Three methods were used to make differential counts of living and dead bull spermatozoa in samples of frozen semen in an egg-yolk citrate medium containing glycerol.

With two methods (‘phase’ and ‘nigrosin’ methods) dead spermatozoa were identified by their altered structure. With a third method (nigrosineosin) dead spermatozoa were identified by their staining affinity. With the phase method spermatozoa were immobilised by treatment with approximately M/40 sodium fluoride and were examined by phase-contrast microscopy in unfixed wet preparations. With the other two methods the spermatozoa were examined in smears stained either with nigrosin alone (nigrosin method) or with nigrosin and eosin (nigrosin-eosin method).

Analysis of variance of the results of a factorial experiment involving fluoride-treated and untreated samples from 6 bulls with the three methods showed that differences between semen samples contributed 66% of the variation. A defect of the phase method was that the variance between counts was greater than the theoretically expected value.

All spermatozoa in nigrosin-eosin stained preparations were stained with eosin within a few days of the smears being made, so that living and dead spermatozoa could not be distinguished by their differing affinities for eosin. Repeat counts on nigrosin-stained preparations did not differ significantly from counts made several days previously. Sodium fluoride in the concentration used here (M/40) tended to reduce the percentage of dead spermatozoa.

The larger the mature size of a mammal, the longer tends to be the time it takes to mature. In an attempt to quantify this relationship, Brody's (1945) studies on post-natal growth and Weinbach's (1941) study on pre-natal growth are re-examined. Both these authors described growth by attributing to each species a live-weight scaling parameter, an age scaling parameter, and a parameter for age origin. By examining the interrelations of these six pre- and post-natal growth parameters, a general empirical relationship between mature weight and time taken to mature is obtained. The time a species takes to reach any particular degree of maturity, that is any fraction of its mature weight, tends to be directly proportional to its mature weight raised to the 0·27th power. This result is in general agreement with previous theoretical work and with results on the time required to reach adult weight.

The simplest way to make use of this general relation is considered. When age measured from an origin at or near conception is divided by the 0·27th power of mature weight, then on this modified scale, the age at which a species reaches a given degree of maturity has an expectation independent of mature weight. This age scale has been called metabolic age, since it amalgamates the properties of Brody's physiological age and Kleiber's metabolic turnover time. The most useful working form, however, is the logarithm of metabolic age which is approximately normally distributed with constant variance at all degrees of maturity. Equations are derived giving the expected metabolic age of a species at any degree of maturity in the range covered by Brody's and Weinbach's growth curves. Metabolic age thus appears to furnish a one-parameter representation of comparative mammalian growth.

Regression analyses were made of the inter-relations among weights at day-old, 3 and 8 weeks, teat order, social order and litter size in 41 litters of young pigs.

Birth weight and teat order accounted for 40 % of the variation of 3-week weight within litters. Social rank was strongly influenced by 3-week weight, but not by birth weight or teat order except through their effects on 3-week weight. About 70% of the within-litter variation in 8-week weight was attributable to 3-week weight and social rank. Of the total variation in 8-week weight about 55 % could be explained in terms of the other variables. The effect of litter size on 8-week weight appeared to differ considerably in the Berkshire and Large White pigs used in this study.

On the assumption of a causal sequence in time, the within-litter variation in 8-week weight was partitioned into fractions of 19% due to birth weight, 5 % due to teat order, 29 % due to 3-week weight and 17 % due to social rank.

The paper reports the results of experiments to study the effects of different levels of dietary protein on the performance and carcass quality of bacon pigs fed on a high-energy diet: (a) to make similar rates of live-weight gain on all treatments, (b) to make similar rates of live-weight gain but with the level of protein on some treatments being reduced at 130 lb., (c) to allow ad libitum feed intake on all treatments, (d) to obtain two distinct

patterns of growth (fast-fast and slow-fast) on each of two levels of dietary protein.

In the comparison of the two contrasting patterns of growth there was no significant interaction between rate of gain during the period 40–125 lb. live-weight and level of dietary protein. Differences in carcass density and linear measurements were significant and the results suggest that irrespective of growth pattern there was a carcass response to level of protein.

