Nutrition is the driving force behind a functional and responsive immune system, and the cow’s ability to convert dietary substrates into meat and milk. Robert Van Saun, DVM, PhD, Dipl. ACT and ACVN, Pennsylvania State University, says dairy practitioners need not have an understanding of nutrition at the level of formulating diets but should be proficient enough to monitor nutrition-based animal responses. “Dairy practitioners recognize the critical role of nutrition in disease and production. They can and should become involved in their clients’ ration program in a role of monitoring agent.”

Identifying problems such as butyric acid in ensilage or ensiled feeds causing unresponsive ketosis, unexplained milk fat depression or solving general transition cow issues with a well-balanced dry cow/pre-fresh ration are examples of diagnosis and prevention of problems.

Feed quality and feeding management issues account for the greatest percentage of feed-related problems on the farm. The veterinarian deals most directly with subsequent disease processes and visualizes the animals most often and, therefore, is the most obvious candidate in performing diagnostic investigations. “A veterinarian with an understanding of feed quality and management diagnostics is a critical component in the overall evaluation and monitoring process,” Van Saun says.

Mark Thomas, DVM, Dipl. ABVP, Countryside Veterinary Clinic, LLP, Lowville, N.Y., is the primary nutritionist for five herds and provides nutritional consulting and working with the primary nutritionist for other clients. To investigate nutrition-related problems, Thomas uses a variety of diagnostic tools such as the Penn State particle separator, rumen pH, metabolic and fermentation profiles, mold/yeast counts and basic forage analysis.

Van Saun believes many of the most commonly recognized clinical problems can be attributed to poor-quality silage, especially silage with high pH indicating a poor fermentation. “In my approach, silage is considered the most variable feed on the farm and is always to be considered first in the face of any problem that might be nutritionally related.”

But the ration is only one part of the puzzle, Thomas notes. “Forage quality is one important aspect, followed by facilities and management. I have herds with suboptimal production that is not limited by the ration. Cow comfort areas are critical.”

Therefore, Thomas says observation of the cows, facilities, forages and manure during regular herd-health visits to the farm is important. “Watching the cows is the most useful tool,” he says.

Look for inconsistencies

Consistency is the goal on a dairy — just ask any dairy producer that is able to maintain high production in a herd. “Dairy practitioners need to understand the desire to have consistency, but should focus on finding inconsistency,” Van Saun suggests. “It is through recognition of inconsistencies within a given system that appropriate corrections can move the process more toward the desired goal of consistency. To me, this is the focus of any diagnostic process, especially nutritional problems.”

Thomas suggests watching the cows and looking at forages. “I don’t think ration balancing is rocket science in most instances. We can tweak things for a bit more milk or a more economical ration without losing milk, but it is all the other things that really matter,” he says. Nutrition includes forage quality (harvest time, chop length, storage, feed out/mixing), cow comfort (stalls, bedding, overcrowding, heat abatement), water access/quality, social groups, time budget and overall management.

Van Saun agrees that the ideal, though not practical, diagnostic scenario would be to watch the cows throughout the entire day to understand just how they interact with feeding management and the environment. “In my experience, many times it is not a nutritional formulation problem but more of an environmental or feeding management issue,” he says.

How often should you monitor different aspects of the nutrition program? It depends. Van Saun says if silage quality has been identified as a potential risk in a problem, then it might be evaluated two to three times per week over a period of time. Moisture content might be monitored twice per week. “If I am monitoring particle size or nutrient content,” Van Saun says, “I might only take samples when changes are observed or when we know a different cutting or field of the stored forage has been started.”

Work with nutritionists

When practitioners and nutritionists work together, the client and the cows benefit greatly, as well as the practitioner and nutritionist.  “The dairy practitioner really does not have the time to be formulating diets, but based on their integrative knowledge of physiology, pathology, and other disciplines, they are positioned best to provide a monitoring service to the quality of the nutrition program,” Van Saun explains.

