The effects of conventional and novel methods for the manipulation of growth in meat animals are reviewed within the context of the fundamental laws that determine the biological efficiency of energy conversion. Interspecies comparisons reveal large differences in the energetic efficiency of growth between mammals and birds. The similarity between mammals of different sizes is remarkable, both between and within species, which suggests that manipulation of growth rate per se has little effect on efficiency. The best way to improve the efficiency of growth is to maximize the conversion of metabolizable energy (ME) to lean tissue at all stages of maturation. The principal destination of ME is heat, however thermogenesis linked to essential metabolic functions is resistant to manipulation. It is more profitable to manipulate the partition of retained energy between protein and fat. Whether this is achieved by nutrition, conventional breeding or bioengineering, it is necessary to ensure that it does not compromise the normal health and vigour of the growing animal.

A trial was performed to investigate the interaction between energy and protein source for cows in negative energy balance. Six cows were assigned to each of four types of concentrate (metabolizable energy (ME) 12 MJ/kg dry matter (DM), crude protein (CP) 180 g/kg DM) with low or high fibre contents (LF or HF) and protein degradability (LD or HD). For groups HDLF, LDLF, HDHF and LDHF respectively, acid-detergent fibre contents (g/kg diet DM) were 69·2, 66·1, 117·5 and 113·3; protein degradability values were determined as 0·78, 0·61, 0·72 and 0·66. Low-fibre diets were given at the rate of 11 kg/day concentrates with 6 kg/day hay (ME 8 MJ/kg DM, CP 84·5 g/kg DM) and high-fibre diets at the rate of 10 kg/day concentrates with 7·5 kg/day hay from weeks 4 to 13 of lactation. Cows were given a standard diet over the first 3 weeks of lactation and performance in week 3 was used as a covariate.

Milk yield was not affected by treatment but the butterfat content of milk from cows given the high-fibre diets (44·9 g/kg) was higher than the low-fibre diets (36·4 g/kg; P < 0·01), which resulted in significant differences in fat-corrected milk yield (HDHF: 25·1, LDHF: 26·2, HDLF: 22·7, LDLF: 21·5, s.e.d. 1·5 kg/day). ME balance was lower for the LDHF group (−4·1 MJ/day) than for groups LDLF and HDLF (-15·4 and -16·8 MJ/day; P < 0·05) but was not significantly different from the HDHF group (-29·4 MJ/day). Undegradable protein (UDP) balances were 53·4, 93·8, -21·2 and 193·8 (s.e.d. 45, P < 005) g/day for groups HDLF, LDLF, HDHF and LDHF respectively. Differences from zero in ME and UDP balance were accounted for in all groups except LDHF by changes in live weight plus a systematic correction of approximately 10 MJ/day. It is considered that the cows given high-fibre diets responded to high UDP by increasing fat-corrected milk production but mobilization of body fat to support this increase was accompanied by retention of protein with associated water, resulting in very little change in live weight. It is also probable that the high UDP levels improved the digestion of fibre i n the rumen, but this is unlikely to have been sufficient to have accounted for all of the response.

With a view to incorporating identifiable environmental factors such as month of calving as random effects in models for dairy sire and cow breeding value estimation, an analysis was undertaken of environmental components of variance for fat yield in lactations 1 to 5 of pedigree British Friesian-Holstein cattle. Records of fat yield and of log fat yield on daughters of widely used sires were first corrected for age and month of calving and for sire in each lactation on a national basis. Variance components for herd-year, herd-year × lactation, herd-year × month of calving, herd-year × month of calving × lactation and error were then estimated for pairs of lactations.

The results were most consistent for log fat yield, where heterogeneity of variance was less. Correlations were, approximately, 0·45 and 0·42 for records in the same herd-year and lactation for lactation 1 or a later lactation, respectively, and approximately 0·40 for records in the same herd-year and different lactations. Within herd-year and lactation, correlations of records in the same month were approximately 0·10 for lactation 1 and 0·08 for later lactations, and for different lactations the correlations were 0·06 if lactation 1 was included and 0·08 otherwise. Thus, the effects appear to be similar for later lactations, which can be pooled, but effects for month and month × lactation 1 v. later should be fitted.

