An animal model was used to estimate heritabilities of faecal egg count (FEC) and packed cell volume decline (PCVD) in lines of Merinos selected for divergent levels of resistance to Haemonchus contortus. The estimated heritability of FEC was 0·23 (s.e. 0·03) and of PCVD was 0·21 (s.e. 0·03). A cube root transformation was found to be effective in normalizing FEC data and reducing the range of within selection line-birth year variances from 118-fold to 10-fold. Transforming FEC data increased the heritability estimate to 0·29 (s.e. 0·03) and reduced selection bias due to heterogeneity of variance, but the further step of pre-adjusting the transformed data to a common variance had only a trivial effect. Heritability estimates for FEC in years with high means and variances were similar, as were estimates for transformed FEC. The estimated genetic correlations between measurements in years with high and low means and variabilities were 0·77 to 0·91.

PCVD and pre-adjusted transformed FEC had a phenotypic correlation of 0·48. Estimates for the genetic correlation ranged from 0·76 in the decreased resistance line to 1·00 in the increased resistance line and 0·87 with pooled data. Other effects on resistance included birth type and dam age, with twins and progeny of maiden dams being more resistant than their cohorts. Sex effects were unimportant for FEC but males had higher PCVD than females in most, but not all, years. Younger animals had higher FEC and PCVD than older animals. Maternal genetic effects were found to be unimportant, as were the effects of low levels of inbreeding.

There is limited information on the behavioural and physiological responses of sheep to the components of road transport. Behavioural observations and physiological measurements of ‘stress’, injury and dehydration were made on weaned lambs (35 kg) before, during and after either stationary confinement or transport for 22 h at four space allowances (0·22, 0·27, 0·31 and 0·41 m2 per sheep). Two groups were not loaded (a control group with access to food and water, and a group with no food and no water for 12 h). During the confinement and transport period, the proportion of scans spent lying and the proportion of scans spent ruminating was significantly less than that before treatment (P < 0·01). After 3 h of transport, the proportion of scans spent lying was significantly less at the 0·22 m2 per sheep space allowance than at the other space allowances. The proportion of scans spent lying down was only significantly greater during confinement compared with transport at the 0·22 m2 per sheep space allowance and during the first 6 h at the 0·31 m2 per sheep space allowance. During transport, the heart rate and plasma cortisol concentration were greater than during stationary confinement (P < 0·05), indicating that some aspect of the journey was acting as a stressor. During transport the frequency of losses of balance and the frequency of slips was less at the 0·22 m2 per sheep space allowance than at the 0·27 and 0·41 m2 per sheep space allowances. However, there was no effect of space allowance on either plasma cortisol concentration or biochemical measures of injury. The median frequency of potentially traumatic events during transport was <5 per h and there was little evidence to suggest that increasing space allowance increased the risk of traumatic injury. During the first 12 h after treatment, the proportion of scans spent eating was greater and the proportion of scans spent lying were less than those spent before treatment (P < 0·001). Post-treatment, water intake and packed cell volume were greater in transported sheep than in control sheep (P < 0·05). However, there was no significant effect of 12 h without water on total plasma protein concentration and plasma vasopressin concentration (P > 0·05). Under the conditions of this study, sheep with a live weight of 35 kg can be transported for 12 h at space allowances of between 0·22 and 0·41 m2 per sheep without showing major physiological changes indicative of injury and dehydration. However, the sheep appeared to be hungry after 12 h without food and showed a cortisol and heart rate response to transport, indicating that some aspect of transport was acting as a stressor. A space allowance of 0·22 m2 per sheep cannot be recommended for 35 kg sheep as there is insufficient space for most of the sheep to lie down during transport. Whereas a space allowance of at least 0·27 m2 per sheep does allow most sheep sufficient space to lie down.

