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1、Nutrient requirements,XIANYAO LI,Content,Beef cattlePoultry,Nutrient requirements of beef cattle,A balanced and cost effective nutrition program is essential to the success of any beef cattle operation.Expensive grasslands demand efficient utilization of forages.Supplemental feeding and complete fee
2、ding programs must be designed to meet the nutrient needs of beef cattle and,at the same time,make the most of the available feed resources.,Nutrient requirements of cattle change with age,stage of production,sex,breed,environmental conditions,and basal diet quality and amount.Therefore,gaining know
3、ledge of nutrient requirements and the factors influencing these requirements is a necessary first step to designing a nutrition program that is both efficient and cost effective.This section will discuss the protein,energy,mineral,and vitamin requirements of beef cattle.In addition,tables of nutrie
4、nt requirements are provided.,Dry Matter Intake,There really is no requirement for feed intake,although an estimate of how much forage and feed that a cow will consume is essential when evaluating rations,supplements,or predicting animal performance.Dry matter(DM)intake is influenced by a number of
5、different factors.The dry matter(or otherwise known as dry weight)is a measurement of the mass of something when completely dried.The dry matter of plant and animal material would be its solids,Dry Matter Intake,A few of the more important variables include animal weight,condition,stage of productio
6、n,level of milk production,forage quality,amount and type of supplement or feed provided,as well as environmental conditions.,Cattle have a daily requirement for a certain quantity of specific nutrients such as protein,calcium,and vitamin A.The necessary concentration of these nutrients in the diet(
7、to meet the animals requirement)is then determined by the amount of feed consumed.,For example,steer calves gaining 2 lb per day may require 1.6 lb of protein per day.If they consume 15 lb of DM daily,the protein requirement could be expressed as 10.7%of DM intake.On the other hand,if they are limit
8、 fed to consume only 10 lb of DM daily,the protein requirement for 2 lb of gain could be expressed as 16%of DM intake.Intake in forage fed cattle is generally limited by the forage capacity of the digestive tract.,Forage digestibility values rarely exceed 70 to 74%of dry matter.Calves（牛犊）and yearlin
9、gs（一两岁的牛）are frequently fed higher quantities of concentrate feeds 浓缩饲料 to improve weight gain and feed conversion above what can be achieved with forage alone.When diet digestibility approaches around 70%,feed intake is no longer regulated or limited by the capacity of the digestive tract.,Rather,w
10、ith diets high in digestible energy,physiological mechanisms are turned on to limit intake,This response can be thought of as a built in safety mechanism so that cattle are less likely to consume too much of a highly digestible diet,causing digestive upset,bloat,and founder（蹄叶炎）.,Forage intake is hi
11、ghly correlated with forage quality,The more rapid rate of digestion and passage of higher quality forage results in considerably higher dry matter intake compared to forage that is lower in digestibility.Intake estimates assume that protein requirements are met by the forage or through supplementat
12、ion when forage protein is not adequate.,Cattle with greater mature body weight and frame consume more forage compared to smaller frame cattle and lactating cows consume considerably more of the same quality forage compared to gestating cows,Cattle that are fleshy consume 3 to 10%less feed or forage
13、 compared to cattle that are in average to thin condition.Cold stress increases dry matter intake,while heat stress reduces dry matter intake.With this many factors influencing this trait,it is obvious that dry matter intake is very difficult to accurately predict.,Estimates of dry matter intake pre
14、sented in the nutrient requirement tables are determined using published prediction equations.These equations take into account the effects of the animals weight,level of milk production for lactating cows,energy content of the diet,stage of production,and body condition in the case of the pregnant
15、replacement heifers（后备母牛）.,It is important to note that all of these equations assume that adequate protein is supplied in the diet to maximize ruminal fermentation.In other words,if the diet is deficient in protein,these dry matter intake values will overestimate the amount that the cattle will act
16、ually consume.,Protein,Proteins are large chemical units made up of hundreds of amino acids.Amino acids,in turn,are organic(carbon containing)compounds that also contain nitrogen,oxygen,and sometimes sulfur.Animals consume proteins in their diets and then utilize the amino acids for synthesis of mus
17、cle,blood proteins,and other body components.,In swine,poultry,and other non-ruminants,the amino acids must be supplied in definite proportions in the diet.However,in ruminants,microorganisms(bacteria and protozoa)breakdown most dietary proteins and incorporate the nitrogen and amino acids into thei
