Individually recorded milk yields, yields and concentrations of milk components, food intakes and live weights of multiparous dairy cows given silage ad libitum and concentrates at a flat rate in weeks 4 to 13 of lactation and data for silage and concentrate composition from experiments conducted at four sites, were used to obtain simple correlations and multiple linear regressions of yields and concentrations of milk constituents on other variables.

Simple correlations between yields and concentrations and other variables were low. Yield terms were most highly correlated with intake terms. Milk fat concentration was most highly correlated with silage fibre concentration. Milk protein concentration was most highly correlated with digestible energy intake. The best multiple regression models including time effects accounted proportionately for 0·35 of the variation in fat yield, 0·51 in protein yield, 0·55 in lactose yield, 0·39 in total milk yield, 0·19 in fat concentration, 043 in protein concentration and 0·19 in lactose concentration. Most of these models included terms for silage intake and cow live weight which are not generally available on farms. More practical models including fewer independent variates were therefore produced. These models accounted proportionately for 0·33 of the variation in fat yield, 048 in protein yield, 0·50 in lactose yield, 0·32 in total milk yield, 0·19 in fat concentration, 0·40 in protein concentration and 0·17 in lactose concentration.

Lactating Holstein-Friesian cows from two calving groups (no. = 90) were studied during the early post-partum period to determine the effect of dry-matter intake (DM1), 40 g/kg fat-corrected milk (FCM) production, energy balance (EB), parity, and food additives (calcium salts of long-chain fatty acids [CaLCFA] and niacin) on the recrudescence of ovarian function and establishment of pregnancy. Cows that ovulated early during the post-partum period (15 to 21 days after calving) consumed more food and tended to produce more FCM compared with cows ovulating later (22 to 42 days or after 42 days). Primiparous cows had lower EB and tended to have longer intervals to first ovulation compared with multiparous cows but the average interval to pregnancy was similar for primiparous and multiparous cows. Feeding CaLCFA tended to extend the interval to first service and decreased pregnancy rate. Production characteristics (including DMI and FCM production) seem to determine interval from calving to first ovulation as well as interval from calving to pregnancy (days open). Fertility was affected negatively by feeding CaLCFA.

Two experiments were carried out to evaluate extracted soya-bean meal, fish meal and maize gluten feed as protein supplements for calves offered grass silage ad libitum. The five treatments used in experiment 1 consisted of 1·4 kg per head daily of concentrate dry matter (DM) consisting of (g/kg) 50 molasses and 25 minerals and vitamins plus (1) 925 barley (B), (2) 700 B and 225 extracted soya-bean meal (SBM), (3) 785 B and 140 fish meal (FM), (4) 925 maize gluten feed (MGF) and (5) 2·25 kg DM per head daily of concentrate (1). Those used in experiment 2 consisted of 1·4 kg per head daily of concentrate DM consisting of (g/kg) (1) 1000 B, (2) 800 B and 200 SBM, (3) 860 B and 140 FM, (4) 1000 MGF and (5) 2·25 kg DM per head daily of B. In each experiment the diets were offered to 70 calves which were initially 131 and 130 kg live weight, for periods of 14 and 13 weeks in experiments 1 and 2 respectively. The silages contained 155 and 154 g crude protein (CP) per kg DM; 45 and 77 g ammonia-nitrogen per kg total nitrogen and 698 and 726 g digestible organic matter per kg DM in experiments 1 and 2. Concentrates 1 and 5 contained 104 to 110 g CP per kg DM and concentrates 2, 3 and 4 contained 195 to 204 g CP per kg DM in both experiments. For diets 1 to 5 respectively silage DM intakes were 2·31,2·50,2·53,2·59 and 1 -61 (s.e. 0·097) kg/day; live-weight gains were 0·84,0·98,1 -01, 0·88 and 0·95 (s.e. 0·032) kg/day in experiment 1 and 2·38, 2·53, 2·54, 2·82 and 1·77 (s.e. 0·045) kg/day and 0·90,1·04,1·03,1·05 and 0·99 (s.e. 0·038) kg/day for experiment 2. It is concluded that the use of soya-bean meal rather than fish meal did not affect silage intake or animal performance. Replacing mixtures of barley and soya-bean meal or barley and fish meal with an equal quantity of isonitrogenous maize gluten feed did not affect animal performance in one experiment but significantly reduced it in the other experiment.