Commercial application of multiple ovulation and embryo transfer (MOET) technology will be subject to practical constraints and economic rationalism. This study examines use of MOET in its most profitable arena: to breed stud rams which will disseminate genetic improvement widely through multiplier studs to commercial flocks. A deterministic prediction is used to evaluate schemes based on an open nucleus MOET group within a Merino parent stud, taking account of genetic merit and inbreeding. Selection is based on clean fleece weight with an assumed heritability of 0·4. Embryos are collected at a rate equivalent to 3·45 live lambs per donor. Benefits of MOET were calculated from the discounted expressions of rams sold, and compared with the costs incurred.

As the proportion of the flock born from MOET increases, the rate of genetic gain increases rapidly at first, but diminishing returns are observed. The costs ofMOET increase linearly with the number of lambs produced, so the optimum proportion ofMOET lambs is for practical purposes always less than 100%.

Some use of MOET was profitable provided the stud sells sufficient stud rams each year. Sensitivity tests found that other parameters had only a small impact on the optimum level ofMOET. In general however, changes which increased the rate of genetic gain (heritability, flock size) or increased its value (wool price, lower discount rate) increased the optimum number ofMOET lambs.

The results should provide guidelines to optimum investment in MOET for the wool industry. An across flock genetic evaluation scheme is probably necessary to motivate this investment.

Six cereal straws and two traditional hays were used to study the relationship between voluntary dry matter (DM) intake and chemical composition and ruminal degradation characteristics. The voluntary DM intake was measured during 60 days using Barbarin adult ewes given food individually in four groups of six animals. The forages were offered to the ewes twice daily and were supplemented with 10 g DM of soya-bean meal per kg M0·75 per day and 30 g per ewe per day of a commercial mixture of minerals and vitamins. The chemical composition and the leaf/stem (L/S) ratio of the forages were determined. Their ruminal degradation characteristics were measured by using the nylon bag technique according to the exponential model Dg = a + b (1 – e−ct). Crude protein contents of straws ranged from 22 to 35 g/kg DM and that of hays from 35 to 57 g/kg DM. The corresponding values of L/S ratio varied from 0·68 to 0·88. The voluntary DM intake was highly variable and the hays were ingested at greater amounts than the straws, although their degradable (b) and their rate of digestion (c) were not significantly different (P > 0·05).

Significant relationships were established between voluntary DM intake and the neutral-detergent fibre (R2 = −0·72; P < 0·001), acid-detergent fibre (R2 = −0·75; P < 0·001) and a values (R2 = 0·83; P < 0·001). The precision of the prediction was significantly improved using ruminal degradation characteristics (Syx = 4·42) compared with the chemical composition (Syx = 5·60).

This experiment involved a commercial evaluation of carcasses of extensively reared crossbred lambs. These were sired by Suffolk rams from either a selection line or a control line of a Scottish Agricultural College (SAC) selection experiment, in which selection wasfor lean growth, or by Suffolk ‘reference sires’ from an industry co-operative breeding scheme (SSRS). The lambs were slaughtered at a target live weight of 42 kg between June and October 1992. In total, 421 lamb carcasses were included in the evaluation, 173 from six selection-line rams, 193 from six control-line rams and 55from three SSRS rams. Each of the carcasses was visually appraised for estimated subcutaneous fat proportion and for conformation of the shoulder, loin and leg, as well as being classified using conventional Meat and Livestock Commission (MLC) scales for fat and conformation. Animals were slaughtered at an average age of 139·5 (s.d. 25·6) days and achieved an average cold carcass weight of 20·04 (s.d. 0·96) kg. Carcasses had an average estimated subcutaneous fat proportion of 122·3 (s.d. 22·4) g/kg — equivalent to MLC fat class 3L to 3H. Overall conformation scores, on a 15-point scale, averaged 8·63 (s.d. 1·80) points. Carcasses were cut into joints according to a leading supermarket specification. The weights of pairs of shoulder, flank, loin and leg joints were obtained for each carcass, as well as weights of bone and fat removed during jointing. Saleable meat weights and proportions averaged 15·31 (s.d. 0·76) kg and 765·9 (s.d. 10·0) g/kg respectively. At a constant carcass weight, the SAC selection-line progeny were significantly younger (-11 days), had a significantly higher carcass value (+£1·50), a significantly lower estimated subcutaneous fat proportion (-13 g/kg), and a significantly higher weight of saleable meat (+0·1 kg) and higher proportion ofsaleable meat (+4 glkg) than control-line progeny, but had lower conformation scores. SSRS progeny had similar growth and fatness to selection-line lambs, but had poorer conformation, and significantly more bone in the carcass than either of the SAC lines. When comparisons were made at a constant estimated subcutaneous fat proportion, all differences in conformation between SAC lines disappeared. However, SSRS progeny remained poorer in conformation. The SSRS rams werefrom afoundation generation of the scheme, and were not expected to be markedly superior for carcass characteristics. Carcass weight was byfar the most important predictor of weight of saleable meat, or leg and loin joint weights. Conformation and estimated fat proportion made only marginal improvements, if any, to the precision of prediction, with fat proportion being the more important of the two predictors.

