A number of observations have been made on 5- to 6-month old wether Hampshire heep undergoing uninterrupted growth (36·2% gain in shrunk wool-free live weight over 58 days), undernutrition (a 21·7% fall in body weight over 27 days) and then followed by compensatory growth (a gain of 62·2% in live weight over 52 days).

Sheep being underfed had increased, and compensating sheep had decreased, apparent digestibility coefficients of feed dry matter compared to control sheep. Sheep undergoing compensatory growth drank more water, ingested more food per unit body weight, laid down less body fat, more protein and retained more water in their bodies than did control sheep. Tritiated water allowed estimation of total body water with an accuracy comparable to other reports in the literature.

Changes in the weight and in RNA-P and DNA-P content of anterior pituitary, thyroid and adrenal glands were measured. Sheep thyroid glands were examined histologically to assess relative TSH outputs and no significant differences detected.

Rat bio-assay of cavernous sinus plasma for somatotrophin and ACTH activity was made on these sheep. Somatotrophin was detected, but experimental groups did not statistically significantly differ in relative potency (TJ.S.P. units/ml fresh plasma). Compensating sheep had. significantly lower plasma somatotrophin potency per unit empty body-weight values than did the underfed sheep.

No ACTH activity was detected in the sheep plasma of the several groups.

During severe undernutrition the anterior pituitary gland decreased in size, but not in cell numbers, and still elaborated somatotrophin. Decrease in body size tends to increase the ratio of circulating somatotrophin per unit body size and thus may facilitate, in a permissive manner, the enhanced growth rate of animals undergoing compensatory growth.

Restitution and gain of body size by compensatory growth is accompanied by hypertrophy of the anterior pituitary gland. This gland, after compensatory growth, showed evidence of enhanced synthesizing capacity.

Fifteen sheep were fed ad libitum from 2 days to 27 months of age, and another 15 sheep were each fed exactly half the average amount consumed by the first group, age for age. The body composition of each sheep (water, fat, protein, energy) was estimated from tritiated water space on 13 occasions during this period.

To describe the course of growth in individual sheep in terms of the relationships between the various body components and body weight, a model was set up in which 4 phases of growth were distinguished, viz. the milk-feeding phase, the period of rumen development, and a prefattening followed by a fattening ruminant phase. Each phase was represented by a linear equation.

Except for phase 1, mean composition within each phase differed significantly between well-fed animals and those which had been given a restricted diet. Individual animals differed in the body weight at which the final phase commenced; the average weight was ca. 31 kg. Fat storage was zero or negative during the main period of rumen development; otherwise the fat and therefore energy content of weight gain increased from phase to phase. The protein and water content of gain was high in phases 1 and 2 and decreased subsequently.

Calculations based on data in the literature indicated that, in phase 4, the composition of weight loss was the same as that of weight gain. It is also suggested that the body weight at which this fattening phase commences is related to mature weight, with animals of large ultimate size starting to fatten at heavier body weights than those of small ultimate size.

The application of the results to the determination of nutrient requirements is discussed.

The results obtained for the digestibility of the carbohydrates with 116 different rations fed to 242 non-pregnant dry cows and 96 lactating cows were studied.

Except for some roughages, reducing sugars, non-reducing sugars, and starch digestibility is always very high. Reducing-sugars digestibility is related to starch content and starch digestibility to crude-fibre content.

Pentosans and crude-fibre digestibility is related to dry-matter intake and to starch, pentosans and crude-fibre content. When the ration contains less than 12% protein, a significant correlation coefficient also exists between crude-fibre digestibility and protein content. But pentosans and crude-fibre digestibility depends above all on the nature of the feeds and on the stage of maturity of the forage.

In this investigation the largest amount of nitrogen used, 44 kg per hectare, increased leaf size, yield and amount of nicotine in the leaf. The three carriers of N had similar effects on growth and yield at each amount applied but calcium ammonium nitrate produced tobacco inferior in quality to that with ammonium sulphate and urea. Increasing topping height from 8 to 10 and to 12 leaves increased the total leaf area per plant and yields, delayed maturity and lowered the quality of the tobacco. The greatest yield was produced by using 44 kg of N and topping at 12 leaves, but the best quality resulted from using 44 kg of N and topping at 8 leaves.

Thirty sheep were pen-fed from age 2 days to nearly 2 years. Fifteen were fed ad libitum and the others were restricted to half that rate, age for age; daily food intakes were recorded. Sequential estimates of body composition were made on each sheep so that protein and energy gains could be obtained for specified age ranges.

