Insulin-like growth factors (IGFs) and their binding proteins play an essential role in regulating animal growth and metabolism. The initial portion of the current review focuses on the physiological effects of the IGFs and delineates their role as regulators of animal growth and metabolism. The role of IGFs as mediators of growth hormone effects, as insulin-like metabolic regulators and as foetal growth regulators is discussed. The remainder of the review is devoted to the IGF binding proteins, their modulation of IGF action and their role in foetal and postnatal regulation of growth.

Variance components were estimated from an animal model using a restricted maximum likelihood procedure which allowed for unequal design matrices and missing observations (VCE). Data sets containing: (i) 15 275 records of linear type classifications on heifers, (ii) 3399 live weight and condition scores measured at calving and (iii) 1157 records of yield, dry-matter intake, average live weight and condition score during the first 26 weeks of lactation; were analysed jointly.

Heritability estimates for dry-matter intake, live weight and condition score in the largest data set were 0·44, 0·44 and 0·35 respectively and the genetic correlation between condition score and the yield traits ranged from −0·29 to −0·46. The genetic correlation between milk yield and average live weight was negative (−0·09) but after adjusting for the genetic variation in condition score this correlation was positive (0·29). Genetic correlations between live weight and stature, chest width, body depth and rump width were consistently high (0·52 to 0·64; 0·75 to 0·86; 0·59 to 0·81; 0·56 to 0·74, respectively). Chest width and body depth were little to moderately correlated with dry-matter intake (0·25 to 0·28 and 0·20 to 0·34 respectively), and angularity (−0·47 to −0·77) and chest width (0·32 to 0·73) appeared to be good predictors of condition score. These correlations showed that (i) the relative value of live weight compared with food intake capacity determines the optimum direction of selection for stature, chest width, body depth and angularity, and consequently the optimum size of the dairy cow, and that (ii) live weight, condition score and food intake can be predicted from the type traits with little loss in accuracy. A restricted index which maintains condition score at its current level was predicted to reduce overall (economic) genetic gain by 5%.

In a 7-week experiment, the ability of lactating Holstein-Friesian cows to select a consistent diet from two similar foods differing in calculated metabolizable protein to energy (MP/ME) yield was investigated. The effect on diet selection of training through previous access to foods separately, was measured. Food intake was recorded with 28 computer-linked feeders. All foods were mixtures of grass silage and concentrates. In week 1, all feeders contained a standard food. In weeks 2 to 7 a low protein food (LP) and a high protein food (HP) were offered in 14 feeders each. Group CHOICE had access to both foods as a choice from week 2. Group TR1 was trained by access to one food during days 8 to 10 and to the other during days 11 to 13. Group TR2 received the same training as group TR1 during days 8 to 13 which was repeated once during days 14 to 19. After training, TR groups had access to both foods as a choice. Groups LOPRO and HIPRO had only access to LP or HP, respectively in weeks 2 to 5 and to both foods as a choice in weeks 6 and 7. In weeks 2 to 5 LOPRO COWS consumed less dry matter and produced less milk than CHOICE or HIPRO cows. After a week of adaptation, untrained CHOICE COWS selected 662 (s.e. 27) g HP per kg of intake, a choice that differed significantly (P < 0·01) from random. In weeks 4 to 7 TR cows established similar diet choice: 696 (s.e. 21) g HP per kg intake and the proportion selected was unaffected by length of training. The between-day variation in diet choice within cows was not affected by treatment. It is concluded that, under the circumstances tested, training was not required for cows to distinguish between two mixed foods with different calculated MP/ME ratios and to select proportions significantly different from random.

The effect on digestibility, ruminal metabolites, microbial protein synthesis and milk production of manipulating the non-structural (NSC): structural (SO carbohydrate ratio in a predominantly pasture diet was investigated in cows in early (trial 1) and late (trial 2) lactation. Twenty-four cows in trial 1 and 15 cows in trial 2 were offered pasture only (P), 0·85 P plus 0·15 NSC/protein mixture (PR), and P plus an additional 0·1 (trial 1) or 0·15 (trial 2) NSC (PE) in a Latin-square arrangement. All diets were isonitrogenous and P and PR were isoenergetic. PE but not PR increased microbial protein synthesis and decreased ruminal ammonia and milk urea levels, compared with P. Efficiency of microbial synthesis (g N per kg digestible organic matter intake) was not altered by treatment. Treatments had minor effects on ruminal pH and no effect on volatile fatty acid concentrations. PE and PR did not affect milk yield or protein yield and decreased fat yield compared with P in trial 1. Milk yield was increased on PE and PR compared with P and was greater on PE than PR, in trial 2. Yields of fat and protein were higher on PE than on P and yield of protein was higher on PR than on P. The results suggest that increasing the ratio of NSC: protein by increasing total carbohydrate intake was more effective in improving nitrogen utilization in the rumen than was increasing the NSC: SC ratio without increasing carbohydrate intake.

