Six boars weighing about 65 kg were penned individually in preliminary observations to investigate their response to increasing levels of faeces in a concentrate diet fed as a gruel. During an introductory 5-day period pigs were restricted to 1·5 kg concentrates plus 100 g fresh faeces daily. The daily concentrate allowance was then increased to 2·2 kg and faeces increased by 50 g/day providing the ration was consumed completely. Two animals showed diarrhoea at intakes of 1 kg faeces per day while the remaining four animals showed no signs of ill health at the maximum allowance of 1·4 kg faeces per day.

In the main experiment littermate pairs of the same sex (16 boars plus 16 gilts in total) were allocated to control (concentrates only) or treated (concentrates plus fresh faeces) groups. Animals were housed in metabolism crates from about 55 kg live weight and the diet allowances were increased gradually up to 2·5 kg concentrates with or without 500 g fresh faeces per day. This was achieved on day 17 and continued to slaughter some 40 days later when pigs weighed around 85 kg live weight. Levels of skatole and indole were significantly higher in the caecal contents of treated pigs at slaughter but similar in faeces compared with controls. There was no effect of dietary treatment on skatole or indole levels in subcutaneous fat.

It seems unlikely that natural coprophagy would contribute significantly to skatole and indole levels in carcass tissues.

Eighty-nine crossbred gilts were used in an experiment to assess the effects of age at puberty on growth and their carcass characteristics at market weight. From 100 days of age each gilt was exposed daily to a boar and observed for standing heat. The gilts were slaughtered in a commercial abattoir as they reached market weight (approximately 109 kg live weight). Thirty-two gilts (36%) reached puberty before slaughter. These 32 earlier-maturing gilts grew more slowly than the other 57 (P<0·001) yet, paradoxically, within the group of 32 which had reached puberty, there was a significant negative correlation between age at puberty and average daily gain (r=−0·565; P<0·001). Of the 32, the date at first oestrus was known in 30 cases. Among these 30, 10 had ovulated more than once (early-maturing) and 20 had ovulated once (intermediate maturing). Consistent with the paradox there was a significant negative correlation between age at puberty and rate of gain within each group but the regression line for the early-maturing gilts had a significantly lower intercept, on the gain axis, than that for the intermediate group (P<0·01). There were no significant differences between sexual maturity groups for any of the large number of physical and chemical carcass characteristics studied.

Dried molassed sugar-beet pulp in Great Britain has for many years contained about 400 g molasses per kg dry matter (DM). Whilst this high concentration of molasses might help to maximize palatability, in many places outside Great Britain considerably lower amounts of molasses (100 to 300 g/kg) are normally added to sugar beet. The relative costs depend on year-to-year fluctuations.

An experiment was carried out using lambs reared from 1 day to 23 days of age on milk substitute given either ad libitum or at a restricted rate of 250 g dry matter per day, in rooms maintained at three temperatures, 7, 14 and 21°C.

Lambs fed milk substitute ad libitum showed similar growth rates (about 365 g per day) at all environmental air temperatures. Total dry-matter intake of milk substitute per lamb over 22 days was slightly higher in those kept in an environmental air temperature of 7°C. The efficiency of lambs in the 7°C environment was lower than those in the 14 and 21°C environments.

When dry-matter intake was held constant, at the restricted level, growth rate increased linearly between 237 and 265 g per day as the environmental air temperature was increased.

At each of these temperature levels the restricted-rate lambs were more efficient than the respective lambs fed ad libitum.

Growth performance and carcass quality (linear measurements) were studied in pigs grown from 25 to 90 kg on barley stored and prepared in different ways. Half the barley was dried to about 14% moisture content for storage and half was not dried but treated with 0·8% propionic acid. Each was given after hammer-milling (3·2 mm screen) or rolling. A total of 144 pigs was used at four centres.

