Journal of Agricultural Science, 47

M. L. Ryder. The pre-natal development of follicle population in the Romney lamb (Vol. 47, Pt. 1)

M. L. Ryder. Observations of nutritional and seasonal changes in the fleeces of some Masham sheep (Vol. 47, Pt. 2)

Will readers please note that the plates illustrating the above articles have been incorrectly placed. The present Plate 7 facing p. 144 should be Plate 1 facing p. 10 and the present Plate 1 facing p. 10 should be Plate 7 facing p. 144.

Journal of Agricultural Science, 47

M. L. Ryder. The pre-natal development of follicle population in the Romney lamb (Vol. 47, Pt. 1)

M. L. Ryder. Observations of nutritional and seasonal changes in the fleeces of some Masham sheep (Vol. 47, Pt. 2)

Will readers please note that the plates illustrating the above articles have been incorrectly placed. The present Plate 7 facing p. 144 should be Plate 1 facing p. 10 and the present Plate 1 facing p. 10 should be Plate 7 facing p. 144.

Journal of Agricultural Science, 47

M. L. Ryder. The pre-natal development of follicle population in the Romney lamb (Vol. 47, Pt. 1)

M. L. Ryder. Observations of nutritional and seasonal changes in the fleeces of some Masham sheep (Vol. 47, Pt. 2)

Will readers please note that the plates illustrating the above articles have been incorrectly placed. The present Plate 7 facing p. 144 should be Plate 1 facing p. 10 and the present Plate 1 facing p. 10 should be Plate 7 facing p. 144.

Journal of Agricultural Science, 47

M. L. Ryder. The pre-natal development of follicle population in the Romney lamb (Vol. 47, Pt. 1)

M. L. Ryder. Observations of nutritional and seasonal changes in the fleeces of some Masham sheep (Vol. 47, Pt. 2)

Will readers please note that the plates illustrating the above articles have been incorrectly placed. The present Plate 7 facing p. 144 should be Plate 1 facing p. 10 and the present Plate 1 facing p. 10 should be Plate 7 facing p. 144.

1. An experiment was carried out in summer when sheep do not normally shed their wool fibres to see if a poor diet would induce fibre shedding. Observations were then continued for a year to follow seasonal variations in the fleece.

2. The two experimental sheep lost about a quarter of their body weight during the nutrition experiment. Measurement of areas tattooed in the skin showed that there was a reduction of about 5% in these areas.

3. Histologieal observations of skin samples showed that there was very little fibre shedding during the nutrition experiment. This suggests that poor nutrition alone will not cause sheep to shed their fibres. More fibre shedding took place during the winter even though the sheep were well fed, suggesting a seasonal stimulus for shedding.

4. ‘Brushes’ which are normally formed when fibres shed in primary follicles were also seen in secondary follicles.

5. Observations were made during the nutrition experiment of the blood vessels in the skin and glycogen in the outer root sheaths of the follicles. No changes were seen in either the numbers of vessels, or the amount of glycogen present.

6. The weight of wool produced per unit area per day was determined at each sampling time during the whole year. The experimental sheep behaved differently from the controls in their wool production during the nutrition experiment. Thereafter all sheep behaved the same, and seasonal fluctuations in wool production were found.

7. The mean length and mean diameter of the wool produced was determined at each sampling time throughout the year.

The design and analysis of rotation experiments present problems which are not encountered in annual experiments. The problems of design have been discussed by Yates (1949) and Stevens (1951 b). This paper is concerned with problems of statistical analysis. The experiment described is sufficiently general in its design for it to serve usefully as a basis of discussion of methods of analysis, both of the mean yields and of the measures of secular trend. It is shown that rotation experiments, without replicates within series, can be adequately analysed.

