Download 1 Interpretive Summaries FAT EFFECTS ON FEED INTAKE Michael

Interpretive Summaries
FAT EFFECTS ON FEED INTAKE
Michael S. Allen, Michigan State University
Fat sources are often added to diets of dairy cows with the goal of increasing energy intake to increase
milk yield or energy balance. However, fat addition has had inconsistent effects on feed intake of dairy cows,
partly because of differences in fat sources and the amount of fat included in the diet. Feed intake is often
decreased and rarely increased by dietary fat. In several experiments the depression in feed intake by dietary fat
more than offset the increased energy density of the diet resulting in decreased energy intake. The mechanism
by which dietary fat affects feed intake is complex and likely involves effects of fatty acids (FA) on gut
peptides and pancreatic hormones, and direct and indirect effects on the hepatic oxidation of fuels.
Mechanisms by which fat affects feed intake have been studied by both dietary inclusion and abomasal
infusion of fats. The extent of intake depression by dietary fat is related to unsaturated FA concentration, and is
greater for free FA compared to triglycerides. Cholecystokinin (CCK) is a gut peptide that has potent effects on
satiety and is consistently increased as feed intake is decreased by dietary addition of unsaturated FA.
Abomasal infusion of unsaturated FA have failed to increase plasma CCK concentration, but abomasal infusion
eliminates the cephalic phase responses which may be responsible for release of CCK. Other gut peptides are
likely involved in the mechanism: abomasal infusion of more unsaturated FA decreased intake and increased
glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP). Both GLP-1 and GIP
affect pancreatic hormone release, increasing insulin secretion (GLP-1 and GIP) and decreasing glucagon
secretion (GLP-1). In addition, dietary fat (both saturated and mostly unsaturated) tended to suppress the peak
of the “hunger” hormone ghrelin at conditioned meals in lactating cows.
The Hepatic Oxidation Theory of feed intake control might also explain feed intake response to fat
sources. The theory is based on the premise that the liver is connected to brain satiety centers via the hepatic
vagus and that feeding behavior is controlled by the oxidation of fuels in the liver; increased oxidation results in
a satiety signal decreasing meal size, and decreased oxidation results in a hunger signal causing an eating
response. Unsaturated FA are more likely to be oxidized while saturated FA are more likely to be stored,
consistent with greater hypophagic effects of unsaturated compared to saturated fats. Gut peptide responses
likely affect hepatic oxidation through their effects on pancreatic hormones. In addition, CCK may directly
affect the firing rate of the hepatic vagus. Effects of fat supplementation on milk energy output and energy
partitioning likely affects feed intake indirectly by altering hepatic oxidation of fuels.
While dietary fat supplementation can decrease feed and even energy intake, fat addition sometimes
increases milk yield, energy balance, efficiency of feed utilization and reproductive performance. Therefore, a
better understanding of the role of FA on control of feed intake is important to formulate diets to improve
profitability of dairy farms.
Allen, Michael S., Department of Animal Science, 2265G Anthony Hall, Michigan State University, East
Lansing, MI 48824-1225, Tel: (517) 432-1386, email: [email protected]
1
Molecular opportunities in lipid metabolism.
Ransom L. Baldwin, VI
Bovine Functional Genomics Laboratory, USDA ARS Beltsville 20705
The role of adipose tissue in dairy cattle is multifaceted and related to productive function (reproduction,
milk secretion, growth) in general. The hallmark of the high genetic merit dairy cow for milk production is her
ability to sustain high levels of milk production while in negative energy balance, largely facilitated by the
mobilization of body stores of energy in the adipose tissues. Analysis in vivo and in vitro, of lipolytic and
lipogenic enzyme systems through late pregnancy and early lactation has clearly demonstrated patterns of
expression related to energy balance in the cow. In fact, adipose tissue lipolysis rates in vitro in early lactating
dairy cow exhibit increased sensitivity to lypolytic stimuli compared to the adipose from the late pregnant cow.