Where diets of different protein content were given ad libitum or to obtain a uniform growth pattern on all treatments, growth rates were generally good, with little difference in feed intake between the treatments within each experiment; variations in level of protein therefore had little effect on growth rate. In some of the comparisons, significant carcass differences were found in terms of density, dissection data and linear measurements; in others only the density differences were significant.

The results suggest that with each of the feeding systems a level of about 17% crude protein, associated with 12% fish meal, is more likely than lower levels to give lean bacon carcasses. In the one experiment in which the protein level was reduced at 130 lb. live-weight there was no marked effect on carcass composition.

Lambing records of 3,500 Scottish Blackface ewes and 2,000 Welsh Mountain ewes were used for a study of repeatability of ewe fertility and litter size. The repeatability of litter size at birth (calculated as an intra-ewe correlation) was higher in both flocks (0.19 and 0.24 for Blackface and Welsh ewes respectively) than that for barrenness (0.09 and 0.08) or for number of lambs born per mating (0.07 and 0.10). Repeatability of the corresponding traits at weaning were generally about half these values.

About two-thirds of the ewes had sires recorded and were used for a heritability analysis. The heritability of litter size at birth in both flocks was higher (0.14 and 0.16 for Blackface and Welsh respectively) than either the heritability of barrenness (−0.03 and 0.03) or of numbers of lambs born per mating (−0.01 and 0.07).

It was concluded that the greatest improvement in numbers of lambs weaned would be obtained by selection on litter size at birth. There would be correlated changes in live-weight (genetic correlations of 0.44 and 0.78 for Blackface and Welsh respectively) but not in fleece weight (genetic correlations of 0.09 and −0.13).

The extraction of sire proofs from non-orthogonal field data of the type met with in cattle A.I. populations presents special problems.

A weighted least squares procedure for the estimation of sire effects from data of this kind, cross-classified by sire and herd, is described. Expected Breeding Values computed from these estimates have certain optimum properties. The standard errors of the estimates of the Expected Breeding Values are derived. The method makes it possible to classify the sires into groups before the proofs are computed. This sub-division of the stud could be useful in young sire evaluation and in measuring genetic trends in the proven stud. The computations are readily programmed for a computer, and the assumptions involved in the use of the method are particularly well suited to A.I. progeny field data, especially where an annual draft of young sires is being tested. A worked example is given.

The results of two experiments, involving 72 individually fed pigs during a growing period between about 40 and 200 lb. live-weight, indicated that a water allowance of 1½ lb. per 1 lb. meal in place of 2½ lb. water had little effect on the performance of the pigs or on carcass measurements. With unrestricted water there were considerable differences in intakes between experiments but these were without significant effects on the criteria studied, when compared with the respective fixed water to feed ratios.

In the first experiment, but not in the second, a dietary supplement of penicillin was associated with a reduced voluntary intake of water. The penicillin was without overall effect on performance or carcass composition, but was associated with a significant growth response up to 100 lb. live-weight in the first experiment.

In both experiments females were less fat than castrates, as indicated by significantly different carcass densities and by some linear measurements.

All possible inter-age genetic correlations were calculated for each of twelve linear body measurements taken at 3-monthly intervals up to 2 years of age on 120 pairs of uniformly reared, liberally fed one-egg and two-egg twin dairy heifers. Genetic correlations between first and second-year mean size are also given. The influences of age, age interval, degree of maturity and body part on genetic correlation are examined.

Genetic correlation was in general very high. No significant difference was found between body parts in mean genetic correlation over the period studied. For a fixed age interval, genetic correlation increased with age; from a fixed age, it decreased with lengthening age-interval.

The main systematic trends found in the data were accounted for in terms of the amount of development taking place. Genetic correlation appeared to decrease exponentially with difference in degree of maturity, and a formula is given for calculating an approximate value for the expected genetic correlation between size at any two ages. Its range of applicability and its place in a general study of the genetic properties of a population of growth curves are discussed.

Eight trials involving 522 fattening lambs were conducted to compare rations of shelled corn and either long or chopped alfalfa hay with complete pelleted rations containing various proportions of concentrate.

Feeding lambs on complete pelleted rations that contained 50–100% roughage resulted in increased feed consumption and significantly greater gains. However, efficiency of feed conversion was improved by pelleting in only one trial.

