Twelve Friesian calves were each fitted with an abomasal cannula. The calves were placed in a controlled environment chamber and given a milk substitute diet in buckets at 12-h intervals. The calves were exposed to air temperatures of 25°C from 4 to 10 days of age, 5°C from 11 to 14 days of age, and 25°C at 15 days of age. At 9, 10, 11, 14 and 15 days of age, the abomasal contents of the calves were sampled at 2-h intervals and the temperature and pH of the abomasal contents were recorded at 40-min intervals for a period of 12 h. The rectal and abomasal temperatures of the calves were lower at 11 days of age than at 10 days of age, and were greater at 15 days of age than at 14 days of age (P < 0·05).

In a similar experiment four Friesian calves were each fitted with an ileal re-entrant cannula. The calves were exposed to air temperatures of 25°C from 5 to 19 days of age, 5°C from 20 to 26 days of age, and 25CC at 27 days of age. At 18, 19, 20, 26 and 27 days of age the ileal contents of the calves were collected and sampled for a period of 12 h.

No significant effects of the air temperatures of 25° and 5°C on the abomasal digestion (acidity and proteolytic activity of the abomasal contents) and ileal apparent digestibility of the diet were found.

The comparative effect of spraying wheat straw, maize stover and maize cob with sodium hydroxide and alkaline (sodium hydroxide treated) hydrogen peroxide over a range of moisture contents was evaluated. The effect of concentration of hydrogen peroxide on straw subsequently ammoniated was also investigated. No differences (P < 0·05) were detected between sodium hydroxide and similar concentrations of sodium hydroxide used to provide alkali for alkaline hydrogen peroxide treatments. When however, gaseous ammonia was used as the source of alkali there were significant linear increases in degradability with increasing concentrations of hydrogen peroxide. At 48 h incubation, degradability values for untreated, ammonia-treated, 10, 50 and 100 g alkaline (ammonia) hydrogen peroxide per kg were 528, 595, 640, 676 and 716 for wheat straw, 618, 652, 683, 717 and 743 for maize stover and 392, 467, 585, 632 and 686 g/kg for maize cob respectively. It is concluded that the use of gaseous ammonia as the source of alkali seems a possible practical method of using hydrogen peroxide to increase degradability of straws.

An experiment was carried out to investigate the performance of young steers given either ammoniated hay alone (TA), or supplemented daily with either 112 g fish meal (TF) or 2 kg barley (TB) or 2 kg barley-based concentrate (TC), compared with untreated hay supplemented with either urea (UU), to raise the nitrogen content of the diet to that of the ammoniated hay, or with 2 kg concentrate (UC). Serial slaughter of animals was carried out to examine the effects on body composition during the winter feeding period and subsequent grazing season.

Ammoniation of the hay significantly increased the in vivo digestibility of organic matter, acid-detergent fibre, neutral-detergent fibre and cellulose fractions (0·672 v. 0·643, 0·740 v. 0·670, 0·758 v. 0·638 and 0·826 v. 0·741, respectively). When offered with 2 kg concentrate, intake of ammoniated hay was higher than that of the untreated hay. Empty body weight gains (EBWG) during the winter period were affected by treatment (174, 225, 293, 590, 631 and 692 g/day for treatments UU, TA, TF, UC, TB and TC, respectively), and were highly correlated with total gross energy intakes (56·0, 61·0, 62·9, 74·5, 73·2 and 83·1 MJ/day, respectively). As the rate of EBWG increased, the fat proportion (g/kg EBW) at turn-out also increased. During the grazing season animals which had been on treatments UU, TA and TF showed a marked degree of compensatory growth (759, 686 and 640 g/day EBWG, respectively) compared with treatments UC, TB and TC (623, 572 and 601 g/day EBWG, respectively), and differential rates of tissue gain. This resulted in reduced, though still significant, differences in EBW, although body composition (g/kg EBW) at final slaughter was similar for all treatments. Thus, whilst short-term advantages in intake and performance can be obtained by ammoniation of hay, the benefits so achieved may not persist due to subsequent compensatory growth at pasture.