Moreover, it is reasonably well established that cattle with high genetic merit have a greater capacity to
mobilize body stores of energy from the adipose tissue due to increased Hormone Sensitive Lipase (HSL)
activity and further increased sensitivity to lypolytic stimuli. Demonstration of a gene expression basis for the
increased HSL activity has recently been reported, along with a co-lipase, perilipin following the onset of
lactation. Likewise, the expression of 3 sub-types of beta-adrenergic receptors has been demonstrated to
increase with the onset of lactation and mirror energy balance in dairy cattle.
In ruminants acetate contributes the vast majority of the carbon for de novo fatty acid synthesis, with
minor contributions coming from glucose. However, we have recently demonstrated that small intestinal
infusion of glucose increased adiposity in steers compared with those receiving isoenergetic infusion of ruminal
starch hydrolysate. The observed glucose-induced increase in adiposity was not explained by increased
incorporation of glucose carbon into fatty acids, suggesting that glucose may stimulate lipogensis in adipose
tissue in a manner similar to that described for monogastric species. Differential expression of lipogenic
regulatory genes in adipose depots of the bovine were demonstrated with respect to depot as well as form and
site of energy digestion. Moreover, expression of putative transcription factor genes in the visceral adipose
depots was responsive to alterations in energy intake, in addition to site and physical form of carbohydrate
delivered. A clear positive relationship between the regulatory element binding proteins described in nonruminants and lipogenic enzymes was not established indicating a need for further gene discovery.
Thus, taken in concert, it is obvious that there are molecular opportunities to modify lipid metabolism in
ruminants as there is apparent variation in the genetic elements responsible for the lipogenesis and lipolysis that
ultimately result in mobilization or accretion of tissue. Moreover, these processes are affected by factors such
as nutrient supply and exhibit depot specific adaptations. Finally, with the recent increase in the use of
microarray approaches to understanding lipid metabolism in dairy cattle, the opportunities for finding future
candidate genes of interest is similarly increasing. Continued improvement in genetic selection of tomorrows
dairy cattle will require and comprehensive understanding of the underlying physiology, endocrinology, and
metabolism in order to realize the full potential of marker assisted selection strategies.
Dr. Randy Baldwin, Research Animal Scientist, USDA-ARS, Room 214, 10300 BALTIMORE AVENUE, BLDG 162 BARC-EAST, Beltsville,
MD, 20705, PH: (301) 504-8964, FX: (301) 504-8744, EM: [email protected]
2
Mammary Metabolism and the Biology of Milk Fat Synthesis
D. E. Bauman and K. J. Harvatine
Cornell University, Ithaca, NY 14853
Fat is the most variable milk component and is responsible for many of the physical properties, manufacturing
characteristics and organoleptic qualities of milk. Milk fat is comprised of fatty acids (FA) that differ in chain
length and double bonds (number, location and geometric orientation) and they are mainly esterified in
triglycerides. Milk FA originate about equally from two sources – 1) de novo synthesis in the mammary gland
from acetate and to a lesser extent B-hydroxybutyrate and 2) mammary uptake of circulating FA that arise from
intestinal absorption or mobilization from body fat reserves. Many physiological and environmental factors
affect the fat content of milk with nutrition being especially important. Understanding the effects of nutrition
on the yield and composition of milk fat is of commercial importance and most of our knowledge of the
regulation of milk fat has come from investigations of diet-induced milk fat depression (MFD). While many
theories have been proposed to explain MFD since it was first observed over a century ago, only the
biohydrogenation theory has strong support today. This theory proposes that diet-induced MFD is caused by an
inhibition of mammary synthesis of milk fat by unique FA intermediates of ruminal biohydrogenation. Thus,
MFD involves an interaction between rumen digestive processes and mammary synthesis of milk. To date,
three isomers of conjugated linoleic acid (CLA) have been identified as potent inhibitors of milk fat synthesis,
but accounting comparisons suggest that other unique biohydrogenation intermediates with inhibitory ability
must exist. Of the inhibitory CLA isomers, trans-10, cis-12 CLA has been most extensively investigated; dose
response relationships have been established and the biological effects for CLA-induced MFD and diet-induced
MFD are similar. During MFD transcription of key mammary lipogenic genes are coordinately downregulated. Our investigations have established that the SREBP transcription factor family is involved, and
mammary expression of SREBP1 and SREBP-activation proteins are down-regulated during MFD. Most
importantly, key lipogenic enzymes are transcriptionally regulated via SREBP1. Collectively, these results
provide strong evidence for SREBP1 as a central signalling pathway in the regulation of mammary FA
synthesis. Spot 14 is also down-regulated during MFD, consistent with a role for this novel nuclear protein,
possibly as a lipogenic factor. Overall, the last decade has seen a remarkable advancement in our understanding
of the biology and regulation of milk fat synthesis; however, important questions still remain and some of these
will be highlighted in this and related presentations.
