Uterine capacity was estimated in Chinese Meishan (MS), Large White (LW) and crossbred (LW × MS) sows, using unilateral liysterectomy-ovariectomy (UHO) methods. In the first two parities, 20 sows of each genotype, whose left uterine horn and ovary had been removed in the post-pubertal period, were mated, their ovulation rate recorded by laparoscopy and allowed to farrow normally. In the third parity the mated sows were slaughtered at around 30 days of pregnancy and ovarian, uterine and embryo traits were recorded. The ovulation rate in UHO females was similar to that observed previously in intact females of the same population, MS sows producing 4·2 (s.e. 1·0) more ova at parities 1 and 2 and 7·0 (s.e. 1·9) more ova at parity 3 than LW sows. At parity 3, MS sows had 5·9 (s.e. 2·0) more viable embryos at 30 days of pregnancy than LW sows. Crossbred sows were intermediate for both ovulation rate and the number of viable embryos at 30 days. At the first two parities, litter size was higher in the MS by 1·0 (s.e. 0·8) piglets per litter than in the LW, while the crossbred sows exceeded the mid-breed mean by 1·7 (s.e. 0·7) piglets. Uterine capacity, estimated as twice the number of piglets carried to term in a single horn, was 12 foetuses in the LW, 14 in the MS and 16 in the crossbred sow. Piglets born to MS sows were 0·4 (s.e. 0·1) kg lighter than those born to LW sows, with a significantly lower (MS: LW = 0-68, P < 0·01) within-Utter standard deviation, which was found to be independent of the smaller mean weight. At parity 3, MS sows were found to have uteri of similar length with both lighter (-0·36 (s.e. 0·14) g) and shorter (-1·54 (s.e. 0·76) mm) embryos with smaller spaces (-7·8 (s.e. 2·7) cm) between embryo sites than LW sows. Within-Utter standard deviations for embryo size traits were lower in MS than in LW sows, especially for the distance between embryo sites (MS: LW = 0·45, P<0·01). The reduced variability of embryo traits in litters in MS sows was independent of their smaller litter means. Third parity litters from crossbred sows were similar to the mid-breed mean for means and variability of embryo traits but crossbred sows had significantly longer uteri (48·5 (s.e. 18·5) cm) than the mid-breed mean, being longer than either pure breed. It was concluded that differences between the pure breeds in uterine capacity may have arisen through better within-uterus organization, whereas the observed heterosis effects may result in part from physically longer uteri in crossbred sows and that uterine capacity contributes to the genotype differences in prenatal survival and prolificacy, especially in crossbred sows.

