The Professional Animal Scientist 20 (2004):461–469
Responses of Supplementary
Dry, Rumen-Inert Fat Sources in
Lactating Dairy Cow Diets
J. R. LOFTEN and S. G. CORNELIUS
Milk Specialties Company, Dundee, IL 60118
Various fat sources are used to in-
crease energy density of diets for lactat-
ing dairy cows. Greater energy density
should result in increased production re-
sponses if DMI is not decreased. Dry fat
products are generally believed to be ru-
men inert and have beneﬁcial physical
properties particularly for on-farm use.
Partially hydrogenated tallow (PHT)is
limited primarily by its greater melting
point, which reduces its digestibility and
subsequent energy value to the dairy
cow. Free fatty acids (FFA) and Ca salts
of fatty acids (CaSFA) now have a con-
siderable body of literature for compari-
son of effects when fed to lactating dairy
cows. Direct comparison studies re-
viewed, which included these two dry fat
sources, found primary differences be-
cause of increased DMI and palatability
when diets contained FFA. Increased
DMI and palatability have positive ef-
fects on energy balance, milk production,
BW change, and reproductive perfor-
mance with similar digestibility. Mode of
action for reduced DMI when using
CaSFA appears to be primarily due to
negative effects of gastro-intestinal motil-
ity, rumen function, and palatability. Re-
To whom correspondence should be ad-
duced DMI impacts the amount and du-
ration of negative energy balance in early
lactation, subsequent milk production
and reproduction, and economic value.
This review found that CaSFA, com-
pared with FFA, reduced DMI, milk pro-
tein percentage, and milk production
with more variability, but there was a
tendency for reduced milk fat percentage
and increased BW loss.
(Key Words: Free Fatty Acids, Cal-
cium Salts of Fatty Acids, Intake, Pro-
Fat is extensively used in the diets
of lactating dairy cows to increase en-
ergy density and milk production.
Use of various types of fats in a vari-
ety of forage-based diets was exten-
sively reviewed by Smith and Harris
(1992). The current review will con-
centrate on more recent studies with
dry, rumen-inert (i.e., not signiﬁ-
cantly changed in the rumen nor hav-
ing a signiﬁcant effect on rumen func-
tion) supplemental fat sources and re-
sultant responses in DMI, milk
production, milk components, and re-
Three main types of rumen-inert
fats currently used in lactating dairy
cow diets are: partially hydrogenated
tallows (PHT), Ca salts of fatty acids
(CaSFA), and hydrogenated free fatty
acids (FFA). These fat types were de-
veloped to be used in dry form to pro-
vide dairy producers with a more
functional physical product and to fa-
cilitate on-farm handling.
Review and Discussion
Types of Rumen-Inert Fats. Par-
tially hydrogenated tallows were the
ﬁrst generation of rumen-inert fats.
They are produced by hydrogenating
tallow or vegetable fats to increase
the melting point of the end product.
Tallow or vegetable fats may contain
as much as 85% unsaturated fatty
acids prior to biohydrogenation and
as little as 15% after the hydrogena-
tion process. The iodine value, an in-
dicator of the degree of unsaturation,
can vary from 14 to 31 (NRC, 2001).
Hydrogenation of tallow and vegeta-
ble fats reduces negative effects that
fatty acids have on rumen fermenta-
tion. However, the same process se-
verely reduces the digestibility of the
end product and its potential for
value in lactating dairy cow diets. El-
liott et al. (1994, 1999) found that re-
sistance to ruminal and small intesti-
nal lipolysis was a major factor con-
tributing to the poor digestibility of
highly saturated triglycerides con-
tained in hydrogenated tallow.