Dr. Dale E Bauman, Liberty Hyde Bailey Professor, Cornell University, Department of Animal Science, 262 Morrison Hall, Ithaca NY 14853-4801,
PH: 607-255-2262, FX: 607-255-9829, EM: [email protected]
3
Liver Lipid Metabolism and Animal Performance
James K. Drackley, University of Illinois at Urbana-Champaign
The liver is central to coordination of metabolism and plays an important role in regulating lipid metabolism in
dairy cows. In normal physiology, the liver uses some nonesterified fatty acids (NEFA) as a fuel source, and
can process NEFA to the ketone bodies that serve as alternative water-soluble fuels to spare glucose. A small
amount of NEFA are converted to triglycerides (TG) and exported out of the liver in the form of very-lowdensity lipoproteins (VLDL), although the capacity for this process is limited in ruminants compared with many
other species.
During negative energy balance, at the start of lactation for example, adipose tissue releases large quantities of
NEFA. The mammary gland can take up NEFA directly and make milk fat, but a large proportion of the NEFA
in blood are taken up by the liver. The liver produces ketones at a greater rate, and also accumulates TG. When
feed intake is limiting, glucose supply may be strained and cows can develop ketosis and fatty liver. Both
syndromes are associated with greater susceptibility to other disorders and diseases, decreased reproductive
performance, decreased productivity, increased veterinary treatments, greater culling, and even death loss.
We have learned much about the physiological and biochemical control of fatty acid metabolism in the liver of
dairy cows over the last 30 years. Clearly a major target for control of lipid-related disorders is in modulating
the breakdown of body fat. Nutrition before calving is important in this regard, as is environmental and stress
management. Pharmacological approaches also may have merit for problem situations. Another target for
regulation is the liver’s processing of fatty acids. A number of manipulations (diet, feed additives,
pharmacological) can shift the partitioning of fatty acids to oxidation or TG synthesis. Evaluation of the “big
picture” of doing one versus the other remains unclear.
Recent studies have begun to unravel the nature of individual animal variability in liver metabolism, and the
potential association with genotype. In the future, efforts to use marker or genome-assisted selection must be
combined with assessment of nutritional or management requirements of altered genotypes. We eventually may
be able to tailor nutrition programs for particular genotypes to enhance productive responses or prevent adverse
responses.
While much of the lipid metabolism by the liver is “normal” in the sense that it contributes to homeostasis in the
cow, under extreme conditions these metabolic adaptations become detrimental. Potential factors contributing
to cell damage and eventual loss of function are being uncovered in current research. Continued emphasis on
liver metabolism of lipids will be important to continued improvements in economic efficiency and animal
well-being.
James K. Drackley. Address: University of Illinois, Department of Animal Sciences, 1207 W. Gregory Dr.,
Urbana, IL 61801. Tel: (217) 244-3157. email: [email protected]
4
AN OVERVIEW OF FATTY ACID BIOTRANSFORMATIONS IN THE RUMEN
Tom Jenkins
Department of Animal & Veterinary Sciences
Clemson University
Clemson, South Carolina
Lipid reaching the intestines of ruminant species is similar in quantity but dramatically different in
structure compared with lipid consumed. Dietary lipid consists mainly of polyunsaturated fatty acids esterified
as triaclyglycerols in cereal grains and galactolipids in forages. Upon entering the reticulo-rumen, dietary lipid
is hydrolyzed releasing free fatty acids that are then susceptible to structural rearrangement via enzymes of
microbial origin. Rearrangements result from the action of isomerases that shift double bond location to
conjugated positions and alter geometrical orientation from cis to trans. Other reactions include hydration and
oxidation that yield hydroxy and keto fatty acyl derivatives, and hydrogenation reactions that eliminate double
bonds. Ruminal losses of linoleic and linolenic acids averaged 82 and 86% of intake, respectively across a
duodenal flow dataset compiled from 25 published studies that provided up to 93 observations. True ruminal
loss of oleic acid, after accounting for the metabolic fraction, is similar to linolenic acid (86%). The
intermediates of biohydrogenation include a variety of trans 18:1 and conjugated linoleic acid (CLA) isomers.