1. An analysis has been made of milk records from 13,000 cows bred by artificial insemination in Denmark.

2. The herds were divided into three equal groups on the basis of their average production. The variance of yield within herds increased as the average yield increased, but the coefficient of variation declined slightly. The genetic variance was more than five times as large in the high-yielding herds than in the low, and correspondingly the heritabilities in low, medium and high herds were 0·05, 0·15 and 0·22 respectively. These were estimated from the variation observed between progeny groups of the same 152 bulls at each production level.

3. No evidence was obtained of any sire-herd interaction for yield, either within or between management levels. The true ranking of bulls for breeding value was apparently the same at all levels.

4. The heritability of fat content in the three groups was 0·27, 0·47 and 0·49 respectively, and no evidence of sire-herd interaction was found.

5. The contemporary comparison method of assessing A.I. bulls for yield was found to have the accuracy expected in theory.

6. These results are discussed in relation to those of other workers with which there are some discrepancies. On our results, a policy of choosing bulls on the basis of their daughters' performance in high-yielding herds should be the most satisfactory way of progeny-testing bulls used in artificial insemination.

To obtain records of individual animals' habits when a small herd is observed for long periods of time, several observers are essential. The errors between observers were so much less than those between animals and between periods of observation that for most purposes records made by a succession of different observers will be adequate.

The errors of observations at 1 and 4 min. intervals, using the grazing records of ten animals, were 3·20 and 7·36% of the mean respectively. The latter figure being of sufficient accuracy for practical application, it is concluded that the 4 min. interval is suitable for records of a major habit.

The errors for the minor habits were large relative to the mean time occupied on them, but still reasonable in relation to the purposes for which work of this sort would usually be required.

1. This work presents an analysis of the ecological differences between populations in terms of one important developmental system, the timing of inflorescence development on the shoot apex, and its corollary, the partition of energy between seed production and continued vegetative growth.

The object of the first paper is to establish rapid and accurate greenhouse methods for testing response to low temperature and photoperiod, the most important environmental factors influencing inflorescence development.

2. The timing of inflorescence development was studied by the dissection of the shoot apex in several lines of cereals under various temperatures and photoperiods. The rate of leaf appearance is linear on any shoot and is unaffected by the initiation of spikelet buds on that shoot. The elongation of the shoot apex is exponential, being gradual during vegetative growth but increasing at spikelet initiation. The elongation of internodes begins only at the late spikelet bud stage, and progresses stepwise, one internode beginning to elongate as the preceding one ceases.

The general pattern of inflorescence development is similar in all material, but differences occur between lines in the time at which the spikelets are initiated and in the rate of subsequent elongation. These pilot results make it possible to choose the most suitable measures of reproductive development and the most effective environmental treatments to distinguish between populations. The leaf number before heading on the main shoot is used as a quantitative measure of inflorescence development. It records the physiologic age at which spikelet initiation occurs, and is only slightly affected by temperature fluctuations between 10 and 20° C.

3. In the tests for response to vernalization, the germinating seeds are exposed to low temperatures (0–5° C.) for varying lengths of time, and then planted in long day or continuous light. The temperature immediately after planting is kept at 10–15° C. (50–60° F.) to avoid either further vernalization or devernalization. The photoperiod is optimum, and the rapidity of heading is a measure of response to low temperature.

4. The usual method of testing for response to photoperiod under a range of constant photoperiods has the disadvantage that in short days the plants may head slowly or not at all, thus increasing the demand for time and labour. A more rapid turnover can be obtained by exposing the seedlings to differential photoperiods from germination onwards and transferring at a series of dates to long day or continuous light. The leaf number at transfer and the leaf number before heading are recorded, and from these the inductive effects of the initial photoperiods can be calculated. All seedlings must be fully vernalized, i.e. competent to respond to photoperiod, before the tests begin.

The following applications of the methods are suggested:

(i) The agronomic classification of populations and the prediction of their behaviour under specified local climate and farming practice.

(ii) The rapid selection and progeny testing of parental material in plant breeding work.