The performance and carcass quality of pigs given acid-treated barley were as good as those given dried barley. While feed utilization, expressed on the basis of air-dry feed, was poorer for pigs fed on acid-treated barley this difference disappeared when account was taken of the different moisture contents of the barley samples. Pigs fed on diets based on milled barley grew more quickly, had better feed utilization but greater fat measurements than pigs fed on rolled barley. There was a significant interaction between storage method and feed preparation (milling or rolling). Pigs given the acid-treated barley grew more quickly when it was in the milled form than when it was rolled, whereas for the dried barley there was a small, non-significant difference in favour of the rolled form.

To determine whether lactating cows select a nutritionally appropriate diet when given grass silage ad libitum and a choice of concentrates high or low in digestible undegradable protein (DUP), 24 mid-lactation Holstein-Friesian cows were given, in different 3-week periods, a concentrate high in DUP (HP), one low in DUP (LP), or a choice between the two (CHOICE), all at an allowance of 5·4 kg dry matter per day. Milk yield was significantly lower, and silage intake slightly but significantly higher, on LP than on either HP or CHOICE. The mean proportion of HP taken in the CHOICE period was 0·47 which was greater than the proportion required to satisfy the cows’ calculated requirements for effective rumen degradable protein, DUP or metabolizable protein but not significantly different from the ratio of 0·50 expected if no choice was made. Individual cows had a strong tendency initially to continue to eat from the feeder from which they had obtained concentrates in the period before CHOICE but this changed to eating significant amounts of both foods within about a week. The fact that the relationship between the proportion of HP in the concentrate intake and milk protein output was significant and positive, and became more so as the CHOICE period progressed, supports the hypothesis that protein demand was directing diet selection but must be viewed with caution as it was heavily influenced by the results of one animal: the highest-yielding cow which also chose to eat the greatest proportion of HP.

The hierarchic behaviour of 71 goats of the Verata breed from two independent flocks on two different farms (no.2 = 34 and no. 2 = 37) was studied during the milking-period of a year. Two statistical procedures: canonical correspondence analysis (CCA) and a log-linear model were used. In the CCA, the total frequencies of each goat in each of the 12 positions at the milking stalls during 210 days of lactation were computed as original variables. Canonical variables were the average values of dairy milk production, proportion of protein and proportion of fat. The first two CCA axes accounted for proportionately 0·72 of the variance. The first axis showed the effect of rank order (V1 = 0·45) and the second axis the variability between animals for the same group of hierarchy (V2 = 0·27). The first position (AC1, = 0·58; AC2 = 0·23) and the last position (AC1 = 0·11; AC2 = 0·26) of the milking stalls were in absolute contributions the most significant in the distribution of the four observed groups of hierarchy, as defined by their frequency of access to the first position. Two parameters were highly correlated with both axes: milk protein content (r1, = - 0·8; r2 = 0·9) and the day milk production (r1 = 0·6; r2 = 0·5). These results showed a direct relationship between rank order and milk production, whereas the variability in each group was best defined by the protein content. The log-linear model showed that goats of lactation numbers one, two and three have a similar behaviour with respect to their locations at the milking stalls, being distributed more randomly (â1, = 0·68 < â2 = 0·7 < â3 = 0·71) than goats of a lactation number four (â4 = 2·95). This effect could be a consequence of two different but related factors: either the animals develop a preference for a particular position over time, or that animals in their fourth lactation showed a more stable behaviour pattern which affected their body condition.

In three successive years cows from an Aberdeen Angus cross Shorthorn herd were mated to pedigree Charolais, British Friesian and Hereford bulls. A comparison of the progeny of the three breeds of sire under controlled conditions was therefore possible using a random selection of dams for mating, and identical rearing of the calves. Results for live-weight gain of the suckled progeny were analysed and showed superiority of the Charolais breed over the other two when used in this form of beef cattle production.

