Recurrence relationships are used to relate breeding values of age-sex classes from different time periods. Their application to single-stage (progeny) and multi-stage (parent) selection is demonstrated. These relationships enable definition of the effect of age structure, initial genetic differences between age groups, and the extent to which allowances are made for these or later genetic differences between age groups. The expressions derived show that, given initial genetic differences between age groups, subsequent progeny means will fluctuate even under completely random selection. Using these means as a basis for measuring responses to selection, it is shown that there can be selective effects where selection is at random within parental age classes. A careful definition of the alternative programme is therefore important in interpreting results of selection experiments and in investment appraisal of selection programmes.

These models were then used to describe economic returns from parent and progeny selection programmes and from programmes in which returns are realized in more than one age group. A further extension of the model accommodates the effects of finite population size on returns through its effects on genetic variance.

By separating the (constant) within- and (fluctuating) between-group components of the selection differential within the recurrence relationships a number of computational problems are overcome.

The growth and efficiency of live-weight gain of 36 calves confined in pens was studied between 30 and 210 days of age. They were weaned individually at 30, 90 or 150 days old and offered one of three solid foods which contained 200, 300 or 400 g milled roughage/kg both before and after weaning. From 30 to 90 days and from 90 to 150 days weaned calves consumed more (P<0·001) solid food than sucking calves. During both these periods sucking calves consumed more (P< 0·001 and P<0·05 during the first and second periods respectively) metabolizable energy (ME), gained more (P<0·01) body weight and also gained more body weight/MJ ME consumed than weaned calves. Composition of solid food had little effect on calf performance.

The combined efficiency (kg calf weight gain/MJ ME consumed by cow and calf unit) was higher (P<0·001) for suckling cows and calves than for weaned cows and calves between 30 and 90 days. Between 90 and 150 days, weaning had no effect on combined efficiency.

Eight similar calves which were reared by their dams on veld until 210 days of age were heavier at 90 (P< 0·001) and 150 (P<0·05) days than penned calves which had been given concentrates ad libitum since weaning at 30 days. The body weights of these two groups were similar at 210 days.

1. A deterministic model for thermoneutral heat production of growing pigs on barley-based diets has been developed and validated. The model variables are live weight (20 to 100 kg) and metabolizable energy intake (not less than maintenance). The root-mean-square error for 62 data is 049 MJ/day (3·2%).

2. A deterministic model for heat production of growing pigs below their critical temperature has been developed and validated. The model variables are: air temperature, air velocity, floor type, live weight (20 to 100 kg), and group size. The root-mean-square error for 78 data is 0·77 MJ/day (5·6%).

3. The two heat production models are combined to give a model for the lower critical temperature for growing pigs.

4. These models may be used to quantify and compare the effects on energy balance of different combinations of nutrition and environment. They should help to clarify the issues when practical decisions in pig production are made and should also help in the design of nutritional and physiological experiments.

Genetic analyses were carried out on 935 Large White and 767 Land-race boars performance-tested from 25 kg to 80 kg live weight under individual andad libitumfeeding conditions. Traits analysed were daily weight gain (GR), feed conversion ratio (FCR), daily feed intake (FI) and subcutaneous fat depth (F). Genetic parameters were estimated from sire components obtained by conventional hierarchical analyses of variance and covariance.

Large White pigs grew faster, had higher intakes of feed and utilized it more efficiently than Landrace. There was no breed difference in fat depth. Heritabilities, pooled over both breeds, were 0·36 ± 0·10, 0·27±0·08, 0·62±0·13 and 0·47±0·11 for GR, FCR, FI and F respectively. Noteworthy among the correlation estimates were strong and positive correlations between FI and the other three traits. A positive genetic correlation between GR and FCR arose from a very high coefficient of genetic variation for FI.

Selection indexes emphasising efficiency of lean growth were constructed using some or all of the 4 traits as measured variables. Their use is expected to reduce FI and GR on feeding ad libitum. The results indicate the need to select pigs on the same level of feeding as that used in production.