Records ivere collected on Romanov (R), Finnsheep (F), and Booroola Merino (B); first cross; and backcrosses of these breeds with a new synthetic breed of Dorset, Leicester and Suffolk (DLS). The data covered the period from the birth of ewes to weaning of their progeny. The heaviest lambs at birth were the B backcross and R first and backcrosses (4·1 to 4·0 kg) and the lightest were pure R (3·0 kg). The fastest pre-weaning average daily gain was that ofR crosses. R purebreds were more fertile (109%, P < 0·01) than F (81%) and B (62%). They were also more prolific at birth and at weaning (2·44, 2·13) than F (2·04, 1·71, P < 0·01) and B (2·36, 2·09, P > 0·05) purebreds, respectively. Similarly, first-cross R ewes were more prolific than first-crosses of F and B (1·99 v. 2·86 and 1·70), also backcross R ewes were more prolific than backcrosses ofF and B (1·63 v. 1·45 and 1·42, P > 0·05), respectively. R first-cross ewes had heavier litters (6·31 and 26·1 kg) than B (5·17 and 20·3 kg, P>0·01) and F (5·52 and 24·4 kg) at birth and at day 50. The lambs born to DLS ewes were the heaviest at birth and at day 50 compared with those from prolific ewes. Fleece weight in B and its crosses was significantly higher than in R. Crosses showed generally positive heterotic effect in weights, prolificacy and wool production compared with pure breeds. In two data sets, additive direct effect ofR was higher than that ofF at birth (by 0·11 and 0·10 kg) and at day 50 (by 0·57 and 0 kg) but was similar at day 100 and day 365. The additive direct effect of both R and F was non-significantly different to that of B at birth in both data sets, but in only one data set was it higher (P < 0·001) at day 50 (by 2·29 and 1·72 kg), at day 100 (by 5·24 and 5·30 kg) and at day 365 (by 8·7 and 8·4 kg, respectively). Maternal direct effects ofR was higher (P < 0·05) than F in lamb weights at day 1 and 50, and higher than B in lamb weight at day 50. Individual heterosis between both R and F and DLS were -3·7 and -3·6% in weight at birth, 1·46 and 2·09% in weight at day 50 respectively. The corresponding maternal heterosis were, -2·9, -5·2, 1·46 and -0·02%.