The practitioner then can provide a non-biased assessment of the nutrition program and direct necessary information to the nutritionist to make appropriate modifications. “To get this to work well, egos need to be left behind and a working, trusting relationship needs to be cultured between practitioner and nutritionist,” he adds. “This is not always easy, but the client needs to ensure this happens.”

The relationship between the veterinarian and nutritionist is vital to solve herd-health and nutrition problems. “I have excellent relationships with most of the local nutritionists,” Thomas says. “Almost all important diseases of dairy cows are nutrition-related; so it’s important for the veterinarian to work with nutritionists.”

Silage diagnostic tools

It’s important for the dairy practitioner to be comfortable using silage monitoring tools and their interpretation. Practitioners should discuss the range of monitoring possibilities with their clients to find the right fit. “This is a win-win situation in my mind as it provides more service by the veterinarian and focuses on disease prevention for the client,” Van Saun says.

Ensiled forages are the most common feeds used on the dairy farm due to their lower total harvesting and storage nutrient losses, but they are also the most variable feeds on the farm. As a result, they are often the source of feeding-based problems. Van Saun presented the following information on identifying potential problems with ensiled feeds at the 2007 North American Veterinary Conference.

* Measuring pH Silage quality, as defined by the fermentation process and optimum dry matter conservation, is related to a rapid and sustained drop in pH of the harvested forage. Measuring pH is simple, quick and inexpensive and can be completed in the silo. Silage samples can be collected across the bunk face or as the silo is emptied to assess uniformity in the ensiling process. Grab samples can be squeezed to “milk out” a few drops of moisture onto a pH meter. Alternatively, a sample can be placed into a cup and distilled water added to moisten the sample, which then is measured with a pH meter.

A wide range of pH is found in high-moisture silages, good quality silages being associated with low pH. Corn silage should have a pH of 3.5 to 4.2, while hay crop silages should be 4.0 to 4.8. Lower and higher pH values are associated with high and low moisture, respectively. High pH at high water content is associated with proteolysis (aberrant clostridial fermentation) and low pH with good lactic acid production. In high dry-matter silages, pH is less useful since deficiency of water restricts fermentation and acid production. High pH silages (>5.0) are at higher risk for growth of Listeria spores. Be sure to determine pH at the sides of a bunker silo, as inability to pack properly often leads to abnormal fermentation and high risk of mold and Listeria growth.

* Temperature During ensiling, temperature is elevated as a result of heat generation. Silage temperature can be measured with a compost thermometer placed at least 18-24 ins. into the bunk face. The temperature of ensiled feed removed from the silo or total mixed ration that contains ensiled feeds in the feed bunk can also be evaluated. Other than initial respiration when the silage is first placed in the silo, there should be a fairly rapid return of silage temperature back to near ambient temperature. Most bunk silos will maintain a temperature around 60°F.

Temperatures in excess of 120°F during the initial ensiling process suggest aerobic oxidation and extreme risk for heat damage. Elevated temperatures (>80°F) suggest oxidative respiration by molds and fungi, and feed instability. Stable silages should not increase in temperature when removed from the silo and placed out in the feed bunk. Secondary mold growth can often result in temperatures in excess of 100°F in the silo or feed bunk. Heating of silage in the feed bunk does not cause heat damage of the feed but will decrease palatability. Feed with moisture >15% is at risk for yeast and mold growth, as reflected in temperature elevation. 

* Fermentation profile This newer analysis further characterizes fermentation quality. Most labs offering this provide determinations of each important volatile fatty acid (VFA) produced during the ensiling process, as well as measures of pH, titratable acidity, moisture and ammonia nitrogen. Normally lactic acid should be the predominate (>60%) VFA in silages as it is primarily responsible for the drop in pH. Excessive amounts of acetic, pro-pionic, or butyric acids as well as ethanol indicate poor fermentation from other microbes. Acetic acid and ethanol are often associated with yeast fermentation. High acetic acid may indicate other abnormal fermentations taking place in the silage.

