The concentrations of LH and oestradiol-17β were measured in samples of jugular venous plasma collected frequently during an 8-h period from six acyclic cows between 21 and 27 days post partum. Fluctuations in oestradiol-17β concentrations were detected. Although the mean concentrations of oestradiol were similar whether ovulation occurred within 1 week of sampling or not, the amplitude of the fluctuations in oestradiol concentrations was greater in the three cows which ovulated within 1 week of the period of sampling. Increases in the concentration of LH were frequently followed by increases in the concentrations of oestradiol.

Cows (no. = 11) were classified from liver biopsies taken 7 to 10 days after calving as having mild (FL1, no. = 6), or moderate (FL2, no. = 5) fatty infiltration of the liver. Blood samples were collected from the jugular vein: (1) three times weekly and assayed for progesterone and oestradiol; (2) at 10-min intervals for 8-h periods on three occasions during the early post-partum period and assayed for LH; (3) every 2 h, with ovarian palpation performed every 4 h around the second or third post-partum ovulation, and assayed for LH and oestradiol.

Mean weekly concentrations of oestradiol were not significantly different between FL1 and FL2 cows. FL2 cows tended to have short (< 17 days) first cycles (3/4 FL2 v. 0/5 FL1) with significantly lower concentrations of plasma progesterone (P < 0·05). Mean basal concentrations of LH in the samples collected at 10-min intervals tended to be lower in FL2 than in FL1 cows; however, the difference was significant only in the 2nd week of sampling (P = 0·05). Mean basal concentrations of LH were significantly higher in weeks 3 and 4 than in week 2 in FL1 but not in FL2 cows (P < 0·05). The frequency and amplitude of LH pulses were not affected by week of sampling or by fat content of the liver. The total area under the profile of LH during the pre-ovulatory surge was lower in FL2 than in FL1 cows (P < 0·05) but peak plasma concentrations of pre-ovulatory oestradiol and timing of ovulation after the LH surge were similar.

In three successive experiments 32, 30 and 32 autumn-calving, single-suckled cows were subjected to individual planned weight reductions over winter on silage-based diets with various levels of concentrate supplement. At a similar level of weight loss, milk yield and calf gain were increased when protein supplements of low rumen degradability were given. On average, the inclusion of 0·75 kg fish meal in the diet improved calf gain by 0·13 kg/day. Results are discussed in terms of the effect of protein supplement on the efficiency of use of body reserves.

Two experiments were carried out with 12 non-pregnant, non-lactating beef cows (Simmental x Hereford cross), six in each experiment. In experiment 1, the cows were grazing stubble pasture and each cow was hand fed 750 g/day soya-bean meal. In experiment 2, the cows were grazing green pasture at the pre-blossom stage. Paraffin-coated magnesium ferrite (MF) was used as an external marker. A capsule containing 5 g marker was administered to each cow twice daily at about 08.00 and 14.00 h. At the same time the cows were also weighed and faecal grab samples (GS) were taken. Each experimental period lasted 18 days: a 10-day period for attaining steady state of the marker, followed by an 8-day period during which faecal GS were taken.

Average live weight (LW, kg) and daily faecal output (DFO, kg dry matter (DM) per day) were, respectively 364·2 and 3·39 for cows in experiment 1, and 484·4 and 4·62 in experiment 2. DFO (g): LW (kg) ratios were 9·31: 1 and 9·53: 1 in experiments 1 and 2, respectively.

In-vitro digestibilities were used for calculating the voluntary intake (kg DM per day), which was found to be 6·8 and 13·6 for cows grazing stubble and pre-blossom pastures, respectively. The relationships between LW of grazing cattle and their DFO and voluntary food intake are discussed.

