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.

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.

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 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.

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.

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.

A study was made of the effect of increased rectal temperature on digestibility, nitrogen balance and water metabolism in Brahman x British (BX), Africander x British (AX) and Shorthorn x Hereford (SH) steers fed a fixed amount of lucerne hay.

An increase in rectal temperature of c. 1·4 °C caused a decrease in food intake and nitrogen balance and was associated with an increase in dry-matter digestibility in all breeds. Both dry-matter and nitrogen digestibilities were consistently higher in the Zebu crossbreds (BX and AX). Water intakes and ‘water balance’ (water intake – faecal and urinary water) were higher in all breeds when rectal temperatures were elevated. Water intakes were highest in the BX at both normal and elevated temperatures and increased most in the AX with an increase in temperature. ‘Water balances’ were similar in all breeds at normal body temperatures (4–5 1/day) but were lowest in the SH at elevated temperatures. This could partly explain the lower heat tolerance of the SH steers observed under these experimental conditions.

Potato varieties were grown in the field in soil uniformly infected with Streptomyces scabies. In 1969 tubers were severely and evenly infected but in 1971 infection was slight and not uniform. Agreement of varietal ranking with agricultural experience was good in 1969 but poor in 1971.

In 1971, plots protected from rainfall after planting were dry enough at the start of tubering for severe infection; covering the plots for a further 6 weeks followed by irrigation to field capacity resulted in good yields of evenly and severely scabbed tubers. Irrigation during this period suppressed scabbing. The results were easily interpreted in relation to fluctuations in soil-water content measured by a neutron moisture-meter.

The efficiency of using only one site and the need to reduce variability in scab screening tests are discussed.

Some aspects of sexual development and the attainment of puberty in Clun Forest ram lambs were studied during the two seasons 1970–1. Strong correlations existed between parameters of penial, scrotal and testicular development. Sexual development in general appeared to be more closely associated with the body growth than the chronological age of the ram lamb.

Nevertheless, marked variation existed in both age and body weight at puberty. Although the majority of the lambs attained this stage of development at 4·5–5 months the age-range extended from 99 to 176 days. The mean body weight at puberty was 32·5 kg, ranging from 24·5 to 38·0 kg. There appeared to be an interaction between chronological age and general body development in relation to the appearance of sperm in the epididymides. Not only did it seem that a certain degree of body growth and testicular size was required before spermatozoa could be released, but also a limit of chronological age below which puberty was not attained. Large differences existed between individual lambs in both testicular and epididymal weights at puberty. There was a high degree of symmetry in growth between the left and the right testes and epididymides.

Time of birth influenced the pattern and rate of body growth and sexual development. This seemed to be largely due to seasonal fluctuations in nutritional conditions during rearing but the results obtained do not preclude the possibility that other seasonal factors, such as the daylight environment experienced by the ram lamb, might have a certain limited influence on sexual development.

In Southdown sheep, which grazed and were fed during the day to maintain body weight and were housed at night, there was no clear effect of ambient temperature on hoof growth. In these sheep, equatorial or reversed photoperiods did not influence hoof growth.

In an indoor experiment over 19 months on Merino sheep, with natural light and temperature, fleece accumulated normally between spring shearings. Hoof growth in winter was low at a low level of nutrition but was not reduced in sheep at a higher nutritional level. It fell dramatically at both levels of nutrition in the first month after shearing.

Hoof growth was measured in Merino and Southdown sheep exposed to equatorial daylength in two climate-room experiments in which ambient temperature was varied. Fleece length was kept short and nearly constant by clipping. Hoof growth was greatly reduced by low temperature. At a given ambient temperature it was more rapid when ambient temperature was rising from month to month than when it was falling. The low hoof growth observed in the cold was associated with low hoof temperature and there was some evidence suggestive of reduced blood flow to the skin of the lower legs.

These temperature effects would complicate the use of hoof growth as an index of nutrition.

A 6 x 6 Latin Square balance experiment was carried out using six Friesian steers, each of which initially weighed about 304 kg. The six treatments studied were an all-hay diet and five other diets containing 20,40,60,80 and 100 % of rolled barley fortified with mineral and vitamin supplements, accompanied by correspondingly reduced proportions of hay. Each diet was fed at an estimated maintenance level of feeding.

