Prolactin reeeptor gene polymorphism and its association with litter size in Polish Landrace Summary

Prolactin reeeptor gene (PRLR), which is localized on chromosome 16 in pigs, is a candidate eene marker Ihr X Ä t r a V h e eXPen '!; t WaS a i m 6 d ° de teCt t h e D N A m u t a t i " s !" that gene and S Ä J relations between the genotype and some reproduetive traits in Polish Landrace pigs 207 sows and 8 boars from pedigree herd were studied. The polymorphism in PRLR gene locus was detec Ju s ing TCR^L Method w ,h specific primers and restriction enzyme Alul. Two different alleles were identified? S 3 T frequency of PRLR» was estimated at 0.44 and PRLR» 0,56. In the stud d popula o n ofZ'fiSc"ieS of tZZT * B T ?» W r 0 2 4 7 > ° ' 3 8 6 a n d ° 3 6 7 ' '«Pectively. The relations b e Ä Ä S p e and teats number on the left and right body side, total number of teats, number of piglets in the f S t t e f S e ageat t e first parity were analyzed. All data were transformed from the discrete scfle into the qu i, iv" o e The analysis showed the significant dependencies (P < 0,01) between the number of piglets in the firs litter and g e n o g ^ P e P r r e C e P ' r ' Signif >' W " u m b e ' °f Pigl^s characterized the sows carrying AA


Introduction
The reproduction, particularly in the species having large litters, plays an important role in the successful production of farm animals.The cost of one piglet rearing decreases aecording to the increasing number of piglets in one litter.The genes encoding hormone proteins influence the metabolism and, in the result the productivity of animals, so they can be very useful in Performance traits improvement The gene of prolactin reeeptor (PRLR), which is mapped to chromosome 16 in pigs (VINCENT et al., 1997), is such a candidate gene for reproduetive traits in six PIC lines (Large White, Landrace, Duroc, Landrace x Pietrain and Large White x Chinese Meishan).The PRLR gene evidently affected the number of piglets born alive.In the first litters, its effect was estimated at 0,25 piglet per litter (ROTHSCHILD et al., 1998).However, there is still insufftcient information about phenotypic effects of PRLR gene in many lines and races ofpigs.The presented study was aimed to estimate the frequency of PRLR gene mutation and to find possible relations between PRLR genotype and reproduetive traits in the herd of Polish Landrace sows.

Material and methods
The experiment covered 207 sows and 8 boars -reproducers came from pedigree herd of Polish Landrace breed in one farm in Western Pomerania.The studied sows were bred form 40 boars, which were not related to each other.The genotype of prolactin reeeptor was established using PCR -RFLP method.457 base pair long fragment of PRLR DNA was amplified with primers of sequences proposed by VINCENT et al.,199]: forward 5' -CCC AAA ACA GCA GGA GGA CG -3' and the reverse 5' -GGC AAG TGG TTG AAA ATG GA -3'.The PCR reactions were carried out in Perkin Eimer thermoeycler in a volume of 25 LII containing 100 ng of template DNA, 15 pmol of each primer, each dNTP at 100 uM, 1,5 mM MgCl 2 , 10 mM Tris-HCl (pH 8,3), 50 mM KCl, and 0,6 units Taq DNA Polymerase (MBI Fermentas).Cycling conditions were 94°C / 5 min followed by 35 cycles of 40 s at 94°C, 40 s at 60°C, 40 s at 72°C and final 5 min at 72°C.PCR product was than digested with 6 units of restriction enzyme Alul (MBI Fermentas), 3 hours at 37°C.The restriction fragments were separated in 5% agarose gel electrophoresis (PRONA) and stained with ethidium bromide.The results were visualized in UV rays.Performance traits data were collected from farm documentation and they contained the teats number on the left and right body side, total teats number, piglets number in the first litter (boar and sow piglets) and sow age at the first farrowing.The mean age of first farrowing, in studied sows, was 359 days.The number of teats and piglets was transformed from the discrete scale into quantitative one, aecording to SNELL procedure (1964), then those data were corrected for the year of birth, using correction factors (ZUK, 1989), before the analysis was done.The relations between PRLR genotype and studied reproduetive traits were analyzed with one-way analysis of variance and the significance of differences was verified using Duncan test with Computer program Statistica'99.