In the sheep fed ad libitum, food intake increased several fold in the first few months of life but was relatively constant from 4 months despite large increases in body weight. Thus intake per kg¾ declined progressively as the sheep grew.

The data for the well fed and restricted groups were combined within each age range and linear regression was used to relate body growth (protein and energy) to food intake, variates being expressed as multiples of body weight (kg¾). Energy gain was zero when intake was 250–590 kJ metabolizable energy/day kg¾, depending on age. Wool growth per unit food intake was constant for each sheep throughout the experiment but was twice as great in some sheep as in others and was higher in the restricted group.

Efficiency of energy and protein utilization declined at weaning but otherwise did not vary much with stage of growth. Approximately 40% of energy storage was in protein during milk feeding; after weaning, the fraction declined from 25 to 10% (30 to 20% including wool protein) as the sheep grew.

Studies of the relationship between yield and content of N, P and K in the ear leaf of eight varieties of Nigerian maize, tested for three growing seasons, indicated that the varieties have different critical nutrient levels, although the values obtained for individual varieties were not significantly different from the pooled average critical level for any of the nutrients. The critical levels ranged from 2·85 to 3·19% N, 0·20 to 0·27% P and 2·06 to 2·60% K, while their pooled averages were 3·10% N, 0·23% P and 2·44% K.

High ear leaf nutrient content was not a guarantee of high grain yield, and ear leaf nutrient values of low-yielding varieties were similar to those of the high-yielding varieties.

The copper, molybdenum, and total sulphur contents were estimated in 124 samples of oats and 67 samples of barley obtained from various parts of Northern Ireland. Copper contents were in the low-normal range, the average of all oat samples being 3–9 ppm and of barley samples 4–9 ppm, and the range 1–5 to 8–4 ppm covering all samples analysed. The corresponding averages for molybdenum were 0–25 ppm and 0–30 ppm, about 10% of the samples in each case containing less than 0–02 ppm. Sulphur contents (expressed as sulphate) ranged from 0–23 to 0–46 %. The low molybdenum contents are considered to be of significance in the copper metabolism of housed sheep.

One hundred and forty-nine Scottish Blackface ewes (aged 5 and 6 years), from two different farm sources, were group-fed over 6 weeks in such a manner that at 3 weeks before mating there were approximately equal numbers from each source in two widely different levels of subjectively assessed body condition (scores 1·5 and 3 on a scale ranging from 0 = emaciated to 5 = very fat). The majority of ewes were maintained in these levels of condition until mating after which they were allocated alternately to high and low planes of post-mating nutrition for 26±2 days.

Half the ewes in each group were killed on day 26±2, or earlier return-to-service, for ovulation and viable embryo counts. Surviving ewes were fed at or above maintenance until parturition and the number of lambs recorded.

Condition at mating had a significant, positive effect on both ovulation and lambing rates and had an apparent negative effect on embryo mortality up to day 26±2, although this was influenced by differences in the distributions of single and multiple shed ova. Post-mating nutrition had no effect on embryo mortality up to day 26±2. Neither condition at mating nor post-mating nutrition had any effect on embryo mortality from day 26±2 to parturition.

Source of ewe had a significant effect on both ovulation rate and embryo mortality at both levels of body, condition.

The food intake, the apparent digestibilities of dry matter, and of nitrogen were measured in housed Blackface ewes during late pregnancy, lactation, and after the lambs were weaned. The ewes were slaughtered serially together with non-breeding controls, and the liver, ruminal mucosa, intestines, CNS and carcass were weighed. In association with differing reproductive status marked changes occurred in the content of dry matter and protein in the alimentary organs, but not in the CNS, and the mean weight of DNA in the CNS for all the animals was 130 ± 20 (S.D.) mg.

All of the alimentary organs became hypertrophied during lactation, and regressed after weaning. Maximum values for the liver and ruminal mucosa occurred in the sixth week of lactation, and were maintained until weaning. The small intestine reached maximum weight after 4 weeks of lactation.

Twenty-five soils, including some subsoils, with widely differing properties were cropped with perennial ryegrass in the glasshouse, and measures of Mg availability in the soils were related to the Mg concentration in the plants.

No single measure satisfactorily characterized Mg availability. The ion activity ratio, √aMg/√aca+Mg when the soil neither gained nor lost Mg on equilibration with 0–02 N-CaC12, was more highly correlated (r = 0·;75***) with Mg concentration in the ryegrass than was the best of the capacity measures tested (CaCl2-extractable Mg, r = 0·68***), particularly if the potential buffering capacity (PBCMg) of the soils was also taken into account, in which case r = 0·83***.

Exchangeable Mg (r = 0·67***) was a poorer index of Mg availability than percentage Mg saturation (r = 0·73***) or exchangeable Mg expressed as a percentage of the total exchangeable bases (K, Na, Ca and Mg) in the soil (r = 0·81***). This latter quantity was better than the activity ratio as a predictor of Mg availability (r = 0·81*** compared with r = 0·75***).

A significant proportion of the variation in Mg concentration in the ryegrass could be attributed to the K content of the soils, and closer correlations were obtained when K was included in the composite activity ratio, √aMg/(√aca+Mg + B. aK) (r = 0·88***) or when a term for exchangeable K was included in regression analysis with √aMg/√aca+Mg and PBCMg (r = 0·93***).

The concentration of Mg in equilibrium soil solutions was generally a less satisfactory indicator of Mg availability than were the activity ratios. Soils derived from basaltic parent material had much higher contents of readily exchangeable Mg than the remainder: parent materials other than basalt had little influence on the availability of Mg in the soils. Exchangeable Mg and per cent Mg saturation were higher in gleyed soils than in freely drained soils derived from similar parent material.

The terylene-bag technique was evaluated as a means of establishing the rate of intra-ruminal degradation of the following test materials: nassella (Nassella trichotoma), wire grass (Aristida sp.), rice straw, lucerne chaff and cotton lint. The tests were made in sheep fed base rations of lucerne chaff, wire grass and rice straw at different levels of intake. Values established by this technique are of acceptable repeatability and provided a more responsive indicator of intraruminal degradation rates of the test materials than did base diet apparent digestibility.

Supplementation with casein, urea and sucrose did not significantly alter voluntary feed intake of sheep fed rice straw. Supplementation had no statistically significant effects on apparent digestibility of the base diet of rice straw, but had significant effects upon the rate of degradation of test materials suspended in the reticulo-rumen in terylene bags for 72 h.

Results are presented which indicate that casein supplementation of rice-straw-fed sheep enhanced ruminal production of trace VFA's (butyric, iso-butyric, iso-valeric and valeric). Urea supplementation did not lead to statistically significant increases in VFA concentration or proportion of individual acids in rumen liquor, with the exception of valeric acid.

Populations of Lolium perenneL. derived from fields where the management was paddock grazing were compared with plants from breeder's seed of the cultivars originally sown at the collection sites. In the first trial the ‘survivor’ population derived from an S. 24 ley was better adapted to withstand intensive sheep grazing and high nitrogen application (672 kg/ha/ annum) than either S. 24 or Stormont Zephyr. Extra treading by sheep in addition to that involved in the high stock density (1186sheep/ha) used at the time of grazing produced only a small reduction in yield of dry matter. In the second trial, the ‘survivor’ population derived from an S. 23 ley had a higher yield of dry matter than S. 23 at the high level of N application (672 kg/ha/annum). There was no difference in the yields when 168 kg N/ha/annum was applied. In both field trials yield in the year of sowing was high for all swards, although the survivor populations were slower to establish than the original cultivars. The evaluation of the ryegrass populations in terms of dry-matter yield was affected by the small quantity of Poa trivialispresent when this grass was sown with the ryegrasses. In the second trial this conclusion also applied to yield of nitrogen in the herbage.

Results of two in vivo sheep experiments in which gamma-irradiated material in teryleno bags was fermented in the rumen are reported.

Exp. I concerned the testing of rice straw, nassella (Nassella trichotoma) and cotton lint, each subjected to six dose levels of gamma irradiation (0, 5, 10, 25, 100 and 200 Mrad) when wet and when in the dry state. The tests were made in sheep fed either a lucerne hay or a rice-straw base diet.

Dry -matter disappearance of all test materials was influenced by irradiation treatment: levels of 10 and in some instances 25 Mrad depressed, and other levels substantially enhanced, intraruminal degradation rate tested over 72 h. Materials irradiated in the dry state were better dissimilated than those irradiated in the wet state.

On severe shaking for 14 h in water, solubility values as high as 35 % were obtained for irradiated test materials receiving the highest dose of irradiation but such values were never of the same magnitude as total dry-matter losses in the rumen. When irradiated material was immersed in gently flowing water for 12 h solubility values of 1 % were found for material dosed at 100 or 200 Mrad and of nil for other dose levels. At no level of irradiation was solubility depressed. It was concluded that enhanced losses of irradiated dry matter in the ruminal environment arose substantially from fermentation.

