(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.

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.

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.

(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.

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.

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.

Electrical conductivity was measured during the oestrous cycle of cows with electrodes implanted in the vaginal wall. Conductivity was considerably higher during oestrus than during the preceding or following cycle stage. Conductivity was also high in the fresh surgical wound, whereas the healing process was accompanied by a decrease.

With deep frozen bull semen processed in an egg yolk – milk diluent and stored in plastic straws at — 196°C, a lowering of the dose rate from 25 million (3824 inseminations) to 12·5 million total sperm per insemination (3900 inseminations) resulted in a decline in conception rate (CR = 49-day non-return rate) of 6·5 % (60·1 v. 53·6). Development of a processing technique which allowed sperm to be stored at — 196°C at concentrations of 450 or 100 million sperm per ml prior to subsequent rapid thawing and redilution (RDF) allowed dose rates to be reduced to around 5 million total sperm per insemination without any significant reduction in CR. The re-diluted semen was used for inseminations made from 4 to 8 h after thawing and redilution. The use of RDF procedure could reduce semen storage costs, increase the number of inseminations per sire, and has potential application in oestrus synchronization programmes or in countries with developing insemination programmes.

Direct injection of slurry into soil was tested as a means of avoiding the rejection of herbage by dairy cattle when slurry is spread on the surface. British Friesian dairy cows grazed paddocks that had been injected with slurry at 25 t/ha ( = 60 kg N/ha) 9 weeks previously, had slurry spread on the surface at the same rate and time, or received 60 kg N/ha as ammonium nitrate. There was less herbage dry matter available per cow on paddocks with slurry than on the control. The cattle on the surface slurry treatment consumed approximately 30% less herbage dry matter than those on the other two treatments.

Cattle on pasture with surface-spread slurry spent longer grazing, walked about more during grazing, appeared to take smaller bites of grass, engaged in competitive interactions more frequently and drank more often. Behaviour was less affected on injected paddocks. In a second experiment, paddocks which either received inorganic fertilizer throughout the season, or were injected at 25 t/ha in June and August instead of the fertilizer application, were grazed by the herd at intervals during the season. Injecting slurry had no effect on herbage intake or animal behaviour.

1. British Friesian (F) and Hereford × British Friesian (H × F) male calves were raised from about 3 days to 8 weeks of age at air temperatures of 5, 10 or 15°C. They were given a milk replacer diet supplying 950 kJ metabolizable energy/kg M0·75.24 h.

2. There was no effect of environmental temperature on weight gain in calves of either type.

3. Total heat loss measured in a direct calorimeter, increased by about 5 kJ/kg M0·75.24 h per °C fall in air temperature. It was the same whether calves were penned singly or in pairs. Heat loss from F calves was slightly, but not significantly, greater at all temperatures than from H × F calves.

4. The proportion of heat lost by evaporation (a measure of environmental warmth) increased with increasing air temperature and was greater for H × F than for F calves at 15°C.

5. Tissue insulation and external insulation values were similar for H × F and F calves. The calculated lower critical temperatures of the F and H × F calves were 10 and 8°C respectively.

6. The results are discussed in relation to the housing requirements of young calves.

Newborn lambs were separated from their dams before they had an opportunity to suck. They were given bovine colostrum in a single feed and thereafter fed on a milk substitute. Their weight gain compared favourably with that of lambs fed on ovine colostrum followed by milk substitute or suckled naturally. It was concluded that bovine colostrum can be used successfully as an alternative source of immunoglobulin for rearing lambs.

Trials were carried out over two winters to compare red clover and grass silage for cattle finishing.

The silages were mixed to give rations containing 0,25,50,75 or 100% red clover dry-matter and were offered ad libitum to individually fed British Friesian-type steers. Significant differences in dry-matter intake occurred but the effect of silage type on animal performance was not significant. Barley supplementation had a significant effect on both total dry-matter intake and daily live-weight gain.