Three different methods have been used to estimate the contribution of bacterial nitrogen to the total nitrogen in rumen digesta from calves receiving ground diets containing different levels of digestible energy and in which part of the nitrogen was supplied as urea. The method based on the ratio of 2, 6-diaminopimelic acid (DAP)-N to total N for rumen contents and rumen bacteria was not successful because the bacterial fraction isolated from pooled rumen contents contained a similar concentration of DAP to whole rumen digesta. The main source of error in the method based on the nucleic acid N/total non-NH3-N ratio for whole rumen contents and bacteria was probably the variability in the ratio for bacteria growing under different conditions. The method utilizing differences in the amino acid composition of the diets, a bacterial fraction and rumen content estimates bacterial protein rather than bacterial nitrogen. The chief limitation is the different rate of degradation of different dietary proteins. Bearing in mind these limitations calculations by the nucleic acid method gave mean values of 61–94 % bacterial nitrogen in the total nitrogen of rumen contents 3 h after feeding four different diets. Values recorded by the amino acid composition method varied between 66 % and 82 % bacterial protein N in the total protein N of rumen contents. The proportional contribution of bacteria increased as the digestible energy content of the diet was decreased in both cases. However, since the ruminal total protein N concentration fell as the digestible energy content of the diet was reduced, the actual concentration of bacterial protein N decreased with decrease in dietary digestible energy.

Sectional and intrasectional variations in muscle fibre diameter over a restricted axial range were examined in seven bovine muscles from foetuses, calves and steers. Significant sectional variations were found in four muscles, while two muscles showed significant intrasectional variations. The results indicate that sampling sites require accurate definition in comparative studies of muscle fibre diameter.

Two extensor muscles of the foreleg, m. extensor carpi radialis and m. extensor digitorum communis showed neither sectional nor intrasectional variation in muscle fibre diameter and appear to be more satisfactory muscles for use in muscle fibre growth studies than m. longissimus thoracis et lumborum.

A comparison of mean muscle fibre diameter in 60 pairs of contralateral muscles showed that there were no significant differences in 52 of the muscle pairs.

The effect of variety and spacing on growth, development and yield of cassava and the relationship between growth, development and yield in three cassava varieties were investigated during the 1971 and 1972 growing seasons. Msitu Zanzibar outyielded Aipin Valenca and these two varieties in turn outyielded Amani 4026/16. The varietial effect was associated with differences in the rate of bulking. Increase in plant density led to an increase in the yield of tubers per hectare, the mean increase with increasing plant density being greater in Aipin Valenca than in either Amani 4026/16 or Msitu Zanzibar. Increase in plant density from 12000 to 18000 plants/ha led to a decrease in root tuber yield in Amani 4026/16. The calculated optimum density for maximum yield was 6·7, 6·4 and 5·6 plants/m2 respectively for Msitu Zanzibar, Aipin Valenca and Amani 4026/16. The spacing effect on tuber yield was associated with differences in the rate of bulking. Aipin Valenca was usually taller than the other varieties and, in general, increase in plant density increased the height of the plants.

Final total dry matter/m2 was greater in Aipin Valenca and Msitu Zanzibar than in Amani 4026/16 and, with the exception of the last variety, total dry matter/m2 increased with increasing plant density. Total dry matter produced per plant was greater in Msitu Zanzibar than in Aipin Valenca and these two varieties had greater dry weight per plant than Amani 4026/16. In the three cassava varieties, the dry weight per plant increased with decreasing plant density.

A greater proportion of the total dry matter was diverted into the root tubers of Aipin Valenca and Msitu Zanzibar than in Amani 4026/16. Generally, increase in plant density decreased the proportion of total dry matter diverted into the root tubers. Mean crop growth rate increased with increasing plant density while mean net assimilation rate and relative growth rate decreased with increasing plant density. Amani 4026/16 and Aipin Valenca had a greater mean crop growth rate and a greater net assimilation rate than Msitu Zanzibar. Mean relative growth rate was greater in the latter than in the former two varieties.

Leaf area index and leaf area duration were greater in Msitu Zanzibar than in the other two varieties and these tended to increase with increasing plant density.

There was a close and positive relationship between rate of bulking and root tuber yield and the lack of a positive relationship between leaf area duration and tuber yield is discussed.

