The utilization of dietary energy by lactating sows

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Abstract
1. The aim of the experiment was to determine gross efficiency and net efficiency of energy conversion for milk production in lactating sows. 2. Two lactating Wessex Saddleback sows were used for both determinations. Two dry, non-pregnant sows of the same breed were also required for the determinations of net efficiency. 3. Rations were adjusted with the aim of maintaining the sows at constant live weight, but this was only partially successful. 4. Digestible energy intakes and milk energy outputs were measured during three 6-day recording periods in the 2nd, 5th and 8th weeks of lactation. Digestible energy consumed was determined by incorporating 1% of chromic oxide in the rations to be fed, and measuring the energy contents of food and faeces by bomb calorimetry. Milk energy output was determined by measuring milk yields and compositions and calculating the energy contents from percentages of fat, protein and lactose. Milk yields were measured by weighing the young pigs before and after each suckling during each recording period, and samples were obtained by a special milking machine for determination of chemical composition. 5. Data required for the calculation of energy conversion efficiencies for milk production are presented. Gross efficiency was determined as approximately 45% and net efficiency as approximately 85%, but this latter value must be regarded more as an estimation because of the difficulty of determining accurately the maintenance requirements of lactating sows.