1. The effect of A.I. on the structure of the pedigree British Friesian breed has been assessed from analyses of pedigrees of systematic samples of 221 registered females and 200 registered males born in 1960. Samples of 200 registered females and 200 registered males born in alternate years from 1946 to 1958 inclusive were used to estimate the trend in the proportion sired by A.I. bulls.

2. By 1960, A.I. had not affected the hierarchical structure of the breed and had not, therefore, narrowed its base. Current inbreeding was lower in artificially than in naturally sired stock but there was little difference between the two groups in the level of non-current inbreeding.

3. Over 50% of artificially sired stock were sired by bulls likely to have progeny test information. Of the naturally sired stock, only 17% of females and 29% of males were sired by such bulls.

4. 12·2% of genes of registered females born in 1960 derived from the 1950 importation from the Netherlands. At comparable points in time the contributions of earlier importations from the Netherlands were: 1914–39·9%; 1936–24·3%. The increased size of the pedigree breed and the development of progeny testing methods giving an earlier and more accurate assessment of the breeding worth of individual sires, probably contributed to the relatively small influence of the 1950 importation.

A genetico-nutritional experiment is described in which 22 Ayrshire twin cattle, both one-egg and two-egg, were reared and maintained for up to seven years on a standard all-pelleted ration. Six equally spaced constant levels of food intake ranging from 35 1b. to 140 1b. per week were used. Each twin was reared on nearly ad libitum feeding until it had grown sufficiently to be able to consume its pre-assigned level of constant food intake. Thereafter its weekly food intake remained unchanged until the end of the experiment. The number of animals on each of the six feeding levels varied from two to six.

On each constant level of food intake, animals continued to grow fairly rapidly for two or three years, but thereafter their growth tended to slow down and usually an equilibrium weight was eventually attained. The resultant mean weight curves constituted an apparently simple, regular and systematic family with each curve eventually separated from the next by a relatively constant weight difference.

Coefficients of variation were about 3% for unrelated animals strictly conforming to the design, but increased at later ages to around 6% when animals with different pre-treatment were included. Coefficients of variation, however, did not change over the ascending series of feeding levels.

The advantages of the design for exploring the triple relationship of gain, weight and food intake are outlined. The potential use of such results as an empirical feeding scale and the possibility of obtaining paths of maximum efficiency from such a controlled experiment are described.

This paper reports the second of two experiments which examined the possibility of improving pasture utilisation by restricting grazing and giving cows a supplement of concentrates. Two treatments (A and B) were continuously imposed, each on a group of 10 adult Ayrshire cows, for about 4 months. Cows received either pasture alone allocated daily by electric fence (B), or half this area of pasture plus 3 Ib. cubed concentrates per 10 lb. milk (A).

Herbage intakes were estimated by grass cutting techniques and also by faecal index methods, and animal performance was recorded. Over the whole experiment the two treatments gave similar levels of production per animal. Significant differences in milk yield and live-weight gain were detected only in periods 1 and 4, respectively, when the intended restriction was not completely achieved. While production per acre of grass was doubled by treatment a about 4,000 lb. grain was considered necessary to replace one acre of grazing.

The results are discussed in relation to the previous experiment. They suggest that the method of replacing half the normal grazing with barley or other concentrated feeds could be usefully employed to alleviate pasture shortage in parts of the grazing season and might therefore facilitate the maintenance of a high stocking rate.

Regression equations relating the intake factor to the dissolved faeces fraction, faecal nitrogen and faecal cellulose contents were derived in a continous digestibility trial with cut herbage, and also with sheep fitted with oesophageal fistulae grazing the pasture from which the herbage was cut. In the grazing trial the intake factor was calculated from the in vitro digestibility of the fistula samples.

The relationships established in the digestiblity trial differed significantly (P<0·001) from those in the grazing trial. These differences may have arisen from selective grazing or from bias in estimating digestibility from fistula samples.

The digestibility of the diet selected in the grazing trial was estimated from the various faecal index relationships established. These estimates were very variable. In contrast there was reasonable agreement between estimates derived by the fistula technique and those predicted from a ‘general’ relationship between the intake factor and faecal nitrogen as established at this Laboratory with a wide range of herbages.

It is concluded that faecal index relationships must be derived with material similar to that selected by the sheep when grazing.

Closely shorn Scottish Blackface female sheep aged 9–14 months, half on high plane and half on low plane nutrition, were subjected, in climate chambers, to two short acute cold exposures down to – 20° C. The exposures were separated by a period of two weeks in either a thermoneutral environment ( + 30° C.) or a subcritical environment ( + 8° C.). Thirty-seven out of 40 sheep showed a greater resistance to body cooling at the second exposure. The mean rates of fall of rectal temperature (in° C. per 100 min. exposure) were 0·42 at the first exposure and 0·22 at the second exposure. One group of sheep showed virtually complete resistance to cooling at second exposure under the specific test conditions used. The highly significant increase in cooling resistance was taken as a measure of acclimatisation.

