The frequencies of calving difficulties were computed for 458 calvings of first and second parity Friesian, Ayrshire and Jersey dams with pure and crossbred progeny in all possible combinations. It was found that heavier breeds of dams have higher frequency of difficult calvings. For each breed of dam there is also a direct relationship between the mean birth weight of the calves and the frequency of calving difficulties associated with the breed or cross of calf.

An index of calving difficulties calculated in the form of a discriminant function which combined both the birth weight of the calf and the calving weight and parity of the dam was: Z = log BW−0· log DW−0·10 P,

where Z is the index of calving difficulties, BW and DW are respectively the birth and dam weight and P the parity variable withthe values of one for second parity and zero for the first.

Three groups of 10 Large White gilts were allocated on a littermate basis to 3 feeding regimes, for 3 successive pregnancies and lactations, to provide the following daily allowances: (A) 6 lb feed per day in pregnancy and 2 lb plus 1 lb per pig suckled in lactation; (B) the same total as (A) but given as 4 lb per day in regnancy and 6 lb plus 1 lb per pig suckled in lactation; (C) a lower overall allowance distributed during pregnancy as 5 lb during weeks 1, 2, 15 and 16, 3 to 5 lb during weeks 3, 4, 13 and 14 and 2 lb during weeks 5 to 12, and during lactation increasing by 1 lb per day to appetite or a maximum of 26 lb at the 21st day, and then decreasing by 1 lb every alternate day to a minimum of 5 lb. Creep-feed was provided ad libitum from 3 weeks of age until weaning at 8 weeks of age. Differences between groups in litter size and weight at birth were not significant but the combined measure of litter weight was significantly lower in C than in A and B (P<0·05); litter size (P<0·05) and litter weight (P<0·01) but not individual pig weight increased with parity. At 3 and 8 weeks of age there were no significant differences between groups in size or weight of litters or in individual pig weights. Pigs of Group C sows consumed significantly more (P< 0·001) creep feed (7 lb per head) than those of Groups A and B. Sows of Group A gained double the weight of Groups B and C during pregnancy (P<0001) and lost significantly more (P<0·001) during lactation; Groups B and C did not differ significantly in either respect. Efficiencies of feed conversion (EFC) of total food into total weight by sow and litter were poorest in Group A and best in Group C.

A simple expression relating the standardized selection differential (i) to the intensity of selection (p) is given by

i≏0·8+0·41 ln (R−1)

where R equals 1/p. This linear expression may allow simpler solutions to some optimization problems in selection than does the conventional formula for selection differential on truncation of the normal curve.

Using the expression, formulae for the maximum immediate response and optimum selection intensity in mass selection have been developed, taking account of the loss in performance through inbreeding. These formulae were used to study the effect on response of the total number of animals tested. The maximum response over a specified period of time, allowing for the loss in genetic variance from inbreeding, has also been considered. The optimum intensity of selection may then be well below that necessary for the maximum immediate response.

1. An experiment to test the effects on growth rate of lambs to 15 kg live weight of 5, 7 or 9 kg of milk replacer powder given according to four systems of daily restriction is described and the results are discussed.

2. Although the average age at weaning varied from 18 to 50 days according to treatment, the quantity of milk replacer did not affect the lambs' overall growth rate. Lambs deprived of milk consumed extra concentrates at a rate of 1·75 ± 0·219 kg per kg of milk powder.

3. Although severe restriction of the daily allowance markedly reduced the growth of lambs during the milk-feeding period, they subsequently grew at a faster rate and there was no resultant major depression of overall growth rate. The lambs first consumed a measurable quantity of solid food when they were on average 21 days old and this varied little according to treatment.

4. It is concluded that under the conditions of this experiment it was not economic to give more than 5 kg of milk powder and that it was not advantageous to adopt distribution systems that delayed weaning much beyond 20 days.

5. The applicability of these findings to practice is discussed in relation to the possibility of treatment effects from the rearing period being carried over to the period beyond 15 kg live weight, and also to the possible effects of single penning versus grouping on lamb behaviour.

1. In the first experiment, the digestibility of diets containing ratios of 1:1 and 1:4 hay to concentrates was determined at five levels of feeding in castrated male sheep. With diet 1.1, increasing the daily dry matter intake from 600 to 1400 g resulted in a linear decline in organic matter digestibility from 74·4 to 68·6%. The same increase in level of feeding led to a curvilinear decline in the organic matter digestibility of diet 1.4 from 83·0 to 75·9%.

