The effect of selected factors on litter and piglet weight at the age of

The effect of selected factors on litter and piglet weight at the age of

Animal Science Papers and Reports vol. 24 (2006) Supplement 1, 93-101
Institute of Genetics and Animal Breeding, Jastrzębiec, Poland
Presented at the Conference
“Genetic and Breeding Research on Pigs
with Special Reference to Indigenous Breeds”
organized to commemorate the 10th anniversary
of the death of Professor Stefan Alexandrowicz
20-21 October 2005, Poznań, Poland
The effect of selected factors on litter
and piglet weight at the age of 21 days
Jerzy Nogaj1, Antoni Jarczyk1, Dariusz Kowalewski2
1
Department of Pig Breeding, Univeristy of Warmia and Mazury in Olsztyn,
Oczapowskiego 5, 10-718 Olsztyn, Poland
2
Mazowsze Animal Breeding Centre, Topolowa 49, 99-400 Łowicz, Poland
In a pedigree farm of 240 Polish Large White sows litter and piglet weights were assessed in relation
to major traits of sows. A total of 2131 litters from the years 1994-1999 were analysed coming
from 465 sows. Piglet weight increased along with the increase in daily live weight gain and meat
content of carcass of gilts (P<0.05 and P<0.01). However, differences in litter weight were not found
significant. The highest litter weight was affected by the number of piglets in the litter (13 and
more), but piglets from that group of sows were the lightest (P<0.01). The highest mean live body
weight was found in piglets coming from smaller litters (10 piglets and less). A higher litter weight
was also the effect of the number of litters born by a sow during its productive life (P<0.01 and 0.05)
especially when they were litters of sows giving 4-7 litters during their productive life. Successive
years caused an increase in the fertility of sows and in litter weight, but also a decrease in mean
piglet weight (P<0.01). Starting from the 7th cycle the uniformity of weight of piglets and of litters
was deteriorating. The highest uniformity in litter and piglet weights was found when sows exhibited
average weight gain and average meat content of carcass at the age of 180 days, had their first litter
at the age of 331-380 days, as well when the litter contained 11-12 piglets or when the piglet and
litter originated from sows estimated as of medium fertility (11-12 piglets).
KEY WORDS: daily live weight gain / farrowing / litter size / longevity /
piglet /sow / meat
93
J. Nogaj et al.
One of the major aims of selection in pigs is to obtain litters as numerous as
possible. However, usually a bigger litter is related to the piglets being born lighter,
especially under more adverse environmental conditions. At that time the so-called
negative maternal effects are manifested. A low weight of piglets at birth reduces their
survival rate [English et al. 1988, Rydhmer 1992, Grudniewska 1997].
While comparing different breeds Herpin et al. [9] showed that a high piglet
birth weight does not reflect the sufficient maturity of piglet at birth. An appropriate
development of piglets depends also on the lipid metabolism and the level of hormones
[Mersmann et al. 1984, Herpin et al. 1993], as well as several other environmental
factors connected primarily with the feeding of sows and piglets. Coefficients of
heritability (h2) of litter and piglet weight range in different breeds from 0.136 (Polish
Large White) to 0.276 (Duroc) – Tyra i Różycki [2000].
English et al. [1988] and Grudniewska [1997] as well as other authors [Fahmy et
al. 1978, Roehe 1999, Damgaard et al. 2003] are of the opinion that a uniform piglet
weight after birth increases their rate of survival. However, the h2 for a uniform piglet
weight is low and amounts to about 0.10 [Hogberg and Rydhmer 2000].
The aim of this study was to present the effect of live testing traits of gilts and
their selected reproductive traits on litter and piglet weights up to the age of 21days.
Material and methods
Data were collected on a pedigree farm for over 30 years producing breeding
piglets. The foundation stock consists on average of 240 Polish Large White sows. In
this study the material comprised 465 sows born in the years 1994-1999, which in the
period 1994-2003 gave a total of 2131 litters. In order to present the effect of selected
factors on litter and piglets body weights the sows were divided into three groups
(the highest, moderate and lowest values of each trait). This pertained to standardized
daily live weight gain for the age of 180 days, meat content of carcass, longevity, age
at first farrowing and litter size. In turn, the effect of the year of birth of sows and
successive reproductive cycle was connected with the number of years covered by the
study (1-6) and with the number of litters born by the sow (13 reproductive cycles).
