Seventy-two multiparous ewes from two dairy breeds (Manchega, n = 36 and Lacaune, n = 36) were used in a replicated 2 × 2 factorial design to evaluate the effects of diet supplementation with an exogenous fibrolytic enzyme product on lactation performance and feed intake during the suckling period (weeks 1 to 4) according to breed. Ewes were blocked in groups of nine and fed adlibitum after lambing a diet based on 70% forage and 30% concentrate to which the enzyme was added after pelleting. Experimental concentrates were: control (without enzyme) and enzyme (fibrolytic enzyme complex, included at 0.47% volume to weight of concentrate). Twenty-four dry and open ewes (Manchega, n = 12 and Lacaune, n = 12) were also grouped by breed and used to measure the fill value of the ration used. During the suckling period, milk yield, milk composition, dry matter intake, lamb growth, as well as body weight change and body condition score change were not affected by enzyme supplementation. Breed effect was significant for milk yield, the Manchega ewes yielding less milk with a higher content of milk components than the Lacaune ewes. The opposite was observed for dry matter intake. Enzyme supplementation reduced intake by 9% in the dry ewes, resulting in a greater fill value of the diet. In conclusion, no lactational effects were detected when the fibrolytic enzyme product was added to the concentrate fed to dairy ewes.

The increasing use of unconventional feedstuffs in chicken’s diets results in the substitution of starch by lipids as the main dietary energy source. To evaluate the responses of genetically fat or lean chickens to these diets, males of two experimental lines divergently selected for abdominal fat content were fed isocaloric, isonitrogenous diets with either high lipid (80 g/kg), high fiber (64 g/kg) contents (HL), or low lipid (20 g/kg), low fiber (21 g/kg) contents (LL) from 22 to 63 days of age. The diet had no effect on growth performance and did not affect body composition evaluated at 63 days of age. Glycolytic and oxidative energy metabolisms in the liver and glycogen storage in liver and Sartorius muscle at 63 days of age were greater in chicken fed LL diet compared with chicken fed HL diet. In Pectoralis major (PM) muscle, energy metabolisms and glycogen content were not different between diets. There were no dietary-associated differences in lipid contents of the liver, muscles and abdominal fat. However, the percentages of saturated (SFA) and monounsaturated fatty acids (MUFA) in tissue lipids were generally higher, whereas percentages of polyunsaturated fatty acids (PUFA) were lower for diet LL than for diet HL. The fat line had a greater feed intake and average daily gain, but gain to feed ratio was lower in that line compared with the lean line. Fat chickens were heavier than lean chickens at 63 days of age. Their carcass fatness was higher and their muscle yield was lower than those of lean chickens. The oxidative enzyme activities in the liver were lower in the fat line than in the lean line, but line did not affect energy metabolism in muscles. The hepatic glycogen content was not different between lines, whereas glycogen content and glycolytic potential were higher in the PM muscle of fat chickens compared with lean chickens. Lipid contents in the liver, muscles and abdominal fat did not differ between lines, but fat chickens stored less MUFA and more PUFA in abdominal fat and muscles than lean chickens. Except for the fatty acid composition of liver and abdominal fat, no interaction between line and diet was observed. In conclusion, the amount of lipids stored in muscles and fatty tissues by lean or fat chickens did not depend on the dietary energy source.

The results of two experiments, involving 72 individually fed pigs during a growing period between about 40 and 200 lb. live-weight, indicated that a water allowance of 1½ lb. per 1 lb. meal in place of 2½ lb. water had little effect on the performance of the pigs or on carcass measurements. With unrestricted water there were considerable differences in intakes between experiments but these were without significant effects on the criteria studied, when compared with the respective fixed water to feed ratios.

In the first experiment, but not in the second, a dietary supplement of penicillin was associated with a reduced voluntary intake of water. The penicillin was without overall effect on performance or carcass composition, but was associated with a significant growth response up to 100 lb. live-weight in the first experiment.

In both experiments females were less fat than castrates, as indicated by significantly different carcass densities and by some linear measurements.

