Effect of dietary fish meal on the palatability
and fatty acid composition of pork

Jarmo Valaja, Kaija Suomi, Timo Alaviuhkola and Irma Immonen

Valaja J., Suomi, K., Alaviuhkola, T. & Immonen, I. 1992. Effect of dietary fish
meal on the palatability and fatty acid composition of pork. Agric. Sci. Finl. 1: 21-
26. (Agric. Res. Centre of Finland, Swine Res. Sta. SF-05840 Hyvinkää, Finland).

The effect of graded levels of dietary fish meal was studied with growing pigs in two
trials. Test diets contained fish meal 0, 2.7, 6.5 and 13 %in trial 1 and 0, 2,5 and 10 %

in trial 2. In trial 2, diets containing 5 or 10 % of fish meal were divided into four
different treatments, where fish meal was withdrawn from the diet 7,5, 3 or 0 weeks
before slaughter.

There were no significant differences in performance results between the treatments
in trial 1.

The contents of long chain polyunsaturated fatty acids C22:5 and C22:6 in the pork
fat were analyzed in both trials and they increased linearly with increasing level of fish
meal in the diets (trial 1 and 2) (p<0.001) and with length offish meal feeding period
(trial2)(p<o.ool).

In organoleptic analyses of fresh meat samples there were no statistical differences
between the treatments in trial 1. No off-flavours could be found from the fresh meat
samples in trial 2. After a freezing period of 7 - 8 months, the off-flavour of the meat
increased linearly with increasing content of fish meal in the diet in trial 1 (p<0.001).
In trial 2, distinctness of off-flavours increased also with the level offish meal and with
the length of fish meal feeding period.

Key words: pig, fish meal, off-flavour, fatty acid.

Introduction

Fish meal has long been an important protein
supplement in Finland. Due to restrictions in soya
bean import, commercial feed manufacturers had to
increase the fish meal content in the mixtures up to
5-8 %. After a while, consumer complaints of off-
flavour in pork meat started to increase on the
domestic market and in countries where Finnish
pork was exported. Because of the great seasonal
variation in pork consumption in Finland pork
meat, especially ham, has to be frozen and stored
for several months.

It is known that fish oil increases the risk of fishy

taste in pork meat particularly after long storage
(Agerhem et al. 1984,Pike and Barlow 1977). In
Sweden, 0.02 % of fish oil was the recommended
maximum level in the feeds of growing pigs. It was
also found that the content of two long chain
polyunsaturated fatty acids, C22:5 and C22:6, is a
good indicator of off-flavours in pork fat
(Agerhem et al. 1984). For practical purposes,
more information was still needed to find out how
much standard quality fat-rich (8 - 12 % crude fat)
fish meal should be included in pig diet and what is
the effect of withdrawal period on the off-flavour
incidence.

21

Agric. Sei. Finl. 1 (1992)

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Material and methods

Feeding trial 1 was conducted with 112 Yorkshire
and Landrace pigs. The pigs were assigned at
random to four treatments. Two pigs were placed in
each pen, the gilts and castrates being kept apart.
Each diet was tested on seven pens ofgilts and seven
pens ofcastrates.

The diets of trial 1 contained 0,0.2,0.5 or 1.0 %of
fish fat. Fish meal was added 0, 2.7, 6.5 or 13.0 %,

respectively, to complement the fish fat levels. The
control diet contained soya bean meal as a protein
source. In diet 4, all 20 % soya bean meal was
replaced by fish meal (Table 1).

The fish meal used in trial 1 was commercial type
herring meal typically used in feed industry. It
contained 70.5 %of crude protein and 8.1 %of ether
extract. The long chain polyunsaturated fatty acid
C22:5 and C22:6 contents offish meal were 0.6 and
8.4 % of total fatty acids, respectively. The tri-
methylamine content of the fish meal was 340
mg/100g.

