1. A review of the literature indicated: (a) A lack of agreement upon whether or not restriction of the plane of feeding from weaning or 100 lb. live weight to bacon weight improves efficiency of food conversion. (b) That a severe restriction of the plane of feeding improves carcass-quality measurements, (c) That a less severe restriction of food intake brings the total growth period within a range more acceptable to the farmer, but only has a small effect in improving carcass quality, (d) That the small benefits to quality from this less severe restriction may be equalled or surpassed by quite small changes in the genetic ‘type’ of pig fed. (e) That there are probably interactions in the response of different ‘types’ of pig to different planes of feeding.2. Two experiments were undertaken. In Exp. 1 both Large White × Swedish Landrace pigs and Large White × Wessex Saddleback pigs were fed from weaning to bacon weight to one of three planes of feeding. Exp. 2 was very similar in design except for some modifications to planes of feeding and the substitution of Essex Saddleback × Large White pigs in place of the Wessex crosses.3. In Exp. 1 the planes of feeding, according to our stated definitions in terms of total digestible nutrients consumed daily at different live weights, were: very high during both growing and finishing periods (VH-VH); very high during the growing period but restricted during the finishing period (VH-R); and very low during both growing and finishing periods (VL-VL). In Exp. 2 the planes of feeding were: VH-VH; VH-R, the restriction being slightly more severe than in Exp. 1; and low during both growing and finishing periods (L-L).4. In Exp. 1 there was no difference in growth rate between breed crosses. Pigs on the VH-R and VL-VL planes were 12 and 88 days older respectively at bacon weight than those fed to the VH-VH plane. In Exp. 2, Landrace crosses grew faster than the Essex crosses on the VH-VH and VH-R planes, but Essex crosses grew faster on the L-L plane. Landrace crosses fed to the VH-R and L-L planes were 11 and 63 days older respectively at bacon weight than others fed to the VH-VH plane. Essex crosses fed to the VH-R and L-L planes were 16 and 53 days older respectively at bacon weight than others fed to the VH-VH plane.5. In Exp. 1 there was no difference in food-conversion efficiency (f.c.e.) between breed crosses. There was no significant difference in f.c.e. between the VH-VH and VH-R planes, but there was a loss of 14% in F.C.E. on the VL-VL plane. In Exp. 2 the Landrace crosses had better F.C.E.'s than the Essex crosses on the VH-VH and VH-R planes, but Essex crosses were the more efficient on the L-L plane. There was no significant difference in F.C.E. between the VH-VH and VH-R planes for either breed cross, but there were losses in efficiency of 4 and 14% on the L-L plane for the Essex and Landrace crosses respectively.6. In Exp. 1 the Landrace crosses had less back fat over the shoulder than had the Wessex crosses. Pigs of both crosses fed to the VH-R plane had smaller fat measurements than those fed to the VH-VH plane, but this improvement was only significant for minimum back fat. Landrace crosses also had less fat over the ‘eye’ muscle when fed to the VH-R plane, but this did not apply with the Wessex crosses. The difference in carcass quality attributable to the restricted plane of feeding after 100 lb. live weight was considered to be equalled by the difference between breed crosses. The improvement in carcass-quality measurements between pigs fed to the VH-VH and VL-VL planes surpassed the difference between breed crosses, but the carcasses tended to be soft. However, no data were available on the iodine numbers of the fats.7. In Exp. 2 the Landrace crosses had less fat over the shoulder and over the eye muscle and smaller minimum back-fat measurements than had the Essex crosses. Pigs of both crosses fed to the VH-R plane had smaller fat measurements than those fed to the VH-VH plane, the difference being significant for shoulder fat and minimum back fat. Again the differences between the effects of these two planes of feeding and between the two breed crosses were considered about equal, and again the difference between breed crosses was surpassed