Immunoglobulin concentrations were compared in Finnish Landrace and other lambs, born to ewes of their own and of different breeds, to determine if the superiority of the Finnish lambs in obtaining maternal immunoglobulin from colostrum, shown in previous experiments, is due to special qualities of the ewes or of the lambs. The groups compared were, respectively, Finnish lambs born to Finnish, Welsh Mountain or Border Leicester ewes; Finnish, Oxford Down and Soay lambs born to Finnish ewes; Finnish and Merino lambs born to Border Leicester ewes; and Finnish and Southdown lambs born to Welsh Mountain ewes. The immunoglobulin concentrations in the Finnish lambs were in every comparison significantly higher than in the other breeds, and were not related to the breeds of the dams.

Consideration is given to the prospects of producing F1 hybrid varieties of perennial ryegrass, Lolium perenne, and other herbage grass species for commercial use. In the light of the results of interpopulational hydridization in this and other crop species and of the technical and economic disadvantages inherent in other methods of F1 hybrid seed production, it is concluded that the development of interpopulational F1 hybrid varieties, by the field interpollination of parent populations, is a desirable and worthwhile breeding objective.

Rates of added P required for maximum yields of ryegrass grown in pots and of field tobacco and maize were related to functions of P intensity (I) and capacity (AQ/AI, or C) in soils. It was found that log I alone was negatively correlated with optimum fertilizer for ryegrass and tobacco, but not for maize. Capacity alone had little relationship with P requirements of tobacco but was significantly correlated, although having opposite effects, with those of ryegrass (positive) and maize (negative). Optimum fertilizer rates for all crops were best accounted for by multiple regressions including intensity and a capacity term together, using log C when P requirements were increased (ryegrass in pots, R2 = 0.94) or √C when they were decreased by increasing capacity (field tobacco, R2= 0.96; and maize, R2 = 0.98). Inclusion of both capacity terms with log I in regression was of no advantage with ryegrass and tobacco, but with maize all three terms contributed significantly to the correlation, log C tending to increase and √C to decrease fertilizer needs.

Fourteen trials on spring barley and eleven on winter wheat, grown in the east of Scotland, compared the effects on yield of liquified anhydrous ammonia and solid ammonium nitrate at various levels of application.

For grain yield, the optimum N level in these trials was about 100–113 kg N/ha. The object of including in the trials N input levels higher than optimum was attained. Yield response to the two forms of N was similar for both wheat and barley at the different N input levels.

Winter injection of anhydrous ammonia was less efficient than spring application. Injection of anhydrous ammonia into young wheat resulted in frequent reduction of plant population and, on occasion, loss of yield.

At equivalent rates, anhydrous ammonia caused less lodging than ammonium nitrate; it also appeared to be less readily leached from the soil. Ammonium nitrate gave more rapid early growth and this led to a greater proneness to leaf disease.

Considering the complexity of storage and injection equipment required to handle anhydrous ammonia, it is questionable if these agronomic advantages justify its use on cereals where rates of use do not also confer the benefits of cheaper unit cost of nitrogen.

Thirty-two milk-fed Murrah buffalo calves of 3 weeks of age were randomly allotted to four dietary groups: milk, concentrate-berseem hay in the ratios 1:1 and 1:3, or berseem hay alone. Milk intake was gradually reduced and completely stopped after the sixth week of age in the groups given dry feeds. Two calves from each group were slaughtered at 6, 9, 12 and 15 weeks of age. In addition, four buffalo calves were slaughtered at 21 days of age for comparison.

Observations on ruminal tissue weight, content weight and the ruminal capacity indicate that the ruminant stomach of buffalo calves weaned on dry food after the sixth week of age becomes structurally developed by 9 weeks of age, whereas the rumen remains underdeveloped in calves fed milk to 15 weeks of age.

The development of precipitins to Micropolyspora faeni in cattle fed hay treated with a bacterial and mould inhibitor is compared to that in herds fed untreated hay. The results indicate that, even when fed only treated hay, exposure to M. faeni was such that a considerable proportion of precipitin-free cattle did develop precipitins.

A total of 72 pigs comprising 36 boars and 36 castrates of 22 kg live weight were allocated to one of three protein levels in the diet. The crude protein concentrations were 16·0, 18·0 and 20·0%. The diets were fed to appetite for three half-hour periods per day from 22 to 90 kg live weight.

Up to 55 kg live weight both boars and castrates showed an initial positive response to the increased protein concentration. This was followed by a negative response during the 55–90 kg period for both food conversion and daily live-weight gain. For the overall period the differences in performance were not significant. From 22 to 55 kg, and from 55 to 90 kg the average daily feed intake of boars was significantly less than that of the castrates.

Boars had a significantly better overall food conversion, larger eye muscle area and decreased back fat.