Growth and survival from birth to weaning were monitored during three generations of crossbreeding between British Large White (LW) and Chinese Meishan (MS) pigs. The design allowed comparisons between sow genotypes ranging from zero to all MS genes, which were mated toLWor MS boars, to produce progeny with proportions of 0·0 to 0·5 or 0·5 to 1·0 MS genes, respectively. Crossbreeding parameters of both maternal and direct piglet performance were estimated for the first two parities using restricted maximum likelihood (REML) methods for litter traits (litter weight at birth, litter mean and within litter standard deviation of piglet weight at birth, proportion surviving to weaning, litter size and weight at weaning and litter mean piglet weight at weaning) and for traits of the piglet (birth weight, probability of survival and weaning weight). For litter traits, the estimated contribution of the additive maternal effect to the breed differences (MS-LW) was significant for litter mean piglet birth weight (–0·46 (s.e. 0·04) kg), survival to weaning (0·15 (s.e. 0·02)), litter size at weaning (1·6 (s.e. 0·16) piglets), litter weaning weight (–11·2 (s.e. 3·8) kg) and litter mean piglet weaning weight (2·54 (s.e. 0·24) kg). Adding litter size and litter mean piglet birth weight to the model removed the additive maternal contribution to the breed differences in survival, and litter size and reduced that for litter mean piglet weaning weight. The contribution of the direct additive effect to the breed difference (MS-LW) was significant for the within litter standard deviation in birth weight (0·018 (s.e. 0·006)), survival to weaning (0·12 (s.e. 0·02)) and litter size (1·12 (s.e. 0·64)) and weight (11·6 (s.e. 4·0) kg) at weaning, but not for piglet weight at birth or weaning. Fitting litter size and litter mean birth weight had comparatively little impact on the direct additive effects. There were significant maternal heterosis effects for litter weight at birth and litter size and weight at weaning, the estimated deviation of the F1 from the midpoint of the two purebreds 3·22 (s.e. 0·55) kg, 2·20 (s.e. 0·47) piglets, and 20·1 (s.e. 3·3) kg respectively, but none for survival or piglet weights. There were direct heterosis effects for litter weight and litter mean piglet weights, the estimated deviation of the Fjfrom the mid point of the two purebreds being 1·16 (s.e. 0·41) kg and 0·14 (s.e. 0·02) kg, for survival to weaning (0·04 (s.e. 0·02)) and for litter weight (11·2 (s.e. 2·5) kg) and litter mean piglet weight (0·96 (s.e. 0·17) kg) at weaning. Fitting litter size and litter mean piglet birth weight removed or reduced both maternal and direct heterosis effects. Individual piglet analyses gave similar results to analyses of the equivalent sow trait. It was concluded that in litters born to MS cows, the lower piglet survival and lower weaning weights were related to the larger litter sizes and lower piglet birth weights. For their birth weight, however, MS piglets have a greater ability to survive and thrive. The large direct and maternal heterosis effects observed for litter and mean piglet weight at weaning werepartly associated with the heavier birth weight of the crossbred piglet.

Correlated responses in reproductive performance to five generations of divergent selection for daily food intake (DFI), lean food conversion (LFC), lean growth rate on ad–libitum feeding (LGA), and lean growth rate on scale feeding (LGS) were studied. Litter traits were measured on 1220 Large White gilts. Mean litter weights at birth and weaning were 12·9 kg and 63·5 kg, with average litter sizes of 10·3 and 7·9. Responses to selection in the high and low lines for litter size in the DFI and LFC selection groups were 1·9 and –1·5 (s.e.d. VI) at birth and 0·9 and –1·8 (s.e.d. 1·2) at weaning. Responses in litter birth weights were respectively positive and negative for DFI and LFC (3·0 and –2·8 (s.e.d. 1·4) kg) and the response in LGS (3 kg) was greater than in LGA (–0·1 kg). Selection line differences in litter weaning weight followed a similar pattern to birth weight for DFI and LFC (17·5 and –17·3 (s.e.d. 10·1) kg). Responses in litter weights were a result of selection line differences in both litter sizes and piglet weights. The relationships between litter size, litter weights and piglet weights at birth and weaning were essentially linear. An extra piglet at birth and weaning corresponded to an increase of 1·0 (s.e. 0·02) kg and 6·9 (s.e. 0·1) kg in litter weights. Piglet birth and weaning weights were decreased by 0·03 (s.e. 0·003) kg and 0·19 (s.e. 0·02) kg. A uterine constraint on piglet growth was implied, but there was no evidence for a limit to uterine capacity. Heritabilities for litter size, weight and piglet weight at birth of 0·06, 0·11 (s.e. 0·04) and 0·16 (s.e. 0·02) respectively were similar to those at weaning. Common environmental effects on piglet weights at birth and weaning were substantially higher than the heritabilities (0·38 and 0·45, s.e. 0·01). The study indicated that selection for lean growth on either an ad–libitum or restricted feeding regime did not significantly affect reproductive performance, but the high lean food conversion ratio and low daily food intake selection lines had impaired reproductive performance.

