A numerical model of male and female replacement processes in a dairy cattle population was constructed in order to describe the long-term genetic and financial consequences of selection amongst bulls in AI.

Changes with time in the relative contribution of different generations of offspring to the total genetic improvement of the population were described. It was shown that the genetic change resulting from a single selection process amongst the males eventually approaches an equilibrium many years after selection is practised. Owing to the delays involved in the progeny test, individual males made no genetic contribution for a period of 10 years and a small but constant contribution thereafter.

The costs of bull testing and selection, and the monetary benefits obtained from it, were estimated. Current selection procedures proved to be highly profitable at prevailing market prices. Capital invested in the testing programme was recovered within 2 to 5 years of the first offspring calving.

The effect of changes in milk prices and feeding costs on monetary returns was examined. It was concluded that sire testing programmes are likely to prove unprofitable only under extremely adverse economic conditions.

The influence of breed and sex on relative growth patterns of muscle, bone and fat in beef cattle has been investigated. Comparisons were made of growth coefficients estimated using Huxley's (1932) allometric equation relating muscle, bone or fat to muscle plus bone using data from the dissection of half carcasses of 63 young bulls, 106 steers and 22 heifers representing a number of breed groups. Growth coefficients for muscle and for bone were found to be similar among different breed groups of bulls, steers and heifers. The proportion of muscle increased and that of bone decreased as the size of animal, measured by muscle plus bone, increased. Muscle and bone weights adjusted to common muscle plus bone weights were significantly different among breed groups within sex. Differences in amount of muscle relative to bone were therefore established at earlier stages of growth and maintained over the period represented in the present study.

Growth coefficients for fat were significantly different among breed groups within sexes.

Sex within breed group had no statistically significant influence on growth coefficients for muscle or for bone. Muscle and bone weights adjusted to a common muscle plus bone weight were similar for sex groups within all breed group comparisons. Sex did not have a marked effect on rate of fattening since differences between growth coefficients for fat (between sexes, within breeds) were not statistically significant—although in all comparisons growth coefficients for fat were lowest for bulls, intermediate for steers and highest for heifers. Sexes differed in weight of fat adjusted to common muscle plus bone weight, heifers being fatter than steers and steers fatter than bulls, a difference probably resulting more from early onset of the fattening phase in heifers, followed by steers, rather than relative rate of fattening.

The incidence of abortions over a period of eight years was studied in 107 393 progeny of 100 bulls belonging to five dairy and three beef breeds of cattle. The calving records related to the first four artificial inseminations on females with fresh or frozen semen.

The average frequency of abortion was 2·12%. Differences in rates of abortion between the breeds of sire were statistically significant although this may be confounded with the breed of dam. The highest incidence was from matings by bulls of the Channel Island breeds and the least from matings to Ayrshire bulls.

The rates of abortion increased with the number of inseminations necessary for conception.

There was a slightly higher incidence of abortions among twin births than among singles.

A variety of energy and protein supplements for winter diets based on barley straw were tested in experiments carried out over three years with spring-calving suckler cows. All the supplements resulted in satisfactory calf weaning weights and cow performance but there were indications that a low level (2·3 kg) of barley plus 68 g urea adversely affected the birth weights of calves and their performance from birth to turnout.

Two lines of Large White pigs were selected for increased rate of growth and decreased backfat thickness respectively over five generations. Each line was bred from four boars, each mated to four gilts per generation, these being selected on a within-family basis to minimize inbreeding. Response to selection was measured by direct comparison with contemporary control stock. The control line, originating from the same foundation stock as the selection lines, consisted of 15 groups of one boar and two gilts, mating between groups being designed to reduce the rate of inbreeding.

Over three generations the control stock exhibited random variation in the traits measured except rate of daily live-weight gain and backfat thickness ‘K’. The evidence suggests that the time trend in these was mainly, if not entirely, non-genetic in nature.

