Levels of energy and protein for brown-egg laying hens reared in cage free systems from 75 to 90 weeks of age

For decades, the poultry industry has relied on cages to house laying hens, a practice that prioritizes efficiency but often limits the birds' natural behaviors. In recent years, a shift toward cage-free systems has gained momentum, driven by growing concerns for animal welfare. These open environments allow hens to walk, perch, and nest, offering them a life that more closely resembles their natural instincts. However, this freedom comes with a biological cost. Birds in cage-free systems are more active, burning more energy simply by moving around. This increased activity changes how they eat and how their bodies process food, creating a puzzle for nutritionists: what exactly do these active hens need to stay healthy and productive as they age?

The core of the puzzle lies in two main ingredients: energy and protein. In poultry science, energy is measured as the fuel available to the bird after digestion, while protein provides the building blocks for tissues and eggs. Birds have a natural ability to regulate their food intake; if their feed is packed with high energy, they tend to eat less, and if the energy is lower, they eat more to meet their needs. The question researchers faced was whether hens in these active, cage-free settings, particularly as they enter the later stages of their laying life, require the same high-energy, high-protein diets as their caged counterparts, or if they could thrive on a different nutritional balance.

To answer this, a team of researchers in Brazil conducted a detailed study with 288 brown-egg laying hens, all between 75 and 91 weeks of age. The birds were raised in a spacious, open-air aviary designed to mimic a cage-free environment, complete with perches and nesting boxes. The scientists divided the flock into groups and fed them different diets to see how the birds would respond. They tested two levels of energy in the feed and three different levels of protein, creating a variety of combinations to find the sweet spot for older hens. The goal was to see if lowering the energy and protein content would hurt egg production or quality, or if the birds could adjust their eating habits to compensate.

The results revealed a fascinating adjustment in the birds' behavior. When the researchers lowered the energy content of the feed, the hens did not starve or struggle; instead, they simply ate more. The birds on the lower-energy diet consumed significantly more food than those on the high-energy diet. This extra eating allowed them to meet their energy needs despite the lower quality of the fuel. While this increased appetite translated into higher egg production, it also resulted in a higher feed conversion ratio (FCR). This means the birds required more feed to produce each egg compared to those on the high-energy diet, indicating a less efficient use of the feed overall.

The study also looked at the protein levels. The researchers tested diets with high, medium, and low protein content. They found that the amount of protein in the feed did not significantly change how many eggs the hens laid or the weight of the eggs, provided the birds were eating enough to meet their energy needs. Even when the protein was reduced to the lowest level tested, the hens maintained their production, likely because the researchers supplemented the feed with specific amino acids, the essential building blocks of protein, to ensure the birds got what they needed.

Beyond the eggs, the scientists examined the health of the birds themselves. They checked the weight of internal organs and the amount of fat stored in the abdomen, which can be a sign of metabolic stress or poor diet. The study found that the different diets did not cause any harmful changes to the size of the internal organs or the amount of abdominal fat. The only physical difference observed was in the size of the intestines. The hens on the lower-energy diet had slightly larger intestines, a natural response to processing a larger volume of food to extract the necessary nutrients. This suggests the digestive system was working harder but functioning normally.

The quality of the eggs remained consistent across all groups. Whether the hens ate high-energy or low-energy feed, and regardless of the protein level, the eggs were the same size, had the same strong shells, and possessed the same internal structure. This is a crucial finding, as it indicates that reducing the nutritional density of the feed does not compromise the final product. The birds were able to maintain the high standards of egg quality expected by consumers while adapting to a diet that was less concentrated in energy and protein.

Ultimately, the study suggests that older laying hens in cage-free systems do not need the high-energy, high-protein diets often assumed to be necessary. Instead, they can thrive on diets with lower energy levels, provided they are allowed to eat more to compensate. This approach not only supports the birds' natural ability to regulate their intake but also offers a practical way to reduce the amount of protein and energy fed to the flock. By feeding hens less concentrated food, farmers could potentially lower costs and reduce the environmental impact of nitrogen waste, all without sacrificing the number or quality of eggs produced, even if the feed is utilized slightly less efficiently. The hens, it turns out, are quite capable of managing their own nutritional needs when given the right environment and the freedom to eat as much as they require.