Feed consumption and rate of gain were not improved by pelleting ground ear corn. Conversely, lambs fed only pelleted alfalfa hay gained significantly faster than lambs fed only chopped hay.

The use of barley for intensive beef production, as described by Preston, Aitken, Whitelaw, Macdearmid, MacLeod and Philip (1963) is now a well established practice, but one of the hazards of this feeding system is bloat. There is evidence that the risk of this condition is accentuated if the barley husk is broken down too finely as happens if the grain is ground (Preston, Macdearmid and MacLeod, 1963; Preston, 1964). It was therefore recommended that barley should be processed in a roller mill and that the moisture content should be at least 16% (Preston, 1963), for if the grain is drier than this it is difficult to prevent excessive shattering and destruction of the husk. Suitable containers, which can be sealed in order to ensure anaerobic conditions and so overcome the problem of storing damp grain (greater than 16% moisture) have additional advantages at harvest since they can be filled quickly and easily. The purpose of this experiment was to evaluate the nutritive value of barley stored under these conditions.

This note describes the results of various analyses which were carried out to study relations between measurements indicative of the amount of fat and lean in the carcasses of bacon pigs and their weaning weights, rates of gain between weaning and slaughter, and the lengths of the carcasses. The data involved were taken from a series of experiments, the original purpose of which was to compare various feeding treatments used between weaning and slaughter (205 lb.). The interpretation of these analyses presents some difficulty because of the many ways in which variations in weaning weight, for example, may occur; such variations arise naturally (because of variations in genotype, mothering ability of the sow, etc.) or may be induced by changing methods of management (systems of feeding, housing conditions, etc.). Considerable caution should therefore be exercised in attempting to extend the relations discussed here to conditions outside their own context. The difficulties are emphasised by the variety of different results which other workers have reported on the effect of weaning weight on subsequent development (reviewed by Braude, 1964).

1. Pellets of Cr2O3-paper were administered to sheep to reveal the excretion pattern of Cr2O3 in the faeces.

2. Two sheep fed on long hay and pelleted hay for each of two 28-day periods were given a Cr2O3-paper pellet daily at 9 00 hrs. during the 15th to the 24th day inclusive in each period.

3. Total faeces were collected at hourly intervals during the 15th to the 28th day. Dry weight and concentration of Cr2O3 of each fraction was determined.

4. A balance between input and output of Cr2O3 and a minimal standard J deviation of the concentration of Cr2O3 in the faeces between hourly collections was reached in 3 days with long hay and in 2 days when the hay was given as pellets.

5. The decline in the concentration of Cr2O3 in the faeces started the day after the administration of pellets was discontinued.

6. Grinding and pelleting of the hay resulted in a doubling of the standard deviations of the concentration of Cr2O3 in the hourly faeces collections during the period of input-output equilibrium.

7. A pattern of a diurnal cyclic trend was apparent in the concentration of Cr2O3 in the hourly faeces collections, but it varied between animals and between diets.

8. Pellets of Cr2O3-paper are suggested to facilitate the administration of Cr2O3 to ruminants.

9. The effect of sampling frequency and animal replication on estimation accuracy is discussed.

The results of a nitrogen balance experiment with growing pigs have shown that 5 % feather meal was inferior to 7 % white-fish meal, when both supplements supplied the same amount of total crude protein in a barleyweatings- minerals-vitamins ration.

A comparative feeding trial in which white-fish meal was partially replaced by feather meal in the diets given to growing pigs gave inconclusive results.

Although numerous studies on the early weaning system of calf rearing have given information concerning the composition of milk substitutes and concentrate rations which may be used, and the subsequent growth rates which may be expected, few have given information concerning either the relative effects on subsequent growth rate of initial weight, weaning weight, concentrate and hay intakes, or the relationships which exist among these factors themselves.

(1) A survey was conducted to determine the concentrate usage during the winter (1962–63) of each of 125 high-yielding dairy cows. The bulky foods consumed by each cow were also recorded.

(2) On average the cows were given 3.64 lb. concentrates per gallon of milk produced, and their intake of starch equivalent in excess of that needed for maintenance was 2.54 lb. per gallon. The margin per month (milk sales less cost of concentrates) was £14 13s Od.