The low rate of progress achieved in both lines is ascribed to the selection method adopted and to losses of potential breeding stock. It is concluded that the success of such a small-scale breeding operation is dependent on achieving optimum husbandry conditions, and even then it cannot achieve the same rate of progress as in larger herds. The necessity of using a control strain to assess genetic progress in experiments of this nature is emphasized.

Seven research and teaching centres have co-operated in an experiment involving 154 sows. The experiment compared the effect of feeding four different patterns of feed intake during pregnancy upon reproductive performance of sows. In each case approximately 220 kg of feed were given during each gestation according to four patterns of intake designated Constant (C), Low-High (L-H), High-Low (H-L) and High-Low-High (H-L-H). During lactation all animals were given a daily ration of 3·7 kg of feed for litters of five pigs or less, and 0·4 kg for each additional piglet. Wherever possible the sows remained on the same nutritional regimes for three parities.

Although the pattern of feed intake slightly affected the live-weight changes of the sows during the course of pregnancy, the treatments had no significant effects on overall change in weight of the sows in pregnancy or in lactation in any of the three parities. The live weights of the sows at the end of the third parity were very similar for all treatment groups.

The patterns of feed intake had no appreciable or significant effect on the numbers of pigs born, their average weight at birth or upon the numbers of pigs which survived to weaning at 6 weeks or their live weight. The health and breeding regularity of the sows were also unaffected by the treatments.

There were differences between the centres in many of the variables which were compared, but there was no evidence of any important centre × treatment interactions.

It is concluded that, at the levels of intake given in pregnancy and lactation in this experiment, there are no beneficial or detrimental effects of changing the pattern of intake during pregnancy.

The feeding value of moist barley (approximately 27% moisture) which had been treated with 1·3 % of a mixture of formic (70 %) and propionic (30 %) acids was compared with that of dried barley for growing pigs from 23 to 85 kg live weight. Two experiments were undertaken; 96 pigs were fed ad libitum on one of three diets containing dried or acid-treated moist barley and another 48 pigs were individually fed on one of four diets containing dried or acid-treated moist barley in controlled amounts. These amounts were governed by an allowance of dry matter at a certain live weight.

In neither experiment were significant differences found between the treatments in growth rate or efficiency of utilization of food dry matter. Pigs fed ad libitum showed no significant difference in intake of dry matter, but those given the diet containing dried barley had a higher content of fat in their carcass than those on the acid-treated barley. A total of 21 pigs, 16 fed ad libitum and all receiving diets containing acid-treated barley had a discolouration of fat in the carcass.

Seventy Duroc × Landrace weanling pigs (initial weight 20 kg) were used in a 91-day experiment in a semi-tropical environment, to determine the effects of deletion of the vitamin-antibiotic or mineral supplement to a corn-sucrose-soya bean meal diet on performance of pigs in Coastal Bermuda grass pasture lots. Pigs fed the complete diet in confinement in concrete-floor pens had significantly faster body-weight gain than pigs fed the same diet on pasture. Pigs fed the complete diet on pasture gained weight significantly faster than those given the same diet but without a vitamin-antibiotic premix. Those fed the complete diet without a Ca-P-trace mineral supplement on pasture gained weight significantly more slowly than all other groups, and showed lameness and femur and rib fractures (2 animals) indicative of Ca deficiency rickets.

1. Rates of heat loss from 12 groups of pigs were measured over 4-week periods in a large direct calorimeter equipped as a pig pen.

2. The levels of feeding in different groups were 34, 39, 45 and 52g/kg body weight per day, and the calorimeter temperatures were 7°, 12°, 20° and 30°C.

3. At 12°, 20° and 30°C the rates of heat loss were related to the level of feeding.

4. At 7°C the mean rate of heat loss was higher than at the other temperatures, and was not related to the level of feeding.

1. The total rate of heat loss from individual pigs (20 to 40 kg body weight) was measured over 6-hr periods in a small heat sink calorimeter at 7°, 20° and 30°C, with feeding levels of 34, 39, 45 and 52 g/kg body weight per day.

