Responses to metabolic challenges were measured in 8-month-old Friesian bull calves with a view to identifying possible predictors of genetic merit for milk fat production. Seven ‘high’ breeding index bulls (mean breeding index for milk fat = 128·9 (s.d. 4·8) percentage units) were compared with six ‘low’ breeding index bulls (mean 107·3 (s.d. 2·4) percentage units). Bulls were from two selection lines and breeding indices calculated as the average of parental breeding index values.

Challenges involved intravenous injection of the following (dose rates per kg body weight): adrenalin (1 μg); glucose (0·17 g); glucagon (0·175 μg); insulin (0·01 mg); and arginine (40 mg). Blood samples were withdrawn prior to and after each challenge (two challenges daily). Bulls were then fasted for 3 days before being refed.

Relative to the low breeding index bulls, those in the high breeding index group exhibited: (a) greater pancreatic sensitivity to circulating glucose as indicated by increased insulin concentrations following the glucose challenge; (b) more rapid clearance of glucose from plasma following the insulin challenge; (c) reduced sensitivity to the glycogenolytic/gluconeogenic effects of glucagon as indicated by lower blood glucose concentrations following intravenous injection of this hormone; (d) elevated plasma insulin and growth hormone concentrations during the fasting period; (e) elevated plasma concentrations of insulin, glucose and urea during refeeding; (f) no difference in responses to intravenous arginine or adrenalin, or in circulating concentrations of Insulin-like Growth Factor-1 or alkaline phosphatase. Results are consistent with previous observations that metabolic differences between cattle in the Massey University high and low breeding index lines are most evident in the metabolism of glucose and insulin. Metabolic challenges offer a potentially useful means of predicting genetic merit for milk fat production but the conditions under which repeatable differences between the lines can best be demonstrated are yet to be determined.

Records of beef cows on a ranch in south-east Mexico gave 1377 ages at first calving (AFC) and 3932 calving intervals (CI) for the comparison by least-squares analysis of the genetic groups: commercial zebu (CZ), Brahman, other zebu breeds and their zebu crosses (zebu), F, crosses born to zebu dams by Bos taunts or Santa Gertrudis sires, and 3/4 bred zebu and 3/4 Bos taurus. Subsamples of 1090 ages at first calving and 3154 intervals were analysed considering the breed groups: CZ, Brahman, Guzerat, Gyr and Indo-brazil, and the F1 crosses resulting from matings between these zebu breeds, Santa Gertrudis and Charolais as sire breeds and the CZ as the dam breed. Three populations were analysed for each model, the original ranch population and two populations reduced by retrospective culling. The original population had a mean AFC and CI of 1226 and 489 days respectively reduced by the first and second culling by 24 and 37 days and by 62 and 83 days respectively. Repeatability of CI increased from 0·06 to 0·11 and 0·14 respectively.

Genetic group significantly influenced AFC. In the original population F1 heifers had a significantly younger AFC than Brahman and zebu heifers but not significantly younger than the other genetic groups. Heifers with 0·25, 0·75 and 1·00 zebu genes did not have significantly different AFCs. After the retrospective culling only the 3/4 bred zebus were significantly superior to the worst group, the zebus. The effect of breed group was only significant in the original population but generally the same rank order was maintained after the retrospective culling. F, Charolais × CZ heifers had the youngest AFC, a superiority of 67 days over CZ and 92 days over Brahman. Purebred zebus and their F, crosses with CZ did not calve earlier than CZ dams. Genetic group had a highly significant effect on CI. Females with 0·50 and 0·75 Bos taurus genes had shorter CIs than females with 0·75 and 1·00 zebu genes. The superiority was maintained after culling. Breed group had a significant effect in each population. F1 Charolais × CZ dams had the shortest CI. CZ had equivalent or shorter CI than all zebu breeds and their F1 crosses with CZ. Heterosis effects for AFC and CI in the zebu crosses were generally advantageous but small, while the heritabilities for the zebu population were negative for AFC and 0·05, 0·22 and 0·06 for CI in the original and two culled populations respectively.

