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.

Interrelationships between carcass measurements were studied in 83 purebred Clun Forest lambs slaughtered at approximately 80 lb. live-weight and ranging in carcass weight from 29 to 42 lb. Individual carcass measurements did not have a worthwhile predictive value; apart from loin (C) and rib (J) fat depths none of 12 external or internal carcass measurements showed a correlation with carcass composition greater than r = 0·70. Similarly, none of 9 offal measurements recorded had a worthwhile predictive value. In multiple regression certain combinations of these measurements accounted for as much as 77% of the variation in carcass fat, 64% in carcass muscle and 64 % in carcass bone.

The predictive efficiency of sample joint composition, specific gravity determinations and carcass measurements were evaluated in terms of the increased error variance using predicted values and the effect of this increase on sample size in treatment comparisons. Generally the results indicated that increasing treatment group size by relatively few animals is sufficient to absorb the additional error variance arising from the use of predicted values. This is particularly true where treatment differences of the order of one standard deviation exist and where part-carcass dissection values are used.

1. The feed intakes of 18 Ayrshire cows continuously grazing a timothy-meadow fescue-white clover sward were estimated by the chromic oxide-faecal nitrogen method for two 6-weekly periods, one in 1960 and one in 1961. The cows consisted of (1) 6 lactating cows, 6–7 months post partum (Low yield), (2) 6 lactating cows, 2 months post partum (High yield) and (3) 6 dry cows; their live-weights, milk yields and milk composition were recorded.

2. The mean organic matter digestibility of the herbage consumed in the two experiments was 78·2 and 76·2%. The mean digestible organic matter intakes (DOMI) were 23·3, 24·7 and 17·6 Ib./day for low yield, high yield and dry cows respectively.

3. The mean daily fat-corrected milk (FCM) yields of the low and high yield cows were 29·1 and 34·3 lb. in the first experiment, and 26·8 and 42·8 lb. in the second. The mean live-weights of the lactating groups were 1036 lb. and 1106 lb. in the two experiments and did not differ between yield levels.

4. DOMI was partitioned between maintenance, live-weight gain and FCM yield by regression analysis. Significant partial regression coefficients of DOMI on FCM varying between 0·221 and 0·272 were obtained. It was concluded that milk production accounted for about 0·24 lb. DOMI per lb. FCM.

5. The results are discussed with particular regard to other estimates of the effect of milk production on the DOMI of the grazing cow and to the estimation of the maintenance requirement for DOM by the grazing animal.

Relationships between specific gravity and carcass tissue were studied in 83 purebred Clun Forest lambs slaughtered at approximately 80 lb. liveweight and ranging in carcass weight from 29 to 42 lb. Carcass specific gravity accounted for 86·1% and 78·1% of the respective variances in carcass fat percentage and muscle percentage. Specific gravity determinations on a single joint were also highly correlated with the carcass tissues. Correlation coefficients between loin specific gravity and carcass fat and muscle were −0·89 and 0·82 respectively; corresponding figures for best-neck specific gravity were −0·86 with carcass fat percentage, and 0·76 with carcass muscle percentage. In partial correlation analyses, muscle/bone ratio failed to have a significant effect on these relationships. The usefulness of estimates of carcass composition based on specific gravity determinations is discussed in relation to the maximum probable errors associated with predicted values and with reference to the accuracy of these estimates under different experimental conditions. The magnitude of the confidence limits (P = 0·05) on individual predictions varied from ±2·98% to ±3·48% for fat and muscle respectively and for group (n = 12) predictions, from ±0·88% to ±1·01% respectively. This suggests that little confidence can be placed in specific gravity determinations as a reflection of real individual differences or small treatment differences.

Muscle colour has been recorded on pigs tested at the national pig progeny testing stations in Great Britain since 1958. From September 1960 a muscle colour score on a scale of 1 to 7 points has been given by comparing the muscle colour with a series of seven coloured discs of increasing colour intensity. These discs were prepared specifically (by Tintometer Ltd. Of Great Britain) to score muscle colour in pigs. The higher the colour score the more desirable the colour was adjudged to be by the testing station personnel. However, scores of 6 and 7 were very infrequent and no assessment of their desirability was made. Carcasses were cut at the last rib on the day after slaughter at about 200 lb. live-weight and muscle colour was scored on the cut surface of the longissimus dorsi muscle (eye muscle).

