Least cost rations for specific rates of growth in the growing and finishing periods were given to pigs slaughtered at 200 lb. live-weight. During the growing period pigs grew very close to the planned rates in spite of the fact that some food was rejected. Pigs given rations for a low growth rate in the growing period grew slightly faster than planned in the finishing period. In the finishing period pigs given rations for the high growth rate grew on average very near to this rate. The pigs given the ration for the low growth rate grew slightly faster than planned. Food conversion efficiency was for all pigs very near to, or slightly better than, that planned. The rations had no adverse effect on carcass quality.

1. A statistical analysis has been made of the production records in all lactations, up to the third, of 10,967 British Friesian cows. The work was done in two sections, for those animals by home-bred sires and for those by sires imported from Holland and Canada. Within each section, three parallel sets of calculations were made, based on all animals for lactation 1, on those with at least two completed lactations for lactations 1 and 2, and on those with three completed lactations. The analysis was done in a hierarchical manner, taking variables in the order sire, herd, year, month and age at calving. The production measurements were 305-day yield, fat content and lactation length, the latter having an upper limit of 305 days.

2. It was found that in all three characters the variance between animals identical for all environmental variables was approximately two-thirds of that between animals commencing the same lactation in the same herd in the same year. This difference could not be attributed to any particular variable and appeared to be an effect of exact contemporaneity.

3. Culling produced appreciable selection differentials in yield and lactation length but not in fat content. The regression coefficient, calculated within sire groups, of selection differential for heifer yield within sires on the heifer progeny test was 0·11 for culling at the end of the first lactation and —0·07 for culling at the end of the second. In the analysis of British sires for yield, selection in the first lactation reduced both sire and within sire components by about 20%, so that the heritability was little changed. In the Imported sires, the sire variance was reduced by nearly 40 %, so that the heritability fell from 0·26 to 0·22. Because of the truncated distribution of lactation length, selection reduced the within sire variance for the Imported sires by about 60% and the heritability from 0·13 to 0·09.

4. The heritability of yield was lower in second and third lactations than in first. This seemed to be due to an increase of about 50 % in the within-sire component whereas that between sires remained constant. Fat content showed a similar trend and the heritability was slightly less in later lactations.

5. The repeatability of the characters was in general agreement with the results of other workers. The genetic correlation of first yield with later ones averaged 0·80 (significantly different from unity), but that between second and third yields averaged 0·91. The genetic correlations between fat content in different lactations were all close to unity, as were those between length in different lactations.

6. In agreement with other results, the negative genetic and phenotypic correlations between yield and fat content appeared to approach zero as the animals aged. This was due to an above average increase of fat with age in the daughters of bulls high for yield.

7. As would be expected from the genetic correlations between yield in first and later lactations, the increase of yield with age had a heritability significantly different from zero. First lactation yield was negatively correlated (—0·27) with increase from first to second but positively (0·03) with increase from second to third. The heritability of the average yield and fat content increased little with age.

8. The consequences of these results for the optimum combination of different records in selection decisions are discussed.

In a study of 100 pig carcasses, representing a sample of the pigs used in previously reported work, gross chemical composition of the ham, shoulder, loin, belly and half carcass were determined for one side. Percentage yield (trimmed v. untrimmed) of picnic, butt, ham and loin (PBHL), and certain carcass measurements were recorded on the other side of the carcass. From the covariance analyses, it was concluded that backfat thickness of the carcass alone was of only moderate predictive value for total chemical carcass fat.

Carcass protein could, for most purposes, be predicted with satisfactory precision from the percentages of protein in the loin or in the ham, with residual standard deviations of 0·27 and 0·36% respectively.

Although percentage yield of lean cuts may be considered satisfactory for commercial evaluation of swine carcasses, it was not an accurate index of the true leanness of a carcass expressed as the percentage of chemically determined protein.

Multiple regression equations were computed for predicting the percentage of protein in the carcass and percentage yield of PBHL from conventional carcass measurements. The residual standard deviations for predicting the percentage of protein were 0·49 for the males and 0·42 for the females; for percentage yield of PBHL these were 1·31 and 1·22 respectively. Total backfat thickness was the most important single variable in predictions. Variances among sexes were non-homogeneous for the important traits, with the females in all cases showing the greater variability. The results of regression analysis within sex indicated that, for maximum precision, a separate prediction equation for each sex was required.