In experiment 1, 12 cows (treatment L) received natural daylight (mean 8 h), 10 h supplementary light (mean intensity 481 lux) and dark (mean 6 h), and 12 cows (treatment N) received natural daylight (mean 8 h) and dark (mean 16 h) for 8 weeks. Supplementary light increased milk yield and tended to increase food intake and loss of live weight. There were no significant effects on milk composition although milk fat concentration tended to be reduced for cows in treatment L. Daily feeding times were not affected by treatment although more feeding took place during the supplementary light in treatment L. Supplementary light increased the time spent lying down per day and reduced the distance walked per day, although cows in treatment L spent less time lying during the light supplementation period. In both treatments, the activity rate was increased on the day of oestrus, but in treatment L the incidence of oestrus-specific behaviour was significantly reduced compared with treatment N.

In experiment 2, 16 cows received natural daylight (mean 9 h) and 10 h supplementary light of mean intensity 0, 101, 191 or 529 lux in a change-over design. There were no significant effects of supplementary light or its intensity on the food intake, milk yield or live-weight change of the cows, but milk fat concentration was reduced for cows receiving supplementary light at 101 or 529 lux and milk protein concentration was reduced for cows receiving light at 529 lux.

This study was designed to examine the influence of pre-wilting and season of harvesting of silage on milk production and food utilization by dairy cattle and also the response to protein and fat concentration of the supplement given with silage. Twenty-four lactating British Friesian cows were used i n a four-period, partially balanced, change-over design experiment to evaluate 12 treatments consisting of three silage types (spring harvest unwilted (lUnW), autumn harvest unwilted (3UnW) and autumn harvest wilted (3W), each offered in addition to supplements containing both two crude protein levels (160 and 210 g/kg fresh weight) and two levels of inclusion of a fat supplement (0 and 100 g/kg fresh weight) in a 3 × 2 × 2 factorial arrangement. All supplements were offered at the same rate of 6·8 kg/day. Total diet digestibility and food utilization studies were carried out on all animals at the end of the third and fourth experimental periods.

The wilted silage (3W) had a higher digestibility than the unwilted (3UnW) material and animals offered 3W silage consumed proportionately 0·18 more silage DM and produced 1·6 MJ/day more milk energy output than those offered 3UnW. The total ration digesibility and food utilization data showed the animals given the 3W silage consumed 13·5 MJ more metabolizable energy (ME) per day than those offered the 3UnW silage and were less efficient at converting the ME available for production into milk energy output than those given the 3UnW silage (efficiencies were 0·58 and 0·53 for 3UnW and 3W silages respectively).

There were no differences between the digestibilities of the spring (lUnW) and autumn (3UnW) silages with the concentrations of digestible organic matter in the dry matter (DM) being 650 and 648 g/kg respectively. However, animals offered lUnW silage consumed proportionately 0·12 more DM and produced 1·05 kg/day more fat-corrected milk than those given 3UnW silage. The food utilization data indicated that this milk production difference could be accounted for by the higher ME intake on lUnW and that the efficiencies of conversion of ME available for production to milk energy output were similar with both seasons of harvests (efficiencies were 0·57 and 0·58 for lUnW and 3UnW respectively).

Increasing the crude protein concentration of the supplement from 160 to 210 g/kg increased silage DM intake, milk yield and milk energy output by 0·2 kg, 0·66 kg and 1·9 MJ/day respectively with the response being greatest with lUnW and least with 3UnW silage. Increasing the fat concentration of the supplement depressed silage DM intake but increased milk yield by 0·53 kg/day.

The effects of the treatments on total diet digestibility, energy and nitrogen utilization, and the volatile fatty acid concentrations of rumen fluid are also given.