Some of the newer heterofermentative inoculants (Lactobacillus bucheri) will increase acetic acid up to 3%. Both acetic and propionic acids have antifungal properties potentially making the silage more aerobically stable.

The primary VFA of concern in silage is butyric acid, often the result of aberrant clostridial fermentation. Excessive butyric acid intake can result in “dietary ketosis.” Various toxic amine and amide compounds resulting from clostridial proteolytic activity and butyric acid production are toxic to rumen bacteria and are responsible for reduced palatability and feed intake.

Fermentation profiles are indicated when sensory evaluation (odor or color) of silage indicates potential problems or when animal performance declines.

* Silage density Elimination of oxygen in the silo and the rapid decline in pH, resultant from the fermentation process, are keys to fermentation quality. Silage density (i.e., lbs. dry matter/ft3) provides insight into the silo packing process. Packing quality is influenced by filling speed, tractor weight, time packing, layer depth and harvested forage moisture content, maturity and particle size. Poorly packed silage (14 lbs. dm/ft3, with densities between 16 and 21 lbs. dm/ft3 being achievable.

Silage density varies within the silo. The highest values are typically found in the bottom-center and lowest values on the sides and top. Density is measured with a wide-bore corer attached to a drill to obtain a core sample. Corer diameter and sample depth are used to determine sample volume, and silage density can then be determined. Core depth, sample weight and moisture content need to be measured. Use spreadsheets to calculate silage density. Other spreadsheets are available to evaluate the packing process. Harvested-forage particle size should be evaluated in relationship to moisture content and plant maturity.

Particle size

Particle size, and its interaction with harvested-forage moisture content and maturity, impacts packing ability and the quality of fermentation. Wetter and less mature forages can be harvested at longer particle size and still allow good packing. Drier and more mature forages are less amenable to packing and eliminating oxygen from the silo; therefore, a smaller particle size is necessary to allow better packing.

The Penn State particle separator should be used at the time of harvest to evaluate the appropriate cutting length to optimize packing ability and ensure proper silage fermentation. However, one needs to be cognizant of particle size relative to rumen function and animal health.

The concept of effective fiber (physically effective fiber) relates to a need to provide fibrous foods of a particular length to stimulate mastication and promote good microbial ecology of the fermentation vat. Effective fiber is most often associated with particle size and evaluated relative to rumen function and minimizing milk fat depression. Effective fiber of a given ration can be improved by removing starch sources and replacing with fermentable fiber sources, even those with small particle size (i.e., soy hulls, wheat bran, beet pulp). Physically effective fiber is a measure of how well a feed ingredient stimulates chewing activity and is also related to lignification of the cell wall. Sieving feed ingredients or total diet for variation in particle size is common to evaluate effective fiber.

Insufficient effective fiber in the diet can result in ruminal acidosis and alterations in milk composition. Improper harvesting, processing, or ration preparation can reduce particle size. Particle-size reduction and uniformity during mixing is often a problem and cows also efficiently sort the delivered diet and select against fibrous particles.

Effective particle size of feeds or the TMR can be estimated with a Penn State particle separator that has a series of screens with varying aperture sizes. It is probably the single most important diagnostic tool for nutritional investigations. Information on using the particle separator and spreadsheets for calculations  is available on the Penn State Dairy Nutrition we bsite.

Manure screening

Manure should be inspected for consistency within and between cow groups, presence of grain seeds, and length of fibrous particles. A 5-point (1 = watery diarrhea; 5 = dry, firm manure) scoring system for manure consistency can be used. A typical expected range for manure from cows not on pasture would be from 2.5 (fresh cows) to 3.5 (dry cows). Within any given cow group, variation among manure scores should be minimal. Changes in scores over time and wide variations within a group may indicate underlying problems. A number of nutritional factors including amount of degradable or total protein, total and effective fiber, excess minerals and excess starch, as well as animal health, can influence manure consistency.