Fifty-four multiparous Yorkshire × Landrace sows were allocated equally to receive an intramuscular (i.m.) injection of 3 ing oestradiol-17β (E2) or no injection at 112 days of gestationto determine the effect of E2 on the timing and duration offarrowing. All sows received an injection (i.m.) of 10 mg prostaglandin F2x af 113 days of gestation. Of the soivs allocated to treatment, 21 oestrogen-treated and 19 control sows were assigned to be observed for the onset of parturition. A further six oestrogen-treated and eight control sows were included to increase the data base for litter production. The time of piglet delivery was monitored between 08·00 and 18·00 h on day 114 of gestation. Blood samples were obtained from each offour piglets from four E2-treated and five control litters. More E2-treated (8/21) than control sows (1/19) farrowed before 08.00 h of day 114 (P < 0·05) although, for those sows farrowing during the observation period, there was no effect on the time to onset or duration of parturition. Plasma oestradiol concentrations were higher (P < 0·06) in piglets delivered by E2-treated sows. However,this was not associated with any effect on piglet pre-weaning survival. It is concluded that exogenous oestradiol can influence the timing of onset offarrowing in some sows. Although further refinement in terms of timing of E2 injections is required, it seems likely that exogenous E2 may have a useful role to play in hastening the induction of parturition in sows.

Stochastic simulation was used to compare the results of alternative breeding systems in a sheep population divided into 10 flocks of 120 ewes. The breeding systems compared were selection within closed flocks (CF), a closed nucleus system (CNS), an open nucleus system (ONS) and open nucleus systems with the selection of nucleus replacements being restricted to either nucleus born males (ONSRm) or nucleus born females (ONSRf). Selection was for a best linear unbiased prediction of breeding value for lamb live weight which had a heritability of 0·17. The open nucleus breeding systems (ONS, ONSRm, ONSRf) resulted in higher rates of genetic gain, more predictable selection responses and lower rates of inbreeding than either the closed nucleus system (CNS) or selection within closed flocks (CF). Initial genetic differences between flocks resulted in higher rates of genetic gain in the nucleus breeding systems due to the use of between flock genetic variance. In the ONS system up to 25% of nucleus sires and approximately 50% of nucleus dams were born in base flocks. Nevertheless if selection of either nucleus sires or dams was restricted to nucleus born animals there was very little change in genetic gain or rate of inbreeding.

Intact male pigs from two nucleus breeding herds (one predominantly Duroc, DM; the other purebred Large Wliite, LM) together with intact male (RM), castrated male (RC) and female (RF) commercial hybrid pigs were given one of two diets, with the same balanced protein (180 or 240 g/kg) at three daily rates, the highest being ‘to appetite‘. Six replicates of 30 pigs were allocated to these regimes at 40 kg: one replicate was slaughtered immediately to determine initial carcass composition; the remaining pigs were slaughtered at 85 kg when carcass fat and specific gravity (SG) were measured. For two replicates this was followed by dissection and chemical analysis: daily gains of carcass lipid and protein were estimated directly for these two replicates and predicted from carcass weight and SG for the other three. Fed ‘to appetite’, castrated males and females ate more than males; LM pigs ate least. All males grew faster than females or castrated males, the DM pigs the fastest, these rankings being relatively insensitive to feeding level. However, both in daily weight gain and daily protein accretion only the males responded to additional dietary protein. Daily body protein accretion of DM pigs increased linearly with intake on both diets whereas LM pigs showed little response to the highest level of feeding. At the same daily protein intake all pigs had higher rates of body protein accretion on the low protein diet, showing that they were sensitive to additional dietary energy. Results indicate that an animal's superiority may result from a greater efficiency of protein utilization or a higher lean growth potential but that these two characteristics are not simply related.

