A. Tänavots. Estonian Agricultural University, Institute of Animal Science, 51014 Tartu, Estonia. alo@eau.ee


The number of piglets in litter is an important trait to achieve economic success. Different breeds vary by litter size; breeders must carefully select breeds to realize heterosis. To select breeding gilts, it is important to consider all information a breeder has because the characteristic data about gilts are limited.
The aim of the research was to analyse different factors affecting the litter size of gilts.

Material and Methods

2389 gilts were raised in 41 farms over Estonia at 1998 to 2003. The gilts average litter size at birth was 10.45 piglets and length of pregnancy 115.78 days. The gilts were inseminated at 180 to 290 days of age. Paterson (1989) recommended management strategy, by witch gilts are mated at about 200 days of age with a body weight of >100 kg.

Table 1. Characterization of the analyzed dataset (n = 2389)



Std. Dev.



Piglets born alive, no. 10.45 1.83 5.00 14.00
Mating Age, days 233.62 23.79 180.00 290.00
Gestation length, days 115.78 1.69 110.00 122.00
Live weight at test, kg 100.55 8.95 85.00 125.00
Gilt X1, mm 13.36 2.48 7.00 20.00
Gilt X2, mm 52.92 5.25 39.00 69.00
Gilt X3, mm 13.45 2.28 7.00 21.00
Gilt Y, % 60.66 2.09 54.08 68.24

Dataset was obtained from of Animal Recording Centre and included breed, sex, birth and testing date, weight, backfat thickness, area of loin eye and lean meat percentage, insemination and fertility data on gilts and their parents which was collected by PC program DB-Planer.
Gestation length was divided into three classes - 110…114, 115…117 and 118…122 days.
Meat traits were measured by ultrasonic equipment Piglog 105. Meat traits recorded were: backfat thickness at last (x1) and 11...12th (x3) rib, 7 cm from midline (mm), and diameter of loin eye (x2), 7 cm from midline (mm). Lean meat percentage (y) was calculated using the formula (Piglog 105, 1991).
Calculating the effect of breed combination and gestation length on litter size of gilts, the following general linear model (GLM) was used (SAS, 1991):


Y= dependent variable;
μ = general mean;
Ti = breed combination (n=1...5);
Mj = insemination year (n=1...6);
Kk = insemination season (n=1...4);
Se = gestation length classes (n=1...3);
eijkem = random residual effect

Calculating the effect of insemination traits and gilt breed on gestation length, the following GLM model was used:


Y= dependent variable;
μ = general mean;
Ti = gilt breed (n=1...3);
Mj = insemination year (n=1...6);
Kk = insemination season (n=1...4);
Se = insemination method (n=1...2);
eijkem = random residual effect

Calculating the effect of breed and technician on meat traits of live gilts, the following GLM model was used:


Y= dependent variable;
μ = general mean;
Ti = gilt breed (n=1...3);
Mj = technician (n=1...7);
Kk = test year (n=1...6);
Se = test season (n=1...4);
Fl = farm (1...41);
Wm = weight at test;
eijklemn = random residual effect

The results are given as least-square means (Parring et al., 1997). Level of significances expressed conventionally: *** - P<0.001, ** - P<0.01, * - P<0.05, # - P<0.1. a, b, c … – least square, within each effect with one letter in common do not differ significantly.

Results and Discussion

Usually farmers feed gilts intensively to prepare them for lactation period. According to the results, this could slightly decrease the litter size on the first parity as backfat thickness and number of live piglets in litter are negatively correlated (Table 2). Rozeboom’s (1996) results agreed with these results, where body composition at first mating did not affect litter size of primiparous sows. As expected, meat traits were significantly correlated. Gilts with thin backfat had somewhat larger loin eye. Cleveland (1988) concluded, that selection for lean growth should have little effect on litter size, but may have beneficial effect on carcass traits.

Table 2. Phenotypic correlations between meat and fertility traits


Gilt Y, %

Gilt X3, mm

Gilt X2, mm

Gilt X1, mm

Piglets born alive, no. 0.041* -0.036# -0.005 -0.064**
Gilt X1, mm -0.827*** 0.725*** -0.165***  
Gilt X2, mm 0.511** -0.172***    
Gilt X3, mm -0.904***      

Due to heterosis effect, achieved through crossbreeding, significantly larger litters were found on EL and ELW gilts crossed with white boars (Tabe 3). Number of piglets in purebred litters of EL and ELW gilts was about same – 10.43 and 10.36 respectively. Significantly smaller litters were found in purebred P gilts.
Gestation length does not affect litter size significantly, although somewhat larger litters were found on gestation length 115...117 days.
Gestation length was highly influenced by insemination method, being longer in artificial insemination (Table 4). Significant breed effect was calculated on gestation length as well. Pietran gilts had shorter gestation period (115.03 days) than white breeds, whose gestation was shorter in Estonian Landrace breed (115.66 days). Gilts, inseminated in fall, had much longer gestation, than those inseminated in other seasons and shortest gestation was found in spring and summer.

