Two experiments are described to investigate the effect of different weights of pigs at 56 days of age on live-weight gain, efficiency of feed utilisation and bacon carcass quality.

1. In Experiment I a comparison was made between 32 pairs of weaners, reared on the sow, which weighed 31·0 1b. and 45·4 1b. respectively at 56 days of age. After separation into heavy and light groups the pigs were group fed to bacon weight.

The heavy weaners reached 200 1b. eighteen days earlier than the light weaners but this difference was due completely to the slower rate of growth to 50 1b. live-weight. The heavy weaners required 3·59 1b. of meal per 1b. live-weight gain from 56 days of age to bacon weight compared with 3·50 1b. for the light weaners but there was no difference in efficiency of feed utilisation during the period taken to grow from 50 to 200 1b. There were no significant differences between the carcasses apart from an increased flare weight in the light weaners.

2. In the second experiment both suckled and early-weaned pigs were reared to 30, 40 and 50 1b. at 56 days of age and then fed individually to 200 1b.

The number of days taken to reach 200 1b. was 168·6 for the 50 1b. pigs, 176·6 for the 40 1b. pigs and 182·1 for the 30 1b. pigs; there were no differences due to the methods of rearing. The efficiency of feed utilisation from 56 days to 200 1b. was not affected by method of rearing but as weight increased from 30 to 50 1b. at 56 days, the meal required for a pound of subsequent live-weight gain increased from 3·06 to 3·24 1b.

The number of days to increase from 50 to 200 1b. live-weight was 110·4 for the 50 1b. pigs, 109·3 for the 40 1b. and 106·3 for the 30 1b. pigs, again there being no differences due to the methods of rearing. There were no differences in efficiency of feed utilisation from 50 to 200 1b.

Neither weight at 56 days nor method of rearing markedly affected the quality of the carcass but there was an indication that 56-day weight caused greater differences in the early-weaned treatments than in the suckled treatments.

1. Carcass measurement and dissection data from 250 pigs reared at the stations of the National Pig Progeny Testing Board have been analysed to study the value of the carcass measurements in predicting the percentage lean in the carcass.

2. Differences between sexes in the carcass characteristics were generally larger than those between breeds. Gilts had a higher percentage of lean meat than the hogs, with larger eye muscle dimensions and smaller measurements of backfat thickness.

3. For pigs of the same breed and sex, the best predictions of leanness possible without cutting the carcass were derived from measurements of shoulder and minimum loin backfat (see Figure 1). Mid-backfat measurements improved the accuracy of prediction, but length and depth of carcass did not. The residual standard error in percentage lean at constant shoulder and minimum loin backfat was 2·66% of side weight overall but this was reduced to 2·28% by adjustments for breed and sex.

4. Measurements made after cutting the carcass at the last rib gave more accurate predictions of percentage lean than did the split carcass measurements. The residual standard error in percentage lean at constant B, C and K (see Figure 2) was 1·97 % of side weight overall, reduced to 1·88 % by adjustments for breed and sex.

5. The implications of these relationships in carcass grading and carcass evaluation generally are discussed.

1. Using the data from the dissection of 24 sides of beef from Hereford, Dairy Shorthorn and Friesian steers on four levels of nutrition a critical study has been made of the relation of the weight of tissue in an anatomical joint to the total weight of the same tissue in the whole side.

2. There was a significant eifect of breed and level of nutrition in the case of bone. The heaviest breed (Friesians) had a bigger proportion of bone in those bones which support the animal (i.e. the radius-ulna, humerus, femur and tibia-fibula) than had the lighter breeds (Herefords and Shorthorns). The effect of level of nutrition was not the same for all the bones and was difficult to interpret. There was little or no significant effect of breed or level of nutrition on the distribution of muscular or fatty tissue among the joints.

3. The relation of the weight (in kg.) of a tissue (x) in a joint to that in the whole side (y) was expressed by groups of equations of the form, y = a+bx, there being a separate group for bone, muscular tissue, subcutaneous fatty tissue, intermuscular fatty tissue and total fatty tissue. Tables are provided giving the values for the constants ‘a’ and ‘b’ and standard errors of prediction joint by joint for each tissue.

4. No general significance could be attached to the values for the constant ‘a’ but for each tissue there was a correlation between the value for ‘b’ and the inverse of the average weight of tissue in the corresponding joint. For each tissue there were one or two joints which were significantly aberrant. Aberrance is associated either with exceptionally high or with exceptionally low levels of errors of prediction.

