Progesterone concentrations were measured by radioimmunoassay in fat-free milk samples obtained three times weekly from calving until day 60 of pregnancy from over 700 cows in commercial dairy herds. Profiles of progesterone concentration during the ovulatory cycle and early pregnancy were also examined. In 94% of the animals cycling had commenced by 60 days post partum and a further 3% had shown some ovarian activity. In 34% of cows, the resumption of regular ovulatory activity was preceded by short periods of progesterone secretion which did not meet the criteria for a 'normal cycle’. Peaks of progesterone cross-reactivity (>0·75 ng/1) were detected at the time of ovulation in proportionately 0·06 of all cycles. There was no relationship between the detection of oestrus and the length of the following progesterone cycle or the concentrations during that cycle. However, there was a tendency for the first progesterone cycle post partum to be more variable in length than later cycles (0·56 within the range 18 to 24 days compared with 0·70 of later cycles; P < 0·001). Extension of the length of the luteal phase occurred in 58 second and later cycles (proportionately 0·141) following inseminations which did not result in calving. However, since the comparable figure for 1053 cycles where no insemination was given was 0·048, the overall figure for embryo mortality later than 24 days after insemination was estimated as 9·3%. Concentrations of progesterone in pregnant animals, compared to non-pregnant animals, and the distributions of luteal lengths between 8 and 21 days long following inseminations not resulting in calving could both be explained by early maternal recognition of pregnancy.

Voluntary food intake and body weight were examined over 4-week intervals between 14 and 70 weeks of age in 306 females from 25 British breeds of cattle. At each age, the relationship of the natural logarithm of voluntary food intake to that of body weight was examined by linear regression both within and between breeds.

Of the total variation in voluntary food intake, the proportion accounted for by body weight was extremely high between breeds (phenotypically, 0·80 or more; genetically 0·88 or more, at most ages) but phenotypically low within breeds (0·33 or less). The mean voluntary intake of a breed at any age could be predicted from its mean body weight at the same age with a coefficient of variation (CV) among breeds that declined with age from 0·08 to 0·04. Within breeds, the corresponding CV for individual intake was between 0·12 and 0·15 beyond 9 months of age, and even higher at early ages.

Within breeds, the regression coefficient of log intake on log body weight was close to the value of 0·7 at all ages. Between breeds, it was over 0·8 at early ages, declining to about 0·7 beyond 1 year of age. Thus, genetically larger breeds voluntarily consumed relatively more food at early ages compared with later ages. Breed size should therefore be taken into account when recommending food intake requirements. Breed deviations for high and low appetite are discussed.

Four diets containing 9·6 MJ metabolizable energy (ME) per kg dry matter (DM) (LMEC), and four diets containing 11·3 MJ/kg DM (HMEC) were formulated. One diet of each ME concentration contained 90 g crude protein (CP) per kg DM and served as a negative control (NC). In the three other diets of each ME concentration, the level of CP was raised to 140 g/kg DM by inclusion of poultry litter (PL), non-protein nitrogen (NPN) or fish meal (FM). These diets were examined in a digestion and N balance trial and in a feeding trial.

For the NC, PL, NPN and FM subtreatments of the LMEC diets, DM intakes were 107·1, 112·4, 100·6 and 130·2 g/kg M075 respectively; digestibility coefficients of organic matter (OM) were 0·64, 0·70, 0·67 and 0·71 respectively; and N retention 0·40, 0·76, 0·53 and 1·21 g/kg M075 respectively. For the respective subtreatments of the HMEC diets, the values were: 100·4, 119·4, 109·3, 107·5 for DM intake; 0·64, 0·73, 0·73, 0·73 for digestibility coefficients of OM and 0·40, 0·87, 1·06 and 1·03 g/kg M075 for N retention.

Daily gain on the respective diets in the first 130 days of the feeding trial was 0·85, 0·90, 0·91, 1·04 kg for the LMEC and 1·09, 1·21, 119, 1·24 kg for the HMEC diets, and from the 131st day to slaughter was 0·98, 1·02, 100, 1·08 kg for the LMEC and 1·03, 1·02, 1·07, 1·05 kg for the HMEC diets respectively. Daily carcass gain was 0·49, 0·51, 0·51, 0·53 kg for the LMEC and 0·55, 0·59, 0·59, 0·60 kg for the HMEC diets, respectively.

The relationship between ME concentration in the diet and source of CP is discussed.