1. Two-thousand and sixty serum samples from indigenous cattle in Central Africa were examined for serum transferrin type. The breeds studied were Manguni, Mashona, Tuli, Angoni and Afrikander.

2. The variation in gene frequencies from breed to breed is presented. With the exception of one Angoni herd, the remaining herds fall into distinct breed groups.

3. The Mendelian hypothesis was tested on eight herds including at least one herd of each breed. With two exceptions good agreement with this hypothesis was obtained. The two exceptions were traced to two bulls, a Mashona (TfB/TfD) and a Tuli (TfD/TfF), both of which contributed TfD to their progeny at a rate in excess of Mendelian expectation.

4. The Hardy-Weinberg equilibrium hypothesis was tested for thirteen herds and good agreement was obtained in all cases.

5. In Angoni cattle no evidence was found to reject the hypothesis of independent segregation at the haemoglobin and transferrin loci.

1. Thirty-one gilts were injected subcutaneously with 1,500 i.u. PMS on Day 15 of the cycle, and inseminated on the morning of the 2nd day of oestrus.

2. Twenty of the animals were killed 1 to 4 days after insemination to study fertilisation, and the remaining eleven were killed on the 25th day of pregnancy to study embryonic survival.

3. All animals exhibited normal oestrous behaviour, only two of them failing to return to oestrus by Day 19 of the cycle. Treatment with PMS shortened the follicular phase of the cycle in nearly all instances.

4. Eighteen of the twenty animals in which eggs were studied were fertile and within these 84·2% of the eggs examined were undergoing normal development, 2·1% were fragmenting, 4·0% were polyspermic and 7·8% were primary oocytes. Ten unpenetrated secondary oocytes (1·9%) were also recovered.

5. Of the eleven animals in which embryonic survival was studied, only eight were pregnant at autopsy; the remaining three had 35 to 44 corpora albicantia, but no embryonic remains could be detected in the uterus.

6. The average ovulation rate in the eight pregnant animals was 35·4, with a range of 13 to 48. However, the average number of normal embryos was 17·0, with a range of 7 to 28.

7. The percentage survival of normal embryos varied from 26% to 83%. Embryonic survival was better at ovulation rates below that of the mean (35·4); an abnormally large or complete loss of embryos occurred at ovulation rates higher than 36.

8. Despite the range in percentage survival, the number of normal embryos found at the 25th day of pregnancy in five of the gilts was considerably above that found in untreated gilts.

1. An analysis has been made of the relationship between first lactation progeny test for milk yield and the survival of a bull's daughters to different ages using data for British Friesian, Ayrshire and Holstein-Friesian cows. It was found that the relative effect on survival of differences between bulls in milk yield increased by about 10% per 100 gallons for each lactation survived, e.g. for two bulls differing in heifer progeny test by 100 gallons, that with the higher figure will have 10% more daughters surviving to have a second lactation, 20% more having a third and so on. The probable effect on total length of life is 1·2 lactations per 100 gallons.

2. No evidence was found that selection on first lactation progeny test would reduce productive life in the dairy herd or even that it would increase the proportion culled for reasons other than yield in later lactations.

3. The genetic effects of culling in the first lactation on yield were in agreement with those expected from multiplying the phenotypic selection differential by the heritability. On the other hand, the selection differential in heifer yield produced by culling in later life considerably under-estimated its genetic effect. The effect of culling was to increase the genetic potential of animals for yield in the first lactation by roughly 10 gallons for each lactation survived, so that the average genetic superiority over their heifer contemporaries of cows in the herd at any time would be 30 gallons.

4. The heritability of survival to different ages was significantly different from zero in all analyses. The theoretical prediction that this would have a maximum at the fourth lactation was borne out in one sample but not in the other.

5. The genetic correlation of first lactation yield with survival was lowest in all samples for survival to have a second lactation. For survival to the third or later lactations it was higher than 0·7 in all analyses. As the genetic correlation between first and later yields in these data averaged about 0·8, this can only mean that milk yield is by far the most important genetic determinant of survival at all ages.

1. An experiment was carried out with 24 individually fed castrated male, Large White pigs, to examine the effects upon growth and body composition of an anabolic steroid included in finishing diets of two protein levels.

