Seventy-two crossbred barrows (28.7 ± 0.3 kg live weight (LW)) were used to examine whether there is a relation between eating traits, and performance and carcass traits in ad libitum and restrictedly fed group-housed pigs. The experiment included two replicates, each consisting of 36 pigs. From day 1 to 42, all pigs were maintained with free access to a starter diet containing 12.7 MJ metabolizable energy (ME) and 8.2 g ileal apparent digestible lysine per kg. The experimental period was from day 42 (55.9 kg LW) to the end of the experiment (110.2 kg LW). The pigs in treatment 1 were maintained with free access to a high (H) energy diet (13.1 MJ ME and 7.1 g ileal apparent digestible lysine per kg). For pigs in treatments 2 and 3 the daily energy allowance per pig was restricted to 18 MJ ME above the daily energy requirement for maintenance using diet H, and a low (L) energy diet (12.5 MJ ME and 6.7 g ileal apparent digestible lysine per kg), respectively. The weekly measured LW was used to compute the energy requirements for maintenance (M = 0·719 MJ ME × LW (kg)0.63). Daily food intake and eating traits per pig were determined using transponders and an electronic feeding station equipped with an antenna.

Daily energy intake of the ad libitum and restrictedly fed pigs was correlated with growth and lean meat tissue content of the carcass. In the pigs given food ad libitum, daily energy intake was correlated with daily feeder visiting time, time per meal and food intake per meal, but not with number of meals per day and rate of food intake. In the restricted treatments, number of meals per day was correlated with energy intake, but not with lean tissue content of the carcass. In conclusion, number of meals per day explained part of the variation of lean tissue content of the carcass in ad libitum, but not in restrictedly fed group-housed pigs.

The data used in these analyses were compiled from individual feeding records of 1832 pigs from 70 sire families using FIRE (food intake recording equipment) system from Hunday Electronics Ltd at the Cotswold Pig Development Company. Pigs were on test between 45 (s.d. 2·76) kg and 95 (s.d. 6·78) kg. Daily food intake (DFI kg), food intake per visit (FlV kg), number of visits per day (NV), duration of each visit (TV min), time in the feeder per day (TD min), feeding rate (FR kg/min) and number of non-feeding visits per day (NFV), were measured as means of test and DFI was also recorded as means of bi-weekly periods of test. Performance test traits ofbackfat depth off test (BF mm), food conversion ratio (ECR kg/kg) and average daily gain (ADG kg), over the test period, were also measured.

Parameters were estimated by restricted maximum likelihood with a multivariate individual animal model. DFI had a heritability of 0·21 ranging from 0·18 to 0·26 over the four test periods. Correlations between DFI in each test period were high (rg = 0·75 to 0·99). DFI was highly correlated with performance test traits (0·61 to 0·78) but had low correlations with feeding pattern traits (0·0 to 0·24). The heritabilities of feeding pattern traits were low (0·06 to 0·11) with the exception of FIV (0·27) and NV (0·34) but correlations between feeding pattern traits were high. FIV, NV and TV were moderately correlated with ADG (rg = 0·49, -0·29, 0·33 respectively), BF (rg = 0·35, -0·15, 0·17 respectively) and ECR (rg = -0·12, 0·31, -0·27 respectively). Feeding patterns may be changed substantially by selection and the genetic correlations with performance test traits indicate that feeding patterns traits can be usefully incorporated in selection criteria to improve somewhat the accuracy of selection.

Fertility is an important component of herd production efficiency, as each additional oestrous cycle that does not result in a planned pregnancy adds to the cost of dairy farming. In addition to the negative impact on milk production, the high costs of veterinary intervention, re-insemination and herd replacement, subfertility can affect the rate of genetic gain in traits of economic merit. In contrast with the steady increase in average milk yield per cow during the last 30 years, there has been a decline in conception rate to artificial insemination in both the USA and in the UK.