An experiment has been carried out to examine the effects of implantation with hormonal growth promoters on the response in the performance of castrated male cattle (steers) to protein supplementation of a silage-based diet. The treatments consisted of grass silage offered ad libitum and supplemented with 2·7 kg per head daily of either a low protein (LP, 114 g crude protein per kg dry matter (DM)) or a high protein (HP, 206 g crude protein per kg DM) concentrate. Half of the animals, given each of the two concentrates were implanted with 20 mg oestradiol plus 200 mg progesterone and 300 mg trenbolone acetate at the beginning of the experiment and after 77 days, while the remainder of the animals received no implant, giving four treatments in a 2 × 2 factorial design. Sixty-four British Friesian and Simmental cross steers which were initially 426 (s.e. 3·5) kg live weight were used. The treatments were imposed for 157 days. The silage used was well preserved and of high digestibility. For LP and HP concentrates given to non-implanted animals and LP and HP given to implanted animals respectively silage DM intakes were 5·7, 5·8, 6·3 and 6·6 (s.e. 0·18) kg/day; live-weight gains 0·96, 0·92, 1·22 and 1·33 (s.e. 0·045) kg/day; carcass gains 0·58, 0·53, 0·78 and 0·81 (s.e. 0·024) kg/day; carcass subcutaneous fat depth 6·0, 6·5, 5·8 and 5·5 (s.e. 0·35) mm; areas of m. longissimus dorsi 69·1, 58·5, 69·6 and 74·7 (s.e. 1·91) cm2 and marbling scores 3·0, 3·6, 3·3 and 3·1 (s.e. 0·25). It is concluded that protein supplementation of well preserved grass silage produced a marginal increase in the performance of implanted finishing steers but did not affect carcass fatness. With non-implanted steers protein supplementation produced a marginal depression in performance and increased carcass fatness.

Two experiments have been carried out to compare silage-based and dried forage-based diets for finishing beef cattle, and to examine the effect of supplementing the silage-based diet with additional protein. The three diets used in experiment 1 consisted of (1) grass silage supplemented with a low-protein, cereal-based concentrate (98 g crude protein (CP) per kg dry matter (DM)) (2) grass silage supplemented with a high-protein, cereal/soya-bean meal concentrate (208 g CP per kg DM) and (3) grass hay supplemented with a cereal-based concentrate (130 g CP per kg DM). The two diets used in experiment 2 consisted of (1) grass silage supplemented with barley and (2) a mixture of grass hay and artificially dried grass supplemented with barley. All the diets contained approximately 700 g forage and 300 g concentrates per kg DM except diet 3 in experiment 1 which contained 240 g hay and 760 g concentrates per kg. The silages were of high digestibility (digestible organic matter in dry matter 0·72) and were well preserved (ammonia N 36 g/kg total N). The diets were offered to castrated male cattle which were initially 384 kg in experiment 1 and 515 kg in experiment 2. For diets 1 to 3 in experiment 1 and diets 1 and 2 in experiment 2 respectively metabolizable energy intakes were, 92, 94, 94, 124 and 120 MJ/day; live-weight gains were 1·21, 1·16 and 1·21 (s.e. 0·044) and 1·25 and 1·22 (s.e. 0·060) kg/day; carcass gains were 0·76, 0·76 and 0·75 (s.e. 0·034) and 0·80 and 0·74 (s.e. 0·036) kg/day; carcass fat classifications (five-point scale; 1 = leanest, 5 = fattest) were 2·4, 2·9 and 2·2 (s.e. 0·09) and 3·6 and 3·6 (s.e. 0·18); mean subcutaneous fat depths were 6·8, 8·1 and 6·6 (s.e. 0·74) and 7·8 and 7·4 (s.e. 0·48) mm; areas of m. longissimus dorsi at the 10th rib were 66·4, 69·4 and 71·3 (s.e. 3·16) and 77·6 and 72·3 (s.e. 1·52) cm2 and marbling scores (eight-point scale; 1 = leanest, 8 = fattest) for m. longissimus were 1·7, 2·5 and 2·2 (s.e. 0·24) and 3·2 and 2·8 (s.e. 0·16). It is concluded that performance, efficiency of energy utilization and carcass fatness were similar for silage-based and dried forage-based diets, and that protein supplementation of a silage-based diet did not affect performance but tended to increase carcass fatness.

The response of Hereford × Friesian heifers to large intakes of two types of high glucosinolate rapeseed meal were studied during two 5-month periods in consecutive years. In year 1, six heifers were given a compound concentrate food containing 250 g/kg extracted rapeseed meal and six control animals were given concentrate containing 210 g/kg soya-bean meal. In year 2, a further six heifers were given concentrate containing 320 g/kg expeller rapeseed meal and six control animals were given the same soya-bean meal compound concentrate. The crude protein (CP): metabolizable energy (ME) ratio of all diets was 14·3 g CP per MJ ME. Barley straw was the only roughage offered.