Two experiments were conducted in which growing sheep were given choices between foods differing in their contents of urea. The crude protein (CP) contents of both of the foods of the pair were also varied. The hypothesis tested was that the diets selected would be those that met the effective rumen degradable protein (eRDP) requirements of the animals and would avoid excess consumption of eRDP. Three basal foods, differing in CP were formulated. D was designed to be deficient in CP with 80 g CP and 58 g eRDP per kg DM; H was calculated to be adequate with 159 g CP and 114 g eRDP per kg DM; P had excess with 210 g CP and 148 g eRDP per kg DM. Other foods were made by adding 12·5 or 25 g urea per kg fresh matter to each of the three basal foods to make a further six foods. In both experiments Texel ✕ Greyface female sheep were used. In experiment 1, 34 sheep weighing 37·2 (s.d. 1·85) kg were randomly allocated to one of six groups and each group was offered a choice between a pair of foods. Groups 1 to 3 were offered pairs in the D series (D v. D + 12·5 g urea per kg (no. = 6), D v. D + 25 g urea per kg (no. = 6) and D + 12·5 g urea per kg v. D + 25 g urea per kg (no. = 5)). Groups 4 to 6 were offered the same pairs of foods but with H instead of D. In experiment 2, 96 sheep weighing 29·8 (s.d. 3·37) kg were randomly allocated to one of 12 groups. Groups 1 to 6 (no. = 6) were allocated a single food (D, D + 25 g, H, H + 25 g, P or P + 25 g urea per kg) throughout the experiment. Groups 7 to 12 were given a choice (no. = 10) between two foods. One food of the pair was the basal D, H or P. The other food was the same basal food supplemented with either 12·5 or 25 g urea per kg. On the single foods adding urea to D resulted in an increase in food intake and live-weight gain suggesting that D was deficient in eRDP. Adding urea to either H or P had no beneficial effects on intake or live-weight gain. This suggests that both contained sufficient eRDP in relation to energy. Across all choice treatments in both experiments there was a highly significant preference (P < 0·01) for the food with the higher urea content. In experiment 1 0·62 (s.e. 0·04) of the diet selected was the food with the higher urea content. In experiment 2 the figure was 0·64 (s.e.0·03). The general preference for the food with the higher urea content was unaffected by the CP contents of the foods used. The results do not support the hypothesis that sheep will avoid excess eRDP when given a choice and suggest that eRDP may not be a relevant dimension in diet selection in the conditions of these experiments.

Thirty-three Landrace × Large White multiparous sows were allocated randomly to one of three treatment groups, and were weaned after a 10-day (treatment A), 21-day (treatment B) or 42-day lactation (treatment C). All sows were bled regularly from weaning through to day 24 post coitum, at which time the sows were slaughtered and their reproductive tracts recovered and dissected.

Ovulation rates were similar for all groups. Embryo survival for treatments A, B and C respectively was 0·638, 0·728 and 0·777 but this difference was not significant. Oestradiol 17-β concentrations were significantly higher in sows weaned after 10-day lactations throughout the whole period from weaning to day 10 post coitum compared with the other two treatment groups (P < 0·001).

The main objectives of the study were to: (1) deeply analyse the serum protein composition of Equus caballus, (2) assess the effectiveness of the high-abundant protein depletion and improve the concentration of medium- and low-abundant proteins. The analysis were performed on the blood plasma of three healthy part-Arabian mares. The implementation of two-dimensional electrophoresis and matrix-assisted laser desorption/ionisation – time of flight mass spectrometry allowed us to establish a horse plasma proteome map. Serum proteins were resolved at pH 4 to 7, followed by 12% SDS-PAGE. As a result 136 spots were successfully identified, representing the products of 46 unique genes. Of these, 22 gene products have not been previously identified in horse serum/plasma samples using proteomic tools. Gene ontology analysis showed that almost 30% of all identified gene products belong to the coagulation and complement cascades. These results can undoubtedly serve as a useful and prospective prerequisite for the future analysis of horse plasma proteome changes in different physiological and pathophysiological conditions. The use of the medium- and low-abundant protein enrichment tool increased their abundance and allowed us to identify a higher number of protein gene products. The highest depletion efficiency was observed for the most abundant plasma proteins, that is albumin, IgG heavy chains and serotransferrin.

