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“We are stuck with technology when what we really want is just stuff that works.”

In general, feeds with high moisture and high protein concentrations, eg, legume silages, will have a high proportion of RDP. In contrast, feeds that have been processed and especially those that have undergone drying will have relatively high proportions of RUP.

The proportions of RUP and RDP in diets and individual ingredients are not fixed but can vary somewhat depending on intake rate. At high rates of feed intake, the rate of feed passage through the rumen is high; thus, there is less opportunity for rumen protein degradation than with the same feeds at lower intake rates.

Therefore, on the same diet, RUP proportions are higher in animals with high rates of feed intake than in those with low rates of feed intake. Animals most likely to benefit from supplements selected for high RUP proportions are those with relatively high protein requirements and relatively low rates of feed intake. Cows in very early lactation and young, rapidly growing heifers are the primary examples. Supplements formulated for high RUP proportions are commonly known as rumen bypass protein supplements; however, even with these types of supplements, some portion of the protein is degraded in the rumen.

Along with overall protein requirements, dairy cows, as all other animals, have specific amino acid requirements. However, evaluating dairy cow diets relative to amino acid requirements is more difficult than making similar evaluations of diets for monogastric animals. This is because the amino acid supply for dairy cows and other ruminants is a combination of the amino acids provided by the microbial protein and the RUP.

Microbial protein has an excellent amino acid profile, and diets with a large supply of microbial protein typically meet amino acid requirements if MP requirements are met. In some cases, however, high-producing dairy cows may benefit from the selection of RUP sources with specific amino acid profiles, or from adding rumen-protected forms of specific amino acids.

Software is available that estimates the amino acid supply for dairy cows on different diets. The first limiting amino acids in typical dairy cow diets are lysine and methionine.

With typical feedstuffs, if the MP requirement is met and the dietary lysine: The availability of high-quality water for ad lib consumption is critical. Insufficient water intake leads immediately to reduced feed intake and milk production. Water requirements of dairy cows are related to milk production, DMI, ration dry matter concentration, salt or sodium intake, and ambient temperature.

Various formulas have been devised to predict water requirements. Two formulas to estimate water consumption of lactating dairy cows are as follows:. Water consumed as part of the diet contributes to the total water requirements; thus, diets with higher moisture concentrations result in lower FWI.

Providing adequate access to water is critical to encourage maximal water intake. Water should be placed near feed sources and in milking parlor return alleys, because most water is consumed in association with feeding or after milking. For water troughs, a minimum of 5 cm of length per cow at a height of 90 cm is recommended. One water cup per 10 cows is recommended when cows are housed in groups and given water via drinking cups or fountains. Many cows may drink simultaneously, especially right after milking, so trough volumes and drinking cup flow rates should be great enough that water availability is not limited during times of peak demand.

Water troughs and drinking cups should be cleaned frequently and positioned to avoid fecal contamination. Poor water quality may result in reduced water consumption, with resultant decreases in feed consumption and milk production. Several factors determine water quality. Total dissolved solids TDSs , also referred to as total soluble salts, is a major factor that refers to the total amount of inorganic solute in the water. TDS is not equivalent to water hardness, which is a measure of the amount of calcium and magnesium in water.

Water hardness has not been shown to affect dairy cow performance. Water may be refused when first offered to animals or cause temporary diarrhea. Animal performance may be less than optimum because water intake is not maximized. Pregnant or lactating animals should not drink such water.

May be offered with reasonable safety to animals when maximum performance is not required. These waters should not be offered to cattle. Other inorganic contaminants that affect water quality include nitrates, sulfates, and trace minerals. General recommendations for sulfate concentrations in drinking water are Concentrations of Potentially Toxic Nutrients and Contaminants in Drinking Water Generally Considered Safe for Cattle lists potential elemental contaminants of drinking water with upper-limit guidelines.

Calcium requirements of lactating dairy cows are high relative to other species or to nonlactating cows because of the high calcium concentration in milk. Thus, inorganic sources of calcium, such as calcium carbonate or dicalcium phosphate, must be added to the rations of lactating dairy cows.

For the first 6—8 wk of lactation, most dairy cows are in negative calcium balance, ie, calcium is mobilized from bone to meet the demand for milk production.

This period of negative calcium balance does not appear to be detrimental so long as there is sufficient dietary calcium such that bone reserves can be replenished in later lactation. The availability of dietary calcium for absorption varies with dietary source. Dietary calcium from inorganic sources is generally absorbed with greater efficiency than that from organic sources. Furthermore, cows in negative calcium balance absorb calcium more efficiently than cows in positive calcium balance.