(3) The implications of the results of the survey are discussed in relation to the feeding of dairy cows.

Four litters each containing six female pigs were used to compare the influence of the level of feeding of suckled pigs on subsequent weight gain and efficiency of feed conversion, and on carcass quality and ham composition.

The high level pigs always remained on their dam until weaning at 56 days of age and had free access to a starter ration from the beginning of the 4th week of age. From 7 days of age until weaning the low plane pigs were removed from their dam for 12 hours per day and had no access to starter ration during this time. After weaning the pigs were fed ad libitum on dry feed.

It was found that live-weight gain and feed conversion efficiency during fattening were increased by lowering the feed intake of pigs in the first weeks of life. There were no statistically significant differences between the different butcher's joints of the two groups. Although the differences were statistically non-significant, the ham of the low level pigs had a higher protein content (P = 0·06), a higher water content (P = 0·10), a lower fat content (P = 0·07) and a lower energy content (P = 0·12).

This experiment was designed to compare the average performance of Charollais-Hereford and Hereford-Charbray calves with the average performance of purebred Hereford and Charbray calves as a measure of hybrid vigour in various traits of economic importance.

The ratio of lumbar length to carcass length was larger in the crossbreds. With this exception there was no significant difference between purebreds and crossbreds in any of the measurements that characterise performance of the live animal or the carcass. However, the trend of the carcass measurements possibly indicated that the purebreds were fatter and higher in carcass grade than the crossbreds.

Studies on three cuts of meat from each carcass indicated larger cooking losses (percentage drip loss) in steaks from purebreds and larger ‘shear’ values for steaks from crossbreds. The panel of judges found no significant differences in tenderness, flavour or juiciness. There were no significant differences in colour of lean meat from crossbred and purebred animals.

Meat from the purebred Herefords appeared fatter and more tender than that from the Charbray cattle, but this comparison may be biased due to sire differences.

One of the causes of culling dairy cows is low milk yield and to the extent that this has any genetic basis one might expect the daughters of old cows to outyield their contemporaries from younger and hence less selected mothers. This is quite apart from any confounding effects resulting from the non-genetic influences of dams' parity. The rate of genetic improvement derived from the culling process will be modified within a population by the extent to which farmers choose to retain the progeny of older rather than younger cows. Milk yields for recorded cows in Scotland, available to the Livestock Records Bureau, have been used to obtain some information on these points.

1. The effects of including small quantities of groundnut meal heavily contaminated with aflatoxin in the diets of calves and fattening cattle were studied.

2. Inclusion of 4% or 8% of the toxic meal in concentrate diets for early weaned calves significantly depressed live-weight gain and food intake prior to 3 months. The depression in live-weight gain was due to lowered food intake and to impaired food utilisation.

3. Inclusion of 4% to 12% toxic meal in meal mixtures consumed at 12–13 lb. daily for 20 weeks had no effect on the performance of fattening cattle.

4. Enlarged hepatic cell nuclei were found at slaughter in livers from calves which had received toxic meal and the incidence of these slight lesions varied with toxic meal intake. A very small incidence of similar lesions occurred in fat cattle fed on the highest level of toxic meal.

5. Complete exclusion of groundnut meals containing appreciable amounts of aflatoxin from the diets of calves and dairy cows, and its very limited use in diets for store and fattening cattle is recommended.

An experiment was carried out with 123 pairs of cows located at 11 centres and extending over 3 years, to compare the performance of cows fed at a fixed rate of starch equivalent per gallon with similar cows fed according to an experimental scale, in which the rate of feeding per gallon increased with increasing milk yield.

Records of milk yields and concentrate consumption were made. Feeding according to the experimental scale produced significantly more milk during the first 14 weeks of the lactation. The increase in milk yield for 52 pairs observed over 28 weeks was not significant in either the first 14 or first 28 weeks.

The economic response (lb. milk for each addition lb. starch equivalent for all pairs over 14 weeks was 1·42 and was very near the predicted value. A slightly larger response of 1·64 was obtained from the highest yielding cows. The response over 28 weeks (for 52 pairs only) was 1·30. Considerable variation in this response was found between seasons and between centres.

These results are discussed in terms of the practical application of the feeding scales used and the responses obtained.