Bayesian theory is applied to compare the characteristics of the estimated lactation curves of two groups of 5-year-old Merino ewes. The diets of the two groups were supplemented respectively by DL-methionine and maleyl-DLmethionine. The purpose is to illustrate the Bayesian approach when analysing for the effect of supplement on the lactation pattern of the sheep. Using Wood's model, the posterior distributions of the model parameters are determined for the two groups. This is achieved by assuming a hierarchical Bayes model and applying the Gibbs sampler, a sampling based computer intensive algorithm that is very efficient in obtaining marginal distributions of functions of parameters. The Gibbs sampler enables us to obtain marginal posterior distribution of characteristics of the lactation curve such as peak yield, time of peak yield, persistency and total milk yield. The results are notable differences in the marginal posterior distributions of mean peak milk yield and mean total yield. The posterior probability that the mean peak milk yield of the group supplemented by maleyl-DL-methionine is higher than that of the group with DL-methionine supplement is 0·98, while the same probability for mean total yield is 0·83.

Stochastic simulation was used to compare selection response and rate of inbreeding in four nucleus breeding systems and a sire referencing scheme for sheep: an open nucleus system (ONS), an open nucleus system with sequential selection of the nucleus (ONS-S), a sire referencing scheme (SRS) and a dispersed open nucleus system (DONS). Selection was based on best linear unbiased prediction of breeding values for a single trait measurable on all individuals prior to selection. Selection in a population of 1200 ewes equally divided into 10 flocks was simulated over a 15-year period. The mean rate of genetic gain was proportionately about 0-15 higher in ONS-S and DONS compared with ONS and SRS. The rate of inbreeding in SRS was considerably lower and in ONS-S, considerably higher, than in the other systems. The level of prolificacy in the population did not influence the relative ranking of the breeding systems but may have implications for their optimal structure.

Inert fibre particles were used in a series of experiments in order to quantify the effects of some physical characteristics of dietary long fibre on rumination. Removal of hay from the diet of hay I concentrate-fed sheep reduced true rumination to zero after a period of 8 days, although pseudorumination, much reduced in duration, persisted. Then by introducing loose, chopped, inert polyethylene particles through a rumen cannula, rumination was restored. When different masses of loose inert polyethylene particles chopped into 10-mm lengths were placed in the rumen, the time spent ruminating was found to be directly proportional to mass of fibre placed in the rumen (P < 0·001). By inserting a fixed mass of particles of different lengths, the optimum length of inert fibre for rumination to occur was found to lie between 7 and 30 mm. Finally, when, in place of loose fibre, a polyethylene fibre ‘pompom’, fixed on a rod, was introduced via the cannula and placed so as to brush different areas of the retkulorumen, it was found that the greatest rumination response was evoked when the pompom was allowed to stimulate mechanically the cranial regions of the retkulorumen (P < 0·05). It is concluded that inert polyethylene fibre mimicked the peripheral excitatory effects of dietary fibre by stimulating mechanoreceptors (epithelial receptors) located in the cranial portions of the retkulorumen. Adding about 50 g of 7 to 30 mm inert fibre caused sheep on low-fibre diets to ruminate normally for over 3 h.

Ovulation rate (OR) and litter size (LS) were recorded in a flock of Cambridge sheep from 1984 to 1994 and from 1976 to 1994 respectively. There were 1516 and 2480 OR and LS records with means of 3·2 and 2·5 respectively. There was considerable variation in results between years ranging from 2·2 to 3·2 for LS and from 2·8 to 4·2 for OR. Ewe lamb OR was affected by year of recording, some years having higher OR than others. Rearing type (single, twin or triplet) also affected ewe lamb OR, twins having lower OR than both singles and triplets. Ewe lamb OR decreased with later date of birth reflecting a lower age at OR counting. Ewe lamb LS was affected by year of recording and there was also an interaction between date of birth and year indicating that OR decreased with later date of birth in some years but not in others. OR of adult ewes was affected by year of recording which also interacted with age (2, 3 and 4). Generally, OR increased with age but this trend was not observed in all years. LS of adult ewes was significantly affected by year and increased with ewe age (2, 3 and 4). Heritability and repeatability were determined for ewe lamb OR and LS and adult ewe OR and LS in univariate and two-trait analyses using DFREML. Heritabilities of ewe lamb OR (0·18 to 0·21) and LS (0·05 to 0·08) were lower than corresponding adult ewe values for OR (0·19 to 0·34) and LS (0·19 to 0·22). Ewe OR had a lower repeatability (0·43 to 0·55) than LS (0·30 to 0·80). High genetic correlations (>0·9) were obtained for combinations of ewe lamb OR, ewe lamb LS, adult ewe OR and adult ewe LS. The importance of analysing ewe lamb and ewe records separately is discussed as is the value of ewe lamb OR as a selection criterion.