The genetic correlation between yield and fertility has been equivocal. Attempts to improve the reproductive efficiency in dairy cattle through breeding and selection have been frustrated to date by the lack of heritable reproductive parameters conducive to high fertility. However, the traditional fertility parameters of interval to first service, services per conception, days open and calving intervals are highly influenced by managerial decisions and have, as expected, heritabilities too low to permit a meaningful genetic gain through selection. An alternative approach is to use the growing body of evidence that the majority of endocrine factors affecting reproduction are a result of gene expression at the hypothalamic, pituitary, ovarian or uterine level. Mechanisms such as commencement of post-partum cyclicity, follicle wave patterns, manifestation of oestrus, luteal competence and level of embryo mortality are appropriate for study. Research is required to investigate the genetic component of the variation between animals in these parameters, their phenotypic and genetic correlations with fertility and their association with other production traits.

In summary: (a) subfertility is a syndrome with multiple causes and only the symptom in common; (b) improvement in fertility will continue to be frustrated until recorded traits provide more accurate estimates of breeding values; (c) techniques are now available to estimate the genetic variation in physiological components conducive to improved reproductive efficiency; (d) once the heritable components of fertility are identified, these tools could be introduced into progeny testing and breeding nuclei, from which the genetic improvement can be widely disseminated. Selection for those components with sufficient genetic variation will result in the improvement of the integral endocrine and other physiological mechanisms favourably correlated with high fertility (e) these tools may also assist in detecting quantitative trait loci for faster genetic gain through markers-assisted selection.

Current Welfare Code recommendations suggest one nipple drinker per 10 pigs, while farmers have often used a ratio of one per 20 animals. This statement is based on information from pig farmers and advisors in the United Kingdom. Neither approach is based on empirical investigation. The use of larger group sizes in commercial herds raises further questions, since the relationship between group size and the appropriate number of drinking points cannot be assumed to be linear. The aim was to assess the two conflicting drinker allocations for their effect on welfare, as measured by drinking behaviour, social behaviour and performance, and any effect of group size on these. A total of 640 Large White × Landrace growing pigs were assigned to four treatments in a 2 × 2 factorial arrangement (60 pigs, three drinkers; 20 pigs, one drinker; 60 pigs, six drinkers and 20 pigs, two drinkers). Drinker provision had no significant effect on water use (5.10, 3.88, 4.99 and 3.45 s.e. 0.231 I per pig per day respectively) but in a larger group more water was used in less drinking time (P < 0.001). The diurnal pattern of water use was similar for each treatment. More aggression occurred at the drinker in large groups with a poorer drinker allocation (11.0 v. 3.8% of drinking bouts terminated by aggression for 60 pigs with three drinkers and mean all other treatments respectively, P < 0·05). Overt aggression (2.22, 2.27, 1.76 and 2.07 (s.e. 0.284) aggressive acts per pig per h, respectively) and lesion score counts of a sample of pigs from each pen suggested no difference between treatments. Providing one drinker per 20 animals, even in a large group, did not affect drinking behaviour, social behaviour or production. These findings should not be extrapolated to situations of different ambient temperature, water flow rate or feeding strategy.

A method to establish the economic optimum (minimum) cost of fertility in the dairy herd is described and demonstrated. A Markov chain model is used iteratively to establish the gross margin of the herd in the long term at various levels of oestrous detection rate and under two different rebreeding strategies. These gross margins are required by the optimization methodology. Under the initial assumptions reflecting current commercial practice in the United Kingdom, gross margin was £806 per cow. This figure varied by proportionately 0·15 over the range of oestrous detection rates assumed (0·4 to 0·7) while delaying rebreeding by 20 days caused gross margin to drop by approximately 0·04. It was concluded that it is important to optimize fertility control as well as rebreeding strategy in order to establish the economic impact of fertility in the dairy herd.

The economic value of fertility was also expressed per unit of calving interval and adjusted calving interval (ACI). ACI was calculated by dividing calving interval by the proportion of cows not culled for reproductive failure. Under the assumptions made, the marginal value of calving interval at the optimum oestrous detection rate was £6·22 per day, rising to £7·44 per day if rebreeding was delayed. The corresponding figures for ACI were £1·57 per day and £1·24 per day. The range in marginal values at sub-optimal oestrous detection rates were £4·38 for calving interval and £0·61 for ACI. It was concluded that the lower variation in ACI at different levels of fertility may make it a more representative trait for inclusion in a selection index provided the necessary genetic parameters can be reliably estimated.

