Variance components were estimated from an animal model using a restricted maximum likelihood procedure which allowed for unequal design matrices and missing observations (VCE). Data sets containing: (i) 15 275 records of linear type classifications on heifers, (ii) 3399 live weight and condition scores measured at calving and (iii) 1157 records of yield, dry-matter intake, average live weight and condition score during the first 26 weeks of lactation; were analysed jointly.

Heritability estimates for dry-matter intake, live weight and condition score in the largest data set were 0·44, 0·44 and 0·35 respectively and the genetic correlation between condition score and the yield traits ranged from −0·29 to −0·46. The genetic correlation between milk yield and average live weight was negative (−0·09) but after adjusting for the genetic variation in condition score this correlation was positive (0·29). Genetic correlations between live weight and stature, chest width, body depth and rump width were consistently high (0·52 to 0·64; 0·75 to 0·86; 0·59 to 0·81; 0·56 to 0·74, respectively). Chest width and body depth were little to moderately correlated with dry-matter intake (0·25 to 0·28 and 0·20 to 0·34 respectively), and angularity (−0·47 to −0·77) and chest width (0·32 to 0·73) appeared to be good predictors of condition score. These correlations showed that (i) the relative value of live weight compared with food intake capacity determines the optimum direction of selection for stature, chest width, body depth and angularity, and consequently the optimum size of the dairy cow, and that (ii) live weight, condition score and food intake can be predicted from the type traits with little loss in accuracy. A restricted index which maintains condition score at its current level was predicted to reduce overall (economic) genetic gain by 5%.

The effect on digestibility, ruminal metabolites, microbial protein synthesis and milk production of manipulating the non-structural (NSC): structural (SO carbohydrate ratio in a predominantly pasture diet was investigated in cows in early (trial 1) and late (trial 2) lactation. Twenty-four cows in trial 1 and 15 cows in trial 2 were offered pasture only (P), 0·85 P plus 0·15 NSC/protein mixture (PR), and P plus an additional 0·1 (trial 1) or 0·15 (trial 2) NSC (PE) in a Latin-square arrangement. All diets were isonitrogenous and P and PR were isoenergetic. PE but not PR increased microbial protein synthesis and decreased ruminal ammonia and milk urea levels, compared with P. Efficiency of microbial synthesis (g N per kg digestible organic matter intake) was not altered by treatment. Treatments had minor effects on ruminal pH and no effect on volatile fatty acid concentrations. PE and PR did not affect milk yield or protein yield and decreased fat yield compared with P in trial 1. Milk yield was increased on PE and PR compared with P and was greater on PE than PR, in trial 2. Yields of fat and protein were higher on PE than on P and yield of protein was higher on PR than on P. The results suggest that increasing the ratio of NSC: protein by increasing total carbohydrate intake was more effective in improving nitrogen utilization in the rumen than was increasing the NSC: SC ratio without increasing carbohydrate intake.

Three hundred and eight cattle, comprising steers and heifers from continental and British crosses were finished on an 18-month beef production system at Warren Farm, Lambourn, Berkshire and slaughtered across a range of fatness levels. The eating quality of roasting joints (semimembranosus.) and sirloin steaks (longissimus thoracis et lumborumj was evaluated and the chemical composition of the lean tissue was taken on a subset of the samples. Results suggested that the greatest differences between the breeds was in the joints. There were significant (P < 0·01) differences in the lipid, moisture and collagen contents of the lean tissue of the joints from the different sire breeds. The Belgian Blue sire progeny had significantly lower lipid content than the Charolais or Aberdeen Angus crosses, and significantly lower collagen content than the Aberdeen Angus cross. In addition joints from Belgian Blue crosses were more tender than joints from other breed crosses. Although the lipid and moisture contents of the steaks from different sire crosses were significantly different there was no evidence of differences in eating quality. Perhaps surprisingly there were no significant relationships between the eating quality and chemical composition between or within breed. Irrespective of breed, carcass fatness influenced the juiciness of both the joints and the steaks although the response was different for continental crosses and British crosses and depended on carcass sex. Over and above this response, steer meat was generally more juicy than heifer meat.