For birth weights and daily live-weight gains, particularly during the grazing period, the Charolais cross progeny showed superiority over the other two. There was a consistent although not always statistically significant tendency for these differences between the breed crosses to occur in the male calves only, the females showing little difference between breeds. The data also showed highly significant relationships between gestation period and birth weight, both within and between breed crosses.

A total of 16 multiparous (range 2nd to 9th parity) Camborough sows were housed over parturition and during lactation in a group farrowing system. Two replicates of four sows were studied in the large pen (L) and two further replicates studied in the small pen (S) configuration, providing 13•4 m2 and 8•6 m2 per sow, respectively. A lactation diet providing 14 MJ/kg digestible energy (DE) and 180 g/kg crude protein was supplied ad libitum via a sow-operated feeder, adapted to facilitate the calculation of individual food intakes. The influence of environmental, physical, and production factors upon food intakes and feeding strategies was investigated. Daily food intakes of 7•69 (s.e. 0•31) kg and 7•72 (s.e. 0•35) kg were achieved during lactation by sows in the L and S pen configurations, respectively, accomplished by sows taking a series of small meals throughout the day. Sows in the S pen area made fewer visits to the feeder and spent less time per day feeding than sows in the L pen area. However, more food was consumed per visit by the S sows, resulting in similar daily food intakes in both treatment groups. There was a depression in lactation food intakes of sows housed at a mean daily ambient temperature of 17•5ºC compared with the other sow groups. The majority of sows consumed energy well in excess of their predicted requirements during lactation, whilst one sow in the L and two in the S pen areas had intakes within ±3•4 MJ DE of predictions. Only two of the L sows had food intakes that produced an energy deficit. In the L pen area, two distinct peaks of feeding activity occurred from 09:00 to 13:00 h and from 15:00 to 23:00 h that accounted for 0•77 of the total feeding time. In contrast, in the S pen configuration, one prolonged period of feeding occurred from 09:00 to 22:00 h accounting for 0•88 of total feeding time. The results show that S sows adapted their feeding patterns to maintain similar daily intakes to those of L sows, thus demonstrating that an ad libitum food supply enabled sows to obtain individual nutritional requirements in a communal farrowing system.

The nylon bag technique was used to determine the effects of offering to steers an allowance of turnips in a diet based on straw on the degradation of dry matter and acid-detergent fibre of the straw. Rumen-cannulated steers were offered basal diets of (a) sodium hydroxide (NaOH)-treated straw ad libitum, (b) NaOH-treated straw plus turnips (50 g dry matter per kg W0·73) offered once daily or (c) turnips ad libitum. Samples of straw, treated with NaOH, anhydrous ammonia (NH3,) or untreated straw were incubated in nylon bags in the rumen along with each of the basal diets. Additionally molasses (66 g dry matter per kg W0·75) was infused into the rumen of the steers offered the NaOH-treated straw. Dry matter and fibre losses of straw from nylon bags were in the order NaOH-treated > NH3,-treated > untreated; there was no interaction (P > 0·05) between method of straw treatment and effect of basal diet on 40-h or 72-h dry matter or fibre degradability. Supplementation of the basal straw diet with either turnips or molasses depressed (P < 0·01) degradability of both dry matter and fibre of the incubated straw at 40 and 72 h, molasses infusion producing a greater depression (P < 0·05) than offering turnips. There was a fall in rumen fluid pH shortly after steers consumed their turnip allowance or molasses was infused into the rumen, minimum pH values were 6·09 ± 0·241 and 5·75 ± 0·205 respectively. The pH of rumen fluid and degradability of dry matter and fibre of barley straw were depressed by the presence of carbohydrates in turnips and molasses. A reduction in the activity of cellulolytic bacteria may have been the cause of the depression in straw degradability.

The Maasai of Kenya are typical of many pastoral communities in that they rely on milk as a major part of their diet. Milk production in three herds of Maasai cattle was studied from 1991 to 1996. Weekly measurements of milk extracted for human consumption were used to estimate lactation length, total offtake and mean daily production. Calf live-weight data were used to estimate total milk yield. Least-mean squares regression and analysis of variance tests were adopted to assess the effect of a number of variables on milk production parameters.

