Twenty bulls of three different breeds were tethered individually from 5 months until slaughter at 21 months. On the day of slaughter, the bulls were divided into groups of five animals, transported and then released in a pen. The first bull of the group was slaughtered 60 or 110 min after regrouping. Subsequent bulls were slaughtered individually at 50-min intervals. Social interactions among the bulls were recorded. Muscle pH, light reflectance values and water-holding capacity were measured in samples of m. longissimus dorsi. These characteristics showed correlations with the amount of non-agonistic social activity in which a bull had been involved before slaughter. The characteristics were also correlated with the number of agonistic interactions. Whether a bull was behaving as a dominant or a submissive animal did not influence the incidence of dark-cutting meat as judged by pH values. On the other hand, light reflectance values and water-holding capacity were correlated with the number of passive agonistic interactions (i.e. how many times a bull was attacked) and considerably less with the number of active interactions (number of attacks by the bull). The incidence of butting was not significantly related to muscle characteristics but mounting was significantly correlated with them.

The study indicates that dark-cutting beef is primarily caused by physically exhausting activities such as mounting, and further modified by stress-inducing social interactions.

This study was carried out to investigate: (1) changes in plasma oestradiol-17β and progesterone concentrations in six pre-pubertal beef heifers, 9 months old, subjected to a superovulatory treatment, consisting of a single dose of PMSG followed 120 h later by a single injection of human chorionic gonadotrophin (HCG); and (2) the ability of this treatment to trigger cyclic gonadal activity. After PMSG administration, oestradiol-17β levels increased from 11·8 (s.d. 10·78) to 92·9 (s.d. 38·15) ng/1 just before HCG injection. The oestradiol-17β increase during the superovulatory treatment and numbe r of ovulations were correlated (r = 0·83; P < 0·05). After HCG injection, progesterone concentrations rose significantly reaching values which in some cases were higher than 60 [μg/1. The progesterone peak on days 9 and 10 post HCG was strongly correlated with the number of corpora lutea (r = 0·95; P < 0·01 and r = 0·92; P < 0·01, respectively). Progesterone determinations were performed for a period of 90 days after HCG administration. No evidence was found for the induction of permanent cyclic ovarian activity since all heifers returned, after the induced luteal phase, to their pre-pubertal condition.

Equations for the prediction of forage dry-matter intake, metabolizable energy (ME), rumen degradable protein and undegraded protein, based on those in the current Agricultural Research Council system, were incorporated into a computer program designed to be used by livestock advisors for on-farm rationing of beef cattle. The predictions of silage intake and live-weight gain are compared with experimental data.

Voluntary intake of grass silage was generally over-estimated by the program by proportionately at least 0·06, with a root mean square error of ±0·18 of the mean observed silage intake for the all-silage rations. The prediction of ME requirement for observed production had an error of +0·15 of average ME intake but the calculations of ME intake were themselves dependent on the predictions of the ME concentrations of the silages and supplements. Similarly the comparison of protein supply with requirement was highly dependent on the value assigned to N-degradability. However, the program can be used to assess how changes in the input values would affect ration formulation.

The mathematical basis of the program is described in the Appendix.

