Crossbreeding represents an important technique to improve growth, beef quality and adaptability in beef production systems in tropical countries. The aim of this study was to evaluate sire and dam breed effects on performance and carcass traits of crossbred cattle produced in a tropical environment. Heifers and steers were evaluated during the pre-weaning, the post-weaning (n = 173) and the finishing phase (n = 123). Animals were produced by mating Nellore (N_N), Angus × Nellore (A_N) and Caracu × Nellore (C_N) dams with Braford, Charbray and Caracu sires. After weaning, animals were raised grazing on Marandu grass for 12 months; thereafter they were housed in individual pens and finished in a feedlot, receiving a total mixed ration. Ultrasound carcass evaluations were performed to determine ribeye area (R_A), backfat thickness (B_T) and rump fat thickness (R_T). A_N progeny were heavier at birth than N_N (P < 0.05), and Braford progeny had greater birth BW than Caracu (P < 0.05). Greater weaning BW was observed in the A_N and C_N offspring compared to N_N (P < 0.01). Greater average daily gain during the post-weaning period was verified in the N_N progeny compared to C_N (P < 0.05). No dam or sire breed effects were observed for BW at the end of the post-weaning period (P > 0.05). Progeny of N_N cows had greater B_T (P < 0.05) and R_T (P < 0.01) at the end of the post-weaning period in relation to C_N. Greater R_A was observed in the Caracu progeny than in the Braford (P < 0.05), which showed greater R_T than the Charbray progeny at the end of the post-weaning period (P < 0.05). No dam or sire breed effects were verified for final BW at the feedlot or for feed efficiency traits (P > 0.05). A_N progeny were superior in final B_T compared to C_N (P < 0.01), and Braford progeny had greater R_T at the end of finishing than Charbray (P = 0.05). The use of crossbred dams allows an increase in productivity until weaning, but this is not maintained in the post-weaning and finishing periods. The use of Braford sires produces similar growth performance in the different stages of the production system to those seen with Charbray and Caracu sires but generates animals with higher fat thickness at the end of finishing, which may improve carcass quality and commercial value.

Genetic parameters were obtained for iron content in m. longissimus dorsi (2255 records) and haemoglobin levels recorded at 5 (4974 records) and 21 (2405 records) weeks of age in two sire lines from September 2009 until January 2011. The measure of iron in pork was the mean of two replicates. Genetic associations of haematological traits with meat quality traits (2255 records), as well as growth rate and backfat (close to 60 000 records), were estimated. Analyses were based on an animal model using residual maximum likelihood procedures. Iron content in pork was moderately heritable (0.34 ± 0.07) and genetic correlations with haemoglobin measures ranged from 0.39 ± 0.24 to 0.58 ± 0.13, indicating their potential use as selection criteria for increasing iron levels in pork. However, heritabilities for haemoglobin levels were low, ranging from 0.04 ± 0.2 to 0.18 ± 0.04. Procedures to measure haemoglobin on farm may require refinement. Redness of pork, quantified by a* value, had high genetic correlations with iron content (0.90 ± 0.04 to 0.94 ± 0.03) and moderate genetic correlations with haemoglobin levels (0.31 ± 0.22 to 0.55 ± 0.15). Iron content had significant genetic associations with L* measures (−0.61 ± 0.14 to −0.54 ± 0.23), b* value (0.60 ± 0.14 for dorsal b* measure, 0.50 ± 0.15 for average of dorsal and ventral b* measures) and pH at 45 min post mortem (−0.42 ± 0.14). These high genetic correlations between colour measurements and iron content in pork provide further avenues for selection strategies to improve iron content in pork. Current selection practices are not expected to affect iron content in pork, as no significant genetic correlations between performance and haematological traits were found.