Data from a total of 650 lactations and 383 calvings were collected. Mean daily offtake was 891 ml. The length of lactation of frequently milked cows was 372 (s.e. 7·96) days. Total lactation offtake was estimated at 305 I. Herd, parity level and year of calving differences were observed. Multiple regression analyses indicated that some of the variation in daily offtake could be explained by stage of lactation, season of milking, herd, parity and year of calving. An average total yield of 2·73 I/day was estimated for the first 90 days of lactation. Of this, approximately 0·4 was used for human consumption. Overall, seasonality was seen as the major variable influencing production.

Two studies were conducted to examine the effects of selection for milk-fat yield on pancreatic responses to exogenous glucose, as measured by circulating insulin concentrations following an intravenous glucose load, in heifer calves. The first study involved 6-month-old Friesian heifers, eight each from the Massey University high breeding index (HBI) and low breeding index (LBI) lines. Average breeding indices (BI) for milk-fat yield of the calves based on ancestry BI were 136 (s.d. 2) and 112 (s.d. 2), respectively. Oestrous cycling of the heifers was controlled by intravaginal insertion of progesterone-impregnated controlled internal drug-releasing devices (CIDRs). Challenges of glucose (0, 75, 150 and 300 mg/kg live weight) and insulin (0, 0·1, 1, and 10 fig/kg live weight) were administered via indwelling jugular cannulas and were followed by serial blood sampling to measure responses. Plasma insulin concentrations immediately following the glucose challenge were significantly (P < 0·05) greater in HBI than in LBI heifers, peak insulin concentrations (above baseline) in the HBI group being approximately twice those in the LBI group. Plasma glucose concentrations were marginally lower in HBI heifers, probably due to the secondary effect of the relatively greater hyperinsulinaemia in this group. Although the exogenous insulin challenge significantly reduced circulating glucose concentrations in all heifers, there was no difference between the lines in the magnitude of insulin-induced hypoglycaemia.

The second study was designed to determine whether insulin responses to an exogenous glucose load were influenced by stage of the oestrous cycle in heifers of the two lines. In this study, eight yearling HBI heifers and eight LBI heifers (with BI of 135 (s.d. 4) and 111 (s.d. 1) respectively) were administered an intravenous glucose load (150 mg/kg live weight) on tivo occasions, the first being after 17 days of CIDR treatment (simulating the luteal phase of the oestrous cycle) and the second 46 h after withdrawal of the CIDRs (when the heifers were expected to be in oestrus). HBI heifers again showed significantly greater circulating insulin concentrations than LBI heifers following the glucose challenge but the magnitude of this effect was not influenced by time relative to CIDR withdrawal. It is concluded that heifers selected for high milk-fat yield have an increased pancreatic response to exogenous glucose which is apparently independent of the stage of the oestrous cycle. This difference may provide a useful means of identifying heifers of superior genetic merit for milk-fat production prior to their first lactation.

A total of 142 pigs, born at four different times of the year, were slaughtered between 1 and 9 months of age to study the effects of season of birth and sex on heart weight and body weight in the equatorial climate of southern Nigeria.

Analysis of loge heart or body weight showed that season of birth influenced heart and body growth (P < 0·001). The differences occurred largely during the phase of rapid growth, with smaller differences at weaning and at 9 months. Pigs born during the high-rainfall period (May to September) showed stunted body and heart growth during the subsequent dry and warmer seasons. Those born during the dry seasons (November to March), but which passed their rapid-growth phase through the rainy, cooler seasons, were attaining market weights and adult heart weights earlier in life. However, all pigs with early growth reductions recovered, at least partially, later in life. The males had larger hearts at later ages than the females although the differences were not significant (P > 0·05). Allometric regression analyses for heart and body weight showed no seasonal effects but there was a small but significant sex effect (P < 0·001). The males had a smaller intercept and a larger slope when log, heart weight was fitted to log, body weight.