The main conclusions were as follows:

1. Blackface sheep could acclimatise to cold as a result of one acute exposure to cold lasting about 8 hours.

2. Acclimatisation was slightly greater amongst sheep kept at a subcritical temperature (+8° C.) between acute exposures.

3. Additional data suggested that some acclimatisation resulted from 2 weeks prior exposure to +8° C. alone; but none was induced by 2 weeks prior habituation to the climate chamber environment at + 30° C.

4. Sheep on high plane nutrition showed greater initial cold resistance and slightly greater ability to acclimatise than those on low plane nutrition.

5. Cold resistance was more closely related to recent weight gain than to absolute body weight.

6. There was great individual variation in initial cold resistance and in ability to acclimatise.

7. Sheep kept at + 8° C. between acute cold exposures maintained significantly lower rectal temperatures than those kept at +30° C.

Known genetic loci that affect metric traits may be useful in livestock improvement. Their value depends on the proportion (R) of the total additive genetic variation due to the known loci relative to the heritability of the trait concerned and on the form of selection practised. When normal selection is effective, further information on known loci can add only a little to the rate of improvement. But if normal selection is not very effective, as for characters of low heritability, or if indirect selection on relatives must be used (as for sex-limited or carcass traits) then known loci may add significantly to the rate of improvement possible.

Sampling errors in the estimated effects and in the proportion (R) may cause selection effort to be misdirected and may even lead to losses rather than gains in improvement. Such errors are most likely to occur when the heritability of the character is low.

Reports on several loci with large effects in the various farm species have been summarised, but the evidence is often inconsistent and contradictory. At present, there appear to be no loci that could be used with confidence in the improvement of economic traits in farm animals.

Twelve inbred (coefficient of inbreeding 25%) and 12 outbred, singlereared, Scottish Blackface castrated male lambs were taken at six months of age from amongst the progeny of three rams. They were housed and fed individually on a pelleted diet in three separate phases. In the first two phases restricted amounts were offered. These were calculated to produce, firstly, a small rate of live-weight gain and, secondly, a small rate of live-weight loss. In the third phase feed was offered to maximum voluntary intake during 2 two-hour periods daily.

On restricted intakes there were no significant differences between the groups. In the third phase the outbred sheep consumed 17% more feed than the inbred group and the daily rates of live-weight gain and wool growth were 33% and 27% higher, respectively. Since the inbred lambs were smaller, the voluntary intake per unit live-weight did not differ significantly between groups.

The estimated requirements of feed for maintenance (20·1 ± 0·4 and 21·9±0·6 g./kg. live-weight, respectively, for the outbred and inbred groups) differed significantly. There were no apparent differences in the estimated efficiency of conversion of available surplus feed to body tissue or wool growth.

Six dry cows, six in-calf heifers and six yearling calves grazed in groups of six, arranged either in single age groups or mixed age groups; the arrangements alternated, and each was repeated three times in a continuous grazing sequence with six-day periods. All the animals grazed together for a preliminary period of seven days. Under each arrangement the cattle grazed on a mature sward for two periods, and on an aftermath for one period. Access to fresh and grazed herbage was restricted by electric fences which were moved daily, but the amount of fresh herbage offered was well in excess of appetite at all times.

Records of live-weight, herbage intake, grazing behaviour and social dominance ranking were obtained for all individuals. There was a close relationship between live-weight (LW) and herbage organic matter intake (OMI) in each grazing period, and the regression equations for the six periods were very similar. The best-fit exponent of LW for the pooled results was 0·61±0·038; this was significantly different from 0·73 and 1·0. The exponent increased to 0·71±0·045 when the cow data were excluded. The inclusion of weight change as a third variable was only of value in the mature sward.

The calves ate significantly more, and the cows tended to eat more, when grazing in mixed age groups. These differences could not be explained by differences in the time spent grazing.

There were high simple correlations between LW and OMI, between social dominance rank and OMI, and between LW and rank, particularly in the mixed age groups. When variations in LW were excluded, dominance rank had little influence on OMI in the mixed age groups, but the independent effects of LW and social rank on OMI were of approximately equal importance in the single age groups.

1. Homologous antibodies to Salmonella pullorum were produced by immunising pigs between 100 and 200 lb. live-weight.

2. Standardised doses of antibody, extracted from whole serum after these pigs were slaughtered, were administered to 245 piglets by stomach tube during the first 24 hr. after birth.

3. The marked variation in uptake of the marker antibody, determined by direct agglutination tests on the blood serum of the dosed pigs, was chiefly due to variation between litters. This variation was attributed to maternal effects, associated with agents secreted in varying quantities into colostrum. Concentration of antibody in the dose administered to piglets, time elapsing between birth and dosage and differences between sire families, were subsidiary causes of variation. Possible mechanisms influencing efficiency of antibody absorption were examined and discussed.

1. Sixteen sows were immunised in late pregnancy with Salmonella pullorum antigen. Sows showed marked differences in serum antibody titre at parturition.