The four treatments recieved the same daily
amount of protein and energy. Pigs were given 1.2-
3.0 feed units/day from 25 kg live weight to
slaughter at an average live weight of 100kg. Weight
gain and feed consumption were registered during

Table 1. Composition of diets in trial 1.

the experiment.
At slaughter, pork chop samples were collected for

fatty acid and organoleptic analyses. Both analyses
were conducted at the Finnish Meat Research Centre.
The fatty acid (C22:5 and C22:6) content was
analyzed with a Hewlett Packard 5890 gas
chromatograph using the glass column NB-351
(Helium gas, detector temp. 270 °C and injector
temp. 250 °C). The organoleptic analyses of the meat
samples were conducted both in fresh state and after
7-8 months of frozen storage by a tested expert panel
consisting of 8-10 experts for each analysis. The
rating scale was: 0= no off-flavour, 1= slight off-
flavour, 2= medium off-flavour and 3= strong off-
flavour.

Trial 2 was conducted with 80 Yorkshire and
Landrace pigs, which were divided into ten
treatments of eight pigs. Eight pigs (four gilts and
four castrates) were placed in the same pen. The
experimental diets contained 0,2, 5 or 10 % of fish
meal. The long chain polyunsaturated fatty acid
(C22:5 and C22:6) content of the diets was 0, 0.19,
0.49 or 0.97 %, respectively. The fish meal was
commercial type and containted C22:5 and C22:6
fatty acids 0.8 and 14.0 % of the total fatty acid
content, respectively.

The ten treatments were fed at the same daily

Diet 1 2 3 4

Barley, % 76.0 77.6 80.0 84.0
Fishmeal, % - 2.7 6.5 13.0
Soya bean meal, % 20.0 16.0 10.0
Mineral and vitamin, %' 3.0 3.0 3.0 3.0
Feed phosphate, % 1.0 0.7 0.5

Chemical composition (calculated):

Feed unit (FU/kg)2 0.97 0.97 0.98 1.00
Digestible crude protein,% 13.8 13.9 13.9 14.0
Lysine, 0/» 0.86 0.90 0.96 1.03
Fish fat, % 0.0 0.2 0.5 1.0
Fish fatty acids
C22:5+€22:6, % 0.0 0.020 0.047 0.095

1. Vitamin E supplementation 30 mg/kg diet.
2. FU= 0.7 kg starch equivalent.

22

Agric. Sei. Fint. 1 (1992)



amount ofenergy and protein from 25 kg live weight
to slaughter. Pigs were given 1.2-2.9 feed units/day.
Four treatments were given the same diets from the
beginning to slaughter (0, 2, 5 or 10 % offish meal).
At 5 and 10 % fish meal levels there were three
treatments in each level where fish meal was
withdrawn from the diet 7, 5 or 3 weeks before
slaughter at 45, 60 and 75 kg live weight,
respectively (Table 2). All pens of eight animals
were slaughtered at the same time.The live weight of
the animals varied from 86.0 to 98.2 kg at slaughter.

At slaughter, pork chop samples were collected for

Table 2. Trial design (trial 2).

Treatment Fish meal, Withdrawal period,
% of diet weeks before slaughter

i 0
11

!

I
5
6

5 7
5
3

5
5
5

7
H
9

11l 7
5
3

II)
K)

10 K)

fatty acid and organoleptic analyses. The fatty acid
(C22:5 and C22:6) content was analyzed by the State
Institute of Agricultural Chemistry. Pork chop
samples were organoleptically evaluated both in
fresh state and after six months of frozen storage at
the Swine Research Station. The unprofessional test
panel consisted of 14 members. A three point rating
scale was used (1= worst score; 3 = best score).

The results of trial 1 were investigated using the
analysis of variance with treatment and sex as
factors. The results of each individual animal were
used as an observation. The difference between
treatments was tested with polynomial contrasts.
Because only one replicate was used in each
treatment in trial 2, the performance results could not
be statistically analysed. The results of the fatty acid
analysis in trial 2 were investigated with one-way
analysis of variance and the difference between
treatments was tested withpolynomial contrasts.

Results and discussion

The main purpose of the trials was not the
performance results. However, theresults of trial 1
show clearly that fish meal can be replaced by soya
bean meal for protein source in growing pigs
without any negative effect on the performance of

Table 3. Performance and carcass quality of the pigs, polyunsaturated fatty acid (C22:5 and C22:6) content of the pork fat and
organoleptic analysis of the meat samples. Means of 28 pigs per treatment are presented (Trial 1).