2. Total heat loss at 7°C was significantly greater than at 20° or 30°C; there was no significant difference in heat loss between temperatures of 20° and 30°C.

3. Heat loss per m2 of body surface was independent of feeding level at 7°C. At 20°C, heat loss on the high feeding level was significantly greater than that on the low level, and at 30°C heat loss on both the low and medium feeding levels was significantly greater than that on the very low level.

1. The metabolic rates of 58 individual piglets kept either on a straw or on a concrete floor at ambient temperatures near to 10°, 20° or 30°C have been measured with ages ranging from newborn to 9 days, and body weight from 1·0 to 3·2 kg. The oxygen consumption was measured on each floor material at the chosen ambient temperature thus allowing paired comparisons for each animal.

2. In comparison with the concrete floor, oxygen consumption on straw was reduced by 18% at 10°C, 27% at 20°C and by 12% at 30°C for pigs 2 to 9 days old. The regression coefficients of mean log (oxygen consumption) on log (body weight) were around 0·66 at 10° and 20°C. At 30°C the value was 0·99 ± 0·14. The regression coefficients were not significantly affected by the presence of a straw floor showing that its effect did not vary with body weight. Corresponding values foi piglets below 24 hours of age were 17% at 10°C, 27% at 20°C and 22% at 30°C ambient temperature.

3. Moving a piglet on to a straw floor at 10°C had the same thermal effect as raising the ambient temperature to 18°C. Similar treatment at 30°C was equivalent to raising the ambient temperature to 32°C.

4. Lowering ambient temperature to increase the temperature gradient between the homeothermic body of the piglet and the environment progressively increased heat loss in all cases. There was a concomitant decrease in the calculated conductance between core and environment which was more pronounced for the piglets lying on the concrete floor.

An implantation technique utilizing slow-release selenium pellets was evaluated as a means of controlling nutritional muscular dystrophy (NMD) in sheep. Sixty ewes were fed a dystrophy-producing hay and implantations were made at mid-pregnancy (14 animals) and in late pregnancy (15 animals); the remainder were kept as controls. Selenium was determined at intervals on milk and blood samples from the ewes and on blood samples from the lambs. Various muscles were examined histologically for NMD lesions.

Selenium levels in the milk of implanted ewes were higher than controls up to the 60th day of lactation and levels in the blood of both ewes and lambs were higher than controls during nursing. Selenium implantation at mid-pregnancy resulted in higher selenium concentrations in lamb's blood at birth than implantation in late pregnancy. However, by 30 days of age and thereafter, this difference was reversed. Large variability was encountered in the blood values for implanted ewes and their lambs. While complete protection against NMD was not achieved, implantation reduced the incidence and severity of the disease. The earlier implantation gave slightly fewer deaths from NMD, but the numbers were too small to make critical comparisons.

Results are given of an experiment in which 61 cyclic Finnish Landrace × Dorset Horn ewes were synchronized for oestrus by intravaginal treatment for 14 days using sponges impregnated with 30 mg ‘Cronolone’ (9a-fluro-11-hydroxy-17a-acetoxy-progesterone; SC-9880, G. D. Searle) and 400 mg progesterone. Groups of 31 and 30 sheep were inseminated twice, either artificially or naturally, at predetermined intervals of 48 and 58 hr after sponge withdrawal. All 61 ewes were in oestrus within 48 hr of removing sponges; 26 of 30 (87%) artificially inseminated and 29 of 31 (94%) hand-mated sheep conceived at the controlled oestrus. The incidence of multiple births was not significantly affected by the method of breeding.

1. Forty Greyface (Border Leicester ♂ × Blackface ♀) and 40 North Country Cheviot ewes, due to lamb to a Suffolk ram in April 1969, were housed during December 1968 in eight groups of 10 ewes, the breeds being penned separately.

2. One pen of each breed received a basal diet of either hay, grass silage or arable silage with a ‘high’ level of concentrate supplementation and one pen of each breed was given hay with a ‘low’ level of concentrate supplementation. Within each pen, five of the 10 ewes were clipped at housing and the other five were clipped in the following June.