2. There was a significant interaction between steroid and dietary protein level on the growth rate and food conversion efficiency. On the low protein diet growth rate and efficiency were improved by steroid treatment while with high protein intake the steroid significantly depressed growth. Analysis of the main effects showed no significant differences between steroid and protein means for food conversion efficiency and no significant difference between protein means for growth. There was a significant difference (P<0·05) for rate of growth in favour of the animals not receiving the steroid.

3. Steroid significantly improved the percentage of lean and the eye muscle area, but decreased the length of pigs. High protein feeding also improved the percentage of lean and the eye muscle area and also increased the length.

4. The results are discussed in relation to the use of steroids in other species, optimum time of application and the problem of ascertaining accurate physiological doses.

1. The relationship between first lactation performance and the ability of individual animals to survive to the second lactation has been examined in Friesian and Ayrshire populations in an attempt to isolate the main determinants of survival, and to rationalise an apparently complicated selection procedure.

2. Low milk yield was the most important single cause of culling in the first lactation, though the two breeds differed considerably in the relative importance of milk yield in the selection programme. Natural wastage, caused by factors beyond the control of the farmer, accounted for the disposal of 5·7% of the population during the first lactation. Selection for butterfat was marginal in both populations, and could only be detected at extreme butterfat percentages, where high butterfat tended to compensate for a poor milk yield, and low butterfat to confirm a decision to cull an average yielding animal. Survival was not significantly affected either by the size of the herd or by the age at calving.

3. The proportion culled, and the intensity and effectiveness of selection for milk yield, were inversely related to the level of herd performance, and were greater in summer calving animals than in winter calvers.

4. The analysis indicated that selection for milk yield in different environments could be adequately described in terms of the Normal Curve. Yield-survival curves were computed and compared for groups of animals in different herd and calving season environments. When milk yield was expressed in terms of the deviation from the herd-year average, it was found that summer calvers, and animals in low yielding herds, had to demonstrate a productive capacity of far greater individual merit, if their chances of survival were to match those of their winter calving herdmates, and those of their contemporaries in higher yielding herds. When milk yield was expressed in absolute terms the survival of individual animals of similar yield was comparable in all herd and season environments. It was concluded that all the herds included in the analysis had been subject to the same absolute standards of milk yield in the selection of first calvers.

The voluntary intake and apparent digestibility of three roughages, alone and in mixtures, by six steers and six sheep were studied in 56 individual experiments. The fasting metabolism of each animal was also determined so that maintenance energy needs could be assessed.

No significant differences between the voluntary intakes of roughages by cattle and sheep were found when, for all experiments with each species, voluntary intake (g./kg.W0·73)was regressed on apparent digestibility. Cattle, however, digested the same roughage better than did sheep and consumed more of it. Despite their higher maintenance needs/kg. W0·73, when given the same roughage cattle thus attained the same relative feeding level (energy apparently digested/energy required for maintenance) as did sheep, there being an indication that sheep were more efficient users of low quality roughages than cattle. Sheep with high maintenance requirements tended to eat more than those with low ones, but no such relationship could be established with cattle.

When fixed amounts of higher quality roughage were given to both steers and sheep which were also given a lower quality roughage ad libitum, the total intake of food was in proportion to the voluntary intakes attained when the roughages were given separately.

Freshly-cut forages and lucerne chaff were given to penned sheep fistulated at the oesophagus. The feed given and the samples obtained through the fistula were analysed for in vitro digestibility, nitrogen, ash, phosphorus, sodium, potassium and calcium. Organic matter digestibility was predicted from the in vitro determination.

Three regression equations were calculated relating predicted organic matter digestibility of the feed to the digestibility of the extrusa sample. The most precise of these equations had a residual standard deviation of ±3·4 units.

The relationship between the nitrogen contents of the feed and sample was calculated. The equation did not pass through the origin but the differences in nitrogen content between feed and extrusa were small over the range 4·69 to 1·28% N included in this study. The nitrogen and calcium contents of the feed could be estimated from the sample with errors of ±7·5 and 9% respectively. The sodium, potassium and ash contents of the diet could not be reliably estimated from an oesophageal sample.

