1. References
Faverdin, P The effect of nutrients on feed intake in ruminants.
Proceeding of the Nutrition Society. 58:523
Fisher, D.W A review of a few key factors regulating voluntary
feed intake in ruminants. Crop Science 42: 1651
Allen, M.S., B.J. Bradford and K.J. Harvatine The cow as a model
to study food intake regulation. Annual Review of Nutrition. 25:523
Five Authors Symposium on “Regulation of voluntary forage intake
in ruminants. J. Anim. Sci. 74:
NRC Predicting feed intake for food-producing animals. Washington
D.C. National Academy Press
NRC Nutrient Requirements of Beef and Dairy Cattle publications.

2. Importance of Feed Intake
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

3. Traits of Feeds Related to Intake
Chemical
Energy concentration
- ME or NE
Fiber content
- NDF
- Lignin
Nutrient content
- N, S, salt
Added Ionophores
Physical
Moisture
Particle size
Density

4. Palatability Characteristic of feed Not all agree that palatability
is a characteristic of feed alone
Stimulates the animal to respond
Taste/flavor
Acidity
Sweet
Aroma/smell
Water content
Previous experience
Feed aversions

5. 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

6. Management Factors Related to Feed Intake
Feeds
Accessibility to feed
Method of presentation
Frequency of feeding
Environment
Stress
Handling and care
Housing conditions
Day length
Other
Social interactions
Hormone implants
Ionophores

7. Theories of Feed Intake Regulation Ruminants
1. Physical constraints
Capacity and fill of the digestive tract
Involved when forage-based diets are fed
Rate of digestion
Rate of passage
2. Metabolic constraints
Consume feed to satisfy demands for energy
Involved when grain-based diets are fed
Nutrient effects
Metabolic 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

8. Regulation of Feed Intake by Ruminants
Physical
- - - Fill - - -
Energy
Intake
Dry matter
- - - Metabolic - - -
Nutritive value of feed, NEm

9. 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 ventral
medial hypothalamus and inhibits those in the lateral hypothalamus
Fill of the reticulum-rumen determined by rate of digestion and rate
of 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

10. Factors Affecting Fill of Reticulum-Rumen
Kind of CHOH - starch or fiber
Rate 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 rumen
Increased intake
Prediction equations relate feed intake to NEm or NDF of diets

11. 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

12. Satiety Signals Reticulum-Rumen
Infuse VFA into rumen – decrease size of a meal
Acetate > VFA mix > propionate > butyrate
Increased osmolality seems to be a factor
Intravenous infusion of VFA – no effect
Infuse VFA into portal vein – decrease meal size
Propionate > butyrate Acetate and glucose no effect
Infuse propionate into intestine – decrease meal size
Less effect with glucose
Some effect with long-chain fatty acids
Unsaturated > saturated
Oxidative metabolism in the liver stimulate afferents in vagus
nerve – 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

13. Satiety Signals Physiological
CNS
Ventral medial hypothalamus
Stimulation decreases feed intake
Lesions increase feed intake
Lateral hypothalamus
Stimulation increases feed intake
Lesions decrease feed intake
Regulatory Peptides
Cholecystokinin (CCK) – Decrease feed intake
Neuropeptide Y – Increase feed intake
Corticotropin-releasing factor – Decrease feed intake
Pro-opiomelanocortin peptides – Increase feed intake
Enkephalins
-Endorphin
Ghrelin
Peptide produced in stomach (abomasum of ruminants)
Also produced in hypothalamus
Stimulates release of pituitary growth hormone
Stimulates feed intake
Blood concentrations elevated with fasting

14. Long-term Signals – Energy Balance
Fat mass of the body
Increased accumulation of fat decreases feed intake
Limitation of space
Signals
Leptin
Peptide produced in adipose cells
Interacts with receptors in hypothalamus
Decreases NPY resulting in decreased feed intake
Related 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

15. Plasma Ghrelin – Beef Steers

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

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

18. Effect of Processing Corn Grain and Added Fat on Feed Intake and Performance
886 lb steers fed steam flaked or dry rolled corn
(8% alfalfa hay) 85 days

19. Effect of Diet Energy and Initial Backfat on Feed Intake and Performance
975 lb steers fed 25 or 12% alfalfa pellets 70 days

20. Adding Roughage to High-Concentrate Cattle Diets
DMI, % BW = * Roughage, % of DM; r2 =0.699
DMI, % BW = * NDF, % from roughage; r2 =0.920
DMI, % BW = *; eNDF, % from roughage; r2 =0.931
(JAS 81(E.Suppl. 2):E8-E16, 2002)

21. Effect of Diet Energy and Monensin on Feed Intake and Performance
665 lb steers fed 12.8% haylage 159 days

22. Effects of Stimulating Production
Increased capacity to produce stimulates feed intake
Hormone implants increase feed intake
Growing/finishing cattle
Growth hormone
Dairy cow - increases feed intake
Increased milk production
Growing animal - decreases feed intake
Reduces fat deposition (less energy
stored)

23. Effect of Hormone Implants on Feed Intake
829 lb steers fed high concentrate diet (15%
corn silage) 119 days

24. Effects of Lactation 0 8 16 24 32 40 Week of lactation Milk Production
Feed Intake
Week of lactation

25. Environmental Effects on Feed Intake
Dry, minimum
mud
120
100 80
Cool night
Normal intake, %
Rain
Storm
Deep mud
Hot night
Temperature, C

26. Adjustments for Environmental Conditions
Temperature, Adjustment, %
Lot conditions
> 35 C no night cool -35
> 35 C with night cool -10
25 to
15 to None
5 to
-5 to
-15 to
<
Some mud, 10 to 20 cm -15
Severe mud, 30 to 60 cm -30

27. Predicting Feed Intake of Beef Cattle 1996 Beef NRC
Feedlot
NEm (Mcal/d) = SBW.75 (.2435 NEm NEm )
SBW = Shrunk body wt in kg
NEm (Mcal/d)/NEm of diet = kg feed DM
Decrease intake 4% if monensin is being fed
Decrease intake 6% if no implants are used
All Forage Diet
DMI (kg/kg BW.75) = %CP %ADF
Initial body weight of feeder cattle
DMI (kg/d) = IBW
IBW = initial body wt in kg
Breeding cattle
NEm (Mcal/d) = BW.75 ( NEm )
Equation not accurate for feeds with NEm less than 1

28. Predicting Feed Intake of Dairy Cattle 2001 Dairy NRC
Lactating Holstein cows
DMI (kg/d) = (0.372 X FCM X BW0.75)
X (1- e(-0.192X(WOL )))
BW = body wt in kg
FCM = 4% fat corrected milk in kg/d
WOL = week of lactation
e = base of natural log
Growing heifers
DMI (kg/d) = (BW0.75 X ( X NEm
X NEm ))/NEm

29. Predicting Feed Intake of Sheep
Legumes
DMI (g/d) = BWt.75 ( NEm NEm2)
Grasses and silages
DMI (g/d) = BWt.75 ( NEm - NEm2)
Pelleted diets
DMI (g/d) = BWt.75 ( NEm)
Ensiled feeds reduce intake of sheep more than cattle.
Nursing twins will increase feed intake up to 50%.

30. 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.