It’s More Than Corn: Importance of Physiological Phases
This section of the series, when coupled with the previous posts, begins to layout some of the benefits to having the ability to utilize grain in the diets of livestock, particularly as an animal’s need for energy and protein increase through various stages of physiological maturity.
How do physiological phases affect rations?
When evaluating the science of livestock production, we divide growth into several different physiological phases. All animals, including humans, are involved with at least one of the phases at all times, maintenance, but are rarely involved in more than two or three at any given time. Each phase has its own unique nutritional requirements and thus, rations are changed according to the phase and the animal’s requirements.
Maintenance is the maintaining of an animal’s health and well-being. A maintenance ration meets an animal’s need who is not growing, not pregnant, not storing fat and not yielding a product (milk, wool, etc.). Basic maintenance requirements include energy for vital organs to function properly, maintaining body temperature, protein for body tissue repair; replace mineral loss, vitamins for maintenance and certain fatty acids.
Growth is primarily an increase in muscle, bone, organs and connective tissue. It is essential during the growth phase that nutrient needs are met to insure that the animal can attain its proper mature status and size. During this phase there is an increased need for high quality protein, higher energy and a greater demand for adequate levels of minerals and vitamins. Daily growth rate increases until puberty and then decreases through maturity.
Fattening in an animal is simply put, the deposition of unused energy in the form of fat within the body tissues. Fattening is split into two categories. Abdominal, intermuscular and subcutaneous deposition is for the most part undesirable, but unavoidable is marbling is to occur. The second, intramuscular deposition is commonly referred to as marbling and is difficult to obtain without excessive deposition from the first category. The primary requirement for fattening is energy, net energy (NE). During this phase, protein requirement decreases to an extent, but must be maintained for proper digestion. There is also an increase in need for vitamins related to energy metabolism.
What is the difference between growth and fattening in relation to weight gains?
Weight gain in animals is derived from growth, fattening and fill, or increase in content of feed and water. Growth is a much cheaper form of weight gain than fattening is. Gain from growth is primarily in the form of protein tissue and bone. Gain from fattening is largely in the form of fat. Protein tissue is basically 75% water and 25% protein. As mentioned in an earlier post, protein is one of the most costly nutrients, but water is essentially free. Therefore, protein tissue is a cheap source of gain. On the other hand, gain from fat is considered expensive. There is very little water and mineral deposition in fat. In fact, as in humans, fat will actually replace water in tissues, which makes for a very uneconomical exchange. Additionally, is requires about 2.25 times for net energy (NE) to form a pound of body fat that is required to form a pound of protein. Young animals are more efficient and cheaper to grow than older animals. Also, older animals are easier to fatten than younger, because a greater percentage of their energy consumption is available for fattening.
Fetal Development Phase
There are two considerations to have in mind when feeding during gestation. The first is to provide nutrients for the development of the fetus and the second is to provide nutrients during gestation to build up a nutrient reserve to meet requirements for milk production following parturition. It is also important to consider that females that too fat can have difficulty conceiving and may deposit fat in the mammary system, reducing ability to produce milk. Additionally, bred cows, that are fed to liberally, may experience an oversized fetus and/or difficulty during parturition.
Typically we associate milk production with the dairy cow. While it is a dairy cows specialty, all females produce milk upon giving birth to young. The nutritional requirements for milk production are in proportion to the amount of milk produced. The major requirements are high quality protein, adequate energy, calcium, phosphorus, vitamins A and D and salt.
To summarize this section, it is important to realize that the nutrient requirements for each of these phases is over and above the nutritional requirements for basic maintenance.
Stay tuned for Part 5: Feeds and Feed Groups