The interpretation of dental radiographs for the diagnosis of periodontal disease conditions poses several difficulties. These include the inability to adequately reproduce the projection geometry and optical density of the exposures. In order to improve the ability to extract accurate quantitative information from a radiographic survey of periodontal status, a method was developed which provided for consistent reproduction of both geometric and densitometric exposure parameters. This technique employed vertical bitewing projections in holders customized to individual segments of the dentition. A copper stepwedge was designed to provide densitometric standardization, and wire markers were included to permit measurement of angular variation. In a series of 53 paired radiographs, measurement of alveolar crest heights was found to be reproducible within approximately 0.1 mm. This method provided a full mouth radiographic survey using seven films, each complete with internal standards suitable for computer-based image processing.

1. Three groups of mature ewes were fed during pregnancy and lactation on rations differing in their calcium content. The mean daily intakes of calcium were 1·4 g. (group A), 4·5 g. (group B), and 7·4 g. (group C). Blood samples were analysed monthly for calcium and inorganic phosphorus. The ewes were killed at approximately 100 days after parturition and the skeletons isolated. Individual bones, either whole or divided into definite fractions, were analysed.2. The level of calcium intake was without effect on the number of lambs born, birth weight, or growth while milk fed.3. Blood calcium was significantly lower in group A than in groups B and C, but blood inorganic phosphorus was unaltered.4. The resorption of bone substance was greater in group A than in groups B and C.5. The severity of resorption varied between bones, and in regions within certain bones. Resorption was most severe in the vertebrae and pelvis, and only slight in the metacarpal, the metatarsal and the shafts of other long bones. Resorption of intermediate magnitude was found for the remainder of the skeleton.6. Resorption was accompanied by reductions in the percentages of ash in bones, but this effect was proportionately less than the ash weight reduction.7. Radiological observations made on flesh-free bones at the end of the experiment gave a picture of resorption similar to that presented by the data for ash weights and percentages of ash, namely that resorption was much greater in group A than in groups B and C.

1. When Cheviot ewes were fed a daily ration containing about 5 g. of calcium during pregnancy and lactation there was a loss of 6·5% of skeletal mineral by mid-lactation. Two months after the end of lactation this loss was fully replaced.2. When the daily calcium allowance was about 2 g. the loss was 18·2% by mid-lactation and was not replaced by 2 months after the end of lactation. However, if the calcium intake was raised to about 5 g. at mid-lactation the skeleton was fully recovered by 2 months after the end of lactation.3. Resorption was always more marked in certain bones than others, the cervical vertebrae, skull and mandible being more sensitive than the ends of the radius and metacarpal and these ends more sensitive than the shafts. This follows the pattern of resorption reported in Part I of this series.4. In sheep on low calcium intakes the serum calcium levels rose in early lactation and then fell. If extra calcium was given from mid-lactation onwards serum calcium levels rose to normal. If extra calcium was not given the fall in serum calcium levels continued until the end of lactation, when they rose. Serum phosphate levels had a strong tendency to vary inversely with serum calcium levels.5. The differences in the mineral status of the skeletons, provoked by differences in dietary provision of calcium of the order used in this experiment, were readily seen in radiographs of flesh-free bone. Differences of this magnitude could not be accurately identified in radiographs of live animals.

With Plates 1, 2 and 3 and Two Text-figures)In Part II of this series an experiment was described in which the amounts of mineral matter withdrawn from the skeleton during pregnancy and lactation and the proportion recovered during a subsequent dry period were determined (Benzie, Boyne, Dalgarno, Duckworth, Hill & Walker, 1956). Radiological observations of the skeletons were made, and these, together with the results of bone analyses were compared with changes in serum calcium values. The experiment reported here was similar to that reported in Part II except for the basal diet which was designed to provide a low-phosphorus intake instead of the low-calcium intake of Part II. METHODSThe plan of this experiment is set out in Table 1. The basal ration was designed to provide between 1-0 and 1-5 g. of phosphorus daily. This was converted to a ration of moderate phosphorus content by adding 3-0 g. of phosphorus (as disodium hydrogen phosphate) daily. The two contrasting types of ration are referred to below as ' low -phosphorus' and 'moderate-phosphorus' rations, respectively.Sixty Cheviot ewes, of 3£ years of age, were randomized according to live weight and date of tupping into six groups, each of ten ewes. Cast ewes were not used, and care was taken to ensure that all animals had sound mouths at the beginning of the experiment to permit observation of the effect of resorption of mandibular bone on the mobility of the incisors.The basal diet for most of the experimental period was 100 g. daily of chopped oat straw and 800-1400 g. daily of concentrates. The concentrate mixture fed during the first part of the experiment consisted of 79 % dried sugar-beet pulp, 10 % maize gluten meal, 8 % maize meal, 1 % blood meal, 1 % meat meal and 1 % common salt. Two ml. of codliver oil were poured on to the daily concentrate ration of each ewe. Because of the low energy value and rather poor palatability of this mixture, certain modifications in the diet were necessary. During late gestation, ewes that began to refuse food were given a small amount of chopped turnip (1-2 lb. daily) until appetite improved. These quantities were very small when calculated as a daily intake of air-dry material over the whole experiment. In early lactation the concentrate mixture was modified slightly, maize meal being replaced by a larger amount of flaked maize, maize gluten meal being increased and dried sugar-beet pulp being reduced by a corresponding amount. The new mixture was 70 % dried sugar-beet pulp, 12 % maize gluten meal, 15 % flaked maize, 1 % blood meal, 1 % meat meal and 1 % common salt. Also in early lactation fresh potatoes were introduced, 600 g. being fed daily for about 10 weeks. All feedingstuffs were analysed for calcium and phosphorus content.

1. The voluntary feed intakes of pigs fed on diets having calculated digestible energy contents of 2,970, 3,356, 3,630 and 3,910 kcal/kg. dry matter were measured over four periods from 38 to 105 kg. live-weight.2. The pigs achieved similar daily digestible energy intakes regardless of the digestible energy content of the diet.3. When housed in metabolism crates pigs ate less than when housed in holding pens and the difference was greater than would be expected solely from the reduced exercise of the pigs in crates.4. Daily digestible energy intake was 575 kcal/kg. live-weight 0.675 when the pigs were in holding pens. The daily digestible energy intake of pigs in metabolism crates increased less with live-weight.5. The use of metabolism crates to obtain digestibility coefficients and values for nitrogen retention to be applied to animals housed under other conditions is discussed in relation to the differences found in apparent digestibility coefficients, feed intake and growth rates between pigs in crates and in holding pens.