There were no differences between groups in ovarian activity assessed from plasma progesterone concentrations, nor in behavioural activity around oestrus. The heifers were slaughtered 6 weeks after artificial insemination. Pregnancy rate was proportionally 0·58 (7/12) in the rape-fed and 0·67 (8/12) in the control heifers (P > 0·05). Foetuses from heifers given rapeseed meal were slightly smaller than those from control heifers; the difference was significant in year 2 (P < 0·05).

Thyroid glands of heifers given rapeseed meal showed histological evidence of goitrogenicity but weights of the glands did not reflect this. Plasma thyroxine values were depressed in heifers given rapeseed meal (year 1, P < 0·001; year 2, P < 0·05). Plasma thiocyanate was elevated in rapeseed meal heifers in both years (P < 0·001) compared with values for control animals.

In 22 cows given complete diets of 500 g straw and 500 g concentrates per kg fresh weight the outflow rate of small fibrous particles was determined on two occasions to investigate the consistency of this measurement and its association with apparent digestibility. The correlation between the outflow rates on the two occasions were r = +0·90 and the correlation with apparent digestibility was r = −0·80.

In a second experiment, the outflow rates of long and small particles were determined together with rumen retention time. There was no difference between outflow rate of long and small particles but rumen retention times were greater with the long particles. The correlation between the two estimates of outflow rate was r = +0·84. The outflow rate of fish meal was found to be 0·070 while that of short fibrous particles was 0·031 per h. The average liquid outflow rate was 0·146 per h.

The three cows with the highest outflow rate and the three with the lowest outflow rate from experiment 2 were selected for experiment 3. While voluntary food intakes of the two groups were similar, the differences in outflow rates between the cows persisted both with ad libitum and restricted intakes of both a high and a low roughage diet. The differences were reflected in significant differences between the two groups in apparent digestibility of the diets. The practical implications for breeding and selection are discussed.

An experiment was conducted using medium-sized crossbred beef heifers to study how manipulation of weight gain in late gestation affected production. Forty heifers were fed individually to gain according to one of three regimens for an approximate 90 day period prior to parturition: (1) 1·2 kg gain per head per day for 45 days followed by no gains for 45 days; (2) 0·6 kg gain per head per day for the entire period; (3) no gain for the first 45 days followed by 1·2 kg gain per head per day for the last 45 days. Milk production was measured by weighing of calves before and after suckling at 30, 60, and 150 days post partum. Heifers were weighed, measured for heart girth and hip weight, and visually scored for condition at the start, middle and end of the feeding period to quantify growth and condition changes. Heifers that had a high rate of gain for a short time produced more milk in early lactation than heifers that gained at a slower rate for a longer time pre-partum (P < 0·05). Calf weaning weights and dam reproductive performance were unaffected (P < 0·05) by pre-partum weight gain. It is concluded from these results, that as long as the recommended weight gain is achieved during late gestation, the timing of the weight gain is not critical to sustain productivity.

Forty crossbred heifers, mated to one sire, that calved in a 20-day period were used to study the effect of varying time and level of post-partum nutrition on productivity. Heifers were individually fed for 90 days post partum beginning at parturition: (1) proportionately 1·3 National Research Council (NRC) 1984 recommendations for 45 days followed by 0·7 NRC for 45 days (130·70); (2) 1·0 NRC for 90 days (100·100); and (3) 0·7 NRC for 45 days followed by 1·3 NRC for 45 days (70·130). Milk production, growth and body condition were estimated periodically during the lactation. The 130·70 heifers maintained their weight during the first 45 days of lactation, while the 100·100 and the 70·130 heifers lost weight (−0·33 and 0·60 kg/day, respectively). During the second 45-day period, the 100·100 and 70·130 heifers gained weight (0·24 and 0·72 kg/day, respectively) while the 130·70 heifers lost weight (−0·39 kg/day). Visual condition scores paralleled weight changes during both phases of the feeding period. Milk production varied according to nutrient intake and treatment differences were greatest at 45 days post partum (8·1, 7·3 and 6·1 kg/day for 130·70, 100·100 and 70·130, respectively). Calf weight gains were unaffected by dam nutrition. Days to first oestrus, days to conception or services per conception were not significantly different (P > 0·05) among treatment groups. Based on this experiment, neither of the alternate feeding systems resulted in decreased performance when compared with feeding at a constant level. Therefore, it appears that latitude exists in the way heifers can be fed early in their first lactation, without adversely affecting production.