Five groups of Hereford × Friesian steers (initial weight 340 kg) were given either a diet of rolled barley and ammonia-treated barley straw (AS) in the ratio 60: 40 ad libitum (ASB) to support continuous growth, or were offered over a 143-day period diets of either (i) AS alone (diet AS) (ii) untreated straw (US) plus cassava (diet USC) (iii) US plus grass silage (diet USS) or US plus fish meal (0·27 kg fish meal per day) (diet USF). Both the AS and US were offered ad libitum and allowances of cassava and silage adjusted to allow the USC and USS steers to match the growth of AS steers. Steers i n the restricted groups (AS, USC, USS and USF) were then given freshly cut grass ad libitum until they reached slaughter weight; some steers required additional hay and barley to reach slaughter weight. Steers in group ASB consumed 7·4 kg dry matter (DM), gained 1·16 kg live weight per day taking 112 days to achieve the 455 kg slaughter weight. AS, USC and USS animals maintained body weight over the restricted period, whereas the USF group tended to lose weight and daily DM intakes were 4·63 kg AS (AS steers); 3·81 kg US plus 0·95 kg cassava (USC steers); 0·86 kg US plus 3·31 kg silage (USS steers); 3·5 kg US plus 0·27 kg fish meal (USF steers). When grass or grass followed by barley plus hay was given the live-weight gains of the previously restricted cattle did not differ (mean 1·0 (s.e. 0·10) kg/day). AS provided proportionately 0·30 of the metabolizable energy used to produce growth rates in excess of 10 kg/day or if given as the sole food maintained cattle without supplementation.

Rumen fluid was obtained from rumen fistulated cows (two of high (HS) and two of low (LS) susceptibility to bloat) which were bred in experimental herds subjected to long-term divergent genetic selection for pasture bloat susceptibility. In vitro fermentation using strained rumen fluid from each cow with various pasture juice substrates showed no differences between HS and LS in gas production per unit of rumen fluid or in foam production per unit of gas production. Fluid from cows on grazed pasture produced greatest gas volumes. Clover juices produced more foam of similar stability to ryegrass and mixed pasture juices. Foam production per unit of gas was greater for all juices when the rumen fluid was from cows grazing bloat potent pasture.

Experiments were designed to exchange rumen contents and vary the volumes of rumen contents between two pairs of rumen fistulated cows from herds selected for high (HS) or low (LS) susceptibility o t bloat. After exchanges between HS and LS cows the animals were tested on bloat-potent lucerne. The volume of rumen contents was lower in LS than in HS cows by 3·05 1. Increasing the volume of rumen contents of LS cows caused them to bloat to a degree never previously attained. The degree of bloat (i.e. score) was related to the volume of rumen fluid (r = 0·71) regardless of its origin (HS or LS) or the susceptibility of the recipient cow. The results implied that LS cows from this selection experiment did not bloat because they had a lower relative volume of rumen digesta than HS cows.

Changes in the partitioning of both dissected and chemical fat were examined from birth to maturity, in rams and ewes from flocks of Merino sheep selected for high (weight-plus) and low (weight-minus) weaning weight and from a randomly bred control flock. The partitioning of fat between six dissected and 11 chemical fat partitions in the body was examined in 34 mature animals, and the maturing patterns for these fat partitions calculated relative to the weight of total body fat, using the mean values for the mature animals and individual data from 106 immature animals.

Strain had no effect on the partitioning of dissected fat in the mature animals, but did affect the partitioning of chemical fat in the bone and pelt partitions. Mature ewes had greater proportions of dissected subcutaneous and kidney fat, and lower proportions of dissected intermuscular and scrotal/udder fat, than the mature rams.

There were significant strain and sex effects on maturing patterns for dissected subcutaneous and intermuscular fat. Strain and sex effects were also significant for the maturing patterns of some chemical fat partitions.

Selection for high or low weaning weight had little effect on the partitioning of either dissected or chemical fat when compared at the same stage of maturity of total fat. There were large differences in the partitioning of both chemical and dissected fat between the rams and the ewes when compared at either the same weight of total fat, or the same stage of maturity of total fat in the body.

Thirty-one newborn lambs were allocated to four treatments involving subcutaneous or slowly administered intravenous injections of noradrenaline (a natural predominantly a-agonist) or isoprenaline (a synthetic pure ($-agonist). The thermogenic effect of these treatments, attributed to brown adipose tissue, was assessed by changes in metabolic rate and rectal temperature. The objective was to define the optimum treatment for studying genetic variation between lambs in the thermogenic activity of brown adipose tissue. After all treatments, metabolic rate increased significantly by about 7 W/kg to a peak averaging 2·3 times the resting metabolic rate. Rectal temperature increased significantly by about 1°C. Both drugs administered at 150 [ig/kg were similar in potency with noradrenaline producing slightly, but not significantly, greater responses; subcutaneous injections gave significantly larger and more prolonged responses than intravenous injections. Subcutaneous isoprenaline produced the longest sustained response with peak metabolism difficult to define. Subcutaneous noradrenaline injections provided the simplest satisfactory treatment for large scale experiments.