Selection procedure has been examined in Friesian and Ayrshire populations of dairy cattle in an attempt to determine the extent to which the relatively simple selection process in the first lactation was modified by the effects of age, by the incomplete repeatability of milk yield, and by the availability of production information from more than one lactation.

As a result of a greater intensity of selection for milk yield in the lower yielding herds, effective selection for yield was maintained at the later cullings despite increased wastage for reasons other than yield in the ageing population.

The high yielding animals that were selected by farmers in early life continued to outlive and to outyield their lower yielding first lactation contemporaries, notwithstanding a small amount of evidence that the heaviest yielding group were severely culled in the second lactation, mostly for reasons beyond the farmers' control. There was also some evidence that a high first lactation yield predisposed the animal to disposal for reasons other than yield in later life.

Survival at any particular culling was primarily determined by the milk yield in the previous lactation. In this respect, the culling after each lactation appeared to be independent of previous selection decisions, and the individual animal had to demonstrate its merit repeatedly to survive—earlier merit did not compensate for a subsequent failure.

Four Scottish Blackface rams were mated with a group of their own daughters and a similar number of non-related ewes. The matings were made in three successive years. All ewes were maintained under normal hill conditions. Female progeny from the matings entered the ewe flock unculled. Records of birth type, birth weight, fleece and live-weights throughout life were obtained.

Inbred lambs had lower mean values for all measured characters than did their non-inbred half-sibs and there was a greater number of apparently barren ewes amongst the flock ewes which were expected to produce inbred lambs. The inbred progeny, also maintained in the normal hill flock, showed a higher incidence of barrenness and lower lamb survival rates at all ages than did their non-inbred contemporaries in the same environment. In the final year of the observations, when the standard of nutrition during late pregnancy was raised, the neo-natal mortality rate in both groups was reduced.

Carcass data from 123 pigs slaughtered at either 120 lb., 200 lb. or 260 lb. live-weight have been analysed to study the relative value of four sample joints in predicting tissue composition in the carcass.

Percentage fat, muscle or bone in all joints was highly correlated (P<0·01) with the corresponding percentage of that tissue in the carcass. The highest correlations and correspondingly lowest residual standard errors were found for the loin, rib and composite loin and ham joints.

Significance tests of the a and b constants in regression equations relating percentage fat, bone and muscle in the joint to that in the carcass showed that only with the rib joint was it legitimate to combine the data from each slaughter weight into ‘overall’ equations.

As pooling the data for the combined loin and ham joint had little effect on the magnitude of the residual standard errors, overall equations relating tissue composition of that joint to the whole are also given. The accuracy of prediction, however, was lower than that obtained with the rib joint.

Application of the pooled regression equations relating carcass and rib joint composition to independent data, obtained by identical techniques, gave promising results.

Samples of the longissimus dorsi muscle were removed by biopsy from 4 pigs at intervals during the period from weaning to 125 lb. live-weight. In parallel studies involving 127 pigs attempts were made to relate mean fibre diameter to indexes of lean meat content of a range of bacon pig carcasses but only poor correlations were obtained. It was concluded that fundamental knowledge of the structure of the longissimus dorsi is not yet sufficiently advanced to allow accurate predictions of this type to be made.

1. A mathematical theory of the culling process in dairy cattle has been developed. This was necessary to give a conceptual framework for the discussion of longevity in the dairy herd as a heritable character, of its genetic relationship with milk yield and of the effects of selection on the genetical analysis of yield itself.

2. Culling is assumed to take place at the end of each lactation by truncation selection of a normally distributed variate (the culling variate) of which yield itself is a component.

3. Expressions are then derived for the effect of the culling on various parameters of yield and for survival as a function of yield.

4. The derivation of expressions relevant to progeny groups is dependent on the relative values of the genetic and phenotypic regressions of the culling variate on yield.

5. Because little is known of the actual causes of culling, it is not permissible to predict the genetic gain in yield by multiplying the selection differential by the heritability. This is only justified if the genetic and phenotypic regressions of the culling variate on yield are equal.

6. A direct estimate of the genetic gain by selection can, however, be obtained from the covariance for any character between the mean relative survival of progeny groups and their mean value for the character.

7. The effect of culling on the genetic analysis of yield in later lactations is discussed, as is the effect of later culling on survival to later ages as a function of early yield. It is suggested that the regression coefficient of relative survival of progeny groups on heifer yield will be approximately linear with age whereas that of individuals will probably increase to a limiting value.