The main aims of this study were to predict the increase in the accuracy of selection and the response to selection achieved by including feeding pattern traits, such as number and size of meals, as selection criteria in indices to improve growth rate, lean content of the carcass and food conversion ratio. Genetic and phenotypic parameters obtained for pigs given food ad libitum using single space electronic feeders were used to construct the indices. The predicted genetic gain in the index increased for indices with more feeding pattern traits. The inclusion of part test records for feeding patterns resulted in similar predicted correlated responses and predicted accuracy of selection to those using whole test records of daily food intake. The inclusion of feeding patterns as selection criteria resulted in indices that were less robust to inaccurate parameter estimates. It was concluded that feeding pattern traits could be used to improve the predicted accuracy of selection for the efficiency of lean growth but the most effective and robust index would include only daily gain, backfat depth, daily food intake and mean number of visits to the feeders per day. These traits may also be useful in reducing the length of the test period necessary for accurate measures of food intake, so increasing the potential intensity of selection using a given number of feeders.

A study was conducted at the Asella Station in the Arsi Region of Ethiopia to investigate the dairy performance of indigenous purebred Arsi and Friesian × Arsi crosses under different pre-partum and post-partum supplementary feeding regimes. A total of’343 first-lactation animals were involved in the experiment. Lactation performance was not significantly affected by pre-partum supplementation. Post-partum supplementary feeding significantly affected total lactation milk and butterfat yields of the crosses but not the purebred Arsi. Arsi crosses produced more milk (1873 (s.e. 65·1) v. 258 (s.e. 31·7) kg) and butterfat (92 (s.e. 4·0) v. 25 (s.e. 2·8) kg) than purebred Arsi. The crosses stayed in lactation longer (474 (s.e. 13·0) v. 179 (s.e. 15·4) days) than the latter. Purebred Arsi manifested much more variation in total lactation milk yield (CV: 1·27 v. 0·37), lactation length (0·91 v. 0·30) and butterfat yield (0·71 v. 0·42) than Arsi crosses. F1 crosses produced slightly more milk (+266 kg) and butterfat (+19·3 kg) but had shorter (-30 days) lactations than the backerosses.

The efficiency of marker-assisted introgression programmes, expressed as genetic lag relative to a commercial population under continuous selection, was investigated using analytical methods. A genetic model was assumed for which the genetic variance in the introgression population was a function of the within-breed genetic variance and the initial breed difference. It was found that most of the genetic lag occurs in the latter stages of an introgression programme, when males and females which are heterozygous for the alíele to be introgressed are mated to produce homozygous individuals. Reducing genetic lag through selection on genomie proportion by using genetic markers throughout the genome, i.e. by selecting heterozygous individuals which resemble the recipient (commercial) population most, was effective if the initial breed difference was very large (e.g. 20 within-breed phenotypic standard deviations). In that case, selection solely on genetic markers could be practised to speed up genome recovery of the commercial line. If the initial breed difference is small, phenotypic or best linear unbiased prediction (BLUP) selection is superior in reducing genetic lag under the assumed genetic model.

The coypu (Myocastor coypus) is an aquatic rodent usually bred for fur production. Fluctuations in fur prices have led to coypu meat being considered as a genuine resource in commercial farms, which contribute to the diversification of agro-ecosystems. To characterize coypus as a meat resource, maternal and heterotic effects on birth weight, weaning weight, slaughter weight, number of days required to attain a weaning weight of l kg, and on two parameters of the Gompertz growth curve (asymptotic weight and maturing rate) were studied. Eight males and eight females of Standard (S) and Cognac (C) genotypes and of their reciprocal crosses (C × S) and (S × C), where the first letter denotes the paternal genotype, were used. Significant genotype, sex and (genotype × sex) interaction effects were evident for most traits. S animals were lighter than С at all ages. Hybrids with С mothers were heavier than their reciprocals. Maternal effects on the parameters of the growth curve were observed only in females. Heterotic effects were extremely significant. Favourable heterotic effects in immature animals were explained by a change in the F1 growth pattern. Males showed a dominant deviation toward low asymptotic weights and overdominance for high maturing rate. Females showed partial dominance of high asymptotic weight and over dominance for high maturing rate. This association of genetic effects would justify a productive system based on a terminal cross using С females and S males because of the higher maturing rate of both hybrids and the maternal effect of С genotype, a combination that allows higher weights at the usual slaughter age (6 months) or butchering of animals at earlier ages.