A multivariate analysis of variance according to the SPSS software was applied in
statistical calculations using the following model:
Y = µ +YS ij + C + e
ijk
k
ijk
where:
Y – analysed trait;
µ – overall mean;
YSij – cumulative effect of the year (1-6) and season of birth of sows
(1-4);
Ck – effect of successive reproductive cycle;
e – error for ijk-th effects.
94
Genetic and Breeding Research on Pigs with Special Reference to Indigenous Breeds
Results and discussion
Table 1 presents litter and piglet weights in terms of values of selected traits of
sows. It may be stated that piglet body weight increased along with the increase in
daily weight gain and meat content of carcass of gilts (P<0.05 and P<0.01). However,
differences in litter weight were not found significant. The highest litter weight was
affected by the high number of piglets in the litter (≥13), but piglets with the highest
weight came from smaller litters (≤10). A higher litter weight was also affected by the
number of litters born by the sow during her productive life (P<0.01 and 0.05).
Table 1. Mean liter and single piglet weight on day 21 as related to growth rate and meat content of
carcass on day 180 in sows
Sow trait
n*
Litter weight on
day 21 (kg)
Single piglet weight
on day 21 (kg)
mean
SE
mean
SE
Daily live weight gain (g)
(1) <540
(2) 541-580
(3) 581
significance of differences between means
717
758
656
71.30
71.90
72.04
ns
0.58
0.53
0.56
6.59
6.63
6.56
2b>3a
0.03
0.03
0.03
Meat content of carcass (%)
(1) <55
(2) 55.1-58.1
(3) >58.1
significance of differences between means
947
938
346
71.26
72.52
71.66
ns
0.54
0.56
0.83
6.53
6.65
6.64
1Bb<2A, 3a
0.03
0.03
0.04
*Number of litters.
ab
P<0.05; ABP<0.01.
Sows with the meat content of carcass of 55.1-58.0% showed a tendency to
reach the highest litter weight. In turn, a significantly higher live body weight of
piglets was found in those born by sows in which meat content of carcass exceeded
55%. Thus it could be inferred that smaller adipose tissue depots in sows (i.e. higher
meat deposition) are not at present a decisive factor for a better quality of piglets.
Undoubtedly appropriate feeding during the productive life of sows is essential in this
respect. It needs to be emphasized that litter weights on day 21 amounting to about
65 kg indicate good milk production and proper feeding of sow. On this farm in year
1991 piglets also weighed on average 6.5 kg (6.32-6.83 kg) – Jarczyk et al.[1999]. In
other studies the weight was found to range from 5.52 to 6.05 kg [Klocek et al. 1999,
Rekiel et al. 2000].
95
J. Nogaj et al.
Age at first farrowing did not show any effect on litter or single piglet weights
(Tab. 2). A slightly higher litter weight was obtained from sows serviced for the first
time at the age of 331-380 days. However, the relatively low variation (SE) needs to be
emphasized of both litter and piglet weight in this group. This also pertains to the effect
of another trait, i.e. the number of litters born by sows. This trait, as well as fertility of
sows, is connected with resistance to environmental conditions and the possibility of
its transmission to progeny. However, as it results from Table 2 sows with the lowest
fertility had the heaviest piglets, although litter weight in this group was the lowest. An
opposite dependency was found in the group of the most fertile sows (on average at
least 13 piglets in the litter). Selection for litter size is negatively correlated with piglet
weight, which has been confirmed by numerous authors [e.g. Jarczyk 1991, Grudniewska
1997]. This phenomenon is related to the occurrence of a positive or negative maternal
effect, which disappears or is observed with lower intensity under better environmental
conditions [Steen 1989, Jarczyk 1991, Lewczuk et al. 1994].
Table 2. Mean liter and single piglet weight on day 21 as related to selected reproductive
performance traits
Sow trait
n*
Litter weight on
day 21 (kg)
Single piglet weight
on day 21 (kg)
mean
SE
mean
SE
Age at first farrowing (days)
(1) <330
(2) 331-380
(3) >381
significance of differences between means
220
1359
552
71.24
71.88
71.46
ns
0.82
0.50
0.66
6.60
6.59
6.61
ns
0.04
0.02
0.03
Number of litters born
(1) ≤3
(2) 4-7
(3) ≥8
significance of differences between means
374
843
914
69.69
71.95
71.36
1Bb<2A, 3a
0.54
0.44
0.53
6.55
6.61
6.59
ns
0.03
0.02
0.03
Litter size at birth
(1) <10
(2) 11-12
(3) ≥13
significance of differences between means
989
841
301
64.92
73.99
82.44
B
1 <2A, 3A
0.38
0.34
0.50
6.67
6.60
6.45
Bb
1 >2a, 3A
2B>3A
0.03
0.02
0.03
Litter size on day 21
1) <10
(2) 11-12
(3) ≥13
significance of differences between means
1061
831
239
65.41
74.86
85.63
1B<2, 3A
2B<3A
0.34
0.31
0.51
6.73
6.56
6.43
1B>2A, 3A
2B>3A
0.03
0.02
0.04
*Number of litters.
ab
P<0.05; ABP<0.01.
