ALBERT

Description: 1. Two series of half-brother-sister lambs of balanced sexes have been reared on widely different (High and Low) planes of nutrition from the end of the third month of foetal life to 41 weeks of age. The effect of this on the growth in live weight and relative development of the body proportions has been studied.2. The feeding of the mothers of the experimental lambs during the last 2 months of pregnancy was such that the High-Plane mothers gained 39·5 lb. live weight during pregnancy as compared with a gain of 1 lb. only in the Low-Plane group. The single lambs from both groups were of equal weight at birth, while on the average each individual twin was 47% heavier in the High-Plane than in the Low-Plane group.3. In post-natal life the High-Plane lambs were fed so as to allow them to grow at their maximum rate and the feeding of the Low-Plane ones was controlled so as to allow them to grow at a slow but uniform rate. Lambs from both groups were killed at birth, at 9 weeks old and at 41 weeks old. At 9 weeks old the Low-Plane lambs killed had an average live weight of 14·3 lb. and the High-Plane ones 61·5 lb.; at 41 weeks old the respective weights were 69·5 and 180 lb.4. The study of the age changes in the High-Plane lambs further proved the theory put forward by Hammond (1932) that in the sheep in post-natal life the different anatomical regions and tissues of the body grow differentially and in a definite order of development. The dressed carcass is later maturing than the organs and offal parts as a whole.5. Of all the organs in the body the brain is the earliest developing, followed closely by the eyes. The thoracic organs as a whole are earlier maturing than the abdominal organs. Of the former, the thyroids, lungs and trachea and the heart are the earliest maturing in that order, while the thymus glands are later maturing. Of the alimentary tract, the oesophagus and the abomasum are the earliest developing parts, while the rumen and reticulum are much later maturing, growing at nearly twice the rate of muscle in the carcass from birth to 41 weeks. Of the other abdominal organs, the kidneys are earliest maturing, growing at approximately similar rate as the lungs and trachea, and slower than the heart in post-natal life. The abdominal fats are the latest maturing of all the organs, and of these kidney fat is the earliest maturing and the caul fat the latest.6. The marked heterogonic growth of the organs appears to be related to their function. Those organs of most vital function to the life of the animal like the brain, eyes, lungs, kidneys, heart, oesophagus, abomasum and small intestines, are relatively well developed at birth, and consequently grow proportionately less in post-natal life than organs like the rumen and reticulum, which have an unimportant function until after the lamb begins to consume fibrous foods, or those whose function is largely that of storage of nutrients, which develop mainly in the later stages of growth.7. The development of the different joints or body regions exhibits a marked gradient of increasing growth rate from the head and feet to the loin region, the feet and head growing least and the loin most in post-natal life, while the legs, neck and shoulders are in an intermediate position, the legs being earlier maturing than the shoulders.8. The major tissues of the body exhibit marked differential growth rates in post-natal life. The order of increasing growth rate with age follows an outward trend from the central nervous system to bone, tendon, muscle, intermuscular fat and subcutaneous fat. Consequently, the early maturing nervous tissue and the skeleton make a greater proportion of their growth earlier in life than does muscle and fat; the latter, particularly subcutaneous fat, does not develop to any great extent until late in the growing period.9. Within any of the major tissues, bone, muscle and fat, well-defined growth gradients are observed. Within the skeleton, in post-natal life, waves of increasing growth intensity pass from centres of early (even foetal) maximum rate of growth near the extremities, towards the central region of the body. As regards the axial skeleton, the skull, or rather the cranium, is the earliest part to develop, and from it waves of increasing growth intensity pass backwards to the lumbar region and downwards to the nose and lower jaw. In each limb, similar growth waves pass with age from the early developing metacarpals and metatarsals (cannon bones) down to the distal bones and up towards the lumbar region of the body, the pelvis and scapula being later developing than the femur and the humerus. The ribs appear to be the latest developing bones of the body, while the sternum situated further down in the body, though late maturing, is, however, earlier maturing than the scapula and the ribs. The bones of the fore-limb appear somewhat later maturing than those of the hind-limb.10. As regards growth in length and thickness of the long bones of the limbs, a similar wave of increasing growth intensity passes from