Calcium salts of fatty acids were
the second generation of rumen-inert
fats. Palm oil, soybean oil, and other
Loften and Cornelius462
fat sources are hydrolyzed and re-
acted with Ca to form salts, which in-
creases the end product melting
point. Fatty acids of Ca salts are sta-
ble in the rumen at pH >6.5 (Sukhija
and Palmquist, 1990). However, unsat-
urated fatty acids of CaSFA have been
found to be extensively hydrogenated
in the rumen by Wu and Palmquist
(1991), Ferlay et al. (1993), Enjalbert
et al. (1994), and Van Nevel and De-
meyer (1996). This indicated that dis-
sociation occurred when the pH
dropped below 6.5 after a meal or
when the pH was manipulated in
vitro. Wu and Palmquist (1991) ob-
served that up to 55% of CaSFA were,
in fact, biohydrogenated. Because
Hawke and Silcock (1969) found that
a free carboxyl group of fatty acids is
required for biohydrogenation to oc-
cur, CaSFA have to dissociate prior to
biohydrogenation. This indicated that
CaSFA may not be as rumen inert as
previously thought and may be dele-
terious to rumen fermentation and
possibly to DMI.
Free fatty acids were the third gen-
eration of rumen-inert fats. Rumen-in-
ert FFA are pre-hydrolyzed, mostly hy-
drogenated, and puriﬁed during man-
ufacturing. This form of rumen-inert
fat requires no further chemical modi-
ﬁcation by the cow prior to digestion.
Free fatty acids usually have a lesser
melting point than PHT or CaSFA
and have the tendency to be less solu-
ble in the rumen than fat supple-
ments high in unsaturated fatty
acids. Free fatty acids also have little
or no negative effects on ruminal fer-
mentation compared with fat sources
high in unsaturated fatty acids (Cha-
lupa et al., 1984; Chan et al., 1997).
They also have been shown to have
minimal or no negative effects on
DMI (Davis, 1990; Chilliard, 1993; Al-
Because of the known and accepted
negative effects of PHT on both di-
gestibility and milk production (El-
liott et al., 1994, 1999), the remain-
der of this review will concentrate on
direct comparisons of the other two
types of rumen-inert fats when used
in lactating dairy cow diets.
Effects of CaSFA and FFA Rumen-
Inert Fats on Milk Production and
Milk Components. Although rumen-
inert fats were fed in many studies,
only a few have directly compared
feeding CaSFA and FFA. Seven trials
where these two rumen inert fats
were directly compared are summa-
rized in Table 1. Earlier trials used few
cows to determine differences among
treatments. This might be why differ-
ences were not always found al-
though Grummer (1988) and Harvat-
ine and Allen (2002) did observe a sig-
niﬁcant (P<0.01 and 0.05) decrease in
milk protein response for CaSFA com-
pared with FFA. Weighting means by
number of cows for each study indi-
cated a trend toward greater daily
milk production, fat-corrected milk
(FCM) production, milk fat percent-
age, and milk protein percentage
when FFA were compared with
Effects of CaSFA and FFA Rumen-
Inert Fats on DMI, Fatty Acid Digest-
ibility, and BW Change. Studies di-
rectly testing differences between FFA
and CaSFA on DMI, fatty acid digest-
ibility, and BW changes are shown in
Table 2. Data indicated that there was
little difference in digestibility of FA
delivered by either CaSFA or FFA. The
most pronounced difference between
the two rumen-inert fats was effect
on DMI. In the two most recent stud-
ies conducted by Harvatine and Allen
(2002, 2003), a signiﬁcant (P<0.01
and 0.05) DMI depression occurred
when CaSFA were compared with
FFA. Data also showed that in ﬁve of
seven direct study comparisons, FFA
resulted in numerically greater DMI
Chilliard (1993) reviewed use of ru-
men-inert fats and saturated fats in
lactating cow diets (Table 3). Data
from this review are consistent with
data in Table 2 in that DMI was sig-
niﬁcantly (P<0.01) depressed by the
addition of CaSFA to lactating cow
diets. Saturated fats also resulted in
twice (P<0.01) the amount of 4%
FCM production than CaSFA com-
pared with controls. Milk fat percent-
age was unaffected, but milk protein
percentage was negatively affected, by
both saturated fats (P<0.05) and
CaSFA (P<0.01), but less with satu-
rated fats. Body weight change was
not signiﬁcantly affected by the addi-
tion of saturated fats or CaSFA, but
saturated fats had a numerical in-
crease, and CaSFA had a negative nu-
merical inﬂuence on BW change.
