Effect of Dietary Omega-3 and Omega-6 Fatty Acids Sources on Milk Production and Composition of Holstein Cows in Early Lactation
The objective of this research was to determine the effect of feeding
fish oil, soybean oil, or their combination on milk fatty acid profiles,
especially omega-3, omega-6 and omega-3/omega-6 ratio. Milk was collected
from 20 primiparous Holstein cows that were distributed into four groups
and arranged in a completely randomized design with 35 days period to
determine the effect of feeding fish oil, soybean oil, or their combination
on milk production and composition. Experimental diets consisted of: 1)
control diet; 2) a diet with 3% (DM basis) added fat from menhaden fish
oil; 3) a diet with 3% added fat from soybean oil and 4) a diet with 1.5%
added fat from fish oil and 1.5% fat from soybean oil. Dry matter intake
(18.47, 18.87, 18.33 and 18.63 kg day-1, for control, fish
oil, soybean oil and combination diets, respectively) and milk production
(30.31, 32.15, 31.19 and 31.59 kg day-1) were higher for cows
that consumed 3% fish oil containing diet. Milk from cows fed control,
fish oil, soybean oil and fish oil with soybean oil diets contained 3.45,
2.72, 2.96 and 2.87% fat, respectively. Concentration of total omega-3
fatty acids (0.87, 1.28, 0.96 and 1.18 g/100 g of fatty acids) in milk
fat were higher for cows that consumed either fish oil-containing diet,
especially the 3% fish oil diet. The n-6:n-3 ratio (4.57, 2.62, 6.17 and
4.08) in milk fat was lower for fish oil diet. These results showed that
fish oil modifies fatty acids profile of milk fat and increased the proportion
of beneficial fatty acids for human health.
Positive human health effects caused by food components have been
recently recognized. Fat is the major energy component in milk and accounts
for many of the physical properties, manufacturing characteristics and
organoleptic qualities of milk and milk products (Bauman and Griinari,
2003). Milk fat, due to its relatively high proportion of myristic (C14:0)
and palmitic acids (C16:0), has been associated with human cardiovascular
health problems (Noakes et al., 1996). Increasing dietary concentrations
of unsaturated fatty acids decreases milk C14:0 and C16:0 levels (Palmquist
et al., 1993). Increasing specific unsaturated fatty acids such
as Conjugated Linoleic Acid (CLA), linoleic acid (C18:2), linolenic acid
(C18:3), ecosapentaenoic acid (C20:5) and docosahexaenoic acid (C22:6)
in milk would increase consumer interest and acceptance of milk due to
health benefits associated with these fatty acids (Bauman et al.,
1998; Ramaswamy et al., 2001; McGuire et al., 1997). The
fatty acid content of the lactation diet of the dairy cow has an effect
on the type and the proportion of the fatty acids that make up milk fat
(Grummer, 1991). Conjugated linoleic acid is derived in the rumen from
incomplete biohydrogenation of C18:2 (Harfoot and Hazelwood,
1988). Soybean oil is a good source of unsaturated fatty acids and contains
approximately 50% linoleic acid (NRC, 2001). Marine oils derived from
fish oil or algae are a rich source of omega-3 (EPA, DHA) fatty acids
(Kitessa et al., 2001). The objective of this research was to determine
the effect of feeding fish oil, soybean oil, or their combination on milk
fatty acid profiles, especially omega-3, omega-6 and omega-3/omega-6 ratio.
MATERIALS AND METHODS
Experimental design and data collection:
Twenty primiparous Holstein cows (47±11 DIM) were divided
into four groups and arranged in a completely randomized design with 35
days period. The first 2 week of period was used to allow cows to adjust
to the experimental diets and wk 3, 4 and 5 for data collection. Dietary
treatments consisted of either 0% supplemental fat (control diet; C),
the diet with 3% added Menhaden Fish Oil (FO), the diet with 3% added
fat from Soybean Oil (SO) and the diet with 1.5% added fish oil and 1.5%
added from soybean oil (FO+SO). Cows were housed in tie stall barn and
fed a Total Mixed Ration (TMR) four times daily at approximately 0800,
1000, 1400 and 1600 h in amounts to ensure 5% orts. Total mixed ration
(Table 1) were formulated to contain more than adequate amounts of major
nutrients (NRC, 2001). The TMR offered and orts were measured on a daily
basis during the sampling period. Samples were stored at -20°C until
analyzed. Feed and ort samples were dried in a forced-air oven at 60°C
for 48 h. The dry weights were used to determine feed intake. Subsamples
of feed and ort were dried at 105°C for 24 h to correct to 100% DM.