The ability of the protein nutrition scheme proposed by the Agricultural Research Council (ARC, 1980, 1984) to predict responses to protein supply was examined in two experiments. In experiment 1, groups of nine British Friesian steers implanted with oestradiol-17β and nine non-implanted steers were fed from 133 to 300 kg live weight on each of four all-concentrate diets (metabolizable energy (ME) = 12 MJ/kg dry matter (DM)) containing ratios of soya-bean meal and formaldehyde-treated soya-bean meal such that undegradable protein (UDP) concentration was 19, 25, 32 or 42 g/kg DM. Rumen degradable protein (RDP) concentration was relatively constant (111 to 116 g/kg DM). Implantation did not affect DM intake (DMI, g/kg M0·75). Both live-weight gain (LWG) and food conversion efficiency (FCE) (LWG/DMI) were greater (P < 0·05) for the implanted cattle (LWG = 1·41 (s.e. 0·04) kg/day; FCE = 0·24 (s.e. 0·02)) than for the non-implanted cattle (LWG = 1·23 (s.e. 0·05) kg/day; FCE = 0·22 (s.e. 0·02)). There were no dietary effects on either DMI or FCE. In the non-implanted steers, UDP did not affect LWG but, for the implanted steers, there were positive, linear responses in LWG to both UDP concentration (P = 0·048) and UDP intake (P = 0·026). In experiment 2, groups of eight implanted steers were fed from 132 to 300 kg live weight on each of six diets (ME = 12 MJ/kg DM, soya-bean meal and formaldehyde-treated soya-bean meal as chief protein sources) supplying 17, 26, 34, 39, 54 and 82 g UDP per kg DM and concentrations of RDP up to 1·5 times ARC recommendations. There was no effect of UDP on either DMI or FCE but positive, linear responses in LWG to both UDP concentration (P = 0·019) and UDP intake (P = 0·010). In both experiments, mean DMI exceeded that predicted by ARC (1980) (P < 0·05). LWG predicted by the ME system and the ARC protein scheme was not significantly different from observed LWG for non-implanted steers, but was an underestimate of observed LWG for implanted steers (P = 0·002 in experiment 1, P < 0·001 in experiment 2). Observed responses in LWG to UDP concentration were also poorly predicted (regressions of observed on predicted LWG: experiment 1, r2 = 0·12, residual s.d. = 0·126; experiment 2, r2 = 0·004, residual s.d. = 0·119). It was concluded that oestradiol-17p has significant effects on responses in LWG to UDP, which are not predicted by the current ARC (1980, 1984) protein nutrition scheme.

Eighteen mature (3 to 6 years) Debouillet × Rambouillet ewes (mean weight 79·2 (s.e. 21) kg) producing and nursing single offspring were randomly allotted to one of three groups to examine the influence of ovine growth hormone (oGH) on reproductive, hormonal and lactational responses of springlambing ewes. Each ewe received a daily subcutaneous injection of either 0, 5 or 10 mg oGH from day 11 through to day 20 post partum (day 0 = parturition). Treatment groups were subdivided into two pens (three ewes per pen) and food intake was monitored from day 1 through to day 20 post partum. On days 11 and 20 post partum, jugular blood samples were collected before and hourly for 8 h after treatment. Blood samples were also collected daily from day 10 through to day 21 post partum and on alternate days through to day 40 post partum. Milk production (oxytocin-induced hand milking) and fat and protein concentrations were determined 21 days post partum. Food intake did not differ before or during the treatment period (P > 0·05). Likewise, ewe and lamb weights were similar among treatment groups through to day 60 post partum (P > 0·05). Serum insulin did not differ before or after treatment on day 11 (P > 0·05); however, on day 20 before treatment, serum insulin was significantly higher in ewes receiving 5 (2·3 (s.e. 0·3) μg/I) and 10 (2·4 (s.e. 0·3) μg/1) mg oGH than in controls (1·2 (s.e. 0·3) μg/1) (P < 0·05). After treatment, no differences were detected in serum insulin among treatments on day 20 post partum (P > 0·05). Serum growth hormone (GH) was similar among groups before treatment on day 11 post partum; but by 8 h after treatment, serum GH was significantly elevated in ewes receiving 10 mg oGH (32·4 (s.e. 1·9) μg/1) compared with ewes receiving 5 (13·9 (s.e. 1·9) μg/1) or 0 (4·5 (s.e. 1·9) μg/1) mg oGH (P < 0·01). By 20 days after lambing, serum GH differed significantly among groups both before and after administration of exogenous oGH (P < 0·01). Ewes receiving 5 or 10 mg oGH produced 2·3 (s.e. 0·2) kg milk per day compared with 1·9 (s.e. 0·2) kg/day for controls (P < 0·10). Milk fat and protein concentrations did not differ significantly among treatments (P > 0·05), but total fat yield was higher in ewes receiving either dose of oGH (206 (s.e. 20) g/day) compared with control ewes (141 (s.e. 20) g/day) (P < 005). Serum progesterone remained less than 0·5 μg/1 in ewes through to day 40 post partum. A linear decrease was observed in interval from parturition to first observed oestrus as dosage of oGH increased (116, 108 and 102 (s.e. 6) days for ewes receiving 0, 5 and 10 mg oGH, respectively; P = 0·10). Administration of exogenous oGH to lactating. anoestrous ewes between days 11 and 20 post partum enhances milk production and may influence the interval to oestrus.