When calculating calcium requirements, newer nutritional models take into account the variability in calcium availability from different sources. This approach makes it difficult to generate general recommendations for total dietary calcium concentrations across various diets. Generally, diets with large portions of forage from legume sources will have minimum calcium concentration requirements in the range of 0.

Two approaches are taken with respect to the calcium supply for dry cows, each with the objective of preventing milk fever, or parturient paresis see Parturient Paresis in Cows. One approach is to place cows in a calcium-deficient state during the last 2—3 wk of gestation; the rationale is to stimulate parathyroid hormone secretion and skeletal calcium mobilization before calving. This makes calcium homeostatic mechanisms more responsive at the time of parturition, allowing cows to maintain serum calcium concentrations during lactation.

This approach requires diets with calcium concentrations near 0. Such diets are difficult to formulate with available feedstuffs while still meeting other nutritional requirements. Another approach is to feed an acidifying diet, usually referred to as a diet with a low or negative dietary cation-anion difference DCAD. The low-calcium diet approach is not additive with the DCAD approach to milk fever prevention. When low-DCAD diets are fed, total dietary calcium concentrations should be near 0.

Phosphorus nutrition for lactating dairy cows has dynamics similar to those of calcium. The efficiency of phosphorus absorption is affected by physiologic state and dietary source. As is the case with calcium, most dairy cows in early lactation are in negative phosphorus balance.

Phosphorus mobilized from bone early in lactation is replaced during later lactation when feed intakes are higher. Young animals and animals in negative phosphorus balance absorb phosphorus more efficiently than do older animals or animals in positive phosphorus balance.

Phosphorus from inorganic sources is more available than that from organic feed sources. Judiciously balancing diets to meet, but not exceed, phosphorus requirements is important for dairy cow performance and environmental stewardship.

Excess phosphorus excreted in feces is one of the major pollutant risks associated with livestock production. Newer nutritional models account for variation in phosphorus availability from different sources, but there is less variation in availability among phosphorus sources than among calcium sources. Total dietary phosphorus concentration requirements for most dairy diets will be in the range of 0. Phosphorus supplementation for dry cows is seldom necessary. Serum concentrations of calcium and inorganic phosphorus are of value in assessing the short-term homeostasis of these minerals but of little value in assessing longterm nutritional status.

Bone ash concentrations are the best way to assess longterm calcium and phosphorus nutritional status. Other macrominerals required in dairy cow diets include sodium, potassium, chloride, magnesium, and sulfur. Of these, sodium generally needs to be supplemented, typically as sodium chloride or common salt.

Insufficient dietary sodium results in reduced feed intake with subsequent reductions in animal performance. Signs of severe salt deficiency include licking and chewing on fences and other environmental objects, urine drinking, and general ill thrift. Milk production is reduced within 1—2 wk of removing supplemental salt from the diets of lactating cows.

Completely withholding salt from dry cow diets in an effort to prevent udder edema at calving is not a good practice. Maintenance requirements for sodium in nonlactating cows are estimated at 1. Additional salt is necessary during heat stress. Although salt should be supplemented to dry cows in required amounts, excessive salt supplementation is unnecessary and may contribute to udder edema at calving.

Supplemental magnesium may need to be fed with diets containing high proportions of grass forages, especially those consisting of rapidly growing pasture grasses. Such forages typically have low magnesium concentrations as well as high concentrations of potassium and organic acids, which interfere with the availability of dietary magnesium. Magnesium oxide is the typical magnesium supplement in ruminant diets.

Dairy cattle, like other animals, have no dietary requirement for inorganic sulfur. The dietary requirement for sulfur reflects only the dietary requirement for sulfur-containing amino acids. In ruminants, rumen microbes can synthesize sulfur-containing amino acids from nonprotein sources of nitrogen and sulfur. Dairy cow diets most likely to require supplemental sulfur are those with low protein concentrations and those with supplemental nonprotein nitrogen.

In general, a nitrogen: Recommended dietary concentrations for typical dairy cow diets are: The trace minerals typically supplemented or measured in dairy cow diets include cobalt, copper, iron, manganese, selenium, iodine, and zinc. Of these, selenium and copper are the trace minerals most likely to be deficient. Several areas of North America, Europe, and other continents are characterized by growing conditions that result in feeds with low selenium concentrations. In these areas, livestock feeds need to be supplemented with selenium.

