About 350 single- and 250 twin-born female Ayrshire cattle were compared on the same feeding regime in respect of 12 linear body measurements at 3-monthly intervals up to 36 mo of age, and some two-thirds of them up to 48 mo. The twins were purchased from a wide variety of farms, and it is unlikely that their dams were significantly better fed, in pregnancy, than the dams of single calves.

The effects of month and year of birth and age at first calving (including some pregnancy and lactation effects) were estimated by least-squares procedures. The trends of the differences between single and twin-born animals were analysed as percentages of current and of mature size. Earliness of maturing had no apparent effect. For the traits of height and girth, twin-born animals were smaller than single-born by nearly 2 % of mature size (3 % of current size) at 3 mo of age and for the other traits the difference was around 1 %. By 12 mo the differences were generally about half their initial value and remained at this level, except for head width where the difference declined to zero around 2 years of age.

It is concluded that twin-, compared to single-born, cattle are subject to a small degree of permanent stunting in most linear measurements.

A 2 × 2 factorial design experiment was conducted for 2 years using 72 British Friesian cows to assess the effects of two levels of concentrate input (822 and 610 ± 13·7 kg/cow) and two stocking rates (6·4 and 4·9 cows/ha) on animal performance. The animals, which had a mean calving date of 22 January, were blocked according to calving date and allocated at random to treatments within each block.

All concentrates were given during the post-partum, indoor-feeding period in addition to ad libitum grass silage. All animals received equal concentrate inputs/kg milk produced for the first 4 weeks after calving following which the input to the low concentrate animals was reduced. The animals went to pasture during mid-April and were rotationally grazed for a 24-week period. The pasture received 450 kg N/ha. No interaction between concentrate input and stocking rate was found. The mean milk outputs during the winter period were 2064 and 1971 ±23·9 kg, during the grazing period 2679 and 2739 ± 53·2 kg, and during the total lactation 4991 and 4984 ± 78·8 kg for the high and low concentrate groups respectively. The mean live weights for the two groups were 515 and 496 + 3·1 kg at the end of the winter period and 549 and 537 ± 4·1 kg at the end of the grazing season. The mean values for the high and low stocking rates respectively were: output/cow at pasture, 2571 and 2847 ± 53·2 kg; total lactation yield, 4804 and 5170 + 78·8 kg; live weight at end of grazing season, 529 and 558 + 4·1 kg. Milk composition data are also presented.

Two trials were conducted with two complete fattening diets contain- ing 25 and 45 % fibrous roughage, to examine the effects of three moisture levels and five soaking conditions on the performance and ruminal fermentation of fattening cattle.

Differences between treatments in live-weight gain and carcass-weight gain were not significant but there were differences in the efficiency of conversion of metabolizable energy into live weight and into carcass weight and in some instances these were significant. There was a trend towards increased weight of kidney, pelvic and cod fats and a slight decrease in weight of other fat trim of the carcass (subcutaneous and intermuscular) on the treated diets, as compared with the dry control diet.

The pH of the rumen liquor of animals given the soaked rations was lower and the total volatile fatty acid concentration higher than that of animals receiving the dry control diet. The propionic acid concentration in rumen liquor was significantly higher in animals receiving moistened diets.

Six groups of Israeli-Friesian intact male calves were studied over growth periods of 200 to 300 kg, 300 to 400 kg, and 400 to 500 kg live weight. Different ratios (85: 15, 70: 30 and 50: 50) of concentrate to roughage were compared. Two groups received the same ratio (85: 15 or 70: 30) throughout the experiment. In the other groups, the proportion of concentrates was progressively increased or decreased.

Live-weight gain in the first period ranged from 759 to 1013 g/day, i n the second period from 1095 to 1239 g/day and in the third period from 831 to 922 g/day. Overall rate of gain was highest in the groups receiving a constant ratio, regardless of the ratio used. Increasing the proportion of concentrates as the calves became heavier, which is common practice in Europe, did not improve performance and decreasing the proportion reduced performance. Only at 200 to 300 and at 400 to 500 kg live weight did a concentrate percentage higher than 50 result in improved performance.

Dry-matter intake, relative to live weight, was higher with a ratio of 70: 30 than with one of 85: 15 or of 50: 50 in each period. Animals on a constant ratio of concentrates to roughage gave the most efficient conversion of feed energy to live weight.

There were no significant differences in dressing percentage or in carcass composition.