Most nutritional pig growth models are based on the deposition of whole body protein (P) and lipid (L) mass. Chemical analysis of the whole animal is the best method to determine body composition. However, this method is expensive, time consuming and the carcass is lost. Alternatively, P and L may be estimated using simple indicators that should be precise and easily accessible. Although empty body weight (EBW) is a good indicator for P (through the strong relation between water and P), L is more difficult to estimate. This study was carried out to evaluate the relationship between simple carcass measurements and L. Measurements included backfat thickness in vivo and at slaughter in the hot and cold carcass and the weight of carcass, organs and primal cuts. To maximize variations in adiposity a total of 30 females and barrows from two genotypes (Piétrain×(Landrace×Large White) and Large White) were slaughtered at body weights typically used in Europe (i.e. 90 to 150 kg) and ground for chemical analysis. Backfat mass (in combination with EBW) was the best indicator for L (L (kg)=0·0590×EBW (kg)+2·99×backfat mass (kg), R2=0·96). Different backfat thickness measurements were highly correlated and appeared reasonable indicators for total backfat mass. Backfat thickness measured in the hot carcass between 3rd and 4th last lumbar vertebra at 8 cm from the mid line was the second best indicator for L (L=(0·0855+0·0073×backfat thickness)×EBW, R2=0·94). On average, 18% of total body lipids were located in the backfat. Although these equations can be used to obtain a reasonable estimate of whole body lipid mass, a significant genotype effect remained. Differences between genotypes in the partitioning of lipids between different tissues suggest that the quantification of an external lipid depot alone is insufficient to precisely estimate whole-body lipid mass across genotypes.

A study seeking to estimate phenotypic and genetic parameters for sow body condition around lactation and their relationship with piglet growth and survival is described. It also investigates the genetic relationship between piglet growth and survival, including both direct and maternal effects for both traits. Records were available from 24 549 Swedish Yorkshire piglets born in 2198 litters. Sows had records of weight and backfat depth at farrowing and at weaning. Piglets had individual records for weight at birth and weaning and cause of death for those that failed to survive during lactation. Mixed linear bivariate models were used to estimate correlations between traits. The models for the sow traits took into account the random effects of permanent environment and the genetic effect of the sow, whereas the models for the piglet traits included a litter effect as well as direct and maternal genetic effects. Estimated heritabilities for sow weight and backfat at farrowing and change of weight and backfat during lactation were low to moderate (0·10 to 0·47). We found significant genetic correlations between change of weight and backfat during lactation and piglet survival and growth, indicating that sows with the genetic capacity for rapid early piglet growth and high survival rate may lose more body reserves during lactation. Negative direct-maternal correlations for early piglet growth and survival imply that both the piglet and the sow trait should be included in a genetic evaluation for these traits. Genetic correlations between piglet survival and growth were not clearly favourable. Selection for the direct effect of piglet survival may lead to a decrease in early growth rate. We conclude that in a selection programme aiming at improving piglet survival and growth, attention should be paid to the sow's body condition during lactation. A high enough level of body reserves needs to be maintained in the sow if the incidence of reproductive problems and involuntary culling is not to increase.

Real-time ultrasound data of backfat thickness, longissimus muscle depth and longissimus area were carried out on 335 pigs (164 gilts and 171 barrows) using the Pie Medical Scanner 200 equipped with an ASP-18 probe and 3·5 MHz to predict carcass lean content in positive stress Pietrain (TT) and negative stress Pietrain (CC or CT). They were given food ad libitum and slaughtered at an average age of 213 days and an average weight of 101 kg. The day before slaughter, longitudinal and transverse images were taken at the last rib. After slaughter, the lean meat content was estimated by a CGM (capteur gras-maigre) equipped with an 8-mm diameter Sydel probe. The carcass lean proportion was higher in homozygote TT than homozygote CC and heterozygote CT individuals (P < 0·05). Gilts had more lean meat than barrows (P < 0·05). The correlation between the lean meat proportion and ultrasound backfat thickness (UBFT) or ultrasound longissimus muscle depth (ULMD) respectively was moderate. The prediction of lean meat proportion using UBFT, ULMD and ULMA gave an R2 which varied from 0·35 to 0·79. Real-time ultrasound is a tool that could potentially be used to predict the composition of pig carcasses before slaughter particularly if measurements can be taken with a higher degree of accuracy than at present.

