References

Faverdin, P. 1999. The effect of nutrients on feed intake in ruminants.Proceeding of the Nutrition Society. 58:523

Fisher, D.W. 2002. A review of a few key factors regulating voluntaryfeed intake in ruminants. Crop Science 42: 1651

Allen, M.S., B.J. Bradford and K.J. Harvatine. 2005. The cow as a modelto study food intake regulation. Annual Review of Nutrition. 25:523

Five Authors. 1996. Symposium on “Regulation of voluntary forage intakein ruminants. J. Anim. Sci. 74:3029-3081.

NRC. 1987. Predicting feed intake for food-producing animals. WashingtonD.C. National Academy Press

NRC Nutrient Requirements of Beef and Dairy Cattle publications.

• Determines level of production– Production drives ad libitum feed intake– When less than ad libitum, intake determines production– Used in calculation of production response in computer programs

• Affects rate of passage and digestion in the rumen• Determines microbial protein synthesis in the rumen• Important for formulating concentration of nutrients in diets

Importance of Feed Intake

Traits of Feeds Related to IntakeChemical

• Energy concentration- ME or NE

• Fiber content- NDF- Lignin

• Nutrient content- N, S, salt

• Added IonophoresPhysical

• Moisture• Particle size• Density

Palatability

Characteristic of feedNot all agree that palatabilityis a characteristic of feed alone

Stimulates the animal to respondTaste/flavor

AciditySweet

Aroma/smellWater contentPrevious experience

Feed aversions

Animal Factors Related to Feed Intake

– Hunger - Appetite - Smell - Taste – Sight– Body weight– Physiological state

• Lactation increases• Pregnancy decreases (Last trimester)• Temperature stress

Cold increases and Heat decreases• Body composition (Increased fat decreases

intake)• Hormones - brain (Leptin & Ghrelin)

– Fill of digestive tract– Energy balance

Management Factors Related to Feed Intake

FeedsAccessibility to feedMethod of presentationFrequency of feeding

EnvironmentStressHandling and careHousing conditionsDay length

OtherSocial interactionsHormone implantsIonophores

Theories of Feed Intake RegulationRuminants

1. Physical constraints• Capacity and fill of the digestive tract• Involved when forage-based diets are fed

Rate of digestionRate of passage

2. Metabolic constraints• Consume feed to satisfy demands for energy• Involved when grain-based diets are fed

Nutrient effectsMetabolic effects

3. Efficiency of oxygen utilization• Feed is consumed to optimize yield of net energy per unit of oxygen consumed• Involved when intake is limited prior to fill limiting intake

4. Water content of feed• Consumption of wet feeds is limited to amount when water requirements are met

Regulation of Feed Intake by Ruminants

Nutritive value of feed, NEm

Inta

ke

Dry matter

Energy

Physical- - - Fill - - -

- - - Metabolic - - -

Physical Limitations of Fill

Reticulum-Rumen• Fill with balloons decreases intake• Tension receptors located in reticulum and cranial sac of rumen

Increases frequency of discharge of neurons in the ventralmedial hypothalamus and inhibits those in the lateral hypothalamus

Fill of the reticulum-rumen determined by rate of digestion and rateof passage

Abomasum• Distention decreases intake of young calves• Probably not involved in adults (abomasum does not accumulate digesta in adults)

Intestines (Infuse methyl cellulose which is not digested)• Dry matter excretion in feces increases• No effect on feed intake

Factors Affecting Fill of Reticulum-Rumen

• Kind of CHOH - starch or fiberRate of digestion and rate of passage

• Lignification of plant material• Modification of feed

- Grinding - reduce particle size- Chemical - increase rate of digestion

Treat roughage to make cellulose more available- Grinding and pelleting

▫ More susceptible to microbial attack - Increase rate of digestion▫ More susceptible to exit from rumen - Reduced omasal filtration▫ Increased uptake of water by feed particles▫ Change in ruminal location (stratification)

Lower digestibility in rumenIncreased intake

Prediction equations relate feed intake to NEm or NDF of diets

Metabolic Limitations

Short-term: Signals of satiety determine meal size• Signals to stop consumption• Chemical and metabolic