This trend might be expected, as DMI
was signiﬁcantly depressed (P<0.01)
with CaSFA in diets.
More recently, Allen (2000) exten-
sively reviewed effects of fat supple-
mentation on DMI (Table 4). Regres-
sion equations involving 24 studies,
where CaSFA were fed and compared
with controls, indicated that for every
1% of added CaSFA over the control,
a 2.5% DMI depression was found.
This ﬁnding is reiterated in the NRC
requirements (2001). Allen (2000)
also reported that in 11 of 24 compar-
isons, CaSFA signiﬁcantly depressed
DMI. Furthermore, 22 of 24 compari-
sons were numerically less in DMI
when CaSFA were added to diets. Al-
len also indicated that although en-
ergy utilization is more efﬁcient for di-
gested fat than digested carbohydrate,
addition of fat to the diet does not al-
ways result in increased net energy in-
take, especially when reduction in
DMI occurs. From these published
data (Table 2) and critical review pa-
pers (Chilliard, 1993; Allen, 2000), it
is evident that CaSFA in the diets of
lactating dairy cows, even at the low
level of 0.23 kg/d, often fed in ﬁeld
practice with commercial herds, can
signiﬁcantly depress DMI. Allen
(2000) also noted that no effect of
added fatty acids on DMI was ob-
served for hydrogenated fat in 21
comparisons (Table 4).
Based on these published journal ar-
ticles and critical reviews, DMI depres-
sion caused by the inclusion of
CaSFA in the diets of lactating dairy
cows is problematic. It is reasonable
to assume that if a nutritionist or a
dairy producer decided to replace
0.23 kg of corn or 0.45 Mcal of NE
with 0.23 kg of CaSFA or 1.085 Mcal
, the difference should be 1.085
−0.45 or 0.635 Mcal. However, when
Rumen Inert Fat Supplements 463
TABLE 1. Effects of feeding free fatty acids (FFA) and Ca salts of fatty acids (CaSFA) to lactating dairy cows on
milk production, 4% fat-corrected milk (FCM) production, and milk fat and protein percentages. Means are
differences between FFA and CaSFA (FFA −CaSFA).
Item Cows, no. Milk, kg/d FCM, kg/d Fat, % Protein, %
Grummer (1988) 4 −2.80 −2.30 0.24 0.18**
Schauff and Clark (1989) 4 −0.70 −0.80 −0.07 0.07
Schauff and Clark (1989) 6 −0.90 −1.20 −0.04 0.03
Wu et al. (1993) 24 1.27 1.09 0.02 0.04
Elliott et al. (1996) 5 1.49 2.77 0.19 0.16
Harvatine and Allen (2002) 32 −0.68 −0.41 0.04 0.05*
Harvatine and Allen (2003) 8 2.91 2.54 0.03 0.15
Weighted mean 83 0.22 0.31 0.04 0.04
*Difference within study cited (P<0.05).
