1. An experiment is described in which 194 pairs of piglets on 10 commercial farms were reared out of doors with access to soil, either on free range or in field pens. One piglet from each pair received 200 mg. of iron as a parenterally administered iron dextrin complex. The soil type and the iron content of the soil were determined on each farm.

2. During the first 8 weeks of life, the treated piglets showed a small but significant positive growth response of 1–2 lb. (3·0%). The response was greater (2·1 lb.) in piglets reared in field pens, but was non-significant in those reared on free range.

3. Differences in blood haemoglobin levels, mortality and the incidence of runt piglets were not significant.

4. Total body iron increased during the first 3 weeks of life by a mean of 339 mg., of which approximately 295 mg. appeared to be derived from the soil.

Groups of Friesian bull calves were reared on a high intake of milk substitute for either 21 or 28 days, and were then weaned over 7 or 14 days. Dried grass cubes were offered, as the only source of solid food, for 6 weeks from the start of weaning.

The rate of increase of solid food intake of calves weaned from 28 days was considerably greater than that of calves weaned from 21 days, and the later weaned groups were less severely affected by weaning. There was little difference in either the development of solid food intake, or in the severity of the weaning check, between groups weaned at different rates, though the slower rate of weaning tended to delay the intake of solid food temporarily.

The severity of the post-weaning check was inversely related to age at weaning, but was not affected by weaning weight. Growth after weaning was not related to either weight or age at weaning.

There were significant correlations between weight or age at weaning and solid food intake 5 weeks later, and a close correlation between the level of liquid intake established before weaning, and subsequent solid food intake. It was not possible to evaluate the effect of each of these variables, in isolation, on food intake after weaning.

1. All-concentrate diets given ad libitum and containing different levels of fish meal, and varying in crude protein content from 16 to 22% in dry matter were given to eight Friesian steers at 150 kg. and at 240 kg. live-weight.

2. At a mean live-weight of 150 kg., the retention of nitrogen increased significantly to a maximum of 41.5 g. per day on the diet having 22% crude protein in dry matter. At 240 kg. live-weight, the maximum retention of 37 g. per day was achieved at 20% crude protein in dry matter.

3. Faecal nitrogen excretion per unit of metabolic body weight was approximately constant at all protein levels and at both live-weights.

4. Urinary nitrogen excretion per unit of metabolic body weight increased with increasing crude protein level in the diet and for any crude protein level was higher at 240 kg. than at 150 kg. live-weight.

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.

1. An experiment is described in which the individual feed intakes of 16 cows under winter housing conditions in yards, during the transition to spring grazing and on. summer grazing, were determined by faecal indexdigestibility methods. The influence of quality of feed before calving on intake and subsequent performance and the influence of pasture quality and availability on feed intake were included in the study.

2. The provision of a diet of 67% organic matter digestibility, either as high quality hay or as low quality hay with concentrates, increased feed intake before calving when compared with a diet of low quality hay (digestibility 62%) alone. Compared with previous lactation yields the better diets were associated with the maintenance of milk yield, while the low quality hay diet before calving was associated with a 10%, but non-significant, reduction in milk yield.

3. There was a marked rise in faecal output and digestible organic matter (DOM) intake after calving. During lactation, and especially on pasture, faecal output and DOM intake were both correlated with milk yield and metabolic live-weight. Total DOM intake was lower when the availability of feed was restricted and increased when feed was readily available; this increase was associated with a high maintenance requirement.

4. When herbage with OM digestibility of 74–82% was consumed, faecal output rose with decreasing digestibility, but DOM intakes were relatively constant. Provided that efficient utilisation can be achieved, total utilisation per acre might be increased if herbage were grazed at the lower end of this range of digestibility.

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.

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.

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.

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).

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.

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.

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.

Pellets of chromic oxide (Cr2O3) and dental plaster for administration of Cr2O3 to ruminants were developed by Pigden and Brisson (1957). When Cr2O3 was administered to sheep in this manner, Troelsen (1961) observed that digestibility coefficients determined by the Cr2O3-ratio method were very variable, and deviated from those obtained by total collection of faeces. It was also observed that the rate at which the pellets disappeared from the rumen or reticulum was correlated with the percentage of alfalfa hay (r = 0 83) and oat grain (r = –0 80) in the diet and that the abomasal ingesta contained pellets or pieces of same in the process of disintegration.