Newborn Scottish Blackface lambs from lines previously selected for high (H) or low (L) resistance to body cooling were tested for their metabolic response (O2 consumption) to cold exposure in a water bath or to subcutaneous injections of exogenous noradrenaline as a measure of non-shivering thermogenesis (NST). Six rams from the H line and six rams from the L line were used to produce lambs such that each sire had both cold-tested (no. = 48) and noradrenaline-tested (no. = 86) progeny.

The mean elevations in metabolic rate produced by cold exposure and by noradrenaline were, respectively, 3·4 times and 2·4 times resting (thermoneutral) metabolic rate. H lambs showed significantly greater cold resistance and metabolic response to cold than L lambs. H lambs showed greater NST than L lambs but the difference was not significant. There were significant sire effects on NST, indicating genetic variation. There was a significant correlation between the metabolic responses to cold and those o t noradrenaline among the sire progeny groups. NST capability appears to be a phenotypic component of neonatal cold resistance which would respond to genetic selection, but this genetic variation is not a major component of that determining cold resistance.

Adipose tissue cell volume, lipolytic rates, Iipoprotein lipase (LPL) and acetyl CoA carboxylase (ACC) activities were determined in biopsy samples taken from the back, shoulder, rump and groin subcutaneous fat depots of 17-month-old female sheep (no. = 24). Half of the sheep had received a copper (Cu) supplement at 6 weeks of age. Biopsy samples were taken after fasting overnight.

Differences in cell volume and ACC activity were apparent between sites. Supplementation with Cu at 6 weeks of age led to a proportional increase of between 0·24 and 0·45 in adipose cell volume and a proportional increase in lipolysis which varied from 0·70 to 2·27 depending on site and hormone addition. Correlations between sites for cell volume and lipolytic activity were not high in general but those for ACC and LPL activities were higher (for ACC r = 0·40 to 0·79). Overall the best correlations were between the back and rump sites. Correlations between the various metabolic measurements and cell volume were not apparent within treatment groups.

In a 2 × 2 × 2 experiment, 296 Scottish Blackface ewes were fed to achieve one of two levels of body condition (high: condition scores ^2·75; low: condition scores ^2·50) by 2 weeks before joining with rams. Half of the ewes of each condition score were fed dried grass pellets ad libitum and 300 g hay per head daily, between 2 weeks before and 8 days after joining, while the remaining ewes were offered a live-weight maintenance ration comprising 750 g pellets and 400 g hay per head daily. From 8 days after joining the intake of all ewes was gradually changed, over a 2-week period, to 1250 g pellets and 400 g hay per head daily. Two days before joining, half of the ewes of each condition/intake group were passively immunized against testosterone. A total of 99 ewes were slaughtered 18 days after joining and their ovulation rate at the first mating determined. Ovulation rates were significantly affected by immunization (immunized: 2·31, control: 1·86, pooled s.e. = 0·055; P < 0·01) and food intake (ad libitum: 2·24, maintenance: I 92, pooled s.e. = 0·055; P < 0·05) but not by body condition at mating (high: 2·15, low: 2·02, pooled s.e. = 0·059; P > 0·05). Lambing rates were dependent on treatment (immunized: 1·82 control: 1·62, pooled s.e. = 0·044; P < 0·01), food intake (ad libitum: 1·85, maintenance: 1·59, pooled s.e. = 0·043; P < 0·01) and body condition (high: 1·82, low: 1·62, pooled s.e. = 0·044; P < 001). In ewes in a high body condition at mating, the effects of intake and immunization were additive but in ewes in low condition, immunization induced little improvement in performance in ewes fed ad libitum. Circulating antibody titres were lower in ewes fed ad libitum than in ewes offered a maintenance ration (1: 416 v. 1: 534, pooled s.e. = 14; P < 0·001), but ovulation rates and litter sizes were not related to titres.

Selection indices to improve lean meat production of terminal sire breeds of sheep were derived. An aggregate breeding value which comprised growth rate, killing-out proportion and carcass lean proportion was examined. Selection criteria included growth rate and ultrasonic or X-ray computer tomography (CT) estimates of carcass composition. Correlations betwen the index and the aggregate breeding value were about 0·38 for indices using ultrasonic fat measurements, and about 0·40 for those using CT measurements. Dropping ultrasonic or CT measurements from the indices reduced the correlations with the aggregate breeding value by only about 0·01 and 002 respectively, indicating that selection on growth rate alone under current economic conditions was highly efficient. Changes in economic weights, and genetic parameters had little effect on the efficiency of selection. The total national discounted value of returns from a single round of selection on the indices was expected to be between £6 and £30·5 million, depending on penetration rates of improved stock, the breeding scheme used, and with a time horizon of 20 years.

