A review of recent trends in animal science is used to provide a flavour of how, from a purely technical viewpoint, evolving biotechnology may influence animal production systems in the foreseeable future. The areas considered are: the nutritive value of foods and forages, animal health and welfare, the temporary alteration of production traits to meet an immediate goal, and the permanent alteration of traits to meet an immediate goal, and the permanent alteration of traits by genetic selection or by the production of transgenic animals. In improving the nutritive value of foods, modern biotechnology has produced food grade enzymes and amino acid supplements. Genetically engineered cereals, grasses and legumes, rich in essential amino acids, are on the horizon. In disease prevention, genetically engineered vaccines may be preferable to conventional ones in that they have a defined composition, with a degree of control during manufacture which allows amino acid substitution within the peptide to confer specificity to a particular serotype.

Modern techniques with the potential to promote a transitory alteration in a production trait involve either immunization against an inhibitory biochemical pathway or active promotion of a stimulatory pathway by the administration of recombinant-derived hormones and proteins. Strategies for permanent alteration of traits by gene transfer, initially directed to enhancing growth, are now shifting in emphasis towards the transfer of genes for enhanced nutrient digestion, disease resistance, and improved product quality. The role of recombinant DNA technology in the development of diagnostic probes for use in genetic selection programmes and in the monitoring of disease is also expanding rapidly.

In all areas of animal science, molecular biology is promoting a better understanding of the underlying mechanisms that control production. By so doing it should ensure that science fulfils its primary rôle of providing animal production industries with a range of options from which to choose the most acceptable way forward.

The paper explores a scheme for the ethical evaluation of animal biotechnologies, exemplified by animal transgenesis. It begins with an overview of prominent ethical theories (deontological and consequentialist) and proceeds to apply them to four ethical principles, viz. autonomy, justice, non-maleficence and beneficence, in relation to the interests of the treated animals and of different groups of people affected by the technology. Evaluation is facilitated by use of a schematic device — an ‘ethical grid’. The importance of public education and attitudes to biotechnology is illustrated by reference to recent public opinion surveys in the European Community. The paper concludes with a discussion of the impact of future trends in global population, food resources and environmental change, which emphasizes the need for a reappraisal of priorities in animal production systems. It is suggested that attempts to eradicate hunger, to improve animal welfare and to devise sustainable agricultural systems will be facilitated by greater investment in the emerging academic field of agricultural bioethics.

Forty pregnant F1 crossbred cows (20 Holstein-Friesian × Boran and 20 Simmental × Boran) were assigned to a 2 × 2 (work × diet) factorial experiment as follows: supplemented-non-working (SNW), supplemented-working (SW), non-supplemented-non-working (NSNW) and non-supplemented-working (NSW). Working cows pulled sledges 100 days/year (pull = 350 to 450 N, 4 h/day, 4 days/week). Conception and oestrus at fixed times (200 and 365 days post partum) were analysed using linear logistic models. Proportional hazard models were used for analysing ‘failure’ time data such as time to first oestrus or time to conception. Diet supplementation significantly decreased days to first oestrus and days to conception in non-working and working cows. SW cows had similar reproductive performance to NSNW cows. In supplemented cows, work significantly delayed days to conception. However, by 365 days post partum, conception rate was similar for SNW and SW cows. Body condition at calving significantly affected post-partum reproductive ability of non-working and working cows. Natural grass hay alone could not support potential reproductive ability of crossbred cows. Work output of supplemented cows may be associated with longer calving intervals. The economic trade-offs between longer calving intervals and work output should be examined in detail.

A dispersed hybrid MOET nucleus project was implemented in the Canadian dairy industry. Embryo yield, pregnancy rate, and effects of management and selection practices are reported. Repeatability of viable embryo yield was 0.31. Average viable embryo yield was 6.85 (s.e. 5.35) embryos per collection, with average pregnancy rates of 0.58, 0.46 and 0.51 for grade 1 fresh, frozen, and split embryos, respectively. Of the donors selected, 80% produced enough embryos to form a family of at least 15 offspring. Based on observed results, expectations of family size and structure and generation intervals were calculated. Only 10% of completed families are expected to result in less than three milking daughters. Generation interval for sib-tested sires was 58 months of age under practical field conditions, which was shorter by a factor of 0.19 than a traditional progeny test but longer than original theoretical estimates by a factor of 0.32. Realized selection intensities for a total merit index were 2.22 for sires and 3.77 for dams of embryos. Accuracies of selection for sires and dams were 0.93 and 0.73 respectively. To improve the scheme, use of more fresh embryos, embryo splitting and less delay in transferring frozen embryos are recommended.