Thirty-two Border Leicester ♂ × Scottish Blackface ♀ wether lambs, aged about 5 months, were divided into two groups on the basis of live weight, such that group G1 contained the 16 lightest lambs and group G2 the 16 heaviest. Lambs in group G1 were subdivided equally at random either to be sham-implanted controls (Group C1) or to be implanted with 35 mg trenbolone acetate (TBA) + 5 mg oestradiol-17β (OE) (group T1) at 24 kg initial live weight. The lambs in group G2 were also subdivided into two groups (groups C2 and T2), and similarly treated approximately 1 month later at 37 kg initial live weight. The lambs were offered ad libitum a diet containing an estimated 12·5 MJ metabolizable energy (ME) per kg dry matter (DM) and 140 g/kg DM crude protein. Comparisons were made for the main effects of hormonal treatment and initial live weight. Both hormonal treatment and initial live weight gave increases for DM intake, gut fill, empty body weight, carcass weight and, in the half carcass side weight, weights of dissected lean tissue, bone and intermuscular fat and chemically determined DM, crude protein and lipid. Weights of mm. semitendinosus, longissimus dorsi, supraspinatus and gastrocnemius were also increased due to hormonal treatment and in group G2 lambs compared with those in group G1. When expressed as a proportion of carcass side weight, hormonal treatment effects were not significant for individual muscles and dissected carcass lean, bone and fat and chemically determined lipid and ash. Variable effects on other body components were recorded for both treatments in the absence of any significant interactions. The responses to hormonal treatment were essentially similar in groups G1 and G2. The question is raised as to the contribution of the greater food intake in implanted lambs to the maintenance of fatness in these animals.

Thirty-two Border Leicester ♂ × Scottish Blackface ♀ wether lambs aged about 5 months were divided into two groups on the basis of live weight such that group Gl contained the 16 lightest lambs and group G2 the 16 heaviest. Lambs in group Gl were subdivided equally at random either to be sham-implanted controls (group C1) or to be implanted with 35 mg trenbolone acetate (TBA) + 5 mg oestradiol-17β (group T1) at 24 kg initial live weight. The lambs in group G2 were also subdivided into two groups (groups C2 and T2) and similarly treated approximately 1 month later at 37 kg initial live weight. The lambs were offered ad libitum a good-quality diet. They were slaughtered 60 days after implantation. Comparisons were made for the main effects of hormonal treatment and initial live weight.

Concentrations in blood of 17-β-hydroxy-trenbolone (TBOH) and oestradiol-17β (OE) measured by radioimmunoassay peaked within 1 to 3 weeks after implantation and declined thereafter. Maximum concentrations and concentrations at slaughter respectively were 1·46 and 0·32 μg/l (group T1) and 0·78 and 0·28 μg/l (T2) for TBOH and 85 and 33 μg/1 (T1) and 59 and 37 ng/l (T2) for OE. Values up to week 7 were consistently greater in implanted animals in group T1 than in group T2. Hormonal implantation decreased the concentrations of total plasma triiodothyronine and thyroxine and urea and increased values for glucose up to week 5 or 6 after implantation. The animals in group G1 compared with G2 had, on average, variably lower concentrations in plasma of triiodothyronine, thyroxine, glucose and urea.

The highest concentrations of solvent-extractable residues were obtained in samples of kidney and liver (up to about 500 ng/kg for TBOH and 180 ng/kg for OE) with intermediate levels for fat and lowest levels for muscle. Conjugated trenbolone ranging from 45 to 186 ng/kg was present in samples of kidney, liver and perinephric fat. Trenbolone acetate was detected only in samples of fat. Variable effects of live weight at implantation on residue levels were recorded.