Feed samples were ground through a 1 mm screen. The TMR samples were composited
by week and analyzed for DM, CP, EE, ADF, NDF, Ca, Phosphorus and Mg (AOAC,
2000). Cows were milked three times daily at 0830, 1600 and 2400 h, with
individual milk weights recorded at each milking. Duplicate subsamples
of milk were collected at the regular milking over a 48 h period (six
consecutive milkings) in the last week of experiment. One set of samples
was stored at 4°C until analyzed for fat, protein, lactose, SNF and
total solids (Milk-O-Scan 133B Foss Electric Denmark). The
||Ingredient and nutrient content of Control (C), Fish
Oil (FO), Soybean Oil (SO) and fish oil with soybean oil (FO+SO) diets
|1Control = No supplemental fat; FO = 3% fish
oil; SO = 3% soybean oil; FO+SO = 1.5% fish oil + 1.5% soybean oil.
2Mineral and vitamin mix contained 0.8% Ca, 0.7% P, 0.8%
K, 0.4% Mg, 0.3% S, 1.4 mg kg-1 I, 100 mg kg-1
Mn, 100 mg kg-1 Zn, 0.3 mg kg-1 Co, 0.5 mg kg-1
Se, 99, 450 IU kg-1 of vitamin A, 13,260 IU kg-1
of vitamin D and 497 IU kg-1 of vitamin E, 3NFC
= Nonfiber carbohydrates, NFC = 100-(CP + NDF + EE + ash). 4Calculated
according to NRC (1989) values
second set of samples was frozen and kept at -20°C until analyzed
for fatty acids. Fatty acids analysis of milk, fish oil, soybean oil and
TMR samples were carried out using the preparation method of Sukhija and
Production variables were reduced to means for each treatment for
each cow before statistical analyses. Data were analyzed by least squares
ANOVA using the General Linear Models (GLM) procedure of SAS (1999). The
Yij = μ + Ti + eij
Where μ = overall population mean, Ti = effect of treatment
and eij = residual error term. The residual was used as the
error term to test for main effects of treatment The Duncan`s multiple
range test was used for comparing means. Significance was declared at
RESULTS AND DISCUSSION
Results regarding chemical composition of the four diets are shown
in Table 1. Total mixed diets were relatively similar
in NDF. The control diet contained 2.5% EE (DM basis) and the EE content
of the other diets was 5.4, 5.1 and 5.2% as a result of the addition of
soybean oil and fish oil to the diet. Consequently, the diets containing
supplemental fat had a higher NEL concentration (1.62 to 1.66
vs. 1.57 Mcal kg-1 for control diet). Fatty acid compositions
of TMR, fish oil and soybean oil are presented in Table 2.
The lipid of soybean oil contained the high concentration of linoleic
acid (53.2 g/100 g fatty acid).
Fish oil was characterized by its content of long chain (>C20) fatty
acids, being particularly rich in C20:5 n-3 (eicosapentaenoic acid, EPA)
and C22:6 n-3 (docosahexaenoic acid, DHA; 11.5 and 10.3 g/100 g of fatty
Milk yield, milk composition and DMI:
Milk production did not differ significantly (p = 0.94) between
cows fed supplemental fat and the control diet averaging 31.31±0.96
kg day-1 (Table 3).
This results is in agreement with the results of previous researches
in which no effect on production was observed when fish oil and soybean
oil were added to the diet (Cant et al., 1997; Whitlock et al.,
2002; Abughazaleh et al., 2002). Milk production appeared to be
higher when cows were fed fat than when they were fed the control diet.