The objective of this work was to investigate phenotypic sources of variation in the sites of storage of milk within the udder. Ten primiparous and 10 multiparous dairy cows were studied over two successive lactations in order to investigate the effects of age, parity and stage of lactation. Cistern and alveolar milk volumes were estimated at a standard 8 h after a normal morning milking by catheter drainage and machine milking with oxytocin respectively. Measurements were made at approximately 9, 20, 30 and 42 weeks of the initial lactation and weeks 1, 4, 7, 10, 20 and 34 of the subsequent lactation. In the initial lactation, there was a significant difference between primiparous and multiparous animals in the rate of decline of total daily milk yield (P < 0·001). Cistern milk yield (kg/8 h) from multiparous animals declined over the lactation whilst that for primiparous animals was maintained. The effect was shown as a significant interaction effect (P < 0·05). For both multiparous and primiparous animals cistern proportion (cistern yield divided by total milk yield at 8h after a normal milking), increased over the lactation (P < 0·001). This was largely a consequence of the reduced total milk yield. Eleven animals were studied through the subsequent lactation. Cistern yield followed a lactation curve of similar form to that for total yield. The decline in cistern yield over this lactation was much greater than the decline with multiparous animals in the previous year. This may, in part, reflect a faster decline in total daily yield. Stage of lactation and parity must be taken into account if a standardized evaluation of cistern characteristics is to be obtained.

Calving date (CD) records of 68 896 polled Hereford dams of 120 682 calves were coded within herd-year-season with date 1 being the date the first calf was born. Factors affecting CD and its relationship with production traits were investigated. Early calving was found to be associated with high performance, conceivably because dams calving early were able to utilize the season-dependent range pastures to their advantage thus providing adequate milk supply to their calves. Weight and age of dam, weight of calf, initial CD, index of milk production potential, and previous CD were found to have significant influence on current CD. Extremely small cows at previous weaning had a tendency to calve late. Cows calving in the spring produced calves with higher overall weight per day of age than did cows calving in other seasons. Initial CD was found to affect CD in subsequent parities. Repeatability of CD was estimated at 0·23. Heritability was estimated at 0·16 (s.e. 0·05) and indicated that additive genetic variance constitutes a moderate proportion of the variation in CD. Genetic correlation of CD with birth weight (−0·30, s.e. 0·10), post-weaning rate of gain (·0·64, s.e. 0·19) and yearling weight (−0·60, s.e. 0·11) indicated that ‘plus’ additive genes for CD influenced these traits favourably. However, the corresponding correlations with pre-weaning rate of gain (−0·03, s.e. 0·08) and weaning weight (−0·05, s.e. 0·03) were not significant.

The effect of fish-meal supplementation or cimaterol administration on the composition, cellularity and metabolism of subcutaneous and perirenal adipose tissue was examined in young Friesian steers given grass silage. Animals (approx. 117 kg live weight) received either silage alone (group C; no. = 6) or supplemented with fish meal (150 g/kg silage dry matter; group FM; no. = 6) or cimaterol (0·06 mg/kg body weight per day) administered via osmotic minipumps (group CIM; no. = 6) for a period of 6 weeks. Samples of perirenal and subcutaneous adipose tissue obtained at slaughter were used for determination of tissue composition and in vitro rates of lipogenesis, lipolysis and substrate oxidation. FM animals showed significantly greater live-weight gains (0·61 kg/day) compared with C (0·21 kg/day, P < 0·001) while CIM animals had significantly lower rates of gain (0·04 kg/day, P < 0·05). This was considered to be related to increased heat loss from the β-agonist-treated animals as a result of very cold weather encountered during the experimental period. CIM administration reduced adipocyte size suggesting an increased number of cells per g tissue. Both lipolytic and lipogenic rates were reduced by cimaterol and there was some evidence that the response to insulin was diminished, at least with respect to substrate oxidation. FM increased lipogenesis from acetate and acetate oxidation rates in subcutaneous adipose tissue with similar trends in perirenal tissue. The results indicate that both fish-meal supplementation and cimaterol administration caused substantial changes in adipose tissue metabolism as determined using in vitro procedures, even though the magnitude and direction of the changes were not in strict accord with estimates of net fat accretion from related in vivo studies.