Thirty-two Border Leicester ♂ × Scottish Blackface ♀ wether lambs aged about 5 months, were divided on the basis of live weight such that group G1 contained the 16 lightest lambs and group G2 the 16 heaviest lambs. Lambs in group G1 were subdivided equally at random to be either sham-implanted controls (group C1) or to be implanted with 35 mg trenbolone acetate (TBA) + 5 mg oestradiol-17β (OE) (group T1) at 24 kg initial live weight. Lambs in group G2 were also subdivided into two groups (C2 and T2) and similarly treated approximately 1 month later at 37 kg initial live weight. Animals were offered ad libitum, a diet containing an estimated 12·5 MJ metabolizable energy and 140 g crude protein per kg dry matter. The experimental treatments lasted for 60 days.

Samples of pre-heparin plasma were analysed for free fatty acid (FFA) and triglycerides (TG). Post-heparin plasma was analysed for lipoprotein lipase (LPL) activity. Samples of subcutaneous (SCAT), perinephric (PNAT), mesenteric (MAT) and intermuscular (IMAT) adipose tissue, liver and muscle, taken immediately post mortem, were analysed for total lipid concentration and fatty acid composition. Comparisons were made for the main effects of hormonal treatment and live weight.

Plasma FFA concentrations in heavier lambs (group G2) were significantly higher than in group G1 from week 1 pre-implantation to week 3 post implantation. Compared with group G1, animals in group G2 had significantly higher plasma TG concentrations at weeks 1, 2, 5 and 8 when data was analysed using pre-implantation values as covariates. The lipid concentration was lower in group G1 than in group G2. In group G1 compared with group G2 there were greater proportions of C12:0 and C18:2 in SCAT and C16:1 in PNAT and lesser proportions of C18:0 in SCAT and PNAT.

Significant effects due to hormonal treatment were recorded for plasma TG at weeks 1, 5, 6, 7 and 8 mainly due to increases in group T1 compared with group C1. Hormonal treatment increased the proportions of C12:0, C15:0, C16:1 and C18:1 in SCAT and C16:1 and C18:1 in IMAT; reduced the proportions of C16:0 and C18:0 in SCAT and C18:0 in MAT and IMAT and reduced the ratio of saturated to unsaturated fatty acids in SCAT and IMAT and to a lesser extent in MAT.

Wool samples were collected from two groups of Merino sheep, both of which contained animals that were either heterozygous (Ww) or homozygous (WW) for white fleece. Group 1 were sampled in summer and group 2 in winter. These samples were scoured and measured for electron spin resonance initially (ESR1), following irradiation by ultraviolet light (ESR2) and then after wetting and drying the sample (ESR3).

There was no significant difference between WW and Ww sheep in each group for any of the ESR measurements (P > 0·05). However, for ESR1 there was a difference between management groups (group 1> group 2; P < 0·05). The ESR3 on ESR1 values were plotted separately for WW and Ww genotypes. The plotted ESR3 on ESR1 values in both groups showed no differentation into distinct genotype clusters. Nevertheless, for group 2 there was a slight similarity to the cross-like pattern of genotypes reported in an earlier description of this technique and the regression coefficients of ESR3 on ESR1 for WW sheep (b = −0·09 (s.e. 0·28)) differed significantly from those of Ww sheep (b = 1·31 (s.e. 0·52)) (P < 0·05).

It appears that the previously published method for differentiating between sheep that are either heterozygous or homozygous for white fleece was ineffective in this case.

Experiments were made to study the proportion, chemical composition, and rumen degradability of the morphological components of barley straw (Corgi variety) and to study the selection of these components by sheep. The proportions in the harvested straw dry matter (DM) as leaf blade, leaf sheath, stem and chaff were 128, 314, 500 and 58 g/kg DM, respectively. The different components of straw on analysis proved to have very different concentrations of nitrogen and neutral-detergent cellulase digestibility. The leaf blades had the highest and the stems the lowest values. The degradabilities of DM in the components and in the whole straw were determined by measuring DM loss from samples incubated in nylon bags for various periods in the rumen of sheep. Responses were measured using the mathematical model p = a+b (1–e−ct) where p is DM loss, (a+b) potential degradability, c the rate constant of DM loss and t is the time of incubation. DM losses decreased in the order leaf blades > leaf sheath > whole plant > chaff > stems. Leaf blades also had the highest potential degradability and rate of degradation.