The control of nutrient partitioning is complex and affected by many factors, among them physiological state and production potential. Therefore, the current model aims to provide for dairy cows a dynamic framework to predict a consistent set of reference performance patterns (milk component yields, body composition change, dry-matter intake) sensitive to physiological status across a range of milk production potentials (within and between breeds). Flows and partition of net energy toward maintenance, growth, gestation, body reserves and milk components are described in the model. The structure of the model is characterized by two sub-models, a regulating sub-model of homeorhetic control which sets dynamic partitioning rules along the lactation, and an operating sub-model that translates this into animal performance. The regulating sub-model describes lactation as the result of three driving forces: (1) use of previously acquired resources through mobilization, (2) acquisition of new resources with a priority of partition towards milk and (3) subsequent use of resources towards body reserves gain. The dynamics of these three driving forces were adjusted separately for fat (milk and body), protein (milk and body) and lactose (milk). Milk yield is predicted from lactose and protein yields with an empirical equation developed from literature data. The model predicts desired dry-matter intake as an outcome of net energy requirements for a given dietary net energy content. The parameters controlling milk component yields and body composition changes were calibrated using two data sets in which the diet was the same for all animals. Weekly data from Holstein dairy cows was used to calibrate the model within-breed across milk production potentials. A second data set was used to evaluate the model and to calibrate it for breed differences (Holstein, Danish Red and Jersey) on the mobilization/reconstitution of body composition and on the yield of individual milk components. These calibrations showed that the model framework was able to adequately simulate milk yield, milk component yields, body composition changes and dry-matter intake throughout lactation for primiparous and multiparous cows differing in their production level.

To understand the production factors that affect conclusive parameters of sow herd performance can improve the use of the resources and profitability of farm. The objective of this study was to identify associations and quantify the effects of a set of factors related to piglet weight at weaning (PWW), kilograms of piglets weaned per sow per year (kgPWSY) and sow feed conversion (SFC). Data from 150 farms were collected, for a total study population of 135 168 sows, including gilt replacement, breeding (mating), gestation and farrowing/lactation phases. A questionnaire focusing on reproductive performance, management, facilities, feeding, health and biosafety was administered. Multiple linear regression models were used to assess associations among factors with each of the three dependent variables. Increased duration of lactation was positively associated with PWW, kgPWSY and SFC. The increase in the number of live born pigs per litter was positively associated with kgPWSY and with SFC. Farms with higher PWW had farrowing room humidifiers, did not surgically castrate male piglets and used quaternary ammonia compounds for farrowing room disinfection. Farms with higher kgPWSY used lined ceilings in farrowing rooms and winter feeds with higher CP percentages in gestation; they also had more farrowings per sow per year. Sow feed conversion was worse in farms with partly slatted floors during gestation, in farms feeding lactating sows six times a day or ad libitum and farms with a higher sow-handler ratio. This study indicates that farms can increase PWW and kgPWSY and improve the SFC by changing one or more management, biosafety and feeding practices or facilities as well as by focusing on improving several performance parameters, particularly increasing the duration of lactation and the number of live born pigs per litter.

Definition and establishment of a fixed reference lactation length could provide useful tools for on-farm comparison of ewes and flock management as well as genetic evaluations for the breeding programme. The objectives of this study were to (i) evaluate different reference lactation lengths for the Chios dairy sheep and (ii) define the most suitable reference length for the breed. A total of 260 042 test-day milk records from 24 474 ewes in 130 flocks collected between 2003 and 2014 were used; 15 different lactation lengths were evaluated ranging from 120 to 260 days, defined at 10-day intervals as reference for the Chios sheep. The evaluation criteria included: (a) heritability and repeatability of milk yield in each reference lactation, (b) genetic correlation of reference lactation milk yield with actual lactation milk yield and yield at first test-day record and (c) correlated response in reference lactation milk yield from selection based on first test-day milk yield. The latter emulates genetic gains achieved for milk yield based on early lactation selection. Heritability and repeatability estimates of reference lactation milk yield and genetic correlation with actual lactation yield favoured long reference lactations (180 to 230 days). On the contrary, correlation with first test-day record milk yield was higher for short lactations (120 to 170 days). Moreover, selection on first test-day record milk yield would lead to a correlated response in reference yield in 220 days equal to 85% of the highest estimate achieved in the maximum reference length of 260 days (190 days when only considering first lactation milk yield). Based on the results of the present study, an overall reference lactation length for the Chios breed of 220 days post-lambing and a first lactation reference length of 190 days post-lambing are recommended.