Ninety primiparous and 150 multiparous Israeli-Holstein dairy cows were allotted at random into three groups. One group (LSBM) was given 170 g crude protein (CP) per kg dry matter (DM). The two other groups were given 210 g CP per kg DM with the extra 40 g CP per kg DM supplied either by soya-bean meal (HSBM) or by fish meal (HFM). Roughage supplied proportionately 0·20 of the dietary DM and was maize silage with groundnut hay in the winter and wheat silage with oat grass in the summer. The primiparous and multiparous cows were offered the experimental diets for 16 and 24 weeks, respectively.

Milk, milk fat and milk protein production (kg/day), for treatments LSBM, HSBM and HFM, were: 39·3, 40·0, 40·8 (P > 0·05); 1·12, 118, 1·06 (P < 0·05) and 1·21, 1·23, 1·26 (P > 0·05) for multiparous cows and 29·4, 31·2, 33·4 (P < 0·05); 0·89, 1·07, 0·93 (P < 0·01) and 0·92, 0·98, 1·05 (P < 0·05) for primiparous cows, respectively. Cows of high yield potential responded more to increasing dietary protein level than did cows of low yield potential. Average live-weight gains on treatments LSBM, HSBM and HFM were (g/day): 220, 160 and 310 (P < 0·05) in multiparous cows and 220, 170 and 230 (P < 0·05) i n primiparous cows, respectively. Pregnancy rates, 16 weeks after parturition, were 0·65, 0·52 and 0·72 (P < 0·05), in the LSBM, HSBM and HFM groups, respectively. The decrease in pregnancy rate in the HSBM cows, occurred in primiparous cows and cows in their fourth or later lactation but not in cows in their second or third lactation. The milk production of primiparous and multiparous cows in relation to the level and source of dietary CP and the utilization of energy and protein for milk production is discussed.

Lactation curves are fitted to data as a preliminary to estimating summary statistics. Two widely quoted curves are atbe-ct (Wood, 1967) and a(1 - e-bt) - ct (Cobby and Le Du, 1978), each of which has three parameters. Restriction to either of these curves imposes limitations on the fit to the data and can result in biased estimation of summary statistics. Alternatively, lactation curves can be generated by the use of a non-parametric method which requires only weak assumptions about the signs of derivatives of the curves. Because the non-parametric curves are more flexible, estimates of summary statistics are less likely to be biased than those based on parametric models. Use of the non-parametric curves is particularly advantageous around the time of peak yield, where the curves of Wood and Cobby and Le Du are known to fit data poorly.

An experiment was carried out to investigate the performance of young steers given either ammoniated hay alone (TA), or supplemented daily with either 112 g fish meal (TF) or 2 kg barley (TB) or 2 kg barley-based concentrate (TC), compared with untreated hay supplemented with either urea (UU), to raise the nitrogen content of the diet to that of the ammoniated hay, or with 2 kg concentrate (UC). Serial slaughter of animals was carried out to examine the effects on body composition during the winter feeding period and subsequent grazing season.

Ammoniation of the hay significantly increased the in vivo digestibility of organic matter, acid-detergent fibre, neutral-detergent fibre and cellulose fractions (0·672 v. 0·643, 0·740 v. 0·670, 0·758 v. 0·638 and 0·826 v. 0·741, respectively). When offered with 2 kg concentrate, intake of ammoniated hay was higher than that of the untreated hay. Empty body weight gains (EBWG) during the winter period were affected by treatment (174, 225, 293, 590, 631 and 692 g/day for treatments UU, TA, TF, UC, TB and TC, respectively), and were highly correlated with total gross energy intakes (56·0, 61·0, 62·9, 74·5, 73·2 and 83·1 MJ/day, respectively). As the rate of EBWG increased, the fat proportion (g/kg EBW) at turn-out also increased. During the grazing season animals which had been on treatments UU, TA and TF showed a marked degree of compensatory growth (759, 686 and 640 g/day EBWG, respectively) compared with treatments UC, TB and TC (623, 572 and 601 g/day EBWG, respectively), and differential rates of tissue gain. This resulted in reduced, though still significant, differences in EBW, although body composition (g/kg EBW) at final slaughter was similar for all treatments. Thus, whilst short-term advantages in intake and performance can be obtained by ammoniation of hay, the benefits so achieved may not persist due to subsequent compensatory growth at pasture.

