Strategies to Maximize Feed Intake and Milk

Strategies to Maximize Feed Intake and Milk Yield in Early Lactation

Department of Animal Science, Michigan State University, East Lansing, MI 48824-1225 U.S.A.

Take Home Messages

Energy intake in early lactation is affected by many different environmental, management, animal, and dietary factors.

Maximizing energy intake requires appropriate management through all phases of lactation.

Diets must be formulated to balance fermentation acid production.

Introduction

As milk production per cow continues to increase, one of our greatest challenges to maintain health is to increase energy intake in early lactation. Possible benefits of increasing energy intake in this period include reduction in incidence of ketosis and hepatic lipidosis, and increased reproductive performance. Formulating diets for groups of dairy cows is especially challenging because of the physiological diversity of animals within the group. Even when animals are grouped according to their nutrient requirements, differences in their predisposition to metabolic diseases exists because of differences in body condition, liver function, absorptive surface area and blood supply to the rumen, etc. The purpose of this presentation is to review management practices that can increase energy intake for dairy cows in early lactation, thereby improving their health and increasing milk yield.

Factors Affecting Energy Intake

Provide for Cow Comfort

Facilities have a great effect on animal performance and the success of a nutrition program. Factors to consider are good ventilation, adequate space per animal, adequate footing, good clean bedding, and easily cleaned feed bunks. The importance of good facilities cannot be overemphasized; often sub-optimal feeding strategies must be devised to compensate for inadequate facilities. For instance, to reduce incidence of acidosis from slug feeding for cows with inadequate bunk space, higher fiber, less fermentable diets are required which limit energy intake and microbial protein production.

Provide Readily Accessible Sources of Clean Water

Water consumption is related positively with feed intake and milk production, and will be greater during hot weather and when dry feeds are fed. Cows producing 45 kg of milk per day drink approximately 120 liters of water per day which is 2.5 times the amount of water secreted in the milk. Large quantities of water are required for normal rumen function: the water content of digesta in the rumen is typically around 86% and is fairly constant. Cows usually have to drink shortly after or even during a meal to maintain this water content. Water flows from blood into the rumen during meals because of higher rumen osmolality resulting from fermentation acid production. This might stimulate the cow to drink, thereby interrupting the meal. Locating water sources close to the feed bunk might increase the probability of meal resumption following drinking.

Don't Limit Access to Feed

Feed bunks should contain feed throughout the day except when they are being cleaned. Cows should have physical access to feed for 22 hours or more per day. Daily weighbacks should be at least 5% for close-up dry cows, fresh cows, and high producing cows and 2-3% for late lactation cows. Long waits for milking in the staging area limits access to feed and might limit dry matter intake (DMI). Keep in mind that one additional meal per day containing 2 kg of DM will affect milk production up to 5 kg per day.

Keep Feed Fresh

Aerobic stability of silage is often a problem because heating of the silage reduces DMI, particularly in hot weather. Silage should be managed to eliminate stability problems. Forages should be ensiled at the appropriate moisture content and particle size, and bunkers should be adequately packed and covered. Bunker silos should have a clean face and residual piles should be removed after feeding. Enough silage should be removed from the open face of silos (10 - 15 cm per day) to avoid spoilage. Whereas feeding once per day might be adequate during cool weather, feeding frequency should be increased during hot weather and when heating of the feed in the bunk is noticed. Feed should be pushed up to the cows several times per day to stimulate eating, particularly when they are fed only once per day. Feed bunks should be cleaned daily to prevent inoculation of fresh feed with undesirable aerobic organisms.

Adjust Body Condition

Body condition should be adjusted to a score of 3.0 to 3.25 on a 5 point scale (1 = thin, 5 = fat) late in the previous lactation allowing an additional gain of .5 point during the dry period. Body condition score (BCS) of heifers should be adjusted to 3.25 to 3.5 several months prior to calving. Cows calving with excess body condition have increased likelihood of metabolic disorders such as ketosis and hepatic lipidosis because of reduced DMI and excessive mobilization of body reserves before and(or) after calving. Inadequate body condition at calving will limit peak milk production and might reduce reproductive performance.