Observations were made of the behaviour of a home-range group of Scottish Blackface ewes. The group, including replacement ewe lambs, remained on the hill throughout winter and was offered supplemental feedblocks from December to April. Sheep were individually identified and data collected on ranging behaviour between 06.00 and 18.00 h GMT in autumn and winter. Additionally in winter, records were made of time spent eating from the feedblock or standing within 3 m of it.

Age was found to have a strong effect on time spent eating from the feedblock, with older ewes (4 years and over) eating more than younger animals. This was partly attributable to the ewe lambs forming peer groups in winter that were uninfluenced by the movements of mature ewes to the feedblock. Consequently, the majority (0·82) of ewe lambs did not eat feedblock in their first winter. Two- and 3-year-old ewes, although not eating significantly more often from the feedblock than ewe lambs, spent significantly more time standing within 3 m of it and were prevented from eating from it by the competitive behaviour of older ewes. The increased gregariousness of hill sheep in winter appears to be an important factor in preventing the younger ewes taking advantage of the continuous availability of feedblocks. The feedblocks were also found to reduce significantly the size of ewes' home ranges.

The results indicate that the social behaviour of hill sheep limits the use of feedblocks to the older and stronger animals in the group. In addition, feedblocks may reduce the utilization by sheep of available winter forage. Alternative strategies for more effective deployment of feedblocks are discussed.

Twenty-eight inbred (I, inbreeding coefficient 0-375 and 0-5) and 28 matching outbred (O) sheep, aged 26 weeks, were housed and allocated in equal number to two planes of nutrition, a high plane (H), involving ad libitum feeding on a pelleted diet, the other a low plane (L), restricted to an amount of the same diet which would maintain live weight. Food consumption, live weight, linear body dimensions and wool growth were recorded for 19 weeks, and for 4 weeks later in the experiment when L as well H animals received ad libitum feeding. Observations were also made for a final 9 weeks when the sheep were at grass.

The I sheep were substantially smaller in weight and body dimensions than the O sheep throughout the experiment. On ad libitum feeding, the I and O lambs grew in parallel and by the same amount per unit of food consumed. There was also no difference between I and O sheep in the amount of food per kg metabolic live weight (M0·73) required to maintain the live weight of the sheep on the restricted intake. The two types of sheep were therefore similar in efficiency.

During the 4-week period when L sheep were fed ad libitum they showed some compensatory growth relative to the H group, but I and O groups behaved similarly. At grass, a tendency for slightly faster growth continued for the O group formerly on a low plane, but there were no significant interactions between plane of nutrition (as originally allocated) and inbreeding.

Wool growth mirrored the results on body growth, with substantial effects of plane of nutrition, but wool growth per unit area of skin did not differ between I and O groups.

Four groups each of 14 sheep aged 11 to 13 months comprising outbred (O) and inbred (I, inbreeding coefficient 0·37 or 0·5) sheep reared on either a low plane (L, maintenance) or on a high plane (H, ad libitum) of nutrition from the age of 6 months were exposed first to acute cold and 1 week later to heat. Exposures in climate chambers ended for each sheep when rectal temperature decreased to 36°C (in the cold) or increased to 42·5°C (in the heat) subject to a limit of 8 h. Throughout the experiment, sheep were kept in matched quartets comprising one sheep of each type.

The average cold resistance times (min) were 161, 267, 348 and 381 for the LI, LO, HI and HO groups respectively, showing a significant effect of both inbreeding and plane of nutrition (P < 0·01). Five sheep in the HO group lasted the full 8 h in the cold chamber with little or no reduction in rectal temperature. Skin temperature at the mid side was significantly higher in L than in H sheep throughout cold exposure, but there was no effect of inbreeding.

Respiration rates were much higher before and during cold exposure in the H sheep, but there was no effect of inbreeding.

The residual correlation of cold resistance with live weight was 0·58, but differences in live weight do not explain all the differences in cold resistance and particularly do not explain the rapid decrease in rectal temperature of the LI sheep. It was concluded that under cold exposure a high level of nutrition was able to compensate partly for the disadvantages of inbreeding, and that outbreeding was able to compensate partly for the adverse effects of poor nutrition.