**Difference within study cited (P<0.01).
a 2.5% reduction in DMI is factored
in, net effect is a reduction in total
intake. Assuming that a
cow is consuming 22.7 kg/d of DM
and that the diet contained 1.72
Mcal of NE
/kg of DM, total daily NE
intake would be 39 Mcal. If DMI is re-
duced by 2.5%, or 0.98 Mcal, adding
from CaSFA, or 0.635 Mcal,
still leaves a deﬁcit of 0.34 Mcal of
. This is consistent with Chilliard’s
(1993) review that a negative BW
change occurred when CaSFA were in-
TABLE 2. Effects of feeding free fatty acids (FFA) and Ca salts of fatty acids (CaSFA) to lactating dairy cows on
DMI, fatty acid (FA) digestibility, and BW changes. Means are differences between FFA and CaSFA (FFA −
Item Cows, no. DMI, kg/d FA digestibility, % BW change, kg/d
(1988) 4 0.00 −2.50 NA
Schauff and Clark (1989) 4 0.20 NA NA
Schauff and Clark (1989) 6 −0.90 NA NA
Palmquist (1991) 6 NA −0.80 NA
Wu et al. (1993) 24 1.41 −0.40 0.17
Elliott et al. (1996) 5 1.50 −8.00 NA
Harvatine and Allen (2002) 32 0.73** NA 0.31
Harvatine and Allen (2003) 8 1.35* NA −0.20
Weighted means 0.85 −1.65 0.17
Cows in mean, no. 83 39 64
Data corrected for one cow that had a low value as discussed in paper. Free FA and CaSFA comparison was made at 680 g of
daily intake of each fat source. Digestibilities were 87.4 and 84.9% for CaSFA and FFA, respectively.
NA = not available in paper.
*Difference within study cited (P<0.005).
**Difference within study cited (P<0.01).
cluded in the ration. Financial conse-
quences can be calculated with cur-
rent and localized data.
Mode of Action. Mode of action af-
fecting DMI depression from feeding
CaSFA to lactating cows has been
identiﬁed in three possible areas: pal-
atability and ruminal and gastro-intes-
tinal motility effects. Grummer et al.
(1990) determined palatability effects
of four different fat products (sodium
alginate-encapsulated dry tallow, tal-
low, FFA, and CaSFA) on two univer-
sity and two commercial dairy farms
involving 209 lactating dairy cows.
Different fat products were fed alone,
top-dressed on grain, or included in
the grain mix. In all cases, after 15
min of feeding, FFA were preferred
over CaSFA, whether using measure-
ments that were qualitative (scores of
0.33 vs 0.17 for fat fed alone or top-
dressed; intake scored on the basis of
0 = no intake, 1 = partial intake, or
2 = total intake) or quantitative (13.2
vs 8.2 for fat fed alone or fat mixed
Loften and Cornelius464
TABLE 3. Effects of Ca salts of fatty acids (CaSFA) and saturated fats
fed to lactating dairy cows on DMI, 4% fat-corrected milk (FCM), milk
fat and protein percentages, and BW change. Means are differences
between control and CaSFA or saturated fats (Chilliard, 1993).
Cows, DMI, 4% FCM, BW change,
Item no. kg/d kg/d Fat, % Protein, % kg/d
CaSFA 404 −0.70** 0.90* 0.05 −0.10** −0.032
Saturated fats 170 0.00 1.80** 0.05 −0.06* 0.055
*Difference among studies summarized (P<0.05).
**Difference among studies summarized (P<0.01).
with grain; weighbacks were used to
determine intake as a percentage of
amount offered that was consumed).
In addition, it was observed that
cows improved intake of three fat
products, but not of CaSFA, when a
7-d period was allowed for adapta-
tion. This observation was important
because it indicated a possible inhibi-
tory mechanism beyond palatability
or general adaptation that led to con-
tinued and prolonged DMI de-
A second possible mode of action
regarding DMI depression from use of
CaSFA is disruption of ruminal fer-
mentation because of unsaturated
fatty acid effects. Although CaSFA
were observed to be inert in the ru-
men in vitro (Sukhija and Palmquist,
1990), Wu and Palmquist (1991) ob-
served that unsaturated 18 carbon
fatty acids in CaSFA were 58% biohy-
drogenated in vivo (Table 5). The re-
searchers stated that biohydrogena-
tion could only occur after dissocia-
tion of the Ca salt. Hawke and
Silcock (1969) had similar ﬁndings
and concluded that a free carboxyl
group of the fatty acid was required
TABLE 4. Effects of Ca salts of fatty acids (CaSFA) and hydrogenated
fat on DMI, expressed as a percentage of DMI depression for each 1%
of added fat to the dietary DM above the control diet (Allen, 2000).
Item Means DMI, % reduction P
CaSFA 28 −2.52 <0.0001
Hydrogenated fat 29 −0.26 0.57
for biohydrogenation to proceed.
