Nutritional Considerations for
Livestock on Rangelands
Mort Kothmann
Texas A&M University
Herbivore Foraging Strategies
Do animals posses ‘nutritional
wisdom’?
What is the evidence?
• Diet quality is higher than the average of
forage available
• Avoidance of toxic species
• Learned/conditioned behaviors
• Animals remember what they learn
How do animals learn what to eat
and what not to eat?
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•
•
•
•
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Pre-natal influences
From parent
From peers
Trial & error sampling behaviors
Anatomical adaptations
Physiological adaptations
Roles of Feedback in Foraging
Behavior
• Ingestive effects
– Morphological characteristics of forages
• Learning from post-ingestive feedback
– Concentrations of nutrients
– Concentrations of toxins
• Learning from con-specifics involving transgenerational interactions
–
–
–
–
Genetic
In utero
Lactation
Observation
Provenza & Cincotta (1993)
Evidence for Palatability
• Sheep learned to associate flavors with
nutrients and preference for higher nutrient
concentration
• Sheep did not develop an aversion to
lower nutrient foods
• Cattle learned to prefer protein blocks
when ingesting forage low in protein
Provenza & Cincotta (1993)
Evidence for learned avoidance
• Intake of foods decreased as
concentration of toxin increased
• Decreased intake of foods deficient in
essential nutrients
• Increase intake of foods that rectify
nutritional deficiencies
Provenza & Cincotta (1993)
How do animals learn to associate the
flavor of foods with post-ingestive
feedback?
• Food novelty
• Intensity of taste vs concentration of
nutrient
• Relative amounts of two foods ingested
• Temporal sequence of food ingestion
• Prior experience with illness
• Prior experience with a salient flavor
Provenza & Cincotta (1993)
Relating senses to post-ingestive
feedback
• Affective processes
– Taste
– Responses are aversive or positive
• Cognitive processes
– Odor and sight
• Combination of odor & taste results in
stronger leaned behavior
Provenza & Cincotta (1993)
Variation among individuals with a
species
• Anatomical
– Congenital
– Environmentally conditioned
• Physiological
– Congenital
– Environmentally conditioned
Provenza & Cincotta (1993)
Goats and Blackbrush
Blackbrush is a forage low in protein and high in
condensed tannins (nutritionally similar to
liveoak)
• PREFERENCE_Goats reared with mothers on
blackbrush consumed 95% more than naive
goats.
• PHYSIOLOGICAL_Experienced goats excreted
63% more uronic acids per unit of body weight
• MORPHOLOGICAL_Experienced goats had
30% greater reticulo-rumen mass
Provenza & Cincotta (1993)
Models for foraging theory
“Darwin and Spencer thought that selection
would necessarily lead to perfection, but
species, people, and cultures all perish
when they cannot cope with rapid
change.” (Skinner 1981)
“Flexible responses and rapid adaptation are
primary correlates of survival…”
Provenza & Cincotta (1993)
Basic principles of adaptation
• Error-making
• Differential response
• Memory
(Note: These same principles are important
in the design and use of TGM.)
Provenza & Cincotta (1993)
Role of Adaptation and Learned
Behaviors in livestock management
• Naïve animals do not function as efficiently
in a new environment as animals who
have one or more generations of
conditioned experience in that
environment
• Consider this when selecting and
purchasing animals
Questions?
What is the source of the drive to eat (forage)?
What is the source of the feedback responses?
How does the animal integrate the many positive
and negative feedback signals generated during
foraging?
How does an animal sense a nutrient deficiency
and match diet selection with foods that rectify
that deficiency?
How does an animal decide when to forage and
when to stop?
Factors Regulating Intake of
Grazing Animals
Short-term vs Long-term Regulation
P. Faverdin
1. Short-term reduction of intake does not necessarily
indicate long-term reduction.
2. Animals require a “learning period” to adapt to changes
in diet.
3. Dietary preferences shift towards optimum rumen
functioning, rather than animal nutritional requirements
as listed by “NRC Nutrient Requirements…”
Effect of Nutrients on Feed Intake
P. Faverdin
1. VFA have short-term effect to depress feed intake. All
except propionate appear to relate to osmolarity.
2. Local anesthetics in rumen eliminate effects of acetate
and butyrate but not propionate.
3. Propionate effects differ if infused into jugular vein (no
effect) or hepatic vein (reduced intake). Apparently the
effect of propionate is mediated in the liver.
4. Intestinal digestion of starch and glucose have little effect
on intake regulation.
5. Protein in rumen stimulates intake.
6. Fats and other substances that disrupt rumen function
decrease intake.
Glucose & Insulin in Ruminants
P. Faverdin
1. Ruminants obtain little glucose from digestion products
of normal herbivore diets.
