1. A survey of the reasons for disposal of 1000 sows from farms in a selected area of East Anglia showed that the most important causes of sow wastage were ‘failure to breed’, ‘piglet mortality’, ‘old age’ and ‘low fertility’ which together accounted for 64·3% of the sows.

2. The average length of breeding life was 3·75 litters per sow and the modal number of litters was only two. This expectation of life is very short but is in agreement with an earlier estimate based on Breed Society records.

3. Failure to breed was the most important cause of sow wastage and accounted for 21·4% of the sows. The incidence of reproductive failure was greatest in young sows and of all the sows discarded as sterile 30·3% were discarded after having had only one litter. Cases of failure to breed were divisible into two broad groups.

1. Sixty-two commercial sows with a history of sterility were served either less than 7 days or between 12 and 21 days before slaughter and the ovaries examined at autopsy. Thirty-eight sows had apparently normal ovaries and twenty-four abnormal ovaries. Of the sows with normal ovaries, seven out of ten served within 7 days of slaughter were pregnant, but only four out of twenty-two served between 12 and 21 days were pregnant. Two sows were not served because they did not come into oestrus. Of the sows with abnormal ovaries only one out of nineteen which had been served was pregnant. Thus in sows with apparently normal ovaries it is suggested that the main cause of sterility is embryonic mortality, whereas in sows with abnormal ovaries the main cause is lack of fertilization.

2. Sterility associated with cystic ovaries was studied in inbred sows and the oestrous cycle in such sows was found to be irregular, usually with an abnormally long dioestrous interval. There were no cases of nymphomania associated with cystic ovaries.

3. The ovaries of ten sterile sows were examined by successive observational laparotomies. In some cases cysts were present together with apparently normal ovulations and it is suggested that the cysts developed from follicles which failed to rupture. In other cases cyclical growth and regression of cysts occurs without ovulations, whereas in others where the cysts are very large (30-50 cm. in diameter) the cysts may be permanent structures. Sows with large multiple cysts frequently show no signs of oestrus and it seems likely that the breakdown in the ovulation process starts with irregular ovulations and tends to proceed towards the development of these large multiple cysts.

4. Intravenous injections of Prolan (l.h.) had no effect on the ovarian cysts. Implantation of stilboestrol tablets reduced the cystic condition but the treated sows did not come into oestrus although corpora lutea were found in the ovaries at autopsy. Intramuscular injections of stilboestrol also reduced the cystic condition and in one case a sow actually became pregnant.

5. No response was obtained to p.m.s. injections in sows in which the ovaries had reverted to an infantile condition.

6. Cystic ovaries were produced by subcutaneous injections of progesterone and these closely resembled those found in sterile sows. The ovaries of gilts with progesterone-induced cysts tended to revert to normal after the cessation of the injections but the fertility of the gilts was low due to failure of fertilization.

7. Preliminary attempts to graft ovaries met with little success probably due to immunological reaction against and imperfect vascularization of the grafts. Further attempts were postponed pending the results of trials with sheep using a different grafting technique.

8. Evidence as to the effect of fatness in causing sterility in gilts was obtained from the records of the National Pig Breeders' Association. Two overfat experimental gilts which did not come into oestrus were found to have apparently normal ovaries at autopsy and a third came into oestrus and was mated after a period on a submaintenancediet, but though it ovulated normally the ova were unfertilized.

1. An analysis of pre-weaning mortality in inbred Large White pigs showed that the over-all mortality in ten generations of sows was 47·3%. During the first four generations mortality fluctuated between 30 and 45%; from the 5th to the 9th it fluctuated between 50 and 68% and in the 10th rose to 88%.

2. 70·2% of all deaths occurred in the first 3 days post-parturition and the average birth weight of pigs which died within 3 days was only 1003·5 g. compared with 1258·5 g. for those which survived. 83·0% of pigs weighing less than 900 g. at birth died within 3 days, whereas only 18·5% of pigs weighing more than 1400 g. died within the same period.

