Why pullet muscle and bone development matters
Pullet growth and development within the first 22 weeks shapes lifetime productivity. Good conformation, maturity and flock uniformity during this period underpins efficient egg production and sustained performance. Investing in early growth and health supports a smooth transition into lay, improving longevity, consistency and overall farm profitability.
Across rearing, rapid establishment of feed intake, steady growth to breed targets, and tight flock uniformity should be targeted. These fundamentals underpin crop and gizzard development, support early immune maturation, and set the foundations for efficient nutrient use in early lay. Pre‑lay nutrition is particularly critical: pullets must build adequate protein reserves in the breast muscle (the main source of amino acids for albumen and yolk precursors) and mineralise the skeleton (the primary calcium reservoir for eggshell formation). This requires balancing dietary energy and digestible amino acids to favour lean muscle gain while building medullary bone reserves before the first egg is laid.
Breast muscle development and keel bone integrity are predictors of laying performance. Genetic progress has increased persistency and egg numbers, but the physiological burden on the keel bone and calcium balance has also increased, especially in aviary systems where collision risk and perch pressure add stress. Poor mineralisation and/or body composition in rear can lead to more keel damage, downgraded eggs and reduced lay.
Increasing evidence shows that intestinal health underpins the rearing of high‑quality pullets capable of sustaining profitable egg production. It determines how efficiently birds absorb amino acids, calcium and phosphorus, and how much is lost to inflammation or dysbiosis. Proactive gut support during rear improves villi development, stabilises the microbiota and helps birds cope with routine stressors such as diet changes, vaccinations and transfer.
Pullet vaccination programmes subject birds to weekly immune stimulation, and not all birds respond equally, reflecting differences in immunity. If gut microbiota balance is maintained under stress, the gut diverts fewer nutrients toward inflammation and the immune response, preserving amino acids for growth and future egg production.
Average body weight and flock uniformity are key markers of pullet quality, but weight alone is not sufficient, and manual palpation is subjective and can sometimes miss keel fractures. Ultrasound scanning provides an objective, welfare‑friendly assessment tool, allowing measurement of breast thickness and visualisation of keel deviations or fractures in live birds. Lallemand has used handheld ultrasonography for several years to track improvements in breast development resulting from a specific probiotic bacteria.
Bactocell (Pediococcus acidilactici CNCM I‑4622) is a well‑documented lactic‑acid‑producing bacteria registered for use in all poultry species to support digestive function. In more than 60 layer studies, supplementation at the commercial dose (100 g/T feed) improved laying rate, feed conversion, egg mass and reduced downgrades, demonstrating better nutrient conversion into eggs. As well as these benefits in lay, improvements in protein deposition and bone mineral metabolism can be expected from supplementing the probiotic during rear.
Supporting muscle development
Field and experimental work with Bactocell supplementation shows significant increases (p<0.001) in breast muscle thickness in pullets (+41% after 15 weeks) and layers (+2% after 6-10 weeks, +28% after 24 weeks, +40% after 52 weeks) with measurable differences (+6%) found in broilers after only 13 days. Alongside reduced faecal crude protein content, these improvements support the view that more dietary amino acids are utilised for lean gain. Higher calcium and phosphorus levels within the blood and bones translate to harder, more cohesive bones which have been demonstrated with the probiotic fed through lay. There are consequently fewer keel deviations and fractures with a greater proportion of birds with no detectable keel lesions. These are signs of better skeletal robustness under production pressure, demonstrate that increased eggshell quality with fewer downgrades does not come at the expense of bone health.
Well developed pullets with well developed guts become resilient, efficient layers. Focusing on muscle and bone status while supporting gut health helps to sustain performance and enhance egg quality. A targeted probiotic like Bactocell complements good genetics, nutrition and pullet stockmanship, turning efficient early development into long term profitability.