(iii) The assessment of the potential genetic variation within populations and the study of the adaptive changes occurring under selection.

1. By separating the sources of variability in an experiment involving haematological observations it has been shown how to estimate the usefulness of repeated observations on each animal.

2. In the illustration provided it is concluded that when monozygous twin calves are used, random variability accounts for so much of the total variability that a great improvement in accuracy can be achieved by taking repeated observations on each animal. When unrelated calves are used, little additional accuracy is obtainable by taking more than about three observations on each.

3. It is shown that, in consequence, the relative efficiency of monozygous twin and unrelated calves is likely to vary, depending upon the number of observations on each animal. Thus, to benefit fully from the increased efficiency offered by monozygous twins, more observations are required on each animal than in the case of unrelated animals.

4. Although the figures refer to haematological measurements on calves, the statistical method evolved is of wider application.

Previous studies on the development of follicle population in relation to the growth of the fleece have, except for the Merino, been mostly post-natal. The pre-natal study of follicle development in some British sheep by Wildman (1932) was mainly qualitative, as also was the work of Carter (1943) in the Merino. The latter study was, however, followed by some numerical work on the same breed (Carter & Hardy, 1947). Figures were given for the follicle density per unit area and the ratio of the number of secondary follicles to the number of primaries at different ages. The present study therefore helps to fill a gap in our knowledge by considering numerically the pre-natal stages of development in the English Romney, a breed which is important in the northern hemisphere and which might be considered to be comparable with the Romney of the southern hemisphere.

1. A comparison has been made between progeny tests in special stations and those available from field records. The variation between sires in milk yield is much greater at the stations even when they are compared with herds at the same production level.

2. In respect of yield the repeatability of station tests in the field is not good. The regression of field results on station test is only about 0·2 in herds at all production levels. For fat percentage, the regression is 0·5.

3. The tests in special stations (averaging seventeen daughters per bull) were compared with those in high herds (average twenty-seven daughters) in their accuracy of prediction of the performance of bulls in the poorer herds. The field test was slightly (but not significantly) better for both milk yield and fat content.

4. In milk yield, there is undoubtedly some extra variation between progeny groups at the stations which is not repeated in the field. Perhaps the tying of the heifers in distinct daughter groups in the byre may be a cause of this. However, even without this, it is doubted whether the test stations can give as much useful information on the numerical aspects of performance as the field records usually available. It is suggested that the splitting of daughter groups within the byre might increase the accuracy of the special station in the assessment of yield.

1. The results are presented of an investigation in which the growth and development of forty single male sheep foetuses was examined. The material, obtained from slaughterhouses, included seventeen specimens of known age, while further details of the remainder were lacking. For these reasons, and the fact that the specimens were preserved in 10% formalin prior to dissection, relative, rather than absolute, trends were discussed. This had been achieved by expressing all values as percentages of those obtained from four single male lambs dissected at birth.

2. In order to age the experimental material with the greatest possible accuracy, data were collected from the literature on foetal weights and crownrump lengths of specimens of known age. Mean values were computed and normographs established for the pre-natal period between 18 days and fullterm. By employing the method of least squares, it was not possible to fit single curves to the data; in the case of both weight and crown-rump length the curves had to be divided into five segments in order to establish the relationships with age. Apart from a rather marked change in the rate of growth and development between the 109th and 110th days of gestation, the apparent ‘breaks’ in the curves were not considered important. It would seem that lack of data at certain stages, together with the heterogeneity of the population studied, were greatly responsible for the differential rates of growth and development recorded.

3. The data were inadequate to examine fully the effect of fixation on foetal weight; however, it would appear that whereas specimens weighing less than 200 g. and over 1200 g. lost weight during the course of preservation, foetuses intermediate between the above values gained weight. Since the causes could not be satisfactorily explained, the need for further investigation was emphasized.