Pigs reared in this equatorial climate appeared to have higher heart weights relative to body weights than those reared in temperate regions. The highest recorded proportional value of 0·0032 is outside the range of 0·0023 to 00028 recorded in temperate regions. This suggests a probable physiological adaptation to increased work load on the heart under warm tropical conditions.

An experiment was undertaken to compare the carcass characteristics and meat quality of lambs from crossbred ewes produced by crossing Texel sires with Rouge de l’Ouest dams and Rouge sires with Texel dams, relative to lambs from purebred Texel and Rouge ewes. The ewes were crossed with Texel or Rouge sires and the relative performance of the sires assessed in terms of lamb carcass quality. Ewe and ram genotype had a significant effect on conformation classification. Lambs from Texel ewes had a greater conformation classification (4·0) than lambs from Rouge ewes (3·4, s.e. 0·09) (P <0·001) and Texel-sired lambs had a greater conformation classification (4·0) than Rouge-sired lambs (3·6, s.e. 0·06) (P <0·001). Fat depth was significantly influenced by ewe genotype with lambs from Texel × Rouge ewes having greater fat depths compared with lambs from Texel ewes (longissimus dorsi 2·3 and 1·9 (s.e.0·12) mm respectively) (P <0·05). Chemical composition of the carcass and meat quality measurements were unaffected by ewe or ram genotype. Significant heterosis effects on lamb live-weight gain (21 g/day; 15%) (P <0·01) from birth to slaughter, age at slaughter (–37 days; –12%) (P <0·01), weight of perinephric and retroperitoneal fat (76 g; 38%) (P <0·01) and fat depth over the longissimus dorsi (0·3 mm; 16%) and gluteus medius (0·5 mm; 17%; P <0·05) were obtained. The results from this study demonstrate that significant heterosis effects, particularly in terms of lamb growth rate, can be achieved by crossing Rouge and Texel breeds. In addition lambs from hybrid ewes have similar conformation characteristics to the Texel breed which has been intensively selected for carcass characteristics.

An 8-h photoperiod, compared with 12-, 16- or 23-h photoperiods, has been shown to reduce the incidence of injurious pecking and leg problems in intact male turkeys but to result in lower body weights, slower sexual development and less efficient food conversion. The effect of 8 h of illumination given as a solid photoperiod, as eight 1-h periods equally spread through the 24 h or concentrated into a 12-h part of the day on the performance of BUT 8 intact male turkeys was investigated.

Fragmentation of the daily illumination increased body weight, improved food conversion efficiency but did not significantly affect food intake. Increased sexual displaying and significantly better food conversion between 16 and 20 weeks by the two intermittently illuminated groups strongly suggested that both regimens were interpreted as stimulatory daylengths. Generally, losses due to mortality and culling were higher in both fragmented groups, while injurious pecking was higher in 8(1L: ID) birds before 5 weeks and in birds given a 12-h ‘subjective day’ after 5 weeks than in 8-h controls. Culling due to leg problems was significantly higher in birds on the 8(1L:2D) regimen but the incidence of leg imperfections was minimal (< 0·037) in all groups. Both intermittent groups but the 8(1L: 2D) in particular, showed a reduced response to hand movement across the eyes compared with 8-h controls. The controls ate proportionately more food during their 16-h dark period than did the intermittent group during their 12-h ‘subjective night’, though both groups increased their ‘nocturnal’ feeding with age.