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.

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.

Interrelationships between carcass composition and the composition of 7 different sample joints were studied in 83 purebred Clun Forest lambs slaughtered at approximately 80 lb. live-weight and ranging in carcass weight from 29 to 42 lb. Correlation coefficients between physically separated fat, muscle and bone in the loin and in the carcass were 0·96, 0·93 and 0·84 respectively (P < 0·01). Corresponding correlations for the best-neck (7–12 rib joint) were 0·94, 0·92 and 0·76 (P < 0·01). The leg and shoulder provided the best estimates of carcass bone. The usefulness of predictions of carcass composition is discussed in relation to the maximum probable errors associated with individual and group mean predictions of carcass composition based on sample joints and with reference to the accuracy of these indices under different treatment conditions. The 5% confidence limits on individual predictions based on loin composition were ± 2.22%, ± 2.44% and ± 1.62 % for fat muscle and bone respectively; indicating that this index cannot be relied on to reflect small differences in carcass composition between individual animals.

1. Seventy-two individually fed pigs on six treatments were used to determine the effects on performance and in particular on carcass quality of (a) giving quantities of liquid skim-milk (preserved with formalin) in excess of those normally recommended; (b) replacing meal by skim-milk in the ration on a calculated dry-matter basis (1 gal. skim-milk equivalent to 1 · 1 lb. meal) as compared with a calculated energy basis (1 gal. skim-milk equivalent to 1 · 3 lb. meal) and (c) giving skim-milk for only a part of the growing period instead of throughout. The experimental period continued from 9–10 weeks of age until slaughter at an average live-weight of 135 lb.

2. Extensive carcass measurements were taken and in addition assessment of the carcasses was made by a representative of the County Quality Pork Association and by an expert pork butcher.

3. Carcasses from pigs given an all-meal diet were comparable in all respects with those from pigs given skim-milk throughout up to a maximum of either 5¼ or 10½ pints per pig per day.

4. Carcasses from pigs given the highest level of skim-milk (maximum of 15¾ pints per pig per day) were superior in many respects to those on any of the other treatments, but the possibility that this was due to their slower rate of growth rather than to the high level of milk per se, is discussed.

5. Pigs given skim-milk as replacement of part of their meal allowance on a calculated dry matter basis grew significantly faster than those in which the replacement was made on a calculated energy basis or than those given an all-meal diet. The importance is stressed of ensuring that in assessing the value of skim-milk for pigs the caloric value of the rations being compared is similar. The need for experiments based on actual determinations of the caloric value of the rations used is also emphasised.

6. While the performance of pigs given skim-milk up to 75 lb. live-weight only was similar to that of pigs given skim-milk throughout, evidence was obtained that the quality of their carcasses was slightly inferior.

7. There was some suggestion that as the level of skim-milk in the diet increased an eye muscle of a rather paler colour was produced.

Blood groups and haemoglobin (Hb) variants are well defined genetical characters in man and animals. In 1940 Irwin and his associates initiated the study of cattle blood groups in Wisconsin by following the immunization method and haemolytic technique. Now several laboratories all over the world are engaged in this type of study in cattle and other species of animals. There are about 80–90 antigenic factors known comprising eleven blood group systems in cattle (Stormont, 1962).

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.

From 1958 to 1962 over 800 boars and 3,000 sows were progeny tested at the national pig progeny testing stations in Great Britain. Their test results for four traits (daily gain, feed efficiency, average backfat and carcass length) have been used to study the amount and effectiveness of selection and to review the use of the test facilities and their effect on pig improvement.

The amount of selection on test results was studied by measuring the difference in performance of animals with sons subsequently tested and all contemporary tested animals. The selection differentials found were from 0·05 to 0·30 standard deviation units for the four traits studied which represents a rather mild degree of selection. Thus selection could have had only a small effect in improving the testing population. In fact sons of tested animals showed little advantage over their contemporaries in test performance. Parent-offspring regressions were calculated and these, in agreement with theoretical estimates, indicated that selection would be effective and would lead to genetic changes in any of the four traits studied. Genetic correlations among the four traits were also calculated and indicated genetic compatability in improving the four traits concurrently.