This paper addresses the rescaling controversy in the estimation of economic weights for livestock improvement programmes. A model of genetic improvement based on the neoclassical theory of the firm and incorporating genetic improvement is proposed for the estimation of economic weights. Disparities between estimates of economic weights calculated per animal as opposed to per unit of product, per breeding female or per enterprise disappear when economic weights are calculated using this model. Equivalences of economic weights at the different bases of evaluation, previously obtained by rescaling the production enterprise to a fixed input, output or profit are compared with this model. The conventional approach to the derivation of economic weights is characterized as implicitly making unreasonable assumptions about the behaviour offarm firms.

Extension of the proposed model to the level of the farm product market allows assessment of the distribution of gains from genetic improvement between producers and consumers using the economic surplus approach. In an illustrative example, the distribution of benefits among producers and consumers from genetic improvement in the Ontario cow-calf sector is shown to depend on the elasticity of demand for beef products in the North American market. When the demand for farm output is elastic, a significant proportion of the benefits from genetic improvement would accrue to producers. Conversely, when demand is inelastic, the majority of benefits would accrue to consumers. Economic weights calculated from the perspective of all producers could thus be different from those calculated from the perspective of an individual farmer or society as a whole. Finally, the market level model is used to compare the effects of genetic improvement which enhance product quality with cost-reducing genetic improvements.

Formulas were derived to predict asymptotic response to selection on best linear unbiased predictors (BLUP) of breeding values that account for selection-induced gametic phase disequilibrium, also known as the ‘Bulmer’ effect. Breeding programmes in populations of infinite size and with discrete generations were considered. For two-path breeding programmes with equal male and female accuracy of selection, relative reductions in response due to gametic phase disequilibrium were independent of heritability. Reductions in response depended only on intensities of selection and ranged from 0·22 to 0·27 when selected proportions were less than 04 for both males and females. With unequal accuracy of males and females, relative reductions in response depended on the ratio of accuracies, in addition to selection intensities. For given selection intensities, reductions were up to proportionately 0·08 larger with unequal accuracies than reductions obtained for equal accuracies. Relative reductions in response for breeding programmes with four paths of selection depended on intensity and accuracy of selection in each path, but were within a range similar to that observed for two-path programmes. Gametic phase disequilibrium will, therefore, not greatly affect ranking and relative differences among alternative breeding programmes.

Gametic phase disequilibrium had a larger effect on response with selection on BLUP than on phenotype, which is largely due to larger relative reductions in accuracy of selection with BLUP. Despite larger relative reductions, asymptotic response to selection on BLUP is expected to be larger than selection on phenotype.

Maternal behaviour and lamb vigour are both considered major variables affecting lamb survival, but there are few data to describe their relative importance. To investigate the relationship between lamb vigour and maternal behaviour this study compared the behaviour of pure Scottish Blackface lambs with Mule (Bluefaced Leicester ♀. × Scottish Blackface ♂) lambs, all born indoors. Anecdotal accounts suggested a significant reduction in lamb vigour in Mule lambs, a matter also of significant practical importance given the current incease in Mule numbers. Observations on the grooming behaviour of 32 single or twin-bearing ewes, and on the general activity and udder-seeking behaviour of their lambs were made at parturition. In this study, neither ewe grooming behaviour nor general lamb activity were directly related to lamb sucking success. It was shown that, although Mule lambs had high birth weights and stood as quickly as Blackface lambs, they showed significantly fewer sucking attempts (P < 0·01) and took longer to suck successfully (28 min for Blackface v. 55 min for Mules). The inability of Mule lambs to suck successfully was due to their failure to show proper udder-directed behaviour. These results indicate the importance of considering the behaviour of both ewes and lambs as it would seem that it is not ‘poor’ maternal behaviour but inappropriate lamb behaviour that is a limiting factor in lamb survival in the Mule breed.