A breeding experiment in Coopworth sheep where selection was applied to backfat depth was evaluated after 14 years (1981-94). There were three self-replacing lines, two selected for increased or decreased subcutaneous fat depth, and an unselected control (average size = 51 ewes per line per year). Reproductive traits, ewe body weight and ewe fleece weight were monitored in each line as potential correlated responses. In the last 4 years studied, the fat (F), control (C) and lean (L) lines differed significantly in the proportion of ewes lambing (0·87, 0·93, 0·94 respectively), litter size at birth (1·64, 1·83 and 1·89), and lamb survival up to weaning, unadjusted for birth rank and sex (0·88, 0·81 and 0·74). The overall reproductive trait, lambs weaned per ewe joined (1·22, 1·33 and 1·26), did not differ significantly among lines. From pre-mating weights of ewes present in 1993 or 1994, means for mature ewes by line were 60·1, 62·4 and 63·3 kg, respectively (P < 0·01). Means for weight at scanning time (7 months of age) by line, as a proportion of mature weight were: 0·533, 0·561 and 0·559, respectively (P < 0·05). There were also significant line differences in ewe fleece weights, with the 1993 and 1994 data averaging 3·93, 4·05 and 4·27 kg respectively (P < 0·01). For weight of lamb weaned per ewe weaning at least one lamb, the L line had a 0·09 higher mean proportionally than the F line (P < 0·05), but for a composite trait which was a weighted combination of weight of lambs weaned and ewe fleece weight per ewe joined (with or without allowance for different ewe live weights), the L line was no longer significantly different from the F line. Repeatabilities and single-record heritabilities were also estimated for various ewe traits. The implications are that lean-lamb selection would be associated with only small changes in net reproduction, ewe fleece weight and live weight, but larger differences would be expected from selection in the opposite direction.

The aim of this work was to determine whether developmental changes in growth hormone (GH) secretory patterns and carcass composition were influenced by nutrition and genotype in sheep. Four-month-old wether lambs from lean (low backfat), fat (high backfat) and control selection lines were nutritionally restricted to maintain a 28 kg live weight or given food ad libitum for 24 weeks. Plasma concentrations of GH and insulin-like growth factor 1 (IGF-1) were measured at predetermined times and carcass composition of the animals determined at the end of the trial.

From week 3 on, restrictions in dry matter (DM) intake were observed as the ad libitum treatment group had a significantly greater intake than the restricted treatment group (7·70 v. 5·80 kg DM per week, s.e.d. = 0·81). Differences in live weight between the feeding treatments were significant (P < 0·05) at week 9. The restricted feeding regime was associated with significant reductions in plasma levels of IGF-1 but had no effect (P > 0·05) on carcass weight-adjusted carcass fat proportion at the close of the trial. The effect of food restriction on GH secretory patterns was variable. Although there was initially a suppression in mean plasma GH, there was subsequently significantly higher mean plasma GH in the restricted feeding treatment. Periodogram analysis indicated that both the absolute levels of GH and the GH secretory pattern were altered by restricted feeding. In all animals, mean and basal GH concentrations, as well as the frequency and amplitude of pulses, declined from February to March and then increased from May to July (P < 0·001).

DM intake and live weight did not differ (P > 0·05) between genotypes, however the fat genotype had greater carcass fatness than lean or control genotypes (P < 0·01). There were no consistent differences between genotypes in plasma IGF-1 concentrations. In the ad libitum treatment, the lean and control genotypes had higher plasma GH levels than the f at genotype but the pattern of GH release did not vary. Under restricted feeding, both the pattern and the level of plasma GH varied between genotypes.

It is concluded that the developmental change in GH secretory patterns is affected by nutrition but not in a consistent manner. Although restricted feeding resulted in higher mean plasma GH concentrations later in the trial, this did not result in a change in carcass composition. The biological cues which lead to increased fat deposition in older lambs need further study but plasma GH levels may not he an important mechanism in this process.