2. Twelve hours after birth, serum antibody titres in the 173 piglets born to the 16 sows were measured. They were positively related to the serum titres of their mother.

3. Marked variation existed in the antibody titres of colostra from different teats and from different sows. No relationship was found between colostral titres and the titres in sow or piglet sera.

4. Sow and piglet serum titres were negatively related to piglet and litter weight gain from birth to 7 days of age.

5. Those piglets with high serum antibody titres at 12 hr. after birth displayed better growth rates and enjoyed lower mortality than piglets with low antibody titres.

Local cooling of the skin, produced by exposure to wind was shown to depress the rate of length growth of wool. The depression was associated with reductions in skin temperature and blood flow and with increases in heat transfer in the exposed regions. Fibre diameter did not appear to be affected and there were no indications of a systemic response of wool growth rate to exposure.

1. Four experiments are described in which silages or kale were given to groups of ewes in the later stages of pregnancy and their voluntary intake recorded. A concentrate supplement was given in the last few weeks of pregnancy in each experiment. In experiments 1, 3 and 4 the ewes were housed in a semi-covered yard.

2. In the first experiment, three groups of 10 Scottish Halfbred ewes were offered one of three silages. A fourth group was offered all three in equal amounts. The silage with a low DM content, low crude-protein content, low pH and high crude-fibre content was eaten in smaller quantities than the other two silages. The ewes fed on this poor silage gained less weight during the latter half of pregnancy.

3. In a second experiment four groups of 15 ewes were offered either silage or kale and housed in a Dutch barn or left in a small paddock. There was no difference between the results from the two silage-fed groups in any respect. The ewes offered kale outside ate less than those offered it inside; they gained less weight and produced lighter lambs.

4. There were two groups of 13 ewes in experiment 3a, one group lambing 5 weeks before the other. Both were fed on the sanie silage; intake was higher in the late lambing group but there was no difference in lamb birth weights.

5. Experiment 3 was repeated with 15 ewes per group; the silage was of much poorer quality, intake being low and the ewes gaining very little weight. Lamb birth weights and growth rates were low.

6. Groups of 15 Scottish Halfbred (90 kg. live-weight) and 15 Speckle-faced Welsh (45 kg.) ewes were fed on yet another silage. The Specklefaced ewes ate more silage DM per unit weight than did the Halfbred ewes and gained in weight, whereas the Halfbreds did not gain.

7. In all experiments there was a decline in silage intake in the last few weeks of pregnancy. This decline did not always coincide with the start of concentrate feeding.

8. The results are discussed and comparisons made between experiments. Suggestions are made for the feeding and management of ewes fed on silage, including the recommendation that a silage for pregnant ewes should have at least 20% DM and 14% crude protein in the DM, but not more than 32% crude fibre in the DM.

Scotch grain distillers' solubles, known commercially as ‘Scotaferm’, are now available in Great Britain, and feeding trials were made to investigate the value of this material in the diet of the dairy cow. The solubles are a free-flowing light-brown powder produced by evaporating and then spray-drying the liquor (‘spent wash’) remaining in the whisky still after distilling the spirit. The analysis of a typical sample is 5% moisture, 29% protein (20% digestible protein as estimated by pepsin digestion), 9% fat, 5% crude fibre, 11% ash and 41% nitrogen-free extract. The food is a good source of B-vitamins and contains 3·8% calcium.

A Number of controlled environment studies (reviewed by Blaxter, 1962 and 1964) have emphasised the necessity of providing shelter for out-wintered ruminants. The nature of suitable shelter requires definition and this may be sought by observing the use animals make of different forms of shelter. Direct observation of livestock may, however, sometimes be an inappropriate investigational method. In the work reported here, shelter usage by cattle was assessed from the occurrence of defaecations in various regions of a pasture. Evidence of increased sheltering activity under weather conditions encouraging greater body heat loss would suggest that this method of recording behaviour may be recommended for application in relevant situations.

The suggestion has been made (e.g. Anon, 1961; Brown, 1964; Spedding and Brown, 1961; Wixey, 1965) that a method of overcoming the inability of ewes to rear twin lambs well, may be to wean one lamb out of each pair at 2–4 weeks of age. The weaned lamb would be reared on concentrates and/or grass, and the remaining lamb, which would have access to the entire milk supply of the ewe, might then show a similar rate of growth to that of a lamb reared as a single from birth. Studies have also been made of the effect of the removal of one lamb out of twin pairs at 9 weeks of age (Cunningham and Maxwell, 1966) and at 12–16 weeks of age (Cunningham, 1964).

Braude (1965) has recently reviewed the literature on the subject of supplementation of rations for growing pigs with copper, and concluded that as much as 0·1% copper sulphate could be added to the feed without toxic effects, and that this increased growth rate by about 8·1% and improved efficiency of feed conversion by about 5·4%. Both these values are average responses from a very large number of experiments. Similar results have been reported from the Soviet Union by Volkopjalov, Lebedjeva, Spiridonova and Matuskova (1962).