With an increase in the number of candidate genes for important traits in livestock, effective strategies for incorporating such genes into selection programmes are increasingly important. Those strategies in part depend on the frequency of a favoured allele in a population. Since comprehensive genotyping of a population is seldom possible, we investigate the consequences of sampling strategies on the reliability of the gene frequency estimate for a bi-allelic locus. Even within a subpopulation or line, often only a proportion of individuals will be genotype tested. However, through segregation analysis, probable genotypes can be assigned to individuals that themselves were not tested, using known genotypes on relatives and a starting (presumed) gene frequency. The value of these probable genotypes in estimation of gene frequency was considered. A subpopulation or line was stochastically simulated and sampled at random, over a cluster of years or by favouring a particular genotype. Line was simulated (replicated) 1000 times. The reliability of gene frequency estimates depended on the sampling strategy used. With random sampling, even when a small proportion of a line was genotyped (0·10), the gene frequency of the population was well estimated from the across-line mean. When information on probable genotypes on untested individuals was combined with known genotypes, the between-line variance in gene frequency was estimated well; including probable genotypes overcame problems of statistical sampling. When the sampling strategy favoured a particular genotype, unsurprisingly the estimate of gene frequency was biased towards the allele favoured. In using probable genotypes the bias was lessened but the estimate of gene frequency still reflected the sampling strategy rather than the true population frequency. When sampling was confined to a few clustered years, the estimation of gene frequency was biased for those generations preceding the sampling event, particularly when the presumed starting gene frequency differed from the true population gene frequency. The potential risks of basing inferences about a population from a potentially biased sample are discussed.

The effects of food quality, breed type and sex (ram and ewe) on lamb growth and carcass composition, and their changes throughout growth, were measured. The three breed types were Scottish Blackface (B; no. = 24), Suffolk (S; no. = 28) and their reciprocal crosses (X; no. 33). The lambs had free access to a nutritionally non-limiting food, H, or a bulky food, L. Each lamb was scanned using X-ray computed tomography to measure the weights of fat, lean and bone in the carcass at three degrees of maturity (0.30,0.45 and 0.65) in live weight. Live weight and food intake data were recorded weekly. Average daily gains in live weight (ADG) and carcass tissues, intake (ADI) and efficiency (EFF = ADG/ADI) were calculated for each lamb between degrees of maturity. Gompertz and Spillman functions were used to investigate relationships between weight and both time and cumulative food intake.

There was a breed by food interaction for fat and lean proportions (P < 0.05). Only on H was there a breed difference (P < 0.05) with S having less fat and more lean than either B or X, which did not differ from each other (P > 0.1). On food L there were no breed effects (P > 0.1). Across breeds, sexes and stages of maturity, food L caused lambs to have 0.810 as much fat and 1.063 as much lean compared with H (P < 0.001). There were breed by food interactions for ADG (P < 0.05) and EFF (P < 0.01). ADG on L was 0.72 of that on H for S, as compared with 0.79 for B and X. EFF on L was 0.463 of that on H for S, as compared with 0.586 for B and X. These were such that S was more sensitive to food effects on growth. The Gompertz and Spillman functions described growth well.

This paper addresses the inheritance of host resistance to gastro-intestinal nematode parasite infections in commercial Texel lambs, and the rôle of resistance to parasites in breeding programmes. In two flocks of Texel sheep, faecal egg counts following natural parasite challenge were measured on up to three occasions post weaning per lamb over a 4-year period, with 1385 and 287 lambs measured on the two farms. Live weight, and ultrasonically measured fat and muscle depth at weaning were available for each lamb, as were deep pedigrees. Egg counts were moderately to strongly heritable on all occasions, with Nematodirus egg counts more heritable than the Strongyle egg counts. Weighted average heritabilities for Strongyle and Nematodirus egg counts were 0.26 and 0.38, respectively. Within the same category of parasite, genetic correlations across time were positive and strong but somewhat less than unity, as were the correlations between Strongyle and Nematodirus egg counts measured at the same time. Genetic correlations between performance traits and Strongyle egg counts were usually favourable (i.e. negative) but weak, whereas those with Nematodirus egg counts were generally neutral or slightly positive. Whilst Nematodirus resistance may not necessarily be included in a breeding goal, the results suggest that Nematodirus egg counts can be used as an additional genetic indicator of Strongyle egg counts, at little extra cost. Including the epidemiological consequences of decreasing Strongyle egg counts in benefits of increasing parasite resistance, it is suggested that under UK conditions selection goals that place equal emphasis on live weight and log-transformed egg counts will be a robust means of improving growth rate and decreasing parasite larval challenge.