One hundred and twenty spring-born steers comprising 40 Friesians (FR), 40 Limousin × Friesians (LM), and 40 Blonde d'Aquitaine ' Friesians (BL), were reared together from shortly after birth to slaughter at a mean age of 771 days. They were at pasture in summer and were housed and offered grass silage plus concentrates in winter. All were implanted with anabolic agents. During the finishing winter, there was a 3 (breed types) ' 2 (3 or 6 kg concentrates per day) ' 2 (94 or 181 day finishing period) factorial arrangement of treatments.

Slaughter weights per day of age, carcass weights per day of age and carcass weights of FR, LM and BL were 846, 828 and 866 (s.e. 8·0) g, 464, 476 and 497 (s.e. 4·9) g and 358, 368 and 385 (s.e. 3·8) kg respectively. LM had lower carcass length, carcass depth, leg length and leg width values than FR or BL but when these measurements were expressed per kg carcass weight the values for LM and BL were similar. Both LM and BL had better carcass conformation than FR, and BL had a lower carcass fat score than either FR or LM between which there was no difference. FR, LM and BL had carcass lean, fat and higher-priced lean proportions of 634, 669 and 685 (s.e. 3·7), 185, 168 and 144 (s.e. 3·7) and 352, 361 and 361 (s.e. 1·4) g/kg respectively.

Increasing the concentrate level from 3 to 6 kg per day increased side weight by 9·6 kg (P < 0·001). This consisted of 0·6 kg bone, 3·3 kg lean and 5·7 kg fat. Extending the finishing period from 94 to 181 days increased side weight by 30·3 kg (P < 0·001). This consisted of 2·6 kg bone, 12·0 kg lean and 15·7 kg fat. Allometric regression coefficients for side lean, bone and fat weights on side weight were not significantly affected by breed type or concentrate level. The coefficients for lean, bone and fat were 0·80 (s.e. 0·04), 0·58 (s.e. 0·05) and 2·27 (s.e. 0·16) respectively. The coefficients for weights of lean in the hind-shin, fore-shin, fillet and brisket on side lean weight were 0·8 or lower. The corresponding coefficients for silverside, inside round, knuckle, rump and strip-loin were between 0·8 and 1·0 while the flank, shoulder, neck, chuck, plate, fore-rib and cube-roll had coefficients in the range 1·0 to 1·5.

The length of the oestrous cycle and plasma progesterone concentration in Ethiopian Highland zebu cows were monitored after treatment with prostaglandin F2α (PGF) (25 mg Lutalyse®) 12 days after spontaneous oestrus. PGF induced luteolysis followed by a significant drop in progesterone values to proportionately 0·11, 0·04 and 0·03 of the pre-treatment values (range 6·3 to 11·4 μg/l) within 24, 48 and 72 h of PGF injection, respectively (P < 0·001). PGF treatment resulted in oestrus within 72 to 120 h and did not influence the length of the subsequent oestrous cycle (P > 0·05). Mean oestrous cycle length was 19·4 (s.d. 1·3) days. There was good correlation (r = 0·72) between the length of consecutive cycles in the same cow and the amount of progesterone the cow produced on the same day in the cycles (r = 0·69 to 0·95). As a result, a close relationship (r = 0·74) existed in the total amount of progesterone produced in consecutive cycles. These data suggest that events following PGF treatment in Ethiopian Highland zebu cows closely parallel those observed in natural cycles. Two-thirds of the spontaneous heats exhibited elevated progesterone values 2 days prior to oestrus onset.

Blood samples were taken from three Brahman × Friesian cattle while they walked for 1 h daily on a treadmill pulling 20 or 25 kg weights suspended in a cage. Heart rate and energy expenditure during work were closely correlated. The work had no significant effect on blood levels of red cells, haemoglobin, packed cell volume, total protein, albumin, glycerol, urea, Mg, Ca, Na, K and chloride. White blood cells, glucose, lactate, free fatty acids, P-hydroxybutyrate and inorganic phosphate were affected by work although the changes were shortlived and values had returned to resting levels 75 min after work finished. The changes were similar in each animal and indicated work done by draught cattle is largely at a submaximal level. Apart from lactate no blood parameters were identified that could be usefully used to compare performance.

