The following conclusions were obtained from a comparison of growth and carcass characteristics of pigs slaughtered at 150, 200 and 260 lb. liveweight.

(a) The ranking of boars at the three weights, according to the quality of their progeny at each weight, was similar for the carcass characteristics, i.e. percentage of lean meat, length, backfat and eye muscle area—but was not associated for the efficiency factors, i.e. daily gain and food conversion. Results from singly-penned progeny pigs confirm that food consumed up to 150 lb. live weight is not indicative of the food consumed between 150 and 200 lb. live weight. A similar result is true for daily gain. It thus does not appear that the results obtained at 150 lb. live weight could be used to represent results at heavier weights and this is particularly true for performance testing when only one animal is concerned. Rather it would appear that if the pigs were raised to a given weight, carcass information at an earlier weight could be obtained on the live pig by ultrasonic means and by subjective estimates, whilst food conversion and daily gain could be calculated exactly at any live weight.

(b) The weights of the different cuts as a percentage of the side weight does not appear to change much between slaughter weights. The carcass becomes less lean as the slaughter weight increases and this difference in leanness is more observable between the 200 and 260 lb. weights than between the 150 and 200 lb. weights. In these ranges at least as much lean as fat is put on in the shoulder and ham but more fat than lean is put on in the back and in the streak. For example, between 200 and 260 lb., 5 lb. of lean to 9 lb. of fat is added in the back cut.

(c) For all cuts and for both sexes, the percentage of lean meat added in the range 200–260 lb. live weight is less than that for the range 150–200 lb. live weight. This difference is more severe for hogs, especially in the back cut. The sex difference (in favour of the leaner gilt) becomes more pronounced at the heavier weight range. This is not so obvious in the ham but is marked in the shoulder and streak and particularly in the back. 3·9 lb. of food is required to put on 1 lb. of live weight between 150 and 200 lb., whilst 4·3 lb. of food is needed for each 1 lb. gain between 200 and 260 lb. live weight.

(d) Percentage of lean meat prediction equations fitted to the data at the three weights are of equal accuracy. In all cases the reduction in variance is highly significant and the percentage of lean meat of a pig can be estimated with a standard error of approximately 2% of carcass weight.