The advent of genetic evaluations for fertility traits in the UK offers valuable information to farmers that can be used to control fertility problems and safeguard against involuntary culling. In addition to estimated genetic merit, proof reliabilities are required to make correct use of this genetic information. Exact reliabilities, based on the inverse of the coefficient matrix, cannot be estimated for large data sets because of computational restrictions. A method to calculate approximate reliabilities was implemented based on a six-trait sire model. Traits considered were interval between first and second calving, interval between first calving and first service, non-return rate 56 days post first service, number of inseminations per conception, daily milk yield at test nearest day 110 and body condition score. Sire reliabilities were calculated in four steps. Firstly, the number of effective daughters was calculated for each bull, separately for each trait, based on total number of daughters and daughter distribution across herd-year-seasons. Secondly, multiple-trait reliabilities were calculated, based on bull daughter contribution, applying selection index theory on independent daughter groups. Thirdly, (great-) grand-daughter contribution was added to the reliability of each bull, using daughter-based reliability of sons and maternal grandsons. An adjustment was made to account for the probability of bull and son or grandson having daughters in the same herd-year-season. Without the adjustment, reliabilities were inflated by proportionately 0·15 to 0·25. Finally, parent (sire and maternal grandsire) contribution was added to the reliability of each bull. The procedure was first tested on a data subset of 28 061 cow records from 285 bulls. Approximate reliabilities were compared with exact estimates based on the inverse of the coefficient matrix. Mean absolute differences ranged from 0·014 to 0·020 for the six traits and correlation between exact and approximate estimates neared unity. In a full-scale application, sire reliability for the fertility traits increased by proportionately 0·47 to 0·79 over single-trait estimates and the number of bulls with a reliability of 0·60 or more increased by 42 to 115%.

Red Maasai and Dorper sheep were evaluated for their resistance to gastro-intestinal (GI) nematode parasites (predominantly Haemonchus contortus), productivity and productive efficiency (assessed on a metabolizable energy basis) in experiments undertaken at the Kenyan coast (sub-humid environment) and the Kenya highlands (semi-arid environment). In both ewes and lambs there were few significant genotype by environment (G X E) interactions for either resistance (assessed by faecal egg counts-FEC) or resilience (assessed by blood packed red cell volume-PCV) to GI nematodes. Red Maasai sheep were consistently more resistant (low FEC) and more resilient (high PCV) than Dorper sheep. However, there were significant G X £ interactions for ewe reproductive performance and for ewe and lamb mortality rates and live weights. These interactions were due to very poor performance of the Dorper compared to the Red Maasai in the sub-humid coastal environment and to the much improved performance of the Dorper in the semi-arid environment. When these component traits were combined into estimates of flock productivity and productive efficiency there were highly significant GXE interactions with the Red Maasai sheep being considerably more efficient than Dorper sheep in the sub-humid environment, while in the semi-arid environment there was a negligible breed difference in productive efficiency. The results are discussed in terms of breeding strategies for smallholder farmers and pastoralists managing sheep in low-input systems in sub-humid and semi-arid environments.

Genetic and phenotypic parameters for body condition score (BCS), days to first service (DFS), non-return rate (NRR), somatic cell score (SCS), and 305-day milk, fat and protein yields were estimated, using 38930 multiple lactation records of cows across 1830 herds. The cows were daughters of '243 different sires. Single- and multi-trait repeatability animal models were used to estimate parameters based on restricted maximum likelihood methodology. Fixed effects in the model varied depending on the individual trait. Further, genetic relationships between 27 (linear and descriptive) type traits and functional traits (fertility and SCS) were estimated by regressing daughter type records on their sire's estimated breeding values for functional traits, using the same data set. Estimated regression coefficients were then subsequently used to derive approximate genetic correlations between type and functional traits (DFS, NRR and SCS). Body condition score had a moderate heritability (h2) of 0-26 and fertility traits had a low h2 (0-12 for DFS and 0-06 for NRR). Heritability of SCS and milk production traits was 0-14 and around 0-30, respectively. Ratio of permanent environmental variance to phenotypic variance was higher than h2 for all traits considered and ranged from 0-09 for NRR to 0-45 for milk yield. Body condition score had a favourable genetic correlation (rg) with SCS, but it was not strong (-0-08). Milk production was genetically antagonistic with fertility (rg: range 0-12 to 0-27 with DFS and -0-12 to -0-24 with NRR), with BCS (-0-39 to -0-50), and with SCS (0-10 to 0-15) showing that selecting for milk production alone would lead to decline in genetic merit for these functional traits. Body condition score had favourable genetic correlations with fertility traits (-0-35 with DFS and 0-04 with NRR) suggesting that BCS could be considered in a fertility index. Several type traits (especially 'udder' traits) had a favourable genetic relationship with fertility traits and SCS whereas dairy character had an unfavourable genetic relationship. Results of this study on genetic and phenotypic correlations among several functional, type and production traits could be used to design improved selection indexes for dairy producers.