In three experiments with 60, 72 and 72 housed Greyface (Border Leicester × Scottish Blackface) and Suffolk × Greyface lambs on silage-based diets, a range of barley and fish-meal supplementation levels was compared. In experiment 1, six barley levels ranging from 0 to 625 glday were offered to lambs on flail-harvested and precision-chopped silages. In each of experiments 2 and 3, three levels of barley, 200, 400 and 600 g/day, were factorially arranged with four levels of fish meal, 0, 40, 80 and 120 g/day. The daily intake of flail-harvested silage was proportionately 0·76 of that of precision-chopped silage but because of a slower rate of gain the total requirement of silage dry matter (DM) per kg carcass gain was greater with flail-harvested than with precision-chopped silage. On average, over all barley supplemented diets in experiment 1, the requirement per kg carcass gain was 9·2 kg silage DM and 4·9 kg barley DM, with flail-harvested silage, compared with 8·2 kg silage DM and 3·4 kg barley DM with precision-chopped silage. Increasing barley supplementation in experiment 1 from 125 to 625 gl day reduced the silage DM requirement for carcass gain by 4·7 kg/kg increase in barley DM given. The corresponding figure over the range 200 to 600 g barley in experiments 2 and 3 was 2·6 kg silage DM per kg increase in barley DM given. The reduction in silage requirement with increasing barley was generally greater at low than at high levels of barley supplementation within the ranges examined. On silage-based diets optimum barley supplementation level was estimated to be in the region of 500 g/day.

Increasing fish-meal supplementation from 0 to 40 g/day, in experiments 2 and 3, reduced the requirement per kg carcass gain by 2·78 kg silage DM and 1·25 kg barley DM for an increase of 0·40 kg in input of fish meal DM. A further increase from 40 to 80 g/day fish meal reduced the silage DM requirement per kg carcass gain by 1·44 kg and the barley DM requirement by 0·50 kg, for an increase in input of 0·26 kg fish meal DM. A further increase to 120 g/day fish meal resulted in increases in both the silage and barley requirement per kg carcass gain. The optimum level of fish-meal supplementation was between 40 and 80 g/day and was not affected by the level of barley given.

There was evidence of an increase in carcass fat at the higher levels of gain achieved through increasing barley supplementation, but no evidence of increase in carcass fat at the higher levels of gain achieved through fish-meal supplementation.

Thirty-two Blackface female mature sheep weighing 45 kg on average were blocked by weight and randomly allocated 60 days before slaughter to be untreated controls (C) or subcutaneously implanted with 20 (TA1), 40 (TA2) or 60 (TA3) mg trenbolone acetate (TBA). Samples of blood were collected throughout the study and post-mortem samples of selected body tissues were analysed residues.

Concentrations in blood of 17β-hydroxy-trenbolone (TBOH) peaked within 1 to 2 weeks of implantation and declined thereafter. Concentrations in blood of oestradiol-17β (OE) were elevated and generally increased with increasing dose levels of TBA. The highest concentrations of solvent extractable residues (TBOH for group TA3) ranged from 613 ng/kg in kidney to 130 ng/kg for rib muscle. Trenbolone-17β- glucuronide was detected in liver and kidney at maximum concentrations of 157 ng/kg and 94 ng/kg respectively. Implantation with TBA had no effect on concentrations of OE in any of the post-mortem tissues examined.

The performance of two flocks of crossbred Masham ewes (Tees-water × Dales Bred) was measured for 6 and 4 years respectively. The ewes in Flock 1 were mated with Dorset Down rams and the ewes in Flock 2 with Suffolk rams.

The overall mean mating weight of each flock was 68-0 kg with no consistent year-to-year variation. The mating weight repeatability values for ewes entering the flocks as 2-year-olds were 0·532 (±0·0681) and 0·524 (±0·1118) for Flocks 1 and 2 respectively.

Mean litter size increased with age, but repeatability was low. Over- all litter weights for singles, twins and triplets were 5·89, 9·88 and 12·43 kg respectively. Two-year-old ewes had lighter litters than mature ewes. Repeatability for litter weight in Flock 1 was 0·337 (±0·0755).

Lamb growth rate to 4 weeks of age was lower for 2-year-old ewes in both flocks and the repeatability was 0·322 (±0·0947) in Flock 1. For ewes having twin lambs, significant correlations (P < 0·01) were found between mating weight and birth weight and between birth weight and lamb growth rate to 4 weeks of age.

Perinatal mortality was higher for lambs with a birth weight below 3·9 kg, but overall lamb mortality was only 8%: this low figure was probably due to the relatively high birth weight of the twin and triplet lambs.

Two experiments were designed to test the efficacy of two different methods of administering prostglandin F2α-tham salt for oestrous synchronization in mature cyclic ewes maintained under normal husbandry conditions. The effect of these agents on ewe fertility and lambing performance was also assessed.

A total of 180 Clun Forest ewes were used in this investigation conducted during the 1983 and 1984 breeding seasons. In the 1983 breeding season, 80% of ewes treated with a single injection of 20 mg prostaglandin F2α-tham salt were mated by fertile rams within a 3-day period, compared with 100% of ewes treated with progestagen pessaries or 23% of ewes treated with saline. Returns to service for the three groups were 23%, 3% and 16%, respectively. In 1984, a single injection of 20 mg prostaglandin F2α-tham salt resulted in oestrus synchronization in 73% of treated ewes, compared with 27% of saline-treated controls and 97% of ewes given two injections of prostaglandin F2α-tham salt, 11 days apart. Returns to service following these treatments were 36%, 6% and 20%, respectively. There was no difference between treatments in lambing performance.

The results indicate that acceptable levels of oestrus synchronization and fertility can be obtained with a single injection of 20 mg prostaglandin F2α. Furthermore, two injections of 20 mg prostaglandin F2α given 11 days apart produce levels of synchronization of oestrus comparable to those previously obtained with commercially available progestagen pessaries.

The effects on reproductive performance of different strategies of pasture management designed to conserve herbage in situ during the late growing season for use during the pre-mating and mating period were studied in three experiments over 3 years with Greyface ewes. Two experiments with 341 ewes compared set-stocking of pasture at 12 ewes per ha on two initial levels of herbage mass with a conservation strategy which left half of the area ungrazed and grazed the other half of the area at 24 ewes per ha from late August until mid October (2 weeks before the start of mating) after which the total area was grazed at 12 ewes per ha. In a third experiment with 124 ewes, the conservation strategy left a quarter of the area ungrazed and varied stocking rate to a minimum of 12 ewes per ha to maintain two initial levels of herbage mass on the other three-quarters of the area and then compared set-stocking at six ewes per ha on this area with set-stocking at 18 ewes per ha on the previously ungrazed quarter of the area during the pre-mating and mating period.

Initial levels of herbage mass were within the range of 2000 to 2100 kg dry matter (DM) per ha (7 cm sward height; high) and 1500 to 1700 kg DM per ha (4 to 5 cm; low). Mean herbage accumulation rates between August and October were estimated to be 25 and 44 kg DM per ha per day in the first two experiments. Initial live weight and body condition score also varied considerably between years and subsequent response was influenced by herbage growth rate. Where mean ewe body condition was within the score 2·75 to 3·00, range over the mating period and herbage mass on set-stocked areas was not higher than 2200 kg DM per ha (8 cm sward height) in the pre-mating period or not lower than 1300 kg DM per ha (3·5 cm) at about 3 weeks after mating, the strategy of management did not influence reproductive performance in terms of the number of lambs born. Within these limits, however, reproductive performance was positively related to herbage mass in late August (low = 1·60, high = 1·94).

When herbage mass fell below the 1300 kg DM per ha level before or during mating, reproductive performance was improved by a herbage-conservation strategy which maintained ewe body-condition score within the 2·75 to 3·00 range. When herbage mass and growth rate were high, reproductive performance was also improved by a herbage-conservation strategy which restricted the development of excessive body condition before mating by avoiding the increase in barrenness shown to derive from very high levels of body condition.