2. In a similar way the crude fibre digestibility of the diets declined as food intake increased. Also the increase in level of feeding caused a decrease in the mean retention time of stained hay in the alimentary tract.

3. In a second experiment the digestibility of long dried grass offered ad libitum to eight dry and eight lactating cows was measured and compared with the digestibility of similar dried grass offered at maintenance level and ad libitum to eight castrated male sheep.

4. On a metabolic live-weight basis (kg W0·73), the lactating cows ate 34% more organic matter than the dry cows and the mean voluntary intake of sheep was only 54% of the intake of dry cows.

5. The organic matter digestibility for the dry cows was 1·9 units higher than that of the lactating cows and at ad libitum intake the organic matter digestibility for the sheep was 5·6 and 3·7 units lower than that of the dry and lactating cows respectively. The results are discussed in relation to the validity of extrapolating results obtained with sheep to cattle, and with non·lactating to lactating animals.

1. Forty-five Large White gilts were given 2·20 kg daily of a diet containing 14·0% crude protein during three successive pregnancies. During a 6-week lactation they received 5·30 kg daily of one of three diets containing 19·0% (HP), 16·5% (MP) or 14·0% (LP) crude protein.

2. Daily milk yield was estimated on the 10th, 20th, 30th and 40th day of lactation. Milk samples were obtained from the same sows for the determination of protein, fat, lactose and total solids on the 11th, 21st, 31st and 41st day.

3. One sow and litter from each treatment in each lactation was placed in metabolism cages during lactation and estimates of nitrogen and dry matter excretion obtained.

4. As the concentration of protein in the diet decreased the average 42-day gain in litter weight from birth increased significantly in the first lactation. This trend continued in the second lactation although it was not significant but did not appear in the third.

5. There was no marked difference in daily milk yield between treatment groups.

6. There was a significantly greater loss of live weight by the sows on the lower levels of protein in the first lactation. These differences were not significant in the second and third lactations.

The lactation curve in cattle has been explained by the expression yn = Anbe-cn where yn is the average daily yield in the nth week, and A, b, and c are constants. In general, in a sample of 859 Friesian lactations recorded during 1964–65 daily yield was depressed during the winter months (18·8% in January) and stimulated during the spring (14·7% in May) to an extent which was independent of the stage of lactation. Winter calvers on the other hand tended to produce more in total lactation than spring calvers (14·5% for animals calving in November as opposed to those calving in April).

Using a suitable technique it is possible to predict month by month output from a cow, or herd, accurately enough to furnish a basis for forward planning.

Six diets providing ratios of concentrate to hay of 100 : 0, 95 : 5, 90 : 10, 80 : 20, 70 : 30 and 60 : 40 were given ad libitum to 24 British Friesian steers. The hay (in the long form) was offered separately from the concentrates. From 91 to 136 kg live weight, as the proportion of hay in the diet increased, daily dry-matter intake decreased. Over the weight range, 136 to 363 kg live weight, the addition of small amounts of hay to the concentrate diet caused an increase in intake. At 42 weeks of age a digestibility trial was carried out. Daily drymatter intake was maximal when the diet contained 80% concentrates. The apparent digestibility and mean retention time of the diets increased as the proportion of concentrates increased. Differences in estimated gut fill were not significant. The diet consisting of concentrate only resulted in the lowest concentration of acetic acid and the highest concentration of propionic and butyric acids in the rumen liquor. Net-energy intake tended to increase as the proportion of concentrates increased from 60 to 90% but then remained fairly constant.

The growth and carcass characteristics of autumn-born Hereford × Ayrshire castrated male calves reared on two planes of nutrition have been studied. Restricted feeding for 12 weeks after weaning from liquid feed to the time the calves were turned out to grass created a difference of 52·0 lb per head in live-weight gain and 15·2 lb of this difference persisted at slaughter. There were small differences in carcass conformation and composition.

Data from a boar progeny testing scheme based on ad libitum feeding were analysed to test the hypothesis that the resultant correlations of food conversion ratio with related factors would differ from those found under conditions of restricted feeding.

The results support the hypothesis, showing that the primarily genetic correlations derived from boar effects for growth and conversion ratio, are lower than those reported elsewhere for restricted feeding. It was also shown that these primarily genetic correlations could vary between breeds, the leanness associated with rapid growth in Wessex not being found in Large White, and that the correlations due to residual effects containing a greater environmental component varied widely from test to test.

