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.

Twenty-seven castrate male cattle were used in two nutritional balance and slaughter experiments to measure the effects of increasing levels of dietary protein (9 to 15% in the dry matter) at two levels of feeding (approximately 16 and 22 MJ metabolizable energy (ME)/100 kg live weight (LW) per day) on digestibility, nitrogen (N) balance and carcass growth and composition over the LW range 130 to 390 kg.

The higher level of feeding increased LW gain and carcass gain (CG) but higher protein intake increased LW gain and CG only at the higher feeding level as a result of its favourable effect on digestibility. N balance tended to overestimate carcass N retention at higher levels of protein intake.

The higher level of feeding increased the separable fat and total fat in the carcass. Increased protein intake had no effect on the lean meat content but increased the percentage protein in the edible portion of the carcass. LW gain, CG and carcass energy deposition were related to ME intake only but N balance and carcass protein gain were related to both ME and digestible crude protein intake.

(1) Both the anabolic agent trienbolone acetate (3-oxo-17-β-hydroxy- 4,9,11-estratriene acetate) and testosterone subcutaneously injected into entire female rats caused an increase in growth rate compared with placebo controls (P<0·01 and P<0·001 respectively). The trienbolone acetate rats grew slower than the testosterone-treated animals (P < 0·01). This may reflect differences in the mode of action of the steroids.

(2) In castrate males there were no significant differences in growth rate between the trienbolone acetate, testosterone or placebo control rats (P>0·05).

(3) Trienbolone acetate reduced the rate of myofibrillar protein degradation in female rats, within 3 days of treatment, at least as judged by Nt-methylhistidine excretion. The treated rats had superior nitrogen retentions (P<0·01) and feed conversions (P< 0·001).

(4) The data suggest that the rat is a suitable model on which to test the mode of action of trienbolone acetate.

Thirty male piglets weaned at 20 days of age were fed on either a control diet with 20% crude protein containing 1·1 % lysine or one of two diets with 14·6 or 16·6% crude protein. Synthetic lysine was added to the latter two diets at the rate of 0·00, 0·18, 0·36 and 0·54% to provide four diets with 14·6% crude protein and 0·54, 0·72, 0·90 or 1·08% lysine and four diets with 16·6% crude protein and 0·72, 0·90, 1·08 or 1·26% lysine. All diets were offered ad libitum to piglets between 5·5 and 20·0 kg live weight.

Over the live-weight periods 5·5 to 20·0 and 12·0 to 20 kg, live-weight gains and food conversion improved with increasing total lysine to 1·08 % and 0·90 % respectively when pig performance was equal to that achieved on the control diet. The improvement in performance with an increasing level of total lysine during these two periods did not depend on the total protein content of the diet. During the live-weight period 5·5 to 12·0 kg, optimal performance was obtained when pigs were fed on the highest lysine level in the diets with 14·6 and 16·6% crude protein. However, only the diet of 16·6% crude protein promoted pig performance equal to that achieved on the control diet.

Carcass quality did not respond to lysine supplementation independently of protein level. With thedietof 14·6% crude protein, optimal carcass quality was obtained with 0·90 % lysine but was significantly poorer than that for the control. With the diet of 16·6% crude protein, carcass quality improved over the entire range of lysine supplementation and with 1·26% lysine was superior to that for the control.

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.

Carcass composition and growth patterns for muscle, fat and bone were compared among 277 young male progeny of eight sire breeds, serially slaughtered at 300 kg live weight, 12 months and 15 months of age. The sire breeds were Simmental (SIM), Charolais (CHA), Danish Red and White (DRK), Romagnola (ROM), Chianina (CHI), Hereford (HER), Blonde d'Aquitaine (BDA) and Limousin (LIM). Tissue growth patterns among breeds were examined by regression estimates from the allometric growth equation (Y = axb) and compositional differences were estimated from the intercepts. No significant sire breed differences were found in the regression of muscle, fat or bone on various size dimensions. In regressions involving fat, however, the fattest (HER) had higher regressions and the leanest (BDA) fattened more slowly relative to muscle and bone growth. Breeds differed significantly in amount of muscle, fat and bone when compared at standard weights.

Sire breed ranking for muscle at common bone weights was LIM, BDA, CHA, SIM, HER, ROM, DRK and CHI, while at common carcass weights the ranking was BDA, CHA, LIM, CHI, ROM, SIM, DRK and HER, reflecting differences in fatness. Minor changes in ranking occurred when comparisons were made at a common live weight reflecting differences in dressing percentage. For fat at standard muscle, carcass or live weight the breeds ranked HER, LIM, DRK, SIM, ROM, CHA, CHI and BDA.