Cows fed Fish Oil (FO) produced more milk (32.15 kg day-1)
than cows fed Soybean Oil
||Fatty acid composition of total mixed ration, fish oil
and soybean oil
|1Control = No supplemental fat; FO = 3% fish
oil; SO = Soybean oil; FO + SO = 1.5% fish oil + 1.5% soybean oil,
2Expressed as number of carbons:number of double bonds
||Milk yield, milk composition and DMI from cows fed control
(C), fish oil (FO), soybean oil (SO) and fish oil with soybean oil
|abMeans in the same row with different letters
differ (p<0.05). 1Control = No supplemental fat; FO
= 3% fish oil; SO = 3% soybean oil; FO+SO = 1.5% fish oil +1.5% soybean
oil. 2ECM = (0.327 *milk production (kg day-1))+(12.95
* fat yield (kg day-1))+(7.2 * protein yield (kg day-1).
3SCM = (12.3 * fat yield (kg day-1))+(6.56 *
SNF yield (kg day-1))-0.0752 * milk production (kg day-1))
(SO) (31.19 kg day-1). In contrast to milk production, energy-corrected
milk, FCM and SCM of cows fed diets containing supplemental fat were lower
than when cows were fed control diet. The lowered milk fat concentration
led to overall lower FCM, ECM and SCM yields for the three diets containing
supplemental fat, which would agree with Whitlock et al. (2002).
Milk fat percentages and yield were lowered (p<0.05) when cows were
fed diets with supplemental fat (2.85 vs. 3.45% and 0.9 vs. 1.05 kg day-1,
for cows fed the fat-supplemented and control diets, respectively). Cows
fed the soybean oil diet had a higher fat concentration (2.96%) and yield
(0.92 kg day-1) than cows fed the fish oil diet (2.72% and
0.87 kg day-1). This decrease in milk fat concentration and
yield has been reported before (Cant et al., 1997; Donovan et
al., 2000; Whitlock et al., 2002; Ramaswamy et al.,
2001). Abughazaleh et al. (2002) did not show a decrease in milk
fat percentage and yield of cows were consuming fish oil. Milk protein
concentration was lowered (p<0.05) when cows were fed diets with supplemental
fat (2.68 vs. 3.07%, for cows fed the fat supplemented and control diets,
respectively), but protein yield was similar among all treatments. Our
results would agree with Chilliard and Doreau (1997) and Cant et al.
(1997). In contrast, Ramaswamy et al. (2001) and Whitlock et
al. (2002) did not observe a decrease in protein concentration with
fish oil and soybean oil supplementations. There was no difference (p>0.05)
in lactose, total solid, SNF and Milk Urea Nitrogen (MUN) concentrations
and yields in the milks. Dry Matter Intake (DMI) was similar among all
treatments (p>0.05). In contrast, fish oil has shown to have a negative
effect on DMI (Donovan et al., 2000; Abughazaleh et al.,
2002; Whitlock et al., 2002).
Milk fatty acid composition:
Fatty acid composition of raw milks was altered when FO, FO+SO,
or SO was incorporated in the diets (Table 4). There
were no treatment effects on milk concentrations of short-chain fatty
acid, indicating a similar extent of de novo synthesis of these
fatty acids among treatments. Similar result was reported previously (Qiu
et al., 2004), but in other researches, fish oil or soybean oil
were reduced the proportion of short-chain fatty acids in milk fat
||Fatty acid composition of raw milk from cows fed Control
(C), Fish Oil (FO), fish oil with soybean oil (FO+SO), or Soybean
Oil (SO) diets
|a,b,cMeans within a row without common superscripts
differ (p<0.05). 1Control = No supplemental fat; FO
= 3% fish oil; SO = 3% soybean oil; FO+SO = 1.5% fish oil + 1.5% soybean
oil. 2Expressed as number of carbons:number of double bonds.
3Unidentifiable peaks. 4Short-chain fatty acids
(C10:0-C12:0). 5Medium-chain fatty acids (C14:0-C17:0).