Two proposals intended to increase the impact of testing on pig improvement are put forward. These are (1) to restrict the testing facilities to a small nucleus set of breeders who could concentrate on testing and selection and (2) to replace the progeny testing by performance testing which would allow a more intense selection and a greater rate of improvement for the same testing facilities.

(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.

The growth and carcass data were determined for pigs reared on two creep rations to different weights, and subsequently fattened with and without an antibiotic.

Pigs weaned at a ‘standard’ weight of 43·8 lb. at 56 days of age grew more quickly over the range 120 to 210 lb. live-weight than pigs weighing 51·0 lb. at weaning. Both groups were fed according to a fixed scale related to live-weight. Heavy weaners growing slowly in the later stages had slightly thicker backfat measurements, indicating that they were at a more advanced stage of physiological development than the light weaners.

The presence of antibiotic in the fattening ration caused no significant difference in growth rate or carcass measurements, but there were significant interactions between weaning weight and presence or absence of antibiotic in the fattening ration for length of carcass, and between sex and presence or absence of antibiotic for the traits of age at 70 lb. live-weight, carcass length and depth of mid-backfat.

Weaning weight and rate of gain from 70 to 120 lb. live-weight were significantly and positively related to carcass length.

It is concluded that further studies of the growth curve of the pig are required to determine the scope and importance of compensatory growth, and the interaction of growth rates in the different phases of the pig's life and their relationships to carcass traits.

1. All-concentrate diets containing four different levels of Peruvian (anchovy) fish meal and varying in crude protein content from 14·8% to 21·7% in dry matter were given ad libitum to 8 early-weaned Friesian calves over a live-weight range of 60–100 kg.

2. Nitrogen retention was significantly higher on diets containing 21·7% and 19·4% crude protein in dry matter than on diets with 16·8% and 14·8% crude protein. Nitrogen retention as a percentage of dietary intake appeared to be less on the diet with 21·7% crude protein in dry matter than on the other diets.

3. From these data it was calculated that the digestible crude protein requirement for a calf of 82 kg. live-weight gaining at 909 g. daily is between 270 and 340 g.

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.

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).

1. For 4 weeks before calving in December or January a group of 7 Ayrshire cows each received daily 6 lb. hay and silage to appetite, whilst a second group of 9 received the same roughages and 6–10 lb. concentrates. After calving, cows from both of the pre-calving treatments were placed in each of two post-calving groups of 8 cows. A High treatment received approximately 8 lb./day more concentrates at the same milk yield than the Low treatment. Both groups continued to receive 6 lb. hay/cow/day and silage to appetite. The cows were allowed to graze by day from 21 February and by day and night from 13 April. Hay, at 5 lb./cow/day and reducing rates of concentrates were offered until 8 May.

2. Individual feed intakes were estimated from faecal output and digestibility. Direct measures of the intakes of different treatment groups on indoor feeding agreed fairly closely with the mean individual estimates.

3. The digestible organic matter intake (DOMI) of 1,300 lb. cows in the last stages of pregnancy was increased from 10 up to 14–16 lb./day by giving 8–10 lb./day concentrates. Immediately after calving, the increases in DOMI compared with pre-calving levels were about 2.5 lb./day for cows which received concentrates before calving and 8.5 lb./day for cows which received no concentrates before calving.

4. When all cows had calved and were in full milk production there were no significant differences in DOMI, milk yield or rate of live-weight gain attributable to pre-calving treatment. Mean DOMI on the High and Low post-calving treatments were 23.8 and 19.4 lb./day, mean fat-corrected milk yields 44.5 and 38.8 lb./day and mean rates of live-weight gain 05 and nil lb./day, respectively.

5. DOMI increased by 0.7 and 4.9 lb./day for High and Low post-calving treatments when cows were turned out to night as well as day grazing, and milk yields increased by 1.0 and 2.2 lb./day respectively.

6. Regression equations relating animal production and feed intake, and substitution rates of concentrate usage were calculated. Faecal output and DOMI were closely related to milk yield. When additional concentrates were given the resulting increase in total DOMI was greater when the bulk feed was of low digestibility than when it was of high digestibility.