The progressive increase in the proportion of concentrate gave a significantly linear increase (P < 0·001) in both digestible and calculated metabolizable energy. The actual increase in digestible energy was from 2·62Mcal/kg dry matter (59·3% of the gross energy) on the all-hay treatment to 3·42 Mcal/kg dry matter (79·5% of the gross energy) on the all-concentrate treatment. Use of the determined digestible energy values for the all-hay and fortified barley diets to calculate the digestible energy of the four mixed diets gave results in reasonably good agreement with the determined values, the maximum difference being 0·12 Mcal/kg dry matter, which represented 3·83 % of the determined value. The losses of energy in the urine expressed as percentages of the gross energy of the diets showed a small but significantly linear decrease (P < 0·01) with increase in proportion of barley in the diet. The molar proportions of steamvolatile acids in samples of rumen fluid taken from two animals on each treatment indicated that increase in the proportion of concentrate was associated with tendencies for increase in acetic acid, decrease in propionic acid and little change in butyric acid. The mean digestibility of the organic matter was 62·6 % on the all-hay treatment and 81·8 % on the all concentrate treatment. The progressive increase in the proportion of concentrate gave a significantly linear increase (P < 0·001) in digestibility of the organic matter. Although intakes of nitrogen decreased with increase in the proportion of concentrate due to a decrease in the amount of dry matter fed, the weights of nitrogen retained were well maintained and when expressed as percentages of intake showed a significantly linear increase (P < 0·01).

The characteristics of ion active transport by excised roots of hybrid and inbred maize were evaluated in short-term uptake experiments with 35S-labelled sulphate. Hybrids showed a higher transport rate per unit of both dry matter and protein, in comparison with inbred lines.Vmax and Km were quite different for inbreds and hybrids, demonstrating an effect of crossing on the characteristics of the transport system. An effect on the transport system was also shown by better adaptation of the hybrids to low temperatures: the hybrid to inbred transport-rate ratio increased with the temperature decrease.

Thirty-six rams of Chokla breed of about 1–1½12 years of age were randomly divided into six groups and were fed for 4 months on a basal ration of Cynodon dactylon grass or its hay ad libitum. One group acted as the control, while the rations of the remaining groups were respectively supplemented with 250 g of a concentrate mixture, 250 g of lucerne hay, mg CoCl2.6H2O, 10 mg CuSO4.5H2O and 1 mg CoCl2. 6H2O plus 10 mg CuSO4. 5H2O per animal per day. The mean copper, sulphur and cobalt ingestion in the different groups respectively ranged from.1 to 9·7, 475 to 2030 and 0·10 to 0·53 mg per animal per day. The copper, sulphur, fibre diameter, staple length, medullation percentage, crimp per cm and staining grade were not significantly (P > 0·05) affected by the different dietary treatments. The wool copper was strongly correlated with wool sulphur (r = + 0·79) and both were inversely correlated with fibre diameter and medullation percentage. Wool sulphur, but not wool copper, was inversely correlated with staple length. Wool copper, but not wool sulphur, was inversely correlated with the staining grade of canary coloured wool. Staining grade was inversely correlated with fibre diameter as well as crimps per cm. The results suggest that copper plays an intrinsic role in the marshalling of the sulphur component of wool and in the synthetic mechanism of the wool fibre. A suggestion has been made that copper may be playing a biochemical part in the physiological processes causing canary coloration in Indian wools.

Samples were prepared to simulate the populations which would be obtained from the random interpollination of known numbers of inbred lines. This was done by mixing together seed of a vigorous and a less vigorous genotype in calculated proportions. The less vigorous represented the inbred component which would result from selling and sibbing within the constituent lines, while the more vigorous represented the hybrid fraction. The difference in yield between the two genotypes was comparable with the level of enhancement which could be expected in the hybrids as a result of heterosis. Root yields of these populations in the field suggest that depression due to the presence of inbred individuals in a synthetic variety may be predicted by a mathematical model. Yields calculated from the model to allow for various levels of compensation enabled the order of magnitude of the compensation to be estimated. However, the presence of quite small numbers of less vigorous individuals was detectable. Given the limitations imposed by the assumptions necessary to simulate these varieties, the optimal number of lines for an open-pollinated variety may be predicted.