This experiment indicated that there was no advantage in feeding boars a protein concentration higher than that generally used for gilts or castrates while on a semiad libitum feeding system.

A study of correlations among certain morphological traits of progenies from a 6 x 6 diallel cross was made. In general, genotypic correlations were similar in sign to the phenotypic correlations in all but two of the 21 cases, but there were differences in magnitude (nine differed by 0·40 and four of these by more than 0·70). Some estimates of the environmental correlations were large (1·57, 1·52, 0·78, 0·75, 0·73 and 0·54). Positive and significant correlations indicated that improvement in some characters related to forage and seed yield should be possible by selection among the diallel progenies.

Path analysis was used as a means of analysing phenotypic correlation coefficients among seven contemporary variables. The method was employed to analyse the system of all possible correlations among certain plant measurements. By this technique one may find the maximum effect, compatible with the data, which can be assigned to a general size factor (common to all variables) and determine the nature and degree of influence of residual, group, and special factors. In most of these the influence of the general size factor predominated (minor in the case of leaf width, pCX = –0·31; and florets per spikelet, pGX = –0·09). Only two of the 21 correlations required factors in addition to the general size (florets per spikelet and spikelets per panicle, excess correlation –0·46; and leaf width and culm diameter, excess correlation +0·53). Special factors acting on each part separately from the other were present in all cases. The study indicated that the genetic differences in this study were largely in general size and to a small extent in group and special factors.

A diallel arrangement, which incorporated the essential features of the de Wit density replacement series, was employed to study the effects of competition amongst five genotypes of perennial ryegrass (Lolium perenne). Of the five genotypes concerned two were derived from S·24, two were collected from natural populations in South Wales, while the remaining genotype originated from S· 23. These five genotypes were grown as monocultures and in all ten binary combinations. Within each combination there were three mixture proportions, namely 75:25, 50:50 and 25:75. All mixtures and monocultures were represented by two boxes, one of which was cut at 3-week intervals (frequent cutting) the other being cut at 6-week intervals (infrequent cutting). At each cut all plants within the appropriate mixtures and monocultures were harvested individually and their dry weight recorded.

The results obtained over the first 18 weeks of the experiment (i. e. the first three complete growing periods) establish that competition is occurring in nine of the ten binary combinations. Within these nine combinations competition may be classified into one of three groups: first, it may be compensatory, in which the gains and losses incurred by the two components counterbalance; secondly, it may be positive complete complementation, where the advantage gained by the stronger component is such that the mixture performance matches that of the better monoculture, and thirdly, it may be positive over-complementation, where the yield of the better monoculture is surpassed by the mixture. Further tests disclose that a long-leaved S· 24 genotype is the strongest competitor, while a short-leaved, prostrate, indigenous genotype proves to be by far the weakest competitor.

Estimates of the equilibrium proportions for each genotype combination suggest that most combinations are expected to become monocultures of the strongest component, with only the combination between the long-leaved indigenous and longleaved S· 23 genotypes remaining a mixture at equilibrium. None of these equilibria coincides with the proportions required to achieve maximum productivity from a particular combination. The results are considered in relation to the known characteristics of these five perennial ryegrass genotypes, while the wider agronomic implications are also discussed.

An examination of the role played by associate plants in conditioning the behaviour of a competitor was carried out on a diallel arrangement of five perennial ryegrasa genotypes using regression techniques similar to those devised for the analysis of genotype-environment interactions. By far the largest proportion of the significant genotype x associate interaction could be ascribed to differences between the slopes of the fitted regression lines, with the three long-leaved genotypes (A, C and E)having the highest slopes and hence being the most sensitive to changes in the associate environment. Significant departures from the fitted regression lines occurred, however, but these could be traced solely to genotype C.

Theoretical models capable of identifying those conditions under which 50:50 mixtures may be expected, first, to exceed the average of their component monocultures, and secondly, to surpass the better monoculture, were developed. Applying these models to the present experiment confirms that the performance of the 50:50 mixtures generally exceeds the monoculture average, but rarely surpasses the better monoculture.

The scope of the regression technique was broadened to incorporate the 75:25 and 25: 75 mixtures, thereby revealing that the response of the two strongest competitors (C and E) is frequency dependent. Density dependent effects were also uncovered in this material, with genotype C the strongest competitor, being particularly noteworthy in this respect. The role of this regression technique in the development of new and highly productive mixtures is briefly discussed.

Ryegrass populations collected from intensively used swards, both leys and permanent pastures, were compared under spaced plant and sward conditions.

