Since man started feeding animals he has struggled to understand what controls or affects their intake of feed and forages. Cattle are especially complex creatures when we consider what affects their appetite and drive to consume more or less of the materials that provide for their nutrient intake. Over the years research and practice has revealed a great deal about what drives feed and forage intake in pasture cattle and those in the feedlot.
In most situations, what motivates a producer to attempt to control intake in some fashion is the need to provide appropriate levels of nutrients in a cost effective manner. Additionally, in the case of lactating dairy cows and in many cases, feedlot cattle, the desire is to maximize feed intake, particularly dry matter intake. This is under the assumption that the more feed going in will result in more product produced whether it be milk or meat. As economics has become the predominant force in virtually all cattle operations we sometimes find that maximizing feed intake is not always the most beneficial. Recent research in the feedyard has shown in some situations that feeding at a rate slightly below full feed (referred to as “ad libitum”) can improve gains and feed efficiency and can help control some of the erratic ups and downs we see when we try to keep intake at 100 percent.
In other situations a producer has a desire to control at least a portion of what the animal eats. An example of this is intake of supplements such as protein and energy supplements or mineral supplements while cattle are on pasture. In most cases this requirement is based on a need to insure accurate levels of nutrients delivered, control supplementation costs or the availability of labor. Many times this actually becomes a function of a number of these factors, primarily the need to save labor, thus self feeding becomes under consideration but there is a need to control intake so cattle don't eat more supplement than they should an either create digestive problems for themselves or end up driving up supplementation costs due to excessive intake. The old stand-by in these self-feeding situations has been the inclusion of high levels of salt. Salt/meal mixes have been used for years and normally will include salt with protein meals (i.e. cottonseed meal, soybean meal or some combination) at a ratio of 1:2, 1:3, 1:4, etc. depending on the desired level of intake. Mature cattle can normally tolerate about one pound of salt per day. The positive side of this is that it is relatively inexpensive and easy to do. It also affords some degree of control. The downsides are more numerous: 1) Salt is variable in the level of control it provides to all cattle, in other words, some individuals can tolerate a lot more than others. 2) It is hard on the equipment. Salt is obviously quite corrosive in metal feeders. 3) It requires a lot of room in the mix. With 20 to 33 percent inclusion rate in some situations, this takes up a lot of room where another ingredient cannot be placed to provide more protein, energy, etc. Because of this other technologies have been developed which are more consistent in a smaller package. More of this later.
Feed Intake Basics
To accurately discuss this issue we have to make a number of observations and understand some things:
1) An animal begins to eat when it is in a state of hunger
2) It stops eating because it is satiated (full, satisfied).
3) Meal: The amount of food consumed in a limited period of time. Different species will consume varying numbers of meals per day. This may vary depending on environment and man agent situation. For example: Chickens 31, Sheep 14, cows 18, pigs 9.
4) Ration: the amount of food offered within a given time period, usually 24 hours
5) Voluntary Intake: The total amount eaten during a given period of time, usually 24 hours
6) Palatability: the overall sensory impression the animal receives from the food
7) Dry matter intake: The amount of dry matter consumed in a given period of time, usually 24 hours. Dry matter is the amount of dry material (not containing water) in a given ration, forage, etc. In cattle, because of consumption of high moisture materials such as grass or silage the difference between as fed intake and dry matter intake can be substantial.
8) As fed: This refers to feed as normally fed to animals. It may range from 0-100 percent dry matter.
Once a ration is formulated to meet the nutrient requirements of a given animal or group of animals, the next challenge is to assure that the animal consumes an optimal amount of the ration in question. Both under consumption and over consumption of food provide challenges to the producer and the nutritionist. For example, there is a need to decrease intake in obese animals (i.e. cattle with condition scores of 8+), increasing voluntary intake in cattle in less than optimal condition (BCS < 4) or in newly calved cows with high milk production capacities and finally, increasing intake in sick and anorexic animals.
Some of the factors that influence food intake include internal stimuli such as:
1) Gastric distension will decrease intake but not eliminate it.
2) Glucostatic theory: high blood glucose will decrease intake.
3) Thermostatic control: animals eat to keep warm and quit eating to prevent hyperthermia.
4) Lipostatic control: high fatty acids will decrease intake.
5) Hormonal levels: insulin, glucagon, gastrointestinal hormones
This is an exceedingly complex system: A combination of stretch receptors and chemoreceptors appear to send signals to the brain via autonomic nervous system, metabolites (glucose amino acids, fatty acids), and hormones (insulin, glucagon, cholecystokinin, steroid hormones.
Other factors which effect intake per the animal's physiologic state include:
1) Growth: growing animals eat more as a percent of body weight
2) Obesity: fat deposition decreases intake / abdominal mass vs. GI space
3) Estrus: decrease in food intake
4) Pregnancy: increase in mid-gestation, decrease in late gestation (due to increased size of uterus), drastic decrease at parturition.
5) Lactation: feed intake in lactating ruminants lags behind nutrient requirements
6) Disease usually decreases feed intake
Obviously there are a number of dietary factors which affect these groups again:
1) Energy concentration: As energy content of the diet increases, intake should decrease this tends to be true in ruminants and monogastrics.
2) Rate of passage/digestibility: Ruminants: grinding poor quality hay will increase intake and decrease digestibility because the feed moves through the GI system faster. The increase in intake is greater than the decrease in digestibility so the animal "digests" more nutrients
3) Single nutrient appetites: Ca, P, Na, Zn, Thiamin appetites have been suggested.