4. Of the foetal measurements recorded, head length and, particularly, head width were shown to be earlier maturing than chest circumference and chest depth, while crown-rump length made even greater proportional increases during pre-natal life. In general, the results supported accepted theory that the retardation of rate of development proceeds in an anterior-posterior direction prior to birth.

5. By dissecting the head from the body and weighing each unit separately, it was shown that the head decreases in relative size throughout foetal life. Head:body ratio, however, was found to be unsuitable as a criterion of pre-natal age, since foetuses of equal age may differ appreciably in this respect. It was shown, for example, that a lamb at birth, though above the average in terms of absolute weight, may possess the conformation of a 120-day-old foetus on the basis of head: body ratio.

6. Dissections of the major constituent parts of the foetal body indicated the skinned head to be the earliest maturing, followed in order by the organs (weighed en masse), dressed carcass, total skin and, finally, the skinned feet and tail, which were latest maturing. The order in which these parts grow before birth appeared explicable primarily upon a basis of functional necessity.

7. The skull was shown to develop to a relatively lesser degree during foetal life than the mandibles, while skull measurements indicated the cranial portion to be earlier maturing than the facial. Linear measurements of the various vertebral regions at different stages of development did not yield entirely satisfactory results, but it was evident that the anterior cervical vertebrae are earlier maturing than those of the posterior extremity (caudal vertebrae).

8. Weights of the major units of both thoracic and pelvic limbs indicated the former to be slightly earlier maturing. In contrast to the direction of retardation of growth during post-natal life, in the foetus the gradient followed a proximo-distal direction; scapula and pelvis, for example, being earlier maturing than metacarpus and metatarsus.

9. Linear development of individual bones was shown to be earlier maturing than growth in weight. However, on the basis of length measurements, the course of development proceeded in a similar direction as the trends established in terms of weight, i.e. proximo-distally. Width of pelvis, on the contrary, was shown to be earlier maturing than width of scapula; this was explained in terms, particularly, of earlier developing cartilage in the former bone.

10. In terms of weight, m. longissimus dorsi appeared to be earlier maturing than m. rectus femoris and m. gastrocnemius lateralis; between the latter two muscles no marked difference in rate of growth could be established. The results indicated that these three muscles develop at much the same rate in respect of length and depth during pre-natal life, but m. longissimus dorsi showed relatively less development in width over the same period of time than the other muscles.

11. Of each of the above-mentioned muscles, the cross-diameter of fifty individual fibres was measured by means of an ocular micrometer. Again, a tendency was observed for fibres of m. longissimus dorsi to be earlier maturing than those of m. rectus femoris or m. gastrocnemius.

12. Development of muscle-fibre diameter during foetal life was examined further on the overall mean for the three muscles studied, i.e. the mean of 150 measurements per foetus. The results showed that whereas muscle-fibre diameter increased but slightly (approximately 19·5%) during the first two-thirds of pre-natal life, the increase thereafter was substantial; on the basis of a linear regression, the increase amounted to 113·2% from about 108 days to full-term. The data thus appears to support the accepted view that muscular growth occurs initially by an increase in the number of fibres, and in late foetal life primarily by hypertrophy.

13. The dispersion of muscle-fibre sizes, in absolute measure, was shown to increase with advancing foetal age, the range at birth being considerable. In accord with the results of other investigators, a small proportion of small fibres was observed between approximate ages of 61 and 68 days which, apparently, were not present at either earlier or later stages.

14. Measurement of fibres from muscles situated in different anatomical regions of the body indicated that the muscles of the head were earlier maturing than those of the trunk, and muscles of the thoracic limb earlier maturing than those of the pelvic limb. In agreement with the results obtained on bone weights and measurements, the retardation appeared to proceed in a proximo-distal direction, particularly in the case of the pelvic limb.