Reproductive performance is receiving increased attention from beef cattle producers. There are concerns that intensive selection for carcass traits might reduce the reproductive performance of females. Genetic parameters among six carcass traits and, age at first calving (AFC), gestation length (GL), days open (DO) and calving interval (CI) under year-round artificial insemination were estimated. Reproductive traits were extracted from 174005 calving records of Japanese Black cows and were analysed with 31364 carcass records. The restricted maximum likelihood procedure under animal models was used to estimate the parameters. Heritabilities of AFC, GL, DO and CI were estimated to be 0.20, 0.40, 0.05 and 0.05, respectively, and those of carcass traits were higher, ranging from 0.38 to 0.56. Genetic correlations of CI with AFC and GL were 0.25 and 0.16, respectively, while no relationship was observed between AFC and GL. Correlations among carcass traits were generally favourable and a slightly negative estimate was obtained between subcutaneous fat thickness and marbling score. Genetic correlations for AFC were -0.27 with carcass weight and -0.24 with marbling score. In contrast, GL, DO and CI were genetically independent of carcass traits. Genetic relationships between reproductive and carcass traits were generally low, and therefore serious antagonism was not observed. The results suggested that selection for carcass traits would not compromise genetic progress in reproductive traits.

An analysis of the length of productive life in the Bruna dels Pirineus beef breed was performed with a non-parametric approach giving an average value of 9 years of productive life, and a corresponding replacement rate of 11%. Using a proportional hazards model stratified by herd, the influence of calf birth weight and weight gain until weaning, calving difficulty, calving interval and age at first calving on length of productive life were studied. Two models were explored: the first one included time-dependent variables taking the current value of the covariate at each calving date, while the second one also comprised time-dependent interactions between the value of the covariate of the current calving and its mean value during the last (up to) three previous calvings. Results from the first model showed that the risk of culling increases with very high ages at first calving, increasing calving difficulties, very large calf birth weights, very small weight gains until weaning and very long calving intervals. Furthermore, results from the second model showed that these increases also depend upon a sequence of values for the same covariate in previous calvings. Finally, these higher risks of culling implied lower survival functions that increased replacement rates but only slightly decreased average performances.

The purpose of this study was to assess the deposition of fat, protein and energy during the growth period of lambs. Male and female lambs (no. = 54 of each) were fattened (three feeding levels) and slaughtered at various body weights (BW): 18, 30, 45, and 55 kg. Based on the method of the comparative slaughter technique the total body of each animal was analysed. From the data of empty-body gain, fat, protein and energy deposition in the different fattening periods was calculated.

The male lambs showed at all body weights tested and in all feeding level groups a lower daily fat deposition and a higher daily protein deposition compared with the female lambs. The deposition of fat increased in both genders with increasing body weight. The amount of increase differed between the three feeding levels. The male lambs showed at all body weights and in all feeding level groups a higher daily gain in body weight but a lower daily deposition of energy compared with the female lambs. However, for the latter, the gender difference rarely reached statistical significance. Parallel to the daily deposition of fat the daily deposition of energy increased in both genders with increasing body weight.

Based on the deposition of fat and protein during the growth period of the lambs the body composition was estimated by allometric equations. The equations showed a consistent pattern of protein concentration falling and fat concentration rising with increasing empty body weight. Compared with the literature a higher protein and lower fat concentration in empty body gain was predicted.

Sheep of a line selected on an index to increase carcass lean content at 150 days of age (selected (S); no. = 90), and an unselected control line (control (C); no. = 90), were given ad libitum foods of three different protein concentrations (192, 141 and 120 g/kg dry matter). Growth was measured from about 21 to 114 kg live weight. The carcasses of each line were analysed for lean, fat and bone at three widely varying weights in both males and females. Level of protein did not affect the extent to which S was superior to C in the content of fat (0.86 as much) or lean (1.08 as much) in the carcass. The fat concentration of the carcass increased, and the lean concentration decreased, as dietary protein concentration was reduced (P < 0.01). On the highest level of protein used, the S line grew 1.17 times as fast and was 1.10 times as efficient compared with C. The extent to which growth rate in S exceeded that in C was greater on the highest level of protein used (92.3 g/day) than on the two lower protein diets (26.4 g/day). The difference of 65.9 (s.e. 18.4) g/day was significant (P < 0.01). On the diet of highest protein concentration, growth was well described by a Gompertz function. The S line had an estimated maximum growth rate 1.25 times that of the C when averaged across males and females. A Spillman function was used to describe weight in terms of cumulative intake. It worked well for all three levels of dietary protein concentration. S sheep performed better than unselected sheep on foods differing in protein concentration and over a wide range of live weights, suggesting benefits are likely within the diverse farming environments found in practice.