To study, after weaning at 6 weeks of age, the effect of age on energy utilization of growing calves and to estimate the requirements of metabolizable energy (ME) for calves weighing less than 100 kg, 243 energy balance trials were conducted using 68 Holstein-Friesian castrated male calves at 7, 9 and 13 weeks of age. Regression analyses of energy retention (ER, kj/kg M0·75) on intakes of ME (kJ/kg M0·75) gave the following equations at the respective age: ER = 0·479 (s.e. 0·070) ME — 197, for 7 weeks, ER = 0·521 (s.e. 0·052) ME - 216 for 9 weeks and ER = 0·523 (s.e. 0·043) ME - 236, for 13 weeks. Amounts of ME for maintenance (MEm) calculatedas ER = 0 were 413, 415 and 451 kJ/kg M0·75 for calves at 7, 9 and 13 weeks of age, respectively. The efficiency of utilization of ME for growth was not significantly different among the ages and was 0·500 (s.e. 0023). ME required for growth was estimated to be 510 kJ/kg M0·75 for each kg gain in weight, irrespective of age. The requirements of ME of calves weighing less than 100 kg were lower than those estimated by extrapolation of British and American standards.

One hundred and twenty spring-born steers comprising 40 Friesians (FR), 40 Limousin × Friesians (LM), and 40 Blonde d'Aquitaine ' Friesians (BL), were reared together from shortly after birth to slaughter at a mean age of 771 days. They were at pasture in summer and were housed and offered grass silage plus concentrates in winter. All were implanted with anabolic agents. During the finishing winter, there was a 3 (breed types) ' 2 (3 or 6 kg concentrates per day) ' 2 (94 or 181 day finishing period) factorial arrangement of treatments.

Slaughter weights per day of age, carcass weights per day of age and carcass weights of FR, LM and BL were 846, 828 and 866 (s.e. 8·0) g, 464, 476 and 497 (s.e. 4·9) g and 358, 368 and 385 (s.e. 3·8) kg respectively. LM had lower carcass length, carcass depth, leg length and leg width values than FR or BL but when these measurements were expressed per kg carcass weight the values for LM and BL were similar. Both LM and BL had better carcass conformation than FR, and BL had a lower carcass fat score than either FR or LM between which there was no difference. FR, LM and BL had carcass lean, fat and higher-priced lean proportions of 634, 669 and 685 (s.e. 3·7), 185, 168 and 144 (s.e. 3·7) and 352, 361 and 361 (s.e. 1·4) g/kg respectively.

Increasing the concentrate level from 3 to 6 kg per day increased side weight by 9·6 kg (P < 0·001). This consisted of 0·6 kg bone, 3·3 kg lean and 5·7 kg fat. Extending the finishing period from 94 to 181 days increased side weight by 30·3 kg (P < 0·001). This consisted of 2·6 kg bone, 12·0 kg lean and 15·7 kg fat. Allometric regression coefficients for side lean, bone and fat weights on side weight were not significantly affected by breed type or concentrate level. The coefficients for lean, bone and fat were 0·80 (s.e. 0·04), 0·58 (s.e. 0·05) and 2·27 (s.e. 0·16) respectively. The coefficients for weights of lean in the hind-shin, fore-shin, fillet and brisket on side lean weight were 0·8 or lower. The corresponding coefficients for silverside, inside round, knuckle, rump and strip-loin were between 0·8 and 1·0 while the flank, shoulder, neck, chuck, plate, fore-rib and cube-roll had coefficients in the range 1·0 to 1·5.