Three randomized block experiments, involving a total of 80 castrated male cattle, were carried out to examine the effects of plane of nutrition and type of diet offered during a winter store period from about 10 to 15 months of age on the subsequent performance of late-maturing, Friesian steers slaughtered at 22 to 23 months of age. A control diet of medium-quality grass silage (mean digestible organic matter in the dry matter (DOMD) 0·617) offered ad libitum and supplemented with 0·3 kg concentrates (17·1 to 25·6 g nitrogen per kg dry matter) per head daily, which was designed to sustain a live-weight gain of 0·4 kg/day, was compared with three diets which were designed to sustain a live-weight gain of 0·7 kg/day. These were medium-quality silage supplemented with 1·6 kg concentrates, medium-quality silage supplemented with 0·6 kg concentrates and 0·25 kg fish meal and high-quality silage (mean DOMD 0·704) supplemented with 0·3 kg concentrates. The animals were at pasture for 5 months after the treatment period and were then given silage and concentrates for 3 months until slaughter. The low and high planes of nutrition sustained mean daily live-weight gains of 0·43 and 0·73 kg respectively, giving a difference in live weight at the end of the treatment period of 45 kg. Compensatory growth at pasture reduced this difference to 30 kg. This resulted in a difference of 17 kg carcass weight between the two planes of nutrition. The type of diet offered at the high plane of nutrition did not affect subsequent performance. It is concluded that, when the live-weight gain of late-maturing, Friesian, yearling cattle was reduced below about 0·7 kg/day, there was relatively little compensatory growth during the subsequent period at pasture and consequently the optimum live-weight gain during the winter for this type of animal may be higher than that previously recommended.

An experiment with a 2 × 2 factorial design was used to assess the effects of offering either 6 (L6) or 12 (H12) kg concentrates daily from day 13 of lactation until turnout to grazing with grass silage (600 to 620 g digestible organic matter per kg dry matter (DM)) ad libitum and either ad libitum (G) or restricted (g) quantities of grass from turnout to the end of August. In each of 3 years, 60 to 70 January- to March-calving British Friesian cows were used. From calving until turnout to grazing the mean daily DM intakes of silage were 7·2 and 8·9 kg, and of concentrates 8·5 and 4·9 kg for the H12 and L6 groups respectively, giving a mean substitution rate of 0·47 kg silage DM per kg concentrate DM. Mean daily milk yields were 26·7 and 22·9 kg giving a direct response of 0·85 kg/kg additional concentrate DM. Milk from the L6 group had a higher fat concentration and these cows were also lighter at the end of the winter. At pasture, there were no significant interactions for milk variates between winter treatments and grass availability. The stocking rate of cows with restricted grass availability was 0·33 higher from turnout to the end of August. It resulted in a 0·10 proportional reduction in milk yield per cow but per ha there was a 0·21 proportional increase. At pasture, the H12 cows gave more milk at both grass availabilities. The total responses to concentrates were 1·59 and 2·11 kg milk per kg concentrate DM at the ad libitum and restricted grass availabilities respectively. The good response to concentrate coupled with a 0·35 cow per ha increase in annual stocking rate as a result of restricting the grazing area ensured that gross margins and grass utilization were highest for the H12g cows. Conception rates were similar on all treatments and there were no significant differences in live weight at the end of lactation.

In crossbred female lambs reared on a concentrate diet between 8 and 20 weeks of age, a restriction in food intake to 40 g/kg body weight per day decreased live-weight gain (155 g/day) compared with that in control lambs fed ad libitum (284 g/day) and significantly reduced final live weight and the size of the mammary fat pad (P < 0·001). However, restricted lambs at 20 weeks had more total parenchymal deoxyribonucleic acid (DNA; 54·7 v. 47·5 mg) occupying a greater mass of mammary fat pad (17·0 v. 13·2 g) than control lambs (P > 0·10). Restricted feeding had little effect on mean plasma growth hormone (GH) concentrations at 12 and 18 weeks of age, but decreased plasma insulin and prolactin concentrations.

In lambs fed ad libitum, daily subcutaneous (s.c.) injections of 0·1 mg bovine pituitary GH per kg live weight between 8 and 20 weeks of age significantly increased daily live-weight gain (347 g/day; P < 0·001) and also increased total mammary parenchymal DNA (71·2 mg; P < 0·10) and the mass of fat pad occupied by parenchymal tissue (20·6 g; P < 0·05), compared with the control treatment. Daily s.c. injection of bromocriptine (1 mg/day) had no effect on either body or mammary growth, but tended to reduce the effects of bovine GH when given in combination. Secretory activity was observed in the parenchymal tissue of the eight lambs receiving bovine GH alone, and also in five control lambs and three lambs receiving bromocriptine alone. Three lambs that had attained puberty by 20 weeks of age had the poorest mammary development of their respective treatment groups.