Long-term: Concept of energy balance• Feed is consumed to maintain a constant “set point” or body weight• Ruminants however will over consume energy and accumulate body fat

Satiety Signals

Reticulum-RumenInfuse VFA into rumen – decrease size of a mealAcetate > VFA mix > propionate > butyrateIncreased osmolality seems to be a factor

Intravenous infusion of VFA – no effectInfuse VFA into portal vein – decrease meal size

Propionate > butyrate Acetate and glucose no effectInfuse propionate into intestine – decrease meal size

Less effect with glucoseSome effect with long-chain fatty acids

Unsaturated > saturated

Oxidative metabolism in the liver stimulate afferents in vagusnerve – Signal carried to the brain

• Propionate extensively metabolized in liver• Little acetate metabolized in the liver• Glucose converted to lactic acid in intestine – minimal oxidation in the liver• Unsaturated fatty acids more extensively metabolized in the liver

Satiety SignalsPhysiological

CNSVentral medial hypothalamus

Stimulation decreases feed intakeLesions increase feed intake

Lateral hypothalamusStimulation increases feed intakeLesions decrease feed intake

Regulatory PeptidesCholecystokinin (CCK) – Decrease feed intakeNeuropeptide Y – Increase feed intakeCorticotropin-releasing factor – Decrease feed intakePro-opiomelanocortin peptides – Increase feed intake

Enkephalins-Endorphin

GhrelinPeptide produced in stomach (abomasum of ruminants)Also produced in hypothalamusStimulates release of pituitary growth hormoneStimulates feed intakeBlood concentrations elevated with fasting

Long-term Signals – Energy Balance

Fat mass of the bodyIncreased accumulation of fat decreases feed intake

Limitation of spaceSignals

LeptinPeptide produced in adipose cellsInteracts with receptors in hypothalamusDecreases NPY resulting in decreased feed intakeRelated to mass of body fat

Interaction of short- and long-term signals• Not well understood• Long-term signals might alter threshold to short-term signals

Leptin increases sensitivity to CCK

-200

0200

400600

8001000

1200

18:00

18:40

19:20

20:00

6:20

7:00

7:40

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9:30

10:30

11:30

12:30

13:30

14:30

15:30

16:30

17:30

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19:30

pg/ml

FED FAST

Plasma Ghrelin – Beef Steers

Relationships of Plasma Concentrations of Leptin and Ghrelin with Backfat – Small Frame Angus Steers

0

0.2

0.4

0.6

0.8

1

1.2

0 28 56 84 112 140 168 196

Days

Ba

ckfa

t, cm

0

5

10

15

20

25

Le

pti

n, n

g/m

l

Gh

relin

, ng

/ml x

10

F

ee

d In

tak

e, k

g D

M/d

Back Fat Leptin Ghrelin Feed Intake

Relationships of Plasma Concentrations of Leptin and Ghrelin with Backfat – Large Frame Angus Steers

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 28 56 84 112 140 168 196

Days

Ba

ck

fat,

cm

0

5

10

15

20

25

30

Le

pti

n, n

g/m

l

Gh

relin

, ng

/ml x

10

F

ee

d In

tak

e, k

g D

M/d

Back Fat Leptin Ghrelin Feed Intake

Effect of Processing Corn Grain and Added Fat on Feed Intake and Performance

Diet

----SFC---- ----DRC----

+Tallow +Tallow

Feed DM/d, lb 21.4 20.3 21.2 20.9

ADG, lb 4.03 3.86 3.44 3.48

Feed/gain 5.56 5.26 6.25 5.88

886 lb steers fed steam flaked or dry rolled corn(8% alfalfa hay) 85 days

Effect of Diet Energy and InitialBackfat on Feed Intake and Performance

Initial backfat, in

----0.08---- ----0.16----

Diet, Mcal/lb 0.59 0.64 0.59 0.64

Feed DM/d, lb 24.1 22.6 25.6 22.7

ADG, lb 4.08 4.06 3.98 3.92

Feed/gain 5.97 5.60 6.44 5.79

975 lb steers fed 25 or 12% alfalfa pellets 70 days

Adding Roughage to High-Concentrate Cattle Diets

DMI, % BW = 1.866 + 0.0169 * Roughage, % of DM; r2 =0.699

DMI, % BW = 1.856 + 0.0275 * NDF, % from roughage; r2 =0.920

DMI, % BW = 1.858 + 0.0290 *; eNDF, % from roughage; r2 =0.931

(JAS 81(E.Suppl. 2):E8-E16, 2002)

