Calcium Tetany Paralysis in Broiler Breeders

Prof. Dr. R.N. Sreenivas Gowda*                                                                                                                  

Broiler breeders undergo intensive genetic selection and assortment to improve progeny performance every year. High-performance broiler breeders normally face high challenges like stress, metabolic disease, etc., which lead to increased mortality and high economic losses in the flock. Calcium tetany is one of the important metabolic diseases in heavy-yielding broiler breeders. 

What is Calcium tetany (CT)?

It is one of the metabolic disease of chicken. A condition known as hypocalcemia, or calcium tetany (paralysis), has been seen in modern or high-yielding broiler breeder hens that appear at the onset of lay to peak egg production.

This syndrome is characterized by an acute and sudden onset, usually in flocks with good hen/day production. Birds die with or without any clinical symptoms and birds typically die in the morning to early afternoon hours.

The preliminary signs such as panting, spread wings, and prostration may be seen in the early morning hours preceding paralysis and death by asphyxia. Hens may be down on the litter or cages, unable to rise. They become paralyzed and are the object of male aggression (often misdiagnosed as male kills).

. Similar conditions seen in other animals are:

1. “Milk fever” in cattle
2. Eclampsia in horses and small animals.
3. Cage fatigue” in Caged layers
4. Acute onset, usually with good production up until that point

Cause for Calcium Tetany is by deficiency of calcium in the bloodstream of broiler breeder hens (fig1). The risk factors associated in the development of calcium tetany are:

1. Poor pullet uniformity,
2. Flocks coming into early production,
3. Irregular lighting
4. High calcium (> 1.2% Ca) being fed before the onset of production  
5. Small particle sized calcium. that increase blood pH cause blood Ca to become unavailable

Calcium Tetany Theories:

1. High calcium diets for pullets and young hens that have not started producing eggs may negatively influence the metabolic systems needed to actively absorb and transport calcium for eggshell formation.
2. The presence of excessive calcium levels before the onset of egg production may trigger a physiological response to eliminate the excess amount, which r or may not be reversible.  Low blood Ca

Fig-1 Flow diagram showing the development of CT related to Metabolic stress

Calcium Tetany Predisposing Factors are:

• Young breeder hens (25 – 32 weeks)
• Poor uniformity in pullets
• High calcium being fed prior to production
• Breeder diet containing >3% Ca
• Rapid onset of production
• Exaggerated separation of heavy minerals in mash feed
• Small particle size calcium.
• Too small limestone particle size
• Early stimulation with light in pullet house or in the hen house
• Season of year – Flocks coming into production in the spring and summer

Clinical signs:

• Weakness,
• panting and depression,
• Visible in early morning , afternoon or evenings,
• Hens may be “down” in the scratch area,
• unable to rise,
• May look similar to “male kills”,
• Mortality 0.5-1%/ week or higher,
• Good hen/day production

Careful postmortem examination reveals a fully active ovary (8–9 large, yellow follicles), the presence of a partially or fully formed egg in the shell gland, and signs of asphyxia such as a cyanotic comb, congested lungs, and dark musculature. This indicates that the hen used all available calcium from the bloodstream in an effort to complete the egg shell. 

What happens if chickens have too much calcium?

If the chicken fed with too much calcium, like all vitamins and nutrients, the excess is released in urine. Additionally, calcium excretion causes phosphorus deficiency. The phosphorous deficiency can manifest in up to three ways: Eggshell issues: eggs with sharp ends, pimply eggshells, or soft or no-shell eggs.

• Usually No gross lesions noticed.
• Signs of asphyxia (cyanotic combs, congested lungs, dark musculature).
• Very active ovary: 8-9 follicles
• Partial or completely formed egg in the oviduct

Diagnosis

• Calcium tetany in broiler breeder hens is a condition characterized by muscle weakness or paralysis caused by inadequate levels of available calcium in the blood.
• Birds typically die in the morning to early afternoon and often appear as “male kills”.
• The typical necropsy findings include an active, congested ovary, with a partially or fully formed egg in the oviduct and damage to the back of the bird from male abuse in breeder hens with no other lesions.
• Definitive diagnosis is very difficult as it requires testing blood calcium levels in affected birds which can be difficult to find in the acute phase.

How do you treat hypocalcemia in chickens?

Mortality can be reduced by the administration (“topping of the feed”) of 5 g of oyster shell per hen for 3 consecutive days, and addition of vitamin D ₃ to the drinking water. This treatment should be suspended for 3 days and then repeated.

Calcium Tetany Treatment Options

• Calcium Supplementation – Oyster shell/or large particle limestone (i.e. 1/8” calcite crystals) – 2.5 g Ca/bird/day for 3 consecutive days
• Vitamin D supplementation concurrent with the calcium supplementation -Forms of 25-OH-D3 is ideal ü After 3 days treatment with Ca and vitamin D supplementation, discontinue the treatment for 3 days
• Repeat treatment 2 – 3 times Over treatment is harmful!!!

Calcium Supplementation – Ensure uniform distribution by top dressing as the feed exits the hopper, or by broadcasting in litter – Flakes of oyster shell or large limestone particles are retained in the gizzard – Recommend a large oyster shell particle size – i.e. for hens, not pullets – Some Oyster shell can be contaminated with Salmonella or other agents, check the source from where it is procured.

Treatment

• Individual inra venous administration of calcium gluconate (helps to confirm diagnosis)
• For heat stress provide clean cold water and it can reverse the condition.
• Prevention is far superior to treatment

Suggestions to prevent calcium tetany

• Maintain growing bird body weight and maintain uniformity as per breed standard recommendation of 85%.
• Avoid high calcium breeder feed up to 5% production and maintain a calcium level of 1.2% in pre lay feed to 5% production.
• Utilize large particle sized Ca when possible – large particle Ca stays in the intestinal tract longer, increasing the time that it is available for absorption.
• Provide access to oyster shell in the afternoon – it is an excellent large particle Ca source, with good Ca availability
• Maintain proper water quality by regular sanitation and acidification of drinking water at 1ml/4 liters of water and periodic cleaning of water tanks.
• Maintain intestinal health by using strong probiotics at 200 g per ton of feed
• Proper maintenance of shed temperature, ventilation, and humidity to avoid metabolic disturbance and reduce the stress on the birds.
• Blood pH and electrolyte balance should be maintained with proper calcium and phosphorus homeostasis throughout the bird life cycle
• Avoid heat stress.
• Manage blood pH changes – e.g. ensure adequate ventilation and water supplementation, maintain electrolyte balance, bicarbonate supplementation.

(*Former and Founding VC ,KVAFSU, Bidar, Former Director, IAH&VB, Bangalore, Former Prof and University Head, Dpt. Of Pathology, Veterinary College, UAS, Bangalore.)