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 urine of pigs contains a substance with an anorexigenic effect when injected into pigs or rats. When injected into rats or pigs on ad libitum feeding a urine extract caused a reduction in food intake only when the extract had been obtained from the urine of satiated pigs, and not from hungry pigs. The pig urinary anorexigen there-fore appears to be similar in nature to the anorexigen extracted from rat urine. Like rat urinary anorexigen, its anorexigenic effect is largely dose dependent and it is soluble in distilled water. Rats injected with plasma from satiated pigs showed an anorexigenic reaction but injection of plasma from hungry pigs had no effect on food intake. The possible role of these anorexigenic substances in the control of voluntary food intake in the pig is discussed.

Starlings had free access to cattle food placed in open troughs in a calf yard. During the winters 1974/75, 1975/76 and 1976/77 birds took 1·49, 1·70 and 1·991 of calf food respectively, this ranging from 6·4 to 12·4% of the food given to the calves. These losses were eliminated using enclosures made of Terylene netting or PVC strips. Both enclosures kept starlings out of the yard: the latter was more manageable to farm staff, and calves within grew significantly faster than controls, probably due to a combination of the absence of bird competition for food and the elevated temperature within the enclosed area.

Designs of open nucleus breeding schemes, which comprise a nucleus having the best males and females and a base comprising the remainder, with some base-born individuals used in the nucleus and vice versa, are studied.

Steady-state genetic responses, optimum transfer rates between nucleus and base in both sexes, and genetic differences between nucleus and base are estimated for a range of age structures, selection either within or among age groups (selection methods), nucleus sizes, mating ratios, fertility rates and survival rates appropriate to sheep and cattle populations. With optimum transfer rates between layers maximum or near maximum genetic responses are obtained with nucleus sizes varying from 2 to 15% of the population. Optimum transfer rates are fairly stable for nucleus sizes larger than about 5% and where the same selection procedures are used in both layers. However, a small nucleus with more efficient age structures and selection procedures and more accurate selection than in the base is economically desirable, and then almost no base-born females should be selected as nucleus replacements and up to 70% of male replacements for the base should come from the base. Optimum age structures differed markedly between selection methods.

Although few ‘rules of thumb’ about optimum age structures and transfer rates are sufficiently robust to be widely recommended in commercial situations, the nucleus breeding system behaves according to a few basic principles that can be used to predict the direction if not the magnitude of effects of changes in structure.

The use of an artificial rearing system to provide controlled environment conditions for performance testing of male lambs was investigated in two trials. A sample of lambs from 5 fat-lamb sire breeds was included.

Performance during the initial restricted milk-feeding period was uniform but large differences in solid food intake gave variable performance in the adjustment period immediately following weaning. Lambs were evaluated from 40 days onwards in terms of growth rate and efficiency of food conversion. Some breed differences were significant and the variation within groups was sufficiently high to suggest that performance might be improved by within-group selection.

Estimates from Trial 2 show that food conversion efficiency was related to growth rate, but early and late performance in the evaluation period were not correlated (r = 0·12, 0·16 and 0·14 for growth rate, food intake and efficiency, respectively). Some refinements of the method are suggested, and it is concluded that the system could provide suitable conditions for testing male lambs at an early age without the variable influence of the dam.

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.

(1) Eight groups of newly weaned lambs were given diets containing 15, 30, 45 or 60% dried poultry waste (DPW) from battery or broiler units in a 4x2 factorial experiment lasting 16 weeks. The Cu content of the diets increased from 12·7 to 35·5 and from 16·1 to 47·1 mg/kg DM with increasing levels of battery and broiler waste, respectively.

(2) As inclusion rates increased, final liver Cu concentrations were 269, 318, 379 and 441 with battery waste and 686, 1009, 877 and 874 mg/kg DM with broiler waste. Total liver Cu accumulation, though higher on broiler than on battery waste, was not proportional to inclusion rate and reached a plateau at the 30% level for both sources.

(3) Mean hepatic Cu retention was constant at 4·8 % of Cu intake with battery waste but decreased from 8·3 to 3·2% as level of broiler waste increased.

(4) Plasma asparate amino transferase (PAAT) levels were highest in groups given broiler waste and final PAAT concentrations were correlated with liver Cu concentration, reaching levels associated with Cu toxicosis in some individuals. The effect of DPW on PAAT was not proportional to inclusion rate.

