Force-feeding was considered as a traditional high-efficiency approach to improve growth performance and accelerate fat deposition of Pekin ducks. However, force-feeding is a serious violation of international advocacy on animal welfare, because it can induce serious injuries to animals, such as damages to the digestive tract, effects on immunity and even severe oxidative stress. Therefore, it is urgent to stop force-feeding. The aim of this study was to determine the effects of force feeding on immune function, digestive function and oxidative stress in the mucosa of duodenum and jejunum of Pekin ducks. A total of 500 ducks were randomly divided into two groups. The control group was allowed to feed freely on a basal diet. The experimental group was force-fed by inserting a plastic feeding tube 8 to 10 inches long down the esophagus for 6 days. Compared with the control group, there was a significant (P<0.05) increase in serum diamine oxidase, d-lactic acid, endotoxin and corticosterone levels in the force-feeding group. The crypt depth in duodenum and jejunum showed significant differences (P<0.05) between the two groups and the intestinal villus epithelium cell was severely damaged in force-feeding group. Similarly, the activities of digestive enzymes as well as the levels of immune function in the duodenal and jejunal mucosa in the force-feeding group were significantly higher than the control group (P<0.05). However, there was a significant decrease in the superoxide dismutase, glutathione peroxidase and catalase levels with a marked increase in malondialdehyde level in duodenal and jejunal mucosa (P<0.05). In summary, at the end of the fattening period with force-feeding for 6 days, Pekin ducks experienced an adverse effect on the integrity of their duodenal and jejunal mucosa epithelium cell as well as their immune function and antioxidant capacity of Pekin ducks but also had improvement in digestive enzyme activities.

Replacing grass silage with maize silage results in a fundamental change in the ratio of structural to non-structural carbohydrates with commensurate changes in rumen fermentation patterns and nutrient utilisation. This study investigated the effects of feeding four forage mixtures, namely grass silage (G); 67 g/100 g grass silage + 33 g/100 g maize silage (GGM); 67 g/100 g maize silage + 33/100 g grass silage (MMG); maize silage (M) to four ruminally and duodenally canulated Holstein Friesian steers. All diets were formulated to be isonitrogenous (22.4 g N/kg DM) using a concentrate mixture. Dietary dry matter (DM) and organic matter (OM) digestibility increased with ascending maize silage inclusion (P < 0.1) whereas starch and neutral detergent fibre digestibility declined (P < 0.05). Ratio of non-glucogenic to glucogenic precursors in the rumen fluid increased with maize silage inclusion (P < 0.01) with a commensurate reduction in rumen pH (P < 0.05). Mean circulating concentrations of insulin were greatest and similar in diets MMG and GGM, lower in diet M and lowest in diet G (P < 0.01). There were no effects of diet on the mean circulating concentration of growth hormone (GH), or the frequency, amplitude and duration of GH pulses, or the mean circulating concentrations of IGF-1. Increasing levels of DM, OM and starch intakes with the substitution of grass silage with maize silage affected overall digestion, nutrient partitioning and subsequent circulating concentrations of insulin.