A series of three replicated 3 × 3 Latin-square design experiments was carried out with lactating dairy cows (15 in experiments 1 and 3, and 18 in experiment 2). The objectives of these experiments were to investigate if the feeding of high concentrations of molasses would be detrimental to the performance or health of cows, and if the strategic supplementation of nitrogen or unprotected fat could enhance the efficiency of molasses feeding. In experiment 1, complete diets were based on grass silage with three inclusion rates of a liquid molasses-based supplement (Molaferm 20) to supply molasses dry matter (DM) of 125, 250 and 375 g/kg DM respectively. In experiment 2, the control diet contained (g/kg DM) 460 grass silage, 310 'molaferm 20' and 192 barley and 22 soya-bean meal, and was then supplemented with urea (12 g/kg DM) or soya-bean meal (177 g/kg DM). In experiment 3, the control diet was based on (g/kg DM) grass silage (460), molaferm 20 (310), barley (130), soya-bean meal (65) and oatfeed (20). Two concentrations, low and high, of unprotected tallow were added to the control diet (12·5 and 25·8 g/kg DM, respectively).

In experiment 1, cows suffered from some scouring on the highest molasses treatment, but recovered when changed to either the medium or low molasses treatment. However, there were no clinical symptoms of ill health observed during experiments 2 and 3. In experiment 1, animal intake and performance on the diets containing molasses DM of 125, 250 and 375 g/kg DM respectively were: total DM intake, 12·8, 16·2 and 18·6 kg/day (s.e.d. 1·03, P < 0·001); milk yield, 15·5,17·4 and 17·6 kg/day (s.e.d. 0·53, low v. medium or high, P < 0·01); fat concentration, 39·6, 39·7 and 40·0g/kg (s.e.d. 0·70, P>0·05); protein concentration, 31·6, 32·7 and 33·6g/kg (s.e.d. 0·22, P < 0·05). In experiment 2, supplementation of the control diet both with urea and soya-bean meal significantly increased DM intake (P < 0·01); milk yield (P < 0·01) and protein concentration in milk (P < 0·05), but had no significant effects on fat concentration in milk (P > 0·05). In experiment 3, there were no significant differences in DM intake between the three treatments. However, supplementation with both low and high concentrations of unprotected tallow significantly increased milk yield (P < 0·01) and significantly decreased fat (P < 0·01) and protein (P < 0·001) concentrations in milk.

It is concluded that lactating dairy cows could be given molasses up to 250 g/kg DM in grass silage-based complete diets without adverse effects on milk production or health. When a diet contained a high concentration of molasses (248 g/kg DM), supplementation with urea and soya-bean meal increased intake and milk production, and supplementation with unprotected tallow also increased milk yield, but fat and protein concentrations in milk were decreased.

The Oxylog, a portable breath-by-breath gas analyser, was used on seven animals to determine standing metabolic rate, energy cost of walking on soils of different consistencies and efficiency of work ploughing and carting. The average standing metabolic rate of animals was 5·63 (s.e. 0·12) W/kg M00·75. The consistency of the soil on which animals worked had a marked effect on their energy cost of walking which was 1·59 (s.e. 0·069) on unploughed soil, 2·15 (s.e. 0·084) on ploughed soil and 1·0 (s.e. 0·10) J/m per kg live weight on laterite tracks. The efficiency of ploughing sandy soils (i.e. ratio of work done to energy used for work) was 0·32 and was not significantly different from the efficiency of carting with different loads. The efficiency of doing work was not influenced by the type of work performed, the draught force exerted or the walking speed.

