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发表于 2008-2-19 16:15:19
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It might be possible to affect placental transfer of nutrients by the administration of cortical hormones but it would not appear to be a very practical method.
Would moustgaard comment on the nutrition of the embryo in the very early stages before the implantation of the fertilized ova. What is the significance of uterine milk(子宫乳) in the pig? Is it in any way related to survival of the embryos at that stage.
We have examined the composition of uterine milk in a number of species but not as yet the pig. Large quantities of a muco- protein complex appear in the uterus under the influence of progesterone(孕激素)which probably is intimately involved in the nutrition of the blastocysts. There is a good deal of variation in blastocyst size before implantation but it is not known whether this is related to survival rate. There is certainly evidence of differential growth of blastocysts in relation to differences in the composition of uterine milk. We have examined this by transplantation of ova in rabbits and recorded the influence of uterine milk compositon on the subsequent growth of these eggs. As yet
the precise composition of the muco-protein complex is not defined.
May I refer now to moustgaard’s seventh figure which shows a very high heat invrement in advanced pregnancy; this taken in conjunction with the evidence presented by salmon-legagneur regarding changes in body composition, suggests that whereas the utilization of energy is comparatively low, that for protein is good. This is explained by the influence of oestrogen in the late pregnancy, or in other words, these changes are consistent with the change in endocrine balance.
It appears unlikely that the pig should be very different from other species, notably the sheep, in which birthweight can be readily manipulated by varying the plane of nutrition of the dam. Has experimental work in this field with the pig been complicated by variations in the body composition or degree of fatness of the sows used in relation to the time at which varying planes of nutrition have been imposed?
It would be inappropriate(不恰当的) to ….
It is quite apparent from what has been said that creep feeding has an important influence on the weaning weight of piglets; furthermore the post weaning check is of considerable significance in practice……….this would obviate the post weaning check(断奶后生长受阻).
There is in fact, little information available regarding the factors which affect creep feed intake by piglets. Dempster’s suggestion might conceivably have considerable merit though I would not like to speculate too far as to the success of its operation in practice. Among other things there is considerable variation between piglets in creep feed consumption. This suggestion should be examined experimentally.
Would it not be logical to wean the piglets so that the complications relating to the interaction of feed from the sow and feed from the creep would be eliminated?
The main factor here is the economic one :creep feed of the necessary composition is very much more costly than a sow ration.
How important is access to a water supply in relation to creep-feed consumption by piglets?
There is very little information but certainly piglets will consume appreciable quantities of water even in the very early stages.
It is quite apparent from the data now available that there is considerable variation in performance between even closely related sows. The small numbers used in
some experiments must surely lead to conclusions of doubtful validity.
At leeds groups of 18 sows per treatment are now being used and this number appears to be inadequate. I feel strongly that data should be obtained over 3 or 4 litters before any valid conclusion can be obtained.
Jesperson and olsen in Denmark, in work conducted before the war, divided their sows into groups in relation to their ‘level of performance’. Nutritional treatments yielded different results dependent upon the inherent potential of the sows in question.
Would Lodge comment in connection with the nutrient requirements of sows which are both gestating and lactating?
Simultaneous gestation and lactation is not common but if the sow were to be successfully mated after say three weeks of lactation, the extra nutrient requirements for early pregnancy are of a very low order?
In my experience when pregnancy does occur in the sow during lactation, then agalactia occurs. Would Lodge comment as to the effect of varying creep feed consumption by piglets on the milk they obtain from the sow?
The behaviour pattern with regard to frequency of sucking remains unchanged irrespective of creep-feed consumption. I would conclude that the milk supply of the sow is more likely to influence creep-feed consumption rather than the reverse.
We have been quite successful in the mating of sows during lactation without the untoward effects mentioned by Boaz.
May I raise a question in relation to Morgan’s experimental work on the significance of dietary energy:protein ratio on pig performance. Would not the protein levels be better defined in terms of amino acids? The 14 percent protein level might have an amino acid status equivalent to that in the 20 percent protein diet. In our own work we are working on energy:lysine ratios.