Intraruminal dissimilation of irradiated test material from terylene bags was always greater on lucerne hay base diets than on rice straw base diets.

Exp. II investigated the influence of urea supplementation, at levels of 1 % and 2 % of diet, on the dissimilation of irradiated test samples of cotton lint and rice straw for sheep fed a rice-straw base diet.

Similar effects of irradiation on cotton lint and rice straw to those found in Exp. I were observed. Overall, urea supplementation depressed dissimilation rate of rice straw and severely depressed degradation of cotton lint irrespective of irradiation dose up to an irradiation dose level of 100 Mrad. It is concluded that urea supplementation per se depressed the activity of cellulolytic organisms.

It is considered that feeding trials with low-quality roughages irradiated at levels at or greater than 25 Mrad are warranted.

Ruminal papillae were removed at slaughter from pregnant, lactating and nonbreeding control ewes. The amounts of lactate and pyruvate formed per unit dry weight of papillae during incubation in vitrowith added propionate were not significantly affected by breeding state.

When results were expressed relative to the total weight of mueosa in the rumen, the amounts of lactate and pyruvate formed were significantly greater for ewes slaughtered during the final two thirds of a 10-week period of lactation in comparison with unmated ewes slaughtered at the same time.

The calculated extent of conversion of propionate absorbed from the rumen into lactate and pyruvate was small, averaging 3·0%.

When results were expressed per unit weight of mucosa, breeding state did not significantly affect the activity of four of the enzymes involved in the conversion of propionate into lactate and pyruvate, namely propionyl-CoA synthetase, propionyl-CoA carboxylase, NADP-malic dehydrogenase and lactic dehydrogenase, or of aspartate aminotransferase.

When results were expressed relative to the total weight of ruminal mucosa, the activities of all these enzymes and also of alanine aminotransferase were significantly greater during lactation than in control sheep slaughtered at the same time. The activities in ewes slaughtered during the last 50 days of pregnancy, however, were not significantly different from the control values.

Glutamic dehydrogenase activity per unit weight of tissue was higher after the lambs had been weaned than during lactation. Alanine aminotransferase activity per unit weight of mucosa decreased during the last 50 days of pregnancy.

The effect of reproductive state on the activity in sheep liver of the gluconeogenic enzymes glucose-6-phosphatase and fructose-1,6-diphosphatase, and of the urea cycle enzymes arginase and the arginine synthetase system, was investigated. The sheep were Blackface ewes that were killed during pregnancy, lactation and after the lambs were weaned, together with non-breeding controls.

The total activities in the liver of glucose-6-phosphatase, and of arginase, fell during pregnancy and rose during lactation in proportion to liver hypertrophy, reaching maximum values late in lactation.

In breeding ewes total hepatic fructose-l,6-diphosphatase activity differed little from that in the controls except in the period 14 days before to 13 days after parturition, during which the activity was 10 times higher than at other times. The arginine synthetase system declined in activity during late pregnancy. There were 2 peaks in activity after parturition, one at 30 days post partum and one at 30 days after the lambs were weaned. The peaks possibly were associated with periods of resorption of maternal proteins.

Chalk in the 0–9 in topsoil of Broadbalk has declined from nearly 5% in 1865 to less than 1 % in some plots in 1966, and fastest in plots given ammonium sulphate. Losses were equivalent to 5–8 cwt limestone/acre annually. The paper relates these rates to estimated anion losses, especially bicarbonate, from the plots. Af-ammonium acetate dissolved Ca and Mg from chalk particles in the soils. After correcting for this, exchangeable magnesium had increased during the first 50 years but decreased since 1914 in the F.Y.M. plot. In plots given none or 10 lb/acre of magnesium in fertilizer annually, exchangeable magnesium had changed little since 1865. Thissuggests that equilibrium was soon established between additions and losses of Mg in all except the F.Y.M. plots. Estimates of annual additions and losses of Mg from each plot show that an equilibrium is feasible without large gains from non-exchangeable soil resources. A method of calculating losses of Mg in the drainage using activity ratios and annual calcium losses was developed.

Results of two experiments in which gamma-irradiated low-quality cereal straws were fed ad libitum to sheep, with and without supplements, are reported.