A randomized block design experiment involving 64 lactating dairy cattle was carried out to evaluate a bacterial inoculant and two rates of formic acid as silage additives. Herbage from the primary growth of a predominantly perennial ryegrass sward was ensiled unwilted using two precision-chop harvesters. Alternate loads of herbage were either untreated (UT) or treated with formic acid applied at the rate of 2·7 l/t grass (LF) and 5·7 l/t grass (HF) or an inoculant enzyme preparation applied at the rate of 2·2 l/t grass (I). The mean dry matter (DM) and water-soluble carbohydrate (WSC) concentrations and buffering capacity of the UT herbage were 148 g/kg, 151 g/kg DM and 638 mEq/kg DM. Inoculant treatment had no effect on the rate of silage fermentation post ensiling relative to the UT silage whereas HF treatment produced a restricted fermented silage. For silages UT, LF, I and HF, pH values were 4·53, 3·89, 4·32 and 4·05 (s.e.d. = 0·061); ammonia nitrogen (N) concentrations were 179, 89, 150 and 73 g/kg total N (s.e.d. = 10·4); butyrate concentrations were 6·0,1·9, 5·1 and 2·0 g/kg DM (s.e.d. = 1·24); and WSC concentrations were 14·4, 35·2, 18·0 and 100·7 g/kg DM (s.e.d. = 1·24), respectively. The silages were offered ad libitum. The UT silage was supplemented with either 2 (UT2), 4 (UT4) or 6 (UT6) kg concentrates per head daily while the LF, I and HF silages were supplemented with 4 kg (LF4,14, HF4) of concentrates. For treatments UT4, LF4, 14 and HF4, silage DM intakes were 9·69, 10·89, 9·93 and 10·89 (average s.e.d. = 0·465) kg/day; fat plus protein yields 1·39,1·44,1·32 and 1·49 (average s.e.d. = 0·057) kg/day; protein concentrations 29·2, 31·1, 29·9 and 30·2 (average s.e.d. = 1·01) g/kg. Inoculant treatment increased N apparent digestibility (P < 0·05) of the total diets relative to UT. The apparent digestibilities of neutral-detergent fibre (P < 0·05) and hemicellulose (P < 0·01) were decreased due to HF treatment. For the production of a constant milk fat plus protein yield it was estimated that an extra 0·63 kg per head per day and 1·04 and 1·77 kg per head per day less concentrate would be required for the I, LF and HF treatments, respectively. It is concluded that relative to the UT treatment, I treatment had no beneficial effects on silage fermentation, total diet apparent digestibility (other than N apparent digestibility) or animal performance. The LF treatment improve lage fermentation and intake, and tended to increase the yield of fat plus protein (P > 0·05) whereas HF treatment restricted silage preservation and increased silage intake and the yields of protein and fat plus protein.

Two experiments were conducted to investigate the relationships between work and intake and digestion of food by draught oxen given millet stover. In the first experiment, intake of millet stover, water intake, live weight, plasma concentrations of triiodothyronine, thyroxine and urea-nitrogen were measured in 18 animals that worked 0, 2 or 4 h/day in sequence during three 3-week experimental periods. Digestibility and rate of passage of food residues through the digestive tract were measured in a second experiment on 12 animals working either 0, 2-5 or 5 h/day in sequence during three 2-week experimental periods. Feeding behaviour was monitored on six animals working either 0, 2-5 or 5 h/day. Work did not affect intake of millet stover, apparent digestibilities and the rate of passage of digesta through the gastro-intestinal tract. This suggests that the nutrient supply from intake of roughages by ivorking oxen is unlikely to be sufficient to compensate for the extra energy expended during work. Food intake was affected by the quality of the millet stover offered. The level of intake of millet stover ivas proportional to the amount of leaves in the stover. Food intake increased also as work progressed. However, animals mobilized their body reserves to perform work. Animals consumed more water on working days than on days they were at-rest in shade. The heat stress that working animals were subjected to did not appear to interfere with their digestive function.

Three hundred and eight cattle, comprising steers and heifers from continental and British crosses were finished on an 18-month beef production system at Warren Farm, Lambourn, Berkshire and slaughtered across a range of fatness levels. The eating quality of roasting joints (semimembranosus.) and sirloin steaks (longissimus thoracis et lumborumj was evaluated and the chemical composition of the lean tissue was taken on a subset of the samples. Results suggested that the greatest differences between the breeds was in the joints. There were significant (P < 0·01) differences in the lipid, moisture and collagen contents of the lean tissue of the joints from the different sire breeds. The Belgian Blue sire progeny had significantly lower lipid content than the Charolais or Aberdeen Angus crosses, and significantly lower collagen content than the Aberdeen Angus cross. In addition joints from Belgian Blue crosses were more tender than joints from other breed crosses. Although the lipid and moisture contents of the steaks from different sire crosses were significantly different there was no evidence of differences in eating quality. Perhaps surprisingly there were no significant relationships between the eating quality and chemical composition between or within breed. Irrespective of breed, carcass fatness influenced the juiciness of both the joints and the steaks although the response was different for continental crosses and British crosses and depended on carcass sex. Over and above this response, steer meat was generally more juicy than heifer meat.