Table 3. Effect of breed combination and gestation length on litter size of gilts



piglets born alive, no.
Piglets breed






EL♀ x ELW♂


ELW♀ x EL♂



Gestation length, days








Table 4. Effect of insemination traits and gilt breed on gestation length

Traits n Gestation length, days
Insemination method
Artificial 560 115.94a
Natural 1829 115.22b
Gilt breed
EL 797 115.66a
ELW 1553 116.04b
P 39 115.03c
Insemination season
Winter 699 115.62a
Spring 671 115.34b
Summer 487 115.47ab
Fall 532 115.89c
Insemination year
1998 67 114.82a
1999 474 115.41b
2000 559 115.65c
2001 618 115.69cd
2002 548 115.87de
2003 123 116.03e

Gestation length increased from 114.82 days in 1998 to 116.03 days in 2003. One reason for this could be wider use of artificial insemination of pigs.
Pietran and Estonian Landrace gilts, whose lean meat percentage was over 6% had superior meat quality (Table 5).

Table 5. Breed effect on meat traits of gilts


Gilt breed




n 797 1553 39
X1, mm 13.36a 13.83b 13.85a
X2, mm 50.70a 50.16a 56.81b
X3, mm 13.16a 14.02b 13.51ab
Y, % 60.51a 59.83b 61.04a

Landrace pigs had thinner fat, but showed modest results in diameter of loin eye, compared with Pietrain gilts who were a little fatter, but with large loin eye. The worst results were shown by Estonian Large white breed. Superiority of Landrace breed was found also by Tummaruk et al. (2000).
Lean meat percentage, measured by different technicians, differed about 4% (Table 6).

Table 6. Technician effect on meat traits of gilts


















X1, mm 13.66abc 12.02ac 15.49bd 13.34ab 14.10cd 11.88ac 15.25abc
X2, mm 55.03a 53.57ac 50.99ad 55.29a 53.88bcd 48.32bd 50.82bcd
X3, mm 13.74abc 11.40ac 16.05b 13.63abc 13.85ab 11.19c 15.10b
Y,% 60.71a 62.26a 58.36b 60.90a 60.37ab 61.67ac 58.93bc

Technician F measured the thinnest backfat and the smallest diameter of loin eye. Fatter were the gilts with technician C and loin eye was larger with technicians A and D.


Meat traits (backfat thickness and diameter of loin eye) do not affect litter size of gilts and they are not closely related to each other.
Large difference between white and colour breeds on litter size, whereas crossing white breeds give larger litters in the first parity.
Insemination method and gilt breed affect gestation length highly. Gestation length increases year by year.
Differences between colour meat type breeds and white breeds will decrease.


Cleveland, E.R., Johnson, R.K., Cunningham, P.J. 1988. Correlated response of carcass and reproductive traits to selection for rate of lean growth in swine. J. of Animal Sci. 66 (6):1371...1377.
Piglog 105. 1991. Piglog 105 User’s Guide. Soborg, Denmark: SFK - Technology, 14 pp
Rozebom, D.W., Pettigrew, J.E., Moser, R.L., Cornelius, S.G., El-Kandelgy, S.M. 1996. Influence of gilt age and body composition at irst breeding on sow reproductive performance and longevity. J. of Animal Sci. 74(1):138...150
Paterson, A.M. 1989. Age at mating and productivity of gilts. Manipulating pig production II. Proceedings of the Biennial Conference of the Australasian Pig Science Association, Albury, NSW on November 27-29, 1989. 310...314
SAS. 1991. SAS User’s Guide: Statistics. SAS Inst. Inc., GARY, NC. 305 pp.
Tummaruk, P., Lundeheim, N., Einarsson, S., Dalin, A.M. 2000. Factors influencing age at first mating in purebred Swedish Landrace and Swedish Yorkshire gilts. Animal Reproducton Science. 63 (3/4):241...253.