the cannons up the limbs. The upper bones increase relatively more both in length and thickness than the cannons after birth, and growth rate in length is at its maximum at an earlier age than growth rate in thickness.11. In the case of muscle and fat, gradients have been demonstrated in their order of development from the head and neck backwards, and from the lower parts of the limbs (arms and legs) upwards to the loin region.12. Changes in carcass measurements are of the same order as the changes in weight and/or shape of the tissues and parts measured, thus confirming their values as indices of carcass composition as well as conformation.13. Marked differences between the sexes are apparent. The High-Plane males were on the average 15% heavier at birth than the females, which was found to be significant at the 5% level. At 41 weeks the wethers weighed 215·5 lb. and the ewes only 144·75 lb. This great difference appears to be principally caused by a longer span of growth in the wethers and by their higher rate of growth during the latter part of the growing period, rather than being due to their higher birth weight, for the females grow at a faster rate immediately after birth, and at 2 weeks of age have reached a greater average live weight than the males.14. At 9 weeks of age the ewes were in a more advanced stage of development in respect of all characteristics than the wethers. The latter were proportionally less developed in all the late maturing characters such as dressed carcass percentage, had less fat and more bone, and each tissue was proportionately less developed in the late maturing joints in the wethers than in the ewes.15. At 41 weeks the picture was completely reversed in every respect. The wethers at that age had not only reached 50% greater weight than the ewes but all their tissues and body proportions were in a more advanced stage of development, i.e. the later maturing tissues and anatomical regions were proportionately better developed in the wethers than in the ewes. At both ages these differences were reflected in photographs of the carcasses and the limb bones as well as in the carcass measurements.16. The vastly different quantitative planes of nutrition of the High- and the Low-Plane lambs did not affect all the parts and tissues of the body equally, so that the Low-Plane lambs were not miniature images of the High-Plane lambs at the same age. On the contrary, the restricted nutrition of the Low- Plane lambs affected the different anatomical regions, organs and tissues of the body differentially and in an orderly manner. With but few minor exceptions, the different organs, tissues and anatomical regions of the body have been retarded in development by the restricted nutrition, in the direct order of their growth intensity. At any stage, an organ, part or tissue of high natural growth intensity at that stage was proportionately more retarded in development than organs, parts or tissues of lower growth intensity at that age. Over the whole experimental period the later developing parts or tissues were proportionately more affected than the earlier developing ones, which can only be explained in the same way as McMeekan (1940,1941) did in the pig, that the earlier maturing parts or tissues have a priority claim for the limited nutrients available in the blood stream when the growing animal is insufficiently fed to provide all parts or tissues of the body with an adequate nutritive supply for normal (maximum) growth. This holds at any stage of development, but at birth the differential effects of the restricted nutrition were much less pronounced than at 9 and 41 weeks.17. The dressed carcass is more affected by the restricted nutrition in post-natal life than the organs and offal parts with the exception of the abdominal fats.18. Of all the organs, the earliest developing brain and eyes are least affected in the Low-Plane lambs. At 41 weeks the brain is only 5% heavier in the Highthan the Low-Plane lambs, which is statistically insignificant for the available degrees of freedom; as the difference was proportionately greater at birth, poor nutrition in post-natal life appears to have no effect on the brain weight, while it may do so to some extent in foetal life. The ewes have a significantly lighter brain than the wethers (corresponding to their smaller live weight at birth). The eyes, though but slightly affected compared with other organs and body parts, are significantly lighter in the Low-Plane series at 41 weeks.19. The restricted nutrition in foetal life did not have any effect on the weight of the lungs at birth and but little on the weight of the heart, while it greatly depressed the development of the thymus glands and that of the oesophagus, abomasum, spleen and somewhat less that of the liver, pancreas and kidneys. The development of the digestive tract and the abdominal organs was more retarded than that of the thoracic organs at birth in the Low-Plane lambs. In post-natal life the earlier maturing organs are in general less affected by the restricted nutrition than