High rates of interest (8 to 15%) commonly used in discounted cash flow analysis of genetic improvement schemes have tended to underestimate the value of the returns and to favour breeding programmes with short-term returns. It is shown that inflation should be removed from the interest rate, and an inflation-free rate used in discounting future returns to present-day value.

Various methods for choosing discount rates are discussed. It is concluded that the appropriate rate is the real opportunity cost rate, that is the market cost of borrowing in real terms, in terms of goods rather than money. Taking account of inflation the average cost of borrowing in real terms in the United Kingdom over the past 32 years (1945 to 1976) is estimated as 2 to 3%. This also provides the best available estimate for discounting future returns, and it brings the opportunity cost rate into line with the social time preference rate often proposed for public investments.

The contrast is made between the value of improvements made in the national interest and of those made by breeders or firms. The former benefit from returns on all national commercial production of improved stocks and the returns accumulate and are recouped over many years. On the other hand breeders and firms benefit only from the extra sales of breeding stock due to their temporary marginal superiority over competition and they are often at high risk of getting no returns. Implications to the form and amount of investment in animal improvement are discussed.

When economic returns from current and future generation gains are comparable in magnitude, selection decisions should take account of both sources of gain. A combined selection index is devised to maximize the present value of discounted returns from all sources. The index depends on genetic and phenotypic variances and covari-ances, population structure, discount rate and the relation of annual returns to individual traits. The combined index can be regarded as the sum of separate indices maximizing returns from each source. The method is illustrated with a simple example using wool weight and body weight in sheep.

Subjective scoring data may be analysed by ranking methods, ANOVA methods or by inspection of the score distributions. These methods are discussed with particular reference to body condition scores of cows and ewes. A combination of ANOVA and ad hoc inspection was used to analyse data from trials carried out in 1976 to investigate the precision of condition scoring. On the basis of the results, recommendations are made concerning the use of condition scoring on farms and in scoring trials where the object is to monitor assessor bias and inconsistency.

The usual method of fitting the model y = Anb exp(−cn) to lactation data, by a multiple regression of logey on n and logen, can result in an ill-fitting curve. An analysis of the untransformed data provides a better fit but requires more extensive computation and a simple approximation to this procedure is given. Since the parameters of this model have no direct biological interpretation two alternative models are introduced, each having a parameter measuring the persistency of lactation.

Pregnant beef cows were given 2 kg barley per day and oat straw ad libitum. The digestibility of the organic matter of the diet was approximately 53% when urea included in the barley was given in one or four feeds per day. Supplementation of the barley with di-ureido isobutane improved the organic matter digestibility to 56·7%. When a solution containing urea, phosphorus, calcium and sodium was included in the straw the digestibility of the diet was 59·0%. These improved digestibilities were not associated with any differences in the concentrations of ammonia in the rumen liquor or blood of the cows.

Whole-crop maize was harvested at 20% (L), 29% (M) and 38% (H) dry-matter (DM) content, chopped to 7·67 mm (F) or 33·3 mm (C) average particle length and ensiled. The six silages were offered ad libitum to 36 entire male calves (initially 96 kg live weight), together with supplements of urea and dried ryegrass, for 42 days. Voluntary intake and the apparent digestibility of the diets were measured. Intake of DM was not affected by the DM content of the silages, but was higher for F than C by 6·6% (P<0·01). Apparent digestibility of DM, organic matter and cell walls decreased with increasing silage DM content (P<0·001) and was higher for F than C (P < 0·01).

In three trials, each involving 48 individually-fed pigs grown from 20 to 90 kg live weight, the value of virginiamycin as a performance-promoter either alone or together with 250 mg Cu/kg diet was examined. Both copper and virginiamycin on their own gave significant, although small, improvements in performance and the results suggested that there can be a degree of additive action between the two materials when both are added to the diet.

The possible use of a pig's reaction to the anaesthetic halothane as a field test for Porcine Stress Syndrome in genetic improvement pro-grammes was investigated. A standard 3-min halothane test gave incidences of positive reaction of 20% in a composite Pietrain/Hampshire line, 5% in Norwegian Landrace, 1% in Hampshires and zero in Durocs, Large Whites and N. American Yorkshires. In the Pietrain/Hampshire population, two generations oftwo-way selection on the test gave a divergence in incidence of positive reaction of 85%, and the frequencies of affected progeny supported the hypothesis of monogenic recessive inheritance. From second tests made 20 days after the first, the probability of misclassifying a pig's reaction on one test was 5 ± 1%. Positive reactors had significantly shorter and leaner carcasses, fewer pigs born alive, poorer meat quality, higher mortality and greater plasma creatine phosphokinase activity than negative reactors.