8. The heritability of survival to different ages will probably pass through a maximum at the fourth lactation.

9. Longevity itself, as a function of heifer yield, is the sum of the cumulative survival curves to each individual lactation. The regression of length of life on heifer yield, at the individual or at the progeny test level, can be related to the mean phenotypic and genetic selection applied to animals in the herd at any time.

10. Because culling is to a large extent a voluntary action of the farmer, longevity in the dairy herd, though it is under continual selection and may have a significant heritability, need not necessarily increase.

The investigation was designed to measure the time taken to eat concentrate foods and to determine whether the type and quantity of food, the age of the cow, the length of time between feeds and the eating habits of the cow influence consumption rate.

The data indicate that the main factor affecting eating time is the quantity eaten. Within the range of 2 to 8 Ib., the larger the ration the faster the rate of eating. Further, the data show that up to 20 Ib. of concentrates can be consumed per cow per day in a parlour without any check in the faster rate of eating recorded when the higher levels of concentrates are offered.

The type of concentrate is also important: cubes are eaten faster than meal. There are considerable variations between cows in the time taken to eat.

The results of this investigation did not show any obvious effects on the time of eating of breed of cows, position of manger, nor of the length of interval between bulky and concentrate rations.

Graphs relating the eating times of cows with the times available for eating in parlours are shown, and these can be used for reference on farms in parlour planning.

The mean concentrations of total serum protein, γ-globulin and antibody were almost identical in groups of Finnish Landrace lambs from litters in which one, two or three, respectively, survived till the 3rd day. Lambs from two litters each with four survivors had considerably lower mean concentrations. Merino × Cheviot and Scottish Blackface lambs examined previously had significantly lower serum protein concentrations than the Finnish lambs and higher antibody levels in single than in twin lambs.

The genetic progress in live-weight-for-age (LFA), milk production, and in overall economic value expected as a result of performance and progeny testing of young bulls with respect to milk production and LFA was computed. It was shown that performance testing can contribute considerably to overall progress in economic value, while under certain circumstances progeny testing for LFA can also contribute to genetic progress in overall economic value, but to a lesser degree than performance testing. The relative economic value of LFA and milk production was derived and found to be relatively stable under differing economic conditions.

1. Twelve groups of 3 litter-sister Large White gilts were given during three successive pregnancies a daily meal allowance of either 6 lb. (Group A) 3 lb. (Group B) or 3 lb. for 76 days followed by 6 lb. until parturition (Group C). During 8-week lactation periods all received the same daily allowance of 4 lb. meal plus 0·8 lb. for each piglet suckled.

2. Net weight gains during the three successive pregnancies respectively were: Group A, 114, 97 and 79 lb.; Group B, 11, 10 and 7 lb.; Group C, 47, 44 and 35 lb. The differences between groups were highly significant (P<0·001) and there was a significant parity interaction (P<0·05) in that Group A sows showed a significant decline in net weight gain from parity to parity whereas those of Groups B and C did not. No relationship was found between net weight gain and litter weight at birth.

3. Weight changes during the three successive lactation periods respectively were: Group A, –37, –41 and –36 lb.; Group B, 2, 14 and 4 lb.; Group C, –10, –14 and –5 lb. The differences between groups were significant to various degrees in different lactations. There was no relationship between weight changes during lactation and total litter weight at 3 weeks of age.

4. Overall weight changes from first service to third weaning were: Group A, 160 lb.; Group B, 72 lb.; Group C, 71 lb. The differences between Group A and Groups B and C were highly significant (P<0·001).

5. The implication of the results as an indication of feed requirements for reproduction is discussed.

1. Because dressing percentage increases as body weight increases, an adjustment for body weight is necessary when the dressing percentages of animals of different body weights are being compared. Instead of comparing animals on this basis, it is suggested that the power function y = axb, relating carcass weight and body weight, when computed in the logarithmic form, provides a suitable method for making adjustments of this kind.

2. Using this function, differences in yield of carcass have been shown, between breeds and between seasons, in a study involving Hereford, Aberdeen Angus and Beef Shorthorn cattle.

3. A similar function has been used to describe the relationship between fat content of carcass and carcass weight and body weight, using data from the same breed study.