An electronic meat-measuring equipment (EMME) determination (average of three consecutive readings) and backfat thickness (averaged over two sites) were taken on each of 107 live Yorkshire pigs weighing approximately 110 kg. After slaughter, 10 carcass traits: killing out, grade fat (fat thickness at maximum loin of split carcass), in. longissimus area, total and individual weights of the four untrimmed primal cuts (butt, picnic, loin and ham) and total weight of lean and subcutaneous fat in the four primal cuts, were measured and used to evaluate the EMME and ultrasound backfat probe, alone and in combination, in predicting carcass merit. Value of prediction was measured as significant improvement in correlation over a base model (A/?2). After adjustment for live weight and treatment (diet, sex and housing) differences, the EMME alone was significant in predicting grade fat (A/?2 = 007), weight of the four untrimmed primal cuts (A/?2 = 0·03) and weights of ham (A/?2 = 0·04), lean (A/?2 = 0·17) and subcutaneous fat (A/?2 = 0·08). Backfat thickness alone was significant in predicting grade fat (AR2 = 0·21) and the weights of loin (AR2 = 0·03), ham (AR2 = 0·02), lean (AR2 = 0·09) and subcutaneous fat (AR2 = 0·42). Their combined information was superior in predicting fat thickness (AR2 = 0·24), weight of lean (AR2 = 0·21) and weight of subcutaneous fat (AR2 = 0·44). Similar results were obtained when treatment effects were ignored. Correlations of the EMME number with fat thickness, weight of total lean and total subcutaneous fat were 0·31, 0·49 and -0·30, respectively. Correlations of backfat thickness with grade fat, weight of total lean and total subcutaneous fat were 0·53, -0·35 and 0·72, respectively.

The behaviour of Large White × Landrace gilts tethered in stalls was studied by scan sampling from 07.00 to 17.00 h on 3 days consecutively every 5 weeks. Results are presented on 30 gilts sampled during their first 5 weeks in the house, period 1, and on 36 gilts during the following 5-week period, period 2. Twenty individuals were common to both samples. Gilts were fed at 08.00 h with a pelleted complete diet, either on low food levels (1·25 to 2·00 kg) or on high food levels (2·2 to 4·0 kg).

In both periods behaviour was strongly related to food allowance in individual gilts. Gilts on low food levels spent a greater proportion of their time in the standing position than those on high food levels (period 1, medians 0·31 and 0·12 respectively; period 2, medians 0·27 and 0·11 respectively), spent more time in repetitive behaviour (period 1, medians 0·22 and 0·04 respectively; period 2, medians 0·16 and 0·07 respectively) and spent a greater proportion of their standing time in repetitive behaviour (period 1, medians 0·46 and 0 respectively; period 2, medians 0·30 and 0 respectively). Similarly, all three measures of behaviour correlated negatively with food allowance overall, but there was some indication that food level had a threshold effect, with more activity and repetitive behaviour occurring on food levels below about 2 kg.

These results suggest that if food allowances are low tether stalls are not a suitable system of housing for pregnant sows.

Large White and Duroc semen was used to form a three-breed cross from Large White x Norwegian Landrace dams. A pair of sibs from each litter was fed ad libitum and a further pair on a time-based scale at the Meat and Livestock Commission testing station at Stirling, Scotland. A total of 241 litters was tested. At the end of testing the pigs were slaughtered and standard carcass measurements were made. One side of the carcass of each of a sample of 60 pigs was fully dissected. The Duroc progeny grew faster and had better food conversion efficiency than the Large White progeny when fed ad libitum but there was no difference between the breeds when feeding was restricted. The Large White progeny produced a better trimming yield and were slightly longer. There was no significant difference in fat depths. The proportions of lean, fat and bone tissues did not differ greatly between the breeds although the Large White progeny had slightly more lean tissue and the Duroc progeny were more heavily boned and had more intermuscular fat. The Duroc terminal sires gave an economic advantage of £1·70 per pig when fed ad libitum but a loss of £0·35 when fed to a restricted scale. This was primarily due to the superior growth rate and food conversion efficiency of the Duroc progeny when fed ad libitum.