18、r own body tissue.,The microorganisms are digested in the small intestine of the ruminant animal.The bacteria themselves have a protein requirement and must have adequate protein to do their job of digesting roughages（粗饲料）to end products（终产物）that can be utilized by the cow.,Because of the ruminal br
19、eakdown of dietary proteins and because the amino acid make-up of microorganisms is adequate for most classes of beef cattle,feed and forage amino acid composition is generally not critical compared to non-ruminant diets.On the other hand,a high priority should be placed on providing adequate rumina
20、lly available protein in order to allow the bacteria to grow and digest roughages.,Chemical crude protein concentration is determined by multiplying the feed nitrogen concentration by 6.25 because protein molecules contain an average of 16%nitrogen(1/16=6.25).The crude protein system has been the st
21、andard for evaluating beef cattle protein requirements and dietary supply for a long time.,More recently,the metabolizable protein system has been used to better characterize protein degradability as well as its site and extent of digestion.In order to effectively use this new system,the user must b
22、ecome familiar with several new terms.These include degradable intake protein(DIP)可降解进食蛋白质,undegradable intake protein(UIP)非可降解进食蛋白质,and metabolizable protein(MP)可代谢蛋白质.,Degradable intake protein is the feed protein fraction that is degraded in the rumen.Nitrogen from DIP is either used for microorg
23、anism protein synthesis or passes through the rumen wall into the blood stream and is carried to the liver as ammonia.In the liver this nitrogen can be converted to urea after which it is recycled to the rumen through saliva or filtered out of the blood stream in the kidney to be excreted in the uri
24、ne.,Undegradable intake protein is the feed protein fraction that bypasses fermentation in the rumen to be degraded and absorbed in the small intestine.Metabolizable protein is the sum of protein derived from microorganism origin plus UIP.,Perhaps one of the most practical applications of the MP sys
25、tem is the calculation of the animals DIP requirement to insure optimal rumen function.For this reason,feed DIP values are included in most feed composition tables.The requirement for DIP is thought to be closely associated with the amount of fermentable energy in the diet.,Specifically,the DIP requ
26、irement can be calculated as 10 to 13%of daily total digestible nutrient(TDN)intake.Lower values in this range are used when the cattle are receiving a low quality diet,such as dry winter range forage or low quality hay,whereas higher values in the range are used when the cattle are receiving high q
27、uality forage or a ration including at least 50%concentrate.The UIP value of the feed can also be calculated by subtracting the DIP value from one.,Example of DIP requirement and supply,A cow is consuming 25 lb of hay dry matter that contains 50%TDN.The cow therefore consumes a total of 12.5 lb of T
28、DN per day.The DIP requirement is 12.5 lb x 10%,or 1.25 lb of DIP per day.The hay contains 6%CP(dry matter basis),of which 65%is DIP,this cow would consume 0.98 lb of DIP each day(6%x 65%x 25 lb).The requirement for supplemental DIP would be 0.27 lb(1.25 lb-0.98 lb).,Research demonstrates that rumin
29、al fermentation may be compromised with low protein diets.Therefore,7%dietary crude protein was the minimum value used in the nutrient requirement tables in this publication.The requirements are expressed in both pounds per day of crude protein and in terms of the percentage required in the diet dry
30、 matter.These tables illustrate the influence of age,weight,desired rate of weight gain,stage of production,and genetic milking ability on nutrient requirements.,Replacement heifers need to gain about 1.0 to 1.5 lb/day in order to reach 60 to 65%of their expected mature weight and puberty 初情期 by 15
31、months of age.They also need to gain around 1 lb/day from the time they are bred until they calve 产犊 in order to reach approximately 80%of their mature weight when they calve for the first time.,The requirement of protein for muscle and organ growth is reflected in the large daily requirement for pr
32、otein.Growing heifers require a high concentration of protein in the diet because of their low dry matter intake.They must have access to good quality forage or be fed supplemental protein to achieve adequate growth prior to their first breeding season.,Gestation has little effect on the cows protei
33、n requirement until about the seventh month of pregnancy.About 2/3 of the fetal growth occurs during the last 1/3 of pregnancy and the protein intake of the cow should be increased during the last 1/3 of pregnancy to insure that the cow will be in good condition at the time of calving.,The cow is pr
