Lipids in Dairy Rations

Overview main points: Fat is included in dairy rations to increase energy density. a gram of starch has an energy value of 4.1 kcal a gram of fat has an energy value of 9.3 kcal

Fat inclusion may improve reproductive performance either through improved energy balance or effects of PUFA

Absorption of fat soluble vitamins is dependent on fat in diet

Fat is not fermented by rumen bacteria and does not contribute to microbial growth but fats are “metabolized” by rumen bacteria.

Polyunsaturated fats have a negative effect on rumen bacteria, especially fiber digestors.

Fats are biohydrogenated in the rumen, so absorbed fatty acids differ from dietary fatty acids

Fat absorption decreases as fat exceeds 1,000 to 1,500 g total intake; Maximal fat in ration 7% total fat

Fat sources have different effects on rumen fermentation

Whole seeds, vegetable oils, by-product feeds high in fat; Tallow, hard fats and greases; Rumen protected  (inert) fats

Dietary fats

Sources – basal fats in typical dairy feeds (2 to 4% of DM)

• high fat feeds: whole soy beans, cotton seeds, other whole seeds, by-product feeds of fermentation(distillers’s dried grains), bakery waste, candy, potato chip waste….
• Fat products: greases, tallow, vegetable oils, rumen protected (inert) fats,
  • calcium salts of fatty acids
  • fat prills
  • encapsulated fat in a protein matrix
• animal fats are named tallows when their melting point is >38oC, otherwise they are called greases

Digestion

Rumen hydrolysis of esterified fatty acids to free fatty acids by microbial lipases

Free fatty acids (FA) plus glycerol

Glycerol is rapidly fermented to propionate

Free fatty acids are acted upon by rumen bacteria

Incorporated into bacterial lipids and phospholipids

Biohydrogenation

Multiple types of isomers of CLA produced >20

Depend on the double bond position:

8-10, 9-11, 10-12

and configuration:

cis-cis, cis-trans, trans-cis, trans-trans

cis-9, trans-11 CLA dominant isomer in milk, anticarcinogenic activities

trans-10, cis-12 CLA reduces milk fat synthesis and fat accretion in growing animals

trans-11 C18:1 associated with reduced milk fat yield and percent

Unsaturated FA (USFA) are biohydrogenated; 70 to 90% of USFA are transformed to more saturated FA

Dietary C18:1 are largely in the cis configuration. Saturation process involves isomerization of the FA to trans configuration as well as biohydrogenation

saturation occurs via trans-conjugated dienes and monenes

Reduction of trans-11 C18:1 to C18:0 is the rate limiting step

Dietary factors can influence the extent of this step by influencing rumen conditions – especially low rumen pH slows conversion

Under certain conditions trans-11 C18:1 may accumulate

trans-10 conjugated linoleic acid has been linked with milk fat depression

Absorbed fatty acids are not similar to that in diet and are more saturated

Some long-chain FA are synthesized by rumen bacteria

Total content of lipid of bacterial cells is 10 to 15% DM

FA in bacteria are derived from diet and synthesized de novo

Synthesized FA are largely C16:0 and C18:0 and are incorporated into phospholipids

Bacteria do make some unusual FA, C15:0 and C17:0 which can be in ruminant fat and milk fat

Small intestine: site of fatty acid absorption just as in non-ruminant

85 to 90% of FA flowing from the rumen are free FA’s

10 to 15% are incorporated into microbial phospholipids

A high proportion of TG pass from the rumen only if encapsulated in protein as a protected fat or as dairy fat prills

Estimates of net absorption vary from 55% to 90%

Fatty acids >= C16 absorbed and incorporated in chylomicrons

Fatty acids C12-C14 absorbed into portal circulation to liver           

Efficiency of post-ruminal digestion declines with increasing dietary intake

Above an intake of 1000 to 1500 g/d  absorption is reduced

Most fats enter the SI as FA adsorbed to particulate matter

Small amounts of triglycerides are hydrolysed by pancreatic lipases and phospholipases

FAs are released from particulate by action of bile salts to form micelles

absorption occurs primarily in distal jejunum and ileum into the lymph (primarily as VLDL) and small amounts into portal vein

General patterns:

Increase in saturation and chain length associated with reduced absorption

Digestion is inversely related to melting point

Oleic acid appears to be important in helping emulsify FA for absorption

Iodine value estimates the degree of unsaturation of a fat.

