The influence of manganese in association with other dietary components on certain shell characteristics

Four groups of pullets were given, from 17 weeks of age, a high‐Mn diet, or one of three low‐Mn diets. Hens given low‐Mn diets laid eggs with poor shells, judged by appearance, strength and thickness at the start of lay, but only one low‐Mn diet (diet 4), was associated with poor shells throughout 12 months of egg production. Supplementary Mn (100 mg/kg) added to low‐Mn diets after 12 months had no significant effect during the next 2 months on shell appearance score, strength or thickness.

In a second experiment, four groups of pullets aged 16 weeks were given diets of low or high Mn content and high or moderate P content. At the start of the laying period there was a significant interaction between Mn and P, a high level of P increasing shell defects caused by low Mn. At a later stage, 4 months after the start of egg laying, high P significantly reduced shell strength and thickness but had no effect on appearance score: low Mn had only a small non‐significant effect on any shell characteristic at this stage.

In a third experiment pullets of five White Leghorn type hybrids aged 16 weeks were given diets of low or high Mn and high or low Ca until the point of lay, when all birds received the high‐Ca diet but continued receiving the level of Mn given from 16 weeks of age. Only shells produced at the start of lay were studied. Type of hybrid influenced the number of soft shells produced but had no significant effect on other characteristics. Manganese significantly influenced all shell measurements and a high level of Ca increased the number of soft shells, decreased strength and thickness but had no effect on appearance score. There were no significant interactions.