This is a valid point but I would emphasize that if one considers lysine alone on could very easily overlook a number of other interrelated variables. In our studies we tried to ensure that there were no amino acid deficiencies. In the first instance we were examining the significance of over all protein level without complication by individual amino acid limitations.
The high-energy rations were composed of maize and wheat, low energy status being achieved by using the more fibrous foods. There are a considerable number of variables involved but it is virtually impossible to control everything with equal specificity.
Are the experiments described designed statistically? It is difficult to decide in advance upon the number of animals necessary when one is unaware of the variation which could be expected in relation to the selected dietary treatments, but results are subject to statistical analysis. The experiments are initially designed to answer problems in nutrition.
May I elaborate further the point made by Morgan in reply to Livingston. When we substitute on feed for another, say wheat for oats, are we likely to be overlooking the specific effects which individual ingredients may exert over and above differences in energy level? For example, it has been suggested that wheat exerts a specific effect on fattening in this sense.
I think it is unlikely that individual ingredients have such specific effects. Possibly in some investigations in the past the protein, mineral or vitamin supplements fed in conjunction with cereals have not provided a satisfactory balance. In practical recommendations we ensure that minimum requirements of the diet we are allowing excesses, but this we have to tolerate.
May I elaborate a little on behalf of Rerat and Salmonlegagneur. The levels of feeding quoted refer to the levels of feed intake during the final month of pregnancy, not the entire period. The object of the work was to investigate the effect of two planes of nutrition over this period on subsequent milk production. The sows weighed around 500ib.
Perhaps Lodge would state his views with regard to the question of the desirability of allowing the sow to gain in body-weight during pregnancy, discounting in this sense the weight increase relating to the uterus and products of conception. An analogous situation occurs in the feeding of dairy cows and such an increase is necessary to provide an ‘essential driving force’ for subsequent lactation. Milk-yield potential is determined by the time parturition occurs; foodstuffs, as such, have no direct stimulatory effect on milk secretion. Nutrients are supplied during lactation simply to meet the nutritive demands of lactation.
What level of feeding does Lodge recommend? Should feed input be constant throughout pregnancy or should the plane of nutrition be stepped up over the final month?
I understand that self-feeding of sows is not common practice. We are concerned with the avoidance of overfatness in sows and consequently, in practice we mix a pig-grower ration with ground alfalfa hay or wheat bran in the proportion 2:1. self-feeding with such a ration permits each individual sow to satisfy her appetite but overfatness is obviated.
The difficulty is related to the cost of such high fibre rations. The procedure described by Crampton could not be economic under our conditions.
May I comment with regard to methods of experimentation. We should be as much concerned with interaction of treatments as with the effects of the treatments per se; for example we have examined the effects of dietary protein level on the lean:fat ratio of pig carcasses in relation to climatic environment. The farmer is concerned with what happens to the animal under his unique circumstances.
With reference to Braude’s paper on ‘concepts of nutrition and the formulation of pig diets’, the majority of the paper was an attack on the heavy pig, but since the divergence of opinion between Braude and Messrs. The salient issue is the economic production of lean meat and the savings in the cost of lean through the inherent advantages of the heavy pig such as spread of weaner costs, better killing out percentage, lower labour costs and cheaper finishing rations more than counterbalance the additional cost of fat produced in the later stages.
In presenting his paper Braude made no reference to the compilation of rations for pigs. I interpreted my task as being one requiring some synthesis of the factors which have to be taken into account when attempting to evolve standards for nutrient requirements or a basis for ration compilation. Quite clearly advice given to any individual pig producer must be qualitied in relation to his unique circumstances and with reference to the performance levels that he can reasonably anticipate on the basis of his previous experiences. He has to gamble to some extent on the margins of safety he considers appropriate.
Such observations are very valuable in that they relate to a considerable number of pigs representing a random sample of animals drawn from the pig population as a whole. Would he give his views regarding the factors which govern the variations in response to treatments found in different centres?.