5. The high order of magnitude for the standard errors of prediction for estimating muscular tissue (± 12·2 1b. or more) and for estimating total fatty tissue (± 12·7 1b. for the loin), led to exploring the following rule of thumb method.

6. The weight of muscular tissue in a carcass is approximately one-third of the live-weight of the animal, the weight of bone, tendon etc. is onequarter of the weight of muscular tissue and the remainder of the weight of a carcass is the weight of fatty tissue.

7. Using the weights of the animals on the farm, the weight of the sides after hanging in the slaughter house overnight, and the weights of the tissue after dissection it was shown that the above method of estimation gave values for muscular tissue within ± 10·1 1b., for fatty tissue ± 11·8 1b. and for bone etc. ± 3·1. These values compare favourably with those calculated from the weight of muscular tissue in a joint (±12·2 1b. for the foreshin), and fatty tissue (neglecting thorax ±7·0 1b. and 13th rib ±9·8 1b.) ± 12·7 1b. for the loin. The estimate of bone etc. from the weight of radiusulna (± 1·7 1b.) was somewhat better.

8. The general conclusion is that in studies of meat quality, and of the effect of breed and plane of nutrition on meat quality (including carcass conformation) it will be necessary to dissect the whole side or carcass joint by joint, tissue by tissue and muscle by muscle. There are no adequate short cuts.

This report is an attempt to interpret evidence concerning geneticenvironmental interaction as it relates to the effectiveness of selection.

Methods of estimating genetic-environmental interaction were investigated with the conclusion that the standard analysis of variance is a satisfactory tool provided (1) the interaction component of variance is adjusted for important variation between environments in the scale of genetic effects and (2) the variance component for the average effects of genetic groups is recognised as equivalent to the average covariance of the same genetic group in different environments (i.e. ) to include the real possibility of negative genetic correlation.

It is shown that (1) response to selection for improved average performance over varying environments (ΔGt) is proportional to the genetic correlation between expressions of the same genotype in different environments (rG), that (2) gain in ΔGi, from measuring performance in k environments is proportional to if k times as many animals are tested, but to if total numbers per genotypic class (nk) are held constant, where g2 is heritability of individual variation within environments and rG is the correlation between the phenotypic expressions of the same genotype in different environments.

Evidence is presented that (1) variations among poultry-farm environments in California cause important, but largely unpredictable, shifts in ranking of genetic stocks for egg production, and (2) improved accuracy in measuring genetic differences in average performance across environments probably justifies utilising a sample of 5 to 10 farms representing the range of environments for which the stock is bred.

The influence of maternal and genetic factors on the size of lambs at birth and on their gestation length has been studied from the results of two experiments involving the transfer of fertilised eggs from one breed of sheep to another. In the first experiment, eggs were transferred reciprocally between old ewes of the large Lincoln breed and of the small Welsh Mountain breed. Results are based on 20 transfer lambs and 14 normally born singles. In the second experiment, 35 pure Lincoln and 28 pure Welsh lambs were born as a result of transferring eggs into 18-month-old nulliparous Scottish Blackface sheep.

The breed type of the lamb was found to be the most important factor influencing weight and cannon length at birth, although maternal-foetal interactions were present. As the maternal environment became poorer, genotypic differences remained distinct but decreased in magnitude. The maternal environment provided by 4th parity Lincoln ewes, if judged by lamb's size at birth, was better than that provided by 4th parity Welsh ewes, and this in turn was better than that provided by 1st parity Blackfaces. Lincoln and Welsh lambs in the same maternal environment differed in average birth weight by 5·7, 3·8 and 3·0 1b. respectively in the Lincoln, Welsh and 1st parity Blackface maternal environments. Lincoln and Welsh lambs, each in their own normal maternal environment, differed by 6·5 lb. The maternal influence on cannon length was similar but small. Gestation length of Lincoln lambs in Welsh recipients was almost 4 days shorter than that of Welsh lambs in Lincoln recipients. In the Blackface maternal environment, Lincoln and Welsh lambs differed little in gestation length but males were, on average, carried about a day longer than were females.