With the objective of studying the response patterns of two biotypes of different body (structural) size to stocking rate (SR) in terms of individual growth rate (ADG), meat production per ha (PROD) and backfat thickness (BFT) under grazing conditions, 64 steers of two biotypes of the Angus breed of different body size were used: small-sized (SB: frame score of 1·3 (s.d. 0·7)) and medium-sized (MB: 2·9 (s.d. 0·6)). Four levels of SR were applied (1·8, 2·3, 2·8 and 3·3 steers per ha). The experiment lasted 241 days (April to December). Animals were weighed every 14 days, forage availability (FA) was estimated on four occasions and BFT was recorded at the end of the experiment (between 12th and 13th ribs). There were no differences between biotypes in ADG. SB tended to be earlier maturing showing higher BFT (4·39 v. 3·97 mm; P = 0·22). ADG was affected by SR and was higher at lower SR (0·612, 0·529, 0·414 and 0·375 kg/day, for 1·8, 2·3, 2·8 and 3·3 steers per ha, respectively). Individual average daily gain of the MB was more variable across the seasons of the year. None of the variables showed effects of the biotype × SR interaction but differences in ADG between biotypes as a function of the SR were observed as a trend (P = 0·29). Despite the difference in frame score between biotypes it was not possible to associate it with consistent differences in the response variables. Individual productivity (potential) of MB was not reflected in a greater productivity per surface unit. The data from this experiment do not allow the choice of a particular biotype in order to optimize the productivity of the pastoral production systems.

A 3 × 2 factorial experiment was used to investigate the influence of the breed type of gilts (Meishan synthetic 50% (M), purebred Large White (LW) and purebred Landrace (LR)) on response to insoenergetic diets of differing protein levels (180 g crude protein (CP) per kg, 9 g lysine per kg; or 240 g CP per kg, 12 g lysine per kg) offered to appetite over a 28-day lactation. Body fat reserves were adjusted during pregnancy by supplementing a set quantity of basal diet (131 g CP per kg, 12·7 MJ digestible energy (DE) per kg) with an energy source (maize starch + soya oil), to attain a backfat at P2 (6·5 mm off midline at last rib) of 25 mm at farrowing for all breeds. There were no significant diet effects or breed ×diet interactions on lactational performance. On day 1 of lactation, backfat was: M = 25·9, LW = 24·9, LR = 23·9 mm (P < 0·005). M gilts were lighter at farrowing (M = 173, LW = 192, LR = 182 kg; P < 0·001) and had more piglets than LW and LR. LR gilts had heavier piglets at birth (M = 1·13, LW = 1·18, LR = 1·38 kg, P < 0·001) than M and LW gilts. M gilts had a higher food intake (M = 6·4, LW = 5·2, LR = 5·1 kg/day; P < 0·001) but higher fat (M = 4·1, LW = 2·2, LR = 2·9 mm; P < 0·05) and weight (M = 15·9, LW = 1·0, LR = 4·7 kg; P < 0·001) loss over lactation than LW and LR gilts. LW gilts had a lower lactation output as reflected by lower litter weights at weaning than M and LR gilts (M = 73·7, LW = 59·3, LR = 75·2 kg; P < 0·002). It is concluded that lactation of gilts is not improved by provision of a very high protein diet (240 g CP per kg) and that performance still differs between breeds when backfat levels are standardized.

The aim of this study was to determine whether the decrease in plasma growth hormone (GH) levels during a lamb's first autumn is a function of photoperiodic or developmental changes. Wether lambs (no. = 30) from Coopworth sheep selected for low (lean) or high (fat) backfat plus a randomly selected line (control) were subjected to long (16 h light: 8 h dark) or short (8 h light: 16 h dark) photoperiod over a 5-month period after the summer solstice. The animals were regularly blood sampled to determine plasma hormone concentrations. Daily food intake and weekly live weights were measured and the animals were slaughtered at the end of the trial to determine body composition.

Food intake and growth rate were greater for sheep on long than on short photoperiod but photoperiod had no major effect on carcass composition. Mean and basal plasma GH, as well as the number and amplitude of pulses, were not affected by photoperiod, however GH secretion decreased from January to May. Plasma levels ofprolactin, insulin-like growth factor 1 (IGF-1), insulin and glucose were greater in animals under long than short photoperiod, while non-esterified fatty acids (NEFA) were unaffected by photoperiod.

Lean animals had greater mean and basal plasma GH and increased number and amplitude of pulses compared with fat animals. Prolactin concentrations were also greater in the lean than in the fat sheep, while there were no differences in insulin, glucose and NEFA levels. IGF-1 levels were higher in lean than in fat sheep under long photoperiod but lower under short photoperiod.