Salbutamol (albuterol) is a β-adrenergic agonist marketed as a racemic (50: 50) mixture of R- and S-enantiomers (rac-salbutamol). Since only R-salbutamol is pharmacologically active and S-salbutamol has a longer half-life in humans, we examined R-salbutamol as a performance enhancer and repartitioning agent in domestic chickens. The effects of feeding diets containing R-salbutamol (5, 10 and 15 mg/kg diet) and rac-salbutamol (10 mg/kg diet) from day 21 to 42 post hatching on growth performance, carcass characteristics and tissue concentrations of R- and S-salbutamol in male and female broilers were compared with a control diet. R-salbutamol in the diet lowered the weight gains in both sexes, but the magnitude of reduction was greater in males as indicated by a significant R-salbutamol ✕ gender interaction. R-salbutamol also lowered food intake and improved food conversion ratios in both sexes. The relative weights of breast muscle and leg muscle were significantly increased and the relative weight of the fat pad was significantly decreased in birds of both sexes given diets containing R-salbutamol. Carcass protein content increased and carcass fat content decreased but the differences were not statistically significant. A significant dose-response effect was observed for tissue concentrations of R-salbutamol in all tissues, except the fat. Performance and carcass parameters in chickens given the 5 mg/kg R-salbutamol diet were similar to those given the 10 mg/kg rac-salbutamol diet, but tissue concentrations of R-salbutamol were lower. Chickens given the 10 mg/ kg rac-salbutamol diet had higher tissue concentrations of salbutamol than chickens given the 10 mg/kg R-salbutamol diet and higher concentrations of S-salbutamol than R-salbutamol in liver and leg muscle. Overall, these results demonstrate that R-salbutamol is an effective repartitioning agent in broiler chickens.

Most animal growth models contain an explicit growth function. It determines the pattern of growth over the lifetime of the animal and defines an upper limit to growth rate (the potential). The criterion of the ‘goodness-of-fit’ to one or more sets of data is frequently used to select a suitable growth function. Alternative criteria are described here that can be used to choose between forms that describe potential growth. Of the functions reviewed only a few fulfilled all of the proposed criteria. Of these the Logistic and Gompertz functions were favoured because of an economy of parameters and their ability to describe relative growth rate as a simple function of size. The Logistic function was rejected on the grounds of its numerical consequences for growth in pigs over a wide range of degrees of maturity, leaving the Gompertz function to be tested for its ability to make sensible predictions of potential growth. Pre-natal growth data, assumed to occur under non-limiting conditions as long as the mother is not subjected to extremely adverse nutritional conditions or incidence of infection, were used to estimate the values of the two Gompertz function parameters-the growth coefficient and the initial condition-given an estimate of mature size. The values were comparable with literature estimates based on post-natal growth and predictions of growth rate over a wide range of degree of maturity were thus sensible. On these grounds, and because it uses few parameters all with biological meaning, the Gompertz function is proposed as a suitable descriptor of potential growth.

Four diets were arranged using a 2 ✕ 2 factorial design with two levels of lignocellulose, a high ‘HF’ or a low level ‘LF’ (acid-detergent fibre (ADF) = 191 v. 155 g/kg), combined with two levels of starch replacing 50 g/kg of digestible fibre (DF = hemicelluloses + pectins), a high starch (low DF) ‘HS’ or a low starch (high DF) level ‘LS’ (starch = 193 v. 123 g/kg). Two trials were conducted to measure digestive efficiency and rate of passage, respectively. A third trial was performed in a network of six French experimental breeding units to measure growth and digestive health on 507 rabbits per diet. Foods were offered ad libitum from weaning to slaughter.