When the leaves of sugar-beet crops were sprayed on six occasions in late September and early October with 100 gal./acre of a 3% solution of ammonium nitrate or equivalent urea, in two experiments about 70% of the nitrogen was recovered in the plants in mid-October, compared with 40% recovered from applications of the same amounts of fertilizer to the soil at the same times. In a third experiment the recovery from similar sprayings with urea solution was less than 40%, but very little nitrogen was absorbed from soil dressings, so that the difference between the recoveries from spray and soil applications was nearly the same as in the other experiments.

Nitrogen per cent of dry matter in all parts of the plant was increased by the sprays. More than half of the nitrogen absorbed from the sprays was in the leaf laminae, and the remainder was equally divided between petioles (including crowns) and roots. Between 20 and 30% of the nitrogen supplied in spray in the first two experiments was converted to protein in the leaf laminae, and half of this was present as soluble protein precipitable by trichloracetic acid, a fraction that is extracted in the largescale preparation of leaf protein.

Spraying slightly increased the dry-matter yield of the tops, but not of the roots. It reduced the sugar content of the roots by about 1% of fresh weight. In one experiment it had no effect on sugar yield; in the others it caused losses of 2 and 5 cwt./acre.

The recovery of nitrogen in the tops from a single low-volume spraying (12½ or 25 gal./acre) with nearly saturated urea solution was about the same as from repeated high-volume sprays supplying the same total amount of nitrogen, but in the roots it was higher from the single than from the repeated sprays.

Forty adult (15 months old) fat-tailed Egyptian rams and ewes of the Rahmani and Ossimi breeds were available at the Animal Breeding Research Farm, Giza, Egypt (30° N.). Body temperature and respiration rates were measured twice weekly throughout the year 1953–4. On days of observations, four readings were taken at 10 a.m., 12 noon, 2 p.m. and 4 p.m. Skin temperature was measured once weekly at noon for nine body regions, using a precision bridge thermometer. The effects of docking and pregnancy were also studied.

1. There were seasonal variations in body temperature and respiration rate. The maximum values were during summer and the minimum during winter. The seasonal rate of change was greater in respiration rate than in body temperature.

2. Body temperature was 39·1 and 39·0° C. for the Ossimi rams and ewes respectively, while it was 38·9° C. for both Rahmani sexes. Respiration rate per minute was 42·0, 39·3, for Ossimi rams and ewes and 38·2 and 35·9 for Rahmani rams and ewes respectively. Body temperature and respiration rate were higher in the Ossimi than in the Rahmani breed, and in the males than in the females. Breed differences may be related to anatomical differences such as body conformation, size of skull and tail, thickness of skin and subcutaneous fat and differences in coat characteristics. Sex differences may be associated with the live weight of the animals as well as differences in the hormonal system.

3. Pregnancy had no effect on body temperature and respiration rate in either breed.

4. Different experimental groups reacted similarly with respect to diurnal variations in body temperature and respiration rate; the lowest values being at 10 a.m. and the highest at 4 p.m. Maximum body temperature and respiration rate preceded maximum environmental temperature by 2–4 hr. The diurnal rate of change in respiration rate was higher than that in body temperature. The diurnal changes in body temperature and respiration rate of animals were mainly due to the changes in the environmental temperature throughout the day.

5. (a) Skin temperature varied from 33·7 to 39·7° C., according to season and body region. Seasonal variations in skin temperature of different body regions showed the same trend.

(b) Highest skin temperatures were recorded for middle and upper fat tail, back thoracic and middle scrotum regions, while the lowest were recorded in lower and upper scrotum, lower tail and neck ventral regions. The breast region had an intermediate skin temperature. The different skin temperatures were due to anatomical differences such as the thickness of subcutaneous fat, density of covering wool or to differences in the amount of blood supply.

6. Docked rams had a lower skin temperature and respiration rate than controls, denoting better heat regulation. This may be due to metabolic differences or anatomical changes in the body such as the thickness of subcutaneous fat.