Treatment 1 2 3 4 SEM Statistical significance
of effect

L Q

Daily gain, g/d 860 879 877 883 14.49 NS NS
Feed conversion
efficiency, FU/kg 2.66 2.58 2.60 2.61 0.04 NS NS
Meat in carcass, % 50.1 50.7 50.1 49.8 0.44 NS NS
Fatty acids
(C22:5 and C22:6), % 0.23 0.53 0.88 1.46 0.02 *** NS
Organoleptic analysis'
Fresh 0.63 0.48 0.36 0.46 0.22 NS NS
7-8 months frozen 0.19 0.42 0.81 1.89 0.20 *** NS

SEM=Standard error ofmeans; significance: NS=non-significant; *** (PO.001).
L, Q=linear and quadratic effects offish meal.
1. o=no off-flavour, I=slight off-flavour, 2=medium off-flavour and 3=strong off-flavour.

23

Agric. Sei. Finl. 1 (1992)



the animals (Table 3). Daily gain, feed conversion
efficiency and carcass quality showed no sig-
nificant differences between treatments. The trial
confirms the earlier results ofBarber et al. (1981)
and Lyso (1979). The tendency to a slightly better
gain and feed conversion in fish meal groups could
be due to better amino acid profile of fish meal
compared to soya bean meal. This was also noticed
by Lyso (1979). The performance results of trial 2
are not presented, because they were not subjected
to statistical testing.

There were no statistical differences between the
treatments in the organoleptic analyses of fresh
meat in trial 1. However, the panel found some off-
flavour in individual meat samples of all treat-
ments, but it could not be connected to the fish
meal in the diet. In trial 2, no off-flavours were
found in fresh meat samples. Hvidsten and Astrup

(1963) and Agerhem et al. (1984) have shown a
tendency to off-flavours in the taste of fresh pork
when 9-12 %of fish meal has been included in the
diet.

The off-flavour in pork chops increased linearly
after 7-8 months of frozen storage in trial 1
(pO.001) (Fig. 1). In trial 2, the incidence of off-
flavours increased after 6 months of frozen storage
in groups where 5 or 10 % fish meal was included
in the diet (Fig. 3). This was also reported by
Hvidsten and Astrup (1963), Lyso (1979) and
Hertzman et al. (1988).

The organoleptic scores clearly correlated with

the content of fish oil in the feed in the study of
Kifer et al. (1971). In trial 1 this was true only
when meat samples stored frozen for 7 - 8 months
were tasted (r= 0.59).

The contents of C22:5 and C22:6 fatty acids in
pork fat increased linearly with increasing amount
offish meal (and fish oil or C22:5 and C22:6 fatty
acids) in the feed (Fig. 2) (pO.001). This was
previously observed in experiment published by
AGERHEMetaI. (1984).

Fish fat and especially long chain polyunsaturated
fatty acids C22:5 and C22:6 are highly digestible in
all animals. The apparent digestibility offish fat for
pig is over 90 % (Opstvedt 1984) and apparent
digestibility of C22:5 and C22:6 fatty acids in
chicken 95 % (Opstvedt 1973). Dietary fat is
converted more efficiently to body fat compared to
de novo fat synthesis from carbohydrates (Ber-
SCHAUER 1986). Dietary long chain fatty acids
are predominantly corporated to body fats and
medium chain fatty acids are largely oxidized by the
liver to C02, acetate and ketone bodies (Ber-
schauer 1986). The deposition of digested C22:5
fatty acid is 78.9 % and the deposition of C22:6 is
8.8 % for chicken, when the average deposition of
lipids is 26.2 % (Opstvedt 1973).

The content ofC22:5 and C22:6 fatty acids of the
total fatty acids increased also linearly with the level

Fig. I. Organoleptic scores of fresh and 7-8 months
frozen stored pork chop samples (trial 2).

Fig. 2. Polyunsaturated fatty acid (C22:5 and C22:6) content
ofpork fat (trial 1).