Manure samples collected from multiple piles within a group can be filtered using a #8 screen (2.36 mm) to qualitatively assess feed digestibility. Approximately 8-12 ozs. of sample is filtered using hot water. Filtering with cold water results in starch jelling, which plugs up the wire mesh. Manure is approximately 20% dry matter, so there should be a significant reduction in retained material on the screen following rinsing.

The screen will retain long fiber and partial or whole grain particles. Large fiber particles (>0.5 in.) and increased amounts of retained material indicate poor fiber digestibility associated with poor-quality forages, reduced rumen pH or reduced rumen retention time. Presence of grains also indicates poor digestibility, which may result from inadequate fiber or other factors reducing rumen retention time and microbial fermentation. Manure with a “foamy” appearance is the result of hindgut (cecum and large intestine) fermentation of dietary starch. If excessive undigested starch reaches the hindgut, the resultant organic acids may adversely affect the integrity of the large intestinal epithelium, resulting in mucus or fibrin casts being shed in the feces. These changes are often associated with diarrhea secondary to subclinical acidosis.

Feeding facilities

Housing and feeding facilities should be thoroughly inspected and quantitative measurements of specific parameters (i.e., feed bunk size) made when possible. Interaction of the cow and her environment should also be evaluated. How many cows are using their stalls properly? Are the stalls of adequate size and properly designed? Is there evidence of cow grouping, stress, overcrowding or other problems? Assess quality of ventilation, water quality and availability, and access time to fresh feed.

Assess feeding areas such as bunk space, dimensions and feeding surfaces. At least 18-24 ins. of space per lactating cow and 25–30 ins. for dry cows should be available. The feeding surface should be smooth and 3–6 ins. above the surface the cow stands on. Proper placement of the throat (21 ins.) and neck (48 ins.) rails to facilitate cow accessibility to feed should be evaluated.

How much time is available for the cow to eat? Is the feed presented to stimulate intake? Feeding times and number of feed push-ups relative to the cow’s days need to be defined. Relative to problems associated with transition cows, the actual time spent in the close-up dry cow pen should be determined. Often there is nothing wrong with the close-up dry cow ration, but many of the cows with problems may not have had sufficient time on the diet to realize potential protective effects.

Dietary TPR

It is often stated that there are three rations on the farm: the formulated ration, the feed bunk ration, and the ration the cow consumes. Ideally, all three rations should be equal relative to their nutrient content. Nutrient analyses of the ration from the feed bunk prior to and following consumption by the animals will allow for critical assessment of these three rations. Nutrient content differences between the formulated and feed bunk rations suggests ingredient composition variability, mixing errors or some combination. Significant differences between refused feed and feed bunk analyses would suggest sorting by the cows.

There is some debate as to the validity of interpreting nutrient analyses for mixed rations. Van Saun uses a simple procedure for determining potential problems in the mixed diet, called “dietary TPR.” Like the individual-animal TPR used for evaluating disease presence, he includes a measure of dietary temperature, particle size and ration uniformity. Once an ensiled feed is re-exposed to oxygen, there is potential for microbial respiration to initiate, generating heat. Unstable feeds will rise in temperature in the feed bunk and generally will be unpalatable. Temperature readings >90°F would be of concern and suggest a highly unstable feed.

Ration particle size will be a function of ingredient particle size, fiber content and ration processing by mixers. Ration uniformity will reflect the feeder’s ability to achieve uniform mixing of the feed and the cow’s ability to sort through the diet. Ration uniformity can be evaluated by visual assessment of specific feed ingredients along the length of the bunk. If whole linted cottonseed, for example, is used, then one can assess how well it is distributed within the mixed feed. All of these assessments in addition to nutrient content can provide useful diagnostic evaluation of overall feed quality on the farm.