the later developing ones, the only important exception being the alimentary tract, which though growing at a relatively faster rate in post-natal life than the thoracic organs as a group, is less depressed by the low level of nutrition.20. An organ of great growth intensity at any particular age interval is much more affected by the restricted nutrition during that interval than at other ages, i.e. the abomasum before birth, the rumen and the thymus glands from birth to 9 weeks, and the caul and kidney fat from 9 to 41 weeks old.21. At birth the restricted nutrition in foetal life has had but small effect on proportional development of the different body regions. The head, however, is least and the legs most affected. In post-natal life the various joints are affected by the poor nutrition to a very different extent, and at each age interval they are, with minor exceptions, affected in the direct order of their growth intensity. At 41 weeks the head is 1·6 and the feet 1·8 times as compared with the thorax 4 and loin 4·4 times heavier in the High- than the Low-Plane lambs.22. At birth the major tissues of the carcass are differentially affected by the restricted nutrition, the brain being least affected followed by the skeleton, muscle, tendon and fat. In post-natal life these tissues are affected in the order of increasing growth intensity, with age; the brain is least affected, followed by the skeleton, muscle, intermuscular fat, kidney fat and subcutaneous fat.23. Restricted nutrition produces also differential effects on the relative development of the different anatomical units within each of the three major tissues, bone, muscle and fat. As regards the skeleton, individual bones or skeletal parts are retarded in development in direct relation to their growth intensity at each age interval. At birth the earliest maturing bones, i.e. those with high growth rate in foetal life, are relatively less developed than the other bones in the Low-Plane lambs, while at later ages the development of the late maturing bones is proportionately much more affected.24. Not only does the plane of nutrition affect the weight of the individual skeletal units differentially, but it also affects the form of the bones in a comparable way. The late developing growth in thickness is retarded by poor nutrition to a much greater extent than the earlier developing length growth in postnatal life, while in foetal life the length growth of the early maturing cannon is more affected than its late maturing growth in thickness, the latter having very low growth intensity in foetal life as compared with the length growth. The differential effect on the form of the metacarpals over the whole experimental period is so great that those of the Low-Plane lambs at 41 weeks resemble bones of semi-wild or unimproved late maturing breeds, being very thin and round, while the cannon bones of the High-Plane lambs at 9 weeks and much more so at 41 weeks, have the thick flattened shaft characteristic of early maturing improved breeds.25. The effect of the Low Plane of nutrition on the development of muscle, intermuscular fat and subcutaneous fat, as in the skeleton, exhibits a gradient from the early to the late maturing regions of the body in each case, i.e. the latest maturing parts are most and the earliest developing least affected.26. Marbling or intermuscular fat as measured by chemical analysis of a sample of the longissimus dorsi muscle is affected by the Low Plane of nutrition to a greater extent than intermuscular fat, but less than subcutaneous fat. The plane of nutrition also affects the water content of the muscle, it being 3% higher at 9 weeks and 2% higher at 41 weeks in the Lowthan the High-Plane lambs.27. The resultant effects of the plane of nutrition upon the body conformation and composition in terms of its major tissues is clearly reflected by the various carcass measurements taken.28. The wethers appear to be more sensitive to restricted nutrition than the ewes and more so in the late maturing tissues and anatomical regions of the body. The proportionately more advanced development of the High-Plane wethers at 41 weeks as compared with the ewes is more than completely suppressed by the restricted nutrition of the Low-Plane wethers, the latter being in a less advanced stage of development than the ewes of the same treatment group at the same age.29. Though an animal which has been retarded in its development by restricted nutrition retains more of the juvenile form than another of the same age which has been growing to its full inherent capacity, it is, however, not merely anatomically younger, corresponding to the weight difference, because of the differential effects of the restricted nutrition on the different organs, parts and tissues of the body. That even within a tissue some parts are penalized proportionately more than others by restricted nutrition during a period of active growth, has been tested statistically in the skeleton and found to be true.30. Practical applications of some of the results are discussed.