No significant interactions were detected between the effect of the level of lignocellulose and the effect of starch replacement by DF, on rabbit digestion, performance or digestive health. A proportional increase of overall food digestibility (organic matter (OM) or energy) was observed with the decrease of ADF level. When 50 g/kg of DF was replaced by starch we observed a significant improvement of OM and energy digestibility ( + 0·03 units). The whole-tract mean retention time of particles was 21 h. It was significantly longer with a lower ADF level ( + 5·4 h for LF v. HF diets), and it tended to increase when DF was substituted by starch ( + 2·2 h for HS v. LS diets).

Between weaning and slaughter, food intake was mainly affected by the ADF level (139 v. 130 g/day respectively for HF and LF diets) and to a lesser extent by the replacement of DF by starch (136·2 v. 133·4 g/day, respectively for LS and HS diets). The weight gain was only slightly higher for high starch (low DF) diets ( +1 g/day) without an effect of the ADF level.

Between weaning and slaughter, morbidity and mortality rates (from acute diarrhoea) were significantly reduced with high-fibre diets (-6 and -4 units respectively), while the replacement of DF by starch had no significant effect.

Major gene-marker phase is generally assumed to be family specific. This has the consequence in relation to marker-assisted selection (MAS) that phase information about each family may need to be collected through progeny testing, which could represent a substantial cost. This paper examines the effect of different policies in relation to major gene-marker phase-typing on response to MAS. The different policies considered varied in the criteria by which individuals were selected for phase-typing, the number of individuals phase-typed, and the frequency of establishing phase. Stochastic simulation of a closed breeding nucleus, with either high or low levels of inbreeding and undergoing selection for two traits, was utilized. Total response under MAS was lower than that under genotypic assisted selection (GAS) for all phase-typing policies. For example, additional gains of 70% under GAS, achieved in year 1 and in comparison with non-MAS, corresponded to additional gains of 43% and 15% under MAS for linkage distances of 1 cM and 20 cM, respectively. The different phase-typing policies examined in relation to MAS did not have any effect on total response, although there were small effects on major gene response. For breeding nuclei with either level of inbreeding, higher major gene response was achieved when phase-typed sires were selected on the basis of high ranking for genetic merit rather than connectivity to the other selection candidates. Further, increasing the number of males phase-typed within any year did not increase the rate of major gene response, although phase-typing in more years was favourable for the large linkage distance. An overall conclusion of this study is that additional gain could be achieved under MAS within a closed nucleus when progeny testing to determine major gene-marker phase was limited to from one to a few individuals.

The objectives of this study were to investigate the effects of vitamin A (retinol) on growth hormone (GH) secretion and circulating insulin-like growth factor-1 (IGF-1) concentration in Japanese Black steers. Thirteen 10-month-old Japanese Black steers were divided into two groups: high vitamin A (H) group and low vitamin A (L) group. The animals in the H group were injected with 20 ml retinol palmitate (303 mg as retinol) intramuscularly every month throughout the experimental period. The steers in the L group were injected with vitamin A similarly at the age of 10 to 14 months. All steers were given vitamin A with the food (approx. 100 μg as retinol per kg diet) at the age of 21 to 30 months to prevent clinical vitamin A deficiency. Blood samples for analyses of vitamin A and IGF-1 were collected every 2 months. Series of blood samples for analyses of GH were collected at 15-min intervals over a 6-h period from each animal at the age of 10, 20, and 30 months. Although there was no difference in food intake between the two groups (P > 0·05), the average daily gain of the H group was greater (P < 0·001) than that of the L group. The carcass weight and subcutaneous fat thickness of the H group were significantly greater (P < 0·05) than those of the L group. The longissimus muscle area (P < 0·01) and marbling score (P < 0·001) of the L group were significantly greater than those of the H group. The serum retinol concentrations of the L group were significantly lower (P < 0·01) than those of the H group from the age of 16 months. The serum IGF-1 concentrations of the L group gradually decreased and were significantly lower (P < 0·01) than those of the H group from the age of 18 months. The overall mean concentration, peak height, area under the curve, and nadir of GH in both groups decreased with age. However, there were no significant differences (P > 0·05) in overall mean GH concentration, peak number, peak height, area under the curve, or nadir between the two groups. These results indicate that vitamin A affects the IGF-1 levels, with little or no intermediary effect on GH.