Consequently, CaSFA is not inert in
the rumen. Therefore, negative effects
of unsaturated fatty acids on rumen
fermentation are probable. Wu and
Palmquist (1991) also concluded that
the percentage biohydrogenation in-
creased as level of unsaturation in-
creased (Table 5). Negative effects of
unsaturated fatty acids on ﬁber diges-
tion and milk fat content are well rec-
ognized (NRC, 2001). However, be-
cause studies show only small differ-
ences in ﬁber digestion and milk fat
content when CaSFA are fed to lactat-
ing cows, this mode of action is prob-
ably not the major factor in DMI de-
pression. Interestingly, signiﬁcant bio-
hydrogenation of C18:1, C18:2, and
C18:3 fatty acids resulted in greater
levels of stearic acid reaching the duo-
denum regardless of whether the di-
etary source was CaSFA, oil seeds, or
forages. Ruminal action largely con-
verts these fatty acids to C18:0.
Applying non-ruminant fat digestion
principles to ruminants, particularly
when downgrading digestibility of
stearic vs palmitic or C18 unsaturated
fatty acid, is inappropriate and may
confuse this picture. Most recently,
Bauman et al. (2003) noted that di-
gestibility does not differ signiﬁcantly
between C16 and C18 saturated FA,
and is less for longer chain saturated
fatty acids as compared with polyun-
saturated fatty acids (PUFA). Those re-
searchers further noted that differ-
ences in digestibility among individ-
ual fatty acids contribute very little to
the extensive variation (∼60 to 90%)
in the digestibility of dietary lipids
and that the majority of this varia-
tion reﬂects differences among indi-
vidual experiments, differences in
diets, and to speciﬁc feed com-
The third possible mode of action
regarding DMI depression in cows fed
CaSFA is the effect on gastro-intesti-
nal motility. A number of experi-
ments, where 450 g/d of oils con-
taining higher levels of saturated FA
or unsaturated FA were abomasally in-
fused into lactating dairy cows, were
conducted by Drackley et al. (1992),
Christensen et al. (1994), and Brem-
mer et al. (1998) (Table 6). These data
show an average DMI depression of
8% from abomasally infusing PUFA
into lactating dairy cows. Reviews of
Chilliard (1993) and Allen (2000) esti-
mated a reduction of only 3.5 to
5.0% at this level of DMI. But all of
these researchers, except Chilliard
(1993), also concluded that DMI de-
pression and subsequent drop in total
energy intake were greater than the
energy value of infused PUFA. These
three studies illustrated the most
likely, primary mode of action affect-
ing DMI depression when feeding
CaSFA. As the level of PUFA ﬂow in-
creases into the small intestine, there
appears to be a mechanism that trig-
gers the satiety center to reduce DMI.
Woltman et al. (1995) found that du-
odenal infusion of oleic acid in rats
reduced feed intake and that a por-
tion of the effect was mediated
through a gut hormone, cholecystoki-
nin (CCK). Choi and Palmquist
(1996) observed that feeding increas-
ing levels of CaSFA to lactating dairy
cows decreased DMI linearly and in-
creased concentrations of CCK. Data
Rumen Inert Fat Supplements 465
TABLE 5. Biohydrogenation percentage of unsaturated fatty acids in
the rumen of cows fed Ca salts of fatty acids (CaSFA) at 3% of the
dietary DM (Wu and Palmquist, 1991).
