Transition diets DCAD & Fertility

It is unquestionable that the dry period is the key to efficient milk production and fertility. Although there has been so much research done to quantify these benefits, it is still only partially used. One item I have not covered here is the effects I have seen from raised EPA / DHA levels being fed to dry cows - and the significant  knock on effects to fertility.

The DCAD system as written below always seems so overcomplicated when written. In reality high straw (short) corn silage, proteins, protected choline and magnesium chloride cover most of the requirements. Some of the best systems globally work perfectly as a result of good transition, equalling good fertility if the cow is set up right.  Simply you can cost effectively double the DMI at calving, stop milk fever, ketosis, retained placenta, LDA etc.

Milk fever occurs in dairy cattle after calving because of low blood calcium levels as a result of calcium moving into milk. There are about 23 grams of calcium in 10 litres of colostrum, and when this is added to the normal amount of calcium needed for maintenance, the needs of the cow can be more than 10 times the supply of calcium in her bloodstream. When the demand for calcium is greater than the supply in the blood this can cause the problems of milk fever, retained placenta, Ketosis etc, unless the cow can rapidly mobilise stored calcium in her body (e.g. in bones) to offset the situation. A nutritional approach to managing milk fever involves monitoring specific elements in the diet.

 Cations have a positive charge like sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg). Cations in the diet promote a more alkaline (higher blood pH) metabolic state which has been associated with an increased incidence of milk fever. Anions have a negative charge such as chloride (Cl), sulfur (S) and phosphorus (P). Anions promote a more acidic metabolic state (lower blood pH) that is associated with a reduced incidence of milk fever. A cow adjusts to a lower blood pH by buffering the acidic condition.

 Buffering the blood is done by the cow through mobilisation of calcium phosphate from bones. When a lower pH is achieved by feeding more anions, the result causes the cow to mobilise stored calcium which can better prepare her for the time when calcium will be lost in milk. This is the reason that there are various anionic products on the market: to reduce the incidence of milk fever.

The use of anionic salts and newer products based on hydrochloric acid-treated ingredients to lower blood pH is a common approach in close-up dry cow nutrition to avoid milk fever.

 Typically dry cow diets are high in cations because of feeding high potassium forages that are associated with milk fever. General rule of thumb - if its green then there is high potassium.

 You can evaluate the cation-anion status of ingredients or complete diets to determine the cation-anion difference, and it allows you to decide whether or not a change in forages (to lower potassium ones) or use of anionic products might be an effective strategy to manage milk fever. Calculating a diet's DCAD status to check for potential problems is easily done using a straightforward equation.

 The calculation for DCAD requires converting the various anions and cations in a diet into milliequivalents (mEq). This is done because of the different chemistry of each element and a system that accounts for the impact of each one in the balance calculation is necessary. DCAD is reported in mEq/kg of diet. The DCAB equation involves subtracting the mEq of anions from the mEq of cations and the result can be positive or negative.

 An important aspect of evaluating a diet for DCAD is that the mineral content of the diet has been accurately determined. A mineral analysis by wet chemistry, not by near-infrared (NIR) analysis is important. Another consideration is to adjust for the cations and anions present in drinking water. Not all minerals in water are necessarily nutritionally available to the cow but water high in cations or anions could affect the DCAB.

 Milliequivalents (mEq):

Milliequivalents are calculated by multiplying the content of each element in the diet by a conversion factor. The factors are as follows for mEq/kg (dry matter):

 For example, a diet containing 0.15% sodium, 1.1% potassium, 0.2% chloride and 0.2% sulfur, the milliequivalents would be:

 DCAD Equation:

 The equation for calculating the DCAD for a diet (or ingredient) is:

(sodium+potassium) - (chloride + sulfur) = DCAD in mEq/kg

 From the above example, the result is:

 (65.25 + 281.6) - (56.4 + 124.8) = mEq/kg

(346.85) - (181.2) = +165.65 mEq/kg

 The DCAD equation and conversion to milliequivalents can be combined as follows into one step:

 [(sodium x 435)+(potassium x 256)] - [(chloride x 282)+(sulfur x 624)] = mEq/kg

Guidelines:

If a diet is calculated to be +200 mEq/kg dry matter or more, a switch to lower potassium forages in the dry cow diet should be considered first. In some cases, the introduction of anionic products, particularly the older anionic salts, can reduce feed intake because they may be unpalatable. Reduced feed intake before calving can create bigger problems than milk fever such as displaced abomasum and ketosis.

The DCAD in the transition diet should be between negative 100mEq/kg andnegative 200 mEq/kg dry matter to effectively control milk fever and low blood calcium.

 Check your ration for added cations such as sodium coming from sodium bicarbonate. salt etc. A general rule of thumb is to seriously avoid lactating cow minerals to close-up cows in lead-feeding situations.

 Monitor cow urine when using anionic products. Urine pH is a reasonable indicator of metabolic pH status and reflects the effectiveness of anionic products. Urine pH should be 6.0 to 6.5 for Holsteins and 5.5 to 6.0 for Jerseys. Best time I find to test is when they get up from beds and go to collecting yard then stand - perfect sample time without the wait.