Classification of pig carcasses in the European Community (EC) is based on the lean meat percentage of the carcasses. The lean meat percentage is predicted from instrumental carcass measurements, such as fat and muscle depth measurements, obtained in the slaughterline. The prediction formula for an instrument is derived from the data of a dissection experiment. When the relationship between percentage lean and instrumental carcass measurements differs between subpopulations, such as sexes or breeds, accuracy of prediction may differ between these subpopulations. In particular for some subpopulations predicted lean meat percentages may be systematically too low and for other subpopulations systematically too high. Producers or buyers that largely specialize in subpopulations where the percentage lean is underestimated, are put at a financial disadvantage.

The aim of this paper is to gain insight, on the basis of real data, into the effects of differences between subpopulations on the accuracy of the predicted percentage lean meat of pig carcasses. A simulation study was performed based on data from dissection trials in The Netherlands, comprising gilts and castrated males, and trials in Spain, comprising different genetic types. The possible gain in accuracy, i.e. reduction of prediction bias and mean squared prediction error, by the use of separate prediction formulae for (some of) the subpopulations was determined.

We concluded that marked bias in the predicted percentage lean meat may occur between subpopulations when a single overall prediction formula is employed. Systematic differences in predicted percentage lean between subpopulations that are overestimated and underestimated may exceed 4% and for selected values of instrumental measurements may run up to 6%. Bias between subpopulations may be eliminated, and prediction accuracy may be markedly improved, when separate prediction formulae are used. With the use of separate formulae the root mean squared prediction error may be reduced by 13 to 26% of the expected value when a single prediction formula is used for all pig carcasses.

These are substantial reductions on a national scale. This suggests that there will be a commercial interest in the use of separate prediction formulae for different subpopulations. In the near future, when the use of implants becomes more reliable, subpopulations will be recognized automatically in the slaughterline and use of different prediction formulae will become practically feasible. Some possible consequences for the EC regulations and national safeguards for quality of prediction formulae are discussed.

Two groups of 12 Belgian Blue double-muscled cull females were used successively in a 2-year repeated experiment and divided into three groups according to age, allowing four animals per group each year. The aim of the trial was to relate, during the finishing period, the metabolic and endocrine parameters with age. Females were fattened with a diet based on maize silage and were blood sampled on several occasions. The average daily gain (ADG) decreased with the age of the cows. Plasma glucose and triglycerides decreased also with age while the youngest females showed lower concentrations of urea than those older. The composition of plasma non-esterified fatty acids also differed considerably between groups. The hormones that best related with ADG were IGF-1 and insulin. Plasma concentrations of thyroid hormones were lower in the oldest animals. No difference between groups was found for GH. Heifers presented lower concentrations of GH and IGF-1 than those reported elsewhere in fattening bulls of the same breed. It may be concluded that in Belgian Blue double-muscled females, glucose, IGF-1 and insulin are good indicators of the growth potential. Young adult cows presented intermediate characteristics of metabolic and endocrine status that were close either to younger or to older cows.

Due to the structure of the placenta in the horse (epitheliochorial) and the as yet un-activated immune system of the foal at birth, the transfer of maternal immunoglobulin G (IgG) is essential in the protection of the young foal until its own immune system develops. The fluidity of intestinal cell membranes may affect the transfer of IgG by receptor mediated endocytosis. In the present experiment we studied the effect of the addition of supplements rich in either alpha-linolenic acid or oleic acid to the diet of the mares starting 1·5 months before foaling and for 1 month after foaling on the passive transfer of IgG and the fatty acid composition of mammary secretions and plasma of foals. Twenty-six mares were allocated to one of two treatment groups (L: linseed supplement, no. = 13 and R: rapeseed supplement, no. = 13) according to date of foaling and live weight to produce two homogeneous groups. Mammary secretions were collected to measure IgG and fatty acid composition. Jugular blood samples were taken from the foals at time 0, 12 h, 24 h, 48 h, 1 week, 2 weeks, 3 weeks and 4 weeks after foaling to measure the concentration of IgG. A subsample of foals was used to measure the IgG absorption coefficient and the plasma fatty acid compositon. There was no effect of dietary treatment on the length of gestation, the production and transfer of IgG. Group L mares produced mammary secretions which were richer in C18: 3 and poorer in C18: 1 than group R mares (P < 0·001). Contrary to expectations the C18: 3 content of blood from foals at birth from both dietary treatments was very low and there was no difference between dietary groups. The percentage of C18: 3 and C18: 2 in fatty acids increased in foal blood only after sucking had occurred, with a difference between dietary groups (L > R). In addition, the percentages of C20: 3 and C20: 4 were higher in the foals at birth than 48 h later (P < 0·001) and at birth they were highest in the R group compared with the L group foals (P < 0·05 and P 0·10, respectively). In conclusion, the attempt to increase the supply of C18: 3 during gestation to foals and to improve the transfer of IgG post partum did not appear to succeed, perhaps because the foal uses C22: 6 (produced from C18: 3) for brain growth.

