Understanding hen mortality at peak production

Mortality in a flock can have a detrimental effect on a farm’s overall performance. Pinpointing the root cause of the problem is not always straightforward, as it may be due to disease, but mortality may also be related to a management problem. Poor flock management can cause high mortality leading to production losses or persistent mortality throughout the life of the flock.

To determine mortality issues that are possibly related to management, begin by creating an accurate picture of the causes of the mortality. Post-mortem examinations will provide much of the information. However, be careful when interpreting data from post-mortems. If data is collected from only a few hens, the results may be misleading as several different diagnoses within a small population will not provide an accurate conclusion. A good practice when troubleshooting higher-than-normal mortality in a flock or a complex is to conduct post-mortem examinations on all the daily mortality of the affected flocks once a week. This practice will increase the sample size and give a good picture of the cause.

After collection, it is recommended to group the data into broad categories. Examples of such categories include infection, prolapse, sudden death syndrome, runt, lameness and no lesions. Each case should be put in the category that best describes the primary issue. The data can then be visualised as a graph giving the farm manager a broad overview of the mortality causes. Understanding the main cause of mortality is important to be able to make targeted adjustments to a management programme.

Photo stimulation

A common cause of hen mortality is inadequate preparation for photostimulation. The pullets need to have the right weight, age, fleshing and fat reserves to respond well to photostimulation and achieve a high peak of egg production with low mortality. Poorly conditioned pullets will fail to respond to photostimulation and exhibit low peak production and increased mortality. When photo-stimulated, poorly conditioned pullets may die due to prolapse, sudden death syndrome (SDS), or peritonitis issues and may have issues associated with overstimulation, including a high number of double yolk eggs. Some poorly conditioned pullets do not mature properly and will become overweight, producing few or no eggs. Overweight pullets are also more susceptible to mortality than hens at target weight.

Flock uniformity is an important aspect of preventing mortality. A flock with poor uniformity will have both immature and overweight pullets at photostimulation. Both the poorly conditioned and the overweight pullets will have more issues after photostimulation than the pullets that have been correctly conditioned.

A flock should be ready for photostimulation between days 147 (week 21) and 154 (week 22), depending on the line. If the flock is not in the correct condition at the recommended time, it is possible to wait an additional week before making the first light increase, but it is not advisable to wait longer than a week. The best way to determine whether or not a flock is ready for photostimulation is to evaluate fleshing scores and pelvic fat reserves. At photostimulation, all females should have a fleshing score of 3 or higher. The majority (>90%) of the pullets should also have enough pelvic fat reserves. Having enough (but not too much) fat is essential for the hormonal response to photostimulation.

Photo stimulation programme

Pullets are usually on an 8-hour light programme in the pullet house. The goal is to increase this to 14 hours as quickly as possible. A good strategy is to increase the light from 8 to 12 hours for the first increase. After 2 weeks at 12 hours of light per day, the light duration can be increased by 1 hour per week until the flock receives 14 hours of light a day. If the light is increased too quickly, flocks will show signs of overstimulation, as shown by a high percentage of double yolks, peritonitis and prolapses. Along with duration, light intensity is also increased. The intensity is increased by between 50 and 100 Lux (5-10 fc) from the first increase in day length.

Feeding

Making large feed increases beginning at photostimulation through the onset of production can overstimulate the pullets. Hens are especially sensitive to aggressive feed increases when production is less than 30%. Once 30% of the flock is laying, larger feed increases can be given. For more details on how to manage feed for pullets coming into production, contact your Cobb technical service advisor.

Feed should be equally available to all the hens and distributed in less than 3 minutes. To ensure that all hens have easy access to feed, it is important that there is enough feeder space. We recommend at least 15 cm (approx. 6 inches) of chain feeder space per bird or 10-12 hens per pan (30 cm/11.8 inches in diameter). Poor feed distribution or insufficient feeding space can create problems for the flock. Smaller hens that cannot compete for feed may not consume enough feed to sustain themselves, and egg production will drop or even stop. These hens are also susceptible to diseases like bacterial arthritis. The bigger hens that outcompete the smaller hens will become overweight, leading to an increased risk of weight-related mortality issues.

It is vital that pullets find feed and water after transfer. This is especially important when birds have different feeding systems in the pullet and production houses (i.e., moving from pan feeders to chain feeders). The pullets will also need to learn to jump onto the slats. Placing enrichments (slats or perches) in the pullet house can help train the pullets in how to jump. If chain feeders are used in the pullet house, and they are low enough, birds can also learn to jump over the feeders.

It is recommended to spend time walking the house to move the birds towards the slats so they can find water. Likewise, be present at each feeding time and walk around the house to move birds towards the feeders if needed.

Nutrition

Good nutrition is essential to promote high performance in broiler breeders. If a large number of hens are dying from SDS, it may be that the feed formulation is wrong. High sodium in feed or water can cause SDS, hypophosphatemia (phosphate depletion) and hypokalemia (potassium depletion). Review the feed electrolyte balance and test the water if SDS is occurring in the flock.

Calcium tetany is also a problem associated with feed. Using large particles of calcium in the feed and providing oyster shells in the afternoon are good ways to meet the hen’s calcium requirements. Switching from Developer to Breeder feed should be done at first egg to supply the calcium needed for egg production. If breeder feed is given too early, the birds are unable to absorb calcium efficiently when egg production starts. If breeder feed is given too late, bone calcium reserves can become depleted.

Environment

The environment is very important to promote good performance. Stressors – such as loud noises, visitors and poorly maintained equipment – can cause mortality. A stressful event worth noting is heat stress which happens primarily at feeding time. While eating and digesting, the birds generate a lot of metabolic heat. Observe the flock following feeding and note if hens are panting. In severe cases, acute heat stress can cause immediate death. However, heat stress can also cause peritonitis leading to death. Heat stress can further cause blood pH imbalances which can disrupt calcium metabolism and predispose hens to calcium tetany. To cool birds during feeding, it is recommended to turn on the fans around feeding time (1 hour before feeding and off about 2 hours after clean-up).

Male management

Male aggression can cause hen mortality through back injuries. To help prevent male aggression, sexual synchronisation between the sexes is important. When males are ahead in maturation, the females may be reluctant to mate, causing males to become aggressive. The best way to synchronise a flock is to keep males and females at the standard body weight. The body weight differential between males and females is ideally less than 18%. If the body weight differential is more than 30%, hen mortality due to male aggression often increases. If the body weight differential is more than 30%, lower the male ratio temporarily to give females more time to mature and accept the males. Be aware that even with a well-synchronised flock, a high male-to-female ratio can also lead to high female mortality.