Two fat blends differing in free fatty acid concentration and fatty acid composition were included in cereal-based diets at concentrations of 10, 30, 50, 70, 90 and 110g/kg. The digestible (DE) and metabolizable (ME) energy of each diet were estimated in a metabolism experiment based on three 4 × 4 Latin squares using gilts of 30 kg initial live weight fitted with indwelling bladder catheters. With increasing dietary fat both DE and ME increased linearly (P < 0·001) and the linear equations derived were used to calculate the DE values of the two fats by extrapolation. Values were 26·4 and 24·2 MJ/kg respectively for fats A and B. The change in dietary D E and ME to increasing dietary fat concentration showed a curvilinear trend (P = 0·0987 and 0·1268 respectively for DE and ME ) indicating that fats may not be correctly evaluated at only one rate of inclusion. The quadratic functions derived were interpolated to provide DE and ME data for the two fats. Values for DE for fat A ranged from 32·7 o t 25·7 MJ/kg at 10 and HOg/kg, and for fat B from 38·6 to 26·3 MJ/kg at 10 and 110 g/kg. Data for ME followed similar trends. It was concluded that multi-level assays are important in the evaluation of fats and that the rate of decline of fat DE and ME was specific to the fat examined.

An analysis of doe productivity traits was carried out on 884 litter records including 52 sires and 210 daughters (paternal half sisters) of Bauscat (B) and Giza White (G) rabbits. Traits examined included litter size and weight at birth and at weaning, pre-weaning mortality and mean weight of young at weaning. Year-of-kindling affected most litter traits but no pattern of parity effects on litter size and pre-weaning mortality was observed. Litter weight and mean weight of young at weaning generally increased linearly as parity advanced. Litter size and weight and mean weight of young tended to increase as month of kindling advanced from October to March, and to decrease again during April and May. Pre-weaning mortality decreased as month of kindling advanced up to March and increased thereafter during April and May. The sire of the doe affected all litter traits studied, with the exception of litter size at birth and pre-weaning mortality in the B breed. Estimates of heritability for most of the litter traits were moderate or high. Genetic and phenotypic correlations among litter size traits and between litter size and litter weight traits were positive and relatively moderate or large. Litter weight traits were positively correlated both genetically and phenotypically. The genetic and phenotypic correlations between litter size traits and mean weight of young at weaning were negative and relatively moderate or large.

The effects of various genetic and environmental factors on body-weight traits were studied in 3051 records of Bauscat (B) and Giza White (G) rabbits in the period from October 1976 to September 1983. Sixty-five sires and 289 dams were used for analysis of data of body weight at 6 weeks and bi-weekly up to 12 weeks of age. Year and month of birth exerted a pronounced effect on body weights of rabbits. Sex differences on the other hand were small at all ages studied and no pattern of parity effects was observed. Effects of litter size at birth were significant for 6-week weight but not for weights taken at later post-weaning ages. Body weights at the four ages studied decreased as litter size at weaning increased. Litter-weight effects on body weights decreased significantly as the age of the rabbit advanced. Sire and dam affected significantly most of the body-weight traits studied. The proportion of variance attributable to both sire and dam components for all body weights studied in G rabbits were generally larger than those in B rabbits. Heritabilities from sire and dam components of variance for body weights n i B rabbits were substantially lower than the corresponding estimates in G rabbits. Genetic and phenotypic correlations among body weights at all ages studied were positive and of moderate or high magnitude, and tended to decrease in value as the differences between the two ages increased.

It is widely believed that marketing route—time and distance between farm and abattoir—influences live weight and carcass weight loss in lambs and thus killing out. Killing out s i defined as the ratio of carcass weight to live weight but the value depends upon the live weight and carcass weight used. Differences may exist between the farm live weight immediately before loading, live weight in the market, live weight on arrival at the abattoir and live weight immediately before slaughter. Killing out is influenced by the weight of gut contents, whether the carcass is weighed hot or cold, type of feeding system, maturity (age) of the lamb, breed, conformation and fatness. It may also be influenced by environmental factors such as wetness and fleece contamination. Buyers' estimates of killing out are important when they bid for lambs in auction markets and carcass weight is important in determining price paid to dead-weight sellers.