6Long-chain fatty acids (>=C18:0). 7Total n-3
fatty acids: C18:3 (n-3), C20:5 (n-3), C22:6 (n-3)
(Donovan et al., 2000; Abughazaleh et al., 2002; Whitlock
et al., 2002; Ramaswamy et al., 2001; Cant et al.,
1997). The concentration of medium-chain fatty acid decreased (p<0.05)
when FO+SO or SO was incorporated in the diets. The proportion of C14:0
was lower (p<0.05) in milk from cows fed the fat containing diets,
but the concentration of C16:0 was lower in milk from cows fed FO+SO or
SO (specially in SO containing diet). This apparent reduction in de
novo synthesis of fatty acids (<=C16:0) in the mammary gland has been
reported with diets that increase the supply of long-chain fatty acid
(Grummer, 1991). The concentration of long-chain fatty acid was higher
(p<0.05) in SO and FO+SO milks compared with C and FO milks (Table
3). In this study, the FO milk had a higher concentration of long-chain
fatty acids compared with C milk. Similar results were reported in previous
studies (Abughazaleh et al., 2002; Ramaswamy et al., 2001;
Whitlock et al., 2002; Cant et al., 1997). The C18:0 fatty
acid content was reduced (p<0.05) in the FO milk and was highest (p<0.05)
in the SO milk. Feeding FO, SO, or their combination increased the proportion
of unsaturated FA and decreased saturated FA in milk fat. Similar results
were observed in previous studies (Donovan et al., 2000; Abughazaleh
et al., 2002; Whitlock et al., 2002; Ramaswamy et al.,
2001). In terms of human health, these alterations may represent an improvement
in the fatty acid profile of milk because medium-chain fatty acid and
saturated fatty acid have been reported to constitute the hypercholesterolemic
portion of milk fat (Ney, 1991). In this study, one isomer of CLA (trans-10,
cis-12 C18:2) was identified. The concentration of trans-10, cis-12 C18:2
in milk produced from the FO diet was higher than in milk produced from
the SO diet. Baer et al. (2001) also reported similar increase
in CLA (trans-10, cis-12 C18:2) concentration of milk from cows fed FO.
The concurrent decreases in milk fat concentration agreed with associations
by Baumgard et al. (2000) that trans-0, cis-2 C18:2 isomer is
partially responsible for the decrease in milk fat concentration and yield
observed when supplemental fat is fed. The concentration of total n-3
fatty acids increased (p<0.05) in the FO milk compared with the other
milks (Table 3). Omega-3 fatty acids consist of three
isomers, namely α-C18:3 (α and C22:6 (docosahexaenoic acid)
and have many health benefits including the ability to decrease cardiovascular
disease (Hirai et al., 1980) and rheumatoid arthritis (Kremer et
al., 1987). The α-C18:3 did not increase (p>0.05) in any of
the milks; however, the C20:5 and C22:6 increased (p<0.05) in FO and
FO+SO milks. Similar results were observed in previous researches (Ramaswamy
et al., 2001; Whitlock et al., 2002; Abughazaleh et
al., 2002). The magnitude of increased concentration of EPA and DHA
in milk fat was lower than the concentration of these fatty acids in the
diet. This low transfer efficiency has been attributed to both their biohydrogenation
in the rumen and their association with plasma lipoproteins which are
not desired substrates for mammary lipoprotein lipase (Mansbridge and
Blake, 1997). Another possibility for this low transfer efficiency is
that these fatty acids are preferentially partitioned towards other tissues
in the body (Ashes et al., 1992).
The addition of fish oil, soybean oil, or their combination to diets
of dairy cows influenced the composition of milk, especially the milk
fat composition. Milk produced from the fish oil diet had less fat and
protein than that produced from the other diets. Milk fatty acid composition
was altered due to the dietary fish oil, soybean oil, or their combination.
The concentration of n-3 fatty acids increased in fish oil milk compared
with control, soybean oil and fish oil with soybean oil milks. The concentration
of medium-chain fatty acids decreased in soybean oil and fish oil with
soybean oil milks compared with control and fish oil milks. Long-chain
fatty acid concentrations were higher in soybean oil and fish oil with
soybean oil milks compared with control and fish oil milks. Unsaturated
fatty acid concentrations increased in soybean oil and fish oil with soybean
oil milks compared with fish oil and control milks. The incorporation
of dietary unsaturated fats resulted in milk with improved nutritional
value and possible human health benefits.
The authors extend appreciation to the Shir-va-Dam Bonyad dairy
farm crew for care and feeding the animals and Khorak-e-Chineh for supplying
the menhaden fish oil and soybean oil.
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