The Dutch scrapie eradication programme aims at the exclusive use of homozygous ARR/ARR breeding rams by the end of 2004. As a consequence, breeds with a small population size and a low frequency of the ARR allele may suffer unacceptable losses of genetic diversity and high inbreeding levels. We simulated three breeding strategies to assess their efficacy in eliminating scrapie sensitive alleles and their effect on inbreeding levels. Under mild selection, both homozygous and heterozygous ARR rams were used indiscriminately. Under moderate selection, homozygous ARR rams were used preferably but they were supplemented with heterozygous rams when necessary. Under severe selection, only homozygous rams were used. Severe selection mimics then the proposed eradication programme. Simulations were carried out with allelic frequencies and population parameters of existent rare breeds in The Netherlands. With severe selection all simulated breeds showed unacceptably high inbreeding rates (> 0·5% per year). For some breeds, moderate selection resulted in acceptable inbreeding rates, while for other breeds only mild selection resulted in acceptable rates. The frequency of the ARR allele after 5 years of selection was only slightly lower with moderate selection than with severe selection (0·8% lower on average), but it was clearly lower with mild selection. Based on these simulations, we propose a selection programme where with low frequencies of the ARR allele, mild selection is used initially. Once the ARR frequencies rise to a particular value, the switch can be made to moderate selection. The population size (e.g. below 750, 750 to 3750 and above 3750 ewes) determines the frequency of the ARR allele at which the switch can be made (33%, 25% and 10%, respectively). With even higher ARR frequencies (above 70%, 50% and 33%, respectively) the regime can be changed to severe selection.

Clinical mastitis records on 36 178 first-lactation Norwegian dairy cattle (NRF) cows, daughters of 245 sires from 5286 herds, were analysed to study the impact of trait definition on estimates of genetic parameters and sire evaluations for clinical mastitis. The opportunity interval for infection, going from 30 days pre-calving to 300 days post partum, was divided into either 11 periods (each 30 days long); four periods ((-30, 0), (1, 30), (31, 120), (121, 300)); a single period (-30, 300) or defined as the interval currently used for sire evaluation in Norway (-15,120). Within each period, clinical mastitis was scored as 1 if it occurred at least once and 0 otherwise. Analysis was with Bayesian threshold models, assuming that mastitis (presence v. absence) was a different trait in each period. By use of multivariate or univariate normal link functions, unobserved liabilities to disease were modelled as a linear function of year of calving, age-season of calving, herd, sire of cow and residual effects. Estimates of heritability of liability to clinical mastitis ranged from 0-06 to 0-14, depending on the model and stage of lactation. In multi-period models, estimates of genetic correlations between periods were positive and ranged from 0-13 to 0-55. This suggests that clinical mastitis resistance is not the same trait in different periods of the first lactation, which is not captured by the single-interval models. The single-interval (-30, 300) model gave slightly smaller sire-specific posterior probabilities of clinical mastitis during the first lactation than the multi-period models. Furthermore, the interval used in current Norwegian sire evaluation understated the posterior probabilities of clinical mastitis, relative to the multi-period specifications. This led to some differences in sire rankings between the four models, although there was agreement between the four- and 11-period models. In conclusion, the multi-period models captured more genetic variation than the single-interval models, but the four-period model gave sire rankings that differed little from those obtained with an 11-period definition of clinical mastitis.