Records were analysed on more than 75 000 calvings by 685 Holstein-Friesian bulls tested in commercial dairy herds in England and Wales. The data were collected from 1988 to 1994. The traits analysed were the degree of difficulty at calving, assessed from no difficulty to serious difficulty, calf mortality to 48 h, gestation length and a subjective assessment of calf size. Information was available for the percentage Holstein genes in the sire, dam age (heifer or mature), sex of the calf and the year and month of the calving for all records, while lactation number of the dam and the regional location of the herd were also recorded in 1993 and 1994 (14988 records). Estimates of heritability and genetic and phenotypic correlations were obtained for all traits by restricted maximum likelihood (REML) procedures using a sire model, while also fitting the effects of dam age, calf sex, year and season of calving and significant interations.

Heifers had more difficult calvings, higher calf losses and shorter gestations than mature cows while seriously difficult calvings and mortality were higher for male calves (all P < 0·05). Summer months were associated with lower incidences of difficult calvings, lower mortality and shorter gestations. Heritability estimates were 0·05 (s.e. <0·01) for calving difficulty score, 0·45 (s.e. 0·02) for gestation length, 0·02 (s.e. <0·01) for mortality and 0·08 (s.e. <0·01) for calf size score. Heritability estimates for the scored categorical and binomial (mortality) traits were also obtained using threshold model analysis. As expected, these estimates were higher than the REML estimates; 0·12 (s.e. 0.01) for calving difficulty score, 0·08 (s.e. 0·01) for mortality and 0·14 (s.e. 0·01) for calf size score. Calving difficulty score was genetically correlated with calf size score (-0.81), mortality (0.40) and gestation length (0.34) and calf size score was moderately correlated with mortality (-0.40). In all cases, the genetic correlations were stronger than the corresponding phenotypic correlations.

Sire genetic merit was predicted for calving difficulty score and the distribution of these predictions is described. Sire predictions for calving difficulty score on the underlying scale were backtransformed to predict the expected incidence of serious difficulties in future calvings.

An evaluation of the effects of the proportion of Texel or Rouge de l’Ouest (Rouge) genes in ewes (0, 0·5 or 1·0; the remainder being Greyface (Border Leicester × Scottish Blackface)) on prolificacy, lamb viability and lamb output was undertaken. A comparison of Texel and Rouge sires was carried out on Greyface, Texel and Rouge ewes. Prolificacy was higher in Greyface compared with Texel ewes (P = 0·06) but was lower in Greyface compared with Rouge ewes (P < 0·001). Prolificacy was similar in Greyface and Texel × Greyface ewes mated to Texel rams and in Greyface and Rouge × Greyface ewes mated to Rouge rams. The level of dystocia was similar in Greyface and Texel × Greyface ewes but significantly higher in Texel ewes (P < 0·001). The proportion of Rouge genes in the ewe had no effect on the level of dystocia. Litter weight of lambs at birth was significantly heavier in Greyface (P < 0·001) and Texel × Greyface (P < 0·01) ewes compared with Texel ewes. The proportion of Rouge genes in the ewe had no significant effect on litter weight. Lamb mortality (no. of lambs born dead and died birth to weaning) was significantly greater with Rouge ewes compared with the other ewe breed types (P < 0·001). The number of lambs which died from birth to weaning was lower with Texel × Greyface compared with Greyface ewes (P < 0·01). Expressed on a unit metabolic weight basis, Greyface ewes produced a significantly greater weight of lamb compared with Texel (P < 0·05) and Rouge ewes (P < 0·001). Texel × Greyface ewes produced a significantly greater weight of Texel-sired lamb compared with Greyface (P < 0·01) and Texel ewes (P < 0·001).

Sire had a significant effect on a number of parameters. The number of productive ewes was significantly lower in ewes mated with Texel sires (P < 0·001). Lamb birth weights and pre-weaning growth rates were greater with Rouge sires (P < 0·05). Number of lambs weaned per ewe lambed was significantly greater with Texel sires (P < 0·01). Overall weight of weaned lamb produced per ewe was not significantly affected by sire breed.