Two studies, one using a trained taste panel and the other a consumer panel, were carried out to evaluate the eating quality of the Meishan breed. Entire male and female pigs of four genotypes: purebred Meishan (MS) and Large Wliite (LW) and the reciprocal crosses (MS♂ × LW ♀ and LW♂ × MS♀) were reared in single sex groups and given a commercial diet ad libitum from 35 kg live weight to slaughter at around 70 kg. For the taste panel, a loin joint was roasted under standard conditions and samples of fat and lean were presented to the panellists. There were no statistically significant differences between the genotypes for tenderness, juiciness, flavour, odour, incidence of boar taint or overall acceptability. Purebred Meishan samples had a higher incidence of abnormal odours but lower cooking losses and shear force values than the other three genotypes. Meat from gilts was judged to be significantly more tender and juicy, with a weaker pork flavour but a lower incidence of abnormal flavours and higher overall acceptability than that from boars. There were statistically significant interactions between genotype and sex for tenderness, abnormal odour and shear force which mainly involved the purebred Meishans and were of little practical significance. In the consumer study, loin chops and leg joints from purebred LW and the two crossbred genotypes were evaluated. Households received two samples of the same type of joint from the same sex in two separate distributions. Each household received an LW sample and a sample from one of the crossbred genotypes. In general, consumers found the appearance of the joints from the three genotypes to be equally acceptable. For eating quality, the within-household deviations of the crossbred compared with the LW suggested that MS♂ × LW♀ samples were considered to be of better eating quality, particularly for juiciness (deviation -0·71, s.e. 0·24, P < 0·01). In contrast, LW♂ × MS♀ samples were generally considered inferior, particularly in terms of juiciness (+ 0·59, s.e. 0·26, P < 0·05) and flavour (+0·63, s.e. 0·27, P < 0·05). However, the overall acceptability of both crossbreds was considered little different from the Large White. Overall, the results of this work suggest little benefit in eating quality for the Meishan under United Kingdom production conditions.

One of the more promising techniques for the improvement of sow productivity has been the use of partial weaning or the separation of the sow and litter for periods of between 3 to 12 h/day towards the end of lactation. The purpose of the present study was to examine changes in steroid hormone concentrations, oestrus and fertility responses in lactating sows subjected to altered sucking, boar exposure and gonadotropins in mid lactation and at weaning. Thirty-two crossbred sows were allocated at random to one of four experimental treatments. Treatment 1 sows (no. = 8) were separated from their respective litters for 3 h/day from 12 days post partum through until weaning which was carried out at 21 days post partum. Treatment 1 sows were also given in-pen boar exposure for 1 h/day between day 12 post partum and weaning. Treatment 2 sows (no. = 8) were given the same protocol of litter separation (LS) and boar exposure (BE) as in treatment 1 and they were also given a combination of gonadotropins (Gn) on day 17 of lactation. Treatment 3 sows (no. = 8) were given LS + BE as above and the sows were injected with Gn on the day of weaning. Treatment 4 sows were controls given no LS, BE or Gn (no. = 8). During lactation, treatment 1 sows exhibited significantly (P < 0·05) reduced progesterone concentrations compared with treatment 2 sows. There were no other significant effects of treatment for any of the periods considered. The separation of sows from their piglets with or without gonadotropic treatment did not result in lactational oestrus in any treated sows. No significant treatment differences were found in the subsequent litter size (piglets born alive or total number of piglets). In conclusion, the present results have demonstrated no significant effects of LS, BE and Gn treatment during lactation on sow and litter performance. This was associated with low levels of peripheral plasma progesterone in all lactating sows.