A divergent selection experiment for carcass leanness in Texel-Oxford sheep was established to examine the differences between genetically lean and fat animals derived from the same base population. The selection criterion was designed to change body composition without a corresponding change in live weight, using an index of ultrasonic backfat depth and live weight at 20 weeks of age. The index was constructed using estimates of genetic and phenotypic parameters, which were available at the start of the experiment in 1985. The difference between the high and low lines, after 3 years of selection, for the selection index, live weight at 20 weeks of age, ultrasonic backfat and muscle depths was 0·59,1·30 kg, -0·76 mm and 0·88 mm respectively. The estimated difference for carcass lean and fat weight was 0·72 kg and -0·04 kg respectively with 13·5 g/kg and -13·8 g/kg for carcass lean and fat proportion. The realized heritability for the selection index, estimated from the regression of cumulative response on cumulative selection differential was 0·42, with a standard error of 0·25, after taking account of genetic drift. The selection index heritability, estimated with residual maximum likelihood (REML) methodology, was 0·46 (s.e. 0·14). REML heritability estimates for live weight at 20 weeks of age, ultrasonic backfat and muscle depths were 0·20 (s.e. 0·13), 0·35 (s.e. 0·14) and 0·43 (s.e. 0·14) respectively.

Correlated responses in slaughter and carcass traits to divergent selection for high or low carcass lean content in Texel-Oxford sheep were measured in the crossbred progeny of 23 rams. Rams were selected using the selection index: -0·995 FATD + 0·206 WT20, where FATD and WT20 are the ultrasonic backfat depth and live weight at 20 weeks of age, with both traits standardized to have zero mean and unit phenotypic variance. A total of 329 crossbred lambs were slaughtered at 16 weeks of age and 250 lambs were slaughtered at fixed weight, 38 to 40 kg for castrated males and 36 to 38 kg for ewe lambs. Progeny from high-line rams grew faster, as indicated by the heavier slaughter weight of lambs slaughtered at fixed age (04 (s.e.d. 0·5) kg) and the lower age at slaughter for lambs slaughtered at fixed weight (-5 (s.e.d. 3) days). Subcutaneous and internal fat scores and the Meat and Livestock Commission carcass appraisal and conformation scores were all lower in the high line than in the low line and the magnitude of the selection line differences for lambs slaughtered at fixed weight was essentially double that of lambs slaughtered at fixed age (0·8 v. 0·5 score units).

Shoulder joints of 254 lambs, slaughtered at fixed age, were dissected and half carcasses were dissected on 66 of the lambs. Carcass and shoulder joint information was combined with double-sampling methodology, using multiple regression equations to predict carcass composition. For each tissue type, viz. lean, subcutaneous fat, internal fat and bone, the correlations between carcass content and shoulder joint content were at least 0·90 and the proportions of variation in carcass tissue content accounted for by the prediction equations were also at least 0·90. Progeny of high-line rams had higher carcass lean weight, (402 (s.e.d. 140) g) than progeny from the low line, with no difference in carcass fat weight, such that carcass lean content was higher, (10 (s.e.d. 5) g/kg), and carcass fat content was lower, (-10 (s.e.d. 7) g/kg). Based on the slaughter and carcass traits of these crossbred progeny, divergent selection for high and low carcass lean content has established lines of animals with different rates of lean growth but similar rates offat deposition.

Pure Merinos d'Aries male lambs were reared indoors (IN), with hay and concentrates, or outdoor (OUT) on improved Mediterranean range (Garrigues) and slaughtered when they reached 25 (light) or 32 (heavy) kg live weight. The alimentary tract weight was significantly affected by slaughter weight and by rearing method, which also significantly modified rumen contents. IN lamb body composition was higher in fat and energy and lower in water and protein than OUT lambs but differences induced by the rearing method were reduced when slaughter weight was increased. Allometric equations established for each environment were used to determine body composition and body gain composition at 20 and 25 kg empty body weight. Changes were very limited for IN lambs but protein and fat content of OUT lambs changed greatly as a result of the tremendous increase of grass availability towards the end of the fattening period.