At the individual level, weight of (Blackface) recipient ewe had a somewhat greater effect on lamb's size than had weight of (Lincoln or Welsh) donor ewe. The magnitudes of these ‘genetic’ and ‘maternal’ effects were comparable with those found at the level of group means; even so, donor's and recipient's weight together accounted for only a small part of the individual variation in lamb's size about the group means.

It was concluded that a ewe was able to respond to progressively greater demands made by a lamb or lambs of progressively larger (combined) potential size—but in accordance with the law of diminishing returns—and that the upper limit of maternal accommodation must be considerable. By contrast, the upper limit of mean genetic size at birth appears to be not far above the mean size of single lambs born to their natural mothers in good condition. A model has been constructed from which mean birth weight of lambs can be predicted.

A pilot experiment is described to observe the effect of a constant environment (temperature 65° F., relative humidity, 60%, artificial light for 12 hours daily alternating with 12 hours darkness, and constant diet) on the subsequent reproductive performance of fowls maintained under these conditions from hatching to the end of the 3rd annual cycle of egg laying.

The elimination of normal seasonal moulting of the plumage both at the beginning and at the end of the pullet laying year gave an advantage of 57 eggs for experimental birds over a group of sisters maintained under a more normal system of intensive husbandry.

This advantage in eggs laid was much reduced in succeeding years owing to a persistent and continuing decrease in rate of lay of hens in the constant environment.

All eggs were incubated and, although no differences in fertility, dead germs and hatchability were observed over the first full year of production in the birds in contrasting environments, the deleterious effects of a constant environment became increasingly apparent with age.

It is suggested that control of the environment induces a premature senility in the domestic fowl.

Counts were made before and after fixation of the numbers of fertilised and unfertilised ova recovered from 3 mated sows, 7 unmated sows and from 34 sows inseminated at varying times before and after the onset of heat.

The percentages of fertilised ova for sows inseminated the day before heat (day — 1) on the first day of heat (day 0) the second day of heat (day 1) and the third day of heat (day 2) are respectively for unfixed and fixed ova: 7·1 and 9·8, day – 1 ; 55·9 and 68·8, day 0; 63·4 and 98·2, day 1; 20·1 and 15·2, day 2. No fertilised ova were recorded from unmated sows; the percentages for mated sows were 94·3 and 95·5.

It is concluded that failure of fertilisation is likely to be the greatest source of loss of fertility in inseminations made before heat and late in heat.

Most ova from sows inseminated on day — 1 and from sows inseminated in day 2 had no spermatozoa on the zona pellucida. A few ova from sows inseminated on day 2 had very large numbers of spermatozoa present.

It is suggested that failure of the spermatozoa to reach the site of fertilisation rather than their loss of fertilising capacity is likely to be the cause of the low fertility of early inseminations.

1. A comparison of the performance of Scottish Blackface ewe hoggets with and without an exteriorised flow to the duodenum was carried out while the animals were fed on hay with a low nitrogen content and added salt. No evidence was found from the food and water consumed, from the weight changes or from a comparison of the organic matter, nitrogen and ash contents of the food and the faeces that the operation caused any permanent disturbance to digestion.

2. Regular measurements of the flow of abomasal contents to the duodenum established a pattern of flow that was influenced by feeding. A relationship between the quantities passed per hour from the abomasum and the time devoted to rumination was found, but the relationship appeared to be dissociated in time so that increased rumination preceded the increased passage of contents.

3. The mean quantity of abomasal contents passed from four animals was 398 ml./hour. According to the quantities of chromium sesquioxide administered by mouth, passed from the abomasum, and excreted in the faeces this value represents not more than 90% and not less than 86% of the flow that can normally be expected.

4. The quantities of organic matter that disappear in the stomach were calculated and represent about half or more of the total disappearance in the alimentary tract.

5. Substantially more nitrogen left the abomasum than was eaten in the food daily. Of the nitrogen passing to the duodenum the greater part disappeared in the intestines.

6. About twice as much ash left the stomach as was present in the food and about two-thirds of the ash entering the duodenum disappeared in the intestines.

Reciprocal matings between large, improved Swedish Landrace and small, primitive South African Native pigs produced strong evidence of a maternal effect at birth. However, compared with purebred Landrace piglets, the crossbred offspring out of large dams weighed less; conversely, compared with purebred Native piglets, the crossbred offspring out of small dams were heavier at birth. Differences between the various mean weights were all statistically significant.

