FIG. 2. The shaded portion represents growth of male rats for each week while the unshaded portion represents total growth from initiation of the experiment. The following number of animals were employed: butter (13), corn oil (13), cottonseed oil (14), margarine (13), olive oil (13), peanut oil (13), soybean oil (13).

FIGURE 3.-The shaded portion represents growth of female rats for each week while the unshaded portion represents total growth from initiation of experiments. The following number of animals were employed: Butter (15), corn oil (16), cottonseed oil (15), margarine (15), olive oil (13), peanut oil (15), soybean oil (15).

FIGURE 4.-The total gain of male and female rats in series II and III on the diets containing the various fats over a 12-week period. The following number of rats were employed: Male rats (series II and III, respectively-butter (12, 13), corn oil (14, 13), cottonseed oil (14,14), margarine (12, 13), oilve oil (16, 13), peanut oil (13, 13), soybean oil (13, 13); female rats-butter (15, 15), norn oil (14, 16), cottonseed oil (15, 15), margarine (18, 15), olive oil (12, 13), peanut oil (17, 15), soybean oil (17, 15).

FIGURE 5.-The tibia length in centimeters for male and female rats after 3 and 6 weeks on various diets. The averages are for the following number of animals: Male rats (3 and 6 weeks, respectively)--butter (12, 13), corn oil (12, 10), cottonseed oil (13, 12), margarine (14, 12), olive oil (13, 12), peanut oil (13, 12), soybean oil (13.9); female rats-butter (14, 12), corn oil (16, 13), cottonseed oil (15, 13), margarine (15, 13). olive oil (13, 11), peanut oil (15, 13), soybean oil (15, 13).

The efficiency of transformation of the various diets to body tissue during the first 6 weeks is illustrated in table 2. Because of the slowing down of growth after that period, calculations of these ratios beyond that point are not included. Since the ratio of total food consumed to gain in body weight approaches infinity when the increase in weight approaches zero, we have omitted from the averages all experiments where the growth was 10 grams or less. Practically no experiments had to be dropped for this reason except with the females on fifth and sixth weeks. However, a clearer picture is probably obtained in the second average where all tests are included. This was obtained by dividing the total food consumed by all rats for the 6-week period by the total gain in weight of these animals over this interval.

DISCUSSION

No differences were found in the rate of growth when weaning rats were placed for a period of 12 weeks on diets composed of mineralized skimmed milk powder, vitamin supplements, and the different fats under investigation. The gains in weight of the male rats in series III at 3, 6, and 12 weeks were as follows: Three weeks-butter 73.9, corn oil 78.1, cottonseed oil 79.7, margarine 74.3, olive oil, 70.8, peanut oil 77.2, and soybean oil 78.4 grams; 6 weeks-137.3, 150.2, 153.6, 137.5, 134.0, 147.2, and 159.2 for the groups on the different diets, respectively; 12 weeks-225.5, 230.3, 230.6, 205.0, 206.5, 228.0, and 243.1 grams. With the female rats in the same series, the results were: Three weeks-63.8, 62.5, 65.8, 60.8, 62.6, 63.2, and 62.4 grams; 6 weeks-104.1, 105.0, 110.2, 100.5, 101.1, 102.3, and 101.3; 12 weeks-142.4, 137.0, 147.2, 133.7, 134.8, 136.9, and 134.3 grams. In no single case was the average growth of the rats on the butter diet the highest. In tests on male rats, it was sixth at 3 and 6 weeks and fifth at 12 weeks. With the females the butter group was either second or third. However, in only a few cases were the differences statistically significant. Based on a greater value than 3.00 being significant for the ratio of mean difference to standard error of mean difference, the weights between the sixth and tenth weeks of the male rats receiving the soybean oil diet are statistically higher than those of the rats receiving butter, margarine, or olive oil in the diet. On the other hand, the females on soybean oil did slightly poorer than the rats on the butter diet; however, in the tests with females there is no significant statistical difference between any fats at any period of the study.

1 Experiments on all rats in these tests. Total food consumption of each group for 6 weeks divided by total gain in weight for the same rats over entire period.

2 Corrected for water content of diet.

The figures in parentheses represent the number of animals in the average.

The uniformity in growth for the first 6 weeks on diets containing either butterfat or margarine fat is further emphasized in the results on series I. These data are also confirmed by series II. With male rats the gains at 3 weeks were 80.7 (butterfat), 84.7 (corn oil), 85.8 (cottonseed oi!), 75.6 (margarine fat), 79.3 (olive oil), 83.8 (peanut oil), 82.1 (soybean oil); and at 6 weeks 147.6, 156.7, 160.0, 144.4, 152.7, 152.1, and 149.7 grams, respectively. In the tests on female rats