About 8 weeks after parturition six multiparous British Saanen goats with permanent rumen fistulas were allocated to three dietary treatments in a random sequence for three successive 30-day periods. The treatments were perennial ryegrass hay ad libitum with 1000 glday of concentrates containing 112 (low-protein, LP), 182 (high-protein, HP) or 255 (very high protein, VHP) g crude protein (CP) per kg dry matter (DM) daily. The CP concentration was increased by substitution of soya-bean meal for cereals. From day 19 of each period, when measurements were made, concentrate allowance was reduced to 850 glday and hay intake was offered at proportionately 0·10 more than consumption in the previous 6 days. Hay intake and milk yield increased linearly with CP in the concentrates, but differences between HP and VHP were small and non-significant. Milk composition was unaffected by the treatments, so yields of milk solids followed the same trends as yields of milk, but these were only significant for solids-not-fat. The digestibility of neutral-detergent fibre, acid-detergent fibre and nitrogen (N) all increased with increasing CP, but significantly so only for N; the digestibility of DM and organic matter was unaffected.

The digestibility of the hay incubated in the rumen was unaffected by the treatments. With increasing N intake, faecal, urine and milk N increased linearly as did apparently digested N but N retention did not follow a consistent pattern. Rumen volatile fatty acids and pH were unaffected but concentration of rumen ammonia and blood urea increased with increasing CP as did rumen fluid dilution rate. The results suggest that, with lactating goats given diets of moderate quality grass hay and concentrates containing soya-bean meal, responses to concentrations of CP greater than about 180 g/kg DM in the concentrates or 140 g CP per kg DM in the total diet are likely to be small.

Twenty-four castrated male British Angora goats of Australasian origin aged 11 months and weighing 23·5 kg live weight were studied in a 112-day experiment. They were allocated in a 2 × 2 factorial design to receive diets containing, per kg dry matter, concentrations of estimated metabolizable energy (ME) of 10·2 M] (LE) or 11·9 MJ (HE) and crude protein concentrations of 108 g (LP) or 180 g (HP). The HE diets were offered to provide a dry-matter intake of 30 g/kg live weight and the LE diets to provide 0·85 of the ME intake of HE diets.

In comparison with LE diets, the HE diets, on average, increased live-weight gain, food conversion efficiency, carcass weight, killing-out proportion, empty body weight, cross-sectional area of m. longissimus dorsi and fat thickness over m. serratus dorsalis and weights in the carcass for dissected lean tissue, crude protein (N × 6·25) and dissected and chemically extracted fat. Weights of shoulder, hind barrel, and best-end joints and their weights of dissected lean and fat were increased on HE diets. No consistent effects due to dietary energy were observed for yield or diameter of mohair fibres.

The greater intake of dietary protein resulted, on average, in increased values for live-weight gain, efficiency of food conversion, carcass weight, weight of dissected carcass lean tissue and crude protein, killing-out proportion and cross-sectional area of m. longissimus dorsi. The greater intake of dietary protein increased significantly both yield and diameter of mohair fibre.

Significant interactions between protein and energy for empty body weight, carcass weight and carcass fat indicated that increasing dietary protein intake had a greater positive effect on the low than on the high energy diets. Similarly, increasing the dietary energy consumption on the LP diets produced a greater positive effect than that recorded on the HP diets.

The results indicated that growth and lean tissue deposition were affected by both protein and energy intakes but that mohair fibre characteristics were affected consistently only by protein nutrition.

The effects on the production of indoles of dietary fibre, lactose and antibiotic were examined in a factorial design using 16 crossbred pigs (eight boars and eight gilts) from 40 to 90 kg live weight. The control diet was based on wheat and soya-bean meal which was partially replaced either by sugar-beet pulp (400 mg/g) or lactose (25 mg/g) or both. All diets were offered with or without the antibiotic tylosin phosphate (200 mg/kg diet). Animals were penned individually and the diet restricted to provide 1·3 M] digestible energy per kg M0·75. All faeces were collected for two 4-day periods at about 60 and 75 kg live weight. Animals were slaughtered on completion of the experiment and subcutaneous fat was sampled. Faeces and carcass fat were analysed for skatole and indole. There were no significant effects of treatments on growth rate but killing-out proportion was reduced (P < 0·05) on fibre or lactose diets with an additive effect (P < 0·001) of the combined ingredients. Dietary fibre significantly increased the daily elimination of skatole and indole and the concentration of indole in faeces but because of greater faecal bulk on the fibre diet the concentration of skatole in faecal dry matter was higher (P < 0·05) on the control diet. Dietary lactose had no effect on indole in faeces but significantly reduced the concentration and daily output of skatole. Levels of both skatole and indole in faeces tended to be reduced with dietary antibiotic which had a significant interaction with the fibre treatment on indole levels. The concentrations of skatole or indole in subcutaneous fat were neither affected by dietary treatment nor significantly correlated with concentrations or outputs in faeces.