Increase Nutrient Density of Close-up Dry Cow Diets

The nutrient density of diets for close-up dry cows should be substantially higher than for early dry cow diets. This is because intake is depressed by as much as 30% for the 7 to 14 days prior to calving, yet nutrient requirements increase as gestation progresses. The reason for the reduction in DMI is not clear but a reduction in rumen volume because of fetal growth might cause physical limitations. Lower fiber diets are less filling and there is evidence that the reduction in DMI is lessened when fiber content of the diet is decreased. Increased energy intake has been found to decrease lipid accumulation in the liver prior to calving. Although the amount of lipid accumulation that decreases the capacity of the liver for gluconeogenesis is not clear, a significant accumulation might compromise liver function following calving. Cows should be fed the close-up diet beginning 21 days prior to calving and this diet should be formulated to contain 16% crude protein and approximately 30% NDF. Although physical fill still might limit DMI at this NDF content, lower NDF contents are not recommended because fermentability of the diets should also be high (see below) and adequate effective NDF must be included to maintain adequate ruminal pH. To insure adequate effective NDF, avoid feeding finely chopped forages and(or) high levels of high fiber coproducts.

Increase Fermentability of Close-up Dry Cow Diets

Diets fed to close-up cows should also be more fermentable to adapt the rumen microbial population prior to calving. This is different than increased energy density (see above) because energy content and ruminal fermentability are not highly related. Transition to high grain diets and a higher DMI following calving causes dramatic changes in the rumen microbial population. An abrupt change in diet fermentability and intake following calving can lead to production and accumulation of lactic acid in the rumen resulting in acidosis. This is because microbes that produce lactic acid grow much more quickly than microbes that utilize it. Increasing fermentability of close-up diets will adapt the rumen microbial population so that there is less dramatic shift following calving. Increasing fermentability of close-up diets will also adapt the ruminal papillae, increasing size and possibly blood flow, and might increase the cows ability to remove acids from the rumen by absorption. Absorption of fermentation acids from the rumen occurs by passive diffusion of the associated fermentation acid across the rumen wall. The rate of absorption is determined by the concentration gradient of the fermentation acid from the rumen to the blood, rumen pH, surface area for absorption, and the rate of blood flow in the rumen. There is some evidence that papillae length changes with the fermentability of the diet because the papillae utilize butyrate and propionate as sources of energy. In addition, rate of absorption of fermentation acids was related positively to papillae length in at least one study. Increasing the rate of absorption of fermentation acids should decrease incidence of ruminal acidosis following calving allowing greater energy intake. Fermentability of close-up diets should be increased by feeding corn silage with soft kernels and(or) highly fermentable grain sources such as high moisture corn. Avoid feeding corn silage with hard kernels and dry, cracked corn that have lower ruminal fermentability.

Mobilize Calcium Before Calving

Diets for close-up cows should be formulated to enhance mobilization of calcium to reduce incidence of milk fever following calving. Decreasing incidence of milk fever and the cascade of metabolic disorders that might follow can have a great effect on the rate of increase in energy intake following calving. Generally diets should have low calcium, sodium and potassium concentrations. Low calcium diets stimulate calcium mobilization from bone as long as the dietary cation-anion difference (DCAD) is low. Sodium and potassium increase the DCAD and most forages other than corn silage have higher than desired potassium and(or) calcium concentration for use in close-up dry cow diets. An alternative to this low calcium, low potassium strategy is to include supplemental anion sources (chlorides and sulfates) in the diet to decrease the DCAD. Current recommendations for addition of supplemental anion sources is that they should be added to achieve a DCAD of -10 to -15 milliequivalents per 100 grams of DM, and diet calcium concentration should be increased to 1.5 to 1.8 percent of DM. Some anion sources can be unpalatable and might depress DMI and interested readers should refer to recent guides before use.