An average of 60 Rambouillet and 60 Suffolk ewes was maintained under an intensive management system to lamb about every 7 months. Decreased daylength was used for oestrus induction in normally anoestrous periods. The experiment lasted 3·7 years, during which time six lamb crops were produced, three of them as a result of out-of-season mating. Ewes of each breed were subdivided into three experimental groups and each breed-group was maintained under one of three different light treatments before and during out-of-season mating. Imposed Treatment 1 consisted of a pre-mating period under natural daylight followed by a mating period of short daylength (8 h/day). Ewes under imposed Treatments 2 and 3 were exposed to 16 h of light during the pre-mating period and to 8 h of daylight during the mating period. This did not affect conception significantly in the Rambouillet but it did in the Suffolk. Different intensities and wavelengths of light during the long daylight period (16 h/day) were used in Treatments 2 and 3 but did not cause different responses.

In Rambouillet ewes the first mating (out-of-season) gave 73% conception. It was followed by two in-season matings with 72 and 85% conceptions. The last three matings (out-of-season, in-season, out-of-season) resulted in 57, 42, and 58% conceptions. In the Suffolk ewes, the conceptions were 30, 88, 77, 3, 77, and 10% in the same order as those for Rambouillet. The average production ofRambouil-lets on the three treatments was 166 lambs per 100 ewes per year (165, 177, 157) whereas Suffolks produced 132 lambs (120, 143, 135). Control Rambouillet and Suffolk ewes maintained under natural daylight year-round produced 139 and 117 lambs.

Karakul, Mehraban, Naeini and Bakhtiari sheep were checked twice a day for oestrus using aproned rams and were laparotomized within 5 to 16 h of the end of every second oestrous period. Oestrus was observed for 12 monthly periods commencing on 21 April.

The Mehraban breed with 1 -6 oestrous periods per month was less seasonal in its breeding activity (P<0·01) than the other breeds. Four-year-old ewes were more sexually active (P<0·01) than 3-year-old ewes (1·48 v. 1·28 oestrous periods per month). Seasonal variation in the sexual activity of the ewes was observed (P<001); the peak of activity in July to January was followed by a steady decline in February and March to a low in April and May, and then a steep recovery phase in June. There was only limited sexual activity for at least 4 months (March to June).

The overall mean cycle length was 17·8 days (14 to 23 days), and the means for the four breeds were 17·6, 17·8, 17·8 and 17·9. The oestrous cycle was longer (P<0·05) during the period from December t o February than during that from June to August.

The overall mean duration of the oestrous period was 36·9 h and the means for the four breeds were 35·2, 38·0, 37·4 and 37·1 h, respectively (P<0·05). The duration showed some monthly variation (P<0·01) but did not follow a special seasonal pattern. The ovulation rates for the four breeds were 1·07, 1·13,0·94 and 0·95 respectively, (P<0·01). There was a non-significant decline in the mean ovulation rate from March to June. Right ovaries were more active than left ovaries as judged by the observation of a higher average number of corpora lutea per ewe per laparotomy (0·58 v. 0·43, P<001).

The pre-weaning records (birth weight, weaning weight and gain from birth to weaning) of 291 male and female lambs and the post-weaning records (body weight, feedlot gain and food conversion) of 136 male lambs were used to study relationships between different traits. The lambs were derived from three fat-tailed Iranian sheep breeds (Karakul, Mehraban and Naeini) and their crosses with Corriedale and Targhee rams. All lambs were weaned at 75 + 5 days of age and the males were fed in a feedlot for 100 days after weaning. Feedlot measurements were taken at 20-day intervals.

Weaning weight and pre-weaning average daily gain showed positive and significant associations with birth weight. Birth weight, weaning weight and gain from birth to weaning were positively associated with body weight at subsequent ages in feedlot as well as with final weight (P<0·01). Birth weight, weaning weight and pre-weaning average daily gain were positively and significantly associated with total feedlot gain.

Of the different traits, total gain during the first 20 days in feedlot (adjust period) had the lowest and total gain during the second 20 days had the highest association with total feedlot daily gain. There was no evidence that the heavier lambs at weaning and those showing high growth rate before weaning, were more efficient in the feedlot. Gain during the second 20-day period in the feedlot had a significant negative association with the total food conversion (unit food/unit gain) and therefore was a good predictor for food conversion.

When the feedlot period was divided into two 40-day periods, it was found that gain during both had a significant negative association with the corresponding food conversion. A similar association was observed between total feedlot gain and food conversion, indicating that the rate and efficiency of gain improved simultaneously.

Twenty-one mature ewes of each of two breeds, the Scottish Black-face and the Welsh Mountain, were allocated in equal numbers to three diets based on a complete cobbed feed with a 0, 5 and 15% inclusion of dried seaweed meal (Ascophyllum nodosum). All diets were made up to a Cu content of approximately 30 mg/kg by adding CuSO4 to the mix. Sheep were housed and fed individually for 15 weeks.

