It is now well known that the skeleton serves as a store of calcium and phosphorus, and that a part of the mineral requirements of lactation is met by bone resorption. In an earlier communication (Warnock & Duckworth, 1944) the literature was surveyed and the role of the spongiosa as a source of minerals for lactation in the rat was studied under conditions of adequate calcium intake.Certain interesting questions about the resorption of bone in lactation and its subsequent repair after lactation remain unanswered. In the first place, the extent to which the response of the skeleton to lactational needs is modified by differences in the level of calcium intake is unknown. Secondly, the extent to which cancellous and compact bone are individually resorbed in lactation and the degree to which these changes can be modified by alterations in calcium intake have not been studied. Thirdly, the extent to which calcium intake affects the capacity of cancellous bone and compact bone to recover after depletion does not seem to have been examined. Fourthly, it is not clear whether resorption of bone is the only process by which minerals are released from skeletal stores to meet the needs of lactation in the calciumdeficient animal. The possibility of demineralization of bone, that is of extraction of the mineral component without resorption of the organic matrix, must also be considered. Finally, it seems that no study has been made of changes in physical dimensions of bone in pregnant and lactating animals receiving diets differing in their calcium content.The present experiment was designed to answer these questions and to afford an opportunity to study the effects of different dietary calcium levels on the reproductive performance of rats and their ability to rear their young. The diets were composed of natural feeding-stuffs, selected for their low calcium content. Most earlier investigators in this field used synthetic diets.
EXPERIMENTALExperimental design. A factorial design experiment was constructed to study the effects of calcium intake upon reproductive performance, skeletal change and organ size and simultaneously the effects associated with the gestation-lactation cycle. One hundred and forty-four female rats were randomized in twenty-four equal groups, of which six were assigned to each of four diets. Thus, in Tables 7-10, 12 and 13, each
Protein concentrates obtained as by-products from the alkali-reduction treatment of herrings have been analysed for some important vitamins and amino-acids, and also tested as supplements t o basic cereal rations for poultry. All the products showed considerable destruction of riboflavin and pantothenic acid in the process, but those prepared by the mild ' treatment have a gross protein value of 7504, of that for conventional fish meals. This niay be explained by the destruction of much of the cystine in the herrings during the reduction process. When a ' mild process ' alkali-reduction meal replaced white-fish meal in growing and laying rations of the ' regulation ' type used in the U.K. there was no dccline in growth or egg-production. The meal had no tainting effect on either the meat or the eggs * produced in these experiments.
1. Birds fed on rations devoid of animal byproducts from hatching until 18 months of age were equal in laying performance and health to those that had received animal supplements.2. The stimulation of early growth by feeding aureomycin did not affect the final weight of pullets, their egg production or the incidence of broodiness.3. The ‘animal protein factor(s)’ was of limited importance for egg production. There was a suggestive indication of an effect of a deficiency of the factor(s) when birds on an all-plant ration had been laying for 6 months without access to their droppings. Limited access to ‘unfermented’ droppings, which provided the only dietary source of the factor(s) during both rearing and laying periods, was sufficient to meet the need of the birds for sustained egg production.
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