Group Lactating Cows

Farms feeding total mixed rations (TMR) should group cows according to their requirements. It is important to recognize that any diet formulated for a group of cows will not be optimal for all cows within the group. Some animals within the group will have DMI limited by physical fill while others will have DMI limited by chemostatic factors. Increasing homogeneity of cows within groups allows diet formulation to maximize energy intake for more animals within a group. Rate of increase in DMI following calving might be the primary factor for reducing incidence of metabolic disorders in early lactation and fresh cows should be grouped separately, if possible, to reduce competition and slug feeding. Also consider grouping primiparous cows separately; young cows generally do not compete well with older dominant cows and separation of these animals might increase their energy intake. Grouping also allows for management of body condition in mid- to late-lactation. Primary considerations for group size to maximize energy intake is adequate bunk space per cow to reduce competition for feed and increasing milking parlor throughput to reduce time away from feed and water. Fresh cows and high producers should be in smaller groups with 0.6 meters of bunk space per cow and less time away from feed and water (to and from the milking parlor) while late lactation cows can tolerate 0.3 to 0.45 meters of bunk space per cow and relatively more time away from feed and water.

Reduce Variation in Feeds

Variation in feeds, particularly forages, is a major factor affecting ruminal acidosis and subsequent laminitis. Abrupt reductions in silage DM and(or) fiber content that sometimes occurs for haylage stored in upright silos, can increase the fermentability and decrease the effective fiber content of a TMR, resulting in a rapid decrease in rumen pH. Horizontal silos (except bags) have an advantage over upright silos because they are filled as layers which are mixed upon removal from the silo whereas mixing is minimal for upright silos. One strategy to minimize variation in a TMR when silage is stored in multiple upright silos is to feed several forages at once; abrupt changes in one silage will have limited effect on composition of the TMR. Forages might include one or more haylages, one or more corn silages, and(or) chopped hay. However, this strategy limits the ability to allocate highest quality forages to the highest producing cows, and the number of silos open at one time depends on the stability of the silage; the proper amount of silage must be removed to prevent spoilage, limiting the number of open silos.

Don't Trust the Energy Content of Feeds

Net energy for lactation (NE_l) is normally predicted from the acid detergent fiber (ADF) content of the feed because there is a negative relationship between ADF and energy content for some feeds including forages. However, ADF is not related to digestibility of NDF or starch which are quite variable; together they account for over 60% of the DM of dairy cattle diets. Although ADF is related to energy content for some feeds, the relationship is generally poor. Book values are used for energy content of other feeds for which there is no relationship between ADF and energy content. However, energy content of many of these feeds are also quite variable. For all feeds, residence time in the rumen and lower digestive tract is affected by intake and other dietary ingredients and can dramatically affect energy content. Because of the great variation involved with the prediction of energy content of individual feeds, there is uncertainty associated with the calculated energy content of diets; diets formulated to contain 1.72 Mcal NE_l per kg might commonly range from 1.58 to 2.13 Mcal NE_l per kg DM. Furthermore, the energy content of diets has a poor relationship to ruminal fermentability or to their filling effect, both of which can have a great effect on energy intake. Therefore, energy content should not be a primary criteria for formulating diets.

Don't formulate for energy content, formulate to increase energy intake!