Myofibre composition in longissimus dorsi (LD) muscle of Erhualian (EHL) and Large White (LW) pigs was investigated by determining the ratios of mRNA abundances of four myosin heavy chain (MyHC) isoforms (MyHC I, MyHC 2a, MyHC 2x and MyHC 2b) using multiplex RT-PCR. The relationship between expression of growth hormone receptor (GHR) and peroxisome proliferator-activated receptor α coactivator-lα (PGC-lα) mRNAs and changes ofmyofibre type composition during postnatal growth from 3 to 180 days of age were analysed. At 3 days of age, proportions of MyHC I, 2a and 2x fibres were high while only a few MyHC 2b fibres were differentiated. Dramatic changes were observed from day 3 to day 20 with significantly decreased MyHC I, 2a and 2x fibres but abrupt increases in MyHC 2b fibres in both breeds of pigs. Breed difference was exhibited only from day 90, with higher MyHC 2b but less MyHC I and 2a expression in LW pigs. Developmental pattern of GHR mRNA expression in LD muscle coincided with that of MyHC 2b, with LW pigs expressing higher abundance of GHR mRNA. PGC-lα mRNA expression followed distinct patterns in the two breeds of pigs, a higher level of PGC-lα mRNA being expressed in LD muscle of EHL pigs, the breed that possessed more oxidative fibres (MyHC I and MyHC 2a).

Castrated and entire Boer bucks (no. = 60) in groups of between three and five animals were slaughtered at 5,15, 30, 45, 60, 75, 90 and 105 kg live weight (5- and 15-kg animals were not castrated). Ultimate pH, muscle colour (subjective and objective measurement), subcutaneous fat colour, total pigment concentration, shear force values and eating quality were investigated. The ultimate pH o/longissimus muscle increased from 5-7 to 6-2 (P < 0-05) as animals were slaughtered at heavier weights. Slaughter weight had an influence on chromameter muscle colour (L*, a*, b* values) and subjective muscle colour scores recorded using a nine-point colour scale (P < 0-05) for both entire and castrated bucks. Muscle redness (a* values) and subjective muscle colour scores increased gradually in older animals while muscle lightness and yellowness (L* and b* values) decreased. Subcutaneous fat colour became more yellow at heavier slaughter weights (P < 0-05). Shear force values were affected (P < 0-05) by slaughter weight but not by castration of bucks. All eating quality scores were influenced by slaughter weight but not by castration, and flavour, as predicted by eating quality scores, was the most important attribute that contributed to overall acceptability of the goat meat.

In several countries the gastro-intestinal parasites of sheep show evidence of resistance to the commonly used anthelmintic treatments. The use of animals with genetic resistance to such parasites has been shown to be a viable alternative in a number of resource flocks. However, the genetics of host resistance to parasites in industry flocks and the effects on production traits of using resistant sheep is relatively unknown. This study addresses these questions using data from 55 commercial Merino flocks in Australia. The heritability and genetic correlations were estimated for faecal egg count (FEC), an indicator of host resistance, and eleven fleece and body production traits. The heritability of FEC (0·26 (s.e. 0·018)), using a sire model, was found to be similar to other estimates reported in the literature from resource flocks. The heritabilities of production traits were also consistent with published reports from resource flocks. The genetic correlations between FEC and the 11 production traits, calculated using a sire model, were mostly zero, except for staple strength (-0·17 (s.e. 0·096)), fat depth (-0·26 (s.e. 0·088)) and eye-muscle depth (-0·18 (s.e. 0·091)). Animal model estimates of heritability and the genetic correlations between the traits were largely similar to the sire model estimates. Correlated responses to selection for reduced FEC based on the sire model genetic parameters were calculated to be less than 0·15% of the trait mean per generation for all traits except staple strength, fat depth, muscle depth and live weight. These were expected to increase slightly under selection for reduced FEC. Thus industry-based selection programmes to increase host resistance to parasites should be effective and have no detrimental effect on production characteristics of Merino sheep in Australia. The full benefit of such industry-based schemes could be improved by a better level of recording in the flocks studied.

Changes in ultrasound measures of muscle area (UtM) during lactation in different breeds and parities and with different feeding levels were examined. Random regressions were fitted to repeated measures of UtM in order to study changes in variance components of UtM during lactation. Correlations between measures taken in different stages of lactation and in different parities were also calculated. The shape of UtM curves during lactation appeared to be fairly consistent for all breeds and parities. The lowest point of all curves coincided with the expected nadir of body reserves during lactation. With lower-than-normal feeding level, the drop of UtM after calving was deeper and the overall level was lower. A major proportion of the variance in UtM was found to be determined by additive genetic variation. In all three breeds studied, repeatability and heritability estimates were high and fairly consistent during lactation and between parities. The very high genetic correlations between measures taken in different periods of lactation suggested that muscle growth and recovery are controlled by the same gene complex throughout lactation.