by the difference between the carcass measurements of pigs fed to the VH-VH and L-L planes. In Exp. 2 the effects of planes of feeding upon length of carcass, thickness of streak, percentage fore and percentage middle differed significantly between the two breed crosses.8. When carcass data from both experiments were compared it was apparent that differences between breeds or strains of bacon-type pigs are likely to be of more importance in the production of high-grade bacon than attempts to alter the conformation by varying the plane of feeding—and thus the growth curve—within the limits acceptable in practice.9. Although previous evidence indicates that males grow faster than females, there was in Exp. 1 no significant difference in growth rate between the sexes. In Exp. 2 there was again no overall significant sex effect, but during the finishing period females grew faster than males on the VH-VH and VH-R planes, but males grew the faster on the L-L plane. In Exp. 1 there was no significant difference between sexes in F.C.E., but in Exp. 2 males were less efficient than females on the VH-VH and VH-R planes, but were the more efficient on the L-L plane, this interaction again developing principally during the finishing period.10. In both experiments females had carcasses which were longer, had less fat, larger areas of ‘eye’ muscle and larger hams than males. In both experiments the restricted plane of feeding after 100 lb. live weight reduced the shoulder-fat measurements of females but had no effect on those of males which, being the fatter, had the greatest need of improvement to achieve the highest grade. However, the statistical significance of this interaction was low and it requires confirmation.11. It is not the intention of the authors that these results should be taken to apply in general to the breed crosses used. The breed crosses were chosen solely as pigs which would differ somewhat in genetic type from each other.12. The results from these experiments confirmed the indications from the literature which have been noted in paragraph 1 of this summary. The results and some of their implications have been discussed in the text.

Two 2 × 4 factorial experiments each involved 8 litters of 8 pigs, one pig from each litter being allocated to each treatment. Diets containing supplements of a commercial grade of copper sulphate were compared with others containing Analar (Experiment 1) or micro-analytical reagent grade copper sulphate (Experiment 2). Four levels of each of two grades of CuSO4.5H2O, providing 16, 62, 125 or 250 p.p.m. Cu in the diets, were given in each experiment.The pigs were put on experiment at 8—9 weeks of age and most were slaughtered as their individual weights reached about 200 lb. The exceptions were 4 litters in Experiment 1 which were taken off experiment at that weight but not slaughtered. The pigs were fed in individual compartments, meal allowances being determined from a fixed scale based on live-weight.Purity of copper sulphate did not affect growth rate, feed conversion efficiency or carcass measurements in either experiment.Response to level of copper sulphate between about 45 and 100 lb. liveweight differed somewhat between experiments. In Experiment 1 pigs receiving 125 or 250 p.p.m. in the diet grew 4 or 9% faster and had better feed conversion efficiencies than those receiving 16 or 62 p.p.m. Cu. In Experiment 2, pigs receiving 62, 125 or 250 p.p.m. Cu all grew about 4–5% faster and had 1–5 % better feed conversion efficiencies than those receiving 16 p.p.m. Cu, but the effect on feed conversion efficiency was not statistically significant.Increase in copper sulphate above the trace level supplying 16 p.p.m. Cu in the diet had no effect on growth rate or feed conversion efficiency between 100 and 202 lb. live-weight or on killing-out percentage or carcass measurements.Comparison of the results with those from a previous experiment showed that in pigs fed according to a fixed scale the greatest consistent increases in growth rate and feed conversion efficiency have occurred with copper sulphate as 0·1% of the diet, giving 250 p.p.m. Cu. This supplement has only improved performance between 100 and 200 lb. live-weight in one experiment out of five.

