In 40 ewes exposed to thermoneutral or cold environments during the last 5 to 6 weeks of pregnancy (experiment 1), and in 10 ewes treated in the same way during the last 3 to 9 days of pregnancy (experiment 2), cold exposure lengthened mean gestation times by 1·7 and 2 days respectively. This effect was statistically significant only in experiment 1. Blood samples were taken from the right atrium of ewes in experiment 2 and the concentrations of some hormones in the plasma were measured. Cortisol concentrations were higher in plasma from cold-exposed ewes than control ewes. Plasma progesterone concentrations were lower in cold-exposed ewes than control ewes during a period from 36 h before parturition to 36 h after parturition, but the changes in plasma total unconjugated oestrogens, 17a, 20o-dihydroxypregn-4-en-3-one and oestrogen sulphates were associated with parturition in the normal way.

The mechanism underlying the prolongation of gestation during cold exposure requires further investigation; events that precede the change of steroid production by the placenta at parturition are most likely to be involved.

Individual dry matter intakes were measured using four groups of 16 ewes, indoors or at sparse winter grazing. In periods of varying duration (14 to 35 days) the ewe groups received 14 feedblock supplements competitively, eight trough supplements competitively or two feedblock supplements individually. In each period hay was available ad libitum. All supplements contained chromic oxide and individual supplement intakes were estimated by total faecal collection. Individual hay and total dry-matter intakes were estimated by faecal apportionment according to indigestibility of dietary components.

Metabolizable energy content (0·81 × digestible energy) of the feedblocks ranged from 7·9 to 9·2 MJ/kg dry matter compared with a value of 13·0 MJ metabolizable energy/kg dry matter for concentrates. The variation in individual supplement intake was large, irrespective of type of supplement. However the mean coefficient of intake variation for 14 feedblock supplements (0·56) significantly (P < 0·05) exceeded that (0·39) for eight trough supplements at equivalent mean dry-matter intakes.

Thus, ‘free-access’ feedblocks did not allow a more uniform supplementation than trough supplements. Supplement intake variation was higher outdoors and increased as total feedblock intake reduced.

The variation in individual hay and total dry-matter intake was lower, and generally independent of that for the supplements. Mean coefficient of variation of 0·24 and 0·22 were obtained for hay and total dry matter, respectively, based on 22 collections with competitively fed sheep.

Total daily metabolizable energy intakes of individual ewes outdoors ranged from 5 to 22 MJ per collection.

Masham ewes carrying single, twin or triplet foetuses were offered a ration of concentrates which increased from 200 to 650 g per ewe per day over the last 7 weeks of pregnancy in 2 years. Silage was offered ad libitum and the voluntary intake of each ewe was measured. In the first year, 30 ewes were offered a poorly-preserved, wet silage (A) which had a low digestibility, followed by a better-preserved silage (B) which had a higher digestibility and dry-matter concentration. There was an increase in silage intake when the change was made from A to B. In the following year, 32 ewes were offered silage (C) which was well preserved, similar in digestibility to B but with a lower dry-matter concentration. The ewes ate more silage organic matter (g/kg live weight) with C than A (12·77 v. 9·34) in weeks 15 to 17 of pregnancy but more of B than C (13·76 v. 10·38) in weeks 19 to 20. Ewes carrying single lambs ate more silage and had a slower rate of decrease in silage intake when the concentrate ration was increased as pregnancy progressed. As litter size increased there-was either greater loss or smaller gain in body condition score.

Maturing patterns of carcass muscle, bone and fat were established using dissection data from 20 large mature size strain and 19 small mature size strain Merino rams. The rams were fed a pelleted ration soon after weaning and individual rams from both strains slaughtered at 6 kg increments in live weight from 18 kg to maturity at 116 and 91 kg for the large and small strains respectively.

Composition of mature rams of both strains was similar for the proportion of muscle and bone but there was a slightly greater proportion of fat in the larger strain.

The progress of each carcass tissue to maturity was assessed relative to progress of shorn full live weight to maturity. Maturing patterns of the three carcass tissues were not significantly different in the two strains. Muscle and bone were early maturing relative to live weight and fat late maturing.

The composition of the large and small mature size strains at the same live weight and at the same proportion of maturity was predicted from the maturity patterns of the carcass tissues and the composition of the mature rams. At the same live weight the large mature size strain had a greater proportion of bone and a smaller proportion of fat than the small mature size strain. At the same proportion of mature live weight, differences between the strains in proportional composition were reduced, and the large mature size strain had slightly more fat.