As many as 16 CLA isomers have been identified in ruminal contents taken from cattle, and several of these
were shown to have potent physiological effects in both the host animal and in humans consuming animal
products. Yet, most published pathways of biohydrogenation account for the synthesis of only one or two CLA
isomers. The ability to regulate CLA synthesis in ruminal contents to deliver specific isomers with specific
physiological functions to animal tissues is dependent on delineating the exact synthetic pathways for all
isomers. Production and proportion of CLA isomers are influenced by pH and fatty acid concentrations in
ruminal contents. Research to identify transformation intermediates and their regulation, especially for the
omega-3 fatty acids, continues to be a priority.
Dr. Tom Jenkins, Professor, Clemson University, 145 Poole Agricultural Center, Clemson, SC 29634, PH: 864-656-2707, FX: 864-656-3131, EM:
[email protected]
5
Key Issues Related to Lipid Analysis Jana Kraft, Courtney P. Preseault, Adam L. Lock Department of Animal Science, University of Vermont Lipid analysts define the term lipids as fatty acids, their derivatives, and substances related biosynthetically or functionally to these compounds. In recent years, analysis of lipids in livestock science has gained importance because characterization of feedstuffs, fats, oils, and animal‐derived products is required for improved understanding of their nutritional implications. In addition, there is an increasing need for a comprehensive database which can be utilized for livestock management/performance and nutritional modeling. Classical lipid analysis starts with the extraction of lipids. The fat content of the sample is determined gravimetrically (ether extract), fatty acid composition after formation of methyl esters, commonly through base‐ or acid‐catalyzed transesterification, is identified and quantified by gas‐liquid chromatography (GLC). The ether extraction method is unspecific especially for feedstuffs, such as forages, because all components of low polarity extracted, which are of nonnutritive value, are quantified as fat. Recently developed methods, however, determine both fatty acid quantity and composition of feedstuffs in one single analysis. This in situ procedure avoids a separate lipid extraction and fatty acids are simultaneously extracted and transesterified. Modern requirements for characterizing lipids call for highly efficient separations offered by capillary GLC columns. A properly chosen column provides accurate information about complex lipid samples. For routine analysis, short capillary columns (25m, 30m) with Carbowax‐type stationary phases are recommended. More polar longer columns (100m, 200m) are essential in research to effectively resolve isomeric unsaturated fatty acids. These specific columns though require much longer analysis times and are particularly sensitive to physical handling and temperature extremes. Milk fat is one of the most complex naturally‐occurring fat which results in considerable analytical challenges. Although more then 400 different fatty acids have been reported, only about 20 of these make up approximately 95% of the total. Whereas the separation of the fatty acids is unproblematic, the quantification is fraught with difficulties as a result of I.) the high content of short‐chain fatty acids (C4 to C10) which show a lower than expected flame ionization detector response in the GLC, II.) of the high content of C18:1 isomeric fatty acids, and III.) the occurrence of the minor fatty acid group conjugated linoleic acids for which health implications are ascribed. These characteristics require the use of response factors and special chromatographic techniques. In summary, accurate fatty acid analysis is imperative for continued efforts to improve animal performance, efficiency, and product quality. Good knowledge about the sample characteristics (lipid classes, nonsaponifiable lipids etc.) and the shortcomings of the various analytical methods is essential to carry out sample analysis in order to obtain accurate and reliable results. Jana Kraft, PhD, Department of Animal Science, University of Vermont, 208 Stafford Hall, 95 Carrigan Drive, Burlington, VT 05405‐0148, Phone: (802) 656‐5852, Fax: (802) 656‐8749 Email: [email protected] Understanding the Causes of Milk Fat Depression
Adam L. Lock