Wool growth, staple strength and fibre diameter are reduced during pregnancy and lactation. This may be due to the increased requirement for protein for foetal growth, udder development and milk production causing a lack of amino acids for wool. Responses in wool production, ewe live weight, lamb birth weight and growth, plasma amino acids and levels of cortisol, insulin and growth hormone were measured when different sources of protein were offered. Either lupin seed (L), fish meal (F) or formaldehyde-treated egg white (E) were included in an oaten hay-based diet offered during the final 3 weeks of pregnancy and first 3 weeks of lactation. Provision of diets containing E or F resulted in significant (P < 0·001) increases in wool growth and trends towards increased staple strength (4 to 6 N/ktex) and clean fleece weights (0·17 to 0·38 kg) compared with the sheep given L. Feeding the E diet increased the concentration of cystine in plasma and sulphur in wool in late pregnancy. Feeding the F diet increased the concentrations of arginine, histidine, lysine and threonine in plasma in early lactation. Ewes given E had higher circulating insulin and increased insulin resistance, compared with sheep given L, on 2 of the 4 days of sampling during pregnancy and lactation during the treatment period. There were no treatment effects on lamb birth weight or growth but ewes given the E diet were significantly (P < 0·05, 3·3 kg) heavier than the ewes given L after 3 weeks of lactation. The results indicate that a lack of protein available for absorption in the small intestine causes reduced wool growth during late pregnancy and early lactation. Wool growth is more sensitive to a reduced protein supply than foetal growth, maternal weight or milk production.

An investigation was conducted to compare late embryonic losses in ewe lambs and ewes and to determine the effect of inducing embryonic mortality on day 15 of pregnancy on reproductive function in ewe lambs. Ovulation rate and embryo survival were determined, at 15 and 30 days after mating, in a total of 83 ewe lambs and 67 ewes. Ovulation rate was lower, at spontaneous oestrus, in ewe lambs (1·07) than in ewes (1·25; P < 0·05). There was no difference in embryo survival at day 15, as 79% of ewe lambs and 80% of ewes contained expanded conceptuses. However, embryo survival was lower in ewe lambs (69%) than ewes (88%) at day 30 (P < 0·05). Embryonic mortality was induced in an additional 18 ewe lambs with an intrauterine injection of colchicine on day 15 post mating. Four of these animals had normal length oestrous cycles, six had inter-oestrus intervals ranging from 22 to 35 days and eight did not return to oestrus. Overall, the results of this study demonstrate that low ovulation rate and late embryonic losses make a significant contribution to subfertility in ewe lambs. Moreover, conceptus death is associated with luteal persistence, which may reduce reproductive performance by preventing remating.

Genotype × environment and genotype × sex interactions were investigated using lines of Scottish Blackface sheep that had been divergently selected under intensive husbandry conditions for predicted carcass lean proportion, and offspring of rams from these selection lines which were reared under extensive hill conditions. Traits considered were live weight and ultrasonic fat and muscle depth. These were measured at 20 weeks of age on the intensively reared lambs and at 17 weeks of age on the extensively reared animals. Heritabilities for the two environments were 0-39 and 0-20 for fat depth, 0-36 and 0-25 for muscle depth and 0-23 and 0-12 for live weight. Genetic correlations between the environments were 0-54 (s.e. 0-17), 0-90 (s.e. 0-14) and 0-11 (s.e. 0-43) for fat depth, muscle depth and live weight, respectively. The extensive environment may be subdivided according to whether the lambs are reared on improved pasture or on the hill side. The genetic correlations (with s.e.s where estimable) between performance in these two environments were 0-70 (s.e. 0-33), 0-71 (s.e. 0-23) and 1-00 for fat depth, muscle depth and live weight. Genetic correlations between male and female performance under extensive conditions were 0-84 (s.e. 0-28), 0-99 (s.e. 0-14) and 1-00 for fat depth, muscle depth and live weight. T-or fat depth, the genetic correlations of the intensively reared lambs (males only) with extensively reared females and males were 0-37 (s.e. 0-22) and 0-67 (s.e. 0-17), respectively.