Higher the iodine value, the more unsaturated FA in the fat

Digestion of fats with an idine value below 45 is poor compared with fats with and iodine value >45

Fat source	Iodine value
Hard or granular fats
Calcium salts of palm oil	49
Partially hydogenated tallow	14-31
Hydrolyzed tallow	12
Animal and Animal-vegetable blends
Tallow	48
Choice white grease	62
Yellow grease	72
Poultry fat	82
Fish oil, Menhaden	31
Fish oil, herring	25
Vegetable oils
Canola (rapeseed)	119
Corn	126
Soybean	131
Cottonseed	107
Peanut	95

Fatty acids are absorbed by intestinal cells and FA are reconverted to triglycerides (TG)

TG are packaged into lipoprotein particles (chylomicrons or very low density lipoproteins) secreted into lymph and then to the blood stream

TG in chylomicrons or VLDL are broken down to free FA by lipoprotein lipase in capillaries in mammary gland, adipose tissue, muscle, and heart. Free FA can enter cells and be converted back to TG in the cell (adipose, mammary gland) or oxidized.

Dietary fats do not reach the liver directly and therefore do not contribute fatty liver.

Small amounts of PUFA absorbed from the small intestine are not formed into TG but are attached to phospholipids and cholesterol esters. They are protected from being burned for energy and can be incorporated into cell membrane phospholipids or metabolized to prostaglandins and leukotrienes. The problem is 90% of PUFA may be biohydrogenated.

The main use of fatty acids from the diet is incorporation into milk fat or adipose fat

Milk fat incorporates FA into TG

FA in milk fat are classified as
Short chain FA            C4 to C8         synthesized in gland
Medium chain FA       C10 to C14     synthesized in gland
Long chain FA            >=C16
C16                 synthesized or preformed
>=C18             all preformed

FA are taken up from NEFA, chylomicrons, or synthesized in mammary cells

Uptake by the mammary gland incorporates FA into milk fat

FA in milk fat are synthesized de novo – C4 to C14

Short (C4 to C8) and medium chain FA (C10 to C14)

Acetate is the primary building block

Reducing equivalence (NADPH) from glucose is needed to add acetate chains to produce FA for milk fat

Dietary and synthesized de novo – C16:

All preformed >=C18 (dietary origin or from NEFA from body fat)

Uptake of preformed FA depresses de novo synthesis of FA in mammary gland

Inclusion of fat in diet increases the content of >=C18 in milk fat

Decreases content of

Variable effect on C16

Mammary gland Δ9 desaturase increases oleic acid and other unsaturated FA to maintain fluidity of milk fat

Composition of reference milk fat

Fatty Acid	wt%
4:0	3.32
6:0	2.34
8:0	1.19
10:0	2.81
12:0	3.39
14:0	11.41
14:1	2.63
16:0	29.53
16:1	3.38
18:0	9.84
18:1	27.39
18:2	2.78

But this composition will be effected by fat included in dairy rations

Approaches to fat feeding: increase energy density in high producing cows from a nonstarch source

Fat can be used to increase the energy density of the ration without increasing starch

Advantages of using a rumen inert fat source:

Does not depress fiber digestion

Escape biohydrogenation – depending on type of source

Ease of handling

Dry granular form as opposed to “lumps”

Tallow – need a heating device to liquefy

Oils are liquids need a tank to hold

Methods to make rumen inert

Saturate the fatty acids so melting point above 100 oF

Hydrogenated tallow

Prill the fat

Partially hydrogenate so solid fat and spray process so fine particles of TG

Complex with calcium to form a soap

Complex separates at low pH in abomasums

Coat with a protein complex

Fatty acid profile of common fat sources

Disadvantage of producing hydrogenated fats

Some recommend that stearic acid be less than 20% of FA

Fat sources and digestibilty

Megalac and Energy Booster have high digestibilities

Change from control Fat sources 0 = whole seeds 1 = rumen active fats, tallow 2 = inert fats In general, milk increased about 2 kg, but there is a lot of scatter 0.48 kg of milk / � in diet at same DMI Why the scatter?

Added fat may decrease dry matter intake;
Added fat may displace fermentable carbohydrate;
Added fat does not grow rumen bacteria, need additional by-pass protein;
Added fat may depress rumen fiber digestion

In fact, DMI tended to decline as EE of the diet DM increased

Fat yield tended to increase, but again there is a lot of scatter

Added fat has often decreased milk protein content, with little change in protein yield People have speculated that more protein should be included in the diet with added fat

Summary of trials with fat without and with added by-pass protein (RUP)

Influence of more RUP Same milk response Fat yield increased No effect protein yield DMI decreased Fat % increased Trend to protein % increase Overall means

Across studies with different sources

	Phase I – increase diet with whole oil seeds and rumen active fat sources Phase II increase fat in diet with rumen inert fat sources Phase III – too much fat
Added fat diet relative to control diet
	Data summarized by Staples Change in milk from control on X axis Change in CR from control on Y axis When milk response less than 2 kg, CR tended to increase ( .05 to .10, so 30% to 35% to 40%) If milk increase was more than 2 kg, CR decreased At 4 kg more milk, decreases about -.30
Reproduction response may depend on milk yield response.