It is concluded that the parameters used in the design of a genetic improvement scheme should be derived specifically for each breed and feeding system. However, if the marked variability in phenotypic correlations noted here is generally applicable, this could present a difficult problem in the design of pig improvement programmes with multiple objectives.

The errors of the slaughter and tritiated water techniques of estimating energy retention were compared in a group of grazing sheep deprived of feed and water for 48 hr. It was calculated that the mean energy retention of the experimental animals would have had a standard error of 3·64 Mcal if estimated by the slaughter technique, and 1·56 Mcal if estimated by the tritiated water technique. It was concluded that in other experimental groups the precision of the relationship between energy content and live weight is likely to be the most important determinant of the relative precision of the two methods. In neither method would worthwhile gains in precision result from knowledge of the weight of the contents of the alimentary tract.

A series of animal feeding trials was designed to determine differences between grasses in dry-matter intake and animal live-weight gain, with a view to indicating better selection criteria for improving the feeding value of herbage.

Wide differences were demonstrated in feed intake and live-weight gain between single-variety grass feeds at similar levels of digestibility.

S.37 cocksfoot gave consistently good and S.51 timothy, consistently poor responses.

Supplementation of grass feeds with red clover frequently resulted in marked improvement in feed intake and animal performance.

Two experiments were carried out to compare the performance and carcass quality of pigs given diets based on barley, wheat or maize meal, and another two experiments comparing these cereals, flaked maize and sorghum. In general, differences in the utilization of feed for live-weight gain could be related to differences in the digestible energy content of the cereals used in the diet, although in some experiments pigs behaved atypically on individual diets. Flaked maize was consistently inferior to the other cereals in the efficiency of conversion of its digestible energy, possibly because of its poorer amino acid balance and its low levels of lysine and tryptophan in relation to energy. Differences between experiments in the performance of pigs fed on the various diets are also discussed. Differences between treatments in killing-out percentage and predicted lean percentage were small, and carcasses of pigs from all treatments were acceptable for bacon curing.

1. The rates of eating silages and hay throughout a meal were recorded in eight cows consecutively using a special manger and an automatic recording apparatus. At each meal the rate of eating was highest in the first five or ten minutes and then fell gradually. These characteristics were observed both on silages and on hay and for all the experimental cows. The mean rates of eating hay, but not of silages, agreed with previous reports.

2. The highest rate of eating was slightly faster at the evening meal than at the morning meal, when cows received equal amounts of feeds twice each day. The rate of eating declined at much the same rate throughout each meal when the cows received from 2 to 5 meals daily.

3. When the cows were fed twice daily, the rate of eating throughout a meal was not affected by changing the interval between meals from 12 hr to 6 hr.

4. When cows were given large amounts of feed at any one time, three stages of rate of eating, fast, decreasing and slow, were recognized.

5. The quality of feed, individuality of cow and pregnancy evidently affected the rate of eating throughout a meal.

The effects of culling, natural wastage and different correction and exclusion procedures on estimates of lactation parameters have been examined in test station records of 1042 Danish Red cows. A total culling rate of 20% was applied to the initial material, of which 11% represented obligatory culling for disease, injury and infertility and 9% ‘paper’ culling for performance at four different stages of lactation.

Exclusion and correction of short records generally resulted in overestimates of the sample mean and underestimates of the selection differential produced by culling. In all instances, the variance of the sample prior to culling, and the loss of variance attributable to culling, was underestimated in samples containing short or corrected records.

It was concluded that field data cannot provide material suitable for objective studies of selection and that a reappraisal of the effects of age, lactation, season, etc., in the controlled conditions of test stations may well be justified. An absence of culling in test stations contributes to the large estimates of variance and heritability characteristic of station material.

1. A comparison was made of the output per hectare and per cow of 3 systems of grazing management each based on a cycle of 5 days grazing followed by a 20-day rest period. The treatments were: C, strip grazing within a paddock, varying the area allotted so that a similar quantity of herbage was available each day, the pasture being frequently trimmed; treatment R, restricted grazing; the cows being allotted a fixed area of the paddock each day (67–5 m2 per cow per day) which was not trimmed or cut after grazing; and treatment RS, as treatment R but with each cow receiving cereal concentrates. Eight cows were on each treatment. Nitrogenous fertilizer was applied at the rate of 86 kg N per ha [1 kg per ha = 0.891b per acre] four weeks before the first grazing and at the same rate after each grazing; a total of 516 kg/ha was applied. The feed intake of each cow was measured on six occasions during the experiment.