Balance Diets for Fermentation Acid Production and Removal

A goal in formulating diets for dairy cows is to maximize ruminal fermentation and the production of microbial protein while managing the risk of ruminal acidosis. To maintain ruminal pH and prevent depression in fiber digestibility, microbial efficiency, and DMI, it is important to balance fermentation acid production with fermentation acid removal from the rumen. The primary factors to formulate diets should be ruminal fermentability and effective fiber content, both of which vary greatly in dairy cow diets. Ruminal organic matter digestibility ranges from less than 30 to over 65% resulting in great differences in daily production of fermentation acids. The fermentability of the diet can be reduced by bypassing starch and(or) increasing the fiber content of the diet. Contrary to popular opinion, the non-fiber carbohydrate content (NFC) of the diet is not highly related to diet fermentability; ruminal fermentation of NFC ranges from less than 40% to over 90%. Acid is removed from the rumen primarily by absorption but neutralization by salivary buffers is an important factor to maintain ruminal pH. Saliva secretion increases during chewing which is stimulated by the coarseness of the diet. The chemical component of the diet most closely related to its ability to stimulate chewing is NDF. However, effectiveness of NDF to stimulate chewing varies greatly with the size of feed particles and NDF of each feed must be adjusted by an effectiveness value. Increasing the effectiveness of NDF allows diets with greater fermentability to be fed while maintaining ruminal pH. The effective NDF content of the diet can be increased by chopping forages longer, adding chopped long hay to a TMR, and(or) reducing use of high fiber coproduct feeds. Addition of buffers such as sodium bicarbonate or alkalizers such as magnesium oxide to the diet also neutralizes excess fermentation acids allowing higher energy intakes.

Reduce Physical Limitations to Intake

For high producing herds, even if cows are grouped to minimize variation, DMI of some cows will be limited by physical fill. Reducing the NDF content of the diet will allow greater DMI for the highest producing cows in the group, but might result in lower ruminal pH and milkfat depression for lower producing cows. Finding the balance for the group is a primary challenge to maximizing energy intake and increasing homogeneity of cows within groups makes this easier. Forages with higher NDF digestibility also allow greater energy intake because the NDF is less filling, provides more energy, and yet is effective at stimulating chewing. Identifying forages with high NDF digestibility and targeting them for diets of cows limited by physical fill such as fresh and high producing cows is important to increase energy intake and decrease metabolic disease. Fiber digestibility of alfalfa and corn silage is related to the extent of lignification of the NDF, and lignin can be used as an indicator of NDF digestibility.

Reduce Pulsatile Nutrient Flow

Another goal for feeding management and diet formulation is to provide a steady state supply of nutrients to the rumen and to the udder. Increased pulsatility of diet consumption will decrease mean ruminal pH, increase range in ruminal pH and affect partitioning of energy from milk to body condition. Pulsatility is decreased by feeding grain frequently or in a TMR, allowing adequate bunk space to reduce competition for feed among cows and slug feeding, feeding diets higher in NDF with high NDF digestibility, and by limiting rapidly fermented grain. This will allow more fermentable diets to be fed that are less filling while maintaining a higher minimum pH, increasing microbial efficiency, fiber digestion, DMI, and energy intake. Decreased pulsatility of propionate and(or) glucose in the blood also should decrease insulin secretion and allow greater energy partitioning to milk synthesis.

Add Fat if Needed

Vegetable, animal, and ruminal bypass fat sources can be included to compensate for poor quality feeds. Forages with low NDF digestibility, and corn silage or grains with poor starch digestibility will limit energy intake, resulting in lower milk yield and body energy reserves. Fat sources should be used to increase energy intake when high quality feeds are not available. Fat cannot be used to produce lactose, the primary determinant of milk volume, so dietary energy might be partitioned more towards body condition. Most diets containing forage and grain without supplemental fat average about 3% fat on a DM basis. An additional 2% fat can be safely added from vegetable fat sources such as whole cottonseeds, soybeans, or distillers grains. Diet fat content should be restricted to 6.5% unless ruminal bypass fat sources are used. Fat cannot be used as an energy source for microbial protein production in the rumen and diets high in fat require additional bypass protein

Determining the Optimal NDF Level for Cows in Early Lactation

The following discussion describes a simple system to select the optimum NDF content for diets of cows in early lactation for a given farm. The optimum NDF which will maximize energy intake of cows in early lactation ranges from about 25-35% of DM. The level of NDF within this range is dependent on the cow or group of cows, the feeds available, and the feeding system used. Beginning at the midpoint of this range (30% NDF), several factors will allow ruminal pH to be maintained at lower NDF contents, while other factors will raise the optimal NDF content. As intake may be limited by physical fill as NDF content of the ration increases, and NDF is generally less digestible than other feed components, the goal to increase energy intake should be to balance rations with lower NDF levels while providing sufficient buffering of fermentation products. Figure 1 illustrates how several of the primary factors affect the optimal NDF content of the ration. Each of these factors is described below.