With heat exposure, there were no significant differences among the four groups in heat tolerance time, but within the 1st h, H sheep had slightly higher rectal temperatures and much higher respiration rates than L sheep. Inbreeding affected only the time taken to reach a respiration rate > 200 per min, which was longer in I (131 min) than in O sheep (113 min) and longer in L (149 min) than in H animals (96 min).

Crossbreeding of desert goat does with the temperate Saanen x Toggenburg buck was found to result in a significant increase in the daily live-weight gain and the empty body weight of their progeny slaughtered at about 30 kg live weight when compared with purebred desert goat kids (P < 0·001). Food intake did not differ between the two types of kids, but live-weight food conversion efficiency was significantly superior in crossbred kids (P < 0·05).

Carcass weight and killing-out proportion tended to be greater in the crossbred kids reflecting lower weights of head, skin, internal organs and gut fill. Breed types did not differ in the weights of individual wholesale cuts. Carcass dissection revealed significantly higher muscle proportion (P < 0·05), significantly lower fat proportion (P < 0·01) and higher muscle: bone ratio in the crossbred kids.

Two experiments were conducted to test different milking procedures for dual-purpose goats that would be suitable for smallholder farmers. In experiment 1, 105 East African and Galla does that kidded to singles were randomly assigned to three treatments: (a) milking in absence of kid and kid sucking residual; (b) milking in presence of kid and kid sucking residual; and (c) milking once a week and kid sucking all milk 6 days of the week. In experiment 2, 45 Galla does that kidded to singles were randomly assigned to three treatments: (a) weigh-suckle-weigh; (b) milking half udder while kid sucking other half and (c) kid sucking all milk in the evening and milking mornings. Measurements of milk yield, milk sucked and weights of kids were taken for 12 weeks of lactation.

Results were analysed using least-squares techniques for unequal subclass numbers. Milking in the presence of kids increased does' milk yield. This increase was attributed to the stimulation of milk let-down by the presence of kids. Although this method potentially provided most milk for dairy use, less residual milk was left to sustain growth of kids. Estimates of total milk yield by milking once a week underestimated milk yield potential of the East African and Galla breeds. Results indicated an appropriate method for estimating milk potential should combine both milked and sucked milk measurements. Restricting milk available to the kids reduced their growth rates and thus indirectly affected their maturing rates. No milking procedure proved to be superior all-around for the smallholder for milking goats. To resolve this dilemma, use of an optimizing technique including socio-economic weighting of milk for family use relative to milk for kids was proposed.

Outflow rate of small particles from the rumen of dry and lactating Chios ewes and Damascus goats were measured in two separate trials using Cr-treated soya-bean meal (SBM). In another trial, the in situ degradation of fish meal (FM) and SBM in the rumen of Chios ewes and Damascus goats were measured. Outflow rate (per h) of small particles from the rumen of the two species was similar but higher outflow rates were observed in lactating than in dry animals (dry ewes 0·054, lactating ewes 0·086, dry goats 0·057, lactating goats 0·081). With the exception of dry-matter degradability of SBM at 6-h incubation periods there were no significant differences between ewes and goats in crude protein or dry-matter degradability of both supplements at all incubation intervals. Degradation measurements at various incubation periods and effective degradation values were different between supplements.