A visual image analysis (VIA) system provided continuous, automatic collection of size and shape data for a total of 116 pigs slaughtered serially from 25 to 115 kg live weight. Males and females of three types of pigs (‘Meishan’ type, ‘Pietrain’ type, and ‘Landrace’ type) were selected to provide variation in both composition and conformation (the three types being, respectively, ‘fat’, ‘blocky’, and ‘lean’). Results below are presented in this order. Regression analysis was used to relate VIA size to platform weigher (FIRE) measurements of live weight. Residual maximum likelihood (REML) analysis showed that at the observed growth rate, a change in pig state could be detected by VIA after 8, 9, and 10 days respectively for the three types, and by the platform weigher system after 12, 4, and 13 days (in both cases with a confidence of 95%). Artificial neural network and canonical variates analysis were used to test the ability of VIA to distinguish between pig types and sexes. With cross validation, the canonical variates analysis correctly classified the three types in 72, 83, and 64% of observations, and the neural network in 81, 81, and 64% of observations. The VIA system is considered to be a valuable monitoring system which may play a rôle in the construction of integrated management systems (IMS).

The effect of vitamin A (retinol) on ovine stearoyl-CoA desaturase (SCD) mRNA levels and fatty acid composition was investigated. Sheep adipose tissue explants were maintained in culture for 24 h in the presence of all-trans retinoic acid (RA). Tissue SCD mRNA levels were increased with 25 μmol/l RA but the levels of SCD mRNA in tissue treated with 100 μmol/l RA were not different from control. The effect of vitamin A supplement on SCD mRNA levels in vivo was then characterized: growing lambs were given a concentrate diet (2 kg/day) containing 0, 0.225, 1.125 and 3.375 mg vitamin A per kg diet for 21 days. Treatment resulted in a concentration-dependent increase in adipose tissue and liver SCD mRNA levels, although the greatest effect was seen in the liver. SCD mRNA levels were highest in tissue from animals given 0.225 mg vitamin A per kg diet and further increases in vitamin A supplementation were not accompanied by corresponding increases in SCD gene expression. Fatty acid composition was also determined. Overall, tissue from animals given vitamin A had greater levels of both palmitoleic and oleic acid relative to their precursors. These data clearly show that SCD gene expression in adipose tissue and liver is regulated by retinoic acid and the liver appears to be most responsive. However, although significant, the change in the proportion of oleic acid was only small indicating that dietary manipulation with vitamin A is not a suitable method for increasing the unsaturated fat content of sheep meat.

An experiment was conducted to examine the digestible energy (DE) content for weanling pigs in a cohort of wheats grown in Western Australia, and to establish relationships between DE content and their chemical composition. The 3 ✕ 3 ✕ 2 factorial experiment examined the wheat variety (Arrino, Stiletto and Westonia), growing location (high, medium and low rainfall zone) and harvest year (1999 and 2000). Pigs (no. = 5 per diet) aged about 28 days were given a diet at a level of 0·05 ✕ live weight containing 900 g/kg of the wheat and an acid-insoluble ash marker for 10 days, with samples of faeces collected from each pig for the final 5 days. The average live weight of pigs was 6·6 (s.d. 0·77) kg. The DE content of wheats harvested in 1999 varied by up to 1·3 MJ/kg, while wheats harvested in 2000 varied by up to 1·8 MJ/kg. When the 2 years’ data were combined, the DE content ranged from 12·5 to 14·4 MJ/kg. Both the variety and growing region significantly influenced (P < 0·05, P < 0·001, respectively in year 1999; P < 0·001, P < 0·01, respectively in year 2000) the DE content of wheat. Also, DE content of wheat differed significantly due to growing season (P < 0·001). Correlation studies between chemical composition and DE content of the wheats found significant inverse relationships between DE content and total xylose (r = –0·719, P < 0·05), insoluble xylose (r = –0·742, P < 0·05), neutral-detergent fibre (r = –0·839, P < 0·01), total-P (r = –0·833, P < 0·01), and phytate-P (r = –0·753, P < 0·05) contents with the wheats harvested in 1999. However, such relationships were not significant (P > 0·05) with the wheats harvested in 2000. In addition, the precipitation level (mm) during the growing season of wheats was strongly correlated (r = –0·821, P < 0·01) to the DE content of wheat in year 1999, but was not correlated in 2000. The results indicate that the genetic and environmental conditions during the growth of wheat have a significant impact on the utilization of plant energy in weaner pigs, and that greater attention needs to be paid to these influences in the assignment of energy values for wheats given to weaner pigs.