96
Genetic and Breeding Research on Pigs with Special Reference to Indigenous Breeds
Table 2 shows that selection of the best – i.e. usually the heaviest – piglets may
be connected with their selection from the least fertile dams which do not possess the
high genetic predispositions in fertility. The difference of 0.22 kg between the mean
weight of a piglet out of sows from groups 1 and 3 at the age of one day increased
to 0.3 kg at the age of 21 days. As can be seen, sows from group 3, which to day 21
reared on average at least 13 piglets, created even worse rearing conditions, although
they should be considered superior or hyperprolific sows. This term was used by
Vangen [1995] pertaining to sows which in three successive litters had at least 14.5
piglets/litter, hoping for genetic improvement of fertility. While discussing the effect
of fertility of sows on litter and piglet weights it again needs to be stressed that the
superior uniformity (expressed by standard errors) of these traits was found for piglets
reared by sows from group 2. These differences might be explained by the theory of
genetic homeostasis (after Lerner) which according to Maciejowski and Zięba [1982]
assumes that intermediate forms are the most heterozygous and the most elastic in
the adaptation to the environment. However, selection prefers the best animals and
these should come from highly productive sows. Thus, the problem is in the fact that
not always progeny from these sows phenotypically meets the criteria of the selector,
although it exhibits better adaptation and resistance traits. On this farm in spite of
the fact that piglets born by the most prolific sows (≥11 piglets from all the litters)
were the lightest on day 1, 21, 42 and 84 (figures not tabulated) but the percentage of
weaner piglets selected from this group for further breeding was 52% in comparison
to 30% and 45% of weaner piglets coming from litters of low producing sows (≤8.9
piglets). Thus, it may be stated that piglets of the least prolific sows are characterized
by the worst adaptation and immune potential.
Sows which gave only 1 to 3 litters had significantly lighter litters than sows
giving a higher number of litters. The highest litter weights were found in sows giving
from 4 to 7 litters. Reproductive efficiency of sows increases with age in successive
reproductive cycles until the 6th-7th farrowing [Czarnecki 1976, Grudniewska 1997]
or even up to litter 10 [Jarczyk et al. 1990]. In the past years body weight of piglets
born in litters with a parity from 4th to 7th was lower than of those out of primiparous
sows [Jarczyk 1991]. Later this phenomenon was not observed [Jarczyk et al. 1999].
Body weight of piglets aged 42 and 84 days coming from primiparous sows and those
coming from old-lived sows (at least 6 litters) was similar, although heavier (P<0.01)
than of piglets coming from litters 3rd to 5th. On day 84 from litters nos. 4, 5, 6 and
successive, a total of 66, 66 and 60% piglets were selected for further breeding, while
from litters nos. 1 and 2 - only 37 and 26%, respectively. Hence, piglets born in later
litters have better adaptation and immune potential transmitted by their dams than
those born by dams with short productive lives.
Table 3 presents mean body weights of litters and single piglets out of sows born
in the years 1994-1999. The lowest mean litter weight was found for sows born in
1994, being significantly lower than that of sows born in successive years. It may be
stated that a gradual increase in litter weight is connected with the effects of breeding
97
J. Nogaj et al.
Table 3. Mean liter and single piglet weight on day 21 as related to the calendar year and season in
which the sow was born
Factor
Year
(1) 1994
(2) 1995
(3) 1996
(4) 1997
(5) 1998
(6) 1999
significance of differences
between means for years
Season
(1) spring
(2) summer
(3) autumn
(4) winter
significance of differences
between means for years
No. of
litters
Fertility
Litter weight on
day 21
(kg)
Single piglet weight
on day 21 (kg)
mean
SE
mean
SE
mean
SE
297
827
574
183
172
78
10.68
11.00
11.01
11.05
11.22
11.46
1Bb<5a,
6A
0.16
0.07
0.10
0.14
0.18
0.23
68.50
71.69
71.45
72.45
71.63
72.90
Bb
1 <2, 3,
4, 6A, 5a
0.93
0.44
0.60
0.84
1.06
1.38
6.58
6.63
6.62
6.67
6.49
6.47
A
2 , 3A>5B, 6b
4A>5, 6B
0.06
0.02
0.02
0.04
0.06
0.06
475
554
666
436
11.09
11.08
11.12
10.84
0.12
0.11
0.09
0.12
71.47
71.82
71.20
71.15
0.71
0.62
0.53
0.73
6.59
6.57
6.60
6.63
0.03
0.03
0.03
0.03
ns
ns
ns
*Number of litters.