The aim was to investigate if selection of a balanced diet by growing and finishing pigs from foods differing in protein content is modified by the intrinsic nutrient and chemical properties of the high protein food ingredient offered. The treatments were as follows: a free-choice was offered between milled barley and either soya-bean meal (SBM) or low-glucosinolate rapeseed meal (RSM) or an equal mixture of SBM and RSM (SBM+RSM). In two further treatments (SBM/RSM and RSM/SBM) the protein supplements were changed when pigs reached 50 kg. These were compared with a control diet (CONT) formulated to provide 13-0 MJ digestible energy (DE) and 10 g lysine per kg and containing barley (680 g/kg), SBM (150 g/kg) and RSM (150 g/kg). A total of 72 pigs weighing about 30 kg were randomly allocated to the treatments in groups of six (three boars and three gilts). Pigs were slaughtered at about 90 kg and the chilled carcasses were assessed by measuring subcutaneous fat depths and cross-sections of the eye-muscle at the last rib. Responses from 30 to 90 kg on treatments CONT, SBM, RSM and SBM+RSM were, for food intake 2·57, 2·37, 2·21 and 247 (s.e. 0·08) kg/day (P < 0·05), for growth rate 0·93, 0·87, 0·70 and 0·82 (s.e. 0·05) kg/day (P < 0·05) and for food conversion 2·77, 2·72, 3·17 and 3·01 (s.e. 0·181) kg food per kg growth (P > 0·05) respectively. The amount of protein supplement selected in the diet from 30 to 90 kg on treatments SBM, RSM and SBM+RSM averaged 524, 495 and 483 (s.e.d. 64·9) g/kg respectively. With SBM this proportion decreased with increasing body weight (P < 0·01; R2 = 0·58). Changing RSM to SBM at 50 kg increased preference for the protein supplement and intake of SBM averaged 983 g/kg from 50 to 90 kg. On the other hand, switching from SBM to RSM increased preference for barley and intake of RSM averaged 572 g/kg. There were no significant differences in carcass quality but treatments RSM and SBM/RSM tended to produce increased fat depths. In conclusion, the use of RSM did not give a satisfactory level of -performance under the restricted free-choice feeding environment of this study. Preference and nutrient intake were adversely modified by RSM possibly due to the undesirable effects of antinutritive factors.

Two experiments were conducted to examine the effects of dietary inclusion of an ephedrine (Eph)/caffeine (Caf) mixture on finishing (55 to 100 kg live weight) castrated male pigs. The first experiment was conducted as a dose-response study and showed that the mixture had an optimal effect on performance and carcass composition at a dietary inclusion level of approximately 56/560 mg/kg of Eph and Caf, respectively. In the second experiment, interactions between the compounds were studied by dietary inclusion of Eph (56 mg/kg) and Caf (560 mg/kg) separately or as a mixture (56/560 mg/kg). The mixture reduced food intake by 0·12 and improved the food: gain ratio by 0·08. Muscle protein deposition rate was increased proportionately by 0·25, lipid accretion rate was decreased proportionately by 0·27, and gross energetic efficiency of energy deposition decreased proportionately by 0·09. This resulted in a changed proportional carcass composition towards more muscle (0·08) and less fat (0·21) after treatment with the mixture. The reduction in food intake was sustained due to an interaction over the first 3 weeks of treatment changing to additive effects by the compounds. The increased muscle protein deposition rate after feeding the mixture was entirely due to Eph, while the decreased gross energetic efficiency of energy deposition was caused by Caf. On the other hand, both compounds contributed almost equally to the decrease in lipid accretion rate. These results show that an Eph/Caf mixture markedly improves performance and body composition in finishing castrated pigs.

Forty-eight 4-week-old White Rock growing chickens (mean live weight 500 (s.e. 9·3) g) were given, by crop intubation, four isoencrgetic (13·1 M] metabolizable energy (ME) per kg dry matter (DM)) and isonitrogenous (120 g crude protein (CP) per kg DM) semisynthetic diets based on vetch (V) or bitter vetch (B) seeds, untreated or antoclaved at 120°C for 30 ruin (diets V, AV, B and AB, respectively). Autoclaving of the seeds caused some changes in amino acid (AA) composition but did not reduce the availability of A As, especially of lysine.

The average apparent AA digestibility values derived from ileal content were 0·75, 0·85, 0·59 and 0·85 for diets V, AV, B and AB, respectively, corresponding to true absorption values of 0·90, 1·00, 0·74 and 0·97, respectively. Although the apparent digestibility values of several AAs were relatively low (methionine, isoleucine, tyrosine and cystine), most were higher than 0·70. Heat treatment resulted in a significant increase (P < 0·05) in the AA apparent digestibility of both seeds. It is concluded that heat treatment is useful for improvement of vetch and bitter vetch seeds for inclusion in poultry diets.

Although the extent of ossification between the caracoid and clavicle bones of the pectoral girdle (ossa cinguli membrii thoracici) in the ostrich carcass can be used to determine between ossification classes within the age range 8 to 14 months (considered as the optimal time of slaughter of ostriches), it is not an accurate tool for estimating the exact age at slaughter. It is possible to distinguish between carcasses originating from the birds between 10 and 12 months of age, at which ostrich meat toughens.

