Published online by Cambridge University Press: 27 March 2009
1. Each of three litter sister sows was fed one of three levels of crude protein in the diet during two 8-day periods in the fourth and seventh weeks of lactation. The three protein levels were 11, 15 and 19% of the diet on an air-dry basis. The scale of feeding was varied to maintain each sow at constant weight throughout the 8-week lactation period.
2. During two 3-day collection periods following 5-day preliminary periods, intake of nitrogen from the diet and outputs of nitrogen in faeces, urine and milk were measured.
3. The sow receiving the medium level of protein in the diet was in positive nitrogen balance during both collection periods.
4. The major effect of increasing the protein level of the diet was an increase in the output of urinary nitrogen. Neither milk yield nor output of protein in the milk appeared to be affected over the limited period studied.
5. Apparent digestibility of dietary protein was 75% on the low level and 85% on the medium and high levels of intake.