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%.

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.

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.

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.

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.

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.

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.

Seventy-five enzootic pneumonia-free female pigs (sows) were allocated at random to one of five treatment groups. Four of these groups were weaned following a 10-day lactation period and were fed either 2 or 4 kg per day in lactation and either 2 or 4 kg per day from weaning to remating, such that the patterns of feeding for the four groups in the two periods were: 4 kg, 4 kg (HH); 4 kg, 2 kg (HL); 2 kg, 4 kg (LH) and 2 kg, 2 kg (LL). A fifth treatment group (control) was weaned following a 42-day lactation period and was fed up to 6·3 kg/day, depending on litter size and 2·7 kg/day from weaning to remating. Level of feeding for the four early-weaned groups in both lactation and in the interval from weaning to remating significantly (P < 0·001) affected the weight changes of the sows during these periods. The interval from weaning to oestrus for the early-weaned sows (8·2 days) was significantly (P < 0·001) greater than for the control sows (4·5 days), but this interval was not affected by level of feeding either in lactation or in the remating period for the early-weaned sows. Litter size at the subsequent farrowing for the early-weaned sows (9·3 piglets) was significantly (P < 0·001) less than litter size for the control sows (12·0 piglets). Level of feeding in lactation or in the weaning to remating period had no effect on subsequent litter size of the early-weaned sows.

Forty-five female pigs (sows) were allocated at random to one of three lactation lengths: 7 days, 21 days, 42 days. All sows were remated at the first post-weaning oestrus and were slaughtered at 20 days post coitum. The reproductive tracts were removed, dissected and examined. Ovulation rates as determined by luteal count were similar for all three groups, but the number of viable embryos decreased significantly (P < 0·05) from 13·0 for the 42-day lactation group to 9·2 for the 7-day lactation group. This difference was reflected in a significant (P < 0·01) reduction in the percentage embryo survival rate as lactation length was reduced. Uterine lengths for the 7-day lactation group were significantly (P < 0·05) shorter than the other two groups. Six sows in each treatment group were blood sampled: at weaning, at remating, at 2 days post-mating, at 10 days post-mating and at 20 days post-mating. The plasma samples obtained were assayed for progesterone. No differences were observed between treatment groups for plasma progesterone concentration at any of the sampling times. It is concluded that the reduction of the litter size at the next farrowing following a short lactation length is largely a result of increased embryo death in the first 20 days of gestation.

A model designed to simulate growth in pigs has been developed to include the following aspects of protein and energy use.

1. It is proposed that the ratio of protein accretion to protein synthesis is a function of protein mass. Synthesis rate influences the efficiency of protein use, the energy cost of protein accretion and the energy cost of maintenance. A calculated energy cost for protein synthesis of 7·3 MJ ME/kg is suggested; the calculated energy yield from deaminated protein is 11·5 MJ ME/kg.

2. Urinary losses of nitrogen are derived from estimates of protein quality by essential amino acid index, endogenous losses and the rate of protein accretion.

3. A minimum fat to protein ratio in the gain of growing pigs of 1: 1 is assumed.

4. An estimate of critical temperature which is dependent upon live weight and heat output is used to calculate energy expenditure for cold thermogenesis.

Two experiments were carried out using 130 Friesian-type castrated males (steers) to compare pelleted dried grass with rolled barley as supplements to high quality grass silage for fattening steers. There were six treatments in each experiment and, in addition, Experiment 1 had a pre-experimental slaughter group. The animals on each treatment were group-fed grass silage ad libitum for 98 and 112 days in Experiments 1 and 2 respectively. The treatments were (1) no supplement, (2) 1·5 kg dried grass, (3) 3·0 kg dried grass, (4) 4·5 kg dried grass, (5) 1·5 kg barley and (6) 3·0 kg barley per head daily. Each increase in the level of supplement depressed silage DM intake but there was no difference between dried grass and rolled barley. At each level of supplementation, live-weight and carcass-weight gain for animals fed dried grass and barley were similar. Responses in terms of live weight and carcass weight to increasing increments of supplementary feed declined as the level of supplementation was increased.

1. The effect of gathering reindeer on the composition of the blood was studied in female reindeer and their calves herded in northern Finland. Blood samples were taken in summer at three gathering places, under differing conditions and in autumn at the same places during gatherings which lasted for longer than 2 days. These were compared with samples taken from little-disturbed animals during winter.

2. Measurements were made of concentrations of glucose and lactate in whole blood and of urea, calcium, sodium, potassium and magnesium in serum, together with serum creatine phosphokinase (CPK) and glutamine oxalacetic transaminase (GOT) activities.

3. Gatherings affected nearly all the blood parameters studied. In summer the temperature during separation seemed to influence glucose and lactate concentrations. The duration of the gathering and the distance the animals were driven clearly affected serum GOT and urea values.

4. During the long autumn gathering serum urea concentration increased about eight-fold in 2 days accompanied by a simultaneous decrease in serum calcium.

5. Serum CPK and GOT activities were higher during the summer and autumn than during the winter. Serum CPK and blood glucose concentrations were higher in young calves than in adult females.

In 1968-69 for a mean period of 101 days before lambing, 72 cross-bred ewes, and in 1969-70 for a mean period of 88 days, 107 ewes were given roughage daily in the form of (a) 0·91 kg field-cured hay (b) 0·45 kg of hay plus 0·23 kg dried sugar-beet pulp nuts, or (c) 0·45 kg of pulp nuts. Each diet was supplemented by a concentrate allowance. From the 6th week before lambing was due to start, this allowance was progressively and uniformly increased.

There was no evidence that the dried sugar-beet pulp had adversely affected performance in terms of ewe body-weight change, lamb numbers, litter weight at birth or 4 weeks of age, fleece weight or general health. It is therefore concluded that dried sugar-beet pulp can be used safely as a replacement for hay in supplying up to 67% of the energy needed for maintenance by ewes.

An investigation was made of the association of transferrin types with birth weight, weaning weight and average daily gain from birth to weaning in three breeds of Iranian sheep. Transferrin type was not a significant source of variation in weight.

A short-term selection experiment was undertaken to estimate the realized heritability for birth weight in mice.

A cross of two strains was used as a base population, from which heaviest and lightest birth weight individuals were selected to initiate an up (JU) and a down (JD) selected line. Selection was applied on a within-litter basis for six generations. By the end of the experiment, the two lines differed by 0·20 ± 0·01 g. The heritability, estimated from the regression of cumulative response on cumulative selection differentials and adjusted to that of individual values, was 0·14 ± 0·02. Six-week body weight, averaged over both sexes, was higher in line JU than in JD by 1·0 ± 0·3 g at generation 6. Litter size was higher in line JU in every generation, the regression of the divergence between JU and JD on generation number being 0·13 ± 0·03.

M. biceps brachii and m. tibialis anterior were studied at a fixed body weight in mice selected for high and low body weight at a fixed age. Muscle weights were approximately equal in the two lines. In general, muscles from high-line mice appeared to contain a larger number of smaller fibres than low-line mice in which there were fewer but wider fibres than in the unselected control population from which the lines were derived.

ANIMAL PRODUCTION, Volume 21, part 3, pp. 199-207