1. Barium sulphate suspensions were given to young sheep by mouth or by injection via an oesophageal catheter. Closure of the oesophageal groove was assessed by observing radiographically whether the suspension passed to the ruminoreticulum or to the abomasum.2. Complete closure of the groove took place in lambs that were trained to drink small meals from a trough after being weaned from their dams, a finding similar to that for lambs weaned on to a teat-bottle.3. When barium was injected into the oesophagus of lambs that were excited by being offered their bottle or trough beyond their reach, the barium passed direct to the abomasum if the normal feeding routine was closely imitated. When the lambs were able to discriminate between this teasing procedure and the normal routine, the barium frequently passed to the ruminoreticulum. If the lambs were not teased the barium passed invariably to the ruminoreticulum.4. It is concluded that the reflex closure of the groove can be conditioned by the feeding procedure adopted at weaning so that it no longer depends on the stimuli associated with sucking and swallowing.

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.

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