On average, the bred ryegrasses were higher yielding, more resistant to crown rust, and more persistent under intensive conditions than the permanent pasture populations, but there was no significant difference in cold-resistance between these two groups.

The potential yield of dry matter of the best of the permanent pasture populations was similar to that of the highest-yielding leys. Several of even the most intensively used pastures were, however, dominated by ryegrass that was not nearly as high yielding as the best of the bred varieties. In addition to differences in yield of dry matter, there was a wide range in persistency, resistance to low temperature and crown rust (Puccinia coronata), as well as in mean date and variance of inflorescence emergence and in yield of digestible organic matter in dry matter (DOMD). Thus, no one type of ryegrass could be associated with permanent pastures, even when the sample was restricted to a narrow range of managements associated with intensive use.

Some of the highest-yielding swards were based on complex mixtures of ryegrass cultivars; this might give rise to difficulty in relating management to stage of maturity and in predicting the composition of the sward established.

A comparison of survivor material derived from S·23 leys revealed no difference in yield of dry matter or DOMD under sward conditions. Other data, however, showed that the populations differed in yield as spaced plants, rust resistance, cold-hardiness, persistency and date and variance of inflorescence emergence.

There was no indication of ryegrass yield decreasing with the age of the ley from which the plants were derived.

The effects of fatty acids, at low concentrations (0–005-O5 g/1), on the growth of seven species of rumen bacteria were examined. Anaerovibrio lipolytica(strain 5 S), Peptostreptococcus elsdenii(type 2), Bacteroides ruminicola46/52 and Selenomonas ruminantium(strain 17) were unaffected by addition of oleic acid to the medium. Growth of ButyrivibrioB 835 was stimulated by low concentrations of oleic (< 0–01 g/1), lauric (< 0–1 g/1) or capric (< 0–1 g/1) acids while higher concentrations of these acids were inhibitory. Myristic, palmitic and stearic acids were inhibitory at all concentrations tested. Ruminococcus4263/1 was inhibited at all concentrations of the six acids. Production of methane by pure cultures of Methanobacterium ruminantiumwas also inhibited by the additions of long-chain fatty acids. Oleic acid was the most inhibitory of the series of acids. These results are consistent with the reported effects of lipids on rumen function.

The effect of soil water potential of the root media on the vegetative growth, seed and oil yield of sunflower (var. Record) grown in containers under field conditions was investigated.

The weight of shoots and the total leaf area of plants before flowering significantly decreased with decrease in the water potential of the root media. There was a sharp reduction of shoot weight as the potential decreased from —0–32 to — 1–25 bars and then a further slow decline as soil water potential dropped to — 8'6 bars. There were no significant differences in the 100-seed weights and percentage. of oil among the treatments, but the total number of seeds was significantly different.

The data did not indicate the existence of a threshold water potential above which yield was independent of soil water potential, but rather that yield was a continuously decreasing function of soil water potential.

Pure swards of cocksfoot and perennial ryegrass cut on three occasions and of lucerne cut on two occasions were ensiled in test-tube silos after three treatments: (i) unwilted without additive, (ii) unwilted after the addition of formic acid at 0-23 % of fresh weight, and (iii) wilted to a water content of about 70 %, with no additive. Replicate silos were opened at intervals up to 105 days in order to follow the course of fermentation.

Silages from the final sampling could be divided into two clearly defined groups. Those where the lactic acid content, expressed as a percentage of total fermentation acids (L %T), was over 60 (19 silages) were considered stable while those with a value less than 20 (5 silages) were considered unstable.

The addition of formic acid resulted in a reduction in pH of the ensiled material from 5–86 + 0–12 to 4–60 ±0–11. This value changed little during the first 6 days after ensiling but then fell as lactic and acetic acids were formed. Stable silages made from unwilted crops without additive contained more lactic acid than those made with formic acid, but the converse was true for unstable silages. The ammonia content of silages made from unwilted material was always lower when formic acid had been applied. Wilting before ensiling gave stable silages from all crops.

Seed of nine F1 hybrid wheat genotypes was produced by wind pollination. In one trial, grown at two seed rates, the extent of heterosis for yield and two yield components was small and was not affected by seed rate. In an adjacent trial the extent of heterosis in three hybrids was found to be affected by seed size.

In soya beans (var. 3H55F4/149/1) grown in Tanzania, the total dry matter per plant, pod weight/stem weight, shelling percentage, number of nodes per plant, number of pods per plant, percentage number of nodes with pods, number of filled pods per plant, