A model is derived that relates yield to levels of applied fertilizer in terms of parameters that have direct physical meaning. N8, P8, and K8 define the contribution of the soil to the supply of nitrogen, phosphorus and potassium for plant growth; BN, BP and BK define the responses to nitrogen, phosphorus and potassium fertilizer at low nutrient levels and aN is the level of nitrogen required to raise the osmotic pressure sufficiently to prevent growth.

To test the model, field experiments were carried out on French beans and summer cabbage in which 125 different combinations of levels of nitrogen, phosphate and potassium fertilizers were applied. The yield data from each block of each experiment fitted the model very well. Fitted values differed from block to block but these differences could be attributed to the fact that for each block equally good fits were often obtained with widely differing parameter values. Estimates of N8 were made from chemical analysis of the (NH4 + NO3) — N of soil samples from the field plots, and P8, and K8 from chemical studies of the adsorption of phosphate and potassium on untreated soil. They were in substantial agreement with the average values obtained by the entirely different procedure of fitting the model to the yield data. Also estimated values for BN, BP and BK and aN from other chemical studies were consistent with those obtained by model fitting.

It is concluded that although the theory has limitations it is broadly in accord with the results of the detailed field experiments.

Meat quality comparisons were made between a total of 43 infertile bulls and 42 steers in five separate trials. Tenderness, juiciness and flavour were tested by taste panel for each of the five trials, making 15 subjective tests, while objective tests were made of tenderness (Warner-Bratzler shear) and juiciness (industrial press) in the five trials, making a further ten tests.

From this total of 25 different groups of assessments no significant difference between bull and steer meat was detected in 21; of the four groups of assessments where significant differences were detected, two favoured the bulls and two favoured the steers; the quality of all the samples was acceptable.

It is concluded from the overall results that in terms of practical meat quality there was no difference between the bulls and steers used in these five trials.

Barley plants were grown at low, high, increasing and decreasing densities in an attempt to manipulate the environment. The effects on tiller production and development were measured.

Increasing density with time had less effect than decreasing it. Tiller number was the most plastic character, tiller production being earlier in those plants which emerged into low density, being delayed or inhibited in other treatments. The number of spikelets/ear and the length of the inflorescence were found to be less stable characters than the stage of ear development. Percentage spikelet survival showed a downward trend, with increasing density stress.

The systemic fungicide benomyl was used as a seed dressing and as a spray at two concentrations, 250 and 500 ppm, on the winter barley variety Pella. An additional treatment was a spray application of CCC at 500 ppm. All spray treatments were applied at growth stage 3–4. Without fungicide treatment, total yield in the inoculated plots was approximately 40% of that in the uninoculated plots. The 500 ppm fungicide-spray treatment significantly decreased incidence and severity scores of eyespot, the seed dressing being significant only for the latter. The seed dressing and 500 ppm spray treatments significantly increased mean yield/head, fertile tiller number and 1000 grain weight. All the fungicide treatments significantly increased total yield in the inoculated plots. There were no significant effects of CCC upon disease or upon yield, neither was there any interaction between benomyl and CCC.

Preweaning litter traits of 289 Large White (LW) and of 167 Landrace (LR) litters born between 1 January, 1967 and 31 December, 1969 were analysed for seasonal effects. The month during which farrowing occurred exerted highly significant effects on the average piglet weight at birth and at weaning, as well as on the preweaning piglet weight gain (P <0·001). Piglet weight at birth was higher during the hot and dry months of the year, while the preweaning piglet weight gain was greater during the cooler season. The heaviest piglets at weaning were those born in August, the coldest month of the year. Piglet weight at birth was negatively correlated with the mean relative humidity of the month of farrowing (r = -0·79; P <0·01). The percentage of stillborn piglets was high in litters born during March and April (P < 0·005), and the positive correlation between the mean physiologically effective temperature and the percentage of stillborn piglets (r = +0·57) approached significance (P < 0·10).

The considerable variations in litter size and litter weight at birth and at weaning as well as the variations in preweaning mortality were not significant.

The two breeds differed significantly (P < 0·005) in piglet weight at birth (LW: 2·8 lb; LR: 3·0 lb), in litter weight at birth (LW: 24 lb; LR: 28 lb), and in the percentage of stillborn piglets (LW: 4·5%; LR: 7·5%).

An experiment was conducted in which 57 North Country Cheviot ewes, bearing variable foetal loads, were offered different amounts of feed intake during the latter half of gestation. Plasma free fatty acid (FFA) concentrations were estimated at 10-day intervals during the last 55 days of gestation. From the relationship between FFA concentration, energy intake, lamb birth weight and ewe body weight, estimates of the energy requirements of the pregnant ewe were predicted.

The additional metabolizable energy (ME) intake above maternal maintenance required to prevent elevation of plasma FFA concentrations above a predetermined basal level 5 days pre-partum was calculated as 335 kcal/kg lamb birth weight.

The results obtained from the use of plasma FFA concentrations in assessing the energy requirements of the pregnant ewe are discussed in relation to those obtained by other methods.

One hundred and sixty mature Merino ewes were randomly allocated to a factorial experiment designed to investigate the effects of short-term progesterone administration on oestrous cycle length. Groups of ewes received a series of four daily injections of 0, 10, 25 or 40 mg progesterone in peanut oil beginning either on the day of oestrus (day 0) or the next day. Equal numbers of ewes (ten per group) received subcutaneous and intramuscular injections, and those in the control groups received injections of the vehicle only.

Oestrous cycle length was significantly reduced in all progesterone-treated groups, but a consistent trend for this reduction to be greatest in ewes treated first on day 0 gave rise to a significant ‘day x dose’ interaction (P < 0·001). Route of progesterone administration had no significant effect on subsequent cycle length which, in control ewes, averaged 17·2 ± 0·1 days. For ewes first treated on days 0 and 1, mean oestrous cycle lengths for groups receiving 0, 10, 25 and 40 mg of progesterone per day were 17·3, 14·6, 12·1 and 10·7 days and 17·1, 15·2, 13·6 and 13·0 days respectively.

Considerable information is available in the literature concerning the levels of organic and inorganic constituents of blood of normal animals. It is well established that levels of many of these constituents are affected by season, age, breed, growth and other factors (Greatorex, 1957; Bhannasiri, 1960; Luitingh, 1962; Wilson, 1965). It is surprising, however, that little attention has been given to the relationship between these constituents of blood. Occasional reports on the relationship of a few constituents are available, but these were mostly studied in connection with the response of animals to a specific ration or certain ailment.

The voluntary intake by sheep of seventy silages was measured in experiments in several years. Linear and multiple regression analyses were made between these voluntary intakes and the contents of dry matter, various acids and nitrogen and the digestibility value determined in vivo. There were some differences in these relationships for silages made from different groups of species, particularly those made from legumes. Voluntary intake was positively correlated with the contents of dry matter, nitrogen, lactic acid as a percentage of total acids and with the Flieg index. Voluntary intake was negatively correlated with the contents of acetic acid and ammonia as a percentage of total N. Although pH alone did not account for a significant part of the variation in intake, multiple regressions in which pH and one of the measurements of fermentation quality were included were significant, with pH positively related to intake. When all silages were considered, the correlation between voluntary intake and the apparent digestibility of dry matter was not significant. However, for legumes this correlation was significant and positive and for grasses other than ryegrass the correlation was significant and negative.

For seed crops other than cereals there have been comparatively few comprehensive field studies which have analysed the physiological basis of the effects of genotype and agronomic treatments on growth, development and yield. Milbourn & Hardwick (1968), working on vining peas (Pisum sativum L.), have recently shown that pod growth rate and the yield of seeds are not simple functions of leaf area index and that sourc es of materials other than the leaves are important in affecting the yields of pods and seeds. Furthermore, Flinn & Pato (1970) have shown that the pods themselves can contribute to assimilation in the field pea (Pisum arvense L.). Field experiments carried out at Cambridge in 1968 and 1969 have produced evidence on the relative importance of leaves and other photosynthetic tissues in determining the yields of pods and seeds in another seed crop, namely oilseed rape. The experiment in 1969 is described and discussed below.

A perennial ryegrass silage was treated to give a range of acetic acid contents (2·0–8·8); pH and moistvire levels were held constant by adding solutions of the acid and of potassium hydroxide. When fed to sheep, ad libitum, the pattern of eating during the day was affected by acetate content in the silage but the intake over 24 h was unaffected. In a second experiment the infusion of acetic acid into the rumen depressed silage intake but this effect was not observed when part of the infusate was replaced by potassium acetate. It is considered unlikely that high acetate level per se will result in a low intake of silage.

Experiments were done on three sheep fed several diets to determine the usefulness of the marker 51Cr-EDTA in the caecum of the sheep to study changes in weight of digesta and its turnover time. The activity of the marker decreased exponentially with time, indicating that it had mixed with a pool of digesta. Variation in the results was attributed mainly to the slowness of mixing and to the periodic nature of filling with digesta from the ileum.