In 1945 Braude described how pigs chewed copper rings which were a part of the structure of their piggery. To test whether this apparent craving for copper reflected a dietary deficiency, 8-and 14-week-old pigs were fed a basal diet containing about 5 p.p.m. of copper, and some were given a daily supplement of 50 mg. copper in the form of a copper sulphate solution, poured on to their rations. During the first 8 weeks of one experiment, the addition of copper improved both rate of growth and efficiency of food conversion by about 8 %, but data from the second experiment in no way confirmed this. Braude (1948) later reported that weaned pigs given a choice of mineral licks greatly preferred those containing copper and, in another small trial, two pigs ate greater amounts of a meal mixture if it contained copper added at the rate of 120 g./lOO lb. Mitchell (1953) also found that young pigs, if given a choice, preferred a creep-fed meal supplemented with about 0-05 % CuSo 4 . 5H 2 O to one with no copper added. In another experiment, when there was no choice of meals, litters offered the copper-supplemented meal in the creep ate no more and grew no faster than those offered the unsupplemented meal (Barber, Braude & Mitchell, 1955a).In these tests copper and copper salts were certainly most palatable to pigs, and, in more recent experiments, high levels of copper sulphate when added to diets fed after weaning have caused improvements in both the rate and efficiency of liveweight gain.Barber, Braude, Mitchell and Cassidy (1955) added a 'mineral mixture XF' to a diet, and over 18 weeks the weaned pigs receiving it consumed more food and grew 6% faster than the controls. These effects were most marked during the first 8 weeks of the experiment, when pigs fed the supplemented diets also had better food conversion efficiencies. The most notable feature of the' mineral mixture XF' was that it contained 4% copper sulphate, which thereby supplied 0-1 % of the diet when this mineral mixture was added to it. The differences observed in this experiment were not statistically significant but in a subsequent co -ordinated experiment, involving 182 pigs at eight centres, those animals fed diets supplemented with 'XF minerals' grew significantly faster by 6 % than the controls, and had slightly-but not significantlybetter food conversion efficiencies (Bowler, Braude,

Three experiments were carried out to obtain more information upon the effects of varying the plane of feeding for bacon pigs.Exps. 1 and 2 followed the same 3 × 2 factorial design in which (a) diets were fed with or without procaine penicillin and (b) a comparison was made between very high (VH-VH), high (H-H) and low (L-L) planes of feeding for pigs from about 8 weeks old to slaughter at about 200 lb. live weight. The planes of feeding were defined according to the amount of t.d.n. offered to each pig daily.For each of these two experiments eight lots of six litter mates were used. One pig from each litter was allocated to each of the six treatments, and although litter mates were housed as a group, all pigs were fed individually in separate compartments.Exp. 3 was a 2 × 3 × 2 factorial to compare two breeds and three planes of feeding during 2 years. During each year three lots of pure-bred Landrace and three lots of Wessex Saddleback × Large White litter mates were used. Each lot consisted of three gilts and three barrows and one pig of each sex was allocated to each of the three feeding treatments. From the start of the experiment, when the pigs were about 8 weeks old, to about 100 lb. weight, all animals were kept to a very high (VH) plane of feeding. From then to slaughter at about 200 lb. live weight the following planes of feeding were compared: (1) very high plane (VH), (2) increasingly restricted plane (R) and (3) low plane (L). As in Exps. 1 and 2 these planes were denned in terms of t.d.n., and litter mates were housed together but fed individually in separate compartments.In both Exps. 1 and 2 pigs with procaine penicillin in their feed grew very slightly faster and more efficiently than those not fed antibiotic, but the differences did not reach the 5% level of statistical significance. The feeding of antibiotio did not affect the response of the pigs to variations in the plane of feeding.In comparison with pigs kept to the VH-VH plane of feeding, pigs kept to the H-H and L-L planes grew 13 and 22% more slowly in Exp. 1, and 11 and 26% more slowly in Exp. 2, but plane of feeding had no effect upon food conversion efficiency in either experiment. These results are for the total experimental period.In both Exps. 1 and 2 reductions in plane of feeding had no significant effect upon length of carcass or thickness of streak, but they caused increases in killing-out percentage and decreases in all measurements of fat thickness. They also caused increases in the area of ‘eye’ muscle (statistically significant in Exp. 2, but not in Exp. 1) and a lengthening in the shape of the ‘eye’ muscle in the bacon rasher (statistically significant in Exp. 1, but not in Exp. 2).In Exp. 3 the Wessex crosses grew faster and more efficiently