In another trial, five sheep were offered unchopped barley straw ad libitum. There were five treatment periods in which sheep were allowed to leave uneaten proportionately 0·2, 0·3, 0·4, 0·5 and 0·7 of the straw on offer for assessing the animal's selection of the morphological components of that straw. The amount of leaf blade in the material consumed increased in largely a linear (P < 0·01) fashion with the amount of excess allowance. The proportion of stem eaten varied conversely. The selection of leaf sheath was less apparent. Little stem was consumed until the proportion of leaf blade in the food available decreased below proportionately 0·4. The practical significance of the study is discussed.

The performance of 32 Cambridge (C) and Suffolk × Cambridge (S × C) twin and triplet rearing ewes and their progeny was investigated from lambing until the lambs reached slaughter weight. The ewes and lambs were housed and penned in individual family groups until 35 days after lambing. From 7 to 35 days the effect of rearing type was studied in combination with feeding the ewes a complete diet containing either 250 (diet 250) or 400 (diet 400) g milled hay per kg. After 35 days ewes and lambs grazed pasture. Ewes suckling triplets produced slightly more milk at 20 days 4·3 v. 4·1 (s.e.d. 0·20) kg/day and significantly more at 30 days 4·1 v. 3·7 (s.e.d. 0·18) kg/day, but consumed similar amounts of dry matter (3·9 kg/day) and so tended to lose more body condition. The latter was also a feature of ewes given diet 400 which produced similar milk yields but had lower complete diet intakes than those on diet 250. S × C had higher yields than C ewes.

Triplet lambs grew faster than twins 361 v. 290 (s.e.d. 9·0) g/day to 35 days but during the outdoor period triplet males but not females grew as fast as their twin counterparts 337 v. 317 for males and 269 v. 302 for females (s.e.d. 12·7) g/day. A selection of male twin and triplet lambs was slaughtered within the range 39 to 42 kg when 102 and 105 days old respectively. Triplet lambs had a lower killing-out proportion 0·458 v. 0·477 (s.e.d. 0·0085) and hence carcass weight but all carcasses qualified for Meat and Livestock Commission certification.

Sixty crossbred females received one of three pregnancy feeding rates over five parities: high (2·3 kg/day); medium (2·0 kg/day) and low (1·7 kg/day) to produce variation in body fatness and live weight. During a 32-day lactation all sows were fed the same allowance according to litter size. At the start of parity 5 ultrasonic P2 backfat depths for the high, medium and low treatments respectively were 11·2, 11·0 and 10·6 (s.e. 1·77) mm while live weight was 184, 177 and 167 (s.e. 8·6) kg. Averaged over five parities, backfat depths at conception were not significantly different between treatments. Sows given higher pregnancy feeding rates in pregnancy were heavier and fatter pre-partum but lost relatively more live weight and backfat during lactation. Regression coefficients for the slope of the relationship between total sow pregnancy weight (kg) and fatness (mm) change, and food intake (kg/day) were 0·2 and 0·04 respectively. Pregnancy feeding rate did not influence the number of live births but total litter weight at weaning was positively related to the weight and fatness of the sow at parturition and her subsequent rate of weight and fat loss during lactation (these characteristics of the sow also being positively related): live weight of litter at 32 days (kg) = 67 – 1·8 sow backfat change in lactation (mm) – 0·4 sow live-weight change in lactation (kg). Absolute sow live weight and fatness were positive influences on readiness to rebreed after weaning.

Operant conditioning techniques were used to measure the feeding motivation (hunger) of pigs restricted to the low food levels used under certain commercial conditions. Six Large White × Landrace boars were maintained in individual pens where they received their daily food allowance. Initially food was available ad libitum; subsequently boars were restricted proportionately to 0·8, 0·6 and 0·4 of their ad libitum intake in a Latin-square design. Finally boars were again offered their previously measured ad libitum intake (treatment 1·0). Hunger was measured by conditioning boars to press a panel 10 times to receive a 7-g reward of food. Operant response rates were measured over 20-min sessions during each of the treatments and at three times of day (pre-feeding, immediately post feeding and 5 h post feeding).

Operant response rate was strongly affected by restricting food allowance (means: treatment 1·0, 42 panel presses; 0·8, 212; 0·6, 266; 0·4, 320). There was a signficant interaction between food allowance and time of day (P < 0·001). Treatments did not vary in response rate before feeding. Treatments 1·0 and 0·8 depressed response rate post feeding (P < 0·001) and treatment 1·0 also 5 h post feeding (P < 0·001). Response rates on treatments 0·6 and 0·4 did not vary significantly from one another or with time of day.