Two trials, one with 36 twin-suckling Chios ewes and the other with 32 twin-suckling Damascus goats, were conducted to study the effect of protein source (fish meal v. soya-bean meal) on the pre-weaning milk yield of the dams, and the growth performance of their offspring. The control (C) concentrate mixture was similar in both trials, using soya-bean meal (SBM) (195 kg/t) as a source of supplemental protein. In the experimental diet (FME) of the ewe trial, SBM was replaced completely by fish meal (FM) whereas in the goat trial (FMG) 83 kg of SBM were replaced by 50 kg FM. Dry matter (DM) and crude protein (CP) degradation of the three isonitrogenous mixtures were measured using nylon bags incubated in the rumens (2, 6, 16, 24 and 32 h) of three Damascus goats. There were no significant differences between mixtures for DM and CP effective degradability at 005 per h outflow rate. At 0·08 per h outflow rate however, lower degradability values were obtained with the FME than with the C diet. There were differences in the effective CP degradability of SBM and FM used in the ewe trial, but the FM used in the goat trial was of higher CP degradability and similar to that of SBM. Ewes on FM produced more milk than those on the control diet (C 3·44 v. FME 3·84 kg/day), whereas milk yield of goats was similar in the two treatments (C 3·87 v. FMG 3·82 kg/day). There were no differences between treatments for ewe milk fat (C 44 v. FME 43 g/kg) or protein concentration (C 54 v. FME 53 g/kg). Goats on fish meal (FMG) produced milk of higher protein (C 37 v. FMG 40 g/kg), but of similar fat (C 42 v. FMG 43 g/kg) concentration to those on the SBM (C) diet. With the exception of the better conversion (milk: gain ratio) efficiency (C 5·17 v. FME 4·44) of male lambs sucking ewes on the FM diet, no other differences were observed in the performance of lambs or kids. Lambs consumed less milk than kids (lambs: males 4·69, females 5·13; kids: males 6·63, females 6·98) per unit of weight gain.

During the transportation of pigs over a long distance, the environment in individual compartments may be related to the climate outside the trailer and may affect the animals. During three international and six experimental transport trials over long distances the relationships between outside and inside temperature and humidity were determined. During the experimental journey pig behaviour was studied and the effect of the environment on meat quality was also measured subsequently.

During the three international journeys the correlation coefficients between the outside and inside temperatures of the trailer were 0·88, 0·81 and 0·54, respectively, whereas there were low positive or negative correlations for relative humidity. The live-weight losses were 60, 80 and 60 g/kg, respectively, and the mortality averaged 0·3%.

The live-weight loss averaged 40 (s.d. 6) g/kg during each 25-h experimental journey, while the mortality was 1·4%. During the course of the journey, a majority of pigs was sitting or lying. During the night and at stops in transit most pigs were lying down.

The correlation coefficients between the outside and inside temperature averaged 0·94 in the artificially, and 0·95 in the naturally, ventilated compartments, while the coefficients for the humidity were 0·66 and 0·77, respectively. Pigs ventilated artificially showed a lower rigor mortis and lower temperatures of the m. longissimus dorsi (LD) and m. semimembranosus (SM) muscles post mortem compared with those ventilated naturally.

A higher temperature in the compartment was related to a lower temperature in the LD and SM muscles at 24 h (P ≤ 0·05) and a higher pH of the SM muscle in the carcass (P ≤ 0·05). However this was also affected by the location of the compartment on the vehicle. A major temperature fluctuation was related to a lower rigor value (P ≤ 0·05).

I t may be concluded from these experiments that the environmental conditions during transport over a long distance may change markedly. High temperatures in the compartment may increase stress, while correct artificial ventilation may decrease stress.

An experiment was carried out over 11 years to investigate selection for economy of production and carcass lean content under ad libitum feeding in Large White pigs. Two lines, a selection (S) and a control (C) line, were involved in the study. The S line comprised 80 females and 10 males and was based at two centres. Boars were performance tested centrally at one of the centres and gilts were on-farm tested. Testing was carried out in groups of two or three full-sibs over the live-weight range 27 o t 87 kg. Selection was based on an index (I) incorporating individual daily live-weight gain (DLWG) and ultrasonically measured backfat thickness (USBF) and a group food conversion ratio (FCR) and generations were overlapping. The C line (32 females and 16 males) was maintained at one centre and males were performance tested alongside S boars to monitor genetic progress. Cumulative realized selection differentials over years 1 to 10 were equivalent to 5·5, 51, 7·0 and 9·4 phenotypic standard deviations for DLWG, USBF, FCR and I respectively and generation intervals averaged 17·0 months. There was little genetic change in DLWG, however, USBF, FCR and I showed substantial improvements with cumulative responses in year 11 of —12·3 mm, —0·22 kg/kg and +45·2 points respectively. The reduction in USBF occurred in the first half of the study with no further improvements being achieved after year 6. This study illustrates the effectiveness of index selection for a limited number of economically important traits but highlights limitations to this approach.