The heart rate (fH) and the energy expenditure (EE) of seven Hintenvaelder (Bos taurus) draught oxen and three zebu (Bos indicusj oxen were measured, while the animals were standing, walking and pulling different loads. Linear regressions for all animals relating EE to fH were highly significant (P < 0·001). The standard errors of the estimate expressed as a percentage of the mean EE (PE) ranged from ±6·7% to ±10·5%. Two animals with PE ±13·7% and ±17·1% were beyond that range. One year later, fH and EE were measured on six of the original seven Hinterwaelder oxen while the animals were standing and walking on a treadmill, on the level and at gradients of 3%, 6% and 9%. In the two experiments mean slope and mean intercept of the regressions of EE on fH were not different (P > 0·05). Irrespective of the kind of work (draught work or lifting work),fH allows a reliable prediction to be made of the EE of working oxen.

A model of a birthdate distribution for a herd of beef cows is constructed using the probability distributions of the variables that affect reproduction in the cow — anoestrous interval, oestrous cycle length, conception to each oestrus, gestation length, period of mating and the prior calving frequency distribution. The model is general and can be reparamaterized to deal with issues such as intervention to synchronize oestrous cycles among cows in the herd by changing the form of the relevant probability distributions.

The model is applied to the question of what time to begin mating in a herd of beef cows. The average calf live weight at day 200, herd conception rate and proportion of cows calving before the planned start of calving were calculated from the model output. The model parameters given by the anoestrous period, conception rate to each oestrus and the regression between prior calving date and anoestrous period, were varied in a factorial design to investigate a range of circumstances found on a farm. Prior calving distributions were generated by random sampling from eight actual calving frequency distributions.

Generally starling mating earlier produced an advantage in terms of extra calf live weight and herd conception rate. However, the proportion of the herd calving earlier than expected increased with early mating. Thus, the feasibility of early mating depends on the cost to the farmer of dealing with early calving cows as well as the advantage of heavier older calves.

Altering the fixed parameters in the model (variances and covariances, prior calving distributions, mating period) to accommodate the circumstances of herds run under different conditions may produce different results. Model structure allows easy alteration of these parameters and also the introduction of different probability distributions for some variables. This might be necessary to model oestrous synchronization and artificial insemination, issues not considered in this paper.

The in situ dry matter (DM) and neutral-detergent fibre (NDF) degradability kinetics of eight forages (four grass hays and four legume hays, harvested at two different dates) were compared to assess the fitting ability of a first-order and a Gompertz model.

The Gompertz model fitted DM degradability data as well as the first-order model and differences between fitted and observed data for the two models were very small but the Gompertz model proved to be statistically superior for the NDF degradability data, especially for the early hours of incubation.

A numerical but not significant difference was observed in the estimated rapidly available fraction for DM and NDF, which zvas respectively lower (mean values 24·4 v. 27·8%) and higher (mean values 5·8 v. 1·8%) with the first-order model. More pronounced differences were observed for the estimates of total potential degradability of NDF, which were often significantly lower with the Gompertz model (average values for the eight forages 75·1 v. 72·3%;.

The sigmoidal shape of the Gompertz model was more biologically appropriate to describe the initial phases of NDF degradation and was thus applied to the cellulose and hemicellulose degradability data.

As the harvesting date progressed through the season, a decrease of the immediately available fraction of DM and nitrogen was generally observed but the effect of harvesting date was not so evident for fibre fractions; the differences within forages were very low. Correlation coefficients between lignin content and total potential degradability of fibre were always high (for NDF, r = −0·96; for hemicellulose r = −0·95; for cellulose r = −0·79; P < 0·001), while the acid-detergent fibre content influenced DM and nitrogen total potential degradability (r = −0·91 and −0·82, respectively).