Social learning from peers can trigger herd-wide intoxication with white locoweed (Oxytropis sericea), an alkaloid-synthesizing herbaceous legume that grows on rangelands of western North America. We conducted an experiment to test the hypothesis that restriction of the area allocated to animals to feed in would inhibit social facilitation of locoweed ingestion in yearling heifers. Eight heifers that avoided white locoweed (LA) and eight heifers that readily consumed it (LE) were selected from a pool of 40 cross-bred heifers and were randomly assigned to the social facilitation or social interference treatment groups. We conducted 200 10-min feeding trials in three 5-day phases (pre-treatment, treatment, post-treatment) during which animals were presented with a set of bowls arrayed in a test arena, some of which contained ground wheat straw and others contained air-dried ground white locoweed. During the pre-treatment (days 1 to 5) and the post-treatment phases (days 11 to 15) non-social trials were conducted in which the feeding behavior of individual animals was investigated in an 80 m2 arena containing 12 feeding bowls. During the treatment phase (days 6 to 10) social learning trials were conducted in which LA + LE pairs from the social interference group were exposed to 12 bowls of food distributed in an 80 m2 arena intended to induce social interference, and LA + LE pairs from the social facilitation group were exposed to 36 bowls of food distributed in a 240 m2 arena intended to permit social facilitation. During pre-treatment phase, LA heifers consumed detectably less locoweed and wheat straw and exhibited lower preference for locoweed than LE (P ⩽ 0.05) although wheat straw preference of LA and LE was similar. During social learning trials (treatment phase), LA in the social interference group visited similar number of locoweed bowls (mean ± s.e.m.: 0.2 ± 0.12) as they had during non-social learning (0.2 ± 0.20). Conversely, LA heifers in the social facilitation group visited detectably more locoweed bowls during social learning trials (1.6 ± 0.46) compared with the pre-treatment phase (0.2 ± 0.16). Correlation between daily number of locoweed bowls visited by LA and LE during social learning trials was detected in the social facilitation (r = 0.70; P < 0.01), but not in the social interference group (r = 0.15; P = 0.52). During testing trials (post-treatment phase), locoweed and wheat straw intake and preference of LA and LE in both treatment groups was similar. Manipulation of the feeding environment delayed, but did not inhibit social learning of toxic weed ingestion in this study.

The rate of passage (ROP) in the gastrointestinal tract (GIT) influences the exposure time of food to the digestion and absorption processes. Consequently, ROP affects the efficiency of nutrient utilization and energy from the diet. This study aimed to determine the physiological parameters that characterize the digestive response, such as first appearance time (FAT), ROP, mean retention time (MRT) and transit time (TT) in adult Japanese quail (Coturnix coturnix japonica), and to evaluate the effects of sex, apparent metabolizable energy corrected for nitrogen balance (AMEn) content in the diet and different types of markers on these parameters. In the first trial, we investigated the effects of sex and AMEn level (high- and low-energy diet) on the FAT parameter. Thirty-two male and 32 female Japanese quail were randomly allocated to 8 battery cages and assigned to 4 treatments in a 2 × 2 factorial design with 4 replicates of 4 birds for each treatment. To determine the FAT, ferric oxide (1%) was added to the diet, and the excreta of the quail was monitored until the first appearance of the marker. The results indicated significant differences (P < 0.05) in the FAT between males (100 min) and females (56 min), regardless of the AMEn content. In the second trial, thirty-two 32-week-old female Japanese quail in the laying phase were assigned to four treatments in a 2 × 2 factorial design, in which the main independent variables were type of marker (Cr or Ti) and AMEn level (high- and low-energy diets). In order to determine ROP (ET1%), MRT and TT (ET100%), the markers (0.5%: Cr2O3 and 0.5%: TiO2) were added to the diets, and the excreta were collected for 750 min. The excretion times for 1% (ET1%), 25% (ET25%), 50% (ET50%), 75% (ET75%) and 100% (ET100%) were estimated using cumulative excretion curves. No effect was detected for the AMEn level (P > 0.05); however, the effect of different marker types was significant (P < 0.05). This difference increased with time and ET100% was estimated to occur at 59 min. The ROP was estimated to be 68 min. The TT was estimated to be 540 min using Cr and 599 min using Ti, with an average MRT value of 0930 h. Taken together, our findings support the hypothesis that Japanese quail digestion through the GIT can be dynamic and differ based on sex or marker type.