3. There were marked seasonal variations in mortality, this being highest during the winter months. Mortality was highest in litters of under 5 and over 15, but between 5 and 15 there was no increase in mortality with litter size. There was no difference in mortality between males and females.

4. Foetal growth was studied in 80 outbred sows of various breeds. Foetal weight was affected not only by age but also by litter size. The withinlitter variation in foetal weight increased with litter size but no increase in between-litter variation with litter size could be demonstrated statistically. Male foetuses were slightly heavier than females at all stages of pregnancy investigated.

5. The growth of the inbred Large White foetus was also studied at an early and late stage of inbreeding, and the reduced birth weight in the latter was shown to be reflected in slower growth of the foetus from mid-pregnancy onwards.

6. The anatomical composition of inbred Large White foetuses at a late stage of inbreeding has been compared with that of similar foetuses at an earlier stage and also with normal outbred Essex foetuses, at 51, 74, 97 and 108 days of pregnancy. The chemical composition of inbred Large White foetuses of a later stage of inbreeding was compared with that of outbred Essex foetuses at 51, 74, 97 and 108 days. The differences in anatomical composition between the smallest and largest foetuses within litters are comparable with those found postnatally in pigs fed on a high or low plane of nutrition, but this was not reflected in a very definite way in the chemical composition. X-ray photographs showed that ossification was more advanced in the largest foetus within a litter than in the smallest but the appearance of the ossification centres was not delayed in the latter.

7. Attempts to make reciprocal ovum transfers between inbred Large White and outbred Essex sows met with little success, probably due to the low fertility of the Large Whites, the prolonged exposure of the ovum during transference and the necessity of effecting the transfer of the ova at the 2-cell stage. The latter was conditioned by the rate of passage of the ova through the tube and the fact that they enter the uterus in the 4-cell stage.

During the course of the main investigation the following observations were made on some other aspects of reproduction in the sow.

An examination of the reproductive tract of sows killed at slaughterhouses in East Anglia showed a high percentage of cystic abnormalities in the ovaries (Perry & Pomeroy, 1956). However, the sample of sows necessarily excluded any gilts, so an examination has been made of the incidence of ovarian abnormalities in post-pubertal gilts at two bacon factories. The ovaries of 273 gilts were examined and divided into (a) ovaries containing corpora lutea, (b) ovaries not containing corpora lutea. These were then further classified as normal or abnormal. The chief criteria of abnormality were the presence of cystic follicles, i.e. of greater than ovulatory size (10 mm. in diameter) or cystic corpora lutea, i.e. large flabby corpora lutea with hollow centres. Gilts with numerous haemorrhagic follicles in the ovaries were also classified as abnormal, but it is quite possible that this condition is a common occurrence in gilts just before puberty. However, rather than underestimate the incidence of abnormalities these ovaries were classified as abnormal.

Dilution of fowl semen with phosphate or saline diluents depressed respiration, while dilution with seminal plasma did not affect respiration. Dilution with Tyrode solution resembled dilution with seminal plasma with respect to respiration. The effect of Tyrode solution seemed to be mainly due to its NaHCO3 content.

The effect of Ca, Mg and K ions depended on the anions in the diluents. Phosphate depressed respiration and glycolysis when it replaced saline in the Tyrode diluent.

Dilution did not consistently increase respiration and in most cases depressed respiration.

Fowl sperm preferentially utilized glucose when glucose and fructose were initially present in equal concentration in the diluent. The sperm metabolize glucose at a faster rate than fructose. No evidence was found for the formation of glucose from fructose under our experimental conditions.

Initial respiration and glycolysis of fowl semen was depressed by the addition of glycine to the Tyrode diluent. However, the glycine addition resulted in a less sharp decrease in the hourly respiration rate.

Three experiments were carried out to obtain more information upon the effects of varying the plane of feeding for bacon pigs.