The effects of environment and genotype on growth and yield of cotton were studied in three experiments done at Namulonge, Uganda, from 1966 to 1969. Treatments were date of sowing, variety, fertilizer, plant population and water. Variety BPA66 sown in June at 4–10 plants m-2 outyielded other varieties, sowing dates and population densities. Compound fertilizer at l.25 t ha-1 increased yield by 15% and irrigation increased yield by 38%. The soil water deficit (CSWD) was calculated from meteorological data, and the relative water content (RWC) of the plants was measured. CSWD did not affect growth until a critical value (CD) was reached, which increased from 20 to 50 mm as the crop aged. When CD was reached RWC was s0·094 at dawn and 0·83 at 1400 h. Growth stopped when CSWD > CD, except while any rain, insufficient to make CSWD < CD, was being consumed. Days while such rain was being consumed and days when CSWD < CD were added to give the effective numbers of growing days which accounted for differences in numbers of mainstem nodes caused by sowing date and spacing, and for differences in plant dry weight and leaf area caused by sowing date. Variation in light transmitted by the crop canopy depended on leaf area index (L) alone; spacing, fertilizer and CSWD had no independent effects. The measured extinction coefficient was 1.1 compared with 0·9 predicted by de Wit's (1965) model. Measured value of crop growth rate (C) agreed with values predicted by the de Wit model for the vegetative phase. Spacing and fertilizer only affected C through L. During the reproductive phase C became much less dependent on L, and the form of the relationship changed. Some varieties including BPA66 had a greater net assimilation rate. Maximum C was expected when L ~ 3, but L was seldom > 2. Crops sown at current and previously recommended spacings had sparse canopies and did not fully use light available for dry matter production.

The growth of the progeny from self-pollination was studied in seven cultivars of Lolium perenne and five cultivars of Lolium multiflorum. All cultivars otLolium perenne showed a reduction in the dry weight of the selfed progeny after one generation of inbreeding, although only four of these attained statistical significance. By contrast the reduction in Lolium multiflorum was less marked with only one cultivar showing a significant reduction on inbreeding. An analysis of the growth of two of the Lolium perenne cultivars which showed reduced vigour in progeny from self-pollination suggested that a lower germination rate and a slower development of leaves in the seedling were two factors which resulted in reduced weights in inbred progeny. The possible effect of the environment in which the inbreds were produced on seedling performance is discussed.

In a randomized block 3x2 factorial experiment 72 Large White type and Large White x Landrace pigs were restrictedly fed to 160 lb (72–5 kg) live weight on diets (as wet mashes) containing high levels of maize, wheat or barley in either ground meal or ground flaked forms. A further five groups of six litter-mate Large White type hog pigs per group were used in digestibility and nitrogen balance studies. The diets of meal were formulated to be iso-nitrogenous and to contain similar levels of lysine and for each cereal similar levels of protein and vitamin/mineral supplements were included in the flaked diets. There were no significant cereal x processing interactions for any of the parameters studied. Overall, flaking improved digestibility and this was reflected in a higher (P >0-05) digestible energy content of the flaked diets (3402 kcal/kg air dry weight) compared with the meal diets (3334 kcal/kg air dry weight). The digestible energy contents of the maize, wheat and barley diets were significantly different (P < 0-001) at 3477, 3431 and 3195 kcal/kg air-dry diet respectively. Nitrogen retention, growth rate and efficiency of food conversion were all significantly poorer for the flaked, compared with the meal based diets. The nitrogen retained from the wheat-based diets was significantly lower than that retained from the maize- and barley-based diets. Growth rates of pigs given the wheat- and barley-based diets were similar but taken together were significantly (P < 0-05) better than those obtained from pigs given the maize-based diet. Efficiency of food conversion followed a similar pattern but the differences were not statistically significant.

In a randomized block 3x2 factorial experiment 72 Large White type weaner pigs were individually and restrictedly fed, from 501b (22–7 kg) to approximately 1601b (72–7 kg) live weight, iso-nitrogenous (16% crude protein) maize-based diets (as wet mashes with 2:1 ratios of water to dry food) containing 0–15%, 0–22% or 0–29% tryptophan and either 0–85% or 0–97% lysine. Overall, for the period in its entirety and in the period from the start to 110 lb (50–0 kg) live weight, the diets containing 0–22% and 0–29% tryptophan gave a similar performance. Together they gave a significantly superior performance compared with that obtained from the diets containing 0–15 % tryptophan. Pigs fed the diets containing 0–85 % lysine converted their food better and grew faster than pigs fed the diets containing 0–97 % lysine. These differences were significant (P <0–05) for both parameters in the period from 110 lb (50–0 kg) live weight to the finish of the experiment at 1601b (72–5 kg) live weight and significant (P <0–05) for efficiency of food conversion in the overall experimental period.