Two experiments were carried out to examine the relative value of soya-bean, sunflower and fish meals as protein supplements for growing beef cattle offered grass silage ad libitum. In each experiment, well preserved grass silage (116 and 119 g crude protein (CP) per kg dry matter (DM) and 69 and 76 g ammonia-N per kg total N in experiments 1 and 2 respectively) was supplemented with (1) barley (107 g CP per kg DM), (2) barley/soya-bean meal (224 g CP per kg DM), (3) barley/sunflower meal (223 g CP per kg DM) and (4) barley/fish meal (218 g CP per kg DM). Each of the supplements was offered at a rate of 1·3 kg per head daily to 32 British Friesian castrated male cattle (mean initial live weight 334 kg) n i each experiment. The treatments were imposed for 118 and 134 days in experiments 1 and 2 respectively and the animals were slaughtered 8 months after the end of the treatment periods. On average over the two experiments for supplements 1 to 4 respectively, silage DM intakes were 6·2, 6·3, 6·3 and 6·2 (s.e. 0·053) kg/day; live-weight gains 0·69, 0·78, 0·71 and 0·80 (s.e. 0·039) kg/day; carcass weights 375, 377, 377 and 374 (s.e. 8·1) kg, carcass fat classification (1 = leanest, 5 = fattest); 3·5, 3·5, 3·4 and 3·6 (s.e. 0·14) and areas of m. longissimus dorsi 19·8, 19·9, 19·7 and 19·3 (s.e. 0·66) mnv/kg carcass weight. It is concluded that when part of a barley supplement given in addition to well preserved grass silage was replaced with soya-bean, sunflower or fish meals, silage intake was not affected. The inclusion of fish meal in the diet increased live-weight gain by HOg/day and the response to soya-bean meal was 0·78 of the response to fish meal per unit of crude protein. Sunflower meal did not affect performance. The treatments did not affect carcass weight or fatness 8 months after the end of the treatment periods.

Operant methods were used to measure the responsiveness to earth of five groups of seven weaner piglets held in a flat-deck cage. Lifts on a lever produced access to an earth trough, an empty trough, or had no effect. Group lever lifting performance was unaffected by earth in the trough, but at least one individual, the ‘worker piglet’, operated the lever more than the others to gain access to earth. Once the lid of the trough was opened other piglets were attracted to the earth and spent more time using the earth trough than the empty trough. Previous experience of earth appeared to modify lever lifting behaviour. In one group, a worker piglet did not emerge, and in another the worker operated the lever for earth at a reduced rate. The number of piglets using the earth trough and the amount of time spent utilizing it was reduced by prior exposure to earth. It is concluded that earth is a mild reinforcer to weaner piglets, that it will sustain a low rate of responding on an operant schedule, and that a component of its reinforcement value is its novelty.

Air temperatures were measured every 2 h in 12 growing-finishing pig houses. All houses were operated on the all-in, all-out, principle. Data were collected for two fattening periods in each house. Stocking density, feeding system, pig type, and the farmer's skill were standardized. Every 2 weeks, the houses were visited and live weight, mortality rate, the incidence of coughing and tail biting, and the extent of dirty lying areas were recorded.

Air temperature limits could be isolated from the complex of factors affecting behavioural and health problems of pigs observed within these experiments. Sensitive periods within the growth period of the pigs seem to exist. At the onset of the fattening period (20 to 30 kg), pigs which have been transported from other farms need special care. During summer, mortality rate was lowered when the periodicity of the temperature cycles was lowered for 40- to 50-kg pigs, whereas for heavier pigs the mean maximal air temperature was important also. With respect to coughing, a statistically significant negative relation with the air temperature in the pig house was found for all weight classes, with interactions from the number of different temperature cycles within a 24-h period. In order to avoid dirty lying areas for 20- to 40-kg animals, air temperatures should be between 20 to 24°C, whereas for diarrhoea, animals of 40 to 50 kg were especially sensitive to the occurrence of low air temperatures. For minimizing tail biting, an optimal air temperature range of 20 to 22°C is suggested.