The heart rate (fH) and the energy expenditure (EE) of seven Hintenvaelder (Bos taurus) draught oxen and three zebu (Bos indicusj oxen were measured, while the animals were standing, walking and pulling different loads. Linear regressions for all animals relating EE to fH were highly significant (P < 0·001). The standard errors of the estimate expressed as a percentage of the mean EE (PE) ranged from ±6·7% to ±10·5%. Two animals with PE ±13·7% and ±17·1% were beyond that range. One year later, fH and EE were measured on six of the original seven Hinterwaelder oxen while the animals were standing and walking on a treadmill, on the level and at gradients of 3%, 6% and 9%. In the two experiments mean slope and mean intercept of the regressions of EE on fH were not different (P > 0·05). Irrespective of the kind of work (draught work or lifting work),fH allows a reliable prediction to be made of the EE of working oxen.

The effect of active immunization against somatostatin and β-agonist administration alone and in combination on growth, carcass composition and endocrine responses was investigated in young steers given a pelleted diet of dried grass and barley (0·7: 0·3) ad libitum for 16 weeks. Immunization alone increased growth rate by proportionately 0·10 but had no effect on plasma growth hormone (GH) or insulin-like growth factor-1 (IGF-1) concentrations (P > 0·10). Carcass protein content was unchanged but fat content tended to be increased. This was possibly associated with increased (P < 0·10) plasma insulin concentrations observed in these animals. Cimaterol administration significantly increased growth rate (P < 0·05) and carcass weight (P < 0·01). Carcass protein content was significantly (P < 0·01) increased and carcass fat was significantly (P < 0·001) reduced. Administration of cimaterol to immunized animals resulted in an enhancement of the repartitioning effect of the pagonist although growth rates were intermediate between the separate treatments. The mechanism by which this was achieved is unclear. Plasma IGF-1 concentrations tended (P < 0·10) to be lower in these animals compared with controls. Plasma insulin concentrations were also reduced (P < 0·05) in these animals. Both immunized animals and those given cimaterol alone showed an increased GH response to a single intravenous injection of growth hormone releasing factor (GRF) (P < 0·05). Animals given the combined treatment however showed a reduced response suggesting that the effects were not mediated through direct changes in GH secretion. The improved lean:fat ratio in the carcass was observed to be mediated through an enhancement of the lipolytic response to the /J-agonist with only small effects on protein accretion. It is suggested that immunoneutralization of somatostatin may increase the sensitivity of adipose tissue to lipolytic stimuli. This could occur through changes in the secretion of gastrointestinal or pancreatic hormones as a result of neutralization of the inhibitory influences of somatostatin. Further work is required to clarify these effects.

Eighteen oxen were allotted to three treatment groups according to their body condition: poor, medium and good. Work output, speed, live weight and body condition were measured during 7 weeks when animals worked 4 days/ week, 4 h/day, pulling loads equivalent to 12-5 kgf/100 kg live weight. The animals were given millet stover ad libitum during hours they did not work plus 10 g/kg M of a concentrate mix. Work did not influence intake of millet stover. However, food intake improved as work progressed and animals in bad condition ate more millet stover than animals in good body condition. Work performance was affected by live weight but not body condition. Live-weight losses did not have a detrimental effect on work performance. Power output improved during the course of the experiment while animals were losing weight Animals in all treatment groups lost body weight during the 7 weeks of work but weight losses were more pronounced in oxen in good than in poor body condition. At the end of the working period, animals were put on natural pastures without supplementation. It took 4 weeks for animals in poor and medium body condition and 6 weeks for animals in good body condition to reach their pre-work live weight.