In Exp. I 12 adult Merino wethers were fed chopped wheaten straw irradiated at 50 Mrad or non-irradiated wheat straw, each roughage was fed with and without a supplement of urea, minerals and vitamins. In Exp. II 16 adult Merino wethers were fed diets of chopped rice straw or chopped rice straw irradiated at 25, 50 or 75 Mrad; each of these roughages was fed with and without a supplement of casein, minerals and vitamins.

Gamma-irradiated diets were invariably associated with reduced mean retention times of undigested feed particles in the digestive tract, and a depressed apparent digestibility of dietary dry matter. Voluntary feed intake of sheep given unsupplemented wheat straw irradiated at 50 Mrad was not significantly affected; nor was the voluntary feed intake of sheep fed unsupplemented irradiated rice straw. Irradiation depressed apparent dry-matter digestibility of unsupplemented wheat straw by 5·2 percentage units; irradiated rice straw diets were depressed by 20·2 (25 Mrad); 9·0 (50 Mrad) and 27·2 (75 Mrad) percentage units compared to non-irradiated diets.

Supplementation of irradiated wheat-straw diets tended to restore them to a nutrient worth approximating their original levels in terms of digestibility and intake. Supplementation of rice-straw diets increased voluntary feed intake, because mean retention time was reduced, but diet dry-matter digestibility remained depressed. Supplementation always increased the animals’ state of nitrogen balance; irradiation per se had little effect.

Distribution of gastro-intestinal-tract dry-matter content showed a strong tendency for a greater proportion of the ingesta to be located in the hind gut of animals fed irradiated rice-straw diets, thus confirming the enhanced rate of passage of these diets through the tract as determined by the use of dual stained feed-particles. For sheep fed wheat straw the average mean retention time for non-irradiated particles was 50·9 % greater than for irradiated particles. For rice straw diets non-irradiated feedparticles had mean retention time (pooled across supplementation and irradiation treatments) 30·8% greater than for irradiated particles.

Distinct changes occurred in the ratio of acetic to propionic acid in the rumen liquor of sheep fed irradiated diets which are suggestive of an alteration in species composition of the foregut microbial population.

Evidence is presented for the presence in irradiated diets of a factor or factors toxic to the ruminal microbiota.

Irradiation at the levels used decreased feed particle size, but any advantage so obtained was offset by an enhanced rate of passage of feedstuff through the tract with consequent depression in digestibility. It is concluded that further work is required to elucidate the effects reported and to further establish optimum conditions for use of gamma irradiation as a technique in the treatment of low-quality roughages for use by ruminants.

Mortality rates, calving intervals, age at first calving, generation intervals and animal productivity of Santa Gertrudis, Sahiwal, Brahman and crossbred animals were determined from 11 years' data collected at the Ebini livestock station in the Intermediate Savannahs of Guyana. These data were condensed and analysed and recommendations made as to the most important factors influencing animal production in the Intermediate Savannahs.

Results are reported of ripening studies with maize (var. Inra 200) at Oxford, 1967–9. Sowings were made in late April or early in May, and crops grown at a standard density of 7–2 plants/m2. Areas were provided with cloche protection, for a 4- to 5-week period from time of sowing, to produce material for studies of the effects of flowering time on ripening patterns. From plants of known flowering date collections of 30–40 ears were taken at intervals from 30 until 100+ days after silking.

Information is presented on water content, grain dry weight and number of grains/ear at the various times of harvest. Asymptotic, polynomial and inverse-polynomial regression models have been fitted to the data to elucidate the interrelationships between time (measured from date of silking), grain water content and grain dry weight.

In plants flowering in mid-July grain continued to increase in dry weight until water content was reduced to 35 %, whereas in plants flowering early in August maximum dry weight was attained at a water content of around 40 %.Maximum dry weight of grain was approximately 10% higher in the earlier flowering plants; the corollary is that in the marginal areas of maize grain production in England maturity in such varieties as Inra 200 is often imposed by the environment with a consequent loss in potential yield.

In the early flowering plants, the time taken from silking to reach the harvestable stage of 40 % grain water content was 69 d in 1967, 79 d in 1968 and 64 d in 1969. Rate of water loss from the grain during ripening was closely related to prevailing air temperatures. In the later flowering plants, differing by an average of 11 d in time of silking, 8 days longer was required for grain to be reduced to 40% water content, giving an average difference of 19 days in permissible dates of harvest.

The results suggest that, in varieties of similar ripening pattern to Inra 200, an advance of about 7 days in flowering time is required to establish the maize grain crop beyond its present confines in south-east England.