Effect of graded levels of high-glucosinolate mustard (Brassica juncea) meal as substitute of soya-bean meal (SBM) in broiler rabbit diets was studied. Forty weaning rabbits of Soviet Chinchilla and White Giant breed were randomly allocated to one of four experimental diets containing mustard meal (MM) 0, 80, 160 and 245 g/kg. The experiment lasted for 8 weeks. MM had 54.8 mg total glucosinolates (TGLSs) per g dry matter (DM). Diets had TGLS 3.8, 8.4 and 11.98 mg/g DM in 80, 160 and 245 g MM diets, respectively. MM-incorporated diets had higher digestible and linearly (P < 0.01) higher metabolisable energy (ME) content. However, the effect on total tract apparent digestibility of DM, and crude protein was quadratic. Average daily gain (ADG) reduced (P < 0.05) linearly with increasing MM levels in diet, still 80 and 160 g MM diets had similar ADG compared to that of SBM diet. Caecum weight reduced linearly (P < 0.05) with increasing MM levels in diet. The pH of caecal content ranged between 5.85 and 6.19, total N between 1.19 and 1.48 (g per 100 g) and total volatile fatty acids between 4.7 and 5.8 mmol per 100 g, and they were not statistically different. NH3-N ranged between 31.2 and 39.0 mg per 100 ml, and reduced linearly (P < 0.05) while trichloroacetic acid-precipitable nitrogen increased linearly (P < 0.01, ranged between 114 and 247 mg per 100 ml) with increasing MM levels in diet. Blood haemoglobin, packed cell volume and lymphocytes were higher (quadratic effects, P < 0.05) on 245 MM diet, whereas white blood cell count reduced linearly (P < 0.01). Serum aspartate aminotransferase increased linearly (P < 0.01) while alanine aminotransferase and alkaline phosphatase activity, protein, erythrocytes sedimentation rate and red blood cell counts were not affected by MM. Serum Cu, Na and K content increased linearly (P < 0.05) with increasing MM levels. Liver Cu concentration showed quadratic (P < 0.05) increase. Rabbits tolerated 8.4 mg TGLS per g diet (160 g MM per kg) during active growth without any apparent effect on health and growth. It is concluded that MM can replace up to 66% SBM protein in rabbit feeding, whereas complete replacement of SBM with MM reduced feed intake and ADG by 23% and 13%, respectively. Further studies are required to confirm these inclusion levels and glucosinolate tolerance of rabbits.

An efficient algorithm for genomic selection of moderately sized populations based on single nucleotide polymorphism chip technology is described. A total of 995 Israeli Holstein bulls with genetic evaluations based on daughter records were genotyped for either the BovineSNP50 BeadChip or the BovineSNP50 v2 BeadChip. Milk, fat, protein, somatic cell score, female fertility, milk production persistency and herd-life were analyzed. The 400 markers with the greatest effects on each trait were first selected based on individual analysis of each marker with the genetic evaluations of the bulls as the dependent variable. The effects of all 400 markers were estimated jointly using a ‘cow model,’ estimated from the data truncated to exclude lactations with freshening dates after September 2006. Genotype probabilities for each locus were computed for all animals with missing genotypes. In Method I, genetic evaluations were computed by analysis of the truncated data set with the sum of the marker effects subtracted from each record. Genomic estimated breeding values for the young bulls with genotypes, but without daughter records, were then computed as their parent averages combined with the sum of each animal's marker effects. Method II genomic breeding values were computed based on regressions of estimated breeding values of bulls with daughter record on their parent averages, sum of marker effects and birth year. Method II correlations of the current breeding values of young bulls without daughter records in the truncated data set were higher than the correlations of the current breeding values with the parent averages for fat and protein production, persistency and herd-life. Bias of evaluations, estimated as a difference between the mean of current breeding values of the young bulls and their genomic evaluations, was reduced for milk production traits, persistency and herd-life. Bias for milk production traits was slightly negative, as opposed to the positive bias of parent averages. Correlations of Method II with the means of daughter records adjusted for fixed effects were higher than parent averages for fat, protein, fertility, persistency and herd-life. Reducing the number of markers included in the analysis from 400 to 300 did not reduce correlations of genomic breeding values for protein with current breeding values, but did slightly reduce correlations with means of daughter records. Method II has the advantages as compared with the method of VanRaden in that genotypes of cows can be readily incorporated into the Method II analysis, and it is more effective for moderately sized populations.