Four silages were prepared from a sward of perennial ryegrass (Lolium perenne cv. Melle). Two were ensiled directly either without (UWN) or with formic acid at 31 1/t fresh material (UWA). The remaining herbage was left undisturbed in the swath for 43 h (WL) or was spread and harvested after 19 h (WS). The dry matter (DM) concentrations at harvest for the unwilted herbage were 229 (UWN) and 238 g DM per kg (UWA) and wilting increased DM concentration to a similar extent for both treatments (WS, 339 v. WL, 346 g DM per kg).

Forty British Friesian steers initially 3·5 months of age and 105 kg live weight were used for the trial. Eight steers were allocated to an initial slaughter group and the remainder were offered the four silages at a restricted level to give 940 kJ digestible energy per kg M0·75. These animals were slaughtered after 112 days to estimate the incremental increases in the components of the body.

Loss of DM in the field by respiration increased from 22·2 to 40·6 g/kg DM cut with increased length of wilting. In silo losses were greater with unwilted (UWN, 222, UWA 183 g/kg DM ensiled) than with wilted silage (WS, 133 WL, 122 g/kg DM ensiled). All silages were well preserved. Wilting was more effective than formic acid in reducing total fermentation acids but a lower proportion of these acids was in the form of lactic acid.

Live-weight gain was lower for the steers given the control (UWN) silage (398 g/day) than for those given silages UWA (463 g/day), WS (476 g/day) and WL (470 g/day). However, a lower proportion of the gain by steers given UWN was in the form of gut contents so that gains in fat, protein and energy were not significantly affected by treatment. In conclusion, when steers were given similar amounts of digestible energy and unwilted silage was well preserved, neither the use of formic acid nor wilting influenced gains in protein and energy. Further, the duration of wilting, in the absence of any differences in DM content, had no effect on animal performance.

The length of the oestrous cycle and plasma progesterone concentration in Ethiopian Highland zebu cows were monitored after treatment with prostaglandin F2α (PGF) (25 mg Lutalyse®) 12 days after spontaneous oestrus. PGF induced luteolysis followed by a significant drop in progesterone values to proportionately 0·11, 0·04 and 0·03 of the pre-treatment values (range 6·3 to 11·4 μg/l) within 24, 48 and 72 h of PGF injection, respectively (P < 0·001). PGF treatment resulted in oestrus within 72 to 120 h and did not influence the length of the subsequent oestrous cycle (P > 0·05). Mean oestrous cycle length was 19·4 (s.d. 1·3) days. There was good correlation (r = 0·72) between the length of consecutive cycles in the same cow and the amount of progesterone the cow produced on the same day in the cycles (r = 0·69 to 0·95). As a result, a close relationship (r = 0·74) existed in the total amount of progesterone produced in consecutive cycles. These data suggest that events following PGF treatment in Ethiopian Highland zebu cows closely parallel those observed in natural cycles. Two-thirds of the spontaneous heats exhibited elevated progesterone values 2 days prior to oestrus onset.

Semen was collected from boars of proven fertility and diluted with Zorpva base using the antibiotic treatments: benzylpenicillin and streptomycin; polymixin B; tylosin; neomycin; gentamycin; kanamycin or lincomycin and spectinomycin. The last combination provided an economical treatment with enhanced quality and preservation of motility. The addition of trehalose (1 g/1) and potassium chloride (0·25 g/1) improved the preservation of acrosomes. The resulting ‘Reading’ variant was compared with Zorpva at days 4 to 6 of storage in a split ejaculate trial using 40 sows slaughtered 9/10 weeks after insemination. Conception rates were significantly higher using Reading (16/20) compared with Zorpva (8/20; P < 0·05) and the effect was particularly marked at days 5 and 6. The mean number of embryos per pregnant sow was 11·6 (Reading) v. 9·4 (Zorpva), representing 51% and 42%, respectively, of ova shed, as measured by counting corpora lutea.