4) Color, shape, odor, and taste can affect dietary intake.
5) Water intake: decreased water intake leads to decreased feed intake and vice versa.
Finally, environmental factors can have a profound effect:
1) Cold environments: feed intake usually increases to maintain body temperature.
2) Hot environments: feed intake usually decreases, however, it takes work to eliminate body heat.
3) Photoperiod: most animals eat more during light periods.
4) Social factors: eat when others eat vs. social order.
Basic Management Considerations
As you can see there are many factors which affect feed intake both positively and negatively. In many cases intake can be positively affected by simple good management. This includes keeping plenty of fresh, clean water available. Research has shown repeatedly that the availability of water has a direct effect on feed consumption. When water intake is restricted, feed intake also decreases.
Feeds and forages must be kept clean, fresh and free of mold and contaminants. Remember that cattle have a much more acute sense of smell than man does and can detect very small degrees of spoilage. This is especially true in high moisture feeds such as silage or high moisture grain rations. Ration including steam-flaked grains (corn, milo, wheat, etc.) are also susceptible to more rapid spoilage due to higher moisture contents. Intake can be stimulated by feeding more than once per day if labor is available. The feeding activity will trigger the intake response but also this helps insure that feeds are kept fresh.
Keep feeders and troughs clean and free of manure or feed that has been contaminated by manure or urine. Check feeders and troughs first for old feed (it may be necessary to reduce feeding levels somewhat for a day or two to allow cattle to “catch back up.”) and then any contaminated feed or other materials that should not be in the bunk including rocks, pieces of metal, etc. It's pretty amazing what can make its way into a feed trough.
In summer months when temperatures increase, feed intake typically is reduced. This is largely due to the simple fact that cattle do not like to get out and eat in the hot sun or warm temperatures. For this reason it is important to feed early in the day and/or later in the evening.
When maximum intake is the goal, texture of the ration is important. High levels of very small particles (fines) will reduce intake and in many cases will create a sorting problem where cattle will eat the larger particles but leave the very fine material. This can lead to nutritional imbalances since this fine material can include much of the vitamin and mineral. Use of a molasses product can help stick the finer material to the larger particles. Pelleting all or at least some of the feed ingredients, especially those which would be of a finer grade is also useful.
Intake Reduction or Control
On the other side of this coin are methods by which the producer can control intake or hold it at a predetermined level. A great deal of study has been applied to this concept both academically and commercially. The primary desire for a controlled intake situation is labor availability. Many producers just do not have the time or labor available to feed all their cattle the necessary feed or supplement needed on a daily basis. Some producers address this situation by feeding every other day or every few days and averaging the amount feed. In other words, instead of feeding 4 lbs per head of a supplement every day they feed 8 lbs every other day or 12 lbs every third day. While this does save labor it can create a whole host of problems digestively for the cow, especially if it is a higher energy supplement and may carry higher levels of grain. In some cases this can cause acidosis and bloat. As a minimum it can upset the pH balance of the rumen for a period, reducing the numbers of certain bacteria, especially those which digest forages, and subsequently reduces the animal's ability to process the fiber levels she normally consumes.
Producers, nutritionists and feed companies have addressed this problem by developing self-fed supplements which are available all the time to the animal and of which the animal will eat only a specified amount. As discussed earlier, salt-limited products have been used for years. While a certain degree of success has been had using salt, and although it is relatively inexpensive, it is inconsistent in controlling intake and definitely corrosive in feeders. Inconsistency in intake often relates to the adaptability of the cow to consumption of high salt levels. Like man, a cow can become accustomed to eating a lot of salt and can, in many cases, over a period of time become capable of eating large amounts. Subsequently, the amount of feed consumed with the salt also goes up.
Research over recent years has shown that the use of palatability as well as the manipulation or blood chemistry (particularly blood pH) can effectively control intake of some supplements. Researchers and feed manufacturers have employed (with varying degrees of success) the use of various fish products such as fishmeal and oils, anionic salts such as ammonium chloride and ammonium sulfate, calcium chloride and calcium sulfate, etc., overall supplement fat intakes as well as other technologies to hold intake in check. No methodology is foolproof and all require a degree of monitoring to achieve effective intake control. Because of the variability of forage conditions over the course of a year, one particular formula will probably not work all the time.
Products such as liquid feeds control intake with overall product palatability by use of differing amounts of more and less palatable ingredients, product pH (lowering pH typically lowers intake) and modification of levels of certain nutrients such as Phosphorus. Intake of supplements in block form are commonly controlled by hardness. A harder block is more difficult for an animal to consume. If higher intakes are required the block can be made softer.
Since no system is perfect it is necessary for the producer to develop and understanding of these concepts and find a method that works on his operation if intake control is the goal. Additionally, he needs to find a program that will fit his budget. Many are fairly effective but quite expensive and by the time it's all said and done the producer could have hired someone to handle feeding for him.
Understanding intake in cattle is complex and as an industry we have a long way to go to grasp it fully. More often than not common sense can be applied and achieve satisfactory results. At the same time producers, academicians and feed industry professionals alike, as they study these concepts more, will probably realize that complete control of certain biological systems will, more than likely, never be achieved.
Dr. Steve Blezinger is a nutritional and management consultant with an office in Sulphur Springs, TX. He can be reached at P. O. Box 653, Sulphur Springs, TX 75483, by phone at (903) 885-7992 or by e-mail at firstname.lastname@example.org.