Two groups, A and B, each consisting of 12 Greek indigenous goats suckling single kids were traditionally fed during a 36-week lactation period. During the suckling period (6 and 12 weeks for the groups A and B, respectively) milk production was estimated at 7-day intervals. During the milking period (30 and 24 weeks for the groups A and B, respectively) the goats were hand milked twice daily and their milk production was measured at intervals of 4 weeks. Milk samples were analysed for fat, protein, lactose, ash and dry matter concentration. Solids-not-fat and energy concentration were calculated. During lactation the goats were weighed weekly up to week 12 and monthly thereafter and body condition score was assessed at each weighing.

Goats with a 6-week suckling period produced significantly less milk throughout lactation but significantly more marketable milk than those with a 12-week suckling period. Yield peaked at the 6th and 10th weeks of lactation respectively, then declined rapidly and tailed off gradually from weeks 7 and 16 respectively. Milk composition was affected only occasionally by the duration of the suckling period. Thus, fat concentration was higher for the group with the 6-week suckling period between weeks 7 and 16, whilst protein was higher between weeks 8 and 12. Lactose concentration was lower for the same group between weeks 7 and 11, whilst ash concentration was similar in both groups. Live weight and body condition of the goats throughout lactation showed similar changes in both treatment groups.

Sheep farming in the UK is characterized by a crossbreeding system where ‘Longwool’ sire breeds are mated with hill dam breeds, with the crossbred (F1) ewe lambs retained for mating to terminal sires. The F1 wether and terminal-sire cross lambs are marketed for meat. At selection, F1 females are typically assessed visually for type traits relevant to dam lines, and these traits could be considered as goal traits. Their offspring and their male sibs derive their value from carcass traits. This study investigated the genetic relationships between type (subjective) and carcass (objective) traits in F1 lambs, and their potential impact on genetic improvement within this production system. Bluefaced Leicester rams were crossed with Scottish Blackface and Hardy Speckled Face ewes to produce F1 (‘Mule’) lambs. The wether lambs (no.=2197) were selected for slaughter at a target condition (a carcass fat score of 2/3L) and a number of live and carcass traits were measured. Carcass dissection data were collected on approximately one-third of these wether lambs. The ewe lambs (no.=2423) were measured for similar live traits but at a fixed age (195±5·5 days). In addition, they were subjectively assessed for a number of functional and type traits. Genetic parameters among these traits were then estimated. Heritabilities for the ewe traits were generally moderate (0·18 to 0·31) and genetic correlations between the traits were variable, with some moderate to high correlations (favourable in direction) of growth/carcass traits with overall type traits. Live weight at slaughter in wethers was highly correlated to live weight at constant age in ewes (r=0·72). In the wethers, live, cold carcass and lean weight had moderately high heritabilities (between 0·26 and 0·46), and were positively correlated with slaughter age (≥0·79). However, age at slaughter in wethers was highly negatively correlated with growth/carcass and overall type traits in ewes (between −0·45 and −0·97), perhaps reflecting differences in maturity in lambs measured at a target fatness versus age. The correlations of most other type traits in ewes with wether traits were non-significant. These results show that the subjectively assessed type traits (at least as measured in this study) will not deteriorate, and some will in fact be improved, in a selection programme aiming to improve carcass merit.