Restricting pigs to low food levels resulted in a high level of hunger throughout the day. This was so even for food allowances that met current recommended feeding levels sufficient for maintenance and low weight gain (treatment 0·6 equivalent to 1·3 times maintenance). Commercial levels of feeding for the pig breeding population whilst meeting production needs do not satisfy feeding motivation. The hunger resulting from low food levels may act as a major source of stress under certain husbandry conditions such as tether and stall systems for dry sows, where sows are subject to both physical and food restriction.

Twenty pregnant sows sharing a double-entry back-out Pig Code feeder with a similar group of 20 were observed over six 24-h feed cycles by a combination of direct observation and video recording. The group had access to an area of 47 m2. Sows were fed once a day on a pelleted diet and water was continually available. Feeding order was relatively constant from day to day, and was positively correlated with parity. A social hierarchy based on displacements and attacks within pairs of sows was found to be basically linear, with the exception of six reversals of dominance. Social hierarchy was positively correlated with feeding order overall, but this was not the case for the latter half of the feeding order. This was partly due to disruption of feeder use by non-feeding visits made by early-feeding dominant sows. Overall the results showed that older sows with more experience of the feeder in two or three previous parities were higher in the feeding order and social hierarchy than younger sows, and may exclude them from the feeder by repeated non-feeding visits.

Selection was carried out in a line of pigs for increased growth rate of lean tissue. The selection criterion was weight of lean in the ham predicted from live backfat and weight measurements after a 12-week performance test commencing at 25 kg live weight. All pigs were given the same total amount of food over the test period. The scale was set to about proportionately 0·85 of predicted ad libitum intake. Boars selected with an intensity of 1/12 were used for 6 months and sows selected with an intensity of 1/4 were kept for two farrowings. An unselected control line was maintained concurrently.

After five generations, performances of selected and control line pigs were compared on ad libitum and scale feeding as they grew to 85 kg. Responses in the selected line on scale feeding were +51 g/day for growth rate (GR), −0·16 for food conversion ratio (FCR), −2·2 mm for backfat (F) and +0·47 kg for ham lean (HL). On ad libitum feeding, responses were much higher in the selected line, giving rise to line × food interactions. Responses were +128 g/day for GR, −0·27 for FCR, −2·3 mm for F, +1·01 kg for HL and +0·15 kg/day for food intake (FI). Estimates of the heritability of HL from variance components were 0·43 (s.e. 0·15) on scale feeding and 0·28 (s.e. 0·19) on ad libitum feeding. The realized heritability of HL on scale feeding was 0·29 (s.e. 0·04) and its co-heritabilities with the other traits on both feeding levels were of similar magnitude to its heritability. Scale feeding exposed genetic variation in the partitioning of food between lean and fat deposition and appeared to be a suitable selection regimen for performance on ad libitum feeding.

Forty Hereford cross steers of 350 kg live weight were allocated to 10 treatments in which straw was offered ad libitum. The straws comprised two varieties of winter barley (Gerbel (G) an Igri (I)), two varieties of spring barley (Corgi (C) and Golden Promise (GP)) and one variety of winter wheat (Norman (N)). Each straw was offered either untreated (with 20 g urea per kg added at feeding), or treated (with 30 g anhydrous ammonia). After 10 weeks the treatments were changed. The mean growth rates for steers receiving the untreated straws were 0·11, 0·13, 0·40, 0·20 and 0·27 kg/day and for treated straws were 0·36, 0·33, 0·61, 0·60 and 0·52 kg/day for G, I, C, GP and N respectively. The straw intakes for untreated straws were 3·4, 3·6, 5·2, 4·4 and 4·6 kg dry matter per day and for treated straws 4·7, 4·8, 5·9, 4·9 and 5·8 kg dry matter per day for G, I, C, GP and N respectively. Chemical and biological measurements were compared as predictors of voluntary intake of straw and growth rate in the steers. Biological measurements were very efficient in predicting performance of the steers while chemical measurements were much less valuable.

Days elapsed from the mid point of the anoestrous period to first (DF) and last (DL) oestrus of the breeding season and duration of this breeding season (DD) within a flock of 60 adult Lincoln ewes are reported in this note. All traits showed considerable variation and the phenotypic correlation between DF and DD was −0·57 (P < 0·01) while that between DL and DD was 0·87 (P < 0·01). However, DF was not correlated with DL (P = 0·10).