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
8:30
9:30
10:30
11:30
12:30
13:30
14:30
15:30
16:30
17:30
18:30
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.