“Some producers would view a lesion score of 2 as being nominal, but in our studies, we saw the average daily gain in birds with this lesion score drop to zero,” Teeter said. “Growers really need to pay attention to their coccidiosis program and get it as close to lesion-free as possible,” he said in an interview after his presentation.

Teeter and colleagues evaluated the metabolic impact of coccidiosis at different points on the broiler growth curve. Teeter has presented results from the studies before, but since then he has more closely examined the data and influence of coccidiosis on the energy costs in broilers.

Further analysis confirms that low-level coccidiosis produces a measurable cost at any age, but the cost is much less if it occurs early in the bird’s life, when there is less overall impact on energy utilization, he said.

In his presentation, Teeter explained how he and his colleagues used metabolic chambers in studies designed to mimic coccidiosis challenge in a commercial production environment. Over 1,000 Cobb X Cobb broilers were evaluated five times over a 48-day period.

Teeter’s team challenged birds with an orally administered mixture of E. maxima, E. acervulina and E. tenella — three common pathogenic species of the protozoan parasite that causes coccidiosis — at days 14, 21, 28, 35 and 42. Control birds received only a sterile saline solution.

After each challenge, investigators placed birds in metabolic chambers, where they were evaluated for a variety of parameters such as live weight, body composition, heat production, retained energy and excretion. After 6 days in the chamber, they necropsied the birds and scored the coccidial lesions.

Lesions, poor performance correlated

As expected, control birds had no coccidial lesions, but the challenged birds did. Compared to controls, birds with lesions had lower live weight and weight gain, and poorer feed efficiency. They also had less energy consumption, and their ability to retain energy worsened with age (see Table 1), Teeter said.

Table 1. Coccidiosis-mediated gross-lesion-score effects on production and energetic criteria at standardized weights.<sup>1

1</sup> Values created using predictive models (R2>.95) and standardized initial weights.
²Mixed lesion scores were utilized for all variables except gain/feed, where homogenous arrays of 0, 1, 2, 3 and 4 were applied.

The metabolic chambers, Teeter noted in the interview, are “very conservative and the costs determined in this study would be less than in the field.”

For instance, at 20 days of age, energy retained by birds with a gross-lesion score of 2 was 100 Kcal/day, at a time when they were eating 300 Kcal/day. By 48 days, energy retained daily by the same birds fell to 0 Kcal, even though the birds were consuming 482 Kcal/day, he said.

Even in birds with a gross lesion score of only 0.5, the results demonstrated the impact of a coccidiosis challenge. At 20 days of age, retained energy was 170 Kcal, compared to 188 for controls. By 40 days of age, it was 191 Kcal, compared to 305 for controls.

Higher maintenance energy cost

Lesions in challenged birds correlated with maintenance energy cost. In other words, the cost for birds challenged with Eimeria increased with the lesion score and became higher later into the broiler-growth curve, he said.

Lesion scores were also positively correlated with excreta energy loss, Teeter said. “With a coccidiosis challenge, you can see an additional 75 to 125 Kcals of energy lost in excreta. Now that’s a pretty big proportion of the bird’s daily appetite,” he observed. “In addition, we saw the maintenance requirements go up and an additional number of K-calories lost as heat and carbon dioxide, which goes into the atmosphere.”

He pointed out that the consequences of coccidiosis challenge were directionally similar for birds with low and high lesion scores. Feed-efficiency responses paralleled energy responses, with the consequences of coccidiosis challenge becoming more profound late in the growth curve.

“The consequence of coccidiosis challenge is much more severe when you get up in the second half of the growth curve, when the bird is consuming most of the feed it will eat during its lifetime,” and at a time when feed costs are soaring, Teeter said. “You absolutely don’t want that bird developing immunity during that time period, because it will be extremely costly and result in a tremendous loss for producers.”

It’s true that birds can bounce back and make up the performance loss that occurs after a coccidiosis challenge. But when that challenge occurs in the second half of the growth curve, there’s not enough time to close the gap. “Once a calorie is lost in excreta, it’s gone. Those calories would just be a direct write-off to the bottom line in terms of profitability,” he said.

The same findings probably apply to any kind of immunity, not just immunity against coccidiosis, Teeter supposes. “A bird that has developed immunity early appears to handle energy more efficiently later on,” he added.

Regresar a North American Edition (#2)