Department of Animal Science, University of Vermont
6
Low milk fat percentage and yield is an important economic issue on many dairy farms. Although our
understanding of the interrelationship between rumen lipid metabolism and milk fat synthesis has progressed
significantly over the last decade, troubleshooting milk fat issues on dairy farms remains one of the more
challenging tasks within overall nutritional management of dairy cows. This is highlighted by the fact that the
magnitude of decrease in milk fat (e.g. 3.8 to 3.4%) may be caused by 1 to 2 g/d or less of trans-10, cis-12 CLA
or a related intermediate leaving the rumen and subsequently taken up by the mammary gland. While milk fat
depression (MFD) has been observed over a wide range of feeding situations, experience indicates that it occurs
as a result of several concurrent diet or management factors rather than as a result of a single factor. Changes in
ruminal microbial processes are an essential component for the development of MFD and are centered on both
an altered rumen environment and an alteration in the rumen pathways of polyunsaturated fatty acid
biohydrogenation (BH). In general, no single dietary factor is responsible for MFD, and this presentation will
highlight the interactions between various dietary components that can increase the rumen outflow of BH
intermediates associated with MFD. Dietary components can increase the risk of MFD by increasing substrate
supply, altering rumen BH pathways, and altering rates of BH. With the latter, it is important to consider factors
that alter rates of BH as not being causative for MFD per se; rather they interact with a predisposing condition
(e.g., altered ruminal BH pathways) to accentuate the effects on milk fat. Our understanding of the effect of
specific BH intermediates on milk fat synthesis in the mammary gland has advanced at a much greater rate than
our knowledge of their production in the rumen. Therefore, further research is required to better understand the
ruminal conditions that promote the formation of BH intermediates that may trigger MFD. Although we do not
fully understand all of the ruminal conditions that may trigger MFD, an improved understanding of these events
will provide the critical framework with which to better troubleshoot MFD.
Dr. Adam L. Lock, Assistant Professor, University of Vermont, 201 Terrill Hall, 570 Main Street, Burlington, VT 05405, PH: 802-656-0142, FX:
802-656-8196, EM: [email protected]
7
Challenges of building a workable lipid model
John Newbold, Provimi Research and Technology Centre, Belgium
Farm nutritionists, milk processors, commercial and academic dairy scientists have different needs from
computer models. These include the robust, reliable prediction of effects of lipids on dry matter intake, milk
yield, milk fat concentration, milk fatty acid profile, health and reproduction. One single model, or one type of
model, will probably not meet all needs.
Drivers of research include new ‘pulls’ from the market place (e.g. effects of milk fat on human health,
realisation of the welfare and economic costs of poor fertility and production diseases) and a ‘push’ from
experimental technology. The field of ruminant lipid nutrition has progressed rapidly partly because of
developments in the analysis of fatty acids: similarly, the application of genomic techniques in rumen
microbiology should push the further development of models of biohydrogenation in the rumen.
Recent modelling initiatives (e.g. CPM) have focused successfully on the prediction of post-ruminal flow of
individual fatty acids for the purpose of predicting the yield of individual fatty acids. In other areas, modelling
activities probably lag behind the progress of experimental science. For example, initiatives to model effects of
lipid nutrition on liver metabolism, immune function and reproductive physiology – all the subject of intensive
recent research - would now be timely. Similarly, efforts to integrate different mechanisms by which the lipid
composition of the diet influences intake could lead both to a ‘workable’ model for field application and a
‘workable’ model to stimulate further experimentation (e.g. role of gut peptides).
John R. Newbold, Provimi Research and Innovation Centre, Lenneke Marelaan 2, Sint-Stevens-Woluwe, B1932, Belgium. Tel: 0032 2 714 7000.
Email: [email protected]
8
HISTORICAL PERSPECTIVE AND CONFERENCE GOALS.