Item 0% CaSFA added 3% CaSFA added
C18:1 44.3 47.1
C18:2 72.9 67.3
C18:3 89.7 81.0
Total C18 67.3 58.3
adapted from that study are pre-
sented in Table 7. Those researchers
concluded that feeding increased
amounts of dietary fat (CaSFA) lin-
early, decreased feed and energy in-
takes, and linearly increased plasma
CCK and pancreatic polypeptide con-
centrations in lactating cows. They
suggested that decreased feed intake
in cows fed CaSFA was mediated by
increased plasma CCK and pancreatic
polypeptide concentrations. Interest-
ingly, even though DMI and NE
take decreased, milk production and
4% FCM production increased. Logi-
cal reason for the increase in produc-
tion would have been from mobiliza-
tion of body fat stores. This is sup-
ported by data from Chilliard’s
review (1993), indicating an average
BW loss of 34 g/d per cow for trials
with CaSFA (an average from 7 trials
with 404 early lactation cows that
had reduced DMI of 0.7 kg daily with
0.9 kg more daily milk production
compared with non-fat control diets)
TABLE 6. Effects of abomasally infusing daily into lactating dairy cows 450 g of either polyunsaturated (PUFA)
or saturated fatty acids (SFA) on DMI, total fatty acid digestibility percentage (TFADIG%), and DE intake (DEI).
DMI, kg/d TFADIG % DEI, Mcal/d
Item no. Control SFA PUFA Control SFA PUFA Control SFA PUFA
Drackley et al. (1992)
4 24.5* 25.1* 22.4* 69.60 70.50 77.80 66.50* 72.10* 63.90*
Christensen et al. (1994)
5 22.9 21.3 20.2 81.00 76.90 76.00 67.10* 68.70* 62.00*
Bremmer et al. (1998) 6 22.8
73.00 75.20 78.20 65.30
Weighted means 15 23.3 22.4 20.7 74.76 74.51 77.36 66.22 66.61 60.07
DMI linear contrast (P<0.02); DEI linear contrast (P<0.01).
DEI orthogonal contrast of SFA vs PUFA (P<0.05).
Means with different superscripts within DMI or DEI differ (P<0.05).
vs an average BW gain of 55 g/d per
cow for trials with saturated fats (an
average from 7 trials with 170 early
lactation cows that had no reduction
in DMI with 1.8 kg more daily milk
production compared with non-fat
control diets). The study of Choi and
Palmquist (1996) clearly indicated a
physiological mechanism associated
with DMI reduction because of
CaSFA addition to lactating dairy cow
diets and is in agreement with Allen’s
(2000) review. Drackley et al. (1992)
also suggested that degree of unsatura-
tion of fatty acids reaching the small
intestine of dairy cows could affect
gastro-intestinal motility and reduce
Given that DMI depression experi-
enced when CaSFA are fed is well doc-
umented, the dilemma becomes how
to meet early lactation, high produc-
ing dairy cows’ energy requirements
for milk production, reproduction,
and BW gain. A recent review (Grum-
mer and Rastanti, 2003) summarized
time required after calving for lactat-
ing cows to reach positive energy bal-
ance and concluded that total energy
intake was the key factor. Energy in-
take was even more highly correlated
than FCM production with days post-
calving before cows reached positive
energy balance. Energy intake is the
product of energy density in the diet
and DMI. If an increase in energy
density is accompanied by a reduc-
tion in DMI, the level of energy in-
take is limited, which in turn limits
the return to positive energy balance
and or reduces production response.
Effects of Rumen-Inert Fats on Re-
production. Inﬂuence of rumen-inert
fat supplements on reproduction is
not well understood and is a current
topic among nutritionists, reproduc-
tive physiologists, and veterinarians.
