2. By: A. Riasi (PhD in Animal Nutrition & Physiology) تغذیه دام در مرتع Animal nutrition on the rangeland (Part 4)

3. Feed intake in grazing ruminants  Intake is the ingestion of feedstuffs by the animal, and is regulated by the following factors, which are all interrelated: Palatability Foraging behavior Chemical characteristics of the feedstuff Forage quantity, density and availability Dietary energy and fiber content Physiological stage of the animal Temperature

4.  Palatability is the flavor and texture of the feedstuff. Ruminants will in turn avoid feedstuffs that are bitter, as these often are associated with toxic secondary chemicals.  Foraging behavior describes how an animal goes about the grazing process.  The study of animal grazing behavior involves understanding: Food habits and habitat preferences The effects of nutrients and toxins on preference Feed intake in grazing ruminants

5.  Chemical factors include nutrients, but also secondary chemicals that are often associated with plant defense. All plants contain toxic secondary chemicals to some degree, but animals have evolved an innate sense of what is good to eat. Animals limit the amount of plants they consume that contain secondary chemicals through a feedback mechanism that results in satiety. Feed intake in grazing ruminants

6.  Forage quantity, density, and availability directly influence forage intake.  Ruminants can take only a limited number of bits per minute while grazing.  Large bits of forage are therefore ensured by maintaining dense pastures. Dense pastures are those with actively growing and tillering forage plants. The length of the grazing period (the time an animal is in a paddock) also has a direct effect on pasture intake. Feed intake in grazing ruminants

7.  The intake decreases when an animal longer remains in a given paddock. This happens due to: The effect of plant disappearance (as plants are grazed) and subsequent searching by animal for the next bit The decrease in forage crude protein content beginning roughly two days after the animals have been turned in to the paddock. Feed intake in grazing ruminants

8.  Dietary energy and fiber content. As has been mentioned, livestock eat to the point of satiety.  Another good definition of satiety is gastrointestinal satisfaction. Ruminants possess nutritional wisdom and will select diets high in digestible organic matter, because the most critical nutrients selected by ruminants are soluble carbohydrates.  What an animal actually eats from a pasture is often of higher nutritional quality than the average of the pasture overall. Feed intake in grazing ruminants

9.  Less digestible forages tend to stay in the animal’s digestive system longer (slowing the rate of passage) so the animal remains “full” longer, and subsequently doesn’t eat as much.  Younger plants therefore are generally more digestible than mature plants. Feed intake in grazing ruminants

10.  Physiological stage refers to the stage of life the animal is in, and what level and type of production are being supported.  The key physiological stages in the life of ruminant animals are: Growth (i.e., young lambs, kids, and calves) Late pregnancy (very important in sheep and goats) Lactation (for dairy production or maintenance of offspring) Maintenance (such as the cow’s dry period) Feed intake in grazing ruminants

11.  Temperature affects the amount of feed an animal needs to maintain its body functions.  An animal’s metabolic rate increases as the temperature drops below the animal’s comfort zone.  Subsequently, animals typically will not graze as much during hot, humid weather. Feed intake in grazing ruminants

12.  Ensure high forage intake by: Keeping forage in the vegetative stage through grazing management, Diversifying pasture composition to include several grass species, with around 30 percent of the pasture in legumes Maintaining a dense pasture so animals will take larger bits Feed intake in grazing ruminants

13. Poisonous plants for grazing animals

14.  Poisonous plants are a major cause of economic loss to the livestock industry.  Each year these plants adversely affect the cattle, sheep, and horses that graze on ranges.  These losses result from death of livestock, abortions, photosensitization, decreased production, emaciation, and birth defects.  In addition to these losses are those of increased management costs associated with such things as fencing, altered grazing programs, and loss of forage. Poisonous plants for grazing animals

15.  Livestock losses can be heavy if animals: Graze ranges infested with poisonous plants when plants are most toxic. are driven, trailed through, or unloaded from trucks onto range or pasture areas infested with poisonous plants. Animals are less selective in their grazing at these times of stress. Poisonous plants for grazing animals