Exps. 1 and 2 followed the same 3 × 2 factorial design in which (a) diets were fed with or without procaine penicillin and (b) a comparison was made between very high (VH-VH), high (H-H) and low (L-L) planes of feeding for pigs from about 8 weeks old to slaughter at about 200 lb. live weight. The planes of feeding were defined according to the amount of t.d.n. offered to each pig daily.

For each of these two experiments eight lots of six litter mates were used. One pig from each litter was allocated to each of the six treatments, and although litter mates were housed as a group, all pigs were fed individually in separate compartments.

Exp. 3 was a 2 × 3 × 2 factorial to compare two breeds and three planes of feeding during 2 years. During each year three lots of pure-bred Landrace and three lots of Wessex Saddleback × Large White litter mates were used. Each lot consisted of three gilts and three barrows and one pig of each sex was allocated to each of the three feeding treatments. From the start of the experiment, when the pigs were about 8 weeks old, to about 100 lb. weight, all animals were kept to a very high (VH) plane of feeding. From then to slaughter at about 200 lb. live weight the following planes of feeding were compared: (1) very high plane (VH), (2) increasingly restricted plane (R) and (3) low plane (L). As in Exps. 1 and 2 these planes were denned in terms of t.d.n., and litter mates were housed together but fed individually in separate compartments.

In both Exps. 1 and 2 pigs with procaine penicillin in their feed grew very slightly faster and more efficiently than those not fed antibiotic, but the differences did not reach the 5% level of statistical significance. The feeding of antibiotio did not affect the response of the pigs to variations in the plane of feeding.

In comparison with pigs kept to the VH-VH plane of feeding, pigs kept to the H-H and L-L planes grew 13 and 22% more slowly in Exp. 1, and 11 and 26% more slowly in Exp. 2, but plane of feeding had no effect upon food conversion efficiency in either experiment. These results are for the total experimental period.

In both Exps. 1 and 2 reductions in plane of feeding had no significant effect upon length of carcass or thickness of streak, but they caused increases in killing-out percentage and decreases in all measurements of fat thickness. They also caused increases in the area of ‘eye’ muscle (statistically significant in Exp. 2, but not in Exp. 1) and a lengthening in the shape of the ‘eye’ muscle in the bacon rasher (statistically significant in Exp. 1, but not in Exp. 2).

In Exp. 3 the Wessex crosses grew faster and more efficiently than the Landrace, but these differences were considerably larger during one year than during the other. In comparison to the Landrace, the Wessex-cross carcasses had a tendency to be shorter (P < 0·10) and to have thicker shoulder fats. They also had 1% more ‘fore’ and 1% less ‘ham’.

Compared with pigs kept to the VH-VH plane of feeding, those kept to the VH-R and VH-L planes grew 18 and 36% more slowly, respectively, during the finishing period. Over the total experimental period there was no difference in food conversion efficiency between pigs kept to the VH-VH and VH-R planes, but efficiency was poorer by 4–5% with the VH-L plane. There was no breed × feeding interaction in the data for growth rates or food conversion efficiencies.

In Exp. 3 plane of feeding had no significant effect upon killing-out percentage, shape index of ‘eye’ muscle or thickness of streak. The two lower planes of feeding caused reductions in the average rump fat, fat (1) over the ‘eye’ muscle and in the proportion of ‘middle’ in the carcasses; they also caused increases in the proportion of ‘ham’ in the carcasses.

Other carcass quality data contained significant interactions which complicated their interpretation. The effects of plane of feeding were inconsistent between:

(A) years, for length of carcass, maximum shoulder fat, area of eye muscle and iodine values of the back fat;

(B) breeds, for minimum back fat and percentage ‘fore’;

(C) sexes, for dressing percentage and fat (2) over ‘eye’ muscle;

(D) breeds and years, for dressing percentage;

(E) breeds and sexes, for maximum shoulder fat.

The results of the three experiments have been compared with other data on planes of feeding from Rowett Research Institute. A table has been given showing the probable average effects of using different planes of feeding in preference to a VH-VH plane for pigs to be slaughtered at about 200 lb. live weight. The variability in these effects under different circumstances has been discussed and a note has been made of the relative improvements in carcass quality which can be affected through feeding and through breeding.