Results and discussion
Prolactin is one of the protein hormones released by pituitary gland, which control reproduetive processes.The signals of prolactin are recognized by specific receptors (PRLR) built into cell membranes.Detection ofthe polymorphism of PRLR gene could increase improving the reproduetive traits in farm animals.In the herd of studied pigs, two different alleles of PRLR gene were identified with PCR -RFLP method: allele A and B that were responsible for three different genotypes: AA, AB and BB.The lengths of restriction fragments detected during the experiment were as follows: 124, 110, 79, 77 and 67 base pair (bp) for allele A and 124,90,79,77,67 and 20 bp for B one (Fig.).The frequency of allele A was estimated at 0,440, while of allele B -0,560 (Table 1).However, VINCENT et al., 1997 reported the frequency of allele A in different pig breeds: ehester White (n = 10) -0.25; Duroc (n = 10) -0.79; Hampshire (n = 10) -0.05; Landrace (n = 9) -0.72; Yorkshire (n = 12) -0.37; Chinese Meishan (n = 9) -0.56 and European Large White (n = 11) -0.32.Among the population of studied pigs, genotype AA was detected with the frequency of 0.247, AB -0.386 and BB -0.367.In the herd of sows, the frequency of PRLR genotype AA was twice as high as in the group of 8 boars (0.251 and 0.125 respectively).However, the frequency of AB genotype (0.382) and BB one (0.367) in sows was not significantly lower than in boars (AB -0.5 and BB -0.375 (Table 1).In the analyzed herd of sows, deviation from genetic equilibrium was observed between the observed and expected numbers of PRLR (x 2 = 10.020;P<0.01).
Comparing the observed and the expected numbers of particular PRLR genotypes, it was demonstrated that genotype PRLR AB occurred significantly (P<0.05)more frequently, than it would be expected on the basis ofthe Hardy-Weinberg equilibrium.
The analysis of the teats number on the left and right body side and total teats number showed small and statistically not significant differences between sows carrying different PRLR genotypes.The greatest total number of teats was counted in sows with BB genotype (15.44), a little smaller -AB genotype (15.38) and the smallest -AA one (15.33)(Table 2).Means in columns designated with the same letter differ significantly at P < 0.01.
Table 3 shows the number of piglets in the first litter of Polish Landrace sows and the sow age at the first farrowing relating to PRLR genotype.The greatest mean number of piglets in the first litter characterized sows with AA genotype (10.51), while AB sows had 10.44 piglets and BB 10,16.The difference between pigs carrying genotypes AA and BB was 0.35 piglet per litter and was statistically significant at 0.1 level In 1998 Rothschild obtained similar results (ROTHSCHILD et al., 1998); the effect of PRLR genotype was 0.25 piglet per litter but in successive litters that effect was greater.
The differences observed between animals with different PRLR genotypes were small and statistically not significant.

Conclusions
Two alleles of prolactin reeeptor gene and three genotypes (AA, AB and BB) were identified in the analyzed herd of Polish Landrace.The frequency of allele A was 0.44 and B -0.56.The genotype AA was present with the frequency 0.47, genotype AB -0,386 and BB-0.67.

fV
The analysis of relation between the genotype of prolactin reeeptor and the studied reproduetive traits showed significantly greater (P < 0.1) mean number of piglets in the first litter (0.5 piglet more) of sows carrying AA genotype then BB one.The analysis ofthe teats number on the left and right body side and total teats number showed small and statistically not significant differences between sows carrying different PRLR genotypes.The greatest total number of teats was counted in sows with BB genotype (15.4), a little smaller -AB genotype (15.8) and the smallest -AA one