1. Two experiments are described in which castrated Ayrshire cattle were reared on a conventional all-concentrate diet to 250 kg live weight. In Experiment 1 the effect of feeding a 1: 1 mixture (by weight) of barley and wet distiller's grains (WDG) from 250 to 408 kg live weight was examined. In Experiment 2 swedes and grass silage were offered in addition to WDG and barley during the growth phase from 250 kg live weight to slaughter. In both experiments a control group was fed an all-concentrate diet.

2. The introduction of WDG to the diet (Experiment 1) caused a significantly lower daily live-weight gain (P < 0·01) and an increase i n time to slaughter (P < 0·01). Carcasses from the control and treated animals were similar in weight, conformation and composition. There were no differences in growth rates in Experiment 2. The treated animals were heavier (P < 0·01) and older at slaughter (P < 0·001) than those in the control group and they produced heavier carcasses (P < 0·05). The carcasses were similar in composition but some differences in conformation occurred. These effects were the consequence of selecting animals for slaughter on the basis of equal finish (i.e. the ratio of muscle plus fat to bone assessed subjectively).

3. The effect of reducing the dietary energy concentration appears t o be smaller with cattle over 250 kg live weight than with younger, lighter cattle. The results, which are discussed in economic terms, suggest that castrated Ayrshire cattle reared on all-concentrate diets should be changed to a diet of lower energy concentration using cheaper feed sources at 250 kg live weight.

1. Herbage was ensiled, fresh at 17% DM or wilted to 32% DM, with and without the addition of formic acid (19·2 kg/tonne DM). The silages were fed individually ad libitum to 36 fifteen-month-old British Friesian steers of about 280 kg initial live weight (nine animals per treatment).

2. Wilting and the application of formic acid both inhibited fermentation, resulting in silages with higher levels of water-soluble carbohydrates, lower concentrations of volatile nitrogen and lower organic acid contents.

3. There were no significant dry matter × formic acid interactions in dry-matter intake or daily live-weight gain.

4. Treatment with formic acid did not enhance significantly either dry-matter intake or daily live-weight gain. Furthermore, it had little effect on digestibility, nitrogen retention or metabolizable energy (ME) concentration.

5. Wilting before ensiling increased dry-matter intake from 5·0 to 8·3 kg/head per day with consequent marked increases in ME intake, nitrogen retention and live-weight gain. Wilting, however, had little effect on digestibility, ME concentration, or the efficiency with which dietary nitrogen intake was retained.

A theoretical equation is proposed which describes the dynamics of foetal growth in mice. The equation is basically of exponential form and takes into account the effects of stage of gestation (T) and number of foetuses (N) on the instantaneous relative growth rate. The model was tested against experimental data by using a stepwise regression technique. Both stage of gestation and number of foetuses had significant effects (P < 0·01) on the instantaneous growth rate. When the model was tested against another set of data 44 out of a total of 52 comparisons had a prediction error less than 15 %. As a result, the following equation is proposed to describe the foetal growth of mice

W = e-14·34Ne(1·302–0·0276T–0·00059)T

An equation of this form could be useful in interpreting prenatal growth data for other species. Other factors which may influence the dynamics of foetal growth, such as maternal age or weight, could also be incorporated into the equation.

Starting in 1959 from a crossbred foundation, a specialized synthetic sire line has been developed with the aim of making rapid genetic improvement in lean meat production. Within-line selection, firston ultrasonic backfat and then on a performance index, was supplemented over 11 generations by a process of competitive immigration, in which individuals of any breed from outside were incorporated into the line on merit. By Generation 11 the Sire Line contained genes from 9 pure breeds and 2 hybrid strains.

After a rapid initial phenotypic decline in backfat, there was little apparent response to index selection. In Generation 11, a centrally tested sample of the Sire Line showed significant improvements over contemporary Large Whites in growth rate, feed efficiency, eye-muscle area, lean percentage and some fat depths, but was significantly worse in killing-out percentage. With the exception of teat number there was no evidence of a decline in reproductive performance, to which no attention was paid during selection. Estimated heritabilities of growth rate and backfat were not sufficiently different from those reported for purebred pig populations to indicate that additive genetic variance had been changed by mixing breeds. Some of the advantages and disadvantages of the ‘open synthetic’ method of genetic improvement are discussed.

A synthetic sire line has been developed over 11 generations by a process of selection accompanied by immigration. In each generation prospective immigrants of any breed were mated to native pigs already i n the Sire Line, and, ignoring breed, their progeny were given the same opportunity of being selected as the progeny from matings involving natives alone. This method of immigration is shown to be biased as a result of (a) heterosis in crosses of immigrants with natives, and (b) treating natives and immigrants as if they were members of the same population. When affected by both sources of bias, the breeding values of inferior immigrant progeny may be seriously overestimated with the result that inferior genes may enter the native population and hold back genetic progress. Methods of removing the bias and alternative systems of immigration are discussed.