Two experiments were designed to examine the effects of ammonia treatment of barley straw on rumen environmental conditions for fibre degradation, and to determine the effect of treatment on the soluble and insoluble fractions of straw. In experiment 1, rumen pH, and ammonia-nitrogen and volatile fatty acid concentrations in the rumen of sheep receiving untreated (US1) or ammonia-treated (TS1) straw were recorded. Also, both straws were incubated in the rumen of both groups of animals. There were no significant differences (P > 0·05) within rumen parameters, except for butyrate proportion, which was higher (P < 0·01) with TS1. Dry matter and neutraldetergent fibre disappearances of TS1 were higher (P < 0·001) than those of US1 at all the incubation times. Degradation of both straws in US1-fed sheep was not smaller, and in some periods of incubation was even greater, than in TS1-fed animals. In experiment 2, samples of untreated (US2) and treated (TS2) straw were incubated in wethers offered a mixture (50:50) of alfalfa hay and straw. Samples of US2 and TS2 were soaked in autoclaved rumen fluid to measure their solubility. It was clear that, although treatment increased the soluble fraction of US2 and TS2 by 52 and 65 g/kg respectively, from 0 to 72 h of incubation, increasing the differences between straws from 45 to 58 g/kg in that period, actual microbial action on the treated roughage was the more important factor, accounting for a difference between US2 and TS2 of 131 g/kg after 72 h incubation.

Six ewes were given a white clover/grass silage with a high content of cyanogenetic glycosides during the last 69 to 97 days of pregnancy (group CN+), while the five ewes of the control group (group CN−) received a white clover/grass silage with a low content of cyanogenetic glycosides during the last 67 to 92 days of pregnancy. Uniodized salt was the only mineral supplement offered. The daily intake of cyanide (in the form of cyanogenetic glycosides) and of selenium per animal was 1000 and 60 mg of cyanide and 30 and 23 μg of selenium in group CN+ and CN− respectively. Initial erythrocyte glutathione peroxidase activity (GPx) was identical in both groups. Two weeks before parturition GPx activity was significantly lower in the ewes of group CN+ than in the ewes of group CN−. The newborn lambs of the group CN+ had significantly lower erythrocyte GPx activities (P < 0·01) and tended to have higher plasma creatine kinase activities (P = 0·07) than the lambs of the group CN−. The results show that the intake of cyanogenetic glycosides affects the selenium status of sheep and increases the susceptibility of lambs to nutritional myopathy if the selenium content of the ration is marginal.

Plasma thyroxine concentrations in the ewes in group CN+ were not reduced but their lambs tended to have slightly lower levels immediately after birth than the lambs of group CN− (P = 0·25). The intake of cyanogenetic glycosides presumably had no or at most only a slight effect on thyroid function, presumably because the body iodine reserves of the ewes were sufficient to offset the goitrogenic effect of thiocyanate.

Six rumen cannulated sheep (26·1 (s.d. 2·24) kg live weight) given maize stover ad libitum were supplemented with either sunflower (Helianthus annus) cake (SFC), decorticated cottonseed (CSC) or noug (Guizotia abyssinica) cakes (NGC) with or without crushed maize grain. The 6×6 Latin-square experiment studied the degradation properties of the oilseed cakes and their effects and that of maize on the degradation of maize, maize stover and the composite diet.

Seedcakes differed in the degradability characteristics of dry matter and nitrogen: intercept (a) (P < 0·001); potentially degradable fraction (b) (P < 0·001); rate of degradation (c) (P < 0·001); and the effective degradability (P < 0·0001). The pooled sum of the degradabilities of the individual ingredients were significantly lower than that of mixed ingredients (composite diet) (P < 0·001).

The main effects of protein and maize were not significant on the degradation of maize stover. Maize had the tendency to depress the rates of degradation of stover by 0·52 with SFC.