2. Glucose is synthesized by gluconeogenesis in liver.
3. Glucose infused into the rumen has little effect on intake.
4. Insulin infusion produces short-term depression of intake
for 30 minutes followed by compensatory increase in
intake following one hour.
Role of Dietary Lipids in Intake Regulation
P. Faverdin
1. Natural diets of herbivores are low in lipids.
2. High levels of lipids in diet disrupt rumen functions.
3. Infused lipids have immediate proportional effects in
reducing short-term intake.
4. Mobilization of body lipids in response to lipolytic
substances (B-adrenergic agonists) has no short-term
effect but does reduce intake in the long-term.
5. Effect of free fatty acids on appetite in ruminants does
not seem to be direct and mechanisms involved in intake
regulation have not been identified.
Integration of Post-ingestive Feedback
P. Faverdin
1. Infusions and other artificial interventions may interfere
with the animal’s ability to link post-ingestive responses
with the diet consumed.
2. Animals “learn” through post-ingestive feedback and
“anticipate” the meal’s post-ingestive consequences.
3. A treatment that has no effect over the very short term may
modify the animal’s feed intake over the long term through a
learning process.
4. Disruption of the animal’s equilibrium may cause short-term
decreases in intake that disappear after several days, if the
animal can adapt to the disequilibrium.
Role of N & Protein
P. Faverdin
1. Intake responds to the ratio of protein:energy in diet.
2. Very low or greatly increased NH3 in the rumen
depresses intake.
3. Effects of protein on rumen functioning may stimulate
appetite independently of its effects on rumen fill.
4. Ruminants prefer diets high in high-quality degradable
N. (There must be a balance of DIP and UIP. MMK)
5. Ruminants rapidly learn to prefer diets that improve the
functioning of the rumen.
Intake in relation to forage quality and
protein supplementation
•N content in diet of >1% is required for optimal
rumen function.
•When diet CP is below 7%, intake and forage
digestibility respond linearly to increases in
dietary N
•Above 7% CP in the diet, intake responses are
primarily a function of metabolic responses in
the ruminant at the tissue level.
Impact of bypass
protein supplementation
(+/- urea) on intake of
low-quality forages in
different climatic zones
Slide from Gordon Carsten
Studies conducted
in tropical or
subtropical climates
Studies conducted
in temperate
climates
From G. Carstens
Leng, 1990; Nutr Res Rev 3:277
Receptors Involved in Intake
Regulation (J.M. Forbes)
1. Receptor locations (stomach, intestines, liver and
metabolizing tissues)
2. Property sensed (volume, osmolality, pH, and
concentration of specific chemicals in digesta and portal
blood)
3. Integration of signals in central nervous system (CNS)
determines what food to eat and whether feeding should
start or stop.
Gastrointestinal Receptors
J.M. Forbes
1. Stretch receptors are found in the anterior dorsal rumen
wall.
2. Stretch receptors are also sensitive to chemicals,
including VFA.
3. Physical responses to distension appear to be primarily
related to short-term regulation; possibly with cessation
of eating at a meal but not with initiation of eating.
4. There is no “fixed” physical capacity that limits intake.
(Forbes 2000; Weston 1982; Pittroff & Kothmann 1999)
Osmotic Pressure Receptors
There are receptors in the GI tract that are sensitive to
osmotic pressure, irrespective of the source. They apparently
function to maintain homeostasis. Significant increases in
osmotic pressure reduce intake.
They also function to regulate flow from the reticulum to the
omasum and to the abomasum. Increased osmotic pressure in
the rumen primarily functions to stop intake and to increase
the flow of digesta within the GI tract.
Liver (J.M. Forbes)
The liver is the first organ which can sense and integrate the
products of digestion after they leave the GI tract. In the
ruminant, infusion of propionate functions to reduce intake
similar to glucose infusion in the non-ruminant. Oxidation of
VFA in liver depresses intake in the ruminant. Liver receptors
appear to be primarily involved with cessation of individual
meals rather than with long-term regulation of intake.
Denervation of the liver leads to larger less frequent meals.
Higher circulating nutrient levels result in less frequent meals.
Supply of metabolites is monitored at the porta hepatis
(entrance of the portal vein into the liver).
Adipose Tissue
Leptin is a hormone that provides feedback from levels of
fat stores to various physiological functions that include:
down regulation of intake, immune system function, and
reproductive hormones. Leptin is a hormone secreted by
adipose cells in proportion to their size. It circulates in the
bloodstream and influences receptors in the brain. The
discovery of leptin negates the need for the “physical
limitation of intake by crowding of the rumen by fat”
hypothesis that has long been postulated to explain why
animals reduce intake as the percentage of body fat
increases above threshold levels.