ab
P<0.05; ABP<0.01.
work in terms of fertility. Improved litter weight was not related to piglet weight. The
lowest mean body weight was found for piglets coming from the most prolific sows
born in 1998 and 1999. Thus, a relationship occurred again showing that the higher
the prolificacy of sows, the lower their piglet weight is. This indicates the need for
further adjustment of feeding for the highest producing sows.
No effect of the season of birth of sows on litter and piglet weights was found (Tab.
3). In other studies this effect was often shown. However, it seems that the effect of
seasons of birth may be manifested especially when feeds are periodically of inferior
quality (e.g. contaminated with mycotoxins). For example Doboszyńska et al. [2005]
reported that sexually immature gilts fed for 14 days a feed containing from 585 to
1314 µg zearalenone/kg showed enhanced processes of histopathological changes in
their ovaries. Symptoms of atresia and atrophy were observed as well as fibroses
affecting most or almost all ovary follicles. These changes may cause reproductive
disorders or infertility.
A significant diversification in litter and piglet weights was found in successive
reproductive cycles (Tab. 4). Litter weight in primiparas was highly significantly
lower than that in later parities. The highest litter weight was observed in sows in
the sixth reproductive cycle. Starting from cycle 7 the uniformity of piglet and litter
98
Genetic and Breeding Research on Pigs with Special Reference to Indigenous Breeds
Table 4. Mean liter and single piglet weight on day 21 as related to litter parity
Factor
Litter parity
1
2
3
4
5
6
7
8
9
10
11
13
13
significance
of differences between
means for parities
ab
P<0.05;
No. of
litters
457
364
313
253
201
153
127
88
66
47
31
23
8
Fertility
Litter weight on
day 21
(kg)
Single piglet
weight on day 21
(kg)
mean
SE
mean
SE
mean
SE
10.27
10.81
11.19
11.25
11.15
11.11
11.08
11.20
11.02
11.11
11.19
11.49
11.60
0.12
0.13
0.15
0.16
0.15
0.18
0.20
0.23
0.24
0.24
0.31
0.35
0.55
64.72
0.69
71.42
0.75
72.58
0.86
73.09
0.97
72.88
0.89
74.00
1.01
71.64
1.20
72.59
1.34
70.46
1.43
72.94
1.44
72.22
1.84
70.09
2.07
72.30
3.28
1Bb<2A...11A,
12a, 13a
2b, 3b<6a
6.42
6.68
6.63
6.58
6.67
6.68
6.60
6.61
6.51
6.64
6.56
6.51
6.66
0.03
0.04
0.04
0.05
0.04
0.05
0.06
0.06
0.07
0.07
0.09
0.10
0.15
1B<2A...13A
2b<3, 4a
1<2...8, 10A
9b<2a, 6a
AB
P<0.01.
weights was decreasing. Studies by Gama and Johnson [1993] and Culbertson et al.
[1997] indicate that with each successive cycle and along with the age of the sow the
potential for bigger ovulation and uterine capacity increases. However, the exhausting
of sow organism appears hence lower and lower number of ageing sows are able to
keep the high level of productivity.
The results presented here can be summarized as follows. The highest litter and
piglet weights at the age of 21 days were found in sows showing moderate standardized
daily live weight gain at the age of 180 days (541-580 g), moderate meat content of
carcass (55.1-58.0%) and having at least four litters. Litter weight on day 21 was
highest when its size amounted to at least 13 piglets. In comparison to litters of 10 or
less piglets the former were by 20.22 kg/litter heavier, but contained piglets by 0.30
kg/piglet lighter. Litter and piglet weights of primiparous sows were the lowest and
were increasing until the 6th reproductive cycle (by 9.28 kg/litter and by 0.26 kg/
piglet).The highest uniformity of litter and piglet weights was observed when sows
exhibited moderate body weight gain and moderate meat content of carcass on day
180, farrowed for the first time not too early and not too late, and when the litters were
neither the most nor the least numerous (in this study 11-12 heads).