D.L. Palmquist, Professor Emeritus
Department of Animal Sciences
Ohio Agricultural Research and Development Center/The Ohio State University
Wooster, OH 44691
[email protected]
Despite in depth and productive studies on utilization of dietary fat by L. A. Maynard and colleagues at Cornell from 19281944, the value of dietary fat in practical diets for lactating cows was not appreciated until after 1960. The key factor
needed to gain appreciation was the improvement in milk yield that came about with advances in genetic potential after
introduction of artificial insemination. As milk yield increased, dairymen began to increase energy intake by feeding high
grain diets, with subsequent frequent problems of milk fat depression, fat cows, acidosis, lameness, etc. Beginning in the
1960’s, intensive research on the physiology of fat utilization by dairy scientists in the UK, Scandinavia and the US
brought focus to utilization of fat as an energy source for high producing cows. Development of rumen inert fats as
energy sources provided means for nutritionists to develop higher energy diets without sacrificing intake of forages
required to maintain rumen function critical for health of high yielding cows.
Other questions have developed with increasing use of fats in dairy diets. What is the proper analysis/expression for
dietary fat? Are all fats created equal? Why does fat decrease feed intake? What is the role of dietary fat in low milk fat
syndrome? Can the quality of dietary fat be modified to improve milk composition/human health, or to improve
reproductive efficiency?
With the emerging information on fat as a key regulator of gene expression, what new
approaches may be found for utilizing dietary fat? These and other questions of fat metabolism and utilization will be
addressed at Discover 14.
Dr. Donald Palmquist, Professor Emeritus, OARDC/OSU, Dept. of Animal Sciences, 1680 Madison Ave., Wooster OH 44691 USA
PH: 330-263-3795, FX: 330-263-3949, EM: [email protected]
9
MILK FAT AND HUMAN HEALTH: OPPORTUNITIES AND CHALLENGES
Professor Andrew M. Salter, Division of Nutritional Sciences, School of Biosciences, University of Nottingham, Sutton
Bonington Campus, Loughborough, Leicestershire, UK.
While, in most industrialised countries, premature death from cardiovascular disease (CVD) has dropped significantly
over the last thirty years, it remains the single greatest cause of death in the USA. Throughout this period reduction of
saturated fat intake has remained central to public health policies aimed at reducing the incidence of CVD. Such advice
usually includes avoidance of full-fat dairy produce, guidance which has been recently reinforced by the USDA “Food
Pyramid” and advice from the American Heart Association. This is primarily based on predicted effects of the relatively
high saturated fatty acid (SFA) content of milk, with dairy products actually providing approximately 30% of total SFA
intake. However, when specifically considering dairy fat intake, a number of epidemiological studies have failed to show
a consistent relationship between high intakes and increased risk of CVD. While some researchers have questioned the
basic premise that there is a relationship between saturated fatty acid intake, plasma cholesterol and CVD, others have
suggested that other potentially bioactive components of milk (such as CLA, sphingolipids or micronutrients) may offset
any detrimental effects of the SFAs.
One response to continued advice to avoid dairy fat has been to investigate possible mechanisms of altering the fatty acid
composition of milk. However, to date, few strategies have been developed that significantly reduce the SFA content.
One area of current investigation is the role of the enzyme stearoyl Coenzyme A desaturase (SCD) in regulating fatty acid
composition. This enzyme is responsible for converting SFAs to monounsaturated fatty acids (MUFA). Recent work has
indicated that variability in fatty acid composition of milk between cows correlates with expression of this enzyme.
Furthermore polymorphisms within the SCD gene are associated with changes in milk fatty acid composition. However,
to date the magnitude of these effects are relatively small and have minimal impact on the overall fatty acid composition
of milk. Many workers have also looked at increasing the polyunsaturated fatty acid (PUFA) content of milk through
feeding “protected” lipids. In general, this is expensive and produces relatively modest changes in overall fatty acid
composition.
In recent years there has been considerable interest in the potential health benefits of conjugated linoleic acids (CLA).