1. A comparison has been made of the progenytest figures for father and son in the Friesian breed.

2. There was a significant regression of contemporary comparison of son on contemporary comparison of father (0·22) and on r.b.v. of father (16·4 lb. per unit of r.b.v.), though both figures were about one-quarter lower than expected. The observed figures were consistent with a heritability of heifer yield of 0·19. The regression of contemporary comparison of son on the average production of the herds in which his half-sibs were milked was small and not significantly different from zero.

3. For fat content, the regression of son's daughter average on father's daughter average was 0·32, in agreement with expectation.

4. A less-detailed analysis for the Ayrshire breed on the above points gave essentially similar results.

5. The possible extent of selection on the basis of progeny-test results was looked into. For yield, the selection was small, leading to a probable improvement of 1–2 gal. a year. For fat content, the probable increase was 0·01% a year.

6. A method is described for evaluating the progeny test of a son in relation to his father's own progeny-test results, which can serve as a method of combining the progeny-test figures from different bulls.

1. Comparisons were made between the two sexes and the various treatments of kids at the 16 lb. stage and the 30 lb. stage. Kids were killed in such a manner that their fatless empty body weights were as uniform as possible at each dissection stage. This was achieved by slaughtering fat H-plane kids at somewhat heavier live weights than the less fatty L-plane kids. The experiment was successful in achieving uniformity of fatless empty dead weights at 16 lb., but not so successful at 30 lb. where significant differences existed between certain subclasses in the male series, the HH and LH having heavier fatless empty body weights than L.L and HL.

2. The dry-matter percentages were in all cases highest for kids on H or eventual H planes of nutrition. On the basis of the total fatty bodies the differences were highly significant at both dissection stages, chiefly due to the larger amounts of fat, with very high dry-matter percentages, in the H-plane kids. On the basis of fatless bodies the differences were only significant at the 30 lb. stage. There were no differences in dry-matter percentages between the two sexes. The order of treatments with increasing dry-matter percentage was LL, HL, LH and HH.

3. The proportions of the joints of the body were very uniform between sexes and the treatments. Male heads were larger than female heads, the difference being just significant at the 16 lb. stage only. Conversely, female hindlegs were significantly larger than male hindlegs at both stages studied. The effect of treatment on body proportions was that H kids had larger hindlegs than L kids, and significantly smaller heads. The female kids thus differed from male kids in body form in a similar fashion to the way H kids differed in body proportions from L kids.

4. The effect of treatment on the carcass composition was greatest for the fatty tissues, H-plane kids in all cases having significantly larger amounts of fat. The treatment effect on all other tissues, that is on the fatless body, was very slight. H kids had slightly more muscle than L kids, but this difference was only statistically significant at the 16 lb. stage. This slightly larger amount of muscle in H-plane kids was offset by smaller amounts of bone, the differences in this case not being statistically significant at either dissection stage, and by smaller weights of alimentary canal, the difference again being significant only at the 16 lb. stage.

The overall picture was one of great similarity in body composition between all the treatments employed in the experiment. The small differences which existed were only statistically significant at the 16 lb. stage when the heterogonic changes in body composition were most apparent. This picture of the effect of plane of nutrition on the body composition is very dissimilar to that claimed by other workers analysing their results on the basis of equal total weight of animal. The results confirm the provisional findings of the present writer using the chicken as the experimental material, and using a different design of experiment.

5. The sex differences in body composition were larger and of greater statistical significance than the treatment differences discussed above. The females contained greater amounts of fat than males, the difference being greatest at the 30 lb. stage. In regard to the composition of the fatless body, the females differed from males in similar manner to the way H-plane kids differed from L kids. Females contained 2% more muscle and 1·5% less bone than males at 30 lb. Males possessed a greater proportion of skin, and a smaller proportion of visceral organs. The males had a much greater percentage of urinogenital organs, due to the basic differences in these structures between the sexes.