Our results suggest that UtM, if used jointly with other body measures such as body condition score, could be a useful indicator of tissue mobilization and deposition in the lactating cow, especially during the early stage of lactation.

Genetic analyses were carried out on Nematodirus spp. egg counts (NEM) of lambs from a set of Romney breeding lines. The lines had been under selection for 22 seasons (1979 to 2000) for divergence in resistance to infection by strongyle nematodes other than NEM, using faecal egg count (FEC) as the selection criterion. Heritabilities and genetic correlations for NEM were estimated using residual maximum likelihood procedures. Correlated responses in NEM were also determined. Heritability estimates for loge(NEM + 100) in lambs at 4 months of age (NEM1) or 6 months of age (NEM2) were 0·15 (s.e. 0·03) and 0·26 (s.e. 0·04) respectively (c.f. 0·28 (s.e. 0·02) and 0·35 (s.e. 0·02) for loge(FEC + 100)). The genetic correlation between loge(NEM1 + 100) and loge(NEM2 + 100) was 0·85 (s.e. 0·08), while the genetic correlations between measurements of loge(NEM + 100) and loge(FEC + 100) on both sampling occasions had a weighted average of 0·43, with estimates ranging from 0·30 (s.e. 0·08) to 0·52 (s.e. 0·07). Divergence in loge(NEM + 100) between the high and low FEC lines, estimated over both sampling times combined, was 1·07 phenotypic standard deviations, compared with 3·6 phenotypic standard deviations for loge(FEC + 100). Expressed in terms of back-transformed eggs per g, the high and low FEC lines differed by factors of 7·6 and 32·2 for NEM and FEC, respectively. The results support earlier parasitological data indicating that the genetic mechanisms in sheep which are responsible for resistance to other strongyle nematodes probably also influence resistance to Nematodirus infection.

The fatty acid composition of longissimus thoracis (LT) muscle and adipose tissues (subcutaneous and intermuscular fat) from castrated and entire male Boer goat bucks was investigated. Sixty Boer bucks in groups of between three and five animals were slaughtered at 5, 15, 30, 45, 60, 75, 90 and 105 kg live weight (5 and 15 kg animals were not castrated). The fatty acid composition of LT muscle from castrated and entire Boers was significantly affected by slaughter weight. The fatty acid content ofLT muscle and subcutaneous and intermuscular fat from both castrated and entire Boer bucks was primarily composed of oleic acid followed by palmitic and stearic acid. Both oleic and palmitic acid increased with slaughter weight whereas stearic acid decreased. LT muscle from castrated Boer bucks contained higher amounts of desirable fatty acids. In contrast to slaughter weight, castration of Boer bucks resulted in only minor changes in fatty acid composition of adipose tissues. It can be concluded that slaughter weight plays a role in changing the fatty acid composition ofLT muscle and adipose tissues from Boer bucks.

Hill ewes undergo large changes in body fat and muscle weight throughout the annual production cycle as they contend with the pressures of reproduction and lactation, as well as harsh environmental conditions. This study modelled seasonal changes in fat and muscle weights in Scottish Blackface hill ewes throughout their productive lifetime using random regression statistical techniques.

Scottish Blackface ewes (no. = 308) were scanned using computed tomography (CT) four times per year, from 2 until 5 years old. Heritabilities of tissue weights were estimated at 2-weekly intervals throughout the productive life of the ewe. Genetic correlations between tissue weights at the same point in the production cycle at different ages, and between tissue weights at different events within each annual production cycle were predicted. Animal solutions from random regression analyses were used to estimate tissue weights, from pre-mating at 2 years old to weaning at 5 years old. The effects of litter size in the current and previous production years on fat and muscle weights were investigated.