Research when feeding FFA (Ferguson
et al., 1990) and CaSFA (Sklan et al.,
1991) showed signiﬁcant positive ef-
fects on services per conception, preg-
nancy rates, and days open. However,
others have observed a combination
of negative results, positive results,
and some contradictory results (Sklan
et al., 1994; Moallem et al., 1997; Gar-
cia-Bojalil et al., 1998; and Moallem
et al., 1999). A review of nine studies
with 701 cows (Table 8) found very
few signiﬁcant differences caused by
high variability in data. Thus, repro-
ductive parameters require more ob-
servations to make meaningful statisti-
cal comparisons. These data indicated
few signiﬁcant differences (P<0.05) be-
Loften and Cornelius466
TABLE 7. Effects of Ca salts of fatty acids (CaSFA) on DMI, milk
production, 4% fat-corrected milk (FCM) production, and milk fat and
protein percentages of lactating dairy cows (Choi and Palmquist,
CaSFA in DMI
DMI, kg/d 23.9 21.7 20.3 19.8
, MJ/d 152 153 142 139
Milk, kg/d 31.9 32.2 32.5 29.9
4% FCM, kg/d 28.5 29.5 29.6 26.8
Milk fat, % 3.30 3.15 3.34 3.41
Milk protein, % 3.10 2.97 2.96 2.99
tween treatments for either ﬁrst-ser-
vice conception rate or pregnancy
rate. Slight improvement in ﬁrst-ser-
vice conception rate appeared from
CaSFA treatments, but a larger numer-
ical reduction was noted in overall
pregnancy rate when CaSFA were
added to diets of high producing
early lactation cows in these studies.
There are fewer published studies re-
garding the effects of added FFA to
control diets on reproductive measure-
ments. Ferguson et al. (1990) com-
pared FFA added at 500 g/d to con-
trol diets fed in three Pennsylvania
TABLE 8. Effects of Ca salts of fatty acids (CaSFA) in diets compared with controls on ﬁrst-service conception
rate and pregnancy rate of lactating dairy cows.
First service First service Control CaSFA
Cows, conception conception pregnancy pregnancy
Item no. rate, % rate, % rate, % rate, %
Schneider et al. (1988) 108 43 60 NA
Sklan et al. (1989) 108 28 44 NA NA
Carroll et al. (1990) 46 33 75 57 30
Sklan et al. (1991) 126 42 39 82 62*
Holter et al. (1992) 58 35 44 83 79
Lucy et al. (1992) 40 44 12* NA NA
Sklan et al. (1994) 122 55 33* 75 61
Moallem et al. (1997) 48 45 45 82 73
Garcia-Bojalil et al. (1998) 45 33 46 52 86*
Weighted means 41 44 75 64
NA = not available in paper.
*Difference within study cited (P<0.05).
herds and one Israeli herd (Table 9).
Researchers generally concluded that
FFA addition to diets beneﬁted repro-
duction by minimizing BW loss and
hastening BW gain postpartum. Both
of these effects have been shown to
beneﬁt conception rate (Butler et al.,
1981; Lopez-Gatius et al., 2003).
Most recently, Frajblat and Butler
(2003) reported reproductive re-
sponses when 81 dry cows were fed
daily either 200 g FFA or no FFA dur-
ing the last 21 d of the dry period
(i.e., close-up cows). Cows were bred
beginning at d 55 postpartum and
were bred by signs of behavioral es-
trus until d 220 postpartum (Table
10). Frajblat and Butler (2003) ob-
served close-up cows receiving 200 g/
d of FFA had greater (P<0.05) preg-
nancy and conception rates and
fewer (P<0.05) days open. Addition-
ally, cows exhibiting their ﬁrst ovula-
tion at less than 50 d postpartum
were observed to be nearly twice as
likely to become pregnant prior to
220 d postpartum than cows having
their ﬁrst ovulation at >50 d postpar-
tum. Frajblat and Butler (2003) also
observed that cows fed 200 g/d FFA
in the close-up period, and that had
an ovulation prior to 50 d postpar-
tum, were even more likely to be
pregnant at 220 d postpartum. Fur-
thermore, cows losing less body con-
dition score in early lactation were ob-
served to have more ovulations prior
to 50 d in milk (Table 11). These re-
sults are the ﬁrst to show a beneﬁt
when fat was fed to dry cows. A possi-
ble mechanism for this response may
be derived from work of Moallem et
al. (1999), who observed that oleic
and linoleic unsaturated fatty acids
were found in lesser concentrations
in nonesteriﬁed fatty acid fraction of
follicular ﬂuid in estradiol-active vs es-
tradiol-inactive or estradiol-less active
follicles. Estradiol-active or -inactive
Rumen Inert Fat Supplements 467
TABLE 9. Effects of mostly saturated dietary free fatty acids (FFA) in
diets on reproductive parameters of lactating dairy cows and body
weight (BW) change per intervals of days in milk (DIM) (Ferguson et
500 g/d of
Item Control FFA P
Cows, no. 138 115
Pregnant cows, no. 119 107
Services/conception, pregnant cows 1.91 1.59 <0.05
Services/conception, all cows 1.96 1.57 <0.05
First service conception rate, % 42.6 59.1 <0.005
Overall conception rate, % 40.7 59.3 <0.005
Overall pregnancy rate, % 86.2 93.0 <0.08
Days open 96.2 91.9 >0.10
BW change, kg/DIM
30 to 59 d −30.3 −24.8
60 to 89 d −16.0 −9.5
90 to 150 d +7.3 +20.1
TABLE 10. Effects of prepartum free fatty acids (FFA) fed to dry cows
during last 3 wk of gestation on reproductive measures (Frajblat and
Item No FFA of FFA
Pregnancy rate, % 58* 86*
Days open 141* 110*
Conception rate, % 26* 40*
*Difference between treatments (P<0.05).
