Thin sows: 2. Observations on the energy and nitrogen exchanges of thin and normal sows in environmental temperatures of 20 and 5 °C

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Summary: The experimental animals were sows which had been made thin by underfeeding for several parities (thin sows), and siblings which had received adequate energy (standard sows).The energy metabolism of three thin anoestrous and three non-pregnant standard sows were measured at 20 and 5 °C. There were no differences between the two groups of sows. The fall in temperature increased the average maintenance requirement by 60% from 476 to 753 kJ/kg0·75/day (1192–1922 kJ/kg0·56/day).The tissue insulation of the thin sows was 28% lower than that of the standard sows, although this difference was not statistically significant. The thin sows compensated by having a better external insulation. The average total body conductance was 306 kJ/m2/°C/day.The standard sows were in positive nitrogen balance (+ 4·2 g/day, 95% confidence limits 1·5 to 7·0 gN) and the thin sows in negative nitrogen balance (– 4·4 g/day, 95% confidence limits – 2·1 to – 6·8 g N) at energy equilibrium. It is suggested that this difference might be explained if the total nitrogen requirement of the two groups of sows was similar, but that their requirement for energy was related to their body surface area.There were no differences between the two groups of sows in their digestive efficiency, but the digestibilities of both energy and nitrogen were reduced at 5 °C.It is concluded that the primary cause of the ‘thin sow syndrome’ is underfeeding, particularly in cold environments. Other features of the syndrome are probably a consequence of undernutrition and depletion of the body energy reserves.

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