An experiment was conducted to examine the effect of ammonia treatment or soya-bean meal supplementation on rumen and lower tract digestion and urinary purine-derivative excretion in sheep given barley straw-based diets. Four wethers each fitted with simple rumen and duodenal cannulae were randomly allocated to four diets in a 4×4 Latin-square design. The diets were, untreated barley straw + molasses meal (diet 1), ammonia-treated barley straw + molasses meal (diet 2), untreated barley straw + soya-bean meal + molasses meal (diet 3) and ammonia-treated barley straw + soya-bean meal + molasses meal (diet 4). Dry-matter (DM) intake, total tract neutral- and acid-detergent fibre apparent digestibility and faecal nitrogen (N) output were higher for diets 2 and 4. Microbial protein yield, determined from total urinary purine-derivative excretion, was also high in sheep on diets 2 and 4. However, supplementation with soya-bean meal in diet 4 reduced DM and fibre digestion but increased intake and microbial synthesis. Despite the lower microbial protein synthesis for diet 3, total tract N digestion was high for the diet, an indication of higher nutrient absorption in the lower tract. The above results indicated that there was a substantial increase in rumen microbial N yield from ammoniated straw-based diets. However, not all the N was made available to the animals. Some of the microbial N absorbed in the lower tract may have been overestimated by the use of the purine derivative-microbial N evaluation method. On the other hand, when protein supplements were given the amount of microbial protein available to the ruminant through absorption in the lower tract may have been underestimated by urinary purine derivatives.

A study was conducted to compare the effects of ammoniation and protein supplementation of barley straw on rumination behaviour of sheep. Four wethers were allocated to four diets offered ad libitum in a 4 × 4 Latin-square design. The diets were, untreated barley straw + molasses meal (diet 1), untreated barley straw + soya-bean meal + molasses meal (diet 2), ammonia-treated barley straw + molasses meal (diet 3) and ammonia-treated barley straw + soya-bean meal + molasses meal (diet 4). Animals were kept in metabolism crates throughout each 16-day experimental period and allowed free access to water and a mineralized salt lick. The first 11 days of each period were for adaptation to the harnesses and diets while the last 5 days were used for rumination studies. Animals given diets 3 and 4 had slower eating rates compared with those given diets 1 and 2. Rumination index and duration of each rumination period was lower for sheep consuming diets 3 and 4 than for those on diets 1 and 2 but not significantly so (P > 0·05). Rumination time per 100 g neutral-detergent fibre (NDF) intake was significantly lower (P < 0·01) for diets containing ammoniated straw. Animals given ammoniated straw diets also regurgitated fewer boluses per unit NDF intake than did those on untreated straw diets. The results showed that increased intake and digestibility, which is usually associated with ammoniated straws, was due to sheep doing less work per unit of time to break down straw for digestion. In this way, potentially digestible tissues within a given amount of straw is more readily exposed. The foregoing suggests that ammonia treatment results in less rumination so that ruminants given ammonia-treated straw diets do less work ruminating.

Thirty-five mature Churra ewes, ranging in live weight from 30·3 to 52·6 kg and in body condition score from 1·25 to 4·00 were used to study the relationship between body condition score (BCS), live weight (LW) and body composition and fat distribution in ewes of this breed, which is one of the major sheep breeds of northern Spain. The procedure at slaughter and at subsequent dissection was designed to partition each body into two components, carcass and ‘non-carcass’. Right side carcasses and ‘non-carcass’ components were used to analyse the chemical composition. From the left side of the lumbar region a joint was cut and dissected into muscle, bone, subcutaneous and intermuscular fat. According to the results obtained, omental fat represented the highest proportion of total internal fat regardless of the level of fatness. Distribution of internal fat was similar to that observed in other milk production breeds. Regressions on LW explained more of the variation than those on BCS for individual internal fat depots and chemically determined ‘non-carcass’ fat. The prediction of total body fat afforded by LW was better than that provided by BCS. The subcutaneous and intermuscular fat depots in the lumbar joint were well correlated with BCS, carcass fat and total fat in the body, validating the use of this region for assessing BCS in Churra ewes. Nevertheless, the correlation coefficient with the omental depot was not statistically significant. The results of this study suggest that BCS was not as accurate for estimating body composition and fat depots in mature Churra ewes as has been shown previously in other breeds. The single most effective prediction index was LW. However, the utilization of both BCS and LW together provided more accurate estimations.