Some guidelines for comparison of strains of animals of different mature size are developed.

Whole-crop barley (cv. Midas) was harvested when the grain dry matter (DM) reached 640 g/kg and was treated with either anhydrous ammonia at 40 g/kg DM or propionic acid (30 g/kg DM) and stored in polythene-lined tower silos. Anhydrous ammonia and propionic acid preserved the early harvested barley whole crop but distribution of ammonia through the silos was not uniform. Coefficients of DM and starch losses from whole grains separated from the ammonia- or propionic acid-treated whole crops or from rolled barley grains and suspended in the rumen of steers in nylon bags weqe, after 42 h incubation 0.73,0.85,0.26,0.21 and 0.78,0.96 respectively. Coefficients of digestibility of the ammonia-treated (AWC), of the propionic acid-treated (PWC) whole crops and of a diet of rolled barley and ammonia-treated straw (RB) with the same grain to straw DM proportion as that in the whole crops were 0·62 (AWC), 0·55 (PWC) and 0K57 (RB). Daily live-weight gains (kg/day) of 350 kg Hereford × Friesian steers offered the diets for up to 100 days were 0·33 (AWC), ·0·61 (PWC) and 0·74 (RB) and DM feed intakes (kg/day) were 4·7,3·4 and 7·6 respectively.

Using a model to simulate food intake and the partition of food between milk production and live-weight gain, an attempt has been made to explore the financial implications of different levels and patterns of concentrate feeding, where silage is fed ad libitum. In the case of high-yielding cows it appeared that, although feeding more concentrates increased overall lactation yield, profits per cow and per hectare declined with increasing concentrate usage. This raises doubts concerning the traditional view that higher profits result from increasing yields per cow. Comparing different patterns of feeding it also appeared that there was no significant economic loss from flat-rate compared to stepped feeding of concentrates, where cows had ad libitum access to silage.

Analyses of variance were conducted on first lactation milk, fat and protein production records in England and Wales of daughters of British Friesian sires. Herds were split on milk yield into high and low levels of mean production and, in subsequent analyses, into high and low levels of within herd variance and coefficient of variation using all first lactation records. Data were then extracted on daughters of 798 young sires undergoing progeny test and on 118 widely used proven sires to generate connections. Least squares analyses were conducted within levels and genetic correlations estimated from the covariance of sire effects. W ith data split on mean yield, the heritability of milk yield was 0·24 at the low level and 0·30 at the high level, that of log transformed yield being 0·25 and 0·35 respectively.

With data split on variance the corresponding figures were 0·24, 0·30, 0·27 and 0·36 respectively, and when split on coefficient of variation, 0·22,0·26,0·26 and 0·32. There were similar increases for fat and protein yield, proportionately smaller increases for fat and protein content.

Genetic correlations were close to 1·0 between high and low levels for all traits on all criteria of data splitting. As a consequence progeny testing of bulls is rather more accurate at high mean or variance of production levels and data can be combined optimally without scaling. Cows of the highest predicted value using an index will be found in high variance herds.

The lactation model of Wood, y = Anbe−cn was fitted, using a logarithmic transformation, to two sets of lactation data obtained from the Agricultural Research Institute of Northern Ireland. The first set was from animals calving in the autumn and the second set from animals calving in winter and early spring. A categorical variable was added to the transformed model to investigate the effect on the parameters of the animals going out to grass. The technique proved more useful with the autumn-calving herd.

Four silages were prepared from perennial ryegrass. Half the crop was picked up soon after mowing and the remainder left to wilt for 24 h. Half the unwilted and half the wilted grass was chopped by a forage harvester with its normal complement of knives; the remainder was chopped by a forage harvester with all but two of its knives removed. The ensiled material was offered ad libitum for 80 days as the sole food to 32 British Friesian male castrates initially 14 weeks of age and 111 kg live weight.