The taste responses of pygmy goats to addition of gymnemic acid (GymA), inosinic acid (InoA), or monosodium glutamate (MSG) t o sucrose or quinine monohydrochloride (QHC1) solutions were studied. Addition of 20, 40 or 100 p.p.m. GymA to 25 % sucrose (aversive) solution caused the goats to show strong preference responses. Addition of GymA to a 30 % sucrose solution did not change the response from strong rejection. Addition of GymA to 1000 p.p.m. QHC1 did not change the strong rejection response, but additions of 10, 20, 60, 80 or 100 p.p.m. GymA to a 200 p.p.m. QHC1 solution changed the response from rejection to non-discrimination or weak preference.

Addition of 50 to 500 p.p.m. InoA to 0·08 % sucrose solution did not change the response from non-discrimination; InoA added to a 6·25 p.p.m. QHC1 solution, changed the response from non-discrimination to rejection at 50 p.p.m. and to strong rejection at 250 p.p.m. When MSG was added to 0·08% sucrose solution, the response remained non-discriminatory until 500 p.p.m. MSG was reached; this elicited a weak rejection. MSG (5, 50, or 500 p.p.m.) added to 10 % sucrose solution, changed the response from moderate preference o t non-discrimination. With 30 % sucrose solution the response was changed from weak rejection to non-discrimination by addition of 5 or 50 p.p.m. MSG but reverted to weak rejection at 250 p.p.m. MSG and to non-discrimination at 500 p.p.m. MSG. The addition of 5 to 250 p.p.m. MSG to 100 p.p.m. QHC1 solution changed the taste response from moderate rejection to non-discrimination; 500 p.p.m. resulted in slight rejection. Addition of 5 to 500 p.p.m. MSG to 6·25 p.p.m. QHC1 solution did not change the response from non-discrimination.

A technique is described for assessing the profitability of selecting sheep for wool production. A model of the breeding system incorporating three submodels is developed: one to represent the flock from which the selection intensities for rams andewes are calculated; a second to determine gains made in wool production and the year in which they accrue; and the third uses discounting procedures to examine the economics of selecting for wool production.

Flock and genetic parameters were set at ‘average’ values for an Australian Merino wool producer and gains were determined for a range of lambing percentages. Three measures were used to evaluate profitability; the net present value of the programme which shows overall profits, the internal rate of return, which gives the earning rate of the programme, and the payback period, which identifies the number of years before early costs are repaid.

sensitivity analysis was used to examine changes in the three measures of profitability resulting from changes in interest rate, wool price, costs for labour and computer analysis, wool testing costs and lambing percentage. Profitability was sensitive to changes in all parameters except wool testing charges, and of the remainder the producer has a degree of control only over labour costs. A programme can be profitable, however, if wool price and lambing percentage are adequate and costs can be kept at reasonably low levels. Simple breeding programmes should be studied in which labour inputs are kept to a minimum or where costs are confined to studs (nuclei) and genetic gain disseminated by the sale (migration) of rams.

Insemination and calving dates were obtained for 2618 British Friesian cows served twice by artificial insemination, the first time unsuccessfully, the second time successfully. The intervals between the two inseminations formed a multi-modal set of normal distributions with peaks at 21-day cycles. The standard deviation of the Kth distribution was 3·0y/K days, with about 58·5% of eligible animals submitted at each cycle. Nearly 84% of all intervals conformed to the normal distributions, suggesting that embryonic mortality occurred in about 16% of cases following the first oestrus after insemination.

Ensiled ear maize was compared with rolled barley as the cereal in a finishing diet for cattle weighing about 400 kg. The diets resulted in similar gains of about 1·2 kg/day.

Over an 8-week period pH measurements were taken in the longis-simus dorsi muscle of 17 157 bacon-weight carcasses at 45 min post mortem (pH1 ) in one abattoir. The overall least squares mean pHt was 6·38 and 9·9% of carcasses had pHt values of 5·9 or less. Neither sex, type of dam, breed nor testing background of sire of the carcasses examined had a significant effect on muscle pHj or the incidence of values below p H 6·0. Although first-grade carcasses had a higher incidence of low pHj values relative to those in the other grades, it was of no practical significance. Carcasses of homebred pigs had a higher incidence of muscle pHt values of 5·9 and below (2%) compared with those from pigs initially purchased as weaners. There was a marked producer effect on muscle pHj and the incidence of values below pH 6·0.