Figure 1.Factors affecting optimal level of neutral-detergent fiber for high producing cows in early lactation to maximize energy intake.

Optimal Diet NDF Content

² long forage particles

no long forage particles ÷

high fiber coproducts ÷

² total mixed ration

grain fed infrequently ÷

high ruminal starch digestibility ÷

² moderate ruminal starch digestibility

² addition of buffers

high fiber digestibility ÷

slug feeding ÷

variation in forage dry matter and NDF ÷

Long hay or coarsely chopped silage will allow lower NDF levels to be fed as the NDF in the ration is more effective at stimulating chewing, increasing saliva flow to buffer fermentation end products. Conversely, finely chopped silage will require higher ration NDF levels as it is less effective at stimulating chewing. If silage is chopped finely, addition of long or coarsely chopped hay may be required. Some particles greater than 3 cm in length are desirable in a ration. High fiber coproduct feeds such as soyhulls and distiller's grains are generally much less effective at stimulating chewing than forage due to fine particle size. A notable exception is whole linted cottonseed which is about 50% as physically effective as long chopped silage. Addition of high fiber coproduct feeds will increase the optimal NDF content of the ration. When assessing particle length it is important to examine the feed as it is offered to the cows, not what goes into or comes out of the silos, as significant particle reduction may occur in the mixing process for TMRs.

Inclusion of some feeds such as rolled barley, wheat, and wet (over 30% moisture) high moisture corn (HMC) must be limited in diets because they are so highly fermentable that the production of fermentation acids exceeds their removal from the rumen resulting in acidosis and depressed DMI. Substituting starch sources that have lower ruminal fermentability but high whole tract digestibility such as drier (25% moisture) HMC or dry, ground corn is a strategy that often results in increased energy intake. Use of feeds with high ruminal digestibility will require greater NDF concentrations than feeds with lower ruminal digestibility.

Offering grain frequently in lower amounts will allow lower ration NDF levels than offering grain just twice per day. Large grain meals result in large fluctuations in ruminal pH which can cause cows to go off feed if insufficient fiber is fed. Feeding a TMR is an ideal way to increase energy intake as ruminal pH fluctuations are reduced allowing lower ration NDF levels.

Buffers can be used to partially replace effective NDF to neutralize fermentation acids and are beneficial when effective fiber and salivary buffer secretion is limited.

Highly fermentable fiber results in increased production of fermentation acids in the rumen and might be less effective at stimulating chewing because it digests and passes from the rumen faster, decreasing the pool size of fiber needed to stimulate rumination. However, feeds with highly fermentable fiber are desirable particularly when intake is limited by physical fill because the filling effect of the fiber is lower, leading to higher dry matter and energy intake. Optimal NDF content of rations containing feeds with highly digestible fiber such as immature or low lignin forages are higher than that using average or less fermentable fiber sources.

Low ration NDF levels (25 - 27% NDF) should not be fed in TMRs if forage dry matter and quality is variable. Variation in dry matter and (or) NDF of forages will cause great variation in ration NDF and starch levels. Cows consuming low NDF rations are not able to deal with this variation as they are "on the edge" at maximal energy intake. If ration NDF content decreases, a precipitous decline in intake and production may result due to ruminal acidosis. However, if forage NDF or dry matter content increases and is undetected and uncorrected, energy intake will be somewhat reduced and this is not a great problem. Therefore, when variation is expected, higher ration NDF levels must be fed to avoid the risk of acidosis. Variation in forage dry matter and quality is often a problem for silage; although it cannot be eliminated, it can be reduced by good silo management. Variation in forage quality at feedout will decrease energy intake and reduce production. Efforts to reduce this variation when forages are harvested (or purchased) and stored will be rewarded with higher energy intakes.

