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 voluntary
feed intake in ruminants. Crop Science 42: 1651
Allen, M.S., B.J. Bradford and K.J. Harvatine. 2005. The cow as a model
to study food intake regulation. Annual Review of Nutrition. 25:523
Five Authors. 1996. Symposium on “Regulation of voluntary forage intake
in ruminants. J. Anim. Sci. 74:3029-3081.
NRC. 1987. Predicting feed intake for food-producing animals. Washington
D.C. National Academy Press
NRC Nutrient Requirements of Beef and Dairy Cattle publications.
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
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
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
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
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
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
Regulation of Feed Intake by Ruminants
Physical
- - - Fill - - Energy
Dry matter
- - - Metabolic - - Nutritive value of feed, NEm
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
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
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-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
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
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
1200
1000
800
600
400
200
0
-200
pg/ml
Plasma Ghrelin – Beef Steers
FAST
FED
19:30
18:30
17:30
16:30
15:30
14:30
13:30
12:30
11:30
10:30
9:30
8:30
7:40
7:00
6:20
20:00
19:20
18:40
18:00
Relationships of Plasma Concentrations of Leptin and
Ghrelin with Backfat – Small Frame Angus Steers
Leptin
Ghrelin
Feed Intake
1.2
25
1
20
0.8
15
0.6
10
0.4
0.2
5
0
0
0
28
56
84
112
Days
140
168
196
Leptin, ng/ml
Ghrelin, ng/ml x 10
Feed Intake, kg DM/d
Backfat, cm
Back Fat
Relationships of Plasma Concentrations of Leptin and
Ghrelin with Backfat – Large Frame Angus Steers
Back Fat
Leptin
Ghrelin
Feed Intake
0.8
0.7
25
Backfat, cm
0.6
20
0.5
0.4
15
0.3
10
0.2
5
0.1
0
0
0
28
56
84
112
Days
140
168
196
Leptin, ng/ml
Ghrelin, ng/ml x 10
Feed Intake, kg DM/d
30
Effect of Processing Corn Grain and Added Fat
on Feed Intake and Performance
Diet
Feed DM/d, lb
----SFC---+Tallow
21.4
20.3
----DRC---+Tallow
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 Initial
Backfat on Feed Intake and Performance
Diet, Mcal/lb
Feed DM/d, lb
Initial backfat, in
----0.08-------0.16---0.59
0.64
0.59
0.64
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
Monensin
Feed DM/d, lb
Haylage, % DM
----20.4-------13.2---+
+
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 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)
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
Milk Production
Feed Intake
0
8
16
24
Week of lactation
32
40
Normal intake, %
Environmental Effects on Feed Intake
Dry, minimum
mud
120
Cool night
100
80
Rain
Storm
Deep mud
-10
0
Hot night
10
20
30
Temperature, C
40
Adjustments for Environmental Conditions
Temperature,
Lot conditions
Adjustment, %
> 35 C no night cool
> 35 C with night cool
25 to 35
15 to 25
5 to 15
-5 to 5
-15 to -5
< -15
Some mud, 10 to 20 cm
Severe mud, 30 to 60 cm
-35
-10
-10
None
3
5
7
16
-15
-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 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) = 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 Cattle
2001 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 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 (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.