Twenty-four crossbred wethers (live weight 27·6 (s.e. 0·36) kg) were divided into three groups and given a concentrate diet. One group was a control, one was given cimaterol (10 mg/kg diet) and one was given clenbuterol (2 mg/kg diet). After 49 days on treatment the animals were fasted for 48 h and slaughtered at a live weight of about 36 kg. The effects of both beta-agonists were similar. Food conversion was proportionately 0·20 better in treated sheep which also produced heavier (18·3 v. 17·0 kg, P < 0·01) carcasses that were leaner. The cross-sectional area of the m. longissimus was increased proportionately by about 0·25 (P < 0·001) and the thickness of subcutaneous fat over the muscle reduced by 0·37 (P < 0·01). The loin joint from treated animals contained proportionately 0·30 more muscle (P < 0·001) and 016 (F > 0·01) less fat. Muscles from treated sheep had higher pHu values (P < 0·01) which resulted in reduced loss of exudate during storage (P < 0·01) and darker colour (P < 0·05). They also contained only about half as much intramuscular fat (13 v. 27 mg/g, P < 0·001) and less haem pigments (2·4 v. 3·9 mg/g, P < 0·001). The results indicate that beta-agonists substantially improve carcass quality but, under certain conditions of pre-slaughter handling, may reduce lean meat quality. The similarity of response to both beta-agonists suggests the observed effects on meat quality may be common to this class of drug.

Two experiments are described investigating the possibility of advancing puberty in Awassi ewe lambs kept under semi-arid conditions in mid Syria using 197 single ewe lambs in 1982 and 165 in 1984. In both years, the animals were allocated to three groups each given different levels of supplementation with a barley/chopped straw mixture to achieve different levels of pre-mating growth (high, medium and low). In 1984, the three groups were further subdivided into four subgroups each given continuous exposure to teaser rams from different ages. These were 175, 200 and 230 days of age and a control group not given continuous access to the ram. The results for the two experiments showed that a higher proportion of ewe lambs on the high and medium treatments showed oestrus in their first season (H = 88%, M = 72%, L = 41%; P < 0·01). The high level of nutrition also advanced the mean date of first oestrus in the high group by 22 and the age at conception by 16·5 days as compared with the low level.

In the second experiment, no interaction between feeding level and presence of ram was observed and although there were no significant effects on occurrence of oestrus, continuous exposure to vasectomized rams from 175 days reduced mean age at first oestrus by 16 and age at conception by 19 days as compared with the unexposed controls.

It is concluded that these practices have important implications for the efficient use of semi-arid range land by Awassi sheep on a semi-intensive system.

The effects of melatonin, administered during anoestrus, on the time of onset of oestrus and on conception rate were investigated in two trials carried out on mature ewes of three indigenous and one imported breed. The ewes lambed between December and February, their lambs were weaned in March and they were hand milked twice daily until September.

In the first trial, 12 Chios and 12 Serres ewes were dosed, orally, for 60 days from 19 April with 3 mg melatonin (M) in 10 ml ethanol and water (1: 4 v/v). A similar number of Chios and Serres type ewes in the same flock were nominated as untreated controls (C). Vasectomized rams were used to detect oestrus from 1 May and detected ewes were immediately mated to entire rams of their own breed. The mean dates of first oestrus in Chios ewes were 4 July (s.e. 1·7 days) and 23 July (s.e. 5·4 days) (P < 0·01) for treated and control ewes respectively. Spread of first oestrus was 19 and 61 days, respectively (P < 0·01). Conception rate and ovulation rate were both higher in M (0·90 and 2·3, respectively) than in C (0·55 and 1·8, respectively) but the differences were not statistically significant. The corresponding results in the Serres ewes were 8 July (s.e. 1·6 days) and 31 July (s.e. 6·8 days) (P < 0·01) for date of first oestrus, 19 and 69 days (P < 0·01) for spread of first oestrus, 0·75 and 0·50 (P > 0·05) for conception rate and 1·8 and 1·2 ( P > 0·05) for ovulation rate.

In the second trial, 12 Karagouniko and 12 East Friesland ewes received a single subcutaneous implant of melatonin (Regulin®) on 5 June and a further 12 ewes of each breed were untreated controls. The procedure was as given for trial 1. The mean date of first oestrus was advanced by melatonin in both Karagouniko ewes (25 July (s.e. 3·91 days) v. 11 August (s.e. 6·7 days); P < 0·05) and Friesland ewes (28 July (s.e. 3·2 days) v. 24 August (s.e. 7·3 days); P < 0·01). Spread of oestrus was reduced (43 v. 68 days in Karagouniko, P < 0·05 and 22 v. 87 days in Friesland ewes, P < 0·01). Conception rate of melatonin-treated ewes was higher (0·60 v. 0·45; P > 0·05) in both breeds. Ovulation rate was higher in melatonin-treated Karagouniko ewes (1·8 v. 1·3; P > 0·05 but, in the Friesland breed melatonin-treated ewes had a lower ovulation rate (2·8 v. 3·7; P > 0·05).

In both trials, melatonin treatment significantly advanced and condensed the dates of first oestrus. Conception rate was consistently increased over all groups (P < 0·05) and there was a tendency towards a higher ovulation rate.

Forty-five Large White × Landrace gilts were given food to realize energy intakes recommended by the Agricultural Research Council (1981) to attain maternal weight gains in pregnancy of either 40, 20 or 10 kg using a diet containing 125 g crude protein and 12·5 MJ digestible energy (DE) per kg over three parities. During a 3-week lactation period all animals were given a standard level of feeding. Maternal weight gains in pregnancy were much greater than those anticipated, for all treatments during each parity. The relationship between the actual and the predicted weight gains (kg) was the same for all three parities, actual AW = 22·62 + 0·71 predicted AW (R = 0·69). There was a large range of weight gains within treatments which was related to backfat thickness (P2 measurement (mm)) at conception in the second and third pregnancies, AW = 10·52 + 0·62 P2 measurement (R = 0·63) and to the change in P2 measurement, AW = 38·37 + 1·68 AP2 (R = 0·38) in the first pregnancy. The daily gain per MJ DE intake decreased wth parity and with decreasing energy intake. Numbers of piglets born and weaned were similar for all treatments; birth weights were also similar but there was an unexplained significant difference in piglet weaning weight in parity 2. There were no significant differences among treatments for either the total number or weights of piglets produced over the three parities.

In order to obtain a better knowledge of the behaviour of the domestic pig, a small population was established in 1978 near Edinburgh in an enclosure with several types of habitat, including woodland and bog. Over a 3·5-year period 13 different groups were studied with each group typically containing a boar, four sows, a young sub-adult boar and an immature gilt. The sow and her piglets were allowed to determine the time of weaning and, apart from providing food for maintenance and reproduction, handling was kept to a minimum. The behaviour of these pigs, which included most of the behaviour of the European wild boar, is described in a general manner for the non-specialist.

To gain approval for use in the revised European Community (EC) Pig Grading Scheme to be introduced in 1989, methods of estimating carcass lean proportion must be shown to do so with a coefficient of determination greater than 0·64 and a residual s.d. of less than 25 g/kg. A trial was carried out to assess a number of methods for use in the EC Scheme as applied in Great Britain. Subcutaneous fat and m. longissimus depths at the head of the last rib and at the third/fourth from last rib were measured using the optical probe (OP), the Fat-O-Meater (FOM), the Hennessy Grading Probe II (HGP) and the Destron PG-100 Probe (DST) on a broad sample of 162 commercial carcasses representative of the ranges in fatness and weight found nationally. The left side of each carcass was separated into component tissues. Although the instruments all achieved similar levels of accuracy in predicting carcass lean proportion, some differences were found. The DST just failed to reach the required statistical criteria for approval in the EC Scheme. The results for the other three instruments were submitted to Brussels as evidence of suitability and they have been approved.