To determine whether gases generated during the breakdown of accumulated manure in an environmentally regulated building affects the onset of puberty in gilts, 42 crossbred gilts, born from 1 o t 15 September 1985, were reared indoors from 10 to 30 weeks of age on concrete slats over a pit that was drained and refilled with clean water biweekly (clean group). Forty-two gilts were reared over a pit where manure was allowed to accumulate (control group). These two groups had similar feeding, water, floor space, lighting and room temperature. A third group of 42 crossbred gilts was reared from 10 to 30 weeks of age in an open-front building with a concrete apron (outdoor group). Concentration of aerial ammonia in the control environment was three- to five-fold higher than in either the clean or the outdoor environment (P < 0·001). Average daily gain and food conversion efficiency were similar for the two indoor treatment groups, but the outdoor group gained less weight than either indoor group (P < 0·05). At 26 weeks of age all gilts were exposed to mature boars daily for 2 weeks, then every 2nd day for an additional 2 weeks. A greater proportion of gilts in the clean environment attained puberty 7 days (P < 0·05) and 10 days (P < 0·07) after first exposure to boars. These data suggest that odorous gases, such as ammonia, in the air of environmentally regulated buildings may diminish the stimulatory influence of boars on the onset of puberty in gilts.

Forty-three entire males were used to determine the pig's tissue requirements for protein and amino acids from 8·0 to 20·0 kg, and provide information on the capacity of diets formulated with conventional ingredients to contain the same levels and balances of amino acids as ideal protein to supply these nutrients. Seven diets with similar digestible energy (15·9 MJ digestible energy (DE) per kg) and crude protein concentrations from 119 to 232 g/kg (8·7 to 17·3 g lysine per kg) were offered ad libitum between 8·0 and 200 kg live weight. The rate of protein deposition was determined by comparative slaughter. The composition of the protein deposited in the whole empty body was determined from amino acid analyses of pigs killed at 8·0 kg and from the two extreme dietary treatments at 20·0 kg. Growth performance and the rates at which protein and lysine were deposited in the empty body increased linearly with increasing dietary protein concentration up to 187 g/kg and remained relatively constant thereafter. The corresponding dietary protein and lysine intakes required to support maximal protein accretion were 178 g/day (11·7 g/MJ DE) and 13·0 g/day (0·84 g/MJ DE) respectively. Based on the maximal deposition rates for protein (91·8 g/day), and lysine (5·96 g/day) and endogenous protein loss (77middot;6 g/day) estimated from the linear component of the relationship determined between protein deposition and apparent digestible protein intake, the pig's tissue requirements for protein and lysine were only 99·4 g/day (6·5 g/MJ DE) and 6·46 g/day (0·43 g/MJ DE) respectively. This disparity between the pig's tissue protein and amino acid requirements and the dietary levels needed to support these was associated with the fact that the apparent digestibility and biological value of the dietary protein were 0·92 and 0·602 respectively. Apart from small differences in the lysine content of body protein and the methionine: lysine ratio, the average amino acid composition of pigs killed at 8·0 kg, and from the diet of highest protein concentration at 20 kg, was similar to that of ideal protein, indicating that the low utilizability of dietary protein for tissue growth and maintenance was probably associated with low amino acid digestibility and/or availability. The implications of the results with respect to expression of the growing pig's requirements for protein and amino acids are discussed.

The effects of long-term oral administration of enkephalinase inhibitors (acetorphan and thiorphan) on food and water intake, live-weight gain and food conversion efficiency were investigated in growing rats and mice. In rats, daily drenching with acetorphan (an absorbable prodrug of thiorphan) at 1 mg/kg per day for 8 days did not alter food and water consumption but significantly increased live-weight gain (32·0 (s.d. 5·1) g for control rats v. 40·7 (s.d. 9·1) g for treated rats (P ≤ 0·05 U test) and improved food conversion efficiency (4·37 (s.d. 0·49) g food per g gain for control rats v. 3·70 (s.d. 0·67) g food per g gain for treated rats). In mice, lower doses (0·2 mg/kg per day) of thiorphan and acetorphan given in the drinking water similarly affected live-weight gain (7·7 (s.d. 0·9) g v. 6·0 (s.d. 1·6) g in 3-week-old mice receiving thiorphan and 2·6 (s.d. 0·4) g in 5-week-old mice receiving acetorphan) with a likely improvement in food conversion efficiency. These results suggest that oral administration of enkephalinase inhibitors may alter growth in rodents, probably by affecting the digestive process.