The Ministry of Agriculture, Fisheries and Food routinely publishes price information for 3-week-old beef + dairy calves sold at major livestock auction centres in England and Wales. For the period 1993/94 to 1996/97, there were average price premiums of £51 for male and £38 for female calves classed as ‘first quality’. We have shown previously that choosing an easy calving beef sire for use on dairy cows will generally lead to calves which are smaller in size and of poorer conformation. To enable dairy producers to maximize returns from calf sales, we propose that beef sires be evaluated for the predicted incidence of first quality’ calves, which can be derived from the sire’s evaluation for calf conformation and the breed incidence of first quality’ calves. Dairy farmers may then jointly consider a bull’s predicted merit for calving ease and calf quality when choosing a sire for use in their herd.

Body length and ultrasonic fat thickness measurements were taken on 86 live pigs in order to find an optimal probing site for estimation of lean meat proportion. The next day pigs were slaughtered and measurements with the Hennessy Grading Probe (HGP) were made in order to estimate the lean meat proportion.

Fat thickness, 6 cm off the dorsal mid line, increased from a value of 9·5 mm at a site 4 cm cranial to the last rib, progressively through intermediate sites to a value of 12·4 mm, 22 cm cranial to the last rib. Fat thickness measurements at different sites (live pigs) were highly correlated with HGP fat thickness at the site between 3rd and 4th from last rib (3/4 LR) and estimated lean meat proportion (carcasses); correlations ranged from 0.80 to 0.89 and -071 to -0.85 respectively. The most accurate predictor of estimated lean meat proportion from the live pig measurements was the measurement at 18 cm cranial to the last rib. Measurement at the site half the distance between the occipital bone and the base of the tail (midpoint) was the second-best for estimated lean meat proportion.

Generally, this midpoint on live pigs was situated around the 3/4 LR on carcasses. However, the range was considerable. Half of the number of animals had a midpoint in the range of -2.5 to 2.5 cm from 3/4 LR. The site midpoint is easily located on the animal and the results of this study suggest that it can be used as an accurate predictor of estimated lean meat proportion. Therefore it can serve as the probing site for classification of live pigs.

Weaning weight in a single flock of 600 ewes and 40 rams was simulated through 30 consecutive lambings. The objective was to compare the simple breeding value model with the maternal effects model for lamb evaluation under the Segureña selection scheme. Three selection strategies were tested: selection on breeding values estimated by a simple breeding value model that ignores maternal effects (method 1), selection on direct additive values only (method 2) or on the sum of direct and maternal additive values (method 3), both latter methods utilizing a maternal effects model. Average values obtained in the last lamb crop were about 18 kg for the phenotypic mean, about 5 kg for direct additive values and about -1 kg for maternal additive values, for all three methods. Average inbreeding coefficient of the last crop was more than 0·13 in method 1 but was less than 0·12 in the others. All differences were not statistically significant (P > 0·05). Consequently, the simple breeding value model can be used for the genetic evaluation of weaning weight of candidates for selection in the Segureña scheme. The effect of variation in the magnitude of parameters was evaluated through four sets of parameters. Results showed that with a higher additive maternal component, method (3) would become increasingly necessary. The need for method (3) is accentuated with more negative additive covariance between direct and maternal effects. Thus, for higher maternal effects or more negative additive correlation, the use of the complete model (with maternal effects) becomes unavoidable. Varying population size, however, affects only the inbreeding accumulated, as long as the same methods of selection are used.