There was a significant breed difference in the Cu level of the liver dry matter; the Welsh increased by 316 mg/kg compared with 240 mg/kg in the Blackface and the amount of Cu accumulated in the liver per kg feed consumed was 0·66 mg in the Welsh and 0·46 in the Blackface. Diets also had a significant effect; the Cu levels in liver dry matter rose by 323, 293 and 220 mg/kg for the 0, 5 and 15% seaweed diets respectively and the Cu stored per kg feed consumed was 0·66, 0·61 and 0·41 mg respectively. There was no corresponding effect of diet on plasma Cu level, but there was a breed difference with Welsh higher than Blackface. Cu level in kidney dry matter showed a breed-by-diet interaction. Total food consumption did not differ among the treatments, and live-weight and carcass-weight data suggested no adverse effects from the inclusion of seaweed meal in the diet.

The voluntary intake of two hays and one dried grass by 48 mature non-pregnant Blackface ewes was measured for 33 weeks. The apparent dry-matter digestibility coefficients of the diets in vitro were 59, 61 and 77% respectively for the hays and the dried grass. At the end of the first phase of the experiment each group of 16 ewes was split into two subgroups of five animals, each of which was subsequently given one of the other diets, and one subgroup of six animals which remained on the same diet. Food intake was measured for a further 8 weeks. Body fat was estimated at intervals from tritiated water space.

The amount of variation in voluntary food intake that could be attributed to variation in live weight and fatness of the animals and in apparent dry-matter digestibility and cell wall constituents of the diet was calculated for various periods.

The range of live weight and fatness increased during the experiment. Initially, and after the change in diets, variation in apparent dry-matter digestibility had an important positive effect on intake, but at the end of the 33-week phase its influence was negligible or, when fat weight was not considered, negative. The negative effect of fat weight on intake increased during the experiment.

Within individual diets during short periods of time (1 to 5 weeks) the highest proportions of the variation in intake that could be attributed to variation in live weight and fatness of the ewes were 50, 94 and 65% respectively for the hays and the dried grass. Taking all three diets together all the variables considered could explain 75% of the variation for a few weeks at a time, but for longer periods seasonal influences, and other factors not included among the independent variables, probably operated.

The distribution of intermuscular fat (IF) was studied in 24 lambs, of balanced sexes, from each of the Dorset Horn, Hampshire and Clun breeds, which were slaughtered at 42 kg live weight. The Clun lambs yielded the least total IF, the Dorset Horn most and the Hampshire an intermediate amount. The Clun lambs had significantly (P<005) less IF in the thoracic limb than the other two breeds; and the IF content of the neck+thorax region in the Hampshire was lower than that in the remaining breeds. Females had more IF than males in all sites examined. At an equally adjusted total IF weight, sex differences disappeared. The Hampshire yielded more IF in the thoracic limb, pelvic limb and back+abdomen, but, exceptionally, less IF in the neck + thorax than in the other two breeds.

Trials involving a total of 401 steers were carried out from 1974 to 1976 to determine the effect of implantation with zeranol on the performance of fattening steers under grazing and feedlot conditions i n Botswana.

Over a 180-day grazing period in 1974, 1975 and 1976 there was a significant improvement in live-weight gain of 11·9, 24·5 and 12·3% i n implanted steers over control steers. Under feedlot conditions there was a mean improvement in live-weight gain of implanted steers over control steers of 17·9% over an average stay in the feedlot of 95 days.

The individual water intakes of 16 (four groups of four) lactating dairy cows, measured on 7 consecutive days, were significantly correlated with dry-matter (DM) intakes (range 4·6 to 14·4 kg/day) and milk yields (range 13·7 to 30·0 kg/day). There was no significant correlation with DM content of the feed (range 833 to 898 g/kg), body weight (range 400 to 620 kg) or mean air temperature (range 7·0 to 20·0°C). Applying a multiple regression analysis to the data, the following relationship was obtained: water intake (kg/day) = 2·15 (± 0·415) × DM intake (kg/day)+0·73 (± 0·197) × milk yield (kg/day) + 12·3 (+ 5·57). After adjusting the data for variations in DM intake and milk yield there was no significant difference between the mean daily water intakes of individual cows. There was, however, a significant day-to-day variation in the mean water intakes of the groups of four cows (P<001) which was not explained by variations in DM intake, milk yield or mean daily temperature.

Measurements of longissimus dorsi pH at 45 min post mortem (pH1) were taken in 27 727 pig carcasses at four bacon factories. The overall least squares mean pH1 was 6·26 and 15·5% of carcasses had pHi values of 5·9 or less. Sex and commercial grade of carcass had little influence on muscle pHi or the incidence of values below pH 6·0. Factory differences were recorded in the distribution of muscle and within each there were marked producer effects in mean and the incidence of values below pH 6·0. Carcasses of Large Whites had fewer muscle pH1 values below 6·0 (12·4%) than those of British Landrace (18·7%), this being mainly due to a large breed effect at one factory. Although breed and testing background of sires of the carcasses examined and the first order interactions with factory had significant effects on muscle pHi and the incidence of values below pH 6·0, they were of little practical significance.