16.  Livestock losses can be heavy if animals: are not watered regularly. are allowed to become hungry. Such animals are more likely to eat lethal quantities of poisonous plants. are grazed on rangelands early in spring when there is no other green vegetation except poisonous plants. are stressed, such as when they are trucked, penned, or handled (branding, vaccination, etc.). Poisonous plants for grazing animals

17.  Livestock losses can be heavy if animals: are not limited on how much and how fast they consume the plants. There are no known treatments for animals poisoned by most poisonous plants. Where a treatment is available, affected animals are usually in remote places and cannot be reached until it is too late to provide treatment. Poisonous plants for grazing animals

18.  Livestock losses can be heavy if animals: Furthermore, the stress of handling poisoned animals may increase the probability of death. If the animals recover enough to be handled, treatment should consist primarily of symptomatic treatment except where a specific treatment is known. Prevention of loss from poisonous plants in general is a problem of range and livestock management. Poisonous plants for grazing animals

19.  Under normal conditions, some poisonous plants form an important part of livestock diets without negative effects on the animals. Poisoning occurs only when these animals are enticed by hunger or other stress conditions to eat too much too fast.  Many of the death losses of livestock from grazing poisonous plants are due to management error.  This includes failure to examine a pasture or range prior to use because the growth of some of these plants varies from year to year. Poisonous plants for grazing animals

20.  Failure to know and understand plants in an area that are toxic to livestock can lead to catastrophic losses.  Hundreds of plants are poisonous to livestock. Many are toxic at all times, whereas others are toxic only under certain conditions.  Livestock producers are urged to become familiar with the plants on their ranges and pastures that are potentially dangerous to their livestock. Poisonous plants for grazing animals

21.  Help in identifying these plants can usually be obtained from the local county agricultural agent or by mailing a sample to the Plant Research Laboratory (PPRL) for identification.  Help with poisonous plant problems can also be obtained from local veterinarians.  Proper diagnosis of livestock poisoning is essential. However, under range conditions, diagnosis can be difficult. Poisonous plants for grazing animals

22.  Symptoms listed for each plant are those most likely to be observed.  Not all symptoms will be seen in all toxicities and signs of poisoning may vary greatly, depending on dosage and the time taken to consume the dose.  Also, individual animals respond differently to specific poisons. Poisonous plants for grazing animals

23.  To protect your animals from poisoning, do the following: Learn to identify the poisonous plants that grow on your range. Learn the conditions under which these plants can be dangerous to your livestock. Develop a grazing plan to improve your range and prevent poisoning. These plans should take into account the poisonous plants on the range, allowing animals to graze them at the most appropriate time or to avoid them. Poisonous plants for grazing animals

24.  To protect your animals from poisoning, do the following: Do not allow animals that have been under stress or that are overly hungry to graze in areas infested with poisonous plants. Provide adequate water for your livestock. Be especially careful when grazing newly acquired livestock on your range. Poisonous plants for grazing animals

25.  To protect your animals from poisoning, do the following: Provide adequate salt and other supplements as needed, but do not put them in an area where poisonous plants are growing. Control poisonous plants where feasible. If your animals get sick, consult your local veterinarian to ensure proper diagnosis and treatment. If a poisonous plant is involved, identification of the plant by an experienced botanist or poisonous plant expert is essential for any corrective action. Poisonous plants for grazing animals

26.  Many poisonous plants can function as useful forage. Poisoning occurs when conditions develop that allow, or cause, the animal to eat too much too fast.  Plants such as poison hemlock, water hemlock, arrowgrass, kochia, hounds tongue, and lupine may be growing on land from which hay is harvested. This is especially true on native pastures. Care must be taken when feeding this hay. Poisonous plants for grazing animals

27.  Drought increases plant toxicities.  Plants growing under stress produce stronger toxins. - High- strength toxins require less energy to produce than lower-strength toxins. Poisonous plants for grazing animals