34、ogrammed to take care of the fetus at the expense of her own body,and losses of body condition frequently occur in late pregnancy when daily protein or energy are not increased to match the needs of the pregnant cow.Adequate dietary protein during this period is also essential for the cow to produce
35、 abundant,high quality colostrum初乳(first milk),which will influence the newborns immune system for the remainder of its life.,Lactation is the most nutritionally stressful activity for the cow.The modern commercial beef cow produces around 20 lb of milk each day during peak lactation.Milk contains a
36、 high concentration of protein.Therefore,lactating cows,particularly during early lactation,require nearly twice the daily protein of dry cows.Research shows that cows in moderate condition at calving should at least maintain body weight from calving to rebreeding for good conception rates.,Failure
37、to take into account the increased protein demand brought on by lactation may result in long intervals before rebreeding.Beef breeds with superior milking ability(25 to 30 lb/day),and high producing cows within a breed or herd have an even higher protein requirement.Increasing cow size adds to the d
38、aily protein requirement but not nearly to the extent that lactation does.,As mature size increases,more protein is required to maintain the heavier muscle mass and to permit faster gains that must be made by young females of larger breeds.,Energy,The cow requires energy for grazing,traveling,fetal
39、development,milk production,temperature maintenance,reproduction,digestion,and voiding of body wastes.In addition,first and second calf cows require additional energy for growth until they mature at about four years of age.If cows are thin,additional energy will be required to restore their body con
40、dition to a moderate level.,The bulk of energy for grazing cattle comes from rumen digestion of forages and roughage products.With proper amounts of protein and minerals,the rumen is capable of getting energy from a wide range of feeds that are useless to non-ruminants.,Because the rumen bacteria th
41、emselves require protein,just as the animals body does,it is impossible to discuss ruminant energy requirements separately from ruminant protein requirements.With too little protein in the diet,the bacteria will not efficiently digest roughages,while with too much protein in the diet,the protein wil
42、l be deaminated(the nitrogen removed)and used as a very expensive energy source.,Energy requirements are expressed in the table in terms of TDN and net energy for maintenance(NEm)and(or)net energy for gain(NEg).TDN is the sum of the digestible starch,fiber,protein,and fat in a feed with a correction
43、 factor for the high energy content of fat and the amount of ash or mineral content.TDN requirements are expressed as a percent of the diet dry matter as well as in pounds per day required.,Net energy requirements are expressed in terms of mega calories per pound of feed and mega calories required p
44、er day.The same factors that influence protein requirements also influence energy requirements:animal weight,rate of gain,lactation,and fetal development.Lactation represents the greatest need for additional energy beyond that needed for maintenance.,An average milking beef cow requires nearly 50%mo
45、re TDN or net energy than she does when dry.It should be noted that lactating cows consume more forage compared to gestating cows due to the increased energy demand.,Energy requirements for first-calf heifers are higher than for mature cows because energy is needed for growth,in addition to body mai
46、ntenance and lactation.Inadequate energy during the last third of gestation and during the critical time from calving to rebreeding can lead to poor rebreeding.,Large cows will require more energy than will small cows.For example,a 1,300 lb dry pregnant cow in the middle third of pregnancy requires
47、32%more TDN per day than a 900 lb cow at the same stage of production.Producers who are increasing the mature size of their cows should recognize the greater energy requirements of the larger cows and reduce their stocking rates to compensate.,Vitamins and Minerals,The National Research Council publ
48、ishes equations to determine calcium and phosphorus requirements and these estimated requirements are shown in Tables 2 through 6.Less is known about specific dietary requirements for the other important macro and micro minerals.Therefore,the National Research Council provides general dietary guidel
49、ines and maximum tolerable levels for each of these minerals.,Water,Do not forget that water is a common but an entirely essential nutrient.Water intake increases dramatically with increased age,weight,and temperature.Clean water is most important for young growing calves,but dirty water can retard
50、performance and be a breeding ground 滋生地for disease in cattle of all ages.,Other Considerations,The requirements shown in the tables are designed for healthy unstressed cattle in good condition.Thin heifers or cows should be fed additional energy and protein to achieve good body condition.Some addit
