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 Intake 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

Plasma Ghrelin – Beef Steers

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

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

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

Effect of Diet Energy and Initial Backfat on Feed Intake and Performance 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 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 829 lb steers fed high concentrate diet (15% corn silage) 119 days

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

Environmental Effects on Feed Intake Dry, minimum mud 120 100 80 Cool night Normal intake, % Rain Storm Deep mud Hot night -10 0 10 20 30 40 Temperature, C

Adjustments for Environmental Conditions Temperature, Adjustment, % Lot conditions > 35 C no night cool -35 > 35 C with night cool -10 25 to 35 -10 15 to 25 None 5 to 15 3 -5 to 5 5 -15 to -5 7 < -15 16 Some mud, 10 to 20 cm -15 Severe 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 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.