Plasma concentrations of growth hormone (GH) are elevated in sheep during undernutrition. The present study attempted to determine whether this increased secretion mediated nutritional effects on reproduction or wool growth, using sheep immunized against growth hormone-releasing hormone and given a low-quality, sub-maintenance diet. Immunization reduced plasma concentrations of GH at all times measured (P < 0·01), through reduced pulse frequency, reduced pulse amplitude, and reduced baseline concentrations. Plasma insulin-like growth factor-1 (1GF-1) was also reduced in the immunized sheep (P < 0·01). Despite this, rates of live-weight loss and wool growth were similar in immunized and control ewes. Plasma concentrations ofLH and FSH were also similar in immunized and control ewes, both during the late luteal phase and after ovariectomy and supplementation with oestradiol and progesterone. Numbers of ovarian follicles and corpora lutea were also unaffected by immunization. It is concluded that high endogenous concentrations of GH in sheep given food below maintenance are necessary to maintain plasma IGF-1, but do not affect the concentration of gonadotropins or ovarian follicular growth. Furthermore, rates of live-weight loss and the depression in wool growth in such animals were also independent of concentrations ofGH or IGF-1.

An experiment was designed to determine whether an injection of 4 μg of the GnRH agonist buserelin (GnRH) followed, 5 days later, by an injection of 100 μg of prostaglandin F2α analogue (PGF), would give a level of oestrus synchronization and fertility comparable with a standard double dose PGF regime. A total of 200 Welsh Halfbred ewes were divided by live weight into two treatment groups using a system of random stratification during the 1994 breeding season. Ninety-one percent of the ewes treated with GnRH combined with PGF were mated by fertile rams within a 3-day period compared with 94% of ewes treated with two injections of PGF, 11-days apart. Returns to service for the two groups were 11·1% and 7·4%, respectively. There was no effect of treatment on lambing performance, as a similar percentage of ewes in the GnRH plus PGF group (88·8%) and the double dose PGF group (92·5%) lambed to synchronized oestrus. Gestation length, litter size and lamb birth weight were similar for both groups. These results demonstrate that GnRH combined with PGF will produce levels of oestrus synchronization and fertility comparable with a double dose PGF regime.