Specific Recommendations

The degree to which ration NDF content should be adjusted from the midpoint NDF level of 30% requires a few educated guesses that will be refined by experience. The following approach is suggested to get started.

Beginning at 30% NDF: Forage particle size: No adjustment for silage with 5-10% of particles > 3 cm. Decrease NDF content 2 units when feeding silage with many particles (>15%) over 3 cm or when feeding 2 or more kg of long hay. Increase NDF content 2 units when feeding forage with few long (>1.5") particles. Increase NDF content up to 4 units for very finely chopped silage with no long particles.

Coproduct feeds: No adjustment when rations do not contain high fiber coproducts. Increase NDF content up to 2 units when feeding high fiber coproducts with fine particle size at up to 10% ration dry matter (less adjustment is necessary for whole cottonseeds). Limit the combination of pelleted forages and high fiber coproducts to less than 20% of the total fiber required.

Frequency of grain feeding: No adjustment for grain fed separately three times per day. Decrease NDF content 2 units if grain is fed 4 or more times per day or a TMR is fed. Increase NDF content 2 units if grain is fed twice a day or less.

Ruminal starch digestibility: No adjustment if 70-80% ruminally digested. Decrease NDF content up to 2 units if 60-70% ruminally digested. Increase NDF content up to 2 units if over 80% ruminally digested. Ruminal starch digestibility lower than 60% will decrease microbial protein production and may lead to lower whole tract starch digestibility .

Buffers: No adjustment if buffers are not fed. Decrease NDF content 1 unit if buffers are fed at .5 to 1% of ration dry matter.

Fiber digestibility: No adjustment for average forages. Increase NDF content up to 3 units for very high NDF digestibility (low lignin forages).

For TMRs, increase the NDF content up to 3 units or more if silage dry matter and NDF content of forages are variable.

Slug feeding: Increase the NDF content up to 3 units when access to feed is limited either by restricted access to the feed bunk, empty feed bunks, or by inadequate bunk space.

As the different factors may not be additive, additional adjustments may be required. Total net subtraction or addition generally should not exceed 5 units of NDF (the range for optimal NDF content is 25 - 35%). In extreme situations (e.g. cows consuming grass hay supplemented with processed barley twice per day) diets over 35% NDF might be necessary. The lowest ration NDF level recommended is 25%. Rations with optimal NDF of 25% will have many long particles, moderate ruminal starch digestibility, contain buffers, are fed as a TMR or grain is fed frequently and have little variation in dry matter and NDF content of forages fed. These recommendations can be used to select the optimal NDF for rations for a given set of feeds and feeding system and can be refined with experience. Remember that the goal is to maximize energy intake and ruminal microbial protein production. This is done by adjusting feeds and feeding systems so that optimal NDF content is at the low end of the range. Feeding low lignin forages with higher fiber digestibility is an exception as it will increase the optimal NDF content but should also increase energy intake.

Don't Lose Sight of the Forest for the Trees!

Complicated models based on digestion kinetics are becoming common tools to formulate diets. These models are intellectually appealing and a great teaching tool. However, they have limited usefulness for ration formulation because of their inability to accurately predict ruminal fermentability of diets, ruminal pH, microbial protein production, ruminal fill, and the effect of fermentation acids and ruminal fill on regulation of DMI. The greatest limitation of these models is in obtaining accurate values for rates of passage and digestion of feed components. Although we have methods to compare feeds for relative rates of digestion, these rates are not absolute. More critical is that our knowledge regarding rate of passage of feed ingredients is totally inadequate to use in combination with rate of digestion to predict ruminal digestibility. Although understanding the principles used to develop the models is critical to formulate diets optimally, the time, effort, and expense required to routinely use these complicated but inaccurate models takes away from that required to make more effective recommendations.