Correlations between CT tissue weights and those predicted by a sin/cos random regression model were 0.87, 0.84, 0.88 for carcass fat, internal fat and muscle respectively. Heritabilities ranged from 0.31 to 0.90 for carcass fat weight, 0.21 to 0.68 for internal fat weight and 0.26 to 0.57 for muscle weight, throughout the productive lifetime of the ewe. Heritabilities were highest during mating for fat weights, and during the dry period and lambing time for muscle weights. Heritabilities of tissue weights in 3-year-old ewes were higher than in other age groups. Genetic correlations were 1.00 between tissue weights at the same scanning event at different ages, but ranged from close to zero to 0.97 between scanning events within age groups. Clearly environmental variation across time was large. The number of lambs produced in both the current and the previous year influenced tissue levels. Ewes that did not produce lambs (barren) in a given year carried more muscle during that year than ewes producing lambs. As ewes aged, barren ewes carried increasingly more carcass fat and muscle than ewes with lambs. Barren ewes also had significantly more muscle during the following year than ewes that had weaned lambs. Ewes that reared twins had significantly less carcass fat the following year than singleton-bearing or barren ewes. These effects of previous litter size increased significantly with age.

Twenty-eight New Zealand White X Californian doe rabbits weighing 3791±141 g were surgically fitted with a glass T-cannula at ileum level. Animals were given ad libitum access to either a casein-based diet (C) or a protein-free diet (PF). The only difference in the ingredient composition of the diets was the substitution of 160g/kg of maize starch by casein in the C diet. Animals were randomly allotted to each experimental diet. Seven rabbits per diet were not allowed to practice caecotrophy. The C diet resulted in higher food dry matter (DM) intake (DMI) (111-5 v. 51-5 g/day), food nitrogen intake (3-12 v. 0-20 g/day), ileal flow of DM (56-0 v. 23-8 g/day) and ileal flow of nitrogen (0-72 v. 0-24 g/day) but lower soft faeces DMI (21-7 v. 41-4 g/day) than the PF diet. A linear relationship between ileal endogenous nitrogen flow and total DMI was found for animals given the C but not for the PF diet. The ingestion ofC diet led to a higher (proportionately 0-41, on average), endogenous ileal amino acid flow than PF diet for all amino acids except for glycine. The ileal flow of glycine was proportionately 0-25 higher in animals given the PF diet than in animals given the C diet. The C diet resulted in higher content of nitrogen, threonine and proline in soft faeces than the PF diet. In contrast, the ingestion of the PF diet led to a higher content of lysine and methionine in soft faeces than the C diet. Within the C diet, animals practising caecotrophy showed higher ileal flow of DM (73-4 v. 56-0 g/day) and phenylalanine (0-834 v. 0-677 g/kg DMI) than animals not practising it. Caecotrophy led to a higher endogenous proportion of some of the most important limiting essential amino acids in rabbits, such as arginine, lysine, phenylalanine and threonine. In rabbits, the use of PF diets has limited practical application in the estimation of nitrogen endogenous losses as the low food DMI and the high soft faecesDMI leads to abnormal food: soft faeces intake ratio. Moreover, due to the important effect of caecotrophy on the amino acid composition of endogenous losses, it is important to correct the total amino acid content of the ileal chyme by the undigested amino acid residue coming from the soft faeces intake. This correction could be made, without the methodological complexity implied, by fitting animals with a wooden collar and thereby avoiding caecotrophy as in the present trial.

The effects of sward, breed type and sex on lamb growth and carcass composition were measured at two degrees of maturity in live weight. The three breed types were Scottish Blackface (no. = 60), Suffolk (no. = 59) and their reciprocal crosses (no. = 60). The lambs grazed swards of either ryegrass, clover or a mixed sward intended to contain both. The proportion of the mixed sward as clover was only 0.014. Each lamb was scanned using X-ray computed tomography to measure the weights of fat, lean and bone in the carcass at two proportions of mature body weight (0.30 and 0.45). Live weights were recorded weekly. Average daily gains (ADG) in live weight and carcass tissues were calculated for each lamb between the 0.30 and 0.45 stages of maturity.

At the 0-30 stage of maturity, breed type differences in carcass composition were small; the Scottish Blackface had 0.942 as much bone as the Suffolk lambs (P < 0.001), with the cross lambs intermediate. At the 0-45 stage of maturity, Scottish Blackface lambs had less fat (0.749 times as much; P < 0.001), more lean (1.065 times as much; P < 0.001) and more bone (1.055 times as much; P < 0-001) than did Suffolk lambs. The values for crossbred lambs were intermediate but closer to those of the Suffolk. Neither sward nor its interaction with breed type had any significant effect on carcass composition at either the 0-30 or 0-45 stage of maturity. The effect of sex on carcass composition was significant at the 0-45 stage of maturity when castrated male lambs had less fat (P < 0.001) and more lean (P < 0.001) than female lambs. There were breed type by sward interactions for ADG in live weight (P < 0.05), in carcass weight (P < 0.001), and in fat (P < 0.001) and bone weights (P < 0.05). The interactions were such that Suffolk lambs had higher growth rates than Scottish Blackface lambs on clover but not on ryegrass or the mixed sward. There were no significant differences between Suffolk and crossbred lambs in growth rates on any sward. In this, and in two other experiments, the extent to which growth rate declined as the nutritional environment became worse was greater (P < 0.05) in Suffolk than in Scottish Blackface lambs; that is, Suffolk lambs expressed greater environmental sensitivity than the Scottish Blackface.

There is considerable concern about the consequences on fitness-related traits of using narrow breeding objectives for production traits. The aim of this study was to assess the potential consequences of selection for growth in French beef cattle breeds by estimating genetic correlations between growth, reproduction, calving and suckling traits of Charolais, Limousin and Blonde d’Aquitaine heifers. Data consisted of the records collected from 1985 to 2002 in progeny test stations that were used in the genetic evaluation of 284 Charolais, 125 Limousin and 118 Blonde d’Aquitaine AI sires. Seven traits were considered simultaneously in the analysis: weights at 18 months and after calving (for measuring heifer growth), sexual precocity and fertility (for measuring heifer reproductive performance), calving difficulty score and pelvic opening (for measuring calving ease) and milk yield (for measuring the suckling ability of the primiparous cow). REML (co)variance estimates were derived using linear multitrait sire models. Estimates of heritability were in the range of values given in the literature. They were very similar in the Charolais and Blonde d’Aquitaine breeds, and rather different for reproductive and suckling performance in the Limousin breed. Estimates were about 0·35 for heifer growth traits and about 0·15 for calving difficulty score in the three breeds. In the Charolais and Blonde d’Aquitaine breeds, estimates of heritability were 0·15 for sexual precocity and 0·05 for heifer fertility. These estimates were close to zero in the Limousin breed. Heritabilities of pelvic opening and milk yield were, respectively, 0·2 and 0·6 in the Limousin breed and around 0·3 in the other two breeds. Genetic correlations between traits concerning the same ability (as, for instance, weight at 18 months and weight at calving) were high and, in general, similar among breeds. Genetic correlations between heifer growth, reproductive traits, calving ease and suckling performance were nil or slightly favourable in the three breeds. Consequently, past selection mainly directed towards increasing growth seems not to have adversely affected the efficiency of female reproduction and the maternal abilities of French specialized beef cattle breeds.

An experiment was conducted with 42 Montbéliard steers to determine if nutritionally induced interrupted growth could influence muscle characteristics of steers and hence meat quality. A restriction/refeeding path was designed in order to induce a discontinuous growth path. At 9 months of age, 21 steers were given a restricted amount of diet for 3 months and were then slaughtered (R steers; no. = 10; intake: 5·28 kg dry matter (DM) per day) or subjected to a 4-month ad libitum refeeding period (R/F steers; no. = 11; intake: 8·99 kg DM per day) with the same diet (11·03 to 11·12 MJ metabolizable energy (ME) per kg DM) prior to slaughter. An additional 21 control steers were offered the same diet but in amounts that allowed them to gain continuously between 9 and 12 months of age, and were then slaughtered (C steers; no. = 10; intake: 7·08 kg DM per day) or maintained on a continuous feeding protocol through to 16 months of age prior to slaughter (C/C steers; no. = 11; intake: 8·07 kg DM per day). M. semitendinosus (ST), m. longisssimus thoracis and m. triceps brachii (TB) were collected for biochemical and histochemical analyses. R steers had a lower average daily gain (ADG; P 0·001), a lower final weight (P 0·01) and a leaner carcass (P 0·01) than C steers. Upon refeeding, R/F steers had a higher ADG than C/C steers (P 0·05) and underwent compensatory growth resulting in compensation of body weight and composition at 16 months. In muscles, glycolytic lactate dehydrogenase activity was lower in R steers (P 0·01) and restored in R/F steers compared with control steers. Among oxidative enzymes, cytochrome-c oxidase activity was higher in the TB of R/F compared with C/C steers (P 0·001) indicating a muscle-specific metabolic adaptation to the feeding level. There was little effect of the nutritional treatment on muscle fibre size and type except for an increase in the frequency of hybrid fibres in R and R/F groups (P 0·05). Total and insoluble collagen content were affected by restriction (P 0·001) in a muscle-specific manner: insoluble collagen content was lower in ST, but total and insoluble collagen contents were higher in TB of R compared with C animals at 12 months of age. No differences were recorded in lipid contents nor in proteasome activities. The data suggest that an alternation of relatively mild nutritional restriction and ad libitumfeeding had only a small effect on muscle characteristics. However, muscles respond differentially to changes in feeding level.