Most estimates of weight of digesta were compatible with the digesta being contained in the caecum and the proximal colon but in one sheep some estimates obtained by one method of calculation were so large as to be unrealistic. Both the estimated weight and the rate of turnover of digesta varied with the weight of the sheep and the level of food intake.

Seven, groups of adult Merino wethers were fed for 16 weeks on a diet of pelleted oat straw and urea, either alone or supplemented with trace minerals and various combinations of the major minerals. In some treatments, the same diet was fed throughout; in others, diets were changed after 8 weeks.

Sulphur (S) was by far the most important mineral supplement; sheep fed diets supplemented with all minerals except S performed as poorly as those on the basal diet. Of the other minerals, only calcium (Ca) and magnesium (Mg), which were fed in combination, had a small, additional beneficial effect. Supplementary phosphorus (P) had no effect whether or not S was included.

Intakes of sheep on S-supplemented diets increased over the first 6 weeks to reach stable levels of 1200–1400 g D.M./day compared with approximately 800 g/day for controls, while O.M. digestibilities stabilized at about 40 and 33% for S-supplemented and unsupplemented diets respectively. Live-weight change and wool growth were closely related to intake. Mean live-weight losses during the first and second 8 weeks for sheep without supplementary S were 9·5 and 4·8 kg respectively, and were about 50% of this for supplemented sheep. Sheep which were changed from diets without supplementary S to S-supplemented diets after 8 weeks showed slight increases in live weight from then on. Wool growth was about 115 g clean wool/sheep on all treatments during the first month, after which it remained steady at about 105 g/month on S-supplemented diets and fell to 60 g/month on diets without supplementary S.

Sheep without supplementary S were in negative nitrogen (N) and S balance throughout. With the S-supplemented diets, urinary excretion of N and S was high, and few positive balances were recorded until the final 4 weeks of the experiment. Serum urea levels were high (60–130 mg/100 ml) throughout, and showed no effect of diet or period. Phosphorus balances were uniformly negative in sheep without supplementary P, and generally positive in P-supplemented sheep. Serum inorganic P levels were apparently affected by P intake and by live-weight loss, but mean values never fell below 4·5 mg/100 ml.

Sheep without supplementary Ca were in negative Ca balance throughout the experiment; however, Ca supplementation generally resulted in high faecal Ca losses and few positive balances were recorded. In some sheep, serum Ca fell to moderately low levels (7·5 mg/100 ml), but this appeared to be associated more with high serum inorganic P levels than low Ca intake or retention. All sheep were practically in Mg, Na and K balance throughout, and supplementation had little effect on the retention of these elements.

All sheep were in very poor condition at the end of the experiment, even when their D.M. intakes had been high, and wool growth rates were mediocre throughout. It appears that urea was poorly utilized in this experiment, and that satisfactory sheep production on diets of ground straw supplemented only with urea and minerals is unlikely.

Isocaloric quantities of casein, and glucose were infused into the abomasum and duodenum of sheep given perennial ryegrass silage ad libitum. Casein infusion significantly increased nitrogen retention but failed to affect silage consumption, suggesting that the positive relationship found between silage intake and silage nitrogen content is unlikely to be due to a low nitrogen status in sheep fed all-silage rations.

Twelve non-pregnant and 20 pregnant North Country Cheviot ewes due to lamb in April 1969 were subjected to an 18 h daylength during the previous December. Thereafter daylength was reduced by 25 min per week. Eight ewes mated naturally in late May and early June and 22 of the remainder mated within 6 days after treatment with progesterone and gonadotrophin. Five of the photostimulated and 14 of the photostimulated plus hormone-treated ewes subsequently lambed in November 1969. The lambs were weaned at 28 days and 16 of the ewes were returned to fertile rams immediately after weaning. All 16 ewes were re-mated to naturally occurring oestrus during January-February 1970 and 13 proved pregnant.

The pH of soil cropped with ryegrass increased with calcium nitrate as a fertilizer and decreased with ammonium nitrate, especially in the mid-range of pH. Changes above pH 7·2 and below pH 4·5 were small.

Yields of 4 cuts of grass given either N-fertilizer were similar over a pH range (in 0·01M-CaCl2) from 4·3 to 7·4. However, the composition of the grass and nutrient uptakes were affected by both soil pH and form of N-fertilizer.