Sixty pigs, equal numbers of boars and gilts of the two breeds Large White (LW) and Gloucester Old Spot (GOS), in litter groups of three, were divided equally between an initial slaughter group and two treatment groups; H, given a diet with 149 g/kg crude protein (CP) at a daily level of 0·1 W0·75; and L, given a diet with 193 g/kg CP at a daily level of 0·075 W0·75. The cumulative total amount of feed given to each pig was the same, 175 kg, but H received more energy per day. All pigs received the same CP per day but L received more CP in total. Pigs started on experiment at 12 weeks of age. The treatments differed mainly in their ability to promote fat deposition: H pigs grew faster than L, due mainly to a greater deposition of fat (as measured by the weight of subcutaneous fat produced) rather than lean (as measured by the weight of hind limb lean produced). H pigs had a poorer feed efficiency than L pigs.

The breeds were similar in most aspects of production and body composition over both treatments but GOS tended to be slower growing and fatter than LW, with shorter carcasses, thicker backfat, and smaller subcutaneous fat-free hind limbs. Boars were faster growing, leaner and more efficient than gilts, with a higher proportion of bone in the subcutaneous fat-free hind limb and a lower muscle: bone ratio (boars 4·74, gilts 5·28).

For several aspects of carcass composition the potential benefits of the lean types (LW and boars) over the fat types (GOS and gilts) were realized on treatment L but not on H. There was a significant breed × treatment interaction for lean content of hind limb: LW had higher values than GOS on L but both breeds were similar on H. Both LW and boars had significantly less subcutaneous fat than GOS and gilts respectively on treatment L but similar amounts on H.

Carcass measurement and dissection data for 1176 pigs were used to examine the suitability of different measurements for predicting carcass lean percentage in commercial classification and grading. Three carcass weight groups with means of 47, 72 and 93 kg, were analysed separately. Similar results were obtained and those for the 72 kg group are given in this abstract. The s.d. of percentage carcass lean in this group was 3·84. Visual conformation score, carcass length and m. longissimus depth were valueless as predictors (residual s.d. of carcass lean percentages were 3·84, 3·77 and 3·80 respectively). Fat thickness measurements taken on the exposed surface of the split carcass provided a less precise prediction (best residual s.d.=2·89) than fat measurements taken over the m. longissimus using the optical probe (best residual s.d. = 2·20). The probe measurements were taken 6·5 cm from the dorsal mid line at fixed positions along the carcass from 4/5th cervical vertebrae to the 5/6th lumbar vertebrae. Precision of prediction showed a regular pattern with highest levels at the last rib (the P2 position currently used in the Meat and Livestock Commission classification scheme) and at the 13th rib, with lower values anteriorly and posteriorly. These two measurements in multiple regression were more precise than any other pair of measurements for predicting both percentage carcass lean (residual s.d. = 2·16) and the lean percentage in individual primal joints.

In two experiments of Latin square design the effect of additives on the ad libitum intake of direct-cut perennial ryegrass silage and its digestibility by steers was determined. The diets were offered to British Friesian castrated male cattle, mean initial live weights 386 and 368 kg for Experiments 1 and 2 respectively. In Experiment 1, untreated silage was compared with silage treated with either formic acid (‘Add-F’) or a formalin and sulphuric acid mixture (‘Sylade’) each applied at the rate of 4·5 1/tonne of fresh herbage. The silages were offered either with or without 5 kg of supplement per day. In Experiment 2, silages treated with 4·5 and 9·0 1/tonne of the formalin and sulphuric acid mixture were compared. Silage treated with 4·5 1/tonne was offered either with or without 5 kg supplement/day. In Experiment 1, the application of an additive had no significant effect on silage digestibility. Although differences were not significant, the intake of silage dry matter was higher from additive-treated silage (91·2 and 80·6 g/kg W0·73 for the formalin and sulphuric acid mixture and the formic acid respectively) than from untreated silage (78·0 g/kg W0·73). Supplementation significantly reduced (P<0·05) silage dry-matter intake and crude fibre digestibility and significantly increased (P<0·05) total dry matter and digestible energy intake. Digestible energy intake from the formalin and sulphuric acid treated silage was significantly higher (P<0·05) than that from untreated silage but differences between the additive-treated silages were not significant.