Decline in fertility of high-producing dairy cattle has become a global challenge to the dairy industry. Because of low heritability and complexity, it is difficult to find genetic markers for fertility traits in cattle. Here, we report the use of an in vitro fertilization (IVF) system and candidate gene approach to test genetic associations of a single-nucleotide polymorphism (SNP) in bovine placental lactogen (bPL), and its interactions with SNPs in the prolactin receptor (PRLR) and growth hormone receptor genes with fertility traits in an IVF system. The associations suggest a possible involvement of genetic interactions between bPL and PRLR in the fertilization and embryonic development processes, and the potential for application in a marker-assisted selection program.

Measurements of live weight and of ultrasonic (Scanogram) fat depth and m. longissimus cross-sectional area at the 12th/13th rib were taken at 4— to 6-week intervals from 10 to 35 months of age (23 occasions) on 15 Hereford males (bulls), 15 castrate males (steers) and 15 females (heifers) managed under grazing conditions.

Mean rates of live-weight change throughout the measurement period (0·51, 0·47 and 0·39 kg/day for bulls, steers and heifers, respectively) were significantly different. When compared at the same ages, fat depth was similar in the steers and heifers, beginning at about 3 mm and increasing to 11 mm. Fat depth changed little in the bulls, beginning at 1·7 mm and increasing to 3 mm. At the same age, bulls had larger m. longissimus cross-sectional areas than steers and steers had larger muscle cross-sectional areas than heifers.

Absolute variation within sex groups increased throughout the experiment in live weight and fat depth, but not in m. longissimus crosssectional area. Simple correlation coefficients, pooled within sex groups, of relationships between the same measurements at various measuring occasions, indicated that measurements of fat depth and of muscle cross-sectional area at 10 to 12 months of age are poor indicators of these measurements at periods of 6 months or more later in life.

When compared at the same live weights, heifers had the greatest and bulls had the smallest fat depth and, within animals, fat depth was closely related to live weight. At any live weight, m. longissimus cross-sectional area was less in heifers than in steers and bulls, which were not significantly different from each other in this trait. Equations relating fat depth and muscle area to live weight are presented and, under the conditions of this study, indicate that there is no basis for adjustment of fat depth for live weight in bulls subjected to contemporaneous selection.

Fish meal and monensin, as supplements to grass silage, were offered either separately or together to Friesian steers from 5 to 9 months of age (period 1). At 9 months, six steers from each of the supplemented treatments were slaughtered to determine body composition. Of the remaining steers, from 9 months of age to slaughter at 490 kg live weight (LW) (period 2), six continued on each of the same treatments, whilst six received silage unsupplemented. A further group of six steers which had received fish meal and monensin during period 1, received monensin only as a supplement to their silage.

During period 1 fish-meal supplementation increased LW, empty body and carcass weight gains, and tissues gains, while monensin had no apparent effect. During period 2, continued supplementation with both fish meal and monensin significantly increased LW, empty body and carcass gains compared with the continuously unsupplemented steers, whilst fish meal and monensin separately produced intermediate increased gains. All three supplement regimes significantly reduced the time taken to reach slaughter.

The only significant effect on body composition was that steers receiving fish meal and monensin had a higher crude protein concentration in the empty body than those receiving only fish meal as a supplement. They also had the highest crude protein concentration in the carcass, although this was not significant. Steers which had their supplements withdrawn after 9 months of age generally maintained gains intermediate between those continuing to receive supplements and those steers unsupplemented throughout. Only those not continuing to receive fish meal and monensin together appeared to perform appreciably worse. Nevertheless, although time taken to reach slaughter from 4 months of age varied by as much as 96 days, there were no other significant differences in body or carcass composition, hi terms of cost effectiveness, use of monensin showed distinct advantages over fish meal.

