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.

Ways of conducting a progeny test for growth of carcass characters are discussed with reference to statistical efficiency. An intensive system (375 kg slaughter weight) is compared with a semi-intensive system (475 kg slaughter weight) and the use of intermediate results as predictors of the final outcome is discussed.

The crossbred progeny of 32 Hereford bulls (1043 calves) were admitted to a Progeny Testing Centre at 2-month intervals at 2 weeks of age over a period of 2 years, and divided between the two feeding regimes. Growth and carcass characters were measured, including taste panel assessments.

The semi-intensive system was found to have a higher power of discrimination between progeny groups, and tended to rank the bulls i n a different order from the intensive system. Truncation of the test at various intervals introduced an element of risk into the formation of the final judgement and showed little advantage as a predictor.

An analysis is undertaken of the effect of errors in estimates of parameters, particularly the intra-class correlations, on the response from selection for one trait using an index of individual together with full- and/or half-sib family records. A distinction is drawn between the response (R) possible with use of the optimum index, that predicted (R) and that achieved (R*) with an index which uses the sample estimates of the parameter values.

It is found that the loss of efficiency (R*–R) using sample estimates is very small even for estimates far from the correct value. R is more sensitive to errors, particularly of the heritability and phenotypic variance estimates. Since the latter also appear in the prediction of response from individual selection, errors in predicting the relative responses from index and individual selection are small. Expected values of the proportional loss in response,

are approximately proportional to the variance of the estimate of intra-class correlation. It is shown that in practice initial experiments with 20 or so families may be sufficient to get average proportional losses down to less than 1%.

Records of 178 593 monoparous births between 1964 and 1970 in Israeli-Friesian dairy cattle were analysed for information on environmental and genetic factors affecting calving difficulties and perinatal mortality. The incidence of difficult calvings (DC) and peri-natal calf mortality (PM) were 6·9 and 9·1% in heifer calvings, and 1·6 and 4·1% in cow calvings. Calving characters were not related t o heifer age nor cow parity, but there was a seasonal trend in heifer calvings, with both DC and PM being high in winter and low in summer calvings.

Heritability estimates for calf-genotype effects on PM were 0·042 in heifer calvings and 0·013 in cow calvings. Heritability estimates for dam-genotype effects on PM were 0·018 and 0·004 respectively. Heritability estimates for DC were similar t o those for PM. The genetic correlations between DC and PM in the same class of calvings ranged between 0·8 and 0·9, while the environmental correlations were considerably lower, about 0·3. The genetic correlations between the calf-genotype effects in heifer and cow calvings were about 0·5, indicating that different factors may affect heifer and cow calvings.

It is proposed that sires already proven for milk yield be tested for their calf effects in heifer calvings, using contemporary comparisons within herds and seasons. Results will be available when the sires are 6 to 6½ yr old. Sires causing fewest calving difficulties would be nominated for heifer matings, so that most heifer inseminations would be by sires proven for both yield and calving characters. Some long-term progress might be obtained if sires with a high incidence of difficulties in their heifer mates were not used to produce young sires.

1. The growth rate, feed-conversion ratio and blood composition of 14 twin calves were compared with those of 14 contemporary singletons.

2. The growth rate and feed-conversion ratio from weaning to 3 months were similar for twin and singleton calves.

3. The twin calves weighed significantly less at birth, weaning and 3 months of age but differences in weight were not significant at 1 year of age.

4. The mean packed cell volume (PCV) and the mean concentrations of blood glucose and haemoglobin, serum albumin, urea nitrogen, calcium, inorganic phosphate, magnesium, potassium, sodium, copper, iron and total iron binding capacity, at 11, 12 and 13 weeks of age were similar in the two groups. Concentrations of globulin were significantly lower in the serum of twin calves than those in the serum of singletons.

5. There was significantly less variation between twin calves than among offspring from different dams for PCV and concentrations of blood haemoglobin and serum potassium and calcium.

6. The results did not reveal any overall disadvantage in twins as compared with singletons.

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.

Forty-two British Friesian castrated male calves of 1 to 3 weeks of age were offered ad libitum unwilted or wilted silage made from the same sward for 21 consecutive weeks. Both silages were supplemented with a cereal and protein concentrate at two restricted levels of intake or with dried grass cobs offered ad libitum. There was little difference i n the chemical composition ofthe two silages except for DM content. Dry-matter intake of wilted silage was slightly but not significantly greater than that of unwilted silage. Differences between silages in daily gain or final live weight were not significant.

