produced per sow is one of the major factors

affecting the economic returns of a pig breeding enterprise (1). Litter size, which is

normally assumed to be dependent on the female, can be affected by a number of

factors, such as, breed, litter parity, farrowing interval and season. The heritability of litter size is low: Legault (2) in a review of 25 references estimated it to be 0.10. Several authors reported finding a significant sire effect on litter size (2, 3, 4, 5, 6, 7, 8), though in many cases the size of the effect was almost negligible. The influence of sire on litter size has also been found to be significant in mice (9, 10).

The object of the present study was to investigate some of the factors, including sire and type of service (natural or A.I.), which affect litter size in commercial pig herds.

Experimental: Field records were available from a co-operative pig enterprise in Co.

Cork, where pigs born on 178 different suppliers' herds were fattened in a central station. Recorded information included details of parentage and litter size, as well as

individual pig performance at the fattening units. A total of 1,248 litters born between 1963 and 1967 and sired by 50 purebred boars (37 Landrace and 13 Large White) were included in this study. Each boar had at least four litters (average 25) born on at least two different farms (average 7). Seven of the boars were used in A.I. exclusively, and the remainder in natural service. The dams of the litters were non-pedigree Landrace and Large White sows and crosses between those two breeds. The average herd size

was less than five sows. Litter size at weaning was not recorded prior to 1965 and it was also omitted from some later records, leaving a total of 710 litters sired by 34 boars for this part of the study. The traits studied were litter size at birth (total number of piglets including deadborn) and litter size at weaning. Litter size at weaning was recorded at an average of 48 days.

Variance analyses were carried out by the least squares method, and the model

included the effects of sire, breed of dam, litter parity and year/season. Breed of dam was divided into five classifications: Landrace, Large White, the two reciprocal first crosses and a fifth category containing other crosses between those breeds. Time was

divided into 15 three-monthly periods. In classifying litters according to parity, all litters from the sixth and later farrowings were grouped together. In the analysis of litter size at weaning, age at weaning (days) was included as a partial regression. A second analysis, which included in the model the effects of breed of sire and type of service (natural or A.I.) in place of sire per se, was carried out for litter size at birth.

The number of litters sired by A.I. which were recorded at weaning was too small to

allow this latter analysis on litter size at weaning.



142 IRISH JOURNAL OF AGRICULTURAL RESEARCH, VOL. 15, NO. 1, 1976

Results and discussion: The mean litter size was 11.2 ? 2.7 and 9.7 ? 2.4 at birth and

weaning respectively. It is difficult to compare litter size at birth (including deadborn

pigs) with the figures in other reports which quote number born alive. However, litter size weaned is in the present study generally higher than that given by other authors for these breeds in Ireland (1, 11) and hi other countries (12, 13, 14). This difference

may be due to a number of factors: the small herd size in which these litters were

born, and the long farrowing interval in the herds as indicated by the age at weaning of the litters, both of which would tend to increase litter size.

The results of the analysis of variance are given in Table 1.

TABLE 1: Variance analysis for litter size at birth and weaning

Litter size at birth Litter size at weaning

Source of Mean % of total Mean % of total variation df square variance df square variance

Sire 49 6.80 ns 0.2 33 7.45 ns 2.3 Breed of dam 4 21.08* 1.0 4 3.41ns 0.0 Litter parity 6 123.42*** 10.2 6 19.32** 2.8

Year/season 14 8.83 ns 0.4 8 8.72 ns 1.0 Error 1174 6.56 88.2 658 5.38 93.9

Sire: Sire did not have a significant effect on litter size, either at birth or weaning. This result differs from the findings of several other authors (2, 3,4, 5, 6, 7, 8) who, however, generally found that the proportion of the total variance due to sire was

very small and in most cases non-significant at weaning. Several explanations of a physical basis for sire effects on litter size have been put

forward. Possibly, in the present instance, none of the factors which adversely affect litter size was significant in the population. Swierstra and Rahnefeld (15) have

postulated that sire effects on litter size are associated with differences in the semen

quality of boars. Evidence of increased piglet mortality in the litters of certain boars due to increased susceptibility to E. coli infection was observed by Crossman et al (16). The possibility of an early lethal factor, resulting in decreased litter size, being linked with a specific serum transferrin in locus has been suggested by Imlah (17), while

severely reduced litter size has been reported for boars with chromosomal abnor malities (18, 19). Positive relationships between conception rate and litter size have been reported for boars (20, 8) and mice (10), indicating that decreased prolificacy and complete infertility may be part of the same syndrome.

Breed of dam: The increased litter size of crossbred compared to purebred dams is well documented (13, 21). However, the only significant breed of dam effect in the present study was that the crossbred sows other than first crosses (fifth category) had larger litters at birth than the first crosses. The fact that more conventional differences




between dam groups were not found, especially in litter size at weaning, was probably due to inaccurate classification of the breed of sow in many small herds concerned

in this study.

Litter parity: Litter parity accounted for the major source of known variation in litter size both at birth and weaning, which agrees with the observation of other workers

(1, 5, 7, 12, 14). Litter size increased with parity and the pattern is illustrated in Fig. 1. An increase of over one pig per litter at birth was found between gilts and sows far

rowing for the second time. Subsequently smaller increases continued up to the fifth

parity. Litter size at weaning increased sharply from first to second parity but there after increases were only marginal up to the fifth parity. There was evidence of a slight decline after the fifth parity, though it is difficult to interpret the results at this point

13

Birth 12-

jy^0*0-?