The genetic and economic efficiency of alternative selection schemes and breeding objectives for the Karagouniki dairy sheep in Greece was investigated by model calculations. Criteria of efficiency were the annual genetic gain for the aggregate breeding value, the profit per ewe in the population and the annual selection responses for single traits. The introduction of a two-tier selection scheme, where the recorded ewes are separated into a nucleus and a pre-nucleus, was found superior in both genetic and economic terms for a breeding objective comprising the traits milk yield and number of lambs weaned per ewe per annum. Highest rates for annual genetic gain and selection responses were obtained when the nucleus size was proportionately 0·05 of the population (200 000 ewes), the size of the test matings 0·50 to 0·60 of the size of the pre-nucleus unit (0·10 of the population) and the number of daughters per test ram 40. Opening the nucleus to replacement ewes from the lower tier did not affect positively the annual genetic gain and the selection responses. Furthermore, a breeding objective comprising the traits fat yield and number of lambs weaned per ewe and per annum was found very efficient in both genetic and economic terms while selection on growth and carcass traits did not seem to be justified.

A model is developed in which the metabolizable energy (ME) requirement for growth and maintenance of the foetus, uterus and udder are described explicitly for sheep. The efficiency of the use of ME for the growth of the products of conception (kp) is assumed to be the same as that for growth in non-pregnant animals. Using the results from the model to calculate the efficiency of the use of ME for conceptus growth (kc) in the conventional manner yields values with a similar magnitude and similar variation with food quality as those estimated experimentally. It is concluded that separately accounting for the growth and maintenance of the foetus, uterus and udder is preferable in models but unnecessary in feeding standards.

This paper describes a general framework which enables responses to selection for resistance to gastro-intestinal parasites in sheep to be stochastically modelled. The model incorporates between-animal variation for pasture intake, the proportion of larvae ingested from the pasture which survive to become adults, the fecundity of the mature worm, along with density-dependent control of this trait and the mortality rate of the worms. The between-animal variation for each component is partitioned into genetic, permanent and temporary environmental components which vary with age. Infection rates are estimated from existing pasture larval contamination and new contamination from infected animals. Using this framework, selection for reduced mean faecal egg count was practised, in silico, for a period of 10 years. Several general patterns emerged. First, a curvilinear response to selection was observed, with responses initially being large then declining over time. Mean faecal egg count declined from approximately 500 to 140 eggs per gin 10 years and worm burdens and pasture larval contamination showed similar patterns of response. The initial responses to selection were approximately 1·7 times that predicted by quantitative genetic theory because the epidemiology of the disease changed as the animals' genetic resistance improved. A method of partitioning selection responses into components due to the altered genotypes of the animals and components due to altered disease epidemiology is outlined. Secondly, the faecal egg count distribution became more aggregated, or skewed, as selection progressed. Thirdly, correlating pasture contamination levels across years (carry-over effects) resulted in even greater apparent responses to selection. Finally, regular anihelmintic treatment reduced mean faecal egg counts but did not alter the patterns of response to selection, indicating that selective breeding should be feasible under a variety of anthelmintic regimes.

Effects were studied on food intake and diet apparent digestibility of giving to goats once daily a basal diet rich in tannin from inclusion of leaves of Quercus calliprinos either supplemented with a high carbohydrate or a high protein food. Also interactions with polyethylene glycol (PEG) were investigated. The results of the present work confirmed our presumption that the content of tannin in some Mediterranean browse is so high that it may negatively affect the utilization of protein in supplementary foods. Neutralizing the tannins with once-daily provision of PEG proved to be an effective means of preventing the negative effect. Providing 10 g/day PEG to goats given Quercus calliprinos leaves ad libitum and supplemented with 300 g/day concentrates containing 160 g crude protein per kg DM increased digestible crude protein intake by 50 g/day. When the concentrate food was given to goats, leaf dry-matter intake decreased significantly (from 664 to 565 g/day) and the goats lost weight rapidly. Therefore, supplementing tannin-rich leaves with concentrate food is recommended only if done in combination with PEG. High protein supplementation increased leaf (from 664 to 844 g/day) and digestible protein intakes (from 4·8 to 92·3 g/day) but a considerable portion of the protein supplementation was wasted due to interaction with tannins. PEG may allow economies in the use of such high-cost foods due to the greater efficiency of protein utilization (digestible crude protein intake increased from 92·3 to 122 g/day) of the supplementary food and to increased intake and protein utilization of the basal leaf diet (from 844 to 1023 g/day).