Three experiments of 2 × 2 × 2 factorial design were made with sheep or cattle given a basal diet of barley straw. Fish meal (FM) and unmolassed sugar-beet pulp (SBP) were given either separately or in combination as supplements to untreated (US) or ammonia-treated barley straw (AS) to form eight diets. The diets were given for 8 weeks in experiment 1 (24 sheep), 10 weeks in experiment 2 (24 steers) and 20 weeks in experiment 3 (32 steers and bulls). Urea was added to the shredded straw US and AS, to give a final concentration of 17 g nitrogen per kg dry matter (DM). n I experiments 1 and 3, both FM and SBP, given alone or in combination, significantly increased the DM and organic matter digestibility of urea-supplemented US, but not of AS. Ammonia treatment of straw given alone increased DM intake from 414 to 729 g/day in sheep and from 4·75 to 6·09 kg/day in cattle. All animals given US as the sole food lost body weight, but cattle gained weight when US was combined with either 50 g/kg FM or 15 g/kg SBP. It was necessary to combine the two supplements to achieve a significant gain in body weight of sheep. Although the diets based on AS promoted growth in all the animals, the body-weight gains achieved with US combined with 50 g/kg FM or 15 g/kg SBP were greater than those when AS was given as the sole food.

Blood samples were taken from three Brahman × Friesian cattle while they walked for 1 h daily on a treadmill pulling 20 or 25 kg weights suspended in a cage. Heart rate and energy expenditure during work were closely correlated. The work had no significant effect on blood levels of red cells, haemoglobin, packed cell volume, total protein, albumin, glycerol, urea, Mg, Ca, Na, K and chloride. White blood cells, glucose, lactate, free fatty acids, P-hydroxybutyrate and inorganic phosphate were affected by work although the changes were shortlived and values had returned to resting levels 75 min after work finished. The changes were similar in each animal and indicated work done by draught cattle is largely at a submaximal level. Apart from lactate no blood parameters were identified that could be usefully used to compare performance.

In two experiments, six silages were offered either alone or with constant daily levels of a barley-based concentrate (450 or 900 g fresh weight per ewe) to Finn Dorset ewes carrying between one and four foetuses in the last 6 weeks of pregnancy. The silages (SI to S3, experiment 1 and S4 to S6, experiment 2) had dry matter (DM) concentrations of 256, 190, 278 and 294, 216, 201 g/kg fresh weight and crude protein (CP) concentrations of 106, 164, 212 and 119, 148, 194 g/kg DM. Mean metabolizable energy (ME) concentrations of the silages (digestible energy × 0·81), in weeks 16 and 20, were 9·2, 10·3, 12·0 and 8·8, 10·9, 11·0 MJ/kg DM. Total ME intakes were 12·6, 13·5, 18·6 and 14·5, 15·1, 16·8 MJ/day in week 16 of gestation and were 11·6, 11·2, 17·2 and 12·2, 11·8, 13·3 MJ/day in week 20. Total ME intakes were increased by offering higher levels of concentrates and for levels of 0, 450 or 900 g/day these were 12·3, 14·8, 17·9 MJ/day in week 16 and 9·6, 12·8, 15·5 MJ/day in week 20. Intakes were similar for ewes carrying twins or multiples in experiment 1, but in experiment 2, intakes by ewes with twins or multiples were proportionately 0·97 and 0·85 of those for ewes with singles. Replacement rates of forage by concentrates were —0·09, —0·08, —0·60 and —0·06, —0·25, —0·38 g silage organic matter (OM) per g concentrates OM for silages SI to S3 and S4 to S6. Only on silage S6 did the replacement rate differ significantly from zero.

There is evidence that the growth of female rats and sheep may be constrained by physiological concentrations of glucocorticoid hormones. This study was designed to examine the effects of trilostane, an inhibitor of adrenal steroidogenesis, on serum cortisol concentrations and growth in pigs.