Although the protein × maize interaction was not significant on maize stover degradability, it is important to note that maize had the effect of increasing stover degradation rate with CSC and NGC, but a depressing effect with SFC. Hence it was concluded that the carbohydrate effect on roughage degradation rate may vary as a function of the difference between the degradation rate of the energy and protein supplements.

Thirty-six male Ethiopian Menz sheep (9 to 22 months old, average live weight 15·8 (s.d. 1·84) kg), given maize stover (1·5 times ad libitum) supplemented with either 75 g cottonseed cake (CSC), 114 g noug cake (NGC; Guizotia abyssinica) or 112 g sunflower cake (SFC) with or without maize grain, were used in an 88-day study comprising growth and balance trials. The trials were undertaken according to a randomized-block design with a 2 × 3 factorial arrangement.

There were no significant interactions (P > 0·05). Sheep consumed significantly more stover when supplemented with CSC compared with NGC and SFC (P < 0·05). Maize grain significantly increased organic matter intake (P < 0·001). Although CSC tended to support lower live-weight gains, the effect of protein was not significant. Maize grain increased live-weight gains (P < 0·01).

Urinary nitrogen (N) excretions were similar between CSC and SFC but about 0·22 higher with NGC (P > 0·05). The faecal N output was 0·33 (P < 0·01) and 0·18 (P < 0·05) higher with CSC than with NGC and SFC respectively. Maize grain had no effect on any of the N-balance measurements.

Cottonseed cake supported lower daily production of purine derivatives (PD) (P < 0·01), microbial purine (P < 0·01) and microbial protein (P < 0·01) than either NGC or SFC. Maize grain increased the daily excretion of total PD (P < 0·05), microbial purine (P < 0·05) and microbial protein (P < 0·05). Neither the protein source nor maize grain affected the efficiency of microbial protein synthesis. It was concluded that SFC was utilized more effectively both in terms of rumen microbial N synthesis, N retention and growth. The addition of a small amount of energy as crushed maize grain increased microbial N synthesis, N retention and live-weight gain.

Seventy-six Large White × Landrace sows from parities 2 to 6 were allocated to one of four treatments at day 110 of gestation on a parity and live-weight basis. The four treatments involved food levels of either 3 or 6 kg/day during a 28-day lactation followed by either 1·75 or 3·50 kg/day during the first 28 days of gestation. Litter size suckled was standardized at 10 piglets wherever possible. Live weight and backfat changes were monitored in all sows and litter growth and survival rates were recorded. Post weaning all sows were given daily boar contact and mated twice at the first observed oestrus. A single blood sample was collected from each sow at days 7, 14, 21 and 28 of gestation for determination of plasma progesterone concentration. Data on litter size and piglet birth weights were collected at the subsequent parturition. Sows low-fed during lactation lost significantly more live weight (31·2 v. 5·8 kg, P < 0·01) and P2 backfat (3·6 v. 1·9 mm, P < 0·05) in lactation than did high-fed sows. Underfeeding the lactating sow also significantly reduced the weaning weight of the litter (62·3 v. 68·7 kg for low- v. high-fed sows, P < 0·05), but did not significantly change either creep food intake by the litter or pre-weaning mortality rate. Parity 2 sows weaned significantly heavier piglets and litters than did sows from parities 3 to 6 (7·48 and 74·9 kg v. 6·72 and 63·8 kg respectively, P < 0·01). Food level in lactation did not significantly influence the length of the rebreeding interval (6·3 v. 7·3 days for high- v. low-fed sows) and although there was a two-fold difference in the proportion of sows failing to exhibit oestrus post weaning (0·08 v. 0·16 for high- v. low-fed sows) this difference was also not significant. Lactation food level did not significantly influence either sow live-weight or backfat change in gestation, plasma progesterone concentrations during early gestation or subsequent litter size. However, sows low-fed in lactation did tend to produce fewer piglets in the subsequent litter (9·54 v. 10·75 piglets born alive for low- and high-fed sows respectively, P = 0·062). Post-weaning reproductive performance was significantly affected by sow live weight (P < 0·05) and backfat (P < 0·01) at parturition, and live weight (P < 0·01) and backfat (P < 0·05) at weaning, but not by changes in these parameters during lactation. Food level in early gestation did not significantly influence either plasma progesterone concentrations, the size of the subsequent litter (10·09 v. 20·29 piglets born alive for high- and low-fed sows respectively) or mean piglet birth weight (1·27 v. 2·22 kg for high- and low-fed sows respectively). It is concluded that (1) both lactation food level and parity may alter pre-weaning piglet growth, and (2) the effects of lactation food level on the subsequent reproductive performance of mature sows appear to be different from those seen in parity 1 sows.

