FEEDING dairy cows diets with a lower crude protein (CP) content reduces nitrogen input, improves nitrogen utilization efficiency and reduces nitrogen losses from manure, according to Dr. Alex Hristov of The Pennsylvania State University.

In an article posted on eXtension.org, Hristov said the primary interest of dairy producers in not overfeeding protein is so they can reduce feed costs. When the price of corn is low and the price of protein supplements is high, it only makes economic sense to feed fewer high-protein feedstuffs.

Dietary interventions that carry the risk of decreasing milk production, however, have to be carefully evaluated before being implemented.

According to Hristov, if an average lactating cow diet has around 17% CP, diets with CP at or below 16% can be considered low protein. These kinds of diets may or may not be deficient in metabolizable protein (MP), which is the unit used by the National Research Council's (NRC) 2001 "Nutrient Requirements of Dairy Cattle" to define protein requirements.

As an example, the two diets in the Table would meet the MP requirements of a dairy cow that is milking around 90 lb. per day and is not in a negative energy balance.

Feeding cows a diet with 17% CP is likely not going to increase milk production or milk protein yields, assuming that dietary energy and amino acids are balanced, Hristov said. It is likely that this extra protein is going to contribute mostly to the rumen degradable protein (RDP) pool, and a significant proportion of it may end up being metabolized to urinary urea and excreted with urine.

Therefore, overfeeding protein beyond the animal's requirements in a balanced diet will increase feed costs and will have no beneficial effect on milk production or composition, he explained.

A simple measure of the cow's efficiency of use of dietary nitrogen is milk nitrogen efficiency (MNE). This is the proportion of dietary nitrogen that is secreted as milk protein.

An accepted threshold for MNE is 25%, and efficient cows usually will have MNE of 30% and above, Hristov reported. Increasing MNE, however, should not come at the expense of decreased milk production.

Example diets formulated using NRC (2001) values to meet the MP requirements of a 1,500 lb. cow 90 days in milk with milk production of around 90 lb./day and 3% milk true protein, consuming around 55 lb./day of dry matter

Item

CP, %

RDP, % of CP

Rumen undegraded protein, % of CP

RDP supply, g/day

RDP balance, g/day

Rumen undegraded protein supply, g/day

Rumen undegraded protein balance, g/day

MP supply, g/day

MP balance, g/day

Net energy of lactation balance, Mcal/day

Dry matter intake. According to Hristov, one way in which low-protein diets may have a negative effect on milk production is through decreased dry matter intake.

In a lactating dairy cow, feed intake is literally what "drives the train," and any negative effects on dry matter or feed energy intake will, in most cases, result in decreased milk production.

Long-term trials (up to 10 weeks) at Penn State have shown a variable effect of decreasing dietary CP or MP on dry matter intake, Hristov reported. For trials in which dry matter intake decreased when feeding MP-deficient diets, milk production also decreased. On the contrary, when dry matter intake did not decrease, milk production also did not differ among diets, he noted.

Rumen effects. Another way decreased dietary CP may affect production is through its effects on ruminal fermentation, Hristov said, explaining that if dietary protein is intentionally decreased, it is usually done by reducing the inclusion of common protein feeds — such as soybean meal or canola meal — in the diet.

This may cause RDP deficiency, which may result in decreased fiber degradability, acetate production and microbial protein synthesis, Hristov reported. These effects may result in decreased milk fat and protein concentrations and yields.

In all Penn State trials with low-protein diets, the total tract apparent digestibility of fiber fractions was decreased.

Although ruminal fiber degradability was not measured, Hristov said it is probably safe to assume that a big part, if not all, of the decrease in total tract fiber digestibility occurred in the rumen. Interestingly, this generally did not affect milk production or milk fat content.

In studies at Penn State, Hristov said a consistent response in microbial protein synthesis in the rumen with the low-CP diets was not detected. Overall, he said the Penn State data indicate that diets with RDP of around 9% of dietary dry matter result in decreased fiber digestibility (compared to diets with RDP of around 10% or higher) but do not appear to have a consistent effect on ruminal microbial protein synthesis.

Amino acids. Supplementation with rumen-protected amino acids that are known to limit milk production and milk protein synthesis may compensate, in some situations, for MP deficiency in dairy cow diets, Hristov explained.

Usually, methionine is the first amino acid limiting milk production in typical North American dairy diets. Methionine intake should be closely monitored, particularly in low-protein diets and when milk protein content is of interest. The responses to rumen-protected methionine have been far from consistent, he said, in large part due to excessive total protein in the diet.

Responses to lysine supplementation have been even less consistent than the responses to methionine supplementation, Hristov noted, adding that while corn-based diets should, in theory, benefit from post-ruminal supplementation of lysine, this does not appear to be the case in most studies.

Caution. Hristov pointed out that there is significant variability in the day-to-day ration composition on commercial dairy farms, and if lower-protein feed is being implemented, extra caution must be taken to stay as close to the formulated diet composition as possible.

Changes in forage dry matter, quality/digestibility or protein content, inclusion in the diet of unanalyzed byproduct feeds or deficiencies of key nutrients, particularly energy, can all have large effects on the amount of protein being consumed by the cows or her protein requirements and may, consequently, have a negative effect on milk yield or composition, Hristov said.

He concluded that dietary protein should not be reduced in diets for dairy cows that do not meet the requirements of the animal for other nutrients, particularly energy.

The first and most important factor for successfully reducing dietary protein close to or below the animal's MP requirements is to keep the dietary energy balance at or slightly in excess of the requirements, Hristov added.

Workforce quality

A dairy in California knows that finding a solution to a milk quality challenge goes beyond retraining milkers, altering procedures and changing the teat dip or mastitis treatment.

These fixes are only temporary and often are not the solution to the problem. Real, lasting change on dairies comes from an engaged workforce that is motivated to execute protocols consistently, according to a Zoetis "Dairy Wellness Quick Tip."

Before implementing a successful management approach on this California dairy farm, the managers constantly struggled with the common issues of employee engagement and effectiveness. Meanwhile, the dairy was stuck at status quo, with somatic cell counts greater than 300,000.

With smart investments in workplace culture as well as better delegation and management strategies, the farm was able to transform its team into one that was more engaged and worked well together, Zoetis said.

The results included reducing somatic cell counts, decreasing clinical mastitis by 25%, increasing milk production and quality, as well as saving a projected $236,220 in mastitis costs.

The farm managers achieved this by:

* Raising standards;

* Changing the culture of the entire operation;

* Modifying how tasks are completed at every level;

* Completing a successful manager training program (the PeopleFirst Supervisory Certificate Program from Zoetis), and

* Improving employee performance both individually and as a team.

Dairy managers can help develop a more effective team by retraining workers, helping them understand protocols and the value of adherence, improving communication, encouraging respectful and calm interaction and implementing new standard operating procedures, including mastitis treatment protocols.

Substantial positive changes come from establishing sound procedures and having a team dedicated to ensuring that procedures are carried out properly, Zoetis noted. These ingredients are essential for success.

When problems on a dairy operation arise, the signs aren't always obvious, and neither is the solution. Evaluate each challenge as an opportunity to assess the people as well as the practices in place to find the root of the problem. The key to success for any business is having engaged employees who understand how their work makes a difference, Zoetis said.

Volume:87 Issue:02