Wilting raised silage dry-matter content by 31 g/kg fresh weight and gave lower concentrations of acetic acid whilst short chopping gave lower butyric acid. Concentrations of acetic acid, butyric acid and ammonia nitrogen were high on all treatments. Organic matter digestibility was significantly increased by wilting (P < 0·001) and significantly depressed by chopping (P < 0·001). There was no response in dry-matter intake to short chopping, but wilting raised daily intake from 18·4 to 19·9 g silage dry matter per kg live weight (P < 0·001). Live-weight gain was increased from 0·42 to 0·46 kg/day by short chopping (P < 0·05) and from 0·40 to 0·48 kg/day by wilting (P < 0·01)

Two separate experiments were conducted with 12 lactating and four non-lactating Ayrshire cows to compare three frequencies of feeding concentrates per day. Milk production was measured in a 16-week experiment in which the lactating cows were given either a low- or a high-protein concentrate 2, 4 or 22 times (×) per day. Eating behaviour was measured in a 15-week experiment in which the non-lactating cows were also given the low- and high-protein concentrates 2 and 22 × per day. The low- and high-protein concentrates had concentrations of 128 and 202 g crude protein/kg dry matter respectively. Grass silage with a digestibility of organic matter in the dry matter of 0·655 was offered ad libitum to all the cows. Frequency of feeding had no significant effects on silage intake, total nutrient intake, milk yield and live weight. The milk fat concentration increased as the frequency of feeding increased but none of the differences in this and the other milk constituents was significant. Total eating time per day and eating and ruminating time per kg dry matter were not significantly different on the 2 × and the 22 × feeding treatments. There were no interactions between the feeding-frequency treatments and the two types of concentrates. It is concluded that there were no advantages in offering concentrates in more than two separate feeds per day when the daily amount averaged about 7 kg per cow and good-quality silage was available ad libitum

Thirty Hereford × Friesian steers initially weighing 320 kg were used in two experiments, to compare the effects of mechanical processing of barley straw and the amount of rolled barley offered on intake and live-weight gain. The straw was offered ad libitum either in the long form or shredded through a 40 mm screen and supplemented with 20, 35 and 50 g barley DM per kgW"75 per day (L, M and H respectively). A solution providing 12 g urea per kg straw dry matter (DM) was sprayed onto the straw and all the animals were offered daily 480 g of soya bean meal with minerals and vitamins. In the first experiment, which had a change-over design, the animals were weighed at the beginning and the end of each period. The daily consumption of shredded straw (kg DM) was L 3·38, M 3·29 and H 3·00 and of long straw L 3·94, M 4·02 and H 3·56 (s.e. of difference, 0·29). There were significant differences in straw intake between steers offered the long and the shredded straw (P < 0·001) but no differences in intake when different amounts of barley were offered within the same physical form of straw. The mean daily live-weight gains for treatments L, M and H respectively were 0·25, 0·66 and 0·80 kg for steers given shredded straw and 0·32, 0·62 and 0·87 kg (s.e. of difference, 0·1) for those offered long straw. At the end of the first experiment the same animals were kept for a further 10 weeks on the same straw treatment but only treatments L and H were continued, the steers from treatment M being distributed between L and H. The straw intakes and live-weight gains were in agreement with those observed in the first experiment

To study their relationship to milk yield, the concentrations, in jugular venous blood, of thyroxine iodine (T4I), thyroxine (T4), 3,5,3'-tri-iodothyronine (T3), glucose, non-esterified fatty acids (NEFA), triglycerides, phospholipids, cholesterol, total protein, albumin, urea, haemoglobin and packed cell volume (PCV) have been measured in 36 cows (Simmental, Swiss Brown, Holstein and Simmental × Holstein) of different ages during a full lactation, pregnancy, dry period, parturition and 150 days of the ensuing lactation. Thyroid hormones and triglycerides were negatively, and total protein, globulin, cholesterol and phospholipids were positively, correlated with uncorrected or corrected milk yield during several periods of lactation, whereas glucose, NEFA, albumin, urea, haemoglobin and packed cell volume were not correlated with milk yield. The 10 animals with the highest milk yield (18·9 to 23·5 kg/day) exhibited significantly lower values of T4I, T4, T3 and glucose, significantly higher levels of total protein and globulin and tended to have higher levels of NEFA than the 10 cows with the lowest milk yield (10·9 to 14·3 kg/day) throughout or during certain periods of lactation, whereas concentrations of triglycerides, phospholipids, cholesterol, albumin, haemoglobin and PCV did not differ. Changes in T4I, T4, T3, glucose and total protein during lactation were also influenced by age, presumably associated with an increase in milk production with age. T3 was consistently lowest and cholesterol and phospholipids, during later stages of lactation, were highest in Holsteins, which had the highest milk yields of all breeds. Changes of blood parameters were mainly caused by shifts in energy and protein metabolism in association with level of milk production