A theoretical function is proposed which describes the individual weight-age relationship for foetuses in pigs. The function is based on total growth of the litter. A maximum uterus capacity, dependent on insemination weight of the sow, and a limitation of this capacity, dependent on litter size, is assumed. A modified Michaelis-Menten function is used as a basic growth function. The model was tested against experimental data and compared with four models from the literature. Goodness of fit, extrapolation outside the range of data, and biological interpretation of the parameters from the model were checked. A maximum uterus capacity of 20·3 kg for the average insemination weight of 119·0 kg was found. The inflexion point of the model was significantly (P < 0·05) dependent on litter size.

The study was conducted to test the hypotheses that sustained restriction of food to maintain constant body weight of market-ready pigs, hereafter terminal maintenance (TM), would (1) decrease the size of gastrointestinal and other visceral organs, (2) increase dressing proportion, and (3) increase lean and decrease fat content and improve the lean: fat ratio of carcass. Forty-eight crossbred castrated male pigs (initial body weight, 23·5 kg) were randomly assigned to eight treatment groups (six pigs per group; one pig per pen). Three comparison groups were included. The ad libitum control group (AL) was slaughtered at the target weight, 105 kg. One group was continuously restricted (CR) to 0·8 of the intake by AL and slaughtered at the target weight. The terminally restricted (TR) group was given food ad libitum to 1·1 times the target weight; then food was restricted to effect weight loss to the target weight before slaughter. Five TM groups were given food ad libitum to the target weight; then TM was administered for various periods (7, 14, 21, 28 and 42 days) before slaughter. CR either had no effect or caused enlargement of visceral organs compared with AL. TR caused reduction of viscera, especially of abdominal-digestive organs. TM caused reduction of most viscera organs (0·001 < P < 0·05). Regression analyses indicated that most abdominal organs were reduced 50 to 70 g/kg per 10 days of terminal maintenance. TM and TR also increased carcass weight (P < 0·05). Catabolism associated with reduction of viscera organs may provide nitrogenous substrates to support the continued lean accretion observed during terminal maintenance. The reduced viscera and increased carcass weight combined resulted in increased dressing proportion (P = 0·06). Regression analyses (weight v. TM-days) showed that lean mass increased (71 g/day; P < 0·05) and fat mass decreased (−52 g/day; P < 0·01). Weight of bone and belly did not change. Differential lean gain, lean gain minus fat gain, during TM occurred at a rate of about 120 g/day.

Plasma oxytocin was measured in 11 multiparous sows for 13 h after the start of parturition to confirm the existence of early milk ejections and determine whether they were associated with pulsatile oxytocin release. The relationship between oxytocin concentrations and duration of parturition was also analysed. Oxytocin was released in pulses during and after parturition and mean concentrations reached maximum 2 to 4 h after the first birth. Discrete milk ejections occurred during parturition but only 42% of these were associated with oxytocin peaks before 4 h post partum. After this more than 80% of milk ejections occurred with oxytocin peaks. Sow grunting increased during milk ejections and peak grunt rate increased after parturition. Oxytocin peaks without milk ejections did not lead to an increased rate of grunting. Sows with prolonged parturition had lower basal and peak oxytocin concentrations. During the first 4 h only half of the piglets were born during an oxytocin peak. Discrete milk ejections with oxytocin peaks can occur before parturition is completed. However, during the first 4 h post partum, basal oxytocin concentrations may be high enough for milk ejection to occur without further oxytocin secretion. Both milk ejection and oxytocin release are necessary for the sow to increase grunt rate. Low oxytocin concentration is associated with prolonged parturition.