The efficiency of utilization of protein for retention was analysed in pre-ruminant kid goats of the Granadina breed. Sixty male kids were used. Six were slaughtered at birth and the remaining 54 were offered different protein and fat intakes using nine different milk replacers. The protein concentrations were 200, 240 and 280g/kg dry matter (DM) and those of fat were 200, 240 and 280 g/kg DM. Animals were maintained on experiment until they were 60 days old. All were slaughtered on day 61. Nitrogen (N) balance trials were performed during the last 8 days of the 1st and 2nd months. Body composition of the animals slaughtered at birth and at 61 days were determined. Rates of energy retained as protein and as fat were determined (kJ/kg M0·75 per day) and the corresponding rates of metabolizable energy intake as protein and as fat (kJ/kg M0·75 per day) estimated.

Once the relationships between the rates ofN retained and those of digestible N ingested had been established, it was evident that by increasing the protein content of the diet the efficiency of protein retention was decreased. In contrast, increasing the fat content of the milk replacer increased the efficiency of protein retention. The latter effect was noted for the milk replacers containing the high and medium levels of protein but not for those that contained the lowest level of protein, indicating that the level of protein was then the limiting factor. Having recorded this protein-sparing effect of the fat, the results obtained from the slaughter trials were used to develop generalized equations expressing the rates of energy retention in the form of protein or fat as a function of the rates of metabolizable energy intake achieved as both protein and fat. From the analysis of these equations conclusions are drawn about the variable contribution to protein retention in these animals of energy ingested as fat. This contribution depended on the energy intake achieved both in the form of protein and in the form of fat.

Eleven maize silages with crude protein (CP) and neutral detergent fibre (NDF) ranging from 77 to 93 and 359 to 542 g/kg dry matter (DM) respectively, were used to study the relationship between ear content, chemical composition, fermentative characteristics, in vitro DM digestibility and ruminal degradation characteristics, on the one hand, and the voluntary DM intake by sheep or in vivo organic matter apparent digestibility (OM digestibility), on the other.

The silages were offered ad libitum to mature ewes given a daily supplement of 85 g of soya-bean meal. DM intake varied from 41·1 to 68·6 g DM per kg M0·75 daily. OM digestibility and NDF apparent digestibility were measured, using the same ewes in a period subsequent to that of voluntary intake measurement. The silages, in this case, were offered at a feeding level of 1·2 maintenance. OM digestibility and NDF apparent digestibility ranged from 0·622 to 0·757 and from 0·377 to 0·605, respectively. Rumen DM disappearance was measured by incubating samples in nylon bags in the rumen of three silage-fed rumen-cannulated wethers for 3, 6, 12, 24, 48 and 72 h and by fitting the exponential model to the results. Potential degradabilities (defined as a + b) for DM ranged from 728 to 815 g/kg.

Accurate prediction of DM intake (r = 0·93; P < 0·01; residual s.d. = 3·9) and OM digestibility (r = 0·86; P < 0·01; residual s.d. = 0·022) was achieved using the soluble fraction (a) and the insoluble but fermentable matter (B) and the insoluble but potentially degradable fraction (b), respectively. However, looking for a compromise between accuracy and simplicity, reliability and inexpensiveness, ear content is proposed as a predictor of OM digestibility (r = 0·85; P < 0·01) and the pH and acetic acid concentration of the silages may be used as a predictor of DM intake (r = 0·80; P < 0·05).