(5) The factors responsible for the observed variations in liver Cu accumulation between sources and inclusion rates and the possibility of Cu toxicity occurring in sheep given DPW are discussed.

Records of piglet mortality were taken on 775 first and 657 second litters farrowed at four locations and representing 28 combinations of two-breed crosses involving eight breeds. All the sows were mated to Poland China boars. Overall mortality was 18% of which 4·2% occurred at birth, 13·2% between birth and 21 days and 1·2% from 21 to 42 days. Landrace x Yorkshire dams had the lowest mortality rate (10·4%) followed by Duroc x Lacombe (12·3%) whereas the highest rate was found in the Hampshire x Lacombe sows (21·6%). Piglets with Tamworth and Yorkshire ancestry had the lowest mortality (16·2 and 16·7%) while those with Berkshire ancestry had the highest (20·0%). Mortality rate was slightly (2%) higher in first than in second parity litters, and highest in summer and similar in the three other seasons. Mortality rate was highest in very small and very large litters and among the lightest and the heaviest piglets. The results showed a linear relationship between mortality rate and homogeneity of piglet weights at birth within litter, mortality rising with the increase in intra-litter variation. The effect of sires on piglet mortality was significant in one, and non-significant in the three other locations.

Eight-hundred-and-fifty-two pigs were weaned at 5 weeks of age, and at an average weight of 8·5 kg were allocated in pens of 14 or 15 to diets having 13·6 or 14·6 MJ digestible energy (DE)/kg combined with 11·0 or 11·8 g lysine per kg.

Over a 5-week experimental period, pigs receiving the diet with the higher DE content had a lower daily feed intake, improved feed conversion efficiency (FCE) but a similar rate of gain to those getting less DE/kg. Efficiency of utilization of energy was poorer when DE content was higher.

Increasing lysine level increased daily feed intake and rate of gain while improving FCE. There were significant energy x lysine interactions. At the lower energy density, increasing the lysine level resulted in increased daily feed intakes whereas the reverse was the case at the higher energy density. Daily gain increased when lysine level was increased at the lower energy density but was unaffected at the higher density. Efficiency of energy utilization was improved by increasing lysine at the higher but not at the lower energy level.

The occurrence of oestrus and ovarian function during the post-partum period was examined in 160 lactating beef cows of the Africander and Mashona breeds. Cows were fed either to gain 12 to 14% (High) or to lose 12 to 14% (Low) of their autumn peak live weight (early pregnancy) by mid-breeding season. Half the cows in each group were subjected to an increase (Low-High) or decrease (High-Low) in nutrient intake for a 25-day period starting at 25 days partum. Nursing was interrupted for an 8-day period in half of the cows at 50 days post partum by the application of nose plates to their calves.

Oestrus occurred significantly earlier in the high than the low plane cows (66 v. 75 days post partum respectively, P< 0·05), but short-term fluctuations in nutrient supply had no apparent effect on the incidence of oestrus. Temporary weaning significantly reduced the mean time from calving to first oestrus in the high-plane (P< 0·01) but not in the low-plane cows, and in Mashona (P<0·05) but not in Africander cows. There was a lower incidence of ‘silent’ oestrus and the mean occurrence of oestrus was significantly earlier (P< 0·001) in the Mashona when compared with the Africander 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).

A simple non-surgical technique was used to recover embryos from lactating dairy cattle, given 3000 IU PMSG to induce superovulation and the results obtained were compared with the ovulation rate and recovery of embryos from slaughtered cows.

In the slaughtered cows, which were treated late in lactation, mean ovulation rate was only 8·3 ± 1·24 or 9·8 ± 1·26 excluding cows that failed to ovulate. A mean of 6·1 ± 0·63 eggs was recovered but only 4·2 ± 0·63 were normally developed embryos. In the cows treated in mid-lactation for non-surgical embryo recovery, 25/92 had fewer than three ovulations. A mean of 3·5 ± 0·45 eggs was obtained non-surgically from 58 cows that were flushed, and 3·1 ± 0·44 were normal embryos. The estimated recovery rate of normal embryos non-surgically was 38 % of those ovulated compared with 43 % from slaughtered animals.

It appears that the lactating dairy cow has a rather low ovulatory response to PMSG but by the repeated use of the non-surgical embryo recovery method described, sufficient numbers of embryos may be obtained on a yearly basis to justify the use of the procedure for the improvement and dissemination of dairy breeds.

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.