Friesian/Holstein dairy heifers require an average daily live-weight gain of about 0·68 kg/day from birth to calving if they are o t reach a target live weight of 540 kg before first calving at 2 years of age. For autumn- born cattle the diet during their second winter is usually based on silage, hay or straw and the level of supplementation depends on the forage quality. When supplementation is necessary the aim should be to feed a least-cost diet. One possible supplementary food is fodder beet which, if grown without the use of purchased fertilizer (West of Scotland Agricultural College, 1984), can be a relatively cheap source of energy and compares favourably with other crops in yield per ha. In the two experiments reported here fodder beet was used for feeding dairy youngstock. The objective of experiment 1 was to evaluate the substitution of barley by fodder beet in straw-based diets. In experiment 2, fodder beet was fed as a partial substitute for silage.

Long-day photoperiods of 16 h light (L) and 8 h dark (D) stimulate a proportional increase in live-weight (LW) gain of peripubertal Holstein heifers of 0·08 to 0·17 compared with heifers exposed to short days of less than 12 h L per day (Peters, Chapin, Leining and Tucker, 1978; Peters, Chapin, Emery and Tucker, 1980; Petitclerc, Chapin, Emery and Tucker, 1983; Zinn, Chapin and Tucker, 1986). One factor that could account for some of this variation in the magnitude of the growth response to long days is that the previous photoperiod exposure may influence the response to a subsequent different photoperiod (Moore-Ede, Sulzman and Fuller, 1982). For example, exposure to 13L: 11D induced pulsatile activity of serum luteinizing hormone (LH) in ewes previously exposed to 16L: 8D, but reduced serum LH to undetectable levels in sheep previously exposed to 8L: 16D (Robinson and Karsch, 1987). Thus, sheep exposed to identical photoperiods exhibited different responses depending on previous photoperiod exposure.

It has been reported that a purified extract from sheep hypothalami inhibited growth hormone (GH) release in rats. This somatotropin-release-inhibiting factor (SRIF), or somatostatin, is a tetradecapeptide and has been prepared synthetically (Brazeau, Vale, Burgus, Ling, Butcher, Rivier and Guillemin, 1973). In addition, _SRIF has been reported t o inhibit the release of other hormones which have major effects upon growth and metabolism such as insulin (Koerker, Ruch, Chideckel, Palmer, Goodner, Ensinck and Gale, 1974), glucagon (Ruch, Koerker, Carino, Johnson, Webster, Ensinck, Goodner and Gale, 1973) and thyroid stimulating hormone (Vale, Rivier, Brazeau and Guillemin, 1974). Furthermore, SRIF has also been shown to be present in large quantities i n the gastrointestinal tract where it controls the release of many gut hormones (Schusdziarra, Zyzhar and Rouiller, 1980). Somatostatin seems, therefore, to be centrally involved in regulating digestion and absorption of food and the subsequent distribution of the absorbed nutrients into tissues within the body. Its removal from the blood circulation by passive immunization increased GH concentrations in plasma in rats (Arimura and Schally, 1976) and prevented decreases in GH concentration as a result of stress (Arimura, Smith and Schally, 1976). Similarly, removal of SRIF by active immunization has been reported to result in higher plasma GH levels in lambs (Varner, Davis and Reeves, 1980; Spencer, Garssen and Hart, 1983b). However, this increase in circulating GH did not appear to have a constant effect in later studies and resulted in inconclusive effects on sheep growth. Laarveld, Chaplin and Kerr (1986) and Spencer, Garssen and Bergstrom (1983a) observed increased growth with improved food efficiency in crossbred and Dutch moor lambs respectively, immunized against SRIF, whereas Varner et al. (1980) reported a significantly lower growth rate in male Columbia lambs and others (Fitzsimons and Hanrahan, 1984; Galbraith, Wigzell, Scaife and Henderson, 1985; Garssen, Welling and Spencer, 1984) concluded that immunization against SRIF did not affect growth in crossbred lambs. It has also been reported that immuno-neutralization of SRIF can lead to enhanced milk production early in lactation n i goats (Spencer and Garssen, 1985).