 A gradual introduction to anionic products and incorporating them into a total mixed ration (TMR) can reduce palatability problems, but upto 200g of magnesium chloride is OK. 

OVERALL TRANSITION DIET

Overfeeding energy during the dry period has resulted in reduced performance and higher incidences of metabolic disorders:

• Lower fresh cow DMI and slower starts in milk production
  
• Higher NEFA (non-esterified fatty acids) in blood and more triglyceride in the liver after calving
  
• Greater deposition of fat in the dry cow with moderate overfeeding of non-lactating cows for 57 days leads to increase in visceral adipose tissues (omental, mesenteric and perirenal) than in cows fed a high-straw diet to control energy intake at requirements
  
• Decreased neutrophil function postpartum (Controlled energy intake during the dry period improved neutrophil function, which may lead to better immune function.)

Many people have adopted the controlled-energy diet with a one-group dry cow feeding scenario. The success of this program is largely related to controlling bodyweight gain and condition through the far-off period.

There is little evidence that two-group strategy (-60 to -30, then -30 to calving)offered any advantage compared with the single-diet (controlled-energy high-fibre) strategy. However, I find that the lower feed cost from -60 to -30 does make the two stage worthwhile.

The potential “stumbling block” for the one-group feeding strategy is the marked difference in the pre-fresh and post-fresh diets.

The pre-fresh diet is bulky and low-energy while the post-fresh is usually a denser, higher-energy diet with shorter material. Improving the transition between these two diets and optimising DMI in the fresh period is critical for success.

The severity of negative energy balance (NEB) for the fresh cow is related to energy output and energy intake. The primary driver for energy intake is not energy density of the diet but the DMI. This has enormous effect on fertility.

Improving DMI in the fresh period will reduce the severity of fresh cow NEB. Research has shown that the fresh cow DMI can be improved by employing strategies such as:

• Feeding sugar and reducing starch
• Reducing forage fibre with non-forage fibre sources
• Reducing forage fibre with non-forage fibre sources and reducing starch levels

Ensuring a smooth transition from the pre-fresh to the post-fresh diet will improve DMI. What other strategies can be used to improve this transition? The dry cow ration and the fresh cow ration are remarkably different on paper but should “look” similar to the cow. This can be accomplished by:

1. Reducing particle size of the dry cow TMR to “mimic” the particle size of the lactating TMR.

• Using finely chopped straw (less than 1 inch) will create a non-sortable ration for the dry cow. Use the Penn State Forage Separator (with three compartments) to evaluate. Aim at:

- Less than 10 percent top

- Less than 45 percent middle

- Less than 45 percent bottom

• The reduced particle size will increase passage rate through the rumen and lead to considerably higher DMI in the pre-fresh group. Because of the higher DMI, more chopped straw should be added to control energy intake.
  
• The higher DMI pre-calving will be closer to the expected DMI post-calving; decreasing this gap will improve the transition between the two diets.Feeding a higher-energy/denser diet (such as a close-up diet) can also lead to higher DMI pre-calving, but this will result in higher concentration of liver fat.

1. Feed similar ingredients pre- and post-calving. Corn silage, quality protein, some slow starch. However, keeping the diet ingredients between the two groups similar will improve the transition.

• Keeping total diet K levels low (less than 1.2 percent of DMI) is a key strategy.
  
• The use of rumen protected Choline helps condition the liver, reduce ketosis and improves liver performance. These areas have significant positive effects on fertility.

1. Increase density (kg per cubic foot) of the pre-fresh diet or lower the density of the fresh cow diet. Because of the bulky nature of the chopped straw diet, there may be a noticeable difference in the density (kg per cubic foot) of the pre-fresh and the post-fresh diet.

• Add water to the pre-fresh TMR. A wetter TMR will both increase the density and reduce sorting behaviour.

1. Ensure fermentability of the diet. The dairy cow’s microbial population requires nitrogen and carbohydrates to fuel growth. Having a healthy and vibrant population at calving will improve the transition to the fresh cow diet.

• Add fermentable carbohydrate sources such as beet pulp or soyhulls in the dry cow diet. These are moderate energy sources as compared to corn but will add fermentability.
  
• Add urea as a fermentable nitrogen source. This also helps control energy while trying to maintain appropriate protein levels in the diet.

1. Using ketogenic ingredients (beet pulp, sugar, whey permeate) in the fresh cow diet may improve the energy available for rumen papillae and encourage rumen microbial growth.

Ketogenic ingredients are ingredients that tend to shift ruminal VFA to increased levels of butyrate. Butyrate is the primary VFA that supplies energy to the rumen and may be involved in rumen papillae growth.

Butyrate is converted to BHBA by the ruminal papillae for fuel. Ruminally derived ketones do not pose a problem, while hepatic-derived ketones are indicative of a problem (incomplete oxidation of fatty acids or ketosis).

Designing a dry cow diet that mimics the physical properties of the lactating diet but is nutritionally designed for the dry cow will improve this delicate transition balance.