1. Results are reported of an experiment with fattening pigs, made under commercial conditions, to obtain further information on the comparative value of dried skim-milk and white fish meal as protein supplements in a basal meal fed in conjunction with unrestricted amounts of whey.

2. All the pigs received, together with the unrestricted supply of whey, 3 lb. of a basal meal, reduced to 2 lb./pig/day by 13 weeks of age, fed dry once daily. Four different basal meals, comprising the four experimental treatments, were used, containing respectively 10, 7 and 5% white fish meal and 10% dried skim-milk as the protein supplement.

3. There were five pens of nine group-fed pigs on each treatment, involving a total of 180 pigs. The pigs were on experiment from approximately 8 weeks of age to bacon weight. Comprehensive carcass measurements were made on all the pigs.

4. None of the treatment differences for any of the variables studied was significant at the 5% level. There was, however, a trend for rate of growth to be reduced, efficiency of food conversion to decline and dressing percentage to improve with reduction of protein level in the diet. There was also an indication that the rate of growth and efficiency of food utilization of the pigs given the basal meal containing 10% white fish meal were rather better than for the pigs receiving the basal meal with 10% dried skim-milk as the protein supplement, although the mean differences were relatively small.

5. The results are discussed in relation to those obtained in earlier experiments completed under similar conditions at the Cow and Gate farm.

6. On the basis of the experimental evidence obtained so far, it was concluded that either 10% white fish meal or 15% dried skim-milk should be considered the minimum amounts of these protein supplements that should in practice be included in the basal meal fed with unrestricted whey in the manner described.

7. Possible effects of season on whey consumption are discussed in relation to some preliminary findings on the effect of whey acidity on the performance of fattening pigs.

8. Results of another preliminary experiment are mentioned in which a reduction in the daily allowance of the basal meal to 1 lb. or less had a very adverse effect on the performance of the pigs. It was concluded that a daily allowance of 2 lb./pig of meal given in conjunction with an unrestricted supply of whey, should be considered the absolute minimum in order to obtain a reasonable rate of growth.

We thank the Director of Messrs C. & G. Prideaux, Ltd., Bacon Curers, Motcombe, Shaftesbury, Dorset, for permission to take carcass measurements of the experimental pigs, and Messrs K. Lawrence and P. Prideaux who most conscientiously took these measurements. The help of Mr J. Rowell of the Agricultural Research Council Statistics Group, Cambridge, in making the statistical analyses is also very gratefully acknowledged. We should also like to thank Mrs J. Sedgwick for making the whey acidity determinations.