Data from 265 female goats (does) from seven herds in Year 1 and 130 does from four herds in Year 2 were analysed using a general linear interactive model for factors affecting gestation period (GP), litter size (LS) and birth weight (BW) of offspring (kids). Gestation period could be described by the regression equation GP = α – 0·890LS –1·072S where S is the proportion of male kids in the litter and the constant (a) depends on breed and herd and was 154·240 (s.e., 0·843) days for British Saanen does in Herd 1. The model established for LS was a quadratic regressional relationship LS = a – 0·000103 (MW - 60))2 + 0-0172 (MW -60) where MW was live weight of the doe at mating and a at MW = 60 kg depends on herd and period of kidding. For early-kidding does in Herd 1 a was 2·277 (s.e., 0·090) kids. The expression BW —α 0·363LS + 0·057P is a simplified multiple regressional form involving BW, LS and parity (P) where a varies according to breed, herd and age of the doe. The estimate of a for kids from British Saanen, 1-year-old does in Herd 1 was 3·879 (s.e., 0·632) kg.

1. Eighteen New Zealand White × Califomian young female rabbits (does) were paired by weight and age and, at 800 g live weight, placed on a restricted intake based on the mean body weight of each pair. On attaining 1 kg one of each pair was then given 10 mg trenbolone acetate by injection on days 1, 3 and 5 of each week. This continued until the animals reached 2·3 to 2·4 kg (5 to 6 weeks).

2. There were no differences in digestible or metabolizable energy intakes between treated and untreated rabbits. However, the treated animals showed small but significant increases in rates of gain for live and empty body weight compared with control does. Treated animals also had significantly more nitrogen (P < 0·001) and less energy (P < 0·05) per unit empty body weight than controls. Although the proportion of total nitrogen retention was 0·19 greater (P < 0·001) in treated does, total energy retention was only slightly less. Treated animals had approximately 40 g (200 g/kg) less fat and 50 g more protein (N × 6·25) than control does at the end of the trial.

3. Increases in liver weight and clitoral size were observed in treated animals.

Genetic relationships among leg and performance traits were estimated for 23 975 Large White and Landrace boars fed twice daily to appetite from 27 to 91 kg live weight at Meat and Livestock Commission testing stations between 1966 and 1972. For each boar, an overall leg score was derived as the sum of scores for 19 individual leg traits categorized as ‘absent’ (0), ‘slight’ (1) or ‘severe’ (2) at 91 kg. Heritabilities of leg score were 017 ± 0·03 in Large White and 0·19 ± 0·04 in Landrace. Genetic correlations with a visual ‘leg action’ score on a scale from 1 to 5 averaged 0·93 ± 0·02 over breeds. Genetic and phenotypic correlations between leg scores on the same boars at 27 and 91 kg averaged 0·50 ± 0·17 and 0·15 ± 0·01 respectively.

Both breeds showed significant adverse genetic correlations ranging from 0·20 ± 0·10 to 0·40 ± 0·08 between leg score and boar ultrasonic backfat. From slaughtered littermates, leg scores showed favourable genetic correlations with eye-muscle area (0·30 ± 0·10) and killing-out proportion (0·35 ± 011) in Large White and unfavourable correlations with carcass length (0·31 ± 0·10), lean content (0·30 ± 0·14) and backfat (0·33 ± 0·11) in Landrace. There were no associations with growth rate, feed efficiency or the performance index on which boars are selected. The study indicates that leg condition and fatness are adversely genetically related, but that selection on the present national performance index would not be expected to cause a rapid decline in leg condition. Culling on leg score would be expected to reduce the frequency of leg weakness.

Three experiments employing 40, 39 and 15 Large White × (Landrace × Large White) gilts respectively were carried out to investigate possible primer pheromone activity (i.e. regulating endocrine systems) for those 16-androstene steroids with known signalling pheromone activity (i.e. immediate behavioural effects) in the pig. Experiment 1 consisted of groups of prepubertal gilts exposed to one of the following odour sources (a) 5α-androstenone (5α-androst-16-en-3-one), (b) 3α-androstenol (5α-androst-16-en-3α-ol), (c) a mixture of both steroids, and (d) a diethyl ether extract of boar submaxillary salivary gland. Age at the onset of puberty in these gilts was compared with that in an unstimulated control group. Experiment 2 was similar to Experiment 1 except that the steroids were used at a higher concentration (100 fold), and a fifth group of gilts was exposed to an intact boar. In the third experiment, age at the onset of puberty was noted following exposure of groups of gilts to one of the following (a) a castrated boar which had received long term injections of testosterone, (b) urine from an intact boar, (c) an intact boar.

