Live-weight gain responses were investigated using 36 individually penned lambs (mean live weight 35·2 kg) given three sodium hydroxide treated straw-based diets: low-protein, low-rapeseed meal (control) diet; high protein, high-rapeseed meal (HR) diet; or high-protein, fish meal (FM) diet. The diets were formulated to provide 3 or 9 g undegradable nitrogen per kg dry matter (DM) respectively for the diets without or with fish meal. Diets were offered once a day in a 50: 50 forage-to-concentrate ratio in amounts calculated to support maintenance plus 150 g gain and were adjusted weekly according to live weight. Live-weight gain, measured for 7 weeks, was improved by the FM diet only (P < 0·05).

The three diets were given also to rumen-fistulated sheep. The FM diet maintained higher rumen ammonia concentrations during most of the day. The FM and HR diets reduced rumen solid particle outflow rate (P < 0·05) and increased the effective degradability of DM and acid-detergent fibre.

Correlated genetic changes in the level and pattern of average daily food intake (ADFI) were evaluated n i a population of pigs under index selection over an 11-year period. Performance testing was carried out in single sex groups of two or three full-sibs over the live-weight range 27 to 87 kg on an ad libitum feeding regime. The selection index incorporated live-weight gain, ultrasonic backfat thickness and a group food conversion ratio. Samples of boars from a contemporary control line were used to measure genetic change over time. Cumulated correlated responses in ADFI for boars and gilts showed considerable variation between years but the values were always negative and tended to increase up to year 7 but increased no further from then on. Thus, in year 11 the cumulated responses for ADFI in boars and gilts were -0·25 (s.e. 0·06) kg (P < 0·001) and -0·19 (s.e. 0·05) kg (P < 0001) respectively, the corresponding regressions of cumulated response on year number being — 0012 and — 0·017 kg. The relationship between food intake and live weight was compared in samples of boars and gilts from the selection line (S) and boars from the control line (C) during the final year of the study. The regression of ADFI on live weight for the two boar lines differed in intercept but not in slope with S line boars consuming, on average, 0·23 kg/day less meal than the C line boars over the test period. The regression equations for S line boars and gilts differed in slope and elevation with gilts consuming relatively more food daily up to around 60 kg live weight and less subsequently.

The effect on productivity of mixing finishing pigs from different litters was studied. Two hundred and ten Yorkshire × Landrace pigs of about 76 kg were assigned in groups of six to each of four treatments. In treatment 1, pigs were retained as unmixed littermates while in treatments 2 and 3, three pigs from one litter were mixed with three pigs from another litter. Additionally pigs in treatment 3 were injected with a tranquilizer prior to mixing. In treatment 4, groups of five littermates were introduced into the pen of either a lighter weight or heavier weight pig. All groups were housed in 6·65 m2 partially slatted pens and fed from a communal food trough.

Besides promoting aggression and fighting, mixing significantly depressed productivity, and both short-and long-term economic returns. Over the 3-week experimental period the proportional live-weight gains observed in the unmixed pigs over those of the mixed groups, were substantial: 0·099 over the 3: 3 mixed groups, 0·141 over the tranquilizer-treated groups, and 0·127 over the 5: 1 mixed groups. Consequently, mixing would necessitate additional inputs of food, housing, and labour because of the increased days to market.

The tranquilizer not only did not eliminate fighting but had a long-term negative effect on production and was thus a contra-indicated expense. Introducing a single pig into a group in an occupied pen also lowered production, as did moving without mixing. However, moving effects were short lived and had minimal negative influences on overall productivity.

The response of 376 weaned bull calves to two different housing types was studied in a 2-year feedlot trial. Overall, animals with shelter had a higher rate of gain than animals with no shelter. The difference in the rate of gain between the housing types was, however, restricted to the coldest periods. No significant interaction between housing type and age of calf was observed. Regression analyses showed that whilst average daily temperature appeared to have a negligible effect on growth, temperature fluctuations between weighing days appeared to affect growth of calves in both housing types. Overall, climatic variables contributed more to the variance in gain of calves with shelter than of calves with no shelter.

A comparison was made between the Heal digestibility of the amino acids in pigs obtained by the use of a basal diet, the apparent Heal digestibility obtained with a semi-synthetic diet where peas were the sole protein source and the true Heal digestibility obtained with synthetic and nitrogen-free diets.