Description: 1. Four groups of half-brother-sister lambs of eight individuals, each of balanced sexes, have been reared on quantitatively different planes of nutrition so as to grow along predetermined growth curves until they reached 30 lb. dressed carcass weight when killed. Treatment differences started at the end of the third month of foetal life. One group was reared on a High Plane of nutrition throughout (High – High), another on a High Plane up to 6 weeks of post-natal life followed by a Low Plane (High-Low), the third on a Low Plane up to 6 weeks after birth, followed by a High Plane (Low-High), and the fourth on a Low Plane throughout (Low-Low). The High-High lambs were killed at 9 weeks old, the High-Low and Low-High at 15 weeks and the Low-Low at 41 weeks old. This allowed for comparison of animals of the same carcass weight but different age and of animals of the same age and carcass weight, but having differently shaped growth curves. The relative effects of the treatments on the development of the body proportions and carcass quality have been studied.2. The proportion of dressed carcass to organs and offals was highest (48·9% of live weight) in the High-High group, lowest (42·9%) in the Low-Low, and intermediate in the High-Low (45·6%) and Low-High (46·3%). Variation in carcass percentage due to sex was not significant, though 4·8% higher in the females than in the wethers of the High-High group.3. The weight of the head is more affected by the age of the animal than by the plane of nutrition or the carcass weight, it being of the same weight in the Low-High and High-Low lambs, but significantly lighter in the High-High and significantly heavier in the Low-Low groups. The skin, with wool, was much heavier in the Low-Low than in the other groups, while the weight of the blood was directly affected by the plane of nutrition prior to slaughter, it being significantly heavier in the High-High and Low-High groups than in the High-Low and Low-Low ones.4. The development of the brain and the eyes was found to be primarily a function of age, these organs being lightest in the High-High and heaviest in the Low-Low group. The brain (as in Part I) appeared to be earlier maturing than the eyes, the differences between the age groups all being significant in the case of the latter, but only the High-High lambs had significantly lighter brain than the other groups.5. Marked differential effects due to the plane of nutrition and/or age on some of the internal organs were observed, though others like the heart appear to be a function of body weight, being equally well developed in all treatment groups.6. Organs like the thymus glands, the liver, the spleen, the kidneys and the small intestines are for their development, like the blood, found to be more dependent on the level of nutrition at the time of slaughter than on age or carcass weight, being heavier in the High-High and the Low-High groups than in either the High-Low or the Low-Low. These differences are in most cases highly significant.7. The development of organs like the oesophagus, the rumen, the reticulum, the omasum and the genital organs, appears to be more influenced by age than the plane of nutrition, while that of the abomasum, the caecum, the large intestines, the rectum and the pancreas is influenced by the plane of nutrition as well as age.8. Apart from the urinogenital organs, the pancreas is the only organ which exhibits a significant difference due to sex, being 14% heavier in the males.9. In general, the organs appear to have priority claim for the available nutrients in the blood stream to allow them to develop to such an extent, which enables them to cope with their function at any age. When the nutritive supply is low, organs, whose function is directly associated with growth, suffer proportionately more than those which are of primary importance for life, like the brain, the eyes and the heart.10. The four treatments produced two distinct types of carcasses. The High-High and the Low-High carcasses were of very similar conformation, short in the leg, blocky and well covered with subcutaneous fat, with the late maturing trunk joints proportionately better developed compared with the HighLow and Low-Low carcasses, which in conformation resembled each other, and were leggy, lank and badly covered with subcutaneous fat. In the latter two groups the early developing legs and neck were proportionately better developed than the later maturing trunk joints.11. Marked differential effects were produced on the carcass composition. Bone in the dressed carcass was significantly lighter in the Low-Low than in the other groups, due to the inhibiting effects of continuous undernutrition on growth in thickness of bone. The difference in bone weight between the other groups was insignificant, though the High-Low had the heaviest bone in the carcass. Muscle was better developed in the High-Low and the Low-Low groups than in the Low-High and High-High groups, while fat, especially the subcutaneous fat, was better developed in the two latter groups.12. A High Plane of nutrition prior to slaughter appears to be essential for good development of the latest maturing tissue, the subcutaneous fat. Under limited food supply the earlier maturing tissues, muscle and bone, especially for growth in length, have priority claim for the available nutrients.13. The ewes had significantly lighter bone, slightly lighter muscle, though insignificantly so, and significantly heavier fat than the wethers.14. As between the tissues, so within the anatomical units of each, marked differential effects were produced. Limited nutritive supply at any age