Sources of supplemental selenium include sodium selenite, sodium selenate, and selenomethionine. The latter source is typically referred to as organic selenium. Selenium deficiency is known to cause myopathies in calves, which may affect cardiac or skeletal muscle ie, white muscle disease, see Nutritional Myodegeneration.

In adult cattle, selenium deficiency appears to suppress immune function and especially neutrophil function. It also increases the risk of retained placenta, although feeding selenium in excess of requirements does not prevent this condition.

Dietary selenium requirements in dairy cattle are estimated at 0. In the USA, 0. The selenium status of cattle can be accurately assessed from blood or serum concentrations. These include primarily sulfur and molybdenum, but iron, zinc, and calcium may also interfere with copper availability. Copper deficiency is characterized by loss of hair pigmentation, loss of hair around the eyes, anemia, and general ill thrift and suppressed immunity.

In severe cases, persistent diarrhea may also occur. The copper status of cattle can be assessed from liver or serum copper concentrations. Liver concentrations Dietary manganese deficiencies in dairy cattle are less common than deficiencies of copper or selenium.

Signs include poor growth and skeletal deformities in newborn calves and reproductive abnormalities, including anestrus, in adult cows. Signs of zinc deficiency include reduced feed intake and general ill thrift. Parakeratosis, particularly around the nostrils and lower legs, and weakening of the hoof horn are signs of prolonged zinc deficiency. Normal concentrations of serum zinc are 0.

Concentrations Iron deficiency is extremely rare in adult cattle, because iron is ubiquitous in the environment and the endogenous concentrations of iron in most feedstuffs will more than meet requirements.

Signs of iron deficiency are primarily anemia and low serum iron concentrations. However, these concentrations drop quickly in the presence of inflammatory disease, and such changes in serum iron concentrations should not be interpreted as being due to a dietary deficiency. Suckling calves are the only group of cattle generally at risk of iron deficiency and to which supplemental iron need be provided. Iodine deficiency occurs with some frequency in cattle and is primarily manifest by goiters in newborn calves.

However, dietary iodine concentrations of 0. Preformed vitamin A, or retinol, does not exist in any plant material, so there is no vitamin A in natural diets for dairy cattle.

Recommended vitamin A consumption rates for various classes of cattle are based on providing supplemental vitamin A, which is derived from commercial sources: Conditions that can increase dietary vitamin A requirements in adult cows include low forage diets, high corn silage diets, poor quality forages, and infection. The vitamin A status of cattle may be assessed via serum or hepatic vitamin A concentrations. The liver stores vitamin A for release during periods of insufficient dietary intake, thus making liver the ideal tissue for nutritional assessment.

Clinical signs of vitamin A deficiency do not occur until these reserves have been substantially depleted. Calves are born with low body stores of vitamin A and depend on colostrum consumption to supply hepatic vitamin A stores.

Most milk replacer diets have substantially higher concentrations of vitamin A, possibly because vitamin A requirements may be increased by infectious diseases, especially those affecting the respiratory or enteric epithelium. Vitamin A deficiency is associated initially with night blindness followed by poor growth, poor hair coats, and suppressed immunity. In adult cattle, vitamin A deficiency is associated with retained placentas and impaired fertility. Vitamin D is necessary for the absorption and metabolism of calcium and phosphorus.

Recent research suggests that vitamin D may also be necessary for immune cell function. Vitamin D 3 cholecalciferol can be formed by the solar irradiation of skin or vitamin D 2 by the solar irradiation of forages. However, reliance on natural vitamin D formation is considered unreliable, and vitamin D requirements are based on recommendations for supplement addition to diets.

Vitamin D status can be assessed via blood serum concentrations of hydroxycholecalciferol. Thus, cattle receiving pasture or fresh-cut forages may require little vitamin E supplement. In contrast, vitamin E degrades in stored forages, so dairy cattle on typical confinement-reared diets require supplemental vitamin E. Vitamin E functions to protect cellular membranes from oxidative damage. Clinical manifestations of deficiency include nutritional myopathy white muscle disease, see Nutritional Myodegeneration in young calves and diseases in older cattle including retained placenta and increased susceptibility to environmental mastitis.

Recommended rates of vitamin E intake vary based on gestation stage: Bulletins dated and earlier are in descending order by bulletin number. California Department of Education. Department of Agriculture Policy Memoranda January Thursday, September 6, This institution is an equal opportunity provider. Esta institución es un proveedor que ofrece igualdad de oportunidades.

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