A study was conducted to compare the performance of Mukota, Large White (LW) and LW ✕ Mukota F1 pigs given increasing levels of maize cob meal. Sixteen female weaners of each genotype were given, ad libitum, diets containing 0, 100, 200 and 300 g maize cob meal per kg of diet for 14 weeks. The diets were designed to contain similar levels of protein (ca. 160 g crude protein per kg) and energy (ca. 9 MJ metabolizable energy per kg). Average daily food intake per unit metabolic body weight (ADFI per kg M0·75), average daily gain (ADG) and food conversion ratio (FCR) were determined. The pigs were slaughtered and cold dressed mass (CDM) and backfat thickness were determined for each pig. The ADFI per kg M0·75 was similar among the four diets for the three genotypes. The rate of decline in ADG was higher (P < 0·05) in the LW than in the other two genotypes. The FCR in the Mukota was poorer (P < 0·05) than that in the LW and the F1 crosses. The Mukota had the highest (P < 0·05) backfat thickness (K5 and K7·5) values of the three genotypes across the four diets, followed by the F1 crosses. The CDM values for the LW and the F1 crosses were similar and were higher (P < 0·05) than those for the Mukota. The findings indicate that F1 crosses and the Mukota were better able to utilize diets containing high levels of maize cob meal than LW pigs.

A 3 ✕ 2 factorial experiment was conducted to investigate the interaction between lactofeed 70 (LF70) (860 g/kg whey permeate, 140 g/kg soya-bean meal, Volac International, UK) levels and soya-bean meal inclusion (SBM) (90 and 225 g/kg) from day 0 to day 25 after weaning (starter period) on growth performance and diet digestibility. A common diet was offered from day 25 to day 38. Dietary treatments were established by substituting LF70 for extruded wheat and soya-bean meal for potato protein (PP) and soya protein concentrate (SPC). Digestible energy and amino acids were maintained by adjusting soya oil and synthetic amino acids. A total of 252 pigs (7·7 kg and 28 ± 2 days of age) were allotted randomly to six treatments containing (1) 0 LF70 with 40 g/kg PP and 40 g/kg SPC and 90 g/kg SBM (2) 0 LF70 with 225 g/kg SBM (3) 175 g/kg LF70 with 40 g/kg PP and 40 g/kg SPC and 90 g/kg SBM (4) 175 g/kg LF70 with 225 g/kg SBM (5) 350 g/kg LF70 with 40 g/kg PP, 40 g/kg SPC and 90 g/kg SBM and (6) 350 g/kg LF70 with 225 g/kg SBM. There was an increase in average daily gain (ADG) (0·182 v. 0·292 v. 0·318 kg, s.e. 0·0089; P < 0·001) and food intake (0·413 v. 0·472 v. 0·489 kg, s.e. 0·0139; P < 0·01) and an improvement in food conversion ratio (FCR) (2·31 v. 1·63 v. 1·55 kg, s.e. 0·037; P < 0·001) as the level of LF70 increased during the starter period. From day 25 to day 38, the pigs given the starter diets containing no LF70 had an improved ADG (P < 0·05) and FCR (P < 0·001) compared with the pigs given 175 and 350 g/kg LF70. The pigs offered diets containing 350 g/kg lactofeed had a significantly higher N digestibility (P < 0·05) than the pigs offered diets containing no lactofeed. There was a significant interaction (P < 0·001) between LF70 and SBM in the apparent digestibility of gross energy (GED). Pigs given higher SBM diets had a higher GED at the 350 g/kg LF70 inclusion than pigs given PP + SPC diets. However, there was no difference in GED at the 0 and 175 g/kg LF70 inclusion. In conclusion, the inclusion of LF70 increased ADG, food intake and apparent N digestibility and improved FCR.