2. The experiment continued for 150 days and the mean stocking rate on treatment C was 4–09 cows per ha [1 ha = 2·47 acre] and on the other two treatments 5·92 cows per ha. The number of cow grazing days per hectare were 610, 890 and 890 for treatments C, R and RS respectively and the outputs of milk were C 8450, R 12 420 and RS 13 380 kg/ha. Allowing for the concentrates given the milk outputs were C 7440, R 10 350 and RS 6660 kg/ha.

3. There were only slight differences between the treatments in output per animal.

4. The average intakes per kg W0·73 were similar in treatment C and R but the average intake of cows on treatment C was more uniform over the season. Cows on treatment RS ate consistently more digestible organic matter than those on treatment C and R but the differences became smaller as the season progressed.

Coat and skin samples were taken monthly from three Wiltshire ewes for two years, and then fortnightly between the spring equinox and the autumn equinox of 1968.

The fleece comprised kemp and wool, having a weight of 1·1 kg and a length of 50 mm. In summer all the primary fibres had a latticed medulla, and although the secondaries were smaller than the primaries, they were relatively coarse and often medullated, over one-third having a latticed medulla at the peak period. The overall mean S/P ratio was 3·5.

Follicle development was studied in four lambs from birth to 84 days. Only 27% of the secondaries lacked fibres at birth, and all had fibres at 14 days. There was a trend of increasing medullation in the primary fibres. Shedding primary follicles were seen from birth onwards, and shedding secondaries from 28 days, although obvious casting of the birth coat did not begin until 84 days (at the beginning of June).

There was a basic seasonal cycle of follicle activity starting in March and lasting until September; inactivity began in September, reached 100%, and continued at this level until March. Subsidiary cycles suspected from the monthly samples were confirmed by the fortnightly samples. Thus peaks of inactivity in June and August separated three cycles of growth of two months duration. Only 80% of the primaries and 50% of the secondaries became inactive in June, with 50% of the primaries and 30% of the secondaries, in August.

In a comparative slaughter trial which covered growth from about 16 kg to 40 kg live weight, five groups of six Romney × Swaledale lambs were offered ad libitum five pelleted diets (A to E) in which rolled barley was gradually replaced by an 80 : 20 mixture of rolled oats : oat husks to the extent that the calculated metabolizable energy (ME) concentration fell from approximately 2–9 (A) to 2·5 (E) Mcal/kg DM.

Although daily live-weight gains did not differ significantly between treatments, the daily carcass gain fell from 143 g/day on A to 105 g/day on E (P<0·05) whereas gut contents increased from 9·9% of live weight to 16·1% (P< 0·001) from A to E. Differences in efficiency of utilization of ME above maintenance were variable but for gross efficiency (i.e. retention/total ME intake), there was a significant decline from A to E.

Dry-matter intakes for the whole experimental period were similar for all five diets, but initially intake was lower for diet E than for A (780 v. 927 g/day) and ultimately it was higher for E (1410 v. 1150 g/day). In a second experiment, involving diets A and E and a third diet of chopped dried grass, the pattern of intake and growth changed with live weight in a similar manner to that described above, except that appetite and growth on dried grass were consistently poorer. Daily variation in intake and rumen pH tended to be greater on the concentrate diets.

It is suggested that, amongst other factors, the stage of maturity of an animal may influence the point at which the digestible energy content of the diet restricts dietary intake in preference to physical limitations.

Genetic parameters of veal calves were estimated from data on 510 Danish Red male calves by 39 sires.

Heritability estimates for the growth and carcass traits were low, those for body dimensions and dressing percentage high.

Correlations between the growth and carcass traits indicated no genetic incompatibility in selection.

The problem of achieving simultaneous improvement in the dairy, carcass and growth qualities is discussed. It is suggested that the adoption of performance testing for growth and carcass quality prior to the entry of bulls into AI service, followed by progeny testing for milk and fat yields, would provide the best method of genetic improvement.

A dramatic fall in the colostral whey proteins of nine sows occurred within 24 hr following the birth of the first piglet. The mean levels fell from 19·6 g/100 ml to 4·1 g/100 ml, 50% of this fall occurring within 4 to 6 hr. It is suggested that as early-born piglets will be able to obtain colostrum of a much higher protein concentration this may give them some physiological and immunological advantages over later-born littermates.