An increase in the intake of the cereal and protein concentrate led to a significant decrease (P < 0·001) in silage DM intake and a significant increase (P < 0·001) in daily gain andfinallive weight. Calves offered dried grass as a supplement to silage ate similar quantities of silage DM to calves offered an equal amount of the cereal and protein supplement but gained significantly less (P < 0·001) live weight. When intakes were presented on a unit metabolic live-weight basis, calves ate significantly more (P < 0·001) silage when supplemented with dried grass than calves offered the cereal and protein supplement.

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.

Imported semen from 10 Italian Chianina bulls was used to inseminate beef and dairy cattle throughout England and Southern Scotland. A total of 2134 records of calving performance were subjected to least squares analyses. Dystocia score was significantly affected by county of birth, parity of dam, sire, type of birth, birth weight (P < 0·001), season of birth and sex of calf (P < 0·01). There were no significant effects of breed or size of cow. Serious dystocia was encountered in 3% of calvings, with the incidence for individual sires ranging from 1·7% to 6·7%. Arithmetic mean gestation length was 284·2 days and it was significantly affected by county, sire (P < 0·05), sex of calf (P < 0·01), and type of birth (P < 0·001). Arithmetic mean birth weight of the calves was 41·2 kg and this was significantly affected by all main effects studied except season of birth and type of herd.

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.

In two feeding experiments, an untreated silage which had received no additive was compared with silages which had received either formic acid (‘Add-F’) or a formalin and sulphuric acid mixture (‘Sylade’). The ‘Add-F’ was applied at the rate of 3·81/t and ‘Sylade’ at the rate of 3·1 1/t of fresh herbage harvested from a perennial ryegrass and white clover sward.

The silages were offered ad libitum to 30 British Friesian male calves (mean fasted live weight 97 kg) in Experiment 1 and to 27 steers (mean fasted live weight 320 kg) of mixed breed in Experiment 2. Concentrate was offered to the animals in Experiment 1 at the rate of 0·86 kg dry matter/head per day.

In each experiment the intakes of dry matter and digestible organic matter were higher from the additive-treated silages than from untreated silage.

In Experiment 1 the application of ‘Sylade’ increased significantly (P < 0·05) the mean daily unfasted live-weight gain (0·87 kg/day) over that for animals offered untreated silage (0·74 kg/day). In Experiment 2 the mean daily unfasted live-weight gains from ‘Sylade’-treated (0·70 kg/day) and ‘Add-F’-treated silage (0·78 kg/day) were significantly higher (P<0·01) than that from untreated silage (0·38 kg/day).

The lactation curves of whole milk production and of compositional quality measures may be represented by one of a family of curves

where the coefficients a, b and c define the curve of production of a character y at week n.

An analysis of protein results from over 600 000 cows, and of fat results from nearly 3000 cows gave shape coefficients (b, c) for fat percentage (-0·1316, 0·0154) and for protein percentage (-0·1223, 0·0109) showing that the lowest percentage of each occurred during weeks 8 and 11 of lactation respectively.

Seasonal variations were calculated to show an expected deficiency of 0·93% fat in the spring and 0·75% protein in winter, which could be attributed to environmental influences associated with varying feeding standards.

1. Water intake was measured in eight lactating cows. Subsequently n i an experiment of a 4 × 4 Latin square design, each cow received 100, 87, 73 and 60% of its voluntary intake for 6 days followed by an 8-day recovery period.

2. Measurements were made of the intake of feed, milk yield and quality, water, Na and K balances, metabolic profiles, and serum and urine osmolalities. The cows were weighed at the beginning and end ofthe experimental periods, and pulse, respiration and rumination rates and rectal temperatures were measured daily.

3. Milk yield decreased significantly with increasing water deprivation. A 40% reduction in water intake was associated with a 16% decrease in intake of dry matter and a concomitant 16% decrease in milk yield. The only significant change in milk composition was a small increase in lactose concentration with increasing water deprivation.

4. There was no significant reduction in urine output, but the output of water in faeces was reduced and there was evidence of a reduction i n total body water which approximated the reduction in body weight. 5. Concentrations of serum Na and urea-N and serum osmolality increased significantly with increasing water deprivation.