Using a completely randomized design, 72 individually penned pigs, comprising two genotypes (Masterbreeders Mastergilt × Large White and Sovereign × Large white progeny) with equal numbers of boars and gilts, were given food ad libitum from 25 to 60 kg live weight. From 60 to 120 kg one-third of the pigs continued to be given food ad libitum whilst the remainder were given one of two levels of restriction (0.85 and 0.925 of maintenance energy × 3.5). Diets were calculated to provide 13.8 and 13.0 MJ digestible energy (DE) per kg air-dry weight for growing and finishing phases respectively. Ultrasonic measurements of backfat at the P2 site were made at 10 kg intervals from 60 to 120 kg live weight and carcass measurements taken at slaughter. Complete dissection of ham joints was carried out. Predicted ad libitum intakes were based on established equations but daily intakes were much lower than these values and no treatment provided food restriction compared with them. Daily DE intakes (mean of both genotypes) obtained at 25, 60, 90 and 120 kg live weight were 204, 30.7, 36.2, and 414 MJ (i.e. 3.5, 3.1, 2.9 and 2.7 × maintenance). During the growing (25 to 60 kg live weight) and finishing (60 to 120 kg live weight) periods boars grew faster (P < 0.01 and P < 0.001) than gilts (881 v. 827 and 944 v. 806 g/day) with corresponding improvements in food conversion ratio (P < 0.001). Boars had lower killing-out proportions (0.787 v. 0.801; P < 0.001). Mean P2 values for boars and gilts were 13.2 and 13.9 mm respectively (excluding skin). Greater quantities of muscle were found in the hams of boars than gilts (662.7 v. 642.3 kg; P < 0.05) but no difference between the sexes for ‘eye muscle’ area was observed (43.3 v. 45.0 cm2). Results show the apparent potential of modern hybrids to achieve good growth rates despite moderate food intakes and their ability, even when given continuous access to food, to produce very lean carcasses at relatively heavy slaughter weights.

The depressing effect of high rearing temperature (30°C) on body weights of heterozygous naked-neck broiler chickens was apparently less pronounced than in control broiler chickens but no effect of genotype, rearing temperature or interaction on abdominal fat pad content was found. Both genotype and rearing temperature affected plasma tri-iodothyronine but not growth hormone or insulin-like growth factor 1 levels in plasma. Rearing temperature of 20°C or 30°C had effect neither on the slope of the thermoregulatory heat production curves nor on the lower critical temperature in either genotypes except at 4 weeks of age.

The effect of exercise (walking 10.6 km/day and climbing 480 m/day) on intake of barley straw and body weight changes in 12 pregnant lactating suckler cows was investigated. Three groups of four cows received ad libitum barley straw and 4 kg per cow per day of different supplements. Neither exercise nor supplement had a significant effect on straw intake. Cows gained weight when not exercised, but lost weight during the exercise period. The experiment confirms previous findings that animals performing moderate work and given poor quality roughage, in the short term cannot increase daily intake to meet energy requirements and that intake may decrease when animals work.

Twenty-five primiparous cows in mid lactation were used in a 2 × 2 Latin-square design experiment. During each 3-week period, cows were offered a diet composed either of grass silage (8.3 kg dry matter (DM) per day) or hay (10.5 kg DM per day). Each diet was supplemented with a mixture of barley, soya-bean meal and urea in proportions calculated to keep the overall rations isocaloric and isonitrogenous. Cows offered grass silage produced more milk (+1.7 kg/day, P<0.01) with less fat and protein (−1.3 g/kg and −0.8 g/kg, respectively, P < 0.01) than those offered hay. All animals gained weight, but they gained more with the hay diet than with the grass silage diet. The rheological parameters of milk were similar in both groups. Rumen juice of cows offered hay had higher concentrations of acetic acid and slightly lower concentrations of propionic and butyric acid (P < 0.01) than cows offered grass silage.

Effects of dietary protein concentration on the amino acid composition of sow's milk was studied using 10 crossbred first-litter sows. At parturition, diets containing similar concentrations of digestible energy but with either 63 or 238 g crude protein per kg and 4.4 and 15.1 g lysine per kg respectively, were given through lactation (five sows per treatment). The ratios of other amino acids to lysine were in excess of those currently recommended for lactating sows. Dietary protein level significantly affected milk yield, gave higher milk protein output (P > 0.05) but was without significant effect on the proportions of amino acids in the milk.