24

Agric. Sei. Finl. 1 (1992)



offish meal in the diet and with the length ofthe fish
meal feeding period in trial 2 (Fig. 3) (p<0.001).
Hertzman et. al. (1988) found also that the content
of C22:6 fatty acid in the pork fat increased linearly
with the length of the fish meal feeding period. In
trial 2, the content ofC22:5 and C22:6 fatty acids in
the carcass fat correlated positively with the fish oil
content of the feed (r=0.54) and with the length of

the fish meal feeding period (r=0.67).
In trial 2, the contents of C22:5 and C22:6

fractions of the total fatty acids were less than 0.5 %

in all pigs fed without fish meal or with 2 % offish
meal. At a 5 % fish meal level, the C22:5 and C22:6
content of samples was less than 0.5 % when fish
meal was withdrawn from the diet 5 or 7 weeks
before slaughter, at 10 % fish meal level 7 weeks

before slaughter. However, the organoleptic scores
of these groups were slightly decreased compared to
groups fed without or with 2 % offish meal.

In both trials, traces of C22:5 and C22:6 fatty
acids were found in carcass fat in the groups not fed
fish meal (0.11 and 0.32 %, respectively). It is
possible that they originate from pre- and post-
weaning feed of the animals which contained fish
meal. However, the results of the study reported by
Valaja (1991) showed that there were no
differences in C22:5 and C22:6 fatty acid contents of
pork fat in pigs fed with or without fish meal in the
pre- and postweaning period.

It seems possible to set recommendations for use
of fish meal concerning percentage in the feed as
well as the length of the withdrawal period. The
problem is the reasonably great variation between
individuals, which makes it difficult for slaugh-
terhouses or authorities to control the use of fish
meal. Further, it is not known which part of C22:5
and C22:6 fatty acids originates from meat meal and
meat and bone meal used, and how much long chain
polyunsaturated fatty acids the pig can produce from
other essential fatty acids.

In conclusion, standard quality fish meal con-
taining 8 - 10 % of crude fat can be added to the diet
of pigs up to 10 % without any risk of fishy taste in
the fresh meat. If the pork has to be stored frozen for
several months the risk of off-flavours increases
clearly. In all situations it is safe to restrict the fish
meal content of the diet to under 2 %. The diet of
feeder pigs up to 45 kg weight may contain fish meal
up to 5 % ifa withdrawal period is used.

References

Agerhem, H., Berg, H., Kölar, K. & Ohlander, I. 1984.
Sensoriska respektive kemiska egenskaper hos kött och
fett från svin utfodrade med foder innehållande olika
mängder fiskmjöl. R-160-3563. Köttforsknings Institu-
tet, Sweden.

Barber, R.S., Braude, R. & Mitchell, M. 1981. Copper
supplementation of isonitrogenous diets for growing
pigs containing white-fish meal or soya bean meal as the
protein supplement. Anim. Prod. 33: 81-86.

Barlow, S.M. & Pike, J.H. 1977. Die Bedeutung des Fettes

im Fischmehl in der Futterung von Schweinen und
Geflugel. Int. Assoc. Fish Meal Manuf. Tech. Bull. n:o 4.

Berschauer, F. 1986. Fats in diets for growing pigs. Pig
News and Information 7(2): 153-158.

Hertzman, C, Göransson, L. & Ruderus, H. 1988. In-
fluence offish meal, rape-seed and rape-seed meal in the
feed on the fatty acid composition and storage stability
of porcine body fat. Meat Science 23: 37-53.

Hvidsten, H. & Astrup, H. 1963. The effect ofvitamin E on
the keeping quality and flavour of pork. Acta Agric.

Fig. 3. Polyunsaturated fatty acid (C22:5 and C22:6) content
ofpork fat and organoleptic scores of 6 months frozen stored
pork chop samples (rating: 1-3, l=worst score; 3=best sco-
re) (trial 2).

25

Agric. Sei. Finl. 1(1992)



Scand. 13 (3): 259-270.
Kjfer, R.R., Smith, P. jr. & Young, E.P. 1971. Effect of

dietary fish oil on the fatty acid composition and paya-
bility of pork tissues. Biological Abstracts. 52 (21):
118655.

Lyso, A. 1979. Ulik forstyrke til purger og gaiter föret med
og uten sildemel og med og uten ekstra E-vitamintils-
kudd. Meld. Norges Landbrukshogskole. 58 (23): 1-17.