causes greatest inhibiting effects on the tissues or those parts of any one tissue, which have the highest growth intensity at that age. Similarly, good nutrition at any age benefits most the parts of highest growth intensity at that time.15. All tissues show great recuperative capacity if provided with adequate food supply after restricted nutrition, unless at that time they have passed their age of high growth intensity.16. A Low Plane of nutrition from 6 to 15 weeks following high feeding, in the High-Low lambs, had the effect that not only was the subcutaneous fat, the tissue of highest growth intensity at that age, more retarded in development than the other earlier maturing tissues, but all the tissues were relatively more affected in the later maturing regions of the body than in the earlier maturing parts. On the contrary, a High Plane of nutrition from 6 to 15 weeks following severe undernutrition, in the Low-High lambs, resulted in proportionately better development of the subcutaneous fat than the other tissues, and within each tissue a proportionately better development in the late maturing regions of the body, as compared with the earlier developing parts. This is because of the relatively greater effect of the poor nutrition earlier on, on the parts of highest growth intensity during that period, and greater beneficial effects of the good nutrition afterwards on the parts which then had relatively higher growth intensity. Thus the bones of the leg (early maturing) were heavier in the High-Low than in the Low-High, while the ribs (late maturing) were heavier in the Low-High group. Muscle in the Low-High was heavier in the loin but lighter in the limbs and neck than in the High-Low, and the difference in fat in favour of the Low-High was much greater in the trunk joints than in the limbs, while the High-Low had even more fat in the neck.17. Comparison of the development of the different anatomical units of the major tissues in the High-High and Low-Low carcasses showed that within each tissue the latest maturing parts suffered proportionately more from the continuous undernutrition, with the exception of the ribs, which, though the latest maturing part of the skeleton, were of the same weight in the Low-Low as the High-High, though total bone in the carcass was heavier in the latter. This is accounted for by the so late onset of high growth intensity in the ribs that the High-High lambs were killed before the ribs could benefit from the good nutrition as much as earlier maturing parts of the skeleton, while in the Low-Low, the ribs, having high growth intensity for a long time after the growth rate of earlier developing parts of the skeleton had declined, could compete for nutrients with considerable success with still later maturing tissues, muscle and fat.18. In the skeleton the shape of individual bones was much more affected by the different treatments than their weight. This accounted for the great treatment differences in carcass conformation. The earlier maturing growth in length is much less affected than the later maturing growth in thickness, and the earlier maturing bones like the cannons are less affected than the later maturing femur or the pelvis.19. The percentage of marbling fat in the longissimus dorsi muscle appeared to be more dependent on age of the animal than on the plane of nutrition or the state of fatness of the animal, being lowest in the High-High and highest in the Low-Low carcasses.20. The iodine number of the marbling fat was also found to be more affected by the age of the animal than by the state of fatness or the plane of nutrition, it being highest in the High-High and lowest in the Low-Low carcasses.21. The water content of the muscle was highest 78%) in the High-High lambs, but lowest in the Low-Low ones (74·9%).22. The four treatments caused great and highly significant differential effects on the various carcass measurements. As some of these measurements have been found by previous workers to be even more important indices of meat quality than is the actual composition of the carcass, it may be claimed that the different treatments have affected carcass quality even more than carcass composition.23. The treatment differences were proportionately much smaller in the external measurements, which are primarily indices of skeletal development, than in the internal muscle measurements and by far greatest in the fat measurements.24. External measurements which should be small for desirable conformation like the leg length, F, the tibia plus tarsus, T, and the length of the cannon, M, were significantly greater in the Low-Low and the High-Low than in the other groups, being smallest in the High-High.25. The most important muscle measurements, such as the depth of the eye muscle, B, and the shape index, B/A × 100, were best developed in the High-High, followed in a downward order by Low-High, High-Low and Low-Low groups.26. The fat measurements were much better developed in the High-High and the Low-High groups than in the Low-Low and the High-Low ones.27. The females had significantly better developed fat measurement than the wethers, while no significant sex differences were observed in the other measurements.28. Considering the several factors studied which affect carcass quality, the High-High lambs yielded carcasses of the best quality, especially the females, closely followed by the Low-High ones, while the Low-Low carcasses were of much inferior quality and the High-Low still poorer. Those of the latter two groups were more typical of an unimproved late maturing breed than being of the same breed as the High-High and Low-High carcasses.