Meat quality was studied in pigs reared in groups kept as units during the fattening period and slaughter (unmixed). The results were compared with conventionally reared pigs, which were mixed during the fattening period, at transport to the abattoir and at lairage (mixed). It is concluded that the unmixed pigs in this study had a better meat quality measured as pH,, pHu, weight loss and also fewer skin lacerations compared with the mixed groups (i.e. less development of pale, soft exudative (PSE) and dark, firm dry (DFD) in the unmixed animals). There were no significant differences in meat colour or in lean content between the unmixed and mixed pigs.

Strategies of introgressing a transgene into a pig nucleus undergoing mass selection for net merit were deterministically evaluated. They consisted of systematically backcrossing hemizygous transgenic sires to females from the selection nucleus, or vice versa, followed by intercrossing of hemizygous individuals, assuming different levels of heritability (h2), polygenic breeding value of the founder animal, inbreeding depression and constraints in availability of resources. The polygenic breeding value of the founder transgenic animal and inbreeding depression were of negligible importance if backcrossing lasted for at least three generations, and there was little advantage in extending backcrossing much further. The best introgression strategy examined was to backcross selection nucleus sires to hemizygous females, but this was a less efficient strategy in terms of testing transgene effects. Testing the survival of homozygous carriers requires approximately five and 100 matings among hemizygous individuals to detect a reduction in viability of 0·5 and 0·1, respectively. Comparing several candidate transgenes in the first generations of backcrossing is feasible, and does not result in substantial delays in improvement of polygenic breeding value in the selected transgene. If resources are limited, the magnitude of the transgene effect (as a proportion of the mean) that compensates for the genetic lag incurred by its introgression is about 0·1 for most economic traits in pigs. To compensate for less selection while backcrossing and for risk in use, transgenes must have an appreciable effect on economic merit to make their introgression worthwhile, even when the additional costs of transgene production are ignored.

Two feeding experiments with housed lambs of the Spanish Manchega breed were carried out over 2 years with the aim of assessing the suitability of field beans in lamb finishing diets. In the 1st year field beans were compared with soya-bean meal as a protein source in a factorial experimental design with the proportion of maize in the diet being 0·15, 0·25 or 0·35. In the second experiment the effect of replacing soya-bean meal and sunflower meal by inclusion of field beans at proportions, 0, 0·1, 0·2, 0·3 and 04 of the diet was studied. All diets were isoenergetic and isoproteic. The composition of the diets had no significant effects on the average daily gain or the food conversion ratio in either experiment. Results from experiment 2 showed that the increasing amount of field beans in the basal diet did not affect protein, fat and water content of a loin sample of meat, or fatty acid composition of kidney fat.

During a series of routine experiments to evaluate 16 foods offered to wether sheep, conventional measurements of digestibility were augmented by measurement of fractional outflow rates (FOR) of solids (ks) and liquid (k1) from the rumen and urinary allantoin nitrogen excretion (UAN) as an index of microbial yield. Fixed (1 kg) amounts of ‘dry’ foods were offered to sheep ranging in weight from 42 to 89 kg which permitted a retrospective analysis of plane of nutrition effects on diet digestibility, ks, k1 and UAN. Each diet was simultaneously offered to three sheep (one each of large, medium and small size). Smaller sheep had significantly higher FOR, significantly lower apparent digestibilities of dry matter and significantly higher UAN (g/kg digestible organic matter (DOM)). Higher UAN (g/kg DOM) indicated higher microbial energetic efficiencies with the smaller sheep.