Opstvedt, J. 1973. Influence of residual lipids on nutritive
value offish meal. V. Digestion and deposition of ma-
rine fatty acids in chickens. Acta Agr. Scand 23: 218-
224.
1984. Fish Fats. In: Wiseman, J. (eds). Fats in animal
nutrition, p. 53-82. Wiseman, J. Butterworths, London.

Valaja, J. 1991. Kalajauho porsasrehussa ei nosta kalanras-
vahappopitoisuutta. Lihantuottaja 3: 28.

Manuscript received June 1991

Jarmo Valaja
Kaija Suomi
Timo Alaviuhkola
Agricultural Research Centre ofFinland
Swine Research Station
SF-05840 Hyvinkää, Finland

Irma Immonen
Agricultural Research Centre ofFinland
Swine Research Station
SF-05840 Hyvinkää, Finland
Present adress:
Kruununkatu 64
SF-05840 Hyvinkää, Finland

SELOSTUS

Kalajauhon vaikutus sianlihan makuun ja rasvahappokoostumukseen

Jarmo Valaja, Kaija Suomi, Timo Alaviuhkola ja Irma Immonen
Maatalouden tutkimuskeskus

Kaksiosaisessa tutkimuksessa selvitettiin dieetin erilaisten
kalajauhomäärien vaikutusta lihasikojen tuotantotuloksiin
sekä lihan rasvahappokoostumukseen ja makuun. Toisessa
osassa selvitettiin myös, kuinka kalajauhon poisjättäminen
rehusta eri aikoina ennen teurastusta vaikuttaa sian silavan
rasvahappokoostumukseen ja makuun. Ensimmäisessä ko-
keessa rehut sisälsivät kalajauhoa 0, 2.7, 6.5 ja 13.0%ja ko-
eryhmät saivat samaa rehuseosta koko kokeen ajan. Toises-
sa kokeessa rehuissa oli kalajauhoa 0,2, 5 ja 10 %. Osa ko-
eryhmistä sai kalajauhopitoista rehua koko kokeen ajan ja
osalla ryhmistä kalajauhon käyttö lopetettiin 7, 5 tai 3 viik-
koa ennen teurastusta.

Kokeissa ei havaittu merkitseviä eroja tuotantotuloksissa
eri ryhmien välillä. Rasvahappoanalyyseissä tutkittiin sila-
van kalarasvahappojen C22:5 ja C22:6 osuutta kokonaisras-
vahapoista. Ensimmäisessä kokeessa ko. rasvahappojen pi-
toisuus silavassa nousi suoraviivaisesti, kun rehun kala-
jauhopitoisuus nousi (p<0.001). Toisessa kokeessa silavan
C22:5-ja C22:6-rasvahappojen pitoisuus oli sitä alhaisempi

mitä aikaisemmin ennen teurastustakalajauhon käyttö lope-
tettiin. Kaksi prosenttia kalajauhoa saaneiden eläinten sila-
van C22:- ja C22:6-rasvahappopitoisuus ei ylittänyt 0.5 %

rajaa kokeessa 2.
Tuoreissa lihanäytteissä ei varsinaista kalanmakua esiin-

tynyt. Puolen vuoden tai 7-8 kuukauden pakastuksen jälkeen
lihan makuvirheet lisääntyivät, kun rehu sisälsi yli 5 % kala-
jauhoa. Mitä pidemmän aikaa eläimet saivat kalajauhoa sitä
selvemmin makuvirheet ilmenivät. Kahden prosentin kala-
jauhomäärä ei aiheuttanut kalanmakua lihaan pakastussäily-
tyksen jälkeen.

Johtopäätöksenä kokeista voidaan sanoa, että tuoreessa
sianlihassa ei ilmene kalanmakua, vaikka dieetissä on kala-
jauhoa jopa 10 %. Pakastuksen jälkeen kalajauhoa syönei-
den eläinten lihassa makuvirheiden määrä lisääntyi selvästi.
Kaikissa tilanteissa turvallista olisi käyttää kalajauhoa alle 2
% lihasikojen dieeteissä. Alle 45 kiloisten lihasikojen rehu
voi sisältää kalajauhoa 5 %, jos loppukasvatusrehu ei sisällä
kalajauhoa.

26

Agric. Sei. Finl. 1 (1992)