Charles Macleod, Commercial Manager Layers
First published in the July issue of The Ranger, Commercial Manager Layers, Charles Macleod, explores the critical role of regular weight monitoring in laying hens. Highlighting how tracking body weight, from rearing through to peak lay, can impact egg output and overall performance.
In the poultry industry weight matters. Broiler farmers rightly focus on bird weight from the beginning to the end of the production cycle. However, for layer farmers, making sure bird weight is tracked throughout is not such a priority. This is largely because as the flock ages, egg weight tends to become the focus.
However, the benefits of weekly weighing and tracking weight and evenness consistently throughout can be significant. You can manage an underweight flock however you cannot effectively manage an uneven flock. Weights can also indicate overall nutritional status – deficit and surplus – providing an ‘early warning’ of impending reductions in egg mass output.
Tracking early weights
Weighing pullets in rear is universally accepted as the best way to track development. Breed companies have developed accurate weight profiles to track and confirm this. For example, there is a strong correlation between the weight of a 5-week pullet and performance in lay – especially for flocks intended for extended laying cycles above 80 weeks. Where flocks are due to depopulate before 80 weeks, achieving the 5-week target weight is vital to getting a good ‘peak’ and sustaining maximum production from the flock.
Flock weight at 16 weeks is the fundamental precursor to light stimulation – if development is not on target – “lighting the flock up” will need to be delayed.
Weighing flocks post transfer for 4 to 6 weeks is common practice. This ensures that the pullets settle into the new environment and start into production.
At this point, the hen will go through a period of rapid development and their nutritional requirements will change to support this. Therefore, regular weighing remains important to make sure the birds are on track.
Beyond 30 weeks
Birds continue to build bone mass, and body weight should continue to increase well beyond 30 weeks, with birds achieving their maximum weight around the 40-week mark. It’s at this time that a producer’s focus tends to switch to careful monitoring of egg weights rather than the bird’s. Beyond 40 weeks weight stabilises and after 60 weeks there can be some decline. As a reminder continue to weigh the birds weekly and combine with egg mass to provide a consistent timeline.
Recording the flock’s weight regularly will provide vital insight into the “input/output” relationship, helping to sustain high production without depleting the hens’ reserves.
The relationship between nutrition and bird weight
Weighing birds consistently can also draw attention to nutritional issues.
Recording egg mass AND body weight will provide an early indication of nutritional balance, deficit or surplus. Today’s hybrid laying hen is bred to provide maximum output with minimal levels of nutrition for maintenance. Monitoring egg mass and hen weight is fundamental to ensuring the nutritional requirements are being met but not exceeded.
Nutrition deficit and surplus are equally problematic to laying flocks.
| Nutritional deficit | Nutritional surplus |
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The relationship between nutrition and egg mass
As weight stabilises around 40 weeks, and in a “healthy” flock, reduction in flock weight can be an early sign that egg mass may be about to decline. This is because the weight decline points to the flock being in nutritional deficit. However, egg mass output may continue unaffected for a short period of time as the hen will use her body reserves to maintain production. Laying hens have very little ‘in reserve’ and at this point it’s vital to ensure that nutrition is adjusted accordingly.
This nutritional deficit and use of reserves can also increase susceptibility to disease – leading directly or indirectly to mortality. Where mortality does not rise, you will see the egg mass output decrease rapidly (both egg size and numbers will go down), then stop.
By the time you see this drop in egg mass, interventions will only mitigate rather than remediate. You will not be able to get production back to the level it was before.
When and how to weigh
Birds should be weighed once a week throughout their productive life so there is a consistent timeline.
How you weigh is as important as how often you weigh. To produce weight data that is comparable over time requires a planned approach. You will not only be looking at the individual bird weights but as a collective group or flock and will be calculating how much weight variation there is.
As farmers are managing a flock and not individual hens, it is important to know what variation of weights there are. This “variation” is commonly represented by Evenness and Coefficient of Variation (CV).
Evenness looks at how many of the individual hen’s weights are either side of the group’s average weight. Evenness disregards any weight that falls outside of that. CV takes into account all of the birds that you weigh and gives a more accurate indication of the flock’s weight distribution
Example of evenness
You weigh 100 hens, and the average weight is 1,389 grams. You want to see how many of the 100 hens weigh between 1,250g and 1,527g which is 10% under and over the average weight. 10% either side of the average weight is the industry standard. You find 83 hens are in this weight bracket, so the flock is deemed to be 83% even.
But that means you still have 17 hens that are not in this 10% band. And this 17% are the ones that you probably need to be most concerned about as they’re the most significantly outside of the norm. And unless you look again at the data in more detail, you will not know how far they are away from the norm – it could be 1g or 30g.
Coefficient of variation
CV doesn’t rely on subjective judgements. It looks at all the weights and works out how far each weight is from the “mean or average”. This is the sum of all the values divided by the number of values. Most manual and automatic poultry scales will do the calculation for you.
This results in a CV ‘score’ and the lower the number, the more even the flock is. A CV below 7 would be considered acceptable for a laying flock, but below 5 would be better and make flock management more efficient. Our management tools are the light and food we provide the birds – tracking CV consistently makes for better informed decision making on any adjustments needed to these.
Selecting birds to weigh
Which birds from a flock are weighed must be “random”. However impartial you are selecting hens as you walk through a pen – this is not random enough.
- Walk and inspect a compartment of birds as normal
- Contain a number of them in a small pen. 20 should be fine in a standard 16k house with 4 compartments
- Weigh all the birds in the small pen and do this in each pen on both sides of the aviary system
- You should have over 160 birds weighed. This is enough but still only represents 1% of the total flock!
Record the weights, evenness and CV weekly and compare the results over the life of the flock.
The results will give you early warning of problems developing within the flock and allow action to be taken to better maintain flock performance and profitability.
If you have any questions on flock weights in general, please call us on 01392 872932 or email info@stdavids-poultryteam.co.uk