3. Voluntary intakes of the basal diets declined with advancing stage of pregnancy, particularly for those receiving grass silage. Feed had no differential effects on the performance of the ewes in terms of wool yield, body-weight change, birth weight of lamb per ewe or perinatal lamb mortality.

4. The Greyfaces clipped at housing yielded less wool than those Greyfaces clipped in the following June. Time of clipping had no influence on the wool yield of the Cheviots. Wool grades were not affected by time of clipping. Ewes clipped in December performed significantly better than ewes not clipped until June with a higher proportion of ewes producing multiple births (P<0·1), a higher total birth weight of lamb per ewe (P<0·01) and a reduced perinatal mortality of the lambs (P<0·05). The total effect of this improved performance was that the clipped ewes produced 53 ·5 % more live lambs than those ewes not clipped until the following June.

Forty-eight Suffolk × Clun lambs were used in an experiment to investigate the effects of two times of removal from the dam and two feeding frequencies upon milk intake over the first 4 days on an artificial rearing system.

Lambs removed at birth consumed significantly more milk replacer at feeding periods up to 32 hr after removal than lambs removed at 24 hr after birth. Removal at birth also significantly increased voluntary milk intake between feeding periods for up to 32 hr and from 64 to 80 hr after removal.

Feeding the lambs during a 16-hr period in a 4, 4, 8 hr sequence instead of 8, 8 hr intervals significantly improved milk intake at feeding periods.

Heritabilities of birth, weaning, 6-month and yearling weights adjusted for significant non-genetic factors and obtained from half-sib correlations were 0·10±0·03, 0·22±0·05, 0·37±0·09 and 0·48±0·07 respectively. Genetic correlations of birth weight with later weights were small and negative except with weaning weight. Genetic correlations among other weights were large and positive. The phenotypic correlations among these weights were positive and statistically highly significant.

The least squares analysis on birth, weaning, 6-month and yearling weights in Magra lambs showed that years of lambing, age and weight of dam at lambing and sex of lamb significantly affected all the body weights except the age of dam which did not significantly affect 6-month and yearling weights. Adjustment of these weights for significant effect will be necessary in obtaining estimates of genetic and phenotypic parameters.

Records of milking rate, milk yield and milk composition were collected over 12 yr from 123 Ayrshire heifers in their first lactation in one herd. Three direct measures of milking rate, i.e. peak flow rate, machine rate and overall rate were closely correlated and each was also correlated with total lactation yield of milk. Milking rate accounted for only a very small part of the variation in fat and total solids percentages. The mean yield of milk per milking in early lactation was a better predictor of total lactation yield than was milking rate but, among animals giving the same early lactation yield of milk, the faster milkers gave higher lactation yields than the slower milkers.

Regression equations predicting weight and percentage of both forequarter and total side retail cuts from 126 beef carcasses were calculated. Dissectable shank muscle weight, shank bone weight and shank soft tissue weight, but not shank fat weight, were useful in predicting weight of forequarter and total retail cuts. However, intact shank weight was as valuable as any single dissection component of the shank in predicting weight of both forequarter and total retail cuts. Separable muscle, fat, bone and soft tissue percentages of the shank were not useful in predicting percentage retail cuts of either the forequarter or the entire right side.

Dried poultry manure, produced locally by sterilization and drying, was evaluated as an addition to a conventional diet, at levels of 10, 20 and 30%, for growing pigs from 23 to 85 kg live weight. The 32 pigs remained healthy and the dried manure had no apparent adverse effect on the carcasses.

There were significant linear relationships between the amount of manure added to the conventional diet and growth rate, feed conversion efficiency and certain carcass characteristics. For every 10% addition of manure, growth was reduced by 0·02 kg/day, feed conversion efficiency by 0·25 units and killing-out percentage by 0·96. The dried manure contained about 30% crude protein and was a rich source of minerals.