In Experiment 2, neither rate of application of the formalin and sulphuric acid mixture nor supplementation had any significant effect on intake.

The effects of type of housing (outdoors on earth v. confinement on concrete) and system of rearing (single v. group) on age at puberty and expression of libido in boars were examined. Boars kept on earth lots and reared in groups reached puberty earlier and demonstrated greater sexual aggressiveness compared with contemporary boars maintained under other treatment combinations. Additionally, the effect of rearing boars either in all-male groups or withprepubertal gilts was examined. Age at puberty was not affected by the presence of females, but boars reared without females attained a higher libido score.

Data from 1357 boars ad libitum fed on a performance testing scheme were analysed to explore the genetic aspects of voluntary food intake. The heritabilities of food intake, daily gain and food/gain were found to be 0·23, 0·41 and 0·18 respectively. The correlations obtained between gain and intake of 0·63 (phenotypic) and 0·89 (genetic) were typical of those reported for ad libitum feeding but greater than those reported for semi-restricted. Estimates of genetic correlation between gain and efficiency ranged from 0·64 to zero and for the phenotypic correlation from 0·44 to zero and were smaller than those reported for restricted feeding. Correlations between intake and efficiency were highly negative on the phenotypic level but small and of variable size genetically, in contrast to reports of small phenotypic and positive genetic correlations under restriction.

Linear measurements and sample joint dissections were examined as predictors of carcass lean percentage using data from 1060 carcasses comprising 108 subgroups (nine genotypes × two sexes × two feeding regimes × three slaughter weights). The potential predictors were examined in terms of precision, cost and the stability of their regression equations.

Probed fat thickness 6·5 cm from the dorsal mid-line at the last rib (P2) was the individual measurement giving the most precise prediction (residual s.d. pooled within subgroups = 2·21 percentage units; r = −0·72). The square root transformation (P2½) gave stable regression slopes over levels of all four factors, though there were important differences in intercepts between genotypes, sexes and slaughter weights.

The precision of prediction from the lean percentage of sample joints was generally improved by including P2½ with each in multiple regression. Used in this way with current Meat and Livestock Commission costings, the ham joint offered the best compromise between cost and precision (pooled residual s.d. = 1·25 percentage units; R = 0·92). Regression slopes on each joint were stable for all factors except for those on the rump back and rib back joints which varied by feeding regime. Intercepts varied by genotypes for all joints except the ham, while intercept differences for feeding regimes were small or non-significant.

The results confirm the value of the ‘sub-sampling with regression’ procedure for predicting carcass composition.

In two experiments, pigs were weaned at 4 to 5 days of age and offered dry diets based on milk proteins and tallow. Live-weight gains between 7 and 28 days of age were 220 g/day with feed conversion ratios of 0·80 when the optimum diets were given.

Expt 1 was a 2 × 2 × 2 factorial with eight pigs per treatment. There were two sources of carbohydrate, lactose and wheat starch, two levels of fat, 40 and 250 g/kg and two levels of crude protein, 140 and 250 g/kg of the diet. There was no significant difference in the performance of pigs when they were fed lactose or wheat starch as the source of carbohydrate. However, the feed intake of the pigs and their weight gains and apparent digestibilities of dry matter and nitrogen were lower when the diets contained 250 g fat/kg than when the diets contained 40 g fat/kg.

In Expt 2 six diets were fed to 12 pigs each. The diets contained 150, 180, 210, 240, 270 or 300 g/kg of crude protein. Weight gains and nitrogen retention showed a positive correlation (r = 0·997) with the dietary nitrogen intake but there was no statistical increase in these parameters above the 270 g crude protein/kg level. The apparent digestibilities of dry matter and nitrogen showed a similar trend. A value of 141 mg nitrogen/day per kg M0·75 was estimated as the metabolic endogenous loss of nitrogen.