These results suggest that the decline in plasma GH with increasing age is not affected by photoperiod. While long photoperiod stimulates plasma prolactin and IGF-1 levels as well as intake and growth, the relationship between these parameters is unknown. Hormonal differences between lean and fat genotype sheep are found within the GH axis and prolactin but not within the gonadotropin or insulin axes.

A selection experiment was established in Coopworth sheep in 1981 to breed for increased or reduced ultrasonic backfat depth (scan C). Foundation females came from four flocks recorded for scan C and live weight, with weight-adjusted scan C data within flock being used for initial screening and subsequent selection. Three groups of animals per source flock, comprising proportionally the fattest 0·12, a random sample, and the leanest 0·12, were used to establish the F, control and L lines, respectively. Ewe flock numbers from 1981 to 1992 averaged 51 per line. Foundation rams were selected in the same manner from four different farms (two sources each in 1981 and 1982) to provide F line (proportionally the fattest 0·04), control line and L line (leanest 0·04) rams for use in 1981 and 1982, with four mated per line per year. Thereafter homebred rams were selected, with 41 or 42 homebred rams being used per line until 1992. Average generation intervals were 2·13 years and annual inbreeding rates per line 0·004. Bivariate heritability estimates for log scan C and log live weight, and a univariate estimate for log scan C using restricted maximum likelihood with an animal model, were 0·28, 0·22 and 0·38, respectively (all with s.e. 0·03). There was a suggestion of lower heritabilities in the L line for log scan C after adjustment for live weight. Realized heritabilities in the F and L lines were 0·34 (s.e. 0·07) and 0·26 (s.e. 0·03), respectively. Deviations of back-transformed weight-adjusted scan C in the last 2 years ofF and L data analysed (1991 and 1992 birth years) from the control flocks were 2·08 and −0·85 mm, which corresponded to responses of +2·50 and −1·03 phenotypic standard deviations, respectively. In addition there were relatively large responses in live weight taken at scanning, with F and L lines averaging 34·0 and 40·2 kg, compared with 38·0 kg for controls in the 1991 and 1992 birth years. The genetic and phenotypic correlations between log scan C and log live weight at scanning were 0·16 (s.e. 0·07) and 0·46 (s.e. 0·01) respectively.

The timing for introducing ad libitum lactation feeding around farrowing was studied in an experiment comprising 20 blocks of three littermate sows and a total of 1085 piglets in 90 farrowings. Sows were given 2·2 kg daily of a diet containing 12·1 MJ metabolizable energy and 120 g digestible crude protein per kgfrom service until ad libitum feeding was introduced either 4 days before expected farrowing (treatment BEF), the farrowing day (AT), or 3 days after farrowing (AFT). BEF and AT sows had a higher total daily food consumption during the experimental period, 5 days before farrowing to weaning at 35 (±3) days, than AFT sows (7·2, 7·2 and 6·6 kg, respectively). BEF and AT sows tended to have deeper ultrasonic backfat (BF) than AFT sows. The mobilization of body reserves during lactation was modest as reflected in negligible losses of live weight (LW) and BF, low serum concentrations of non-esterified fatty acids and creatinine, together with increasing serum urea concentrations as well as the high proportion of sows served within 8 days after weaning (over 90% of the primiparous sows). Sow rectal temperature increased on the farrowing day but was also influenced by feeding level. No cases of agalactia post partum were diagnosed. Litter size, piglet LW, piglet mortality and creep food consumption did not differ between treatments, although there was a tendency for lower LW and increased mortality, particularly of piglets crushed by the sow, in litters of AFT sows. It can be concluded that there was no advantage in delaying the introduction of ad libitumfeeding until after farrowing.