1. In an experiment conducted with eight pairs of monozygous twin heifer calves aged from 7 to 9 months, it was shown that the mean haemoglobin concentration of those reared on a high plane of nutrition was higher than the corresponding value of those reared on low-plane rations.

2. The relative anaemia of the low-plane animals was microcytic but normochromic in type. Its cause must await further investigation, but these features would not be inconsistent with a deficiency of iron.

3. For this type of haematological study, monozygous twins proved more efficient than unrelated animals, as shown by the smaller variability within than between pairs.

4. Day-to-day variation in the same animal must be considered an important possible source of sampling error.

1. The effect of a short, unchanging day-length of 6 hr. on age at sexual maturity and egg production has been observed.

2. The birds matured at the same age as the controls but at a lower body weight.

3. Egg production over 58 weeks was considerably reduced.

4. An increase in day-length between December and August always increased production.

5. A decrease in day-length between February and August always decreased production; this decrease was greater the later in the year that the change occurred.

6. It is concluded that age at sexual maturity is not affected by the absolute length of the day, and that egg production is affected both by the absolute length and by the change in length.

A study has been made of variations in the shrinkage from the live pig to the carcass and from the carcass to the side of Wiltshire bacon. Most of the variation occurs at the first stage when the losses have a variance of 17·67 lb. compared with only 4·59 lb. and the second stage. Similarly, breed differences were found at the first stage, Wessex and Essex pigs giving 1·1 and 2·7 lb. more carcass respectively than the Large White pigs, but not at the second stage. On the other hand, differences between litter groups were found at both stages.

Correlations made between carcass measurements and yield of carcass and bacon were generally found to be small and positive. Antagonisms were indicated between quantity and quality of bacon, in particular by positive correlations between thickness of back-fat and weight of carcass, and between a desirable proportion of cuts and losses on slaughter. The problem of deciding the relative attention which should be paid to various carcass characteristics is discussed and the need for an index of total carcass merit is pointed out.

Glover & Robinson (1953) have recently criticized the use of a transformation in calculating confidence limits of monthly rainfall, and have suggested that the technique is complicated and even misleading. They contend that the use of unadjusted monthly data leads to no serious discrepancies. If this were in fact so, there is no doubt that much time and effort could be saved. It is therefore desirable to compare the two techniques, and to set out against the recorded data the predictions obtained from them.

1. A review of the literature indicated: (a) A lack of agreement upon whether or not restriction of the plane of feeding from weaning or 100 lb. live weight to bacon weight improves efficiency of food conversion. (b) That a severe restriction of the plane of feeding improves carcass-quality measurements, (c) That a less severe restriction of food intake brings the total growth period within a range more acceptable to the farmer, but only has a small effect in improving carcass quality, (d) That the small benefits to quality from this less severe restriction may be equalled or surpassed by quite small changes in the genetic ‘type’ of pig fed. (e) That there are probably interactions in the response of different ‘types’ of pig to different planes of feeding.

2. Two experiments were undertaken. In Exp. 1 both Large White × Swedish Landrace pigs and Large White × Wessex Saddleback pigs were fed from weaning to bacon weight to one of three planes of feeding. Exp. 2 was very similar in design except for some modifications to planes of feeding and the substitution of Essex Saddleback × Large White pigs in place of the Wessex crosses.

3. In Exp. 1 the planes of feeding, according to our stated definitions in terms of total digestible nutrients consumed daily at different live weights, were: very high during both growing and finishing periods (VH-VH); very high during the growing period but restricted during the finishing period (VH-R); and very low during both growing and finishing periods (VL-VL). In Exp. 2 the planes of feeding were: VH-VH; VH-R, the restriction being slightly more severe than in Exp. 1; and low during both growing and finishing periods (L-L).