Evidence to support the existence of a maternal lineage variance component for production and food intake traits at the Langhill experimental dairy herd was investigated. Maternal pedigree records of the herd were traced back to the points of cytoplasmic origin using herd book records. Cytoplasmic origin was defined as the earliest maternal ancestor of a cow and used to assign cows to maternal lineages. This was either a grade-up cow or an ancestor traced back to 1920. The tracing resulted in the cows being assigned to 56 maternal lineages, ranging in size from one to 72 cows. A total of 1118 records of 517 cows, all with a first lactation record, were used in the analysis. Traits analysed were daily milk, fat and protein yield, fat %, protein %, food dry-matter intake, net energy of milk production, a measure of milk production efficiency, average condition, and calving condition, all averaged over the first 26 weeks of lactation. The analysis was performed using a residual maximum likelihood animal model with and without a random component for maternal lineage. Possible bias, due to the fact that the sires were a select sample from the population, was also examined. No significant effect was found in the analysis of the full data set that could be assigned to maternal lineage. Fat yield was the only trait to show a variance component approaching a 5% significance level with a magnitude of 4% of phenotypic variance. However, when maternal lineages of at least five cows were considered, a significant 4% maternal lineage component of phenotypic variance was found for fat yield. The power of the analysis to detect a variance component of less than 4% was shown to be poor. No evidence was found for a maternal lineage component of food intake traits or condition score. Treating sire as a fixed effect or regressing data on sire EBV made little difference to the maternal lineage component.

The metabolic pathways of dietary fatty acids were studied in rabbits by analysing the fatty acid profile of different tissues (liver, perirenal fat, longissimus lumborum muscle). Four groups of 24 hybrid males each were assigned to four semi-purified diets, varying in the source oflipids which differed in n-3/n-6 ratios: 180 g/kg sunflower (S), 80 g/kg flaxseed + 90 g/kg sunflower (SF), 160 g/kg flaxseed (F) and 60 g/kg fish oil (FI). The liver showed a very important rôle in fatty acid syntheses and was the tissue richest in long-chain (≥20 C) polyunsaturated fatty acids (LCP) of n-3 and n-6 series. The S diet gave the highest mono-unsaturated fatty acids and n-6 LCP (respectively, 201·9 and 384·9 g/kg, P < 0·01) also showing a clear antagonism v. n-3 LCP; the FI diet determined the highest enrichment of n-3 LCP (179·5 g/kg, P < 0·01). a-linolenic acid was efficiently converted into n-3 LCP mainly when п-ЗІп-6 ratio was high (Σn-3/С20: 4n-6: 2·74 and 3.61, P < 0·01 in flaxseed and fish-oil diet, respectively). The same trend occurred in the muscle but in a less consistent way. The adipose tissue more closely reflected the composition of the dietary fatty acids, showing variations mainly concerning polyunsaturated fatty acids (S diet), and LCP n-3 (FI diet: 44·9 g/kg, P < 0·01). Results showed the possibility of modifying the fatty acid profile of rabbit meat by dietary means and that the n-3/n-6 ratio of the food is crucial in regulating the relative presence of LCP n-3 or n-6 in meat products.

A dynamic model for simulation of growth in pigs was extended by a module to assess maximum and minimum heat loss (HLcold, HLhot) for a given pig, to compare these figures to heat production (HP), and to take thermoregulatory action when HP < HLcold (cold conditions) or HP > HLhot (hot conditions).

HLcold and HLhot were largely determined according to algorithms obtained from the literature, hut HLcold was made dependent on body fat depth through tissue insulation. Data to establish the relation (Ύ = 0.05 + 0.002 x X) between cold tissue insulation (Ύ in °C.m2 per W) and backfat depth (X in mm) independent of body weight were obtained from the literature. The same data showed that HLhot is not related to backfat depth in pigs.

Cold thermoregulatory action included an increase of ad libitum food intake. Hot thermoregulatory action included reduction of physical activity, increase of body temperature, wetting of a proportion of the skin and reduction of dia libitum food intake.

A sensitivity analysis showed that the model’s output in terms of ãd libitum food intake, HP, protein deposition (Pdep) and lipid deposition (Ldep) is strongly sensitive to the characterization of the genotype being simulated. The model was used to simulate trials from the literature. Although the model does not explicitly calculate lower and upper critical temperatures, these could be adequately predicted from its output. Comparison of model output with experimental data revealed an adequate prediction of ad libitum food intake and of the partitioning of ad libitum ingested metabolizable energy (ME) into HP, Pdep and Ldep in cold, thermoneutral and hot conditions. At restricted ME intake, and especially in cold conditions, the model tends to overestimate HP and underestimate Ldep, probably because it does not take account of long-term acclimatization.