Ruminant meat and milk represent the only “natural” sources of CLA which may have protective effects against both
cancer and CVD. The CLA content of milk can be readily increased through dietary manipulation. However, increasing
the CLA content of milk is normally associated with increasing the overall trans fatty acid (TFA) content. In general
TFAs are believed to increase plasma cholesterol and their effects may be even more detrimental than SFAs. However
work by us, and others, indicates that the predominant isomer of TFA (vaccenic actid, trans11-C18:1) found in milk may
not have the same deleterious effects as those found in partially hydrogenated vegetable oil (PHVO) and may actually act
as a precursor for the synthesis of CLA in human tissues. Confirmation of the differences in effects of TFA from animal
and PHVO becomes increasingly important as the continued removal of PHVO from the human food chain is likely to
lead to dairy products becoming the major source of trans fatty acids in our diet.
Confirmation of the potential health benefits of milk-derived CLA and of the differences in the effects of TFAs from dairy
fat, as opposed to PHVO, represent important milestones in improving the public perception of the impact of dairy fat on
human health.
Dr. Andrew Salter, Professor of Nutritional Biochemistry Head of Division of Nutritional Sciences, University of Nottingham, School of
Biosciences, Sutton Bonington Campus, Loughborough Leicestershire, LE12 5RD, PH: 44(0)115 951 6121, FX: 44 (0) 0115 951 6168, EM:
[email protected]
10
EXPLORING THE LINKS BETWEEN FATS AND REPRODUCTION
C.R. Staples, B. Amaral, F. Silvestre, J.E.P. Santos, and W.W. Thatcher
University of Florida, Gainesville
Pregnancy rate of lactating Holstein cows has decreased significantly in the last 30 years. During this
same period of time, milk production per cow has increased and supplemental fats have become
more common in dairy rations in order to increase energy intake to support and stimulate further milk
production. In addition to energy, fat sources can supply additional essential fatty acids required in
the diet; namely, linoleic and linolenic acids which are classified as omega-6 and omega-3 fatty acids
respectively. Fat sources differ in their concentration of these essential fatty acids. High protein or
high oil fish products can be good sources of omega-3 fatty acids and can be fed to dairy cows.
There is growing evidence that lactating dairy cows can benefit reproductively if good quality fats are
supplemented to the diet in small quantities (1.5 to 3.0% of the diet). In about half of the 33 scientific
studies reviewed, cows consuming fat-supplemented diets had improved pregnancy rates. Fat
sources containing small amounts of the essential fatty acids have sometimes been effective when
the control group of cows were not fed supplemental fat. When fat sources enriched in omega-6 or
omega-3 fatty acids were compared in experiments to fat sources containing smaller proportions of
these fatty acids, the cows fed the omega-6 or omega-3 fat sources often were better able to
establish a lasting pregnancy. Some of the experiments lacked sufficient numbers of cows in order to
provide meaningful results. Future efforts to test whether a reproductive benefit can be obtained from
feeding fat supplements to lactating dairy cows must involve hundreds of cows. How fat supplements
improve pregnancy is not fully known. The fatty acids from the diet can be deposited in reproductive
tissues and become available when needed to influence how the uterus and the ovary function.
Changes in reproductive tissues that have been documented under fat-feeding situations include the
growth of larger follicles and corpus lutea on the ovary. More of the hormone of pregnancy,
progesterone, appears to be in play when fats are supplemented to the diet. This may be the result
of fat-supplemented cows having larger structures on the ovary that synthesize progesterone or
because fat-feeding results in more cholesterol in the blood which is used to synthesize
progesterone. The omega-3 fatty acids are antagonistic to the production of certain prostaglandins
by the uterus which may cut short a pregnancy if released in an untimely fashion. In addition, fats
appear to stimulate the early growth of an embryo so that it may be “healthier and more mature” when
it becomes implanted in the uterus. Lastly, omega-6 and omega-3 fats can influence the immune
system of the cow which, in turn, may influence pregnancy rate. In recent studies, the immune
responses of lactating dairy cows were stimulated when omega-6 fats were fed or were suppressed
when omega-3 fats were fed, based upon neutrophil numbers and functions. It appears that fat
supplements can have a positive influence on pregnancy of lactating cows which has direct bearing
on the economic productivity of our commercial dairy farms.
Contact: Charles R. Staples, professor; 204 ‘Red’ Larson Dairy Building, University of Florida,
Gainesville, FL; phone: 352-392-1958; fax: 352-392-1931; email: [email protected]
11