Heart rate, ventilation measurements and gas exchange were studied in seven Hinterwaelder (Bos taurus) (494 (s.e. 16) kg) and five zebu (Bos indicusj oxen (516 (s.e. 60) kg), while the animals were standing, walking and pulling different loads. During standing, the heart rate, respiration rate, ventilation volume per min, total carbon dioxide production, total oxygen consumption and oxygen consumption per heart beat were lower in the zebu group than in the Hinterwaelder group (P < 0·05). The higher values for the Hinterwaelder were probably due to their higher metabolic rate, because of their younger age, higher level of feeding and better quality diet. The adaptation of gas exchange to higher work loads was achieved mainly by higher ventilation volumes. The composition of the expired air changed minimally. At similar levels of draught power output, the total energy expenditure minus energy expenditure of walking of the zebu oxen was lower than that of the Hinterwaelder oxen (P < 0·02). On the other hand at similar levels of heat production, the heart rate and ventilation volume per min did not differ significantly between the two breeds (P > 0·05). In spite of the differences in environment, feeding level and draught efficiency, the physiological adaptations made by the two breeds in response to work were similar.

A model of a birthdate distribution for a herd of beef cows is constructed using the probability distributions of the variables that affect reproduction in the cow — anoestrous interval, oestrous cycle length, conception to each oestrus, gestation length, period of mating and the prior calving frequency distribution. The model is general and can be reparamaterized to deal with issues such as intervention to synchronize oestrous cycles among cows in the herd by changing the form of the relevant probability distributions.

The model is applied to the question of what time to begin mating in a herd of beef cows. The average calf live weight at day 200, herd conception rate and proportion of cows calving before the planned start of calving were calculated from the model output. The model parameters given by the anoestrous period, conception rate to each oestrus and the regression between prior calving date and anoestrous period, were varied in a factorial design to investigate a range of circumstances found on a farm. Prior calving distributions were generated by random sampling from eight actual calving frequency distributions.

Generally starling mating earlier produced an advantage in terms of extra calf live weight and herd conception rate. However, the proportion of the herd calving earlier than expected increased with early mating. Thus, the feasibility of early mating depends on the cost to the farmer of dealing with early calving cows as well as the advantage of heavier older calves.

Altering the fixed parameters in the model (variances and covariances, prior calving distributions, mating period) to accommodate the circumstances of herds run under different conditions may produce different results. Model structure allows easy alteration of these parameters and also the introduction of different probability distributions for some variables. This might be necessary to model oestrous synchronization and artificial insemination, issues not considered in this paper.

The objective was to determine the daily live-weight gain, behaviour, adrenal and immune responses of finishing beef heifers housed at two different space allowances. Heifers (no. = 32) with a mean live weight of466 (s.e. 3·6) kg were assigned to either 1·5 or 3·0 m2 average individual space allowance in four slatted-floor pens (two per treatment) for a period of 104 days. On days 5, 40, 68 and 96, heifers (no. = eight per treatment, four per pen) were challenged with 1·98 i.u. ACTH per kg M0·75, and serial blood samples were analysed for plasma cortisol concentrations. The other 16 heifers were immunized against keyhole limpet haemocyanin (KLH) on day 28, and blood samples collected on days 28, 42, 56, 70, 84 and 98 were analysed for anti-KLH immunoglobulin (Ig) concentrations. All heifers were blood sampled on days 0, 14, 56 and 98, and red and white blood cell numbers, packed cell volume (PCV) and plasma concentrations of creatine kinase (CK), non-esterified fatty acids (NEFA) and urea were determined. Behavioural observations were conducted on days 8, 43, 71 and 99 by scan sampling for 24 h (10-min intervals), and continuous 4-h observations were conducted on days 100 and 101.

Heifers at 1·5 m2 space allowance had a lower daily live-weight gain compared with those at 3·0 m2 (0·60 v. 0·87 (s.e. 0·04) kg; P < 0·001). Heifers at 1·5 m2 had lower pre-ACTH baseline cortisol concentrations (P < 0·05) and lower post-ACTH peak cortisol concentrations (P < 0·05). There were no effects of treatment on serum anti-KLH IgG1 or IgG2 responses (P > 0·05). Heifers at 1·5 m2 had lower plasma NEFA concentrations (P < 0·05). Red and white blood cell numbers, PCV, CK and urea were not affected by treatment (P > 0·05). The time spent lying down was lower for heifers at 1·5 m2 (10·0 v. 21·1 h/day; P < 0·05). Social interactions were fewer (P < 0·05), and incidence of head-resting behaviour was higher (P < 0·05) among heifers at 1·5 m2 compared with 3·0 m2 space allowance. In conclusion, the restricted space allowance resulted in a substantial decrease in daily live-weight gain, and changes in adrenal response and behaviour.

Intakes and feeding patterns were studied in two groups of 24 Scottish Blackface ewes, with initial mean body condition scores of 2·15 (thin) and 3·15 (fat). Three treatments, allowing access to a dried-grass pellet diet ad libitum for 6, 12 or 24 h/day, were applied in a Latin-square design, with each sheep receiving each treatment for one 12-day period. Food intakes were measured daily and feeding activity was recorded automatically every minute for one 24-h period during the last 5 days of each 12-day treatment period.

Mean intakes were higher for thin than for fat ewes (1720 v. 1467 g dry matter (DM) per day; P < 0·001). There were no interactions between the effects of body condition and food access time and mean intakes over the last 7 days for the 6-, 12- and 24-h food access treatments were 1429, 1686 and 1805 g DM per day respectively (T < 0·001). Time spent feeding was higher for thin than for fat ewes, over the whole day (231 v. 197 mini day; P < 0·05) and in the first 6 h after the introduction of fresh food (140 v. 120 min; P < 0·05), but there were no differences between thin and fat ewes in the frequency of meals or in the rate of intake during meals. Intakes for the first 6 h were higher with restricted food access (1402, 1109 and 819 g DM per day for 6-, 12- and 24-h access; P < 0·001) but there were no differences in time spent feeding. The number of meals during the first 6 h was higher (10·4 v. 8·3; P < 0·05) and the rate of intake was higher (11·4 v. 7·8 g/min; P < 0·05) for 6-h compared with 24-h food access.

It was concluded that long-term differences in intake due to body condition and short-term changes due to restricting food access time, involve different behavioural responses and this may reflect differences in the mechanisms involved in the regulation of voluntary intake. Keywords: body condition, feeding behaviour, sheep.

Five mathematical models were compared to select the most satisfactory model to describe digesta kinetics of solids and fluids in the gastrointestinal tract of buffaloes (Mediterranean bulls), cattle (Friesian bulls) and sheep (Delle Langhe rams) given food at maintenance level, according to a Latin-square arrangement for four consecutive periods of 21 days. Chromium mordanted alfalfa hay and cobalt-ethylenediamine tetraacetic acid were used as nonabsorbable markers and were administered through the rumen cannula in a single dose. Four different isonitrogenous diets (N × 6·25 = 140 g/kg dry matter) with different concentrate:forage ratios (12·5:87·5, 25:75, 37·5:62·5, 50:50) were used.

Faecal chromium and cobalt concentration curves were fitted with five non-linear models: three gamma (G2, G3, G4) age-dependent one-compartment, one gamma age-dependent/age-independent two-compartment (G2G1) and one multicompartment (MC).

Wilcoxon tests on residual sums of squares of the different models for solids showed that MC and G4 gave a better fit than G2G1, G2, G3 for all the data and within the species. The comparison of MC v. G4 did not show any significant difference (P > 0·05) for all the data computed together or within each species. Nevertheless, MC had a higher number of curves with lower residual sums of squares in comparison with G4 and was also able to produce estimates of digesta kinetics in the second compartment.

The cobalt excretion curves for fluids, considering all the data, and only within sheep, showed G4 as the best fitting model. When G4 was compared with other models no significant differences were recorded either for cattle: G4 v. G2 (F = 0·6645), G4 v. G2G1 (P = 0·0620) and for buffalo: G4 v. G2 (P = 0·1575), G4 v.G3(P = 0·0796) and G4 v. G2G1 (P = 0·1641).

It is concluded that the multicompartment model (MC) and G4 model were the best fits for solids and for fluids respectively.

The in situ dry matter (DM) and neutral-detergent fibre (NDF) degradability kinetics of eight forages (four grass hays and four legume hays, harvested at two different dates) were compared to assess the fitting ability of a first-order and a Gompertz model.

The Gompertz model fitted DM degradability data as well as the first-order model and differences between fitted and observed data for the two models were very small but the Gompertz model proved to be statistically superior for the NDF degradability data, especially for the early hours of incubation.

A numerical but not significant difference was observed in the estimated rapidly available fraction for DM and NDF, which zvas respectively lower (mean values 24·4 v. 27·8%) and higher (mean values 5·8 v. 1·8%) with the first-order model. More pronounced differences were observed for the estimates of total potential degradability of NDF, which were often significantly lower with the Gompertz model (average values for the eight forages 75·1 v. 72·3%;.

The sigmoidal shape of the Gompertz model was more biologically appropriate to describe the initial phases of NDF degradation and was thus applied to the cellulose and hemicellulose degradability data.

As the harvesting date progressed through the season, a decrease of the immediately available fraction of DM and nitrogen was generally observed but the effect of harvesting date was not so evident for fibre fractions; the differences within forages were very low. Correlation coefficients between lignin content and total potential degradability of fibre were always high (for NDF, r = −0·96; for hemicellulose r = −0·95; for cellulose r = −0·79; P < 0·001), while the acid-detergent fibre content influenced DM and nitrogen total potential degradability (r = −0·91 and −0·82, respectively).

The effect of previous level of body condition on appetite was studied in 47 housed Scottish Blackface ewes, which had been either thin (L: mean condition score 2·15, s.e. 0·030; no. = 24) or fat (H: mean condition score 3·15, s.e. 0·056; no. = 23) 8 weeks before the start of the experiment. The mean daily voluntary food intake (VFI) of a dried grass pellet diet was higher for the L than for the H ewes (2176 v. 1727 g dry matter per day; P < 0·001) during the first 6 weeks of the experiment (period 1). Over this time, live weights increased from 60·5 or 69·9 (s.e.d. 1·68) to 68·4 or 75·6 (s.e.d. 1·94) and condition scores increased from 2·84 or 3·16 (s.e.d. 0·057) to 3·13 or 3·38 (s.e.d. 0·071) for the L and H ewes respectively.

At the end of the 6-week period, plasma insulin concentrations were measured in 10 ewes from each treatment (mean condition scores 3·15 (L) and 3·27 (H) (s.e.d. 0·091)) when fed both ad libitum and at a fixed level of 1200 g/day for consecutive 11-day periods (period 2). Mean VFI was higher for the L than for the H ewes (2191 v. 1661 g dry matter per day; P < 0·05) over the period of ad libitum feeding. There was no effect of feeding level (ad libitum v. 1200 g/day) on mean plasma insulin concentrations, but the mean basal plasma insulin concentration was higher in the H than in the L ewes (43·0 v. 29·0 mil per 1; P < 0·05). Fifteen minutes after the ingestion of a single 400 g meal, the plasma insulin concentration in the H ewes was higher than the mean prefeeding value (63·3 v. 41·7 mil per I; P<0·05) but there was no corresponding increase in the L ewes. The plasma insulin concentration 15 min after the intravenous administration of a single dose of 0·25 U per kg live weight of insulin ivas higher in the H than in the L ewes (1723 v. 1031 mil per 1; P < 0·01) but there were no differences between treatments in plasma glucose concentrations following insulin administration.

It was concluded that previous body condition can affect contemporary VFI and this effect may be mediated by plasma insulin concentrations providing a long-term feedback signal to the brain. Keywords: body condition, food intake, insulin, sheep.

The need to complement in vitro gas production measurements with residue determination is demonstrated by the recalculation and reassessment of published data on in vitro gas production, in sacco degradabilities and voluntary dry matter intake (DMI). The in sacco degradability — gas volume ratio was determined at 24 and 48 h of incubation, termed partitioning factor (PF) and combined with rate and extent parameters of in sacco degradability and in vitro gas production to predict DMI. In vitro gas production and in sacco degradability characteristics (a + b) and c as described by the equation y = a + b(1−ect) explained 0·373 and 0·668 respectively of the variation in DMI of 19 legume and grass hays. The complementation of gas production parameters by the PF24 increased the R2 value to 0·744 with PF24 accounting for 0·407 of the variation in DMI, the rate of gas production (c) for 0·218 and the extent of gas production (a + b) for 0·119 of the variation in DMI. As a single parameter, PF48 showed the highest correlation (R2 = 0·597) with DMI but the combination of PF4S with rate and extent of in sacco or in vitro gas production measurements did not improve the correlation further, probably due to an intercorrelation between rates of fermentation and PF4S. Hays which were degraded at faster rates had higher PF values indicating proportionally higher microbial yield and lower short-chain fatty acid production per unit substrate degraded. Generally, hays with high in sacco degradabilities but proportionally low gas production i.e. hays with high PF values showed higher DMI.