Male rabbits aged from 4 to 4·5 months were subjected to a 8L: 16D photoperiod for 4 weeks and were then split into two groups. One group of13 males was maintained at 8L: 16D (group 8). The other included 16 males and was submitted to 16L: 8D (group 16). Two successive ejaculates zvere collected and analysed once a week for 6 months. Animals from group 8 were sexually more active and ejaculated significantly larger volumes of semen than those from group 16. Performance of males from group 16 was better for all other measurements, whether these were qualitative (motility, percentage of live spermatozoa) or quantitative. Averages for the total number of spermatozoa and number of live spermatozoa per ejaculate were significantly greater in males submitted to 16L: 8D (509 and 408 v. 452 and 344 × 106 spermatozoa, respectively). However the testes of rabbits in group 8 had a significantly greater volume than those in group 16 (22·3 v. 17·4 cm3, P < 0·001). After the animals were slaughtered when 11 months of age, the volume and weight of the testes and the testis and epidydimis reserves did not differ significantly between groups. Under our experimental conditions, the sperm output of bucks exposed to 16 h of daylength was greater than that of bucks exposed to 8 h of daylength but in vivo and post-mortem measurements did not reflect this difference.

The feeding patterns of sows using electronic feeders were monitored automatically (via a computer interface) over a period of 15 months. This paper reports on the variability in the size of the first meal of the day in relation to total daily food intake. The results demonstrated a pattern that bears some similarity to that observed by other workers, namely that sows tend to take all their daily food allocation in a single meal. In general, sows (79%) ate most of their daily allowance in a single visit to the feeders. However, on a significant minority of occasions (21%) this was not the case. The results also showed that there was a considerable number of sows (87% of the herd) that fed in a variable pattern, i.e. considerable variation in the proportion of their daily allowance taken in a single visit. This unpredictability was found throughout the sow herd. Some, but not all of this variability could be attributed to differences between parities (P < 0·001) and also there was some evidence that some sows, when newly introduced into the herd, were more variable in behaviour than more established sows. However, a large amount of variation remains unexplained. The need to provide flexible sow management to accommodate individual behaviour is discussed. Additionally, appropriate sampling periods of considerable duration are shown to be important in describing feeding patterns of group-housed sows.

The possible influence of social factors on the timing of puberty in the hind was investigated utilizing seasonally advanced (melatonin-treated) hinds and stags. Melatonin treatment of both sexes resulted in a significant advancement in the onset of pubertal ovarian activity (26 days, P < 0·001) and calving (27 days, P < 0·001) in the treated hinds and antler casting (25 days, P < 0·001) in the treated stags. Ovarian activity and calving were not influenced by melatonin treatment of the stags alone and similarly, antler casting was not affected by melatonin treatment of the hinds alone. However, a group of hinds without stags until after the onset of the breeding season, reached puberty later (5 days, P < 0·05) than hinds with stags, suggesting the presence of the male is important in determining the timing of puberty.

The aim of this trial was to determine the effects of a high winter feeding level on the performance of red deer calves from weaning to 15 months of age.

Two groups of 10 calves in each group were fed indoors from weaning to turn-out on good quality hay ad libitum. They received concentrates for 197 days, the first group (treatment H) ad libitum, and the second (treatment L) a daily quantity of 616 g dry matter (DM). At turn-out the two lots were grouped together for 149 days on natural pastures containing grass species characteristic of the area.

During the indoor period, treatment H calves consumed 2·5 times more concentrate than those in treatment L (272 v. 110 kg DM) and 2·8 times less hay (48 v. 234 kg DM). They weighed 19·6 kg more at turn-out (88·9 v. 69·3 kg). The difference in weight decreased to 8·8 kg at 15 months of age, but varied according to sex. This reduction of the weight gap between groups was due to the better adaptation of treatment L to pasture and to compensatory growth resulting from a higher grass intake after turn-out.