follicles were determined by follicular
size. A signiﬁcant negative correlation
coefﬁcient between these two unsatu-
rated fatty acids and the estradiol con-
centration in follicular ﬂuid suggested
that preovulatory growth was accom-
panied by a decrease in these two un-
TABLE 11. Effects of free fatty acids (FFA) fed to prepartum cows on
early ovulation and pregnancy rates during subsequent lactation
(Frajblat and Butler, 2003).
Observed cows pregnant Cows pregnant and with
and with ﬁrst ovulation ﬁrst ovulation <50 d
Item <50 d postpartum, no. postpartum, % P
Control 14 of 21 66.6
200 g/d of FFA 23 of 23 100 <0.05
saturated fatty acids and an increase
in the proportion of the saturated pal-
mitic FA. The saturated stearic fatty
acid was numerically elevated by
nearly 14% at the same time in non-
esteriﬁed fatty acid fraction of follicu-
lar ﬂuid of estradiol-active follicles vs
the -inactive or -less active follicles.
Stearic acid in the phospholipid frac-
tion of follicular ﬂuid of estradiol-ac-
tive follicles was signiﬁcantly greater
(P<0.05) than the less active or inac-
tive follicles (26.4% vs 23.6% of phos-
pholipids). Free fatty acids fed in this
study contained 47% stearic acid,
37% palmitic acid, and only 15%
oleic acid. This research may explain
why CaSFA, which are greater in oleic
and linoleic fatty acids compared
with FFA, have more variable results
in reproductive trials. Another poten-
tial factor is the Grummer and Ras-
tanti (2003). In their study, NE
take is more highly correlated (r =
0.58, P<0.0001) with time required
to reach energy balance; thus, cows
may be in negative energy balance
longer and lose more body condition
when fed CaSFA because of DMI de-
pression. Frajblat and Butler (2003)
concluded that cows losing less body
condition had more ovulations prior
to 50 d in milk and cows with an
ovulation before 50 d in milk were
2.4 times more likely to become preg-
nant before 220 d in milk.
Dry fat products are thought to be
rumen inert and have beneﬁcial phys-
ical properties for on-farm use. Par-
tially hydrogenated tallow is limited
primarily by its greater melting point,
which reduces its digestibility and
subsequent energy value. Free fatty
acids and CaSFA now have a consider-
able body of literature for comparison
of effects when fed to lactating dairy
cows. Direct comparison studies of
these two dry fat sources found pri-
mary differences caused by greater
DMI and palatability when rations
contained FFA. This has correspond-
ing positive effects on energy balance,
milk production, BW change, and re-
productive performance with similar
digestibility. Mode of action for re-
duced DMI when using CaSFA ap-
pears primarily caused by negative ef-
fects of gastro-intestinal motility, ru-
men function, and palatability.
Reduced DMI impacts amount and
Loften and Cornelius468
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