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Vet on Call: Be warned, soft shells will leave egg on your face

Saturday February 18 2017

A worker feeds chicken in Mukui Farm in Nakuru.

A farm worker feeds chicken in Mukui Farm in Nakuru. Stress of any cause may prevent proper functioning of the egg gland in chicken. PHOTO | SULEIMAN MBATIAH | NATION MEDIA GROUP  

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In my veterinary office, calls come in from all over the country. Over time, my wife and I have learnt that it is not all cases that must be attended to personally.

Two weeks ago, I received an SMS reading, “Hic Doc, I’m Cecelia from Matuu – call me Cece. I have a problem on my farm. Some eggs are turning white-shelled and break easily. Can you visit and for how much?”

I responded to Cece on SMS that I needed to know what size and type of chicken flock she had and when the problem started.

She had 3,000 layer chickens of the ISA Brown variety.

“You know, the chicken should give me nice brown eggs but a fairly large number have been laying white cotton-shelled eggs for the last one month. I’ve tried many remedies but none is working,” she added.

The eggs referred to by some farmers as “white cotton-shelled” are actually soft-shelled eggs, which are fluctuant when mild pressure is applied on their surface.


When chickens that are supposed to lay brown eggs shift to laying white eggs, definitely there is a problem.

“I believe I can handle your case over the phone and save you the cost of coming to your farm since you have not seen any other problem with your birds,” I informed Cece.

She paid my consultation fee on M-pesa and we delved into a phone discussion. She explained to me that she was giving her layers calcium, mineral and vitamin supplements but the number of birds laying the abnormal eggs kept increasing. She had only one lot of birds and they had all come in together.

The birds were in the last segment of the third phase of their laying cycle at about 65 weeks of age. The chickens were eating well and drinking water, they were active and looked normal.

She had therefore not given any antibiotics.


I was impressed by Cece’s knowledge of the problem and her choice to exclude antibiotics. She was conscious of the need to keep antibiotics out of the human food chain.

“So what is the problem with my birds?” she enquired. I guided Cece through the various causes of white soft-shelled eggs as a way of isolating the possible cause of the problem.

Laying of the eggs is a common problem on layer farms. Sometimes the eggs may also be misshapen but that is a story for another day.

To appreciate formation of soft-shelled eggs, it is important to understand the reproductive process that yields an egg.

The chicken oviduct or “egg tube” carries an egg from the ovary to the vent where it exits into the egg nest in 24 hours.

The egg leaves the ovary as egg yolk and makes a stop at the egg shell gland along the oviduct where the yolk is wrapped in egg white and egg shell membranes.

Calcium carbonate and pigments are also laid into the outer shell membrane creating the hard coloured or white shell we see enclosing the yolk.

The calcification process may be compared with the process of building a gypsum ceiling.

It takes about 20 hours for the normal egg shell to be formed.

The process of forming the egg shell and secreting the pigments that colour the shell may be affected by a number of factors that may be nutritional, environmental, diseases and their residual effects or age.


As I discussed with Cece, it was evident her case was not due to nutritional causes. She was giving sufficient feed, calcium, vitamins, minerals and water.

Insufficient calcium causes soft or thin shells that are easily breakable.

I also ruled out environmental causes such as stress, predators or excessive light. Predators such as mongoose and hawks may cause fear and the chicken is forced to lay the egg earlier than the 24 hours it takes to travel from the ovary to the vent.

This means the egg may leave the “shelling station” before the shell is fully formed.

Stress of any other cause may prevent proper functioning of the egg gland. All these factors were absent on Cece’s farm.

Cece’s birds were nearing the end of their laying cycle. Age was a probable cause of the eggs they were laying.

However, age alone could not cause so many birds to be affected within one month.

Furthermore, the birds had started laying the abnormal eggs and dropped egg production in the second segment of the third phase of the laying cycle.

Age will normally affect egg shell formation at the beginning or towards the end of the laying cycle.


“Have your birds ever had an infection since they came onto the farm?” I probed. “Yes. I recall they had a serious attack of mycoplasma before they started laying,” she quickly responded.

“I got you Mr Microbe!” I mentally exclaimed. Mycoplasma are some very persistent bacteria that cause respiratory disease in chickens and also leave residual damage in the oviducts.

Even though chickens may be treated, the residual damage to the egg shell gland and the oviduct results in premature termination of laying and improper egg shell colouration and formation.

While mycoplasma is treated by Fosfomycin and Tiamulin antibiotics, the main problem with the disease is the permanent residual damage that it causes in the chicken oviduct as in Cece’s birds case reducing its ability to function properly and making the chicken produce abnormal eggs and complete their laying cycle earlier than the benchmark of 80 weeks of age.

Her only remedy was to continue rearing the chickens and cull all of them once egg production was no longer economical.

Mycoplasma can recur if good hygiene, early detection and treatment and sourcing chicks from disease free hatcheries are not observed. So always be on the lookout.