99
J. Nogaj et al.
REFERENCES
1. CULBERTSON M.S., MABRY J.W., BERTRAND J.K., NELSON A.H., 1997 – Breed-specific
adjustment factors for reproductive traits in Duroc, Hampshire, Landrace, and Yorkshire swine.
Journal of Animal Science 75, 2362-2367.
2. CZARNECKI R., 1976 – Związek wielkości cechy dzielności rozrodczej loch wbp i pbz z terminem
ich urodzenia, kolejnością miotu, z którego pochodzi locha, wiekiem pierwszego oproszenia i
długością międzymiotu (A relationship of breeding efficiency trait in Large White Polish and Polish
White Landrace sows with the date of their birth, litter rank of sow’s birth, age at first farrowing and
farrowing interval). In Polish, summary in English. ZeszytyNaukowe AR w Szczecinie Zootechnika
9, 1-56.
3. DAMGAARD L.H., RYDHMER L., LØVENDAHL, GRANDINSON K., 2003 – Genetic
parameters for within-litter variation in piglet birth weight and change in within-litter variation
during suckling. Animal Science. 81, 604-610.
4. DOBOSZYŃSKA T., JARCZYK A., ROGIEWICZ A., JANA B., ANDRONOWSKA A., POSTEK
A., 2005 – Wpływ zearalenonu na strukturę niedojrzałych loszek (The effect of zearalenone on the
structure of immature gilts). In Polish, summary in English. Medycyna Weterynaryjna 61, 430-434.
5. ENGLISH P., SMITH W., MACLEAN A.,1988 – Zwiększenie produkcyjności loch (Increasing
sow productivity). In Polish. PWRiLWarszawa.
6. FAHMY M., HOLTMAN W.B., MACINTYRE T.M., MOXLEY J.E., 1978 – Evaluation of piglet
mortality in 28-two-breed crosses among eight breeds of pig. Animal Production. 26, 277-285.
7. GAMA, L.L.T., JOHNSON R.K., 1993 – Changes in ovulation rate, uterine capacity, uterine dimensions,
and parity effects with selection for litter size in swine. Journal of Animal Science 71, 13308.
8. GRUDNIEWSKA B., 1997 – Lochy i prosięta. Żywienie i pielęgnacja (Sows and piglets. Feeding
and care). In Polish. Oficyna Wydawnicza „Hoża”, Warszawa.
9. HERPIN P., LE DIVIDICH J., AMARAL N., 1993 – Effect of selection for lean tissue growth on body
composition and physiological state of the pig at birth. Journal of Animal Science 71, 2645–2653.
10. HÖGBERG A., RYDHMER L., 2000 – A genetic study of piglet growth and survival. Acta
Agriculturae Scandinavica. Sectio Animal Science. 50, 300-303.
11. JARCZYK A., 1991 – Użytkowość rozpłodowa loch córek i wnuczek pochodzących od matek (babek)
o różnej płodności z uwzględnieniem wpływu innych cech i czynników (Breeding performance of
sows daughters and granddaughters of dams (granddams) with varying fertility values in terms of
other traits and factors). In Polish, summary in English. Acta Academiae Agriculturae ac Technicae
Olstenensis, supplement 34, 3-48.
12. JARCZYK A., KŁOS J., BRODOWSKI M., KOT Z., 1990 – Wyniki użytkowości rozpłodowej
loch, które urodziły 15 i więcej miotów w warunkach fermy przemysłowej (Breeding performance
of sows which had at least 15 litters under commercial farm conditions). In Polish. Materials for the
55th Scientific Convention of the Polish Scientific Association in Szczecin, 20-21 September, 24.
13. JARCZYK A., ROGIEWICZ A., GROCHOWSKA M., 1999 – Kolejność miotu urodzenia i średnia
płodność loch jako czynniki efektów matczynych, wpływających na jakość oraz liczbę odchowanych
prosiąt i warchlaków (Litter rank of birth and mean prolificacy of sows as factors of maternal effects
affecting the quality and number of reared piglets and weaner piglets). In Polish, summary in English.
Zeszyty Naukowe AR w Krakowie 352, 89-95 .