than the Landrace, but these differences were considerably larger during one year than during the other. In comparison to the Landrace, the Wessex-cross carcasses had a tendency to be shorter (P < 0·10) and to have thicker shoulder fats. They also had 1% more ‘fore’ and 1% less ‘ham’.Compared with pigs kept to the VH-VH plane of feeding, those kept to the VH-R and VH-L planes grew 18 and 36% more slowly, respectively, during the finishing period. Over the total experimental period there was no difference in food conversion efficiency between pigs kept to the VH-VH and VH-R planes, but efficiency was poorer by 4–5% with the VH-L plane. There was no breed × feeding interaction in the data for growth rates or food conversion efficiencies.In Exp. 3 plane of feeding had no significant effect upon killing-out percentage, shape index of ‘eye’ muscle or thickness of streak. The two lower planes of feeding caused reductions in the average rump fat, fat (1) over the ‘eye’ muscle and in the proportion of ‘middle’ in the carcasses; they also caused increases in the proportion of ‘ham’ in the carcasses.Other carcass quality data contained significant interactions which complicated their interpretation. The effects of plane of feeding were inconsistent between:(A) years, for length of carcass, maximum shoulder fat, area of eye muscle and iodine values of the back fat;(B) breeds, for minimum back fat and percentage ‘fore’;(C) sexes, for dressing percentage and fat (2) over ‘eye’ muscle;(D) breeds and years, for dressing percentage;(E) breeds and sexes, for maximum shoulder fat.The results of the three experiments have been compared with other data on planes of feeding from Rowett Research Institute. A table has been given showing the probable average effects of using different planes of feeding in preference to a VH-VH plane for pigs to be slaughtered at about 200 lb. live weight. The variability in these effects under different circumstances has been discussed and a note has been made of the relative improvements in carcass quality which can be affected through feeding and through breeding.

1. The pigs in the three experiments reported were weaned at 10 days old and fed water and drymeal diets ad libitum until they reached 25 lb. live weight. They were housed individually in cages and records were kept of each pig's food consumption and of its live weight every third day.2. Most of the diets fed were based on roller-dried skim milk, rolled oat groats, white fishmeal, sucrose, dried yeast, cod-liver oil, minerals and antibiotic.3. Forty-eight pigs were used in Exp. 1, which was designed as a 4 × 2 factorial. Food-conversion efficiency was significantly improved by 10% when the crude protein in the diet was raised from 24 to 29%. Increasing the protein to 34 or 39% brought no further significant improvement. There were no significant differences between growth rates which were attributable to the four levels of protein.The inclusion of 10% sucrose in the diet did not result in increased food consumption, but there were significant improvements of 8% in growth rate and 10% in food conversion efficiency. There were no treatment interactions.4. Twenty-four pigs were used in Exp. 2, which was designed as a 2 × 2 factorial. Figs fed a diet containing 7% fat grew 4% faster and 6% more efficiently than others fed a diet containing 3·7% fat, but neither difference approached statistical significance. There was no advantage in feeding the meal as a slop, indeed, there was a tendency for the pigs to scour more than on dry feeding. As in Exp. 1 there was no treatment interaction.5. Forty-eight pigs were used in Exp. 3, which was designed as a 2 × 2 × 2 factorial. The basal diet contained about 30% crude protein and 10% sucrose.An increase in the antibiotic level from 18 to 112 mg./lb. diet significantly increased growth rate by 7%, but the 9% increase in efficiency of food conversion was not statistically significant.The addition of a trace mineral supplement significantly improved rate of gain by 7%, but the 6% increase in efficiency of food conversion was not statistically significant.The addition of a complex vitamin mixture had no significant effect upon either rate or efficiency of growth.6. In all three experiments the shape of the growth curve of pigs weaned at 10 days old wag divided into two periods. During the initial ‘check period’, lasting about 10 days, the pigs ate only small amounts of food, grew very slowly, and sometimes scoured. After the ‘check period’ there was a sudden change to the ‘growing period’, during which the pigs ate increasing amounts of meal and grew rapidly.The only treatment which significantly affected the length of the check period was in Exp. 3, when the addition of the vitamin supplement to a diet containing a high antibiotic level shortened the check period by 3 days but then counteracted this advantage by reducing rate of gain during the growing period.7. Between 25 lb. weight and 8 weeks of age twenty-four pigs from the experiments reported were fed ad libitum on a dry-meal diet containing 22% crude protein. The average live weight of these pigs at 8 weeks was 49 lb.