A feeding trial was carried out, using 180 pigs, to assess the effect on performance when intact male and female pigs were housed together in the same pens from 20 to 90 kg live weight. There were no significant differences in daily feed intake, rate of growth or feed: gain ratio between pigs from mixed-sex pens and pigs from single-sex pens. Carcass measurements indicated slightly leaner carcasses for intact male pigs whether housed in separate pens or together with female pigs, while female pigs likewise had a significantly higher dressing percentage.

The repeatability of ultrasonic backfat readings under field conditions was measured in a sample of 57 adult male (boars) and 77 young adult female (gilts) pigs. Repeatabilities of individual fat depths 6·5 cm off the mid-line at the shoulder, mid-back and loin ranged from 0·74 to 0·90. The repeatability of average backfat thickness was 0·92.

A system of feeding concentrates at a flat rate was compared with a step system in which the rate was reduced every 6 weeks. Each system was evaluated at either medium or high level concentrates. There were two trials involving 40 British Friesian cows for weeks 3 to 20 of lactation. The flat rate treatments were 71 (medium) and 9·3 kg dry matter (DM) per day (high) and corresponding step allocations were 8·8, 7·1 and 5·4 kg DM per day or 11·7, 9·3 and 7·0 kg DM per day. Silage was given to appetite. In trial 1 this was lucerne silage of moderate quality (metabolizable energy (ME) = 8·9 MJ/kg DM) and in trial 2 high quality grass silage (ME = 11·1 MJ/kg DM) was used.

In the comparison between systems of concentrate allocation, food intakes, milk production and live-weight change were similar in each trial. In the comparison between medium or high levels of concentrates, silage DM intakes were similar in trial 1 (7·1 v. 7·0 kg/day) but not in trial 2 (9·8 v. 8·7 kg·day, P < 0·05), and milk yields were lower in trial 1 (19·0 v. 21·4 kg/day, P < 0·001) but not in trial 2 (24·1 v. 25·2 kg/day). Milk composition was similar for medium and high concentrate intakes in both trials. Cows given the medium level of concentrates had higher live-weight losses than those given the high level in trial 1 (–58 v. –24 kg, P < 0·01) and trial 2 (–22 v. –kg). When concentrates were given at the medium level with moderate quality silage several cows had acetonaemia. Also, this feeding combination, especially when concentrates were given at a flat rate, reduced the proportion of cows which conceived within a limited breeding period.

A series of experiments was conducted to examine the potential of using ammonia released from the hydrolysis of urea for alkali treatment of straw.

In an initial experiment (1) the effect on urea hydrolysis of adding either hydrochloric acid (HC1) or the surfactant alkyl phenyl ethylene oxide to straw of differing dry matter (DM) concentration was examined. The inclusion of HC1 or surfactant failed to improve the proportion of urea hydrolysed at straw DM concentrations of 450, 600 or 750 g/kg.

In experiment 2, straw was prepared and treated with urea, at a level of 20 (U2), 50 (U5), 70 (U7) g/kg straw DM and ammonia 40 (A4) g/kg straw DM to compare with untreated straw (S). Samples of the straws were milled and degradability at 60 h was estimated using the nylon bag technique. DM loss was significantly higher for all treated straws compared with untreated straw (P < 0·001). However, the proportion of added nitrogen retained from all urea treatments was less than 0·33 but U7 and U5 were approximately double that obtained from A4.

In experiment 3, 3-t batches of straw equivalent to treatments U2, U7, A4 and S were treated during September and later offered to steers in digestibility and food intake trials. Straws were ground through a 40-mm screen and offered to steers in digestibility stalls, in a balanced incomplete-block design. There were increases in the digestibility of DM (+0·08 g/kg), organic matter (+0·08 g/kg), and acid-detergent fibre (+0·09) of U7 and A4 straw compared with values for untreated straw (P < 0·01).