Data were extracted from Meat and Livestock Commission records from 44 herds with 392 progeny-tested sires in both farm and station environments. The farm data contained 4182 and 17 251 male and female progeny respectively, and the station data 2982 and 1490 male and female progeny respectively. Both sets of data were adjusted separately for the effects of month of test within sex. The farm data were also corrected to a constant end-of-test-weight corresponding to that at the station. Comparisons were made between both different and the same sexes in the two environments. Phenotypic correlations between a simple index measure in both environments ranged from +0·20 (farm females:station males) to +0·30 (farm females:station females). Genetic correlations between similar traits ranged from –018 (weight/age, farm males:station females) to +081 (simple index, farm males:station females). The correlations between female farm progeny and station male progeny were generally lower than for any other comparisons.

Cardio-respiratory and mechanical work output variables were measured for four F1 crossbred dairy cows (average weight 475 kg) over a range of work levels. Resting (standing prior to exercise) heart rates (average 62 beats per min) and respiratory rates (average 21 breaths per min) were similar to those previously reported for cattle of similar weight. Minute ventilation was 0·146 l/min per kg. Resting oxygen uptake (average 0·0057 l/min per kg) was higher than values that have been reported for cattle under more relaxed conditions.

The cows were exercised on an oval track by undertaking two bouts of activity for 500 m with a 5-min intervening recovery period. Walking increased minute ventilation by approximately 60 I/min and heart rate by 30 beats per min. Pulling a loaded sledge increased these variables further to approximately 200 l/min and 135 beats per min at 32 kg/min (530 W), the highest work level studied. The calculated oxygen pulse was 72 ml per heart beat, with maximum oxygen consumption approximately 9 l/min.

Overall ivorking efficiency increased with work level to a maximum of approximately 26% at the highest work level. At this level the cows were pulling proportionately about 0·14 of their body weight.

During periods of recovery after work, the cardio-respiratory parameters varied as would be expected and recovery was usually complete within 7 min.

This paper evaluates the consequences of using the wrong genetic model when predicting the merit of previously untested crossbred genotypes. Eight models are considered, seven including different biological interpretations of two-locus epistatic interaction, plus one excluding epistatic effects. Published results from 13 genotypes generated from Hereford and Angus parental breeds were analysed, and predictions of a further seven genotypes made using different models. Under a dominance model, the predicted superiority in pregnancy rate (%) of a ¾ Hereford: ¼ Angus composite over a two-breed rotation was +1·2%, yet under all other models this was a negative value ranging from –1·9% to –3·7%. However, few such cases were found in which significant decision errors could conceivably be made. It is concluded that decisions on the choice of crossbred genotypes are generally quite robust to differences in the genetic model of the type studied here

Melatonin treatment in adult cashmere goats can increase cashmere yield and improve cashmere fibre quality by inducing cashmere growth during cashmere non-growth period, of which time cashmere goats are in the mid and late stages of lactation. However, whether melatonin treatment in adult cashmere goats affects their offspring’s growth performance remains unknown. Therefore, the objectives of the current study were to determine the effects of melatonin treatment in adult cashmere goats on cashmere and milk production performance in dams and on hair follicle development and subsequent cashmere production in their offspring. Twenty-four lactating Inner Mongolian Cashmere goat dams (50 ± 2 days in milk, mean ± SD) and their single-born female offspring (50 ± 2 days old, mean ± SD) were randomly assigned to one of two groups supplemented with melatonin implants (MEL; n = 12) or without (CON; n = 12). The melatonin implants were subcutaneously implanted behind the ear at a dose of 2 mg/kg live weight on two occasions – 30 April and 30 June 2016. The results demonstrated that melatonin treatment in adult cashmere goats increased cashmere production and improved cashmere fibre quality as indicated by greater cashmere yield, longer cashmere fibre staple length, finer cashmere fibre diameter and thicker cashmere fibre density. The milk fat content was higher in MEL compared with CON cashmere goats. The daily yields of milk production, milk protein and milk lactose were lower in MEL compared with CON cashmere goats. Serum melatonin concentrations were greater, serum prolactin concentrations were lower and milk melatonin concentrations and yields were greater in MEL compared with CON cashmere goats. With regard to offspring, there were no differences in cashmere yield, fibre staple length, fibre diameter and fibre density at yearling combing, and the primary and secondary hair follicles population and maturation between treatments. In conclusion, melatonin treatment in adult cashmere goats during cashmere non-growth period is a practical and an effective way in cashmere industry as indicated by not only increasing cashmere yield and improving cashmere fibre quality in adult cashmere goat dams but also having no impairment in hair follicle development and the subsequent cashmere production in their single-born offspring.