The responses in traits measured at the start of the mating period and at farrowing were examined after seven generations of divergent selection for daily food intake (DFI), lean food conversion (LFC), lean growth rate (LGA) on ad-\ibitum feeding and lean growth on scale feeding (LGS). Weight and backfat depth at mating were measured on 330 gilts and 74 boars, which were selected on the basis of performance test traits. Farrowing information was available on 259 gilts. At the start of the mating period, gilts selected for high DFI, LGA or LGS had similar live weights (135, 137 and 137 (s.e.d. 4·5) kg) but different backfat depths (20·3, 14·0 and 11·3 (s.e.d. 1·3) mm) while the corresponding low lines had different live weights (129, 117 and 124 kg), but similar backfat depths (17·5, 17·8 and 17·8 mm). Gilts selected for high LFC had lower mean live weight and backfat depth (114 kg and 10·7 mm) than gilts in the other selection lines. Conception rates of gilts selected for low DFI or high LGS were similar (0·62 and 0·64, s.e.d. 0·12) and lower than for the alternative selection strategies (0-78), but the low DFI gilts were significantly older at farrowing than gilts selected for high LGS (424 v. 408 (s.e.d. 5·5) days). Responses in live weight, backfat depth, age at mating and particular reproduction traits were selection strategy dependent, such that identification of relationships between growth and reproduction traits will require measurement of additional growth traits at an earlier age than in the current study

Effects of a two-diet system combined with ad libitum lactation feeding of sows on food consumption, sow live weight (LW), backfat depth, condition scoring, rebreeding interval, symptoms of agalactia and culling were studied on 60 sows followed for four parities. Feeding regimes were: CR, conventional i.e. restricted during gestation and lactation; SA, a simplified diet offered at a restricted level during gestation and a conventional diet ad libitum during lactation; CA, conventional during gestation and the same diet ad libitum during lactation. During lactation CR sows consumed 5·9 kg food daily (71 MJ metabolizable energy (ME)), whereas SA and CA sows consumed on average 7·0 kg (85 MJ ME), the difference being larger in multiparous than in primiparous sows and larger in the first than in later weeks of lactation. From the second farrowing onward sows on CR treatment were lighter and had thinner backfat and lower condition scores than sows on CA treatment, with sows on SA treatment in between, i.e. approaching the CR sows in the gestation periods and the CA sows in the lactation periods. At first service LW was 130 kg and backfat thickness 14 mm. During the fourth lactation LW averaged 190 kg in CR sows and around 220 kg for SA and CA sows, and backfat thickness was 11 mm in CR sows and around 16 mm in SA and CA sows. SA sows tended to rebreed earlier after weaning than did CR or CA sows. CA sows and in particular SA sows had higher incidences of agalactia symptoms and higher rectal temperatures post partum than CR sows. The culling rates did not differ between feeding regimes, although the predominant causes for culling did, being shoulder lesions and abscesses in thin CR sows and leg disorders in SA and CA sows. At the end of the experiment, however, more SA sows than others were retained in the experimental herd. It was concluded that the SA feeding regime was superior in terms of sow performance, despite an increased incidence of agalactia symptoms.

Reproductive records from 1072 Large White sows (3589 litters) were used to examine the effect ofbackfat depth (Bd) and live weight (Lw) at selection on first litter and lifetime reproductive performance. The variables investigated included mating age, total piglets born, total born alive, piglet birth weight, number weaned, piglet weaning weight, weaning to remating period and number of litters produced. Using backfat depth, sows were categorized into three groups: L, 9 to 13 mm; M, 14 to 16 mm; and F, ≥17 mm. Bd had no significant effect (P > 0·05) on the measured traits for the sows grouped by fat at first parity. When lifetime reproductive data were analysed, the L group had fewer litters (P < 0·05), and weaned fewer pigs (P < 0·01) than either the M or F group. The birth weight for piglets from L sows were significantly higher (P < 0·05) than for piglets from the other groups. The data suggest that the reproductive performance of L sows is not as good as that of M or F sows.

The intestinal production of skatole and its deposition in backfat was investigated in 35 uncastrated crossbred male pigs. The pigs were fed five purified non-commercial diets containing either casein or brewers yeast slurry as protein source. The yeast slurry diet was used alone or supplemented with either wheat bran (200 g/kg), sugar-beet pulp (200 g/kg), or soya oil (100 g/kg).

Skatole concentrations in backfat, and in digesta in different sections of the gastro-intestinal tract were measured at slaughter (mean weight 112 kg). There were large variations in skatole concentrations in the hind gut of different animals given the same diet. Although there was some correlation between skatole in intestinal contents and deposition in adipose tissue, there were also large variations between individual animals in their response to intestinal skatole. Nevertheless, there was a clear effect of diet on both intestinal skatole production and skatole deposition in backfat. The use of casein as a protein source decreased microbial skatole production, the total amount in the gut, and the concentration in the backfat. Addition of sugar-beet pulp to the yeast slurry diet increased microbial activity in the intestine (measured as ATP content, concentration of short-chain fatty acids, and lowering of digesta pH). There was a decreased rate of skatole production during in vitro incubations of intestinal content, and less skatole in the hind gut and backfat.

In vitro fermentations of freeze-dried Heal effluent inoculated with faecal bacteria, and addition of substrates to in vitro incubations of intestinal contents, demonstrated that tryptophan availability rather than microbial activity was the limiting factor for skatole production.

The results show that skatole production depends on the amount of protein entering the hind gut and the proteolytic activity of the intestinal microbiota. Protein fermentation in the hind gut can be decreased either by using more readily digestible protein sources (for example casein rather than yeast slurry) which reduce the amount of protein passing through to the hind gut, or by adding an alternative energy source which is more readily metabolized by the hind gut microbiota (for example supplementation of the yeast slurry diet with sugar-beet pulp). This provides a basis for the rational design of diets which will decrease skatole concentrations in the carcass.

A 2 X 3 factorial experiment was designed to study the consequences of feeding strategy during rearing and pregnancy over eight parities on sow growth and body condition. Two hundred and fifty-four gilts were group-fed on a restricted scale rising to either 2·25 (L) or 2·70 (H) kg/day (12·5 MJ/kg digestible energy (DE), 193 g/kg crude protein (CP) diet) from 70 to 175 days of age. A total of 156 of the L and H gilts were then given either 1·8 (l), 2·1 (m) or 2·4 (h) kg/day during subsequent pregnancies (12·9 MJ/kg DE; 177 g/kg CP diet). The same diet was offered to a standard scale during lactation. Sows were group-housed in pregnancy and given straw bedding. Losses of sows in rearing and each parity were not associated with treatment. After rearing, data have been presented only for those sows which completed eight parities. At 175 days of age, H gilts had grown faster (P < 0·001). From 175 days to service all gilts were given the same feeding regime but L gilts put on significantly more weight than H gilts, exhibiting more efficient utilization of food. There were no statistically significant differences in weights between L and H sows after the third pregnancy but L sows gained more weight than H sows in most pregnancies. The sows grew in each parity, indicating mature body size was not achieved. The pregnancy regimes had a significant (P < 0·05) effect on live weight, P2 backfat measurement, body length, neck circumference and condition score. Pregnancy treatment h produced the heavier and fatter animals but not all treatment l sows maintained adequate backfat levels for six parities. When housed in groups and given a generous supply of straw, the nutritional requirements of sows to sustain growth and body condition suitable for a long life may be less than has been previously identified for sows housed on concrete and slats without bedding.

Data on 3783 Yorkshire, 2842 Landrace and 937 Duroc littermate pairs of boars, station tested between 1976 and 1989, were used to measure genetic parameters of average daily gain (ADG) from 30 to 90 kg, live backfat at 90 kg (BF), estimated lean growth rate (LGR), average daily food intake, food conversion ratio (FCR) and lean food conversion ratio (LFCR), as well as measures of residual daily food intakes over and above requirements for growth and lean growth. A method was developed to obtain restricted maximum likelihood estimates of genetic variances and covariances under an animal model when observations are on the means of sib pairs. Heritabilities of ADG, BF, LGR, FCR and LFCR were 0·43, 0·59, 0·39, 0·28 and 0·34, respectively. Heritability of daily food intake was 0·45, and heritability of measures of residual daily food intake ranged from 0·30 to 0·38. About half of the variation in daily food intake was residual (0·48 to 0·56). Genetic correlations of ADG with daily food intake, FCR and LFCR were 0·80, −0·28 and −0·09, respectively, and were small and positive (0·18 to 0·34) with measures of residual daily food intake. Backfat had genetic correlations of 0·42, 0·24 and 0·52 with daily food intake, FCR and LFCR, respectively, and genetic correlations between backfat and measures of residual daily food intake ranged from 0·15 to 0·61. Selection against residual food intake may be a useful means of improving efficiency of food utilization.