Short-Term Regulation
Short-term intake regulation serves to maintain
physiological parameters of the digesta and the blood
within acceptable ranges. Systems that cause cessation of
eating have received the most research attention. These
include physical and chemical receptors in the rumen and
chemical receptors in the liver. Osmotic and chemical
receptor systems regulate the flow of digesta through the
GI tract. Physical receptors in the anterior dorsal sac of
the rumen may primarily regulate rumination relative
to ingestion. These systems do not appear to have a
significant role in regulating long-term intake.
Long-Term Intake
Systems that initiate eating and stimulate continued
consumption of a meal have received less attention.
These systems appear to be the primary mechanism
for controlling long-term intake. Positive stimuli
may relate to the rates of nutrient assimilation by
metabolic tissues in the animal. Leptin would
provide a negative feedback. Regulation of longterm intake probably involves a balance between
positive feed-forward signals and negative feed-back
signals.
Metabolic Regulation of Intake
•Intake is reduced by either severe deficiency or excess of a
specific nutrient.
•Animals tend to eat protein to match their ability to
synthesize and utilize protein in body tissues and milk
•Animals do not eat to a fixed demand for energy.
Protein as a regulator of energy
utilization
The availability of protein regulates the use
of energy for growth, lactation,
reproduction, and other productive
functions. When the supply of energy
exceeds the availability of protein, excess
energy in the form of VFA is either stored
as fat or oxidized by the liver. Both of
these processes result in negative
feedback to intake.
General intake regulation
(Pittroff & Kothmann 1999)
Potential vs Realized Energy Demand
Pittroff & Kothmann 1999
Potential energy demand (PED) – The animal’s PED is
determined by its current physiological state and genetic
potential for growth, lactation, and other productive
functions.
Realized energy demand (RED) – PED is modified by
climatic and handling stresses, pathogen effects, and
properties of the diet itself (nutrient quantity and balance
over time).
Effect of physiological
function on efficiency of ME
utilization
Physiological
function
Lactating
Nonlactating
ME for
Diet ME
maintenance† to milk
122
64.4
100
--
Diet ME Body tissue
to body
to milk
74.7
82.4
55.0
--
†kcal/BW.75
Moe et al. (1981); JDS 64:1120. Data generated from energy
balance experiments involving measurements of 350
lactating and 193 nonlactating cows.
Slide from Gordon Carsten
Effect of physiological function on
efficiency of ME utilization
Slide from Gordon Carsten
75%
lactating
Fat
Storage
82%
55%
dry
Feed
Direct ME use: 64%
Fat--late lactation: 75 x 82 = 62%
Fat--dry period: 55 x 82 = 45%
Milk
Impact of VFA profile on efficiency of ME
use
Infused VFAs singly or in mixes into rumen of sheep fed
hay diets
Acetate
32.9
Propionate
56.3
Butyrate
61.9
Mix--75% acetate
31.8
Mix--25% acetate
58.1
0
10
20
30
40
50
60
70
Partial efficiency of ME utilization, %
Concept established that net efficiency of ME use for growth was
greater for diets providing more propionate & less acetate acid.
Armstrong and Blaxter (1957, 1958, 1961)
Slide from Gordon Carsten
Effect of basal diet on efficiency of acetate
use--Acetate was infused into rumen of dairy
cows
Slide from Gordon Carsten
100
90
80
70
60
50
40
30
20
10
0
81.8
Hay only diet
30:70 hay:concentrate
68.7
diet
56.6
24.2
Experiment I
28.1
Experiment II
26.6
Average
Exp I; both diets pelleted; Exp II hay fed in long form,
concentrates fed in meal form (Tyrrell et al., 1976; EAAP 19:57)
DE, % of gross energy
Effect of level of intake on Digestible Energy
Pigs & chickens
(conc. diets)
90
Lactating sows
(conc. diets)
80
Horses & rabbits (50:50
forage:conc. diets)
Ruminants (50:50
forage:conc. diets)
70
Ruminants (long or
chopped forage)
60
50
Ruminants (finely
chopped forage)
40
0
1
2
3
4
5
Feed intake, multiple
of maintenance
6
Slide from Gordon Carsten
Effects of ambient temperature on
digestibility in ruminants
• Average decrease
in digestibility
per ˚C decrease is
equal to .18%
[NRC, 1981]
• Occurs in both
ruminant and
nonruminant
animal species
Slide from Gordon Carsten
unshorn sheep
shorn sheep
Effect of level of metabolizable energy
intake on liver mass Slide from Gordon Carsten
Liver weight increased 29 g per increase of 1 MJ of ME
Johnson et al., 1990; J Nutr 120:649
Effect of level of metabolizable energy
intake on gastrointestinal tract mass
GIT weight increased 61 g per increase of 1 MJ of ME
Johnson et al., 1990; J Nutr 120:649
Slide from Gordon Carsten
Maintenance Energy Requirements
• Maintenance energy requirement is
directly related to vital organ mass
• Animals on high plane of nutrition have
higher vital organ mass
• This principle is very important when
shifting animals from high plane of
nutrition to lower nutritional level.