First, trilostane was tested at three doses (250 mg, 500 mg and 1000 mg per pig) to examine its effect on serum cortisol concentrations. A reduction in serum cortisol concentration was observed 2 to 4 h after oral administration of trilostane (P < 0·05) and the adrenal response to a challenge dose of ACTH was reduced 4 to 6 h after administration (P < 0·05), at all doses tested. In a second experiment, trilostane (9·24 mg/kg body weight) was administered orally to 10 pigs twice daily for 35 days to examine its effects on growth rate. A further 10 pigs received a placebo. Trilostane did not affect weight gain or carcass composition, but caused a reduction in food intake (P < 0·05). Adrenal weight was increased by trilostane treatment and liver weight was reduced.

These results show that trilostane is effective at lowering serum cortisol concentrations acutely, but suggest that physiological concentrations of glucocorticoid hormones may not retard growth rate in barrows.

Twenty-four crossbred wethers (live weight 27·6 (s.e. 0·36) kg) were divided into three groups and given a concentrate diet. One group was a control, one was given cimaterol (10 mg/kg diet) and one was given clenbuterol (2 mg/kg diet). After 49 days on treatment the animals were fasted for 48 h and slaughtered at a live weight of about 36 kg. The effects of both beta-agonists were similar. Food conversion was proportionately 0·20 better in treated sheep which also produced heavier (18·3 v. 17·0 kg, P < 0·01) carcasses that were leaner. The cross-sectional area of the m. longissimus was increased proportionately by about 0·25 (P < 0·001) and the thickness of subcutaneous fat over the muscle reduced by 0·37 (P < 0·01). The loin joint from treated animals contained proportionately 0·30 more muscle (P < 0·001) and 016 (F > 0·01) less fat. Muscles from treated sheep had higher pHu values (P < 0·01) which resulted in reduced loss of exudate during storage (P < 0·01) and darker colour (P < 0·05). They also contained only about half as much intramuscular fat (13 v. 27 mg/g, P < 0·001) and less haem pigments (2·4 v. 3·9 mg/g, P < 0·001). The results indicate that beta-agonists substantially improve carcass quality but, under certain conditions of pre-slaughter handling, may reduce lean meat quality. The similarity of response to both beta-agonists suggests the observed effects on meat quality may be common to this class of drug.

A total of 52 ram lambs of different morphological types slaughtered at a comparable stage of body development (carcass weights = 19·5 (s.d. 3·10) kg) were used to study the variation in the relationship between muscle and bone development in the hind limb using multivariate techniques. Development of individual muscles was expressed relative to the weight of the major bone to which they are closest, considered here as their carrier bone.

Variability of muscle: bone ratios of individual muscles varied considerably from one muscle to another. The coefficient of variation (CV) ranging from 0·111 to 0·462 (average CV = 0·199). Relative to the same bone, the variability of muscle: bone ratios for each of the three anatomical regions of the hind limb was still important. This suggests that variability may be due to other factors besides muscle weight, such as bone shape.

The correlation between the various muscle: bone ratios was low in some cases. However, a significant association existed between muscle: bone ratios of individual muscles and the total muscle: bone ratio in the hind limb which indicated that some muscle: bone ratios can be used as indicators of muscling in the selection of meat animals such as m. semimembranosus/femm, m. gluteobiceps/femur, m. adductores/'femur and m. semitendinosus/femur.

The most discriminant variables of the population in multivariate analysis were m. soleus/tibia, m. extensor digitorium lateralis/tibia, m. quadmtus femoris/coxal, m. gemelli/coxal and m. vastus medialis/femur. It was also possible to distinguish the different morphological types of the different breeds by the values of the ratios between these variables.

A food-driven pig growth model was developed from two existing mathematical models. The new model predicts daily growth and heat production of early-weaned pigs. An existing pig growth model was altered by replacing the environmental component with a heat transfer model. The heat transfer model was further refined by partitioning latent heat loss between the skin and lungs, adding a thermal resistance for hair coat, and increasing tissue thermal resistance. Results from this combined model were compared with experimental observations of daily piglet growth and heat production at 15°C, 20°C, 25°C and 30°C. Good agreement existed between observed data and model predictions for piglet growth. Heat production predictions did not compare as well with experimental observations as did growth, especially when piglets lost weight.