6. The division of the body into total saleable percentage and non-saleable percentage showed that the only statistical differences existed between H and L treatments at 16 lb., when H kids had higher total saleable percentages than L kids at this stage, the difference being as great as 8%. Females tended to have a higher total edible carcass percentage than males, due to the larger amount of meat and edible offals in the female sex, but this difference was never statistically significant. The treatment difference demonstrated at 16 lb. is of no agronomic importance, since kids would not normally be slaughtered at this immature stage. By the time maturity was reached, the carcasses of the four treatments were remarkably uniform with regard to their economic composition.

7. Sex and treatment differences were demonstrated by certain of the bone measurements. Male kids possessed thicker leg bones than females, and H kids had larger leg-bone diameters than L. At the 30 lb. stage the order of increasing minimum bone diameters was LL, HL, LH and HH. An identical picture was revealed by the series of data for bone volumes, but statistical differences could not be demonstrated for bone lengths or weights.

8. Significant treatment differences were found in the weights of the rumen, reticulum, omasum, abomasum and in the lengths, but not the weights, of the small intestine. H-plane kids had larger abomasums than L, and L-plane kids had very much larger rumens, reticulums, omasums and bigger large intestines at the 16 lb. stage. These differences were related to the functional requirements of kids on different diets at the 16 lb. stage.

9. Treatment differences were shown to exist in the weights of the heart, pancreas, kidneys and spleen at the 16 lb. stage, and in the liver weights at the 30 lb. stage. In all cases the H-plane kids contained larger visceral organs than L. Sex differences were significant for the heart, spleen and the pancreas. Females had larger hearts and smaller pancreas at 16 lb. than males, and females had bigger spleens at 30 lb. than males. It is suggested that these apparent sex differences may be due to greater amounts of fat contained in the structures of the female viscera.

10. The only head structures to reveal sex and treatment differences were the eyes and tongue, which, like the total weight of the head itself, were larger in the L plane and the male sex.

11. Male kids had significantly heavier skins than female kids at the 30 lb. stage. There were no treatment differences in the weight of the skin, and skins from all treatments alike were placed in the first grade by an experienced dealer.

12. The thymus and abdominal lymphatic glands were significantly heavier in the female than in the male, and treatment exerted a significant effect in favour of the H-plane kids at the 16 lb. stage.

13. The treatments exerted no effect on the early maturing ovaries or female genitalia, but the male kids which were initially on the L plane of nutrition had significantly heavier testes and penes than those which commenced growth on the H plane. The male gonads were the only organs studied in which the effect of initial plane of nutrition persisted at the 30 lb. dissection stage. In all other cases, the effect of initial plane of nutrition was masked or reversed by the nutritional level followed prior to sexual maturity.

A long-term calcium and phosphorus balance experiment with laying hens is described.

The cumulative balances of calcium and phosphorus over a whole year were seen to be physiologically impossible.

Results from other workers using short term balances could be equally impossible and a similar situation has recently been noted in balance experiments with ruminants.

The techniques employed in the experiment were, therefore, investigated in detail.

Only systematic errors could be responsible and it was found that the most likely source of such errors was (a) the spilling of food on to the floor or into the water bowl, and (b) failure to collect all the droppings.

These errors only become apparent in long-term experiments and are more pronounced when diets containing high levels of calcium and/or phosphorus are fed.

1. Thirty-two single lambs were grazed together on pasture. At weekly intervals, from birth to 112 days of age, two lambs were slaughtered and various organs weighed immediately after death. Also the alimentary tracts of seven adult sheep were obtained immediately after death.

2. The rumen had the fastest growth rate of the four stomachs, followed by the reticulum, omasum, and abomasum, in that order.

3. Immediately after birth the four stomachs altered rapidly in their relative proportions, but by about 66 days of age they had reached approximately adult proportions.

4. The weights of the liver, heart and kidneys, relative to live weight, decreased during the first few weeks of life, and thereafter remained constant.

5. The weight of the spleen, relative to live weight, increased during the first week of life and thereafter remained constant.