Serum thyroxine levels were observed in 15 Soay ewes and seven rams for 1 year. From June to November the ewes had thyroxine concentrations 40% higher than the rams, and the level in both sexes increased from December to May, demonstrating a seasonal cycle in thyroxine level that could be associated with the annual wool growth cycle. To hasten the onset of wool follicle activity, nine Wiltshire sheep were given thyroxine implants in autumn when the follicles normally become inactive, but only a slight increase in follicle activity occurred. Eighteen Soay sheep were given thiouracil orally for 1 month in spring in an attempt to block a possible seasonal increase in thyroxine secretion that might be associated with the normal regrowth of wool, but no retardation of the spring regrowth was obtained.

An analysis of the records of ewe weight and condition at mating together with subsequent lambing performance for several commercial flocks in the UK revealed no significant relationship between lambing performance and size, measured by weight transformed to a standard condition. The relationship between mating weight and body condition score at mating was linear though there was considerable variation in weight at a fixed body condition, suggesting a substantial spread in skeletal size. Increases in ovulation rate were not discernible from lambing figures over the range of body conditions observed in these flocks.

There was no evidence from three experiments with 60, 600 and 400 Welsh Mountain ewes producing mostly single lambs that housing, tested as an extreme form of shelter, was of benefit to reproductive performance. This was so when the ewes were kept indoors throughout the whole of the winter, or only at mating or during late pregnancy. Also, housing during early lactation did not lead to improved lamb growth rate.

Housing at lambing was associated in two experiments with reductions in perinatal lamb mortality from 5·1% to 3·1% and from 7·2% to 5·9%, though the differences were not significant.

Flushing had no significant effect on conception rate or reproductive performance, but the data were in accord with the view that when applied to ewes in moderately thin condition it leads to reduced barrenness and some increase in twinning.

The outcome of 37 563 matings of pigs in the Padana Valley of Northern Italy over a 4-year period was studied. The results show a marked reduction in fertility in the hottest months when a fertility rate of less than 50% was found.

Separate studies of sows and gilts show a similar development in the dynamics of the phenomenon, with, however, a time change.

Estimates of heritability for 9 litter traits were derived from data on 38 000 Large White and 35 000 Landrace litters by daughter-dam regression (parities 1 to 5) and by a three-level nested half-sib analysis (parities 1 to 3). The regression and half-sib heritability estimates were similar and overall the estimates were quite low, averaging 7% across traits and breeds. This is in general agreement with estimates from two other large-scale European analyses of field data. Some other reports, including lesser experimental material, show rather higher heritability values.

The performance of progeny sired by Piétrain × Hampshire, Hampshire × Large White and Large White boars was compared over the live-weight range 28 to 65 kg. Feeding was twice daily to ‘appetite’ up to a maximum of 2·27 kg meal/day. Breed of boar did not influence rate or efficiency of live-weight gain, mid-line or internal fat depths nor muscle quality. Progeny of Pietrain × Hampshire and Hampshire × Large White sires, compared with those of Large White boars, had higher killing-out percentages (1·4 and 1·2 units) and larger eye muscles in cross-section (19·3 and 11·6%). Significant but small breed differences were noted in joint proportions of the carcass.

1. Two groups of artificially-reared lambs were used to evaluate electronic equipment which allowed group-housed lambs individual access to their own food supply.

2. Trial group A comprised six lambs in a cross-over design between individual metabolism cages and group-housing with electronic doors to examine the effects of method of housing upon ad libitum food consumption. There were no significant differences in dry-matter intake although it was observed that food consumption was temporarily reduced during the training periods.

3. Trial group B comprised 16 lambs used to test established training techniques and to examine the effects of adaptation to electronic doors upon food consumption and live-weight gain over a period of 50 days. There was a reduced intake of food during days 1 to 7 which resulted in the daily dry-matter intakes and live-weight gains for days 8 to 50 and 15 to 50 being higher (P<0·01) than those for the total period (days 1 to 50). It was concluded that a minimum of 7, and preferably 14, days were required for training lambs and for adaptation to a diet provided through electronic doors.