While the onset of the breeding season in ewes can be advanced up to 7 weeks following exposure to long days (44 days) before lambing, a melatonin implant from lambing and exposure to a ram from the summer solstice, this advance is reduced by the absence of a ram. The aim of this experiment was to determine if earlier exposure to the ram and/or exposure to more long days before lambing would further advance the onset of the breeding season. A further aim was to compare the ovulation rate and duration of the breeding season between ewes with a normal and advanced onset of the breeding season due to this treatment regime. Pregnant ewes lambing in mid March were allocated to treatments as follows: (1) controls, maintained on natural photoperiod; (2) 44 LD + mel, exposed to 44 long days (18L: 6D; LD) before lambing followed by a 700-mg melatonin implant after lambing; (3) 90 LD + mel, as in treatment 2, but exposed to 90 LD before lambing; (4) 90 LD + mel + ram, as in treatment 3, including continuous exposure to a vasectomized ram from 10 April. Reproductive state was assessed from serum progesterone concentrations in blood collected at 3- to 4-day intervals from 10 April and ovulation rate was determined during the luteal phase of the first five oestrous cycles in control ewes and ewes exposed to 90 LD + mel + ram. Ewes exposed to 90 LD + mel + ram commenced the breeding season 10 weeks earlier (median date 25 July, range 28 days; P < 0·001) than controls (median date 8 October, range 68 days). Overall, the onset of the breeding season was not advanced in ewes given 44 or 90 LD + mel in the absence of a ram, but a biphasic response was evident, with 40 to 50% of ewes beginning the breeding season at the same time as ewes on 90 LD + mel + ram. Ovulation rate was similar between control ewes and ewes exposed to 90 LD + mel + ram (P > 0·05). The duration of the breeding season was longer in ewes exposed to 90 LD + mel + ram (210 (s.e. 15) days; P < 0·002) than in control ewes (158 (s.e. 10) days), with no difference in date of the end of the breeding season (P > 0·05). Exposure of ewes to 90 LD before lambing in March, followed by a melatonin implant and exposure to the ram from 10 April advanced the onset and extended the duration of the breeding season without an overall effect on ovulation rate. The ram is an important component of this signal sequence.

This study was performed to assess the relationship between serum growth hormone (GH) and insulin-like growth factor 1 (IGF-1) levels, slaughter weight, and myogenic satellite cell growth kinetics of Targhee rams. Serum was collected from 19 rams at 15-min intervals over a period of 4h. Radioimmunoassays of serum samples for GH revealed considerable variation (within individual rams) over the sampling period, with mean values ranging from 0·63 to 4·88 μg/l (mean overall 2·3 (s.e. 0·33) μg/l; no. = 19). There was no significant correlation between GH levels and slaughter weight (r = −0·11; P > 0·05) at 155 (s.e. 1·08) days. Serum IGF-1 levels of (individual) rams were invariant over the sampling period, with individual means ranging from 62 to 233 μg/l (mean overall of 117 (s.e. 45·6) ugll; no. = 19). IGF-1 was not strongly correlated with slaughter weight (r = +0·35; P > 0·05). Satellite cells were isolated from the left m. semimembranosus of all rams at slaughter and grown in culture to evaluate proliferation amount and differentiation extent. The correlations between serum GH levels and satellite cell proliferation and differentiation in vitro were r = −0·53 (P < 0·05) and r = −0·52 (P < 0·05), respectively. Serum IGF-1 showed no significant correlations to proliferation (r = +0·07; P > 0·05) or to differentiation (r = −0·07; P > 0·05) of the satellite cells. These data suggest that serum GH levels in Targhee rams may not reflect muscle growth potential if correlated to body weight of 155 days. Furthermore, as IGF-1 was not correlated significantly with slaughter weight or to variables of satellite cell proliferation and differentiation, another mode of satellite cell regulation (possibly paracrine controllers) is more likely at play to coordinate the satellite cell involvement in muscle growth in Targhee rams at 155 days.

The effect of long-term treatment of goats with methylthiouracil on the timing, amount and quality of secondary fibre (cashmere) growth and timing of cashmere moult in goats was investigated. From early June, groups of 10 Icelandic × Scottish feral goats were dosed orally each day, for a 15-month period, with 5 mg methylthiouracil per kg live weight in 30 ml water (treated; T) or with water only (control; C). Treatment with methylthiouracil resulted in a significant reduction (P < 0·05) in the proportion of active secondary hair follicles present during March. This was associated with a delayed onset of moult of cashmere in T compared with C goats at both the head (11 March v. 23 February; s.e. 3·33 days; P< 0·05) and mid side (27 March v. 26 February; s.e. 3·58 days; P < 0·001). There was no effect on the time of onset (C, 19 July; T, 19 July; s.e. 5·84 days) or cessation of cashmere fibre growth (C, 9 December; T, 8 December; s.e. 1·69 days) or the mean growth rate (C, 0·473 mm/day; T, 0·451 mm/day; s.e. 0·025) and fibre diameter (C, 16·9 μm; T, 15·4 jim; s.e. 0·266). Wlien present in the fleece, the mean weight and proportion of cashmere was higher in C than in T goats (P < 0·05). It is concluded that methylthiouracil treatment altered secondary follicle activity and the time of onset of the moult of cashmere and that these changes may be a result of reduced triiodothyronine production from thyroxine and associated secondary changes in profiles of insulin and IGF-1.