Mammary gland development at 20 weeks of age was significantly correlated across treatment means with plasma GH concentrations estimated at 18 weeks of age (r = 0·95; P < 0·05), but no correlations of similar magnitude were found between individuals within treatments at 20 weeks. Strongest correlations were found among 8-week-old lambs, where mammary parenchymal DNA was positively correlated with mean plasma GH (r = 0·62) and the GH:insulin ratio (r = 0·79) and negatively correlated with the prolactin:GH ratio (r = -0·65).

Forty Hampshire Down × Mule (Blue-faced Leicester cf × Swaledale 2) ewe lambs, obtained within a week of birth, were reared on milk replacer and from 6 weeks of age on a complete pelleted diet. Food intake of individual lambs was controlled to produce periods of high (H: ca. 210 g/day) and low (L: ca. 110 g/day) rates of live-weight gain from 4 to 20 and 20 to 36 weeks of age. Groups of eight lambs were slaughtered and dissected at 20 weeks having followed either growth paths H or L, and at 36 weeks having followed growth paths LL, HL or LH.

Growth path had little effect on the lean or bone content of the carcass, but had a significant effect on carcass fat content and distribution. At the same carcass weight, the ratio of intermuscular to subcutaneous fat was higher in leaner carcasses. When compared at the same weight (ca. 35 kg) but different ages (H, 20 weeks; LL 36 weeks), the slower growing LL lambs contained 1·22 kg more fat than the H lambs, primarily in the intermuscular and subcutaneous depots but also in the internal omental depot. At the same age and weight (ca. 36 weeks and 48 kg), lambs which had followed the growth path LH contained 2·5 kg more fat than lambs which had followed the HL path. These differences in fatness are thought to have come about through changes in the effective protein:energy ratio of the diet, induced by the manipulation of food intake.

Carcasses of HL lambs would be of more value to the meat trade compared with LH, since they would require less fat trimming before retail sale.

The response of 35-kg store lambs to diets containing increasing rumen-undegradable nitrogen (UDN) concentrations was measured by live-weight gain and nitrogen (N) balance. A range of UDN concentrations from 2·4 to 7·2 g/kg dietary dry matter was achieved by supplementing a basal diet of NaOH-treated barley straw, tapioca, extracted rapeseed meal and minerals with both formaldehyde-treated rapeseed meal and fish meal. Sufficient diet to provide maintenance and a growth rate of 150 g/day was given to the lambs, according to live weight. Increasing levels of UDN promoted a linear increase in live-weight gain and N retention. However, the response to fish meal was greater than that for formaldehyde-treated rapeseed meal. The true digestibility of N of formaldehyde-treated rapeseed meal determined in chickens by ileal analysis was low in comparison to that of untreated rapeseed meal.

Embryo transfer following multiple ovulation could allow faster rates of genetic change in sheep, by increasing the effective female reproductive rate. The gains would come from lower generation intervals or increased selection among females, or both. They require good embryo transfer rates at 6 to 8 months of age. These are not adequate at present and need to be improved by research and development, justified by the extra genetic gains shown here to be possible. If high rates of embryo transfer (10 progeny per donor) could be achieved, then, with appropriate selection schemes, the rates of genetic change could be doubled compared with efficient schemes using normal reproduction. This applies to most traits, to those measured before reproductive age (growth traits and carcass traits estimated in the live animal), to female reproductive traits and to wool traits measured at 14 to 16 months of age. With moderate rates of embryo transfer (5 progeny per donor), gains of 50 to 70% in genetic response could be obtained. To limit the rate of inbreeding to moderate levels in a closed selection flock, some 100 to 200 females (1000 progeny) would be required. Application of the methods may be difficult with current breeding structures, and the development of special nucleus selection stocks i s proposed.

Three experiments measured intake and assessed quality of roughage refused by individually-fed castrated Saanen goats and Suffolk × Mule wethers, aged 21 months.

In experiment 1, in which long, lucerne hay was offered (10 animals per species; 14 days) goats ate more than sheep (33·2 v. 28·3 g dry matter (DM) per kg M daily; P < 0·05). In experiment 2, in which long, ammonia-treated barley straw was offered (eight animals per species; 21 days) consumption was also higher for goats (21·6 v. 16·4 g DM per kg M daily; P < 0·01). Freshly cut, chopped stinging nettle (Urtica dioica L.) was offered with treated straw in experiment 3 (eight animals per species). Over the 10 days, intake of nettle increased linearly and that of straw decreased, but nettle consumption was consistently higher for goats than sheep.