The objective of this study was to analyse the associations between ovine prion protein (PrP) genotypes and reproduction traits in three German meat sheep breeds. Reproduction traits were age at first early lambing, age at first late lambing, first lambing interval, second lambing interval and total number of lambs born. The data set included 595 genotyped German Texel sheep among 5225 recorded sheep, 351 genotyped German Black-Headed Mutton among 10 177 sheep and 282 genotyped Suffolk sheep among 2849 sheep. Linear animal models were employed for the analysis of the PrP-genotype effect. The PrP-genotype effect was analysed by comparing the most frequent PrP genotypes ARR/ARR, ARR/ARQ, and ARQ/ARQ. In a more general analysis three PrP genotype classes of animals with two, one or no copy of the ARR allele were compared.

In most cases, no significant associations were found between the PrP genotypes and the reproduction traits investigated. Only for the traits age at first early lambing in German Texel and second lambing interval in German Black-Headed Mutton and Suffolk could a significant association with the PrP genotype be observed.

One hundred 1-day-old Ven Cobb chicks were used to study the effect of supplementation with 0-2 mg chromium (Cr) per kg diet from potassium chromate (T1), chromium chloride (T2) and chromium-yeast complex (T3). The control group (C) received no supplemental chromium. Each experimental group consisted of five replicates of five birds each and the supplementation was continued for 35 days. The weekly live-weight gain, food conversion ratio and the live-weight gain: food intake ratio were unaffected by the treatments. Metabolizability of the organic nutrients increased in the Cr supplemented groups compared with the C group and significantly higher values were observed in the T3 group indicating beneficial effects of Cr-yeast complex. Intake of the trace elements (copper, zinc, iron and manganese) fulfilled the requirements specified for broiler chickens. Retention of all these trace elements was higher (P < 0-001 for Cu, Zn and Fe, P <0-01 for Mn) in all the Cr supplemented groups compared with that in the C group. Furthermore, in the T3 group the retention of copper, zinc, iron and manganese was higher (P < 0001) than that in the T1 and T2 groups. Two birds were slaughtered from each replicate at the end of 21 and 35 days of feeding to observe Cr in the liver; this was higher (P < 0-01) after 35 days feeding only. Despite supplementation, liver Cr was lower (P < 0-01) in T1 T2 and T3 groups. Cr concentration in the plasma was higher (P < 0-05) in the T3 and T3 groups than that in the C group although its concentration did not change with the age of the birds. Higher (P < 0-01) plasma concentrations of copper were observed in the T1 T2 and T3 groups titan those in the C group. The differences between the Cr supplemented groups in this respect were not significant, however. Liver copper was higher (P < 0-001) in C while liver iron was the lowest (P < 0-05) in that group. The concentrations of copper, iron (P < 0-01) and zinc in the liver (P < 0-05) were higher after 35 than after 21 days while those of manganese were not affected by slaughter age. Protein accretion in the meat tended to be increased in the Cr supplemented groups while deposition of fat in the meat was lower but these differences were not significant (P > 0-05). Other meat quality parameters including sensory evaluation scores improved due to Cr supplementation and Cr-yeast complex was found to have exerted significantly greater effects on these parameters. It was concluded that the supplementation of 0-2mg Cr per kg food dry matter would improve the performance of broiler chickens in terms of metabolizability of organic nutrients, retention of trace elements and meat quality.

The study reported in this paper was conducted to evaluate the digestibility of dietary carbohydrates (‘starch and sugars’ (S), neutral-detergent fibre (NDF), acid-detergent fibre (ADF)) and organic matter (OM) in the different parts of the equine digestive tract (stomach, jejuno-ileum, caecum, right ventral colon, left ventral colon, left dorsal colon, right dorsal colon, small colon and faeces). Three horses were given a standard diet (D1) based on fibrous pellets and straw and four were offered a high energy diet (D2) based on starch pellets and meadow hay. The digesta collection procedure, by total tract removal, permitted measurement of organ length, and dry matter and volume of digesta. Acid-detergent lignin (ADL) and acid insoluble ash (AIA) were used as natural digestibility markers. It was shown that AIA and ADL gave coherent data for ‘starch and sugars’ digestibility evaluation. ADL was a more relevant marker for parietal carbohydrates and OM digestibilities in horses given D1, whereas AIA have been preferred to evaluate these components digestibilities in horses offered D2. In horses given D1, precaecal OM digestibility coefficient varied from -0·04 to 0·20 whereas it varied from 0·46 to 0·62 in horses receiving D2. For both pellets, the results showed a considerable S digestibility occurring in the stomach (0·69 and 0·60 for D1 and D2 respectively) and this continued in the small intestine (0·88 and 0·89 for D1 and D2 respectively). With the exception of D2, structural carbohydrate fractions of the foods were poorly digested in the pre-caecal digestive parts. In the hindgut, OM digestibility coefficient varied from 0·47 to 0·60 for D1 and from 0·33 to 0·51 for D2. In horses given D1, highest digestibility was observed for each dietary carbohydrate in the left dorsal colon where it reached 0·99 for S; 0·45 for NDF and 0·40 for ADF. In horses receiving D2, the dietary components’ digestibilities increased regularly along the hindgut up to the faeces. The D2 structural fractions (NDF and ADF) digestibilities in the hindgut and faeces were lower than in horses given D1. These results not only confirmed that high energy diets like D2 can affect structural carbohydrate digestion in the horse hindgut but also indicated that a large amount of the energy part of the pelleted morning meal is broken down in the stomach.

An experiment was performed to assess the metabolic adaptation and hormonal regulation in young female rabbits during long-term food restriction and subsequent compensatory growth during rearing. Feeding level was either ad libitum (AL, no. = 52) or restricted (R, no. = 52). From 6 to 12 weeks of age, food intake ofR was kept at a constant level. This resulted in an increase in relative restriction as compared with AL to 0-54of AL intake at 12 weeks of age (restriction period). Thereafter food intake gradually increased to 0-95 of AL at 17 weeks of age (recovery period). During the last 5 days before insemination at 17-5 weeks of age, all animals were fed to appetite. Blood samples were taken weekly from 6 to 17 weeks of age from 11 animals in each group. Growth rate of R was reduced during the restricted period (29 (s.d. 2) v. 44 (s.d. 5) g/day for R and AL, respectively; P 0-05), but was higher in the recovery period (30 (s.d. 3) v. 27 (s.d. 4) g/day, respectively; P<0-05). At first insemination, AL rabbits were heavier than R (4202 (s.d. 388) v. 3798 (s.d. 220) g, respectively; P < 0-001). During the restricted period, plasma glucose was constantly lower (P < 0-05) in R. Insulin levels paralleled those of glucose, being lower (P < 0-05) in R than in AL. Restriction reduced (P < 0-05) circulating corticosterone and tri-iodothyronine (T3) levels in R. Leptin, non-esterified fatty acids, and plasma urea nitrogen levels were similar for AL and R during food restriction, whereas triglycerides were similar until 10 weeks of age, after which the levels were lower in R. During the recovery period, the food intake of the R but not AL rabbits increased. Insulin was the only hormone in R rabbits that had returned to levels found in AL rabbits by the 2nd week of the recovery period. Glucose, T3, and corticosterone levels returned to levels found in AL rabbits between 3 to 4 weeks after refeeding. Non-esterified fatty acids, triglycerides, and leptin were higher (P < 0-05) in AL rabbits from 13 weeks of age onwards. The pattern of changes in the endocrine status during food restriction and compensatory growth in rabbits do conform with those from other species, although some specific changes may vary depending on the severity of food restriction and its duration.