The rôle of growth hormone (GH) in normal growth is well established, but its rôle during recovery after live-weight loss in adults is less defined. This study examined the interaction of endogenous GH with energy or protein supplements during re-feeding of ewes in low body condition. Control ewes and ewes immunized against growth hormone-releasing hormone were housed in individual pens and given food below maintenance for 107 days, before re-feeding was initiated by supplementing half of each group with either fish meal or barley for 28 days (P1), after which the supplements were switched for a further 28 days (P2). Following supplementation, the ewes grazed abundant green pasture for 92 days before slaughter. Immunization reduced plasma concentrations of GH, insulin, insulin-like growth factor 1 (IGF-1) and prolactin. Production responses to the two food supplements were similar in the control and immunized ewes, but when grazed at pasture immunized ewes gained live weight more slowly (P = 0·06), grew less wool (P<0·01), and had heavier fat depots, but lighter carcass, skin and liver weights at slaughter. The sequence of re-feeding treatments affected subsequent wool production in both control and immunized ewes. During P2, and for 52 days after supplementation ceased, ewes supplemented with fish meal then barley (F/B) produced less wool (P < 0·05) than those supplemented with barley followed by fish meal (B/F). At slaughter, the F/B ewes had lighter omental and kidney fat depots than the B/F ewes (P < 0·05). It is concluded that during live-weight regain, endogenous GH initially affected fat deposition, which in turn affected food intake and wool growth. Furthermore, provision of supplements with a high protein to energy ratio to sheep in low body condition, followed by supplements with a low protein to energy ratio, caused a prolonged suppression of wool growth. This effect was not mediated by endogenous GH.

The main objective of the experiment was to investigate the mechanism by which progesterone priming eliminates defective luteal function in anoestrous ewes induced to ovulate with GnRH. Animals in group 1 (no. = 10) were primed with a single i.m. injection of progesterone in corn oil 3 days before the start of GnRH treatment, while ewes in group 2 (no. = 10) received corn oil alone and served as untreated controls. Ewes in group 3 (no. = 10), which served as positive controls, were treated with an intra-vaginal progestagen sponge for 7 days, and this was removed just before the start of GnRH treatment. Ewes in all three groups were induced to ovulate by administration of 2-h injections of GnRH (250 ng per injection) for 54 h. Frequent blood samples for LH, FSH and progesterone analysis were taken around the time of both progesterone injection and GnRH treatment, as well as daily thereafter to monitor luteal function, and laparoscopy was performed 3 and 7 days after GnRH treatment.

The incidence of ovulation was similar for all the three groups (8/10, 7/10 and 9/10 for groups 1, 2 and 3 respectively). Hoioever, both laparoscopic examination and plasma progesterone concentrations revealed that the incidence of normal luteal function was significantly higher in progesterone-primed animals group 1:7/8; group 3:9/9) compared ivith controls (group 2:0/7), P < 0-05) with no difference between groups 1 and 3. Injection of progesterone on day −3 significantly suppressed mean LH concentrations (P < 0·05), but mean FSH concentrations were not altered. However, there were no significant differences between groups in LH and FSH concentrations over the period of GnRH treatment, nor in the timing, duration and height of pre-ovulatory LH and FSH surges. These results suggest that progesterone priming may eliminate defective luteal function either by changing LH concentrations at the time of progesterone administration or through mechanisms not involving gonadotropin secretion.