In each experiment, food refusals (0·2 of food offered) were of lower nutritive value (lower nitrogen, higher acid detergent fibre, lower digestibility in vitro) than food offered. Throughout, food refusals by goats were of slightly higher nutritive value than food refusals by sheep.

It is concluded that both sheep and goats are selective feeders under stall-feeding conditions, but the greater intake of roughage by goats cannot be attributed to their selection of more nutritive components.

Models are described which utilize goal programming to maximize hay intake in the formulation of rations for ewes in the last 6 weeks of pregnancy. By treating the energy or protein allowances (or both) as goals rather than restrictions, rations in addition to the linear programming (LP) optimal solution are generated. The approach offers a flexible alternative to the standard LP approach by providing additional rations with known deviations from the allowances. A set of guidelines is given to determine which of these rations could be tolerated when the nutritional requirements cannot be satisfied.

In two experiments, straw diets were supplemented with a concentrate mixture containing either untreated or formaldehyde-treated soya-bean meal. In experiment 1, adult wether sheep were given straw/concentrate mixtures in a 3:1 ratio (air-dry basis) in restricted amounts. In experiment 2, these proportions were adjusted to 3:2 and the growing lambs were offered straw at proportionately 0·05 to 0·1 greater than that eaten daily.

In experiment 1, formaldehyde treatment of soya-bean meal depressed apparent nitrogen (N) digestibility (P < 0·001) although diet organic-matter digestibility was not affected. Formaldehyde treatment also tended to reduce N retention in experiment 1, whereas with growing lambs in experiment 2, it led to improved N retention. Plasma urea concentrations were reduced as a result of formaldehyde treatment of soya-bean meal. Digested N was more efficiently utilized by sheep given the treated soya-bean meal diet in experiment 2 but not in experiment 1. Lambs given the treated soya-bean meal diet tended to gain more live weight with marginally superior food conversion ratios while consuming similar amounts of dry matter as those given the untreated soya-bean meal-supplemented diet.

The voluntary intake and digestibility of four hays were measured with eight sheep using two 4 × 4 Latin squares. Measurements were made during the last 8 days of each 3-week period. The degradation characteristics of the hays were measured by incubating samples (in nylon bags) for 12, 24, 48 or 72 h in the rumen of four sheep fitted with rumen cannulae and given a good hay. The exponential p = a + b(1 − e−α) where p = degradation loss, t = time, and a, b and c are constants, was fitted. The potential degradability (defined as a + b) of the dry matter (DM) of the four hays was 0·76, 0·66, 0·54 and 0·46 with corresponding voluntary intakes of 71, 62, 52 and 45 ± 2·9 g DM per kg M075 per day. The in vivo digestibilities were 0·61, 0·59, 0·46 and 0·45 (s.e. 0·013) respectively and corresponded to 23-, 25-, 31- and 67-h degradation. Voluntary intake was better related to potential degradability (and degradability at 12, 24, 48 and 72 h) than to in vivo digestibility. It is concluded that the degradation characteristics of forages may have useful application in predicting voluntary intakes, and that potential degradability could be used to define the rumen (jegradable nitrogen content necessary with any particular forage.

Seventy-two animals were used in an experiment to study the response of first-litter sows to graded increases in daily food intake during a 28-day lactation. Six food intakes, ranging from 1·5 to 4·8 kg/day were compared. The results showed that both live-weight loss and backfat loss during lactation increased linearly as food intake decreased (P < 0·01).

Subsequent ovulation rate was unaffected by food intake but both weaning to mating interval (Y,, days) and the proportion of sows exhibiting oestrus within 8 days of weaning (Y2)improve d linearly with increase in daily food intake during lactation (X, kg) (P < 0·01); the respective linear regressions being Y, = 39·0 - 6·26 and Y2 = 0·198A - 0·15. A sub-group of 24 gilts which were older at first conception (340·5 v. 213·5 days; P < 0·01) exhibited oestrus sooner after their first litters were weaned (12·8 v. 22·1 days; P < 0·05) than the remaining 48 younger animals.

Nitrogen balance increased linearly with food intake (P < 0·01) but even at the highest food intake, nitrogen balance remained negative (−15·5 g N per day). Food intake had no effect on the growth rate of piglets to 3 weeks of age but in the 4th week of lactation there was a quadratic increase in piglet growth rate as sow food intake increased (P < 0·01).