Using the regression relationships found between carcass composition and fat thickness together with results from earlier studies, it was estimated that the carcass separable fat proportion of British slaughter pigs has fallen at the annual rate of 7 g/kg since 1975.

Sixty Large White ♂ × (Large White ♂ × Landrace ♀) pre-pubertal gilts were allocated at random to one of five treatments. Gilts on treatment A were given oestradiol benzoate (OB) at 160 days of age. They were also given allyl-trenbolone (AT) at 166 days of age for 18 days followed by an injection of gonadotrophins (Gn) at 184 days of age. Gilts on treatment B were given OB and AT, but not Gn. Gilts on treatment C were given OB and Gn, but not AT. Gilts on treatment D were given OB only and gilts on treatment E were given Gn only. Gilts which were in heat after 183 days of age were artificially inseminated twice during the first 2 days of oestrus. All gilts were slaughtered either 20 days after insemination or at 220 days of age if they were still anoestrus.

The percentages of gilts ovulating after Gn injection were 36% (4/11), 91·7% (11/12) and 91·7% (11/12) for treatment groups A, C and E respectively (P < 0·01). Gilts on treatments A, C and E were inseminated at a significantly younger age than those on treatments B and D (P < 0·05). No significant differences were found in ovulation rate or embryo survival between treatments.

The results indicated that the administration of AT prior to Gn injection had an adverse effect on both the percentage of gilts ovulating and the development of embryos.

An evaluation of three automatic recording probes, the Fat-o-Meater (FOM), the Hennessy Grading Probe II (HGP) and the Destron PG-100 (DST) was carried out for use in the revised European Community (EC) Pig Grading Scheme. One hundred and forty-five pig carcasses were selected from four abattoirs covering the national fatness distribution. Two fat thickness depths, one at the head of the last rib (LR) and the other at the 3rd/4th from the last rib (3/4LR fat), and one muscle depth (3/4LR muscle) taken in the same operation for recording 34LR fat were studied as predictors of EC reference lean concentration. All measurements were taken 60 mm from the dorsal mid line. The corresponding cut surface measurements were also recorded and the carcasses were dissected. The prediction of cut surface fat depths from fat depth probes was better than the prediction of cut surface muscle depth from muscle depth taken with the probes. The DST fat measurement predicted more accurately the corresponding cut surface measurements and FOM muscle depth was more precise in predicting muscle cut surface depth. The DST was better in the prediction of EC reference lean concentration with 3/4LR fat and 3/4LR muscle as predictors (residual s.d. 23·1 g/kg). By adding LR as a third independent variable FOM predicted slightly better the lean concentration (residual s.d. 22·3). For Spain, the equations with these three independent variables were submitted to the Pig Management Committee of the EC. All the methods tested predicted EC reference lean concentration with a residual s.d. less than 25 g/kg and a correlation higher than 0·8.

The level of body reserves in first-litter sows was manipulated by giving gilts one of three levels (high (H), medium (M) or low (L)) of food from selection (44 kg live weight) to parturition. The aim of this experiment was either to maintain or to mobilize these reserves during lactation (31·4 days) by feeding sows to appetite (high (H)) or 2·0 kg/day (low (L)).

When the level of body reserves was increased prior to farrowing (171 kg live weight, 32 mm backfat) sows had a lower voluntary food intake during lactation than those animals that farrowed with a low level of body reserves (126 kg live weight, 20 mm backfat) (H-H v. L-H, 3·4 v. 4·9 kg/day; P < 0·001). Both groups had a normal return to oestrous activity after weaning (mean interval between weaning and mating of 14 days) but the heavier animals mobilized more of their body reserves (H-H −30·7 kg live weight, -4·3 mm backfat; L-H -3·6 kg live weight +0·9 mm backfat; P < 0·001). When food intake during lactation was restricted to 2·0 kg/day the interval between weaning and mating was increased by 50% regardless of the level of body reserves present at farrowing. For the same animals, there were insufficient body reserves to support milk production at the same level as for those animals given food t o appetite.