At weaning (eight weeks of age), the weights of crossbred pigs out of large Landrace sows equalled those of purebred Landrace pigs. Crossbred pigs out of Native-pig sows occupied an intermediate position between the above-mentioned and purebred Native pigs. The differences between the latter group means remained significant statistically.

Wool growth on tattoo patches and mitotic activity in follicle bulbs were studied in a sheep on low and high levels of nutrient intake. The rate of wool growth on the high intake was 156% greater than that on the low intake while the rate of cell production from the follicle bulbs was 56% greater. The remainder of the increase in rate of fibre output was attributed to an increase of about 64 % in the volume of the individual cells of the fibres.

Estimates of heritabilities and genetic correlations among 35 measurements and scores of British Large White bacon pigs are reported. The data came from pigs tested at the five National Progeny Testing Stations during the period autumn 1957 to spring 1959, and comprised full records on 1936 pigs from 200 sires. Independent analyses were carried out for each sex, and adjustments were made to the data for differences among stations, six-monthly periods and weight at slaughter.

Genetic parameters were estimated from sire components of variation and covariation obtained by conventional heirarchical analyses of variance and covariance. Estimates of the heritabilities and their standard errors are given in Table 2, and of genetic and phenotypic correlations in Table 3. These estimates, which agree in general with other estimates in the literature,, indicate that a large part of the variation and covariation is of genetic origin and that carcass traits, growth rate and food conversion efficiency are amenable to change by selection. Moreover, no serious antagonisms were found to exist with regard to improvement by selection.

An attempt has been made to summarise the correlation matrix pattern among 24 of the more important traits by using a principal component analysis. The first two principal components account for a disproportionate fraction of the correlation pattern especially of the genetic correlation matrix. Two principal components are given for each trait; the first may be associated with measurements of fat depth.

1. The stability with which dairy cattle develop in body size up to 2 years of age was studied in 60 pairs of uniformly treated identical twins, i.e. an assessment was made of the influence of season, genotype, mean size of twin pair, age and degree of maturity on the level of within-pair variability.

2. The frequency distributions of size differences shown by one-egg twins were in many cases decidedly leptokurtic.

3. The similarity in size of the identical twins studied was only slightly, if at all, influenced by season. Within-pair variability under free outdoor grazing was certainly not any greater than under semi-controlled conditions indoors.

4. The stability with which cattle grew appeared to depend on their genotype. Identical twins of the Shorthorn breed were somewhat more alike in size than were the twins of other breed-types; crossbreds were, on average, 50 % less stable than purebreds in average size () ; although crossbreds grew with somewhat greater stability ().

5. Whatever their mean size, all pairs of identical twins of the same breed appeared to grow postnatally with more or less equal stability (). Small, slow growing pairs showed a greater disparity in average size ().

6. Stability of development continually changed with age but not violently. Each body measurement appeared to have its own characteristic age trend. It is false to believe that variation automatically increases with increasing age. As they grew older, identical twins tended to become less alike in their later maturing body measurements whereas their early maturing body measurements tended to decline in variability. There was an overall trend with degree of maturity; variability steadily increased to a maximum and subsequently declined.

7. It is suggested that environmentally induced instability of development may remain at a minimum level so long as growth curves are not seriously distorted from their exponential path to maturity.

Results of two-way selection for multiple births are reported, in a flock of Australian Merinos.

Base ewes, selected for having multiple or single births at each of two lambings at 5 and 6 years of age have shown a good repeatability, the T group (multiple-bearers) having averaged 31 more lambs per 100 ewes mated than the O group (single-bearers) for 6 subsequent lambings.

Unselected daughters of the base ewes, now ranging in age from 2 to 6 years, have also shown a difference in lamb drop, those in the T group averaging 21 more per 100 ewes mated. The difference in lamb drop has increased with the age of the daughter ewes, reaching 31 lambs per 100 ewes mated at 6 years of age.

A small group of Merino ewes from a property where selection for multiple births is practised has produced 1·60 lambs per ewe mated at 2 and 3 years of age.

It is suggested that earlier low estimates of heritability for the incidence of multiple births have led to unwarranted pessimism, and that in some circumstances selection for multiple births may be successful.

Animal Production, Vol. 4, Part 1, p. 132

The figures in Table 1 for Head weight, Flare weight and Fillet weight should be divided by. 10.