Ninety-six multiparous sows were allocated at random on the 1st day of mating at the post-weaning oestrus to three dietary treatments of: 1·84 kg control diet (C); 0·92 kg control diet plus 0·92 kg pelleted hay (R); or 1·84 kg pelleted hay per day (M) for the following 10-day period to determine if restriction of nutrient intake affected reproductive performance. Subsequent to the 10-day period of nutrient intake restriction, all sows were fed 1·84 kg control diet once daily. The treatments had no effect on pregnancy rate, number of piglets born, number born alive, number weaned, or on piglet weight at birth or at weaning. Sows on the M treatment from oestrus to day 10 lost more weight (8·6 kg) during the 10-day period of nutrient restriction than the sows on the R (3·4 kg) or. the C (0·7 kg) treatments. However, weight gain from oestrus to day 110 of gestation was similar for all three treatments (16·5, 17·8 and 17·1 kg, respectively). Thus, restriction of nutrient intake early in pregnancy is not a critical factor affecting litter size and weight at birth or weaning in the multiparous sow.

The responses of growing pigs to dietary lysine concentration, as influenced by food intake, sex (entire male and female) and live weight were investigated in an experiment involving 128 pigs. The basal barley-soya-bean diet (14·2 MJ digestible energy (DE) per kg) was offered either ad libitum or according t o a restricted feeding scale to both sexes from 20 to 85 kg live weight. The eight dietary lysine concentrations ranged from 8·0 to 12·2 g/kg during the 20 to 50 kg phase and from 6·4 to 9·8 g/kg during the 50 to 85 kg live-weight phase. Performance was assessed by response-surface analysis based on data from successive 10-kg live-weight intervals. Regression analysis was used to assess the response of carcass lean content after slaughter at 85 kg live weight.

Daily gain of females fed ad libitum was curvilinear up to maxima of 0·72 and 0·69 g lysine per MJ DE during the 20 to 50 and 50 to 85 kg growth phases respectively. Daily gain response was small but linear up to the maximum dietary lysine concentration for all other combinations of sex and food intake.

The response of carcass lean for males given food at a restricted level was linear up to the maximum dietary lysine concentration. For males given food ad libitum, carcass lean response was curvilinear with maximum lean content attained with 0·73 and 0·59 g lysine per MJ DE during the 20 to 50 and 50 to 85 kg live-weight phases respectively. Carcass lean content of females was not affected by lysine concentration within the range used.

Fifteen Large White boars were randomly allocated to three groups of five pigs. The boars were slaughtered over a period of time at one of three live weights: group 1 (pork weight), 63 to 68 kg (mean age 141 days), group 2 (bacon weight), 90 to 97 kg (mean age 203 days) and group 3 (heavy weight), 121 to 133 kg (mean age 268 days). Testes, bulbourethral glands, submaxillary salivary glands, blood and thoracic fat were taken from each pig and the glands weighed and steroids determined in extracts of the submaxillary glands, blood plasma and fat. Testosterone and the boar taint steroid, 5a-androstenone (5a-androst-16-en-3-one) were measured in plasma by radioimmunoassay (RIA). 3a-androstenol (5a-androst-16-en-3a-ol) and 5a-androstenone were determined separately in submaxillary glands by gas-liquid chromatography and together semi-quantitatively by a colour reaction. 5a-androstenone was also determined in submaxillary glands by RIA and in fat by enzyme-linked immunosorbent assay. Mean somatic characteristics differed significantly between the groups, but due to the wide variation in steroid concentrations between individual boars, mean differences for steroid concentrations between groups were not significant.

Significant positive correlations were found in boars between bulbourethral gland weight, submaxillary gland weight, concentrations of 3a-androstenol and 5a-androstenone in the submaxillary gland and concentrations of free plasma 5a-androstenone and fat 5a-androstenone (P < 0·05). The application of a simple colour reaction to detect readily extractable 16-androstene steroids (16-androstenes) in submaxillary gland tissue is discussed in relation to other methods for determining boar taint.

The addition of a categorical variable to the lactation model of Wood (1967) has been shown to be useful in the explanation of seasonality of milk production using data from an experimental herd. The technique is further investigated using monthly milk-yield data from 43 commercial herds in Northern Ireland in the years 1978 to 1982. Coefficients, d, of the categorical variable were estimated for each month of calving. The maximum value of d was 0·256 for the month of October and the minimum value was 0·022 for the month of March.

The behaviour of individually-penned lambs was observed and found to include many abnormal as well as normal behaviour patterns. Those with ad libitum pelleted concentrate or hay or greater environmental disturbance spent less time exhibiting abnormal behaviour.