A flock of Cheviot ewes carrying the Thoka gene for fecundity was established in southern Scotland through the importation of frozen semen from two Icelandic rams. Ewes considered to be probable carriers of the Thoka gene were identified on the basis of measurements of ovulation rate as juveniles at 1·5 years of age and again as adults. Analysis of 3 years' records of 8926 Cheviot lambings and lambings of 351 Icelandic × Cheviot ewes considered to be probable carriers showed that fecundity increased with age in both genotypes, the number of lambs born per ewe mated being 1·07, 1·19, 1·31 and 1·41 in the Cheviots and 1·55, 1·74, 2·33 and 2·30 in the Icelandic-Cheviot crosses at first to fourth lambings respectively. The apparent effect of the crossbreeding on fecundity thus also increased with age, values at first to fourth lambings being 0·48, 0·55, 1·02 and 0·89 lambs per ewe mated, giving a weighted mean value of 0·61 (1·20 v. 1·81 lambs per ewe mated in Cheviot and Icelandic × Cheviot ewes respectively). There was a positive effect of the proportion of Icelandic ancestry on the number of lambs born per ewe mated and thus the observed increases in fecundity, although attributed principally to the effects of the Thoka gene, are also due in part to other genetic factors introduced from the Icelandic sheep in the crossbreeding programme. Lamb mortality to 6 weeks of age was only marginally higher in Icelandic × Cheviots (0·10) than in Cheviots (0·08). The increase in fecundity was achieved without an excessive proportion of large litters (<0·02 of probable carriers gave birth to quadruplets). The results demonstrate that the introduction of the Thoka gene to breeds such as the Cheviot can increase fecundity and hence the potential for more efficient lamb production.

Twelve adult male alpacas were given either 0·67 (low) or 2·0 (high) × assumed maintenance requirements for a period of 6 weeks after which time each was transferred to the alternative level of nutrition for a further 6 weeks. Fibre samples were taken from two 10-cm2 areas on the mid-side position of each animal at 2, 6, 8 and 12 weeks, and measurements of fibre weight, yield (clean fibre weight/raw fibre weight), fibre diameter and fibre length made on the samples collected at weeks 6 and 12. The higher level of feeding resulted in higher clean fibre weight (low = 0·42 (s.e. 0·03); high = 0·53 (s.e. 0·04)mg/cm2 per day, P < 0·001) and fibre growth rate (low = 186 (s.e. 10); high = 223 (s.e. 14) yon/day, P < 0·05). Changes in yield (low = 0·917 (s.e. 0·006); high = 0·929 (s.e. 0·009)) and mean fibre diameter (low = 31·4 (s.e. 1·9); high = 32·1 (s.e. 1.6) \xm) were not statistically significant. Calculations showed that the increased weight of fibre attributed to the higher level of nutrition could be explained in terms of the observed increases in fibre-length and diameter but that, unlike the sheep in which the ratio fibre length: diameter remains relatively constant under varying nutritional regimes, the effect of nutrition in the alpaca has a proportionally larger effect on fibre length than on fibre diameter.

All pig nutrition models to date predict growth responses of either an individual animal or the average animal of a given population over time. Translating the predicted nutrient requirements from the average animal to the population introduces a number of errors as the cause-and-effect response of the average animal is different from the population response. To overcome the problem of estimating the requirements for a given population using models it is necessary to simulate a number of individuals representative of a population and then average these results. This approach however, requires a knowledge of those animal characteristics that vary between individuals and the nature of their distribution. In this paper a scaled growth rate constant (B*), protein weight at maturity (Pm) and the ratio of lipid to protein at maturity (LPRm) are the parameters used to define an individual animal. As no data existed from which the nature of the distribution of B*, Pm and LPRm can be estimated for pigs of different strains and sexes, and due to the impracticality of determining this variability by experimentation, a simulation model was used to estimate the variations within each parameter. In addition this paper quantifies the subsequent effects these distributions have on the genetic variability of average daily gains (ADG) and daily food intake (TI) over a live-weight range of 25 to 90 kg. Comparisons were made between the genetic variation determined by modelling and those published in the literature. The results indicated coefficients of variation for B*, Pm and LPRm of 0·01, 0·05 and 0·10, respectively. An increase in the variability of all three parameters resulted in an increase in the variation in ADG whilst only an increase in the variation of B* and LPRm affected the distribution of FI.