4. In Exp. 1 there was no difference in growth rate between breed crosses. Pigs on the VH-R and VL-VL planes were 12 and 88 days older respectively at bacon weight than those fed to the VH-VH plane. In Exp. 2, Landrace crosses grew faster than the Essex crosses on the VH-VH and VH-R planes, but Essex crosses grew faster on the L-L plane. Landrace crosses fed to the VH-R and L-L planes were 11 and 63 days older respectively at bacon weight than others fed to the VH-VH plane. Essex crosses fed to the VH-R and L-L planes were 16 and 53 days older respectively at bacon weight than others fed to the VH-VH plane.

5. In Exp. 1 there was no difference in food-conversion efficiency (f.c.e.) between breed crosses. There was no significant difference in f.c.e. between the VH-VH and VH-R planes, but there was a loss of 14% in F.C.E. on the VL-VL plane. In Exp. 2 the Landrace crosses had better F.C.E.'s than the Essex crosses on the VH-VH and VH-R planes, but Essex crosses were the more efficient on the L-L plane. There was no significant difference in F.C.E. between the VH-VH and VH-R planes for either breed cross, but there were losses in efficiency of 4 and 14% on the L-L plane for the Essex and Landrace crosses respectively.

6. In Exp. 1 the Landrace crosses had less back fat over the shoulder than had the Wessex crosses. Pigs of both crosses fed to the VH-R plane had smaller fat measurements than those fed to the VH-VH plane, but this improvement was only significant for minimum back fat. Landrace crosses also had less fat over the ‘eye’ muscle when fed to the VH-R plane, but this did not apply with the Wessex crosses. The difference in carcass quality attributable to the restricted plane of feeding after 100 lb. live weight was considered to be equalled by the difference between breed crosses. The improvement in carcass-quality measurements between pigs fed to the VH-VH and VL-VL planes surpassed the difference between breed crosses, but the carcasses tended to be soft. However, no data were available on the iodine numbers of the fats.

7. In Exp. 2 the Landrace crosses had less fat over the shoulder and over the eye muscle and smaller minimum back-fat measurements than had the Essex crosses. Pigs of both crosses fed to the VH-R plane had smaller fat measurements than those fed to the VH-VH plane, the difference being significant for shoulder fat and minimum back fat. Again the differences between the effects of these two planes of feeding and between the two breed crosses were considered about equal, and again the difference between breed crosses was surpassed by the difference between the carcass measurements of pigs fed to the VH-VH and L-L planes. In Exp. 2 the effects of planes of feeding upon length of carcass, thickness of streak, percentage fore and percentage middle differed significantly between the two breed crosses.

8. When carcass data from both experiments were compared it was apparent that differences between breeds or strains of bacon-type pigs are likely to be of more importance in the production of high-grade bacon than attempts to alter the conformation by varying the plane of feeding—and thus the growth curve—within the limits acceptable in practice.

9. Although previous evidence indicates that males grow faster than females, there was in Exp. 1 no significant difference in growth rate between the sexes. In Exp. 2 there was again no overall significant sex effect, but during the finishing period females grew faster than males on the VH-VH and VH-R planes, but males grew the faster on the L-L plane. In Exp. 1 there was no significant difference between sexes in F.C.E., but in Exp. 2 males were less efficient than females on the VH-VH and VH-R planes, but were the more efficient on the L-L plane, this interaction again developing principally during the finishing period.

10. In both experiments females had carcasses which were longer, had less fat, larger areas of ‘eye’ muscle and larger hams than males. In both experiments the restricted plane of feeding after 100 lb. live weight reduced the shoulder-fat measurements of females but had no effect on those of males which, being the fatter, had the greatest need of improvement to achieve the highest grade. However, the statistical significance of this interaction was low and it requires confirmation.

11. It is not the intention of the authors that these results should be taken to apply in general to the breed crosses used. The breed crosses were chosen solely as pigs which would differ somewhat in genetic type from each other.

12. The results from these experiments confirmed the indications from the literature which have been noted in paragraph 1 of this summary. The results and some of their implications have been discussed in the text.