It is concluded that despite the good performance of treatment H animals in winter, a high energy level of feeding is only advantageous in certain cases. It is of benefit to animals that are to be slaughtered at 1 year of age and to lateborn calves, and can improve the frame development of females in their first breeding season.

Variance components for litter size (total number of piglets born) were estimated from Danish purebred Landrace and Yorkshire litters by restricting maximum likelihood. The data were collected from the national Danish breeding programme and consisted of 19 666 litters in Danish Landrace and 29 336 litters in Danish Yorkshire. Four different analyses for litter size were conducted within breed. In the first two, genetic groups were included in the model in order to account for the importation of animals from other countries; in the other two, genetic groups were removed from the model. Within each case, herd-year-type of insemination effects were fitted as fixed (H-fixed models), or herd-year-season-type of insemination effects were fitted as random (H-random models). Estimates of heritability ranged from about 0·11 to 0·14 in Landrace and from 0·10 to 0·11 in Yorkshire. Variance due to herd-year-season-type of insemination ranged from 0·029 to 0·041 of total variance, values somewhat lower than those obtained for non-genetic permanent effects. In order to compare the four models, data were divided into different subsets, and records from one subset were predicted using parameters estimated from the other subset. Both the correlation between observed and predicted values, and the mean squared error of prediction indicated that predictive ability was higher in the case of H-random models. There was no evidence that genetic groups improved the predictive ability for litter size. However, group effects affected inferences about genetic trend, particularly in Landrace, where genetic group composition changed consistently over the years.

In a factorial design, animal fat was added incrementally (0, 35, 70 and 105 g/kg) to maize starch (M) or to two sources of fermentable carbohydrates (260 g purified cellulose (C) per kg or 270 g soya-bean hulls (S) per kg). The 12 experimental diets were formulated by replacing maize starch in the control diet with fat, cellulose and soya-bean hulls of equivalent estimated net energy. Ninety-six castrated males were given these diets according to net energy. Apparent digestibilities of crude protein, crude lipid, crude fibre and nitrogen-free extract were measured and were compared with those expected from the separate ingredients. Net energy conversion ratio (nECR) was also measured. Results showed that in the C and the S diets prediction of the apparent digestibility of nutrients was worse than in the M diets (significant effect of source of carbohydrate). Prediction of apparent digestibility of crude protein and crude lipid improved as the added fat increased (significant effect of amount of fat), except in the C and S diets where for digestible crude lipid the 70 g added fat per kg gave the worst prediction (significant effect of the interaction). The net energy calculated from the experimental data on apparent digestibility was proportionately between 0·83 and 0·98 of that calculated from the expected data. The pigs on the C and S treatments showed a significant lower nECR when calculated from the expected apparent digestibility coefficients, but not when calculated from those which were measured. At the highest fat addition, the nECR was poorest. It is concluded that the amounts of digestible components in compound foods cannot always be obtained from those in the separate ingredients.

A study was undertaken to ascertain the effect of pyridoxine in diets of varying protein to energy ratio (P: E) for Mediterranean gilthead seabream fry (Sparus aurata) with respect to protein utilization. Diets were formulated to provide three levels of added pyridoxine (0·5, 5·0 and 50·0 mg/kg), at two protein levels (320 or 470 g/kg) whilst maintaining a similar gross isocalorific profile at 20 MJ/kg. Feeding level was proportionately 0·02 of the fish body weight per day, resulting in the following effects after a 70-day feeding trial. Low P: E ratio diets (15 g/MJ) did not perform as well as high P: E diets (24 g/MJ), with respect to growth related indices. Higher inclusions of pyridoxine into diets of equal P: E ratios, caused elevations in food conversion efficiency, protein efficiency ratio and apparent net protein utilization. A marked improvement of growth rate concomitant with pyridoxine level only occurred in the high P: E diets. It was concluded that incremental additions of pyridoxine in the diet, increased the efficiency of protein utilization for all diets tested. However, the protein sparing effect oflipid was not achieved for the low protein diets indicating the relatively high requirement for protein in the growth of the juvenile seabream.