Two levels of roughage in a complete fattening diet (25 and 45%), two particle sizes of the roughage component (6 and 12 mm diameter of sieve holes), and three levels of moisture (10, 50 and 75%) were examined in a feeding trial designed in a 2 × 2 × 3 factorial arrangement.

Intact male Israeli-Friesian cattle were grown from an initial weight of about 300 kg to a slaughter weight of about 520 kg. Live-weight gains were 956, 1080 and 1025 g/day, and carcass gains were 516, 584 and 563 g/day for diet moisture contents of 10, 50 and 75%, respectively. The roughage content of the diet and particle size had no significant effects. Efficiency of conversion of metabolizable energy into live weight or carcass weight was directly related to the moisture content of the diet.

Weight of gut fill was directly related to the roughage content of the diet, to diet particle size and to moisture content. Animals on the moist diets had less carcass fat but more depot fat than those on the dry ration. Total volatile fatty acid concentration in the rumen liquor of animals fed on moist diets was significantly higher, and the acetate: propionate ratio was significantly lower than that of animals on the dry control diet.

The improvement in performance of animals fed on moist diets may be attributed to the accumulated effect of three factors, even though the effect of each separately may not be great: (a) Increased dry-matter intake; (b) Improvement in digestibility; and (c) Increased concentration of propionic acid and consequent reduction of the acetate: propionate ratio.

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.

Growth coefficients were determined for muscle, bone and fat in the side and in the ham, for six muscles of the ham, and for the femur, using data obtained from the dissection of 66 carcasses of female pigs weighing from 25 to 65 kg live weight.

Irrespective of the independent variable taken for regression, the coefficients showed bone in the side to be earlier developing than muscle, which in turn was earlier than fat. There is good agreement between these coefficients and corresponding values reported for cattle, sheep and pigs.

There was little evidence that the ham as a whole or its muscle, bone and fat components grew disproportionately to the corresponding components of the whole side.

The growth coefficients of the six muscles of the ham agreed closely with those reported for cattle, sheep and pigs with the exception of that for the m. adductor, which was lower.

The combined weights of the m. biceps femoris and m. adductor were related almost as closely to the weight of muscle in the side as was the weight of total muscle in the ham. Of the six muscles taken individually the weight of the m. biceps femoris was most closely related to muscle in the side.

The effects of two levels of energy intake, ad libitum and 80% of ad libitum, of diethylstilboestrol implantation and no such treatment, and of two slaughter weights (‘450’ and ‘490’ kg), on the performance of Israeli-Friesian intact male cattle were studied.

Average daily gain was 1130 g and 959 g and daily carcass gain was 630 g and 553 g for animals on ad libitum and 80% of ad libitum energy intake, respectively. Average daily gain was 1038 g and 944 g and daily carcass gain was 595 g and 562 g, for diethylstilboestrol-treated and untreated animals, respectively. Slaughter weight had little effect on rate of gain.

The differences in conversion ratio of ME into live weight between treatments were small. Diethylstilboestrol-treated animals were slightly more efficient.

The non-implanted animals on the restricted plane of nutrition and which had been slaughtered at ‘490’ kg had a significantly higher dressing percentage, a higher percentage of fat trim and less bone than animals slaughtered at ‘450’ kg body weight on both levels of nutrition.

Among the diethylstilboestrol-implanted male calves, however, the animals fed at 80% of ad libitum feed and killed at ‘450’ or ‘490’ kg live weight had significantly more fat trim in the carcass and less bone than the animals fed ad libitum.

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.

Five groups of 24 Aberdeen Angus steers, initially 8 months old and 185 kg in weight were subjected to varying degrees of restriction of energy intake, by feeding them on diets containing 1·45 to 2·85 Meal metabolizable energy (ME)/kg dry matter (DM) for 16 weeks. During the realimentation period that followed, all animals were fed ad libitum on the diet containing 2·85 Meal ME/kg DM. When realimentation began the feed consumption of all animals, which had been markedly different, rapidly became similar. When compared at equal live weight the restricted animals had higher intakes than the controls; at an equal age, however, feed intakes were practically the same. This led us to discard compensatory feed intake as a possible explanation for compensatory growth. Age explained 65% of the variability in feed intake, live weight explained 43% and both parameters jointly explained 73%. It is concluded that in restricted and realimented animals, age is a better predictor of feed intake than live weight. Compensatory growth is attributed to a lower maintenance requirement in restricted animals because of their lower live weight at the beginning of the realimentation period.