Supplementation and
Monitoring Nutritional Status of
Grazing Animals
Considerations for Supplementation
1.
2.
3.
4.
5.
6.
Will the supplement substitute or complement the
forage intake?
Feed to meet protein needs and manage to meet
energy needs
Feeding for breeding is the most economical
Design the system to balance the cow’s annual energy
budget
It is more economical to reduce energy demand than
to try to feed large amounts of energy feeds.
Creep feed calves during last 45 days prior to weaning
only if part of preconditioning program
Molasses-urea vs Concentrated Protein (CP)
(e.g., Cottonseed or Soybean Cubes)
1. Molasses is self-fed –CP is hand fed
2. Intake of molasses can only be controlled
when there is not a large energy deficit
3. Molasses works best when there is an
abundant supply of potentially digestible forage
4. Do not provide over 1/3 of CP requirement
from urea
5. Hand feeding useful for checking and handling
animals
Feeding Cottonseed Cubes
• Can feed amounts up to 0.3% of BW per
day
• Can feed 1, 2, or 3 times per week with
comparable results
• Feeding after main morning grazing period
has less effect on grazing behavior
• On low quality forages (< 7% CP) will
increase forage intake and digestibility
• Can give large increase in DOMI
Guidelines for using 20% breeder
cubes
• Work best if fed daily in the PM with total
amount not to exceed 0.3% of BW
• Skipping days and feeding larger amounts
may reduce forage intake and digestibility
• Energy in the cube tends to substitute for
energy in grazed forage which reduces net
benefit to the animal
• Feeding daily can disrupt grazing patterns
Forero, et al. (1980) J. Anim. Sci. 50:532-538.
Evaluation of slow-release urea for winter
supplementation of lactating range cows.
•
•
•
•
•
•
Natural protein was superior to both urea and SRU.
SRU was slightly superior to urea apparently because
of improved palatability and intake of the supplement.
The 20% CP supplement with urea and corn fed at
2.44 kg/head/day showed reduced performance
compared to the soybean supplement fed at 1.22
kg/head/day.
Protein supplementation increased forage intake with
the greatest increase from natural protein.
Natural protein increased DMD of diet but urea did not.
Urea as the sole source of N is not highly effective in
enhancing fiber digestion. Animo acids and peptides
with NH3 are more effective.
Forage Intake and Digestibility:
Effects of Supplements
• Forage CP of 6-7% is threshold for major
effect of supplemental protein
• Starch in the diet has a negative effect on
fiber digestion primarily through changing
rumen pH and microbial populations.
• On low CP forages, starch digesting
bacteria compete with cellulose digesting
bacteria for NH3 in the rumen.
Monitoring Nutritional Status of
Grazing Animals
• Vegetation
• Animal
• Feces
Integration of Procedures for evaluating
nutritive status of range animals
1.
2.
3.
4.
Determine forage availability
Determine nutrient content of diet
Estimate nutrient requirements of animal
Determine nature and extent of
nutritional deficiencies
5. Evaluate management practices to
determine causes and possible solutions
Range Site
Monitoring Vegetation
‘Observational’
• Total amount available
– Forage density and distribution
– Potential bite size
• Nutritional heterogeneity
– Live-dead
– Leaf-stem
– Species composition
Vegetation Analysis
• Measuring standing crop
• Chemical analyses
– CP, TDN, IVOMD, minerals
Monitoring Animals
• Animal body condition score
• Animal weight
• Animal appearance
– Fill, hair coat, eyes, ‘body language’
• Animal behavior
– Grazing periods (start and end)
Feces
• Size of pats
• Shape of pats
• Moisture content of pats
Fecal Chemistry
Bonds of:
Diet Quality
Carbon
Crude Protein
Oxygen
Nitrogen
Hydrogen
Dig. Org. Matter
DIET:FECAL PAIRS
0.1
NIR Spectrum
0.05
+
0
-0.05
-0.1
-0.15
Predicted Diet
=
Crude Protein
Digestible Organic Matter
Y = β 0 + β 1x + ε
Diet quality as estimated by NIR analysis of fecal samples
from Garfield Co, MT Rangeland
1996-2001
13
64
CP
12
63
DOM
62
11
61
% CP
60
9
59
8
58
7
57
6
56
5
55
96
4
97
98
99
00
01
54
% DOM
10
Summary – Systems Thinking
• Think holistically
– Climate
– Soils
– Plants
– Animals
– Management
• Work to create synergy between parts of
the system