Feeding for sustainability in the breeding herd

The national cowherd is shrinking, which may threaten the entire supply chain in the beef industry.

It is debatable if we will ever increase the herd to the level of the 1950s as demographics, regulations and economics take their toll on the industry.

It appears that the survival of the industry, as we know it, will require more calves from a shrinking amount of land.

This task will require management and nutritional improvements that result in more calves per acre.

The objective of this article is to discuss the role of nutrition in improving reproduction and immunity of the cowherd. Deficiencies and, in some cases, excesses of energy, protein, microminerals, macrominerals and vitamins have all been linked to suboptimal reproduction and immunity.

Figure 1: energy balance and calving intervals.

Energy

Most nutritionists and beef researchers would agree that energy is the most important nutrient in sustainable and efficient cow-calf production. There is a litany of research that shows low energy intake during pregnancy, especially late pregnancy, can cause the following:

Lower birthweights
Increased calf mortality
Lower milk production
Increased days to first ovulation
Decline in conception rate

Another consideration is overconditioning, which can also reduce pregnancy rates. With rising costs of commodities, fat cows can negatively affect the calving period while simultaneously wasting resources on feedstuffs.

We know that body condition can be used to reliably predict reproductive success. Most would agree that the energy status of the animal is communicated to the reproductive system in order to avoid a pregnancy that would not go to term or jeopardize the dam, a “built-in safety mechanism.”

Most producers know the usefulness of body condition scoring; however, it is surprising how few use this tool to fine-tune energy supplementation in order to optimize production.

The data in Figure 1 illustrates the relationship between energy balance and calving interval.

Protein

Just as with energy, protein balance is highly related to productivity. An important point is that cattle cannot perform above the first limiting nutrient. With this in mind, balance and synchrony between energy and protein becomes important.

Furthermore, it is critical to identify which nutrient is the bottleneck. Crude protein (CP) and carbohydrate balance is key in dormant forage scenarios and on high-concentrate diets.

The reason is due to the protein requirement by fiber-digesting bacteria in the rumen. A bottleneck of protein in this scenario will reduce fiber digestibility and intake, which will form a negative feedback loop on overall intake, further reducing protein and energy.

Research conducted in Nebraska showed the following when a 42 percent CP high-quality supplement was fed three times per week compared to no protein supplementation:

First-service conception rate improved from 45 to 88 percent.
Overall pregnancy rate improved from 73 to 94 percent.
Percent calving in first 21 days of calving season improved from 49 to 77 percent.

While the effect of high-quality protein on reproduction is well understood, the economic considerations must be evaluated with current protein costs. Urea is the most economical source of nitrogen.

However, its use is limited by kinetics. In other words, it is released very rapidly in the rumen, limiting the ability for the rumen bacteria to utilize the nitrogen.

The overfeeding or lack of synchronization of protein has been shown to decrease conception rates and embryo survival in heifers.

However, a slow-release urea can provide an economical way to supply adequate nitrogen to rumen bacteria without these negative effects.

Trace minerals

It is well understood that trace minerals are essential for good health, optimal gain and reproductive function in cattle. Most mineral companies provide trace mineral levels based on NRC (National Research Council) recommendations that should meet requirements.

However, some mineral packages far exceed these recommendations to compensate for a detected or perceived deficiency, or to gain competitive advantage. Mineral deficiencies can be difficult to practically diagnose, as most do not possess unique clinical symptoms or disease.

The most practical and accurate method to determine trace mineral status in a herd is directly measuring the concentration of trace minerals in a specific tissue, such as blood or liver.

Dietary measurements of trace minerals are helpful, but that does not take into account the differences in the bioavailability of trace minerals or antagonisms that reduce utilization.

Liver analysis allows bioavailability differences and antagonisms to be determined. It also reveals the limitations of a one-size-fits-all trace mineral recommendation.

In some cases, liver analysis will show optimal levels of certain trace minerals, which may allow lower levels to be supplemented, potentially saving costs associated with unnecessary supplementation.

Liver analysis has shown some unexpected results in Southeast herds. Selenium and cobalt deficiencies are commonly diagnosed with liver results despite the herd consuming the trace elements at the recommended rate.

In contrast, it is common to find selenium toxicity in conjunction with severe copper deficiency in parts of the Dakotas and Montana. This is despite no selenium supplementation and significant levels of copper supplementation.

Clearly, animal status depends on other factors besides mineral supplementation. Liver analysis is the best way to determine what the animal status is in a particular herd.

The differences in the chemical makeup of trace minerals impact how they are presented to the animal in the intestines.

Why is it common to find deficiencies in herds that supplement minerals? The mineral either is not being consumed at recommended rates, or the mineral is manufactured with low bioavailable trace minerals.

Or there are other minerals, such as iron, that interfere with the trace elements during the digestive process, minimizing their utilization.

The most available form of a trace element is in the organic or chelated form. The process of chelation has been shown to increase the digestibility of trace elements two to four times. Furthermore, chelation eliminates the problem of antagonisms with other minerals found in hard water. The reason why they are not widely used is the added cost of chelation.

The concept of evidence-based nutrition requires collecting sound data to make informed decisions. Liver analysis for trace elements is one method of determining the trace mineral status of a herd.

Using that sound data obtained from the analysis to make trace mineral recommendations seems logical. In many cases, the data can justify the use of chelation to correct deficiencies.

However, it is common that the data will also justify reducing the need for other trace elements. Manganese is usually found in adequate levels in beef cattle using liver data.

However, it is the trace mineral recommended for highest supplementation based on NRC. Thus, the data does not always justify adding more mineral and expense.

It is useful for producers to gather liver data and fit it with the clinical picture of the herd. As stated earlier, trace mineral deficiencies do not generally have unique symptoms, but fitting certain clinical problems with liver data can help solve chronic problems such as reproductive underperformance.

Artificial insemination is becoming more common in cow-calf herds. The use of A.I. commonly exposes an underlying reproductive bottleneck that may not have been observed with natural breeding.

In fact, most of the research that demonstrated a positive effect of correcting deficiencies with chelated minerals was with herds utilizing A.I. and synchronization.

In summary, as cow-calf herds improve genetics and breeding, the nutrition bottlenecks will become more obvious. Management tools such as body condition scoring, strategic protein supplementation and evidence-based trace mineral nutrition will assist the industry in maximizing the benefits of the improvements made in reproduction.