It is impossible to eliminate variations between centres participating in co-ordinated trials. We attempt to assess whether or not the distribution of variance is ‘normal’ but we cannot comprehensively evaluated the factors responsible, though this is the aim.
During the course of this conference the majority of the members have been privileged to listen to a series of expositions, arguments and philosophical reflections on innumerable aspects of the digestive physiology and nutrition of pigs and poultry. The active minority has spoken of its researches and investigations to the edification of all and as this conference draws to a close one may well reflect on what immediate and remote effects these deliberations are likely to have on the pattern of animal production in the various countries and areas represented here. Many of us are responsible for advising farmers or for translating into practical terms on the use and supply of rations for pigs and poultry. We must weigh up what we have learned and heard and consider to what extent present concepts of feeding and formulation of diets should be modified.
I should like to try and sum up a few of the more striking impressions that this conference has left upon me as an adviser. I speak also for my advisory colleagues in expressing our warmest thanks for the great privilege of attending.
First of all we would agree with professor Amoroso’s dictum that agricultural research should be as much concerned with securing new fundamental information for its own sake as with solving practical livestock nutritional problems. The papers of the first evening well illustrated this and subsequent speakers reminded us of the necessity of looking at the nutrition and physiology of pigs and poultry in relation to factors of environment, health, genetics and management. Unfortunately other speakers tended to lose this perspective in their ardent enthusiasm for the particular aspects of nutrition with which they were concerned; in striving to arrive at fundamental truths of nutrition as applicable to pigs and poultry on the farm they often completely ignored the possible modifications of their findings as brought about by farm circumstances.
Those of us responsible for the examination of farm feedingstuffs are only too aware of the wide diversity in composition of even the so-called standard foods such as cereals. It was surprising that some speakers concerned with calculation of the amino acid requirements of different species should be prepared to accept, at least tacitly the present very limited range of data on the amino acid make-up of different foods. Stress was laid and rightly so that there could be an over-all 100 percent variation in the nitrogen content of different samples of barley. Is it unlikely that there is just as great a variation in the individual amino acid make-up of the usual animal and vegetable protein foods? Are the diets we are prepared to recommend necessarily going to be more precise by an acceptance of the validity of the very few published figures of the amino acid contents of certain high protein food sources?
We must always consider the ultimate practicability of our findings. We learn that it may require the addition of 10 percent calcium carbonate as chalk or limestone flour to the diet of the laying hen to ensure that she remains in calcium equilibrium. How many advisers would dare to risk advocating such a dusty type of diet or how many compounders would be prepared to market such a food?
Despite the many considerable advances in our knowledge of the nutrition of farm animals, we still have to rely for practical implementation very largely on the limited range of feedingsstuffs as they have known for a long time. Ultimately we do not feed our animals on so many calories and amino acids, units of vitamins, grams of minerals and so on; we give them their food in the shape of cereals, animal and vegetable protein foods, chalk, salt, ect. One wonders how far there is point in attempting to define too accurately specific requirements for pigs and poultry in the light of all the variable circumstances that surround these biological units. Even when these requirements become more accurately defined, their practical implementations will require somewhat arbitrary margins of safety to cover the ranges of variation inherent in biological systems.
I make theses various points not in a spirit of destructive criticism but to remind our fundamental colleagues that their findings, past, present and future, have still to be interpreted into practical realities. The adviser ultimately has the task of translating fundamental work into practice, whether he suggests to the farmer what needs to be given to his livestock or whether he is responsible for advising the food manufacturer what to do to put a nutritionally adequate diet on to the farm. Moreover he has to stand or fall by the success or otherwise of the advice he tenders. The research worker’s job is done when he has determined as accurately as possible the specific nutrient needs of farm livestock. The adviser and food manufacturer have to carry the work forward into the practical realities of the farm with all its diversities of environment, type f stock.
It would be most appropriate to express thanks on behalf of the food compounding trade, whose representatives comprise roughly one-third of the members of this conference for the invitation to be present. We have all been privileged to listen to a series of extremely well-presented papers on topics which are of great relevance to our own interests. |
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