Two experiments are described investigating the possibility of advancing puberty in Awassi ewe lambs kept under semi-arid conditions in mid Syria using 197 single ewe lambs in 1982 and 165 in 1984. In both years, the animals were allocated to three groups each given different levels of supplementation with a barley/chopped straw mixture to achieve different levels of pre-mating growth (high, medium and low). In 1984, the three groups were further subdivided into four subgroups each given continuous exposure to teaser rams from different ages. These were 175, 200 and 230 days of age and a control group not given continuous access to the ram. The results for the two experiments showed that a higher proportion of ewe lambs on the high and medium treatments showed oestrus in their first season (H = 88%, M = 72%, L = 41%; P < 0·01). The high level of nutrition also advanced the mean date of first oestrus in the high group by 22 and the age at conception by 16·5 days as compared with the low level.

In the second experiment, no interaction between feeding level and presence of ram was observed and although there were no significant effects on occurrence of oestrus, continuous exposure to vasectomized rams from 175 days reduced mean age at first oestrus by 16 and age at conception by 19 days as compared with the unexposed controls.

It is concluded that these practices have important implications for the efficient use of semi-arid range land by Awassi sheep on a semi-intensive system.

The effects of melatonin, administered during anoestrus, on the time of onset of oestrus and on conception rate were investigated in two trials carried out on mature ewes of three indigenous and one imported breed. The ewes lambed between December and February, their lambs were weaned in March and they were hand milked twice daily until September.

In the first trial, 12 Chios and 12 Serres ewes were dosed, orally, for 60 days from 19 April with 3 mg melatonin (M) in 10 ml ethanol and water (1: 4 v/v). A similar number of Chios and Serres type ewes in the same flock were nominated as untreated controls (C). Vasectomized rams were used to detect oestrus from 1 May and detected ewes were immediately mated to entire rams of their own breed. The mean dates of first oestrus in Chios ewes were 4 July (s.e. 1·7 days) and 23 July (s.e. 5·4 days) (P < 0·01) for treated and control ewes respectively. Spread of first oestrus was 19 and 61 days, respectively (P < 0·01). Conception rate and ovulation rate were both higher in M (0·90 and 2·3, respectively) than in C (0·55 and 1·8, respectively) but the differences were not statistically significant. The corresponding results in the Serres ewes were 8 July (s.e. 1·6 days) and 31 July (s.e. 6·8 days) (P < 0·01) for date of first oestrus, 19 and 69 days (P < 0·01) for spread of first oestrus, 0·75 and 0·50 (P > 0·05) for conception rate and 1·8 and 1·2 ( P > 0·05) for ovulation rate.

In the second trial, 12 Karagouniko and 12 East Friesland ewes received a single subcutaneous implant of melatonin (Regulin®) on 5 June and a further 12 ewes of each breed were untreated controls. The procedure was as given for trial 1. The mean date of first oestrus was advanced by melatonin in both Karagouniko ewes (25 July (s.e. 3·91 days) v. 11 August (s.e. 6·7 days); P < 0·05) and Friesland ewes (28 July (s.e. 3·2 days) v. 24 August (s.e. 7·3 days); P < 0·01). Spread of oestrus was reduced (43 v. 68 days in Karagouniko, P < 0·05 and 22 v. 87 days in Friesland ewes, P < 0·01). Conception rate of melatonin-treated ewes was higher (0·60 v. 0·45; P > 0·05) in both breeds. Ovulation rate was higher in melatonin-treated Karagouniko ewes (1·8 v. 1·3; P > 0·05 but, in the Friesland breed melatonin-treated ewes had a lower ovulation rate (2·8 v. 3·7; P > 0·05).

In both trials, melatonin treatment significantly advanced and condensed the dates of first oestrus. Conception rate was consistently increased over all groups (P < 0·05) and there was a tendency towards a higher ovulation rate.