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New research-driven insights on how chickens utilize feedstuffs can help broiler producers develop new strategies for getting the biggest bang from nutritional programs while improving flock health.

Some of those insights were the focus of a presentation delivered by poultry nutritionist and researcher Dr. Robert Teeter, a professor and nutritionist sat Oklahoma State University, at a recent CocciForum symposium in Florianopolis, Brazil.

Teeter pointed out that energy obtained from feed is used to maintain tissue and organs, regulate body temperature, develop immunity and support various physical activities, including acquiring more food to support the growth curve.

After those essential needs have been satisfied, whatever energy that remains is devoted to growth—or at least that's the way it's supposed to work in a perfect world.

In reality, Teeter said, various stressors—especially disease—can significantly drain energy reserves and rob birds of nutrients they need to achieve optimal growth.

Stressors can also work together to have a negative effect. "It's the combination of stressors that have the most impact," he said.

Bigger impact with age

While minimizing stress as much as possible is an important goal for broiler producers, paying attention to the timing of these stressors is also crucial, Teeter said. "Early exposure to stress is, of course, detrimental, but it has a much smaller overall impact in terms of weight gain or feed use," he said.

The growth curve for broilers accelerates rapidly after about 27 days, Teeter explained. "If the bird is hit with a stressor before that 27-day mark, it has time remaining to make up for any performance it loses," he said. "But late stressors that happen from 27 days onward simply don't give the bird enough time to recover lost growth."

For years Teeter and his colleagues have been studying birds placed in high-tech metabolic chambers that allow the researchers to measure even subtle changes in the birds' energy intake and utilization. As part of that work, they developed statistical models that reliably predict metabolizable energy consumption in disease-free birds.

Challenge of disease

But what about energy consumption in birds challenged by disease? According to Teeter, coccidiosis is one of the most significant disease stressors that commercial broilers face. Using tests in his metabolic chambers, his team contrasted healthy with infected birds in terms of growth rate and final mass, average daily gain (ADG), feed efficiency, energy loss from waste excretion, and energy use for maintaining bodily functions.

In past work, Teeter's group confirmed that coccidia—the parasitic organisms that cause coccidiosis—do, indeed, have a significant detrimental effect on all those parameters. However, more recently they have been digging more deeply into how the timing of coccidia challenge affects those measurements.

"Broilers don't grow in a strictly linear way," Teeter reminded the audience of veterinarians, nutritionists and production managers. "Most of their growth takes place after 27 days, the latter part of their growth curve." Based on his findings, he thinks the timing of the "coccidiosis insult" makes a significant difference in how birds utilize energy for growth.

Teeter's group performed a study in which they assigned a group of broilers to either an experimental or control group. The experimental group was challenged with three common coccidia pathogens—Eimeria tenella, Eimeria acervulina and Eimeria maxima—and placed in the metabolic chambers for 6 days to track performance, body composition, metabolic heat production, calorie expenditure and calorie loss due to excretion. Control birds were administered only a sterile solution.

After 6 days of collecting data in the chamber, researchers euthanized and necropsied the birds, ranking lesions for severity using a standardized system.

Teeter reported that coccidia challenge had a negative effect on performance of all birds, with the highest lesion scores correlating with poorest performance.

That was especially true in birds that received a mixed challenge of at least two species of coccidia.

More surprising, however, was that even low lesion scores were associated with a negative impact on performance, especially as birds neared the end of their growth curve.

Late coccidiosis exacts heaviest toll

To more fully assess the importance of timing of coccidiosis challenge, Teeter's group compared two groups of broilers—one reared in an environment that provided a low level coccidia challenge delivered by a live coccidiosis vaccine (Coccivac-B); the other received no challenge.

At 20 days of age, researchers tallied performance numbers and necropsied 50% of the birds. The rest were reared for the full grow-out period of 48 days while researchers monitored their performance.

"In the group of birds necropsied at 20 days, microscopic lesion scores were different from controls in every case, even for this mild level of exposure," Teeter said.

Performance indicators such as live weight and feed conversion also reflected some negative effects of early cocci challenge. However, Teeter emphasized, by 48 days the birds had overcome that reduction in performance—a process known as compensatory gain (Tables 1 and 2).

"At that point the average weight of the birds was not different—about 3.56 to 3.57 kg (7.84 to 7.87 pounds) and the feed-conversion rate was also the same as controls." Overall, he said that the coccidia- challenged birds regained all of their body mass and there was no significant difference in feed conversion between them and the non-challenged controls.

Measuring lost growth

Teeter also told the audience about a useful set of mathematical modeling tools they've developed to track how and when birds metabolize feedstuff—a measurement he calls "metabolizable energy consumption."

These models assume that birds are raised in disease-free conditions. If birds expend more energy than what's predicted by the disease-free model, it suggests that energy is being lost—either as additional energy needed for maintenance (e.g., generating extra body heat, mounting immune responses, increased physical activity) or possibly from decreased digestibility of the ration itself or perhaps extra energy lost in excreta.

He said many of his group's findings confirm the importance of producers guarding against late coccidia challenge.

"When we use these tools to look at the data we've collected," he said, "there is a constant that seems to emerge from the numbers—that is, for each increase in microscopic coccidiosis score, ADG decreases approximately 1.5% of body weight."

That means, he said, that for a 2-kg (4.4-pound) bird with a lesion score of 1, the loss in ADG would be expected to be about 30 grams (0.066 pound) per day. For a similar size bird with a lesion score of 2, the loss doubles to about 60 grams (0.132 pound) per day.

These mathematical tools also show that feed efficiency suffers in the presence of coccidiosis.

"For each increase in visual coccidiosis score, feed efficiency decreases approximately 0.0084% per gram (0.002 pound) of live weight," he said, noting that nearly half of feed eaten by birds is consumed during the final 2 weeks before processing.

"So even with a coccidiosis score of 1, the impact on final feed conversion is going to be enormous."

Field experience confirms lab results

Experience gained in real-world settings lends credence to Teeter's findings about the potentially devastating effects of late cocci challenge.

In one operation in Ontario, Canada, with Ross 308 birds that were not vaccinated against coccidiosis, very high oocyst counts were noted around day 29, though no symptoms of coccidiosis such as bloody droppings were present.

When expected weights for the Ross 308 birds (as provided by the breeding company) were plotted on a graph along with the actual weight of the birds, a significant loss of growth—culminating in zero growth—was seen at day 39 onward . Observers suspect some of the loss in growth may have been due to coexisting necrotic enteritis, though no clinical evidence of that was seen.

In later flocks the Canadian producer decided to use a live coccidiosis vaccine (Coccivac-B) to provide early cocci challenge. The results were dramatic. Late weight loss was avoided due to earlier development of immunity (Figure 3).

Such accumulating data, Teeter says, are powerful. "I've been awe-struck at the tremendous impact late-stage coccidiosis has on performance."

He sums up, "It is critical for broiler producers to make a routine analysis of the timing and severity of coccidiosis challenge because, if it happens early, the birds have time to recover. If it happens late, toward the end of the production cycle, there's just not enough time for them to recover, and even minor lesions can cause huge losses."

Spring 2008

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