In a subsequent food intake trial treatment of long straw, with 20 g urea per kg straw DM (U2) failed to prevent moulding, however digestible organic matter intake (DOMI) of U7 and A4 straws increased by 0·42 and 0·27 kg/day respectively compared with intakes of untreated straw (P < 0·01). The application of 70 g urea per kg straw DM gave results comparable with treatment with 40 g ammonia per kg straw DM in improving digestibility of ground straw and the DOMI and preservation of long straw.

Sixteen castrated male Large White × Landrace pigs were employed to investigate the muscle type-specific changes of gene expression in response to recombinant porcine growth hormone (rpGH) administration. Pigs were injected intramuscularly with rpGH (4 mg/day, n = 8) or saline (n = 8) for 28 days. Semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) was used to determine the mRNA abundance of genes related to muscle growth in longissimus dorsi (LD) and semitendinosus (ST) muscles. Myofibre-type composition was characterised by the ratio of the expression of myosin heavy chain (MyHC) 1, 2a or 2b relative to 2x. The results showed that the relative myofibre-type composition of neither LD nor ST was affected by rpGH administration. rpGH administration did not induce significant changes in the abundances of myostatin and myogenin mRNA in both types of muscle. MyoD and calpain 3 mRNA were significantly increased after rpGH treatment in ST muscle, whereas the difference was not significant in LD muscle. A tendency of down-regulation was observed for PGC-1α mRNA expression in ST muscle of rpGH-treated group (P = 0.16). These results suggest that myoD, calpain 3 and probably PGC-1α may be involved in the mechanism of exogenous GH action on skeletal muscle growth; rpGH up-regulates mRNA expression of myoD and calpain 3 in a muscle type-specific manner, being more remarkable in ST than in LD, whereas no influences of rpGH on the mRNA expression of myostatin and myogenin were detected.

The effect of the high fecundity Booroola Merino gene (F) on wool production and live weight of Booroola x South Australian Merino rams classified as being offspring of FF, F+ or ++ Booroola sires was investigated. The characters studied were: greasy fleece weight in lambs, hogget (approx. 15 months old) greasy fleece weight and the associated scouring yield, clean fleece weight, fibre diameter, staple length and wool style; birth weight and live weight gains from birth to weaning in September (3 months of age), from September to the following March, and from March to September. There were no significant differences among sire genotypes in the characters studied. The results suggest that the F gene had no undesirable pleiotropic effects on wool and live-weight traits.

A simulation study, based on a closed sheepmeat breeding nucleus and incorporating marker-assisted selection (MAS), was used to evaluate response when different proportions of animals were marker typed. Two traits were included in the simulation: trait 1, a production trait where phenotypes were available prior to selection, and trait 2, a carcass trait where phenotypic information was not available on breeding animals. Selection on an index which comprised estimated breeding values (EBVs) for both traits was possible by calculating EBVs for trait 2 as the sum of EBVs for a polygenic component, obtained from a genetic regression, and EBVs for a major gene component, obtained by inferring genotypes at a major gene locus from a linked marker locus. Different marker typing strategies were evaluated. These differed in the criteria used to select progeny for typing, and in the proportion of male and female progeny selected. Typing progeny that were likely to be used as a breeding animal, but excluding those whose marker genotype could be predicted with reasonable certainty, was an efficient genotyping strategy. Close to maximum gain at the major gene locus was achieved when only a proportion of animals were marker typed (for example 90% of maximum response was achieved with a little over one-third of the selection candidates marker typed). This indicates the potential for substantial savings in relation to the cost of marker typing in commercial breeding flocks.

A technique is described for assessing the profitability of selecting sheep for wool production. A model of the breeding system incorporating three submodels is developed: one to represent the flock from which the selection intensities for rams andewes are calculated; a second to determine gains made in wool production and the year in which they accrue; and the third uses discounting procedures to examine the economics of selecting for wool production.

