By Dr Balkar Bains
Ionophores have played a key role in addressing coccidiosis and improving performance in broiler chickens. Back in the early 1970’s resistance to chemical anticoccidials was widespread.
Historical detection of coccidiosis
Routine monitoring of coccidiosis in broiler flocks was based on coccidia intestinal lesion scoring and fecal oocysts counts at three and six weeks of age. Broilers were grown to sixty-five days of age, reaching similar market weights that modern broiler chickens achieve in thirty-three days. Similarly, feed conversion efficacy of was very low as compared to the current standards.
The introduction of ionophore anticoccidials
The first ionophore anticoccidial, Monensin, was introduced in the early 1970’s for the control of coccidiosis in broiler chickens.
Later that decade a second ionophore, Lasalocid, was made available to the broiler industry. The usage of ionophores progressed over time on a global basis, with great success.
Overcoming resistance to chemical anticoccidials
Because of recurring coccidiosis in broilers and resistance to chemical anticoccidials, Monensin offered a better prospect of controlling coccidiosis in broilers. Initially Monensin was perceived as another anticoccidial drug, with the expectation coccidia would eventually develop resistance to the new drug. What followed after the introduction of Monensin and Lasalocid for broilers was a slow learning and beginning of an appreciation that ionophores are different to chemical anticoccidials.
Key learnings for treating coccidiosis with ionophores
The main observations and learned experiences are briefly outlined below for better understanding of the use of ionophores for coccidiosis control.
Range of dose for ionophores
The approved dosage of ionophores in broiler feed was a range rather than a fixed amount like chemical anticoccidials. Irrespective of the dosage of ionophores in feed, coccidia lesions were frequently observed but no clinical signs of coccidiosis were observed in the flock. There was no easy explanation offered at that time.
Leg weakness and sitting in broilers
There were also field observations that broilers were spending more time sitting rather than looking alert and active. These observations were widespread but without any explanation or understanding. The observed condition was similar to what was known as leg weakness in broilers.
Pullets showing leg weakness
In addition, some field observations noted similar behaviour in pullets, exhibiting a higher incidence of leg weakness and a tendency to sit rather than explore feeders or drinkers etc.
Male broilers also showing leg weakness
Some field observations pointed out that more male broilers exhibited leg weakness than the pullets while housed under same conditions.
Ionophore usage encouraged coccidiosis immunity
After several years of ionophore usage, laboratory observation noted that ionophore usage effectively controlled coccidiosis and chickens on ionophore treatment programs developed immunity to coccidiosis. Ionophores at that time were not approved for coccidia immunity applications in chickens.
So, what lies behind the observations mentioned above?
Dosage for ionophores
Ionophores are approved for a usage in broiler feed at a range that is most effective and safe for the chicken. The quantity of feed chickens consume is not controlled; it is the chicken that decides how much feed it needs to eat. The feed consumption of a chicken is influenced by its energy level; the higher the energy content, the lower the feed intake and conversely the lower the energy content, the higher the feed intake. So, there is logic in providing a variable dosage range, offering flexibility and efficiency to poultry production operations.
Low-grade ionophore toxicity
Leg weakness was observed to be linked to low-grade ionophore toxicity, caused by a combination of factors that include higher inclusion level in feed and higher feed intake of the chickens. Depending upon the feeder space in the broiler house, it is not uncommon to observe that aggressive chickens will eat first and weaker ones will eat what is left. In cases where pelleting has broken down to crumbles, it was observed that crumbles and mash had a higher content of ionophores, resulting in toxic signs expressed as leg weakness.
Immunity to coccidiosis
The understanding of immunity came with an appreciation of the mode of action of ionophores, killing coccidia in the lumen of the intestine. Once the coccidia penetrate the cells of the intestines, ionophores are ineffective in intracellular space. The observations of intestinal coccidiosis lesions provided another tool to improve the efficiency of ionophores.
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