Effect of Diet Energy and Monensin on Feed Intake and Performance

Haylage, % DM

----20.4---- ----13.2----

Monensin - + - +

Feed DM/d, lb 19.7 19.6 20.3 19.2

ADG, lb 2.95 3.10 3.32 3.19

Feed/gain 6.70 6.60 6.40 6.25

665 lb steers fed 12.8% haylage 159 days

Effects of Stimulating Production

Increased capacity to produce stimulates feed intakeHormone implants increase feed intake

Growing/finishing cattleGrowth hormone

Dairy cow - increases feed intakeIncreased milk production

Growing animal - decreases feed intakeReduces fat deposition (less energystored)

Effect of Hormone Implants on Feed Intake

Feed/d ADG F/G

Control 21.2 3.09 6.88

S 22.1 3.46 6.40

S/S 22.5 3.66 6.15

SF 22.4 3.67 6.11

S/SF 22.3 3.76 5.93

SF/SF 21.7 3.64 5.97 5.97

829 lb steers fed high concentrate diet (15%corn silage) 119 days

Effects of Lactation

0 8 16 24 32 40Week of lactation

Milk Production

Feed Intake

Environmental Effects on Feed Intake

120

100

80

-10 0 10 20 30 40 Temperature, C

No

rmal

in

take

, %

Dry, minimummud

Cool night

Hot night

RainStormDeep mud

Adjustments for Environmental Conditions

Temperature, Adjustment, % Lot conditions

> 35 C no night cool -35> 35 C with night cool -1025 to 35 -1015 to 25 None5 to 15 3-5 to 5 5-15 to -5 7< -15 16Some mud, 10 to 20 cm -15Severe mud, 30 to 60 cm -30

Predicting Feed Intake of Beef Cattle 1996 Beef NRC

Feedlot NEm (Mcal/d) = SBW.75 (.2435 NEm - .0466 NEm2 - .1128)

SBW = Shrunk body wt in kgNEm (Mcal/d)/NEm of diet = kg feed DM

Decrease intake 4% if monensin is being fedDecrease intake 6% if no implants are used

All Forage Diet DMI (kg/kg BW.75) = 0.002774 %CP - .000864 %ADF + .09826

Initial body weight of feeder cattle DMI (kg/d) = 4.54 + .0125 IBW

IBW = initial body wt in kg

Breeding cattle NEm (Mcal/d) = BW.75 (.04997 NEm2 + .04631)

Equation not accurate for feeds with NEm less than 1

Predicting Feed Intake of Dairy Cattle2001 Dairy NRC

Lactating Holstein cows DMI (kg/d) = (0.372 X FCM + 0.0968 X BW0.75)

X (1- e(-0.192X(WOL + 3.67)))BW = body wt in kgFCM = 4% fat corrected milk in kg/dWOL = week of lactatione = base of natural log

Growing heifers DMI (kg/d) = (BW0.75 X (0.2435 X NEm

- 0.0466 X NEm2 - 0.1128))/NEm

Predicting Feed Intake of Sheep

Legumes DMI (g/d) = BWt.75 (-70.4 + 182 NEm - 53.2NEm2)

Grasses and silages DMI (g/d) = BWt.75 (-81.3 + 166 NEm - NEm2)

Pelleted diets DMI (g/d) = BWt.75 (131 - 18.7NEm)

Ensiled feeds reduce intake of sheep more than cattle.

Nursing twins will increase feed intake up to 50%.

Feed Intake - Summary

Feed intake equations are only estimates.Feed intake controlled by many factors.

Intakes are predicted from feed consumption data collected over an extended period of time, not a specific point in time.

Use experience in projecting feed intake.Records from similar animals.