Flock and genetic parameters were set at ‘average’ values for an Australian Merino wool producer and gains were determined for a range of lambing percentages. Three measures were used to evaluate profitability; the net present value of the programme which shows overall profits, the internal rate of return, which gives the earning rate of the programme, and the payback period, which identifies the number of years before early costs are repaid.

sensitivity analysis was used to examine changes in the three measures of profitability resulting from changes in interest rate, wool price, costs for labour and computer analysis, wool testing costs and lambing percentage. Profitability was sensitive to changes in all parameters except wool testing charges, and of the remainder the producer has a degree of control only over labour costs. A programme can be profitable, however, if wool price and lambing percentage are adequate and costs can be kept at reasonably low levels. Simple breeding programmes should be studied in which labour inputs are kept to a minimum or where costs are confined to studs (nuclei) and genetic gain disseminated by the sale (migration) of rams.

1. The area of eye muscle cross-section of beef carcasses may be accurately measured by tracing the boundary and measuring the tracing with a planimeter. Taking a single area measurement from each of duplicate tracings increases the accuracy by some 30%. If a planimeter is not available, the area may be estimated by superimposing a grid on the tracing and counting squares; although this method is some 25% less accurate than the planimeter method it is sufficiently repeatable for experimental use.

2. Area estimated by combinations of linear measurements is highly repeatable, but predicts true area with insufficient accuracy for experimental use. The standard error of prediction is about 7% of the mean area. Regression equations relating planimeter area and combinations of measurements for various cuts and animals are given.

The ability of the protein nutrition scheme proposed by the Agricultural Research Council (ARC, 1980, 1984) to predict responses to protein supply was examined in two experiments. In experiment 1, groups of nine British Friesian steers implanted with oestradiol-17β and nine non-implanted steers were fed from 133 to 300 kg live weight on each of four all-concentrate diets (metabolizable energy (ME) = 12 MJ/kg dry matter (DM)) containing ratios of soya-bean meal and formaldehyde-treated soya-bean meal such that undegradable protein (UDP) concentration was 19, 25, 32 or 42 g/kg DM. Rumen degradable protein (RDP) concentration was relatively constant (111 to 116 g/kg DM). Implantation did not affect DM intake (DMI, g/kg M0·75). Both live-weight gain (LWG) and food conversion efficiency (FCE) (LWG/DMI) were greater (P < 0·05) for the implanted cattle (LWG = 1·41 (s.e. 0·04) kg/day; FCE = 0·24 (s.e. 0·02)) than for the non-implanted cattle (LWG = 1·23 (s.e. 0·05) kg/day; FCE = 0·22 (s.e. 0·02)). There were no dietary effects on either DMI or FCE. In the non-implanted steers, UDP did not affect LWG but, for the implanted steers, there were positive, linear responses in LWG to both UDP concentration (P = 0·048) and UDP intake (P = 0·026). In experiment 2, groups of eight implanted steers were fed from 132 to 300 kg live weight on each of six diets (ME = 12 MJ/kg DM, soya-bean meal and formaldehyde-treated soya-bean meal as chief protein sources) supplying 17, 26, 34, 39, 54 and 82 g UDP per kg DM and concentrations of RDP up to 1·5 times ARC recommendations. There was no effect of UDP on either DMI or FCE but positive, linear responses in LWG to both UDP concentration (P = 0·019) and UDP intake (P = 0·010). In both experiments, mean DMI exceeded that predicted by ARC (1980) (P < 0·05). LWG predicted by the ME system and the ARC protein scheme was not significantly different from observed LWG for non-implanted steers, but was an underestimate of observed LWG for implanted steers (P = 0·002 in experiment 1, P < 0·001 in experiment 2). Observed responses in LWG to UDP concentration were also poorly predicted (regressions of observed on predicted LWG: experiment 1, r2 = 0·12, residual s.d. = 0·126; experiment 2, r2 = 0·004, residual s.d. = 0·119). It was concluded that oestradiol-17p has significant effects on responses in LWG to UDP, which are not predicted by the current ARC (1980, 1984) protein nutrition scheme.