14. KLOCEK C., MIGDAŁ W., TUZ R., KACZMARCZYK J., 1999 – Użytkowość rozpłodowa loch
czystorasowych i mieszańców utrzymywanych w różnych warunkach chowu (Breeding performance
of purebred and crossbred sows under different management conditions). In Polish, summary in
English. Zeszyty Naukowe AR w Krakowie 352, 115-121.
100
Genetic and Breeding Research on Pigs with Special Reference to Indigenous Breeds
15. LEWCZUK A., RYMKIEWICZ J., GRUDNIEWSKA B., 1994 – The effect of fecundity of Polish
Large White mother sows on the reproductive utility of sows in the subseqent generations. Acta
Academiae Agriculturae ac Technicae Olstenensis, Zootechnica 40, 43-53.
16. MACIEJOWSKI J., ZIĘBA I., 1982 – Genetics and Animal Breeding. Part B. Stock Improvement
Methods. Elsevier – PWN Warszawa.
17. MERSMANN H.J., POND W.G., STONE R.T., YEN J.T., LINDVALL R.N., 1984 – Factors
affecting growth and survival of neonatal genetically obese and lean swine: cross fostering
experiments. Growth 48, 209-220.
18. REKIEL A., WIĘCEK J., KULISIEWICZ J., 2000 – Wpływ grubości słoniny w punkcie P2 i masy
loszek przy kryciu na zmienność rezerwy tłuszczowej i masy ciała oraz użytkowość rozpłodową
pierwiastek (The effect of backfat thickness in point P2 and gilt weight on variation in adipose tissue
stores and body weight and on breeding performance of primiparous sows). In Polish, summary in
English. Zeszyty Naukowe Przeglądu Hodowlanego 48, 29-36.
19. RYDHMER L., 1992 – Relations between piglet weights and survival. Animal Production 15,
183-184.
20. STEEN v.d. H.A.M. 1989 – Czynniki kształtujące cechy reprodukcyjne loch (Factors affecting
reproductive traits of sows). In Polish. Przeląd Hodowlany, 11, 21-24.
21. ROEHE R., 1999 – Genetic determination of individual birth weight and its association with sows’
productivity traits using Bayesian analysis. Journal of Animal Science 77, 330-343.
22. STONE R.T. 1984 – Relationship of alpha-fetoprotein and albumin in fetuses and neonates from
genetically lean and obese swine. Biology of Neonate 46, 122–130.
23. TYRA M., RÓŻYCKI M., 2000 – Odziedziczalność cech rozpłodowych różnych ras świń
(Heritability of breeding performance traits of different pig breeds). In Polish, summary in English.
Zeszyty Naukowe Przeglądu Hodowlanego 48, 387-388.
24. VANGEN O., 1985 – Hyperprofilitic sows in Norway. Proceedings of The British Pig Breeders
Roundtable, Wye College, Kent, 10-12 April, 1-7.
Jerzy Nogaj, Antoni Jarczyk, Dariusz Kowalewski
Wpływ wybranych czynników na masę miotu i prosiąt w wieku 21 dni
Streszczenie
W fermie zarodowej liczącej 240 loch oceniono masy miotów i prosiąt w zależności od ważniejszych
cech loch. Analizie poddano 2131 miotów z lat 1994-1999, urodzonych przez 465 loch. Masa prosięcia
zwiększała się wraz ze wzrostem przyrostu dziennego i mięsności loszek (P<0,05 i P<0,01). Różnice w
masie miotu nie były jednak istotne. Na największą masę pierwszego miotu wpływ miała liczba prosiąt
w miocie (13 i więcej ), ale potomstwo tej grupy loch było najlżejsze (P<0,01), podczs gdy największą
średnią masą ciała charakteryzowały się prosięta z mniejszych miotów (10 prosiąt i mniej). Na większą
masę miotu miała również wpływ liczba miotów urodzonych przez lochę w okresie jej użytkowania
(P<0,01 i 0,05), zwłaszcza gdy były to mioty loch rodzącch 4-7 miotów w okresie użytkowania.
Kolejne lata powodowały zwiększenie płodności loch i masy miotów, lecz także zmniejszenie średniej
masy prosięcia (P<0,01). Od siódmego miotu pogarszało się jednak wyrównanie masy prosiąt i miotu.
Największe wyrównanie masy miotu i prosiąt wystąpiło, gdy lochy przyrastały średnio intensywnie i
wykazywały średnią mięsność w wieku 180 dni, urodziły pierwszy miot w wieku 331-380 dni oraz gdy
mioty te urodzone zostały przez lochy średniopłodne (w tych badaniach 11-12prosiąt).
101