The objective of this research was to design and compare nucleus breeding plans that might be recommended to the breeders of Brazilian dairy cattle. Plans for native dairy breeds were compared for the change of genetic merit in milk yield and in the economic return at 25-year investment periods. Effects of nucleus herd and commercial population sizes on genetic gain and net income were examined. Investment value of plans was studied for differences in the efficiency of embryo transfer techniques and in the sale price of cows and young bulls on genetic merit. Parent selection was based on records on individuals (for females), their full- and half-sibs, their dam, full-and half-sibs of their sire and their dam and their grandam. Within herd sire selection was restricted to a maximum of one bull per full-sib family. No matings of full-sibs were allowed. Annual economic summaries considered the age distribution of animals within herds. Alternative plans were investigated for their revenue, expense and net income streams and their investment value. The cumulative genetic gain of selected animals in lactational milk production was 1639 kg and 1435 kg for large plans with 64 donors (L) and small plans with 32 donors (S), respectively. The initial genetic lift for a population size of 20 000 animals was equal to 279 kg. When the size of the commercial population was increased to 50 000 animals, the lift was increased by 10%. Profitability in the different plans was achieved after the sale of cows and young bulls. The difference between cumulative discounted net returns at year 25 for L and S was proportional to the sale prices placed on the genetic merit of cows and bulls. The programmes of genetic improvement described were profitable and should be recommended to the breeders of Brazilian dairy cattle. Considering the criteria of gain to cost, the smaller plan seems to be the most reasonable to implement.

Heritabilities, dominance variation and genetic correlations (rpc) among purebred and crossbred performance were estimated for egg production (number of eggs produced between 19 and 25, 26 and 38 and 26 and 54 weeks of age) and egg quality traits (average egg weight, shell strength) in four generations of two nucleus lines of egg-laying chickens and their cross, all reared in similar environments. The within-line genetic parameters were estimated using method R applied to an animal model (approach 1) and tilde-hat approximation to restricted maximum likelihood applied to a sire-dam model (approach 2). The genetic correlation between purebred and crossbred performance as well as the crossbred heritabilities were estimated based on a multivariate sire-dam model accounting for all relationships. For egg numbers and shell strength, the purebred heritabilities were low to moderate (0·12 to 0·42). They were higher when estimated under an additive model (0·25 to 0·51) but, in general, lower than the crossbred heritabilities. For egg weight, the heritabilities were always high (0·6 to 0·7). The ratio of dominance variance to total genetic variance varied between 11 and 36% with approach 1 and 5 and 56% with approach 2, indicating a large partial dominance for egg number traits and shell strength but also the difficulty of accurately estimating the dominance variance. For these traits, the estimates of the correlation between purebred and crossbred performance, rpc, were quite high (0·8 to 0·94) which contradicts the theory that traits with larger dominance and/or difference between purebred and crossbred heritabilities present lower rpc. These high rpc estimates, coupled with the absence of obvious heterosis, indicate little advantage to be gained from use of crossbred data in genetic improvement, where pure lines and crossbreds are reared in a similar non-stressful environment.

The influence of genetic and environmental factors on body weight and reproduction and their relationship to milk production traits, were studied in data of about 4700 Sahiwal cows from Pakistan. (Co)variance components were estimated using restricted maximum likelihood (REML) procedure based on the expectation maximization algorithm applying an animal model. Mean weights of females were: at birth, 21·6 kg; at 1 year, 130 kg; and at 2 years, 222 kg. Records of age at calving, cow weight post partum and calving interval were studied in the first three parities, with parities considered as different traits. For primiparous cows the average values of these traits were: 44·1 months, 319 kg and 465 days, respectively. Mean stillbirth rate was 5·3%. Heritabilities ranged for body weight traits from 0·08 to 0·21, for age at calving from 0·10 to 0·13 and for calving interval from 0·03 to 0·07. Genetic correlations of age at first calving with calving interval and 305-day milk yield were low. The genetic correlation between 305-day milk yield and calving interval was positive (unfavourable) in first parity (0·68) but negative in the third (-0·47). Cows with a high genetic value for 305-day milk yield were heavier at first calving than were low-yielding cows (rg 0·57). The genetic change in reproductive traits over the period studied was close to zero, whereas a marked deterioration was found in phenotypic performance. It is concluded that improved feeding and management, along with some selection against poor reproduction in cows, are important for improvement of reproductive performance.