Heart size of purebred boars (13 Landrace, 12 Yorkshire, and 14 Duroc) and crossbred (Landrace × Yorkshire × Duroc) boars (no. =18) and gilts (no. = 24) was studied. Purebred boars were raised from 30 kg for 110 days and slaughtered. Crossbred pigs of various body weights (30 to 110 kg) were selected and their plasma and blood volume were measured before sacrifice. The variation of heart size of pigs was studied and its correlation with growth performance or to vascular space was investigated. According to the principal component analysis heart size was best expressed by its weight, followed by the thickness of the anterior ventricle septum or the thickness of the left ventricle (LV) wall. The food/gain ratio of boars during testing period was significantly correlated with some size characteristics of their heart including weight, width, and LV thickness. The back fat thickness at 100 kg was significantly negatively correlated with heart weight, heart/body weight ratio, and LV thickness. Thus, selection for growth performance would result in a bigger heart in domestic pigs. In the crossbred study, an allometry fitting of H = 12·18B0·73 (r = 0·96) was obtained between heart weight (H, g) and body weight (B, kg). The fittings of heart weight to blood/plasma volume generated values of r of between 0·79 and 0·75 in allometry models or between 0·84 and 0·80 in linear models. Thus, vascular space is no better than fractional body weight as the basis to express relative heart weight in pigs. It is suggested that the normal exponent relating heart size to body weight in growing pig is effectively 0·75, similar to the exponent of metabolic size, 0·734 or 0·75. Therefore, the size of the heart of domestic pigs varies in size proportionally with the changes of metabolism seen in terms of growth or maybe even reproduction. The wild boar, the ancestor of domestic pigs, has a heart proportionately about 0·5 bigger than modern pigs when scaled according to M0·75. The attribution of metabolic difference to the bigger heart of wild boar is uncertain and needs further elucidation. The trend to bigger hearts in domestic pigs under current selection pressure for leanness should not necessarily be interpreted as returning to a natural form but may reflect a pathophysiological change.

An experiment was carried out to study the effect of changes in either the quality or the quantity of dietary protein intake on the free essential amino acid profiles in plasma, muscle or liver of growing chickens. Following a randomized paired-feeding design based on metabolic body weight (kg M0·75), White Rock male broilers were allocated to one of three isoenergetic (14·5 kJ metabolizable energy per g dry matter (DM)) semisynthetic diets containing different levels of protein (60, 120, 180 or 240 g/kg DM). All diets were based on soya-bean meal, as the sole source of protein, either unsupplemented (diets S) or supplemented with 20 g/kg L-lysine (diets SL) or 2 g/kg DL-methionine (diets SM). Samples of blood, biceps muscle and liver were taken and amino acid analysis was determined by high performance liquid chromatography. Plasma was only adequate to detect the effect of the supplementation with methionine to balance the dietary amino acid (AA) profile. Plasma concentrations of free methionine significantly increased as a result of the supplementation with methionine (P < 0·001) and remained unaffected by the amount of protein ingested. When lysine was added to diets S to induce an AA imbalance, a significant increase in muscle concentrations of free valine, isoleucine and phenylalanine (P <0·05) and a significant decrease in liver concentrations of free arginine and phenylalanine were observed (P<0·05). The supplementation with DL-methionine gave rise to a significant fall in the concentrations of free histidine, glycine and threonine (P < 0·05) and increased those of isoleucine and methionine in the skeletal muscle (P < 0·05), while in liver it significantly lowered the concentrations of free arginine, valine, leucine, phenylalanine and methionine (P < 0·001 to P < 0·05) and raised that of free glycine (P < 0·001). The ratios lysine: phenylalanine, lysine: valine and methionine: glycine in muscle together with that of methionine: glycine in liver seem to be appropriate indexes of the adequacy of the dietary AA profile to requirements.