The objective of the two studies was to determine the bioavailability of threonine (thr) and tryptophan (trp) in peanut meal, relative to l-thr and l-trp, for starter pigs using the slope-ratio bioassay. Basal diets (BDs) contained surfeit amounts of all amino acids for 10 to 20 kg pigs, except for thr (Experiment 1) or trp (Experiment 2). In the first study, four reference diets were formulated by supplementing the BD with 0, 0.4, 0.8 or 1.2 g of l-thr/kg at the expense of cornstarch; two test diets were formulated by replacing cornstarch in the BD with peanut meal at 32 or 64 g/kg of diet to supply 0.4 or 0.8 g thr/kg, respectively. Four reference diets consisting of the BD supplemented with 0, 0.15, 0.3 or 0.45 g of l-trp/kg at the expense of cornstarch and two test diets in which cornstarch in the BD was replaced with peanut meal at 30 or 60 g/kg of diet to supply 0.14 or 0.28 g trp/kg, respectively were used in the second study. Body weight gain responded in a linear way to supplemental l-thr or thr from peanut meal (P < 0.001). There was a linear response (P < 0.001) to thr supplementation from l-thr or peanut meal in gain-to-feed ratio. The addition of trp to the BD linearly increased (P < 0.05) body weight gain, feed intake and gain-to-feed ratio regardless of the trp source. Common-intercept, multiple linear regression in slope-ratio methodology using weight gain or gain-to-feed ratio as dependent variables and supplemental thr intake as independent variable gave relative bioavailability estimates of 71.9% or 75.7%, respectively. Corresponding values for trp were 92% and 75.7%. The fiducial limits for none of the relative bioavailability estimates included 100%. The data from these studies suggest that the bioavailabilities of thr and trp in peanut meal are less than those of l-thr and l-trp, and that the bioavailabilities of thr and trp in peanut meal are 72% to 76% and 76% to 92%, respectively.

Elevated dietary nitrate (NO3−) is associated with production losses in ruminant livestock, resulting in substantial economic losses incurred by producers. Severe drought, fertilization practices and poorly maintained pastures increase the risk of elevated NO3− intake among cattle and sheep. Nitrate is metabolized to nitrite (NO2−) in the rumen and further reduced to ammonia. Ruminants consuming high dietary NO3− vary in ability to efficiently reduce excess NO2− to ammonia. This leads to methemoglobin formation and ultimately NO3− toxicity signs. Variation in individual tolerance to elevated dietary NO3− can be partially attributed to rate and duration of exposure, rate of elimination, metabolism, species and dose. Our objectives were to confirm and quantify variation in individual tolerance to subacute levels of dietary NO3−, and determine if individuals could be identified as highly or lowly tolerant to elevated dietary NO3− based on production traits, plasma analytes and(or) signs of subacute NO3− toxicity. Purebred Suffolk ewes were administered supplement mixed with tap water (control; n = 8) or potassium nitrate (NO3− treated; 300 mg NO3−/kg BW daily; n = 47) for 8 days. Coefficients of variation (CV) indicated that supplement intake was more variable in NO3− treated ewes (CV = 59.3%) than in control ewes (CV = 13.6%). Among NO3− treated ewes, six ewes highly tolerant and six ewes lowly tolerant to elevated dietary NO3− were identified based on individual performance, NO3− treated supplement intake, and signs of toxicity. Supplement intake was lower (P < 0.0001) in NO3− treated ewes than in control ewes, indicating elevated dietary NO3− influences feed intake. Supplement intake differed (P < 0.0001) between control, highly tolerant and lowly tolerant ewes. Supplement intake of highly and lowly tolerant ewes was 82% and 23%, respectively, of the control ewes’ intake. Weight change and plasma concentrations of NO2−, cortisol, glucose and retinol were not different (P ⩾ 0.38) among control, highly tolerant and lowly tolerant ewes. Plasma urea nitrogen (PUN) levels were not different (P = 0.25) between control and lowly tolerant ewes, but were lower (P = 0.02) in highly tolerant ewes than in control ewes. Furthermore, PUN and NO3− treated supplement intake were highly correlated (0.71; P < 0.0001) in lowly tolerant ewes. These results confirm and quantify variation in response to subacute levels of dietary NO3− and indicate that individuals can be identified as highly or lowly tolerant to elevated dietary NO3− based on their performance and NO3− toxicity signs.