11- /

._ / #s* / Weaning

I ,0- / ,."'\

/ / / 9- / /

#

8-j-,-j-,-,-,-! 12 3 4 5 6 +

Litter parity

Fig. 1: Effect of litter parity on litter size at birth and weaning (6 + includes all litters

from 6th and later farrowings)



144 IRISH JOURNAL OF AGRICULTURAL RESEARCH, VOL. 15, NO. 1, 1976

as all litters from the sixth and later parities have been pooled. This pattern of relation

ship between litter size and parity is strikingly similar to that found by Legault (14) and Strang (7), though the maximum litter size reached was slightly lower than in the

present study. Least squares deviations, which may be used as the basis for correction

factors in adjusting litter size at birth and weaning for litter parity, are given in Table 2.

TABLE 2: Least squares deviations of litter parity, for litter size at birth and weaning

Litter parity Birth Weaning

1st (gilt) -1.83 -1.00 2nd -0.29 0.05

3rd 0.28 -0.07 4th 0.34 0.21

5th 0.49 0.59

_6th or

higher_(U1_O01_

Year/season: Year/season effects were not significant. Scofield and Penny (6) also found no significant seasonal effect on litter size, while Strang (7) found only small seasonal effects. Legault (14) found a significant combined herd and seasonal effect on

litter size. It was not possible to determine herd effects in the present study, as the

average herd size was so small, less than fiv^ sows.

Type of service: The results of the second analysis showed that there was no significant difference between the size of litters at birth sired by natural service or by A.I. The actual least squares means of litter size at birth found for natural service and A.I. were

11.26 ? 0.28 and 11.20 ? 0.28 respectively. In spite of the fact that the economic

viability of A.I. in pigs would be greatly influenced by even small effects on litter size, there is a distinct lack of information on this subject in the literature. Hemma (22) has quoted some recent Norwegian results which indicate that A.L sired litters were

slightly smaller than naturally sired litters.

Breed of boar: There was no difference between the litters sired by Landrace or Large White boars. As the two sire breeds used in the present study are the same as those of

the sow breeds and crosses, it is reasonable to find that sire breed did not affect litter size. While the average advantage of crossing sows with a boar of a different breed is

quoted by Sellier (21) as 0.2 extra pigs born alive, King and Thorpe (23) have found

considerably greater increases when using Pietrain x Hampshire boars compared to

Landrace or Large White boars.

The present study has shown that litter parity is the major factor influencing litter size in pigs. This should be taken into consideration in planning the replacement rate in a sow herd, as the proportion of gilts in the herd will greatly influence the average




litter size achieved. As there was no evidence to show that individual boars had an effect on the size of the litters they sired, either by natural service or A.I., and in light of the fact that most authors who observed significant sire effects, found them to be of little practical importance, selection of boars on this trait would not be worthwhile.

However, in the rare situation where a boar may be siring litters of greatly reduced size due to a physical or chromosomal abnormality, culling would be recommended.

Acknowledgment: The author wishes to thank the management of Rathduff Pig Co

operative Society for providing the data on which this study was based.

Patricia McGloughlin

An Foras Taluntais, Dunsinea, Castleknock, Co. Dublin

REFERENCES

1. Kearney, B., 'An economic study of costs and returns in pig production.* An Foras Taluntais, Dublin, p. 53, 1972.

2. Legault, C, Ann. Genet. Sel. Anim. 2: 209, 1970. 3. Skjervold, H., Meld. Norg. LandbrHogsk. 42: 1, 1963. 4. Minkema, D., Veeteelt-en Zuivelber. 10: 161, 1967. 5. Ollivier, L. and Legault, C, Ann. Zootech. 16: 247, 1967. 6. Scofield, A. M. and Penny, R. H. C, Br. vet. J. 125: 36,1969. 7. Strang, G. S., Anim. Prod. 12: 225, 1970. 8. Rahnefeld, G. W. and Swierstra, E. E., Can. J. Anim. Sci. 50: 671, 1970. 9. Finn, C. A., J. Reprod. Fertil. 7: 107, 1964.

10. Schilling, P., North, W. and Bogart, R., /. Hered. 59: 351,1968. 11. O'Grady, J. F., Ir. J. agric. Res. 10: 17,1971. 12. Korkman, N., Acta Agric. Suec. 2: 253,1947. 13. Smith, C. and King, J. W. B., Anim. Prod. 6: 265, 1964. 14. Legault, C, Ann. Genet. Sel. Anim. 1: 281, 1969. 15. Swierstra, E. E. and Rahnefeld, G. W., J. Anim. Sci. 26: 149,1967. 16. Crossman, P. J., Wijeratne, W. V. S? Imlah, P., Buckner, D. R. P. and Gould, C. M., Br. Vet. J.

129:58,1973. 17. Imlah, P., Anim. Blood Grps biochem. Genet. 1: 5, 1970. 18. Henricson, B. and Backstrom, L., Heriditas 52: 166, 1964. 19. Akesson, A. and Henricson, B., Acta. Vet. Scand. 13: 151,1972. 20. du Mesnil du Buisson, F., Millanvoye, B., Bariteau, F. and Legault, C, Journees de la Recherche

Porcine en France, Paris, 20-22 Fevrier, 1974. 21. Sellier, P., Ann. Genet. Sel Anim. 2: 145, 1970. 22. Hemma, B., Svineavlsnytt (3) 7,1974. 23. King, J. W. B. and Thorpe, W., Proc. E.A.A.P. Meeting, Vienna, 1973.

Received September 8,1975



Documents

Some Factors Affecting Litter Size in Pigs