The results confirmed that the intact boar accelerates puberty in gilts. Although there was no conclusive evidence indicating that isolated boar odours had an effect on the onset of puberty, it is noteworthy that of those gilts exposed to 3α-androstenol, more reached puberty earlier than control gilts. However there is the possibility that transportation may have enhanced the earlier puberty found in some of the gilts taken to a source of 3α-androstenol. Prolonged treatment of a castrated boar with testosterone did not maintain its ability to accelerate puberty in gilts.

The effect of Oesophagostomum dentatum on the performance of growing pigs over the live-weight range 20 to 80 kg was investigated. Fourteen individually-penned pigs in Experiment 1 and 16 group-penned but individually fed pigs in Experiment 2 were orally dosed once with 80 000 or 20 000 larvae respectively at about 18 kg live weight. Worm-free but otherwise similar pigs served as controls. Three energy and nitrogen balance studies were undertaken in two open-circuit calorimeters on four infected gilts and their paired worm-free counterparts on two levels of feeding at 7, 21 and 49 days after infection. Worm burdens averaging 4 255 and 4 722 in Experiments 1 and 2 respectively were recorded post mortem but performance and carcass measurements were not affected, neither were there any clinical symptoms. No significant differences between infected and worm-free pigs were recorded for either apparent digestibility of nitrogen and gross energy or for nitrogen retention. Possible reasons for the lack of measurable effects on pig performance are discussed.

One hundred tonnes of spring-sown barley harvested as whole crop were treated on a commercial farm with pearl sodium hydroxide at 46 g/kg dry matter.

The treated material was stored in a silage clamp beneath grass and lucerne silage. A thin layer of grass, cut and wilted to hay-making dry matter, was placed immediately on top of the barley to absorb any silage effluent.

Monthly samples were taken for microbiological examination and chemical analysis throughout winter storage, while the material was fed to British Friesian dairy cows. There was no evidence of fermentation by clostridia in the whole-crop barley or wilted grass and there was no spoilage of the exposed feeding face. The treatment increased the in vitro organic matter digestibility and the in vitro digestible organic matter in the dry matter of the whole-crop barley. No excessive urination or other ill effects were observed in the stock.

The method proved practical for the satisfactory storage and feeding of sodium hydroxide-treated whole-crop barley.

Results are presented from six trials dealing with aspects of management on the cold ad libitum system of calf rearing using an acidified milk replacer containing over 600 g skim milk powder per kg.

Thirty-six calves were housed in pens of six for each trial and were fed through a teat and pipeline from a storage barrel. Acidified milk replacer, pH 5·6, was mixed cold at 125 g/1 and made available ad libitum to 3 weeks. A rationed allowance was given daily, on a reducing scale, over the following 2 weeks with weaning completed at 35 days. A pelleted dry food containing 180 g crude protein per kg, together with water in buckets and barley straw in racks, was available ad libitum throughout. Each trial lasted 8 weeks. Results for the mean of the six cold ad libitum trials involving 216 calves were compared with the mean results of 10 conventional bucket-fed trials carried out separately at the same unit, involving 912 calves. All calves were purchased British Friesian male (bull) calves.

Calves on the ad libitum system showed improved live-weight gains of 9·4 kg at 3 weeks, 8·8 kg at 5 weeks and 7·5 kg at 8 weeks, compared with the conventional system. The consumption of milk replacer powder was higher in ad libitum trials at 29·4 kg cf. 12·5 kg by bucket but intake of pelleted dry feed was lower on the ad libitum system at 50·7 kg cf. 71·3 kg to 8 weeks. Calf appearance scores were significantly improved on the ad libitum system which gave the main improvement in performance in the first 3 weeks.

A metabolism trial was carried out to examine the influence of an antibiotic food additive (Avoparcin) on the apparent digestibility of nutrients and nitrogen retention in the growing pig. Two groups of pigs, comprising 12 castrates per group, were fed a barley-based diet (190g crude protein per kg dry matter) with or without the inclusion of the antibiotic (at a dietary concentration of 20 mg/kg). Addition of Avoparcin had no significant effect on the apparent digestibility of dry matter or gross energy but resulted in a small increase in the apparent digestibility of nitrogen (0·012; P < 0·05). There was a corresponding improvement in nitrogen retention (0·051) but the difference was not statistically significant.