Voluntary hay intake and milk yield were measured in 11 singlesuckling and 4 twin-suckling ewes for the first seven weeks of lactation. There was no significant difference between the intakes of the two classes of ewe and milk yield differed only in the seventh week. Variations in milk yield and live-weight change were significantly associated with variations in voluntary intake. Lamb weight gain was correlated with milk yield and voluntary intake of the dam.

In a multibreed experiment in which 292 heifers from 25 breeds were given a single complete pelleted diet ad libitum, body weight and food intake were recorded every 2 weeks. Relative growth rate, relative food intake and food conversion efficiency were calculated as the ratio of weight gain to body weight, food intake to body weight and weight gain to food intake respectively. The traits were measured over 12-week intervals from 12 to 72 weeks of age, and also over longer intervals of 24, 36, 48 and 60 weeks, each beginning at 12 weeks of age. Relative growth rate and food conversion efficiency declined continuously with increasing age, whereas relative food intake increased to a maximum in the 24- to 36-week period and then declined continuously.

The between-breed genetic coefficient of variation (CVb) for relative food intake was very stable at about 0·04 whether measured over 12-week or longer intervals, whereas the CVVs for relative growth rate and food conversion efficiency were usually higher when measured over 12-week intervals compared with longer intervals. For the entire period from 12 to 72 weeks, the CVb was estimated as 0·029 for relative growth rate, 0·040 for relative food intake and 0·034 for food conversion efficiency. The corresponding intraclass correlations (t2) measuring the between-breed variation as a proportion of the total variation were estimated as 0·08, 0·18 and 0·15. Within-breed variation was thus much greater than between-breed variation for all three traits. Using published estimates of within-breed heritabilities, the parameters g21 measuring the between-breed genetic variation as a proportion of the total genetic variation, and g22, measuring the between-breed genetic variation as a proportion of the immediately selectable genetic variation, were estimated as 0·28 and 0·61 for food conversion efficiency and 0·25 and 0·57 for relative growth rate. Thus, for all three traits, despite their low CVb and t2 values, between-breed selection would be useful prior to within-breed selection.

1. Five hundred and fifty-two pigs were used in an experiment having six treatments. High and low protein rations were given (a) unsupplemented, (b) supplemented with 0·1% copper sulphate (CuSO4·5H2O) and (c) supplemented with 0·1% copper sulphate and 0·025% zinc carbonate (ZnCO3).

2. Performance was significantly reduced and 18 pigs died from copper toxicosis, when the low protein ration supplemented with copper sulphate was fed.

3. There were no indications of toxicity and performance was equal to the controls when the low protein diet supplemented with copper and zinc was fed.

4. The addition of copper to the high protein diet slightly reduced performance and six pigs died from copper toxicosis.

5. The addition of copper and zinc to the high protein diet improved growth rate and eliminated the toxicity associated with copper supplementation.

6. No significant treatment effects on haemoglobin or packed cell volume were observed, other than a small effect of protein level on PCV.

7. Copper supplementation of the diets significantly increased liver and kidney copper levels and liver zinc levels. It reduced liver and kidney iron contents. The addition of copper and zinc to the diet reduced the increase in liver copper associated with copper supplementation, and increased the level of zinc in both livers and kidneys.