Responses of gross energy intake and live weight of mice from weaning to maturity to dietary fat level were studied. Six groups of ddY male mice were given purified diets covering the range (0 to 70%) of fat concentration on a gross energy basis for 72 days. The food intake and live weight data in each group were analysed by non-linear regression to obtain values of the six parameters in Parks feeding and growth equations. These parameters, found as a function of the fat content of diet, were then used to construct the response surfaces of food intake and live weight over the dietary fat v. age space. The daily energy intake rose rapidly with age to a plateau at about 7 to 14 days after weaning and was maintained throughout the experiment, independent of the dietary fat content. Live weight as a function of time after weaning increased to a plateau at every dietary fat level, but the details of the pattern of growth were affected by the dietary fat level. After about 30 days of feeding, the higher the fat content of the diet, the greater the gain in live weight. Apparent digestibility of dietary energy decreased with an increase in fat content, especially in the early period.

One hundred and eight New Zealand × Californian growing rabbits (nine per diet) were used to determine the nutritive value (digestible energy (DE), digestible protein (DCP) and digestible acid-detergent fibre (DADF)) of five protein concentrates. In assay 1, the effect of the type of basal diet (BD) (7·6 or 10·0 MJ DE per kg dry matter (DM) for BD1 and BD2 respectively) and the substitution level (150, 300 and 450 g/kg) on nutritive value of soya-bean meal was studied. According to the results of assay 1, one basal diet (BD2) and one substitution level (300 g/kg for sunflower 380, gluten meal and extruded soya-bean meal or 500 g/kg for sunflower 320) were selected in assay 2 to determine their nutritive value.

The effect of the basal diet and the substitution level on the nutritive value of soya-bean meal was evident only for the values calculated from BD1 and the lowest level of inclusion. The data obtained by difference at the highest level of inclusion and by extrapolating the linear equations were very similar (16·32 v. 16·35 MJ DE and 387·62 v. 388.58 g DCP per kg DM for BD2), but the standard errors were lower (0·52 v. 0·72 for DE and 6.76 v. 8.95 for DCP) in the former. The DE values obtained for sunflower meal 320 and 380, extruded soya-bean and gluten meal were 10·29, 14·37, 18·58 and 20·57 MJ/kg DM respectively; protein digestibilities were high (with coefficients from 0·80 to 0·90) except in the case of sunflower-320 (0·73). A stepwise regression analysis was made to predict the nutritive value from chemical composition including values from literature. For prediction of DE, the variables selected were: crude fibre, ether extract and ash, obtaining a determination coefficient of 0·935. The protein digestibility was independent of variables employed.

Growth rate, total body water volume (TBW), dry-matter intake (DMI) and water consumption were determined in ostriches from hatching to 350 days at which time they weighed approximately 100 kg. A Gompertz equation was used to describe the sigmoidal growth curve; mature body mass (Mmb) wascalculated as 104·1 kg from this equation. Highest average daily gain (ADG) was 455 g/day which occurred between 70 days and 98 days. Time to reach 0·5 Mmb and to grow from 0·25 to 0·75 Mmb per Mmb025 were 46·8 days and 39·7 days, respectively. Maintenance energy requirements were 1·07 MJ/kg063per day and energy requirements for kg mb increase were 0·260 MJ/kg109: thes e values were derived from a non-linear regression model. TBW as a fraction of mb declined from 0·84 in 35-day-old chicks to 0·57 in 322-day-old birds, indicating a concomitant increase in the fraction of body lipid content. Mass specific DMI decreased from 0·061 g/g mb in chicks to 0·020 g/g mb in 322 to 350 day old birds, while mass specific water influx decreased from 0·21 ml/g mb to 0·046 ml/g mb during this time. The ratio of DMI to ADG increased steadily from 1·07 to 17·1; the ratio of water consumption to DMI remained relatively constant at approximately 2·3.

Hunger in pregnant sows maintained on commercial restricted rations was measured using an operant conditioning technique. Six sows were trained to lift a lever for a 2·7 g pellet reinforcement on a ratio of 10 lifts per reinforcement. After 1 h of stable responding (no pause greater than 5 min) the ratio was increased to 20 lifts. The point at which a sow stopped responding to this increasing ratio was used as a measure of strength of feeding motivation. Extinction was defined as occurring if the sow did not respond for a 2-h period. The six sows reached extinction at ratios of 70, 130, 210, 210, 230, and 430, and had stable intakes prior to extinction of 15, 22, 17, 10, 11, and 3 reinforcements per hour. Estimates of net energy deficits during responding prior to extinction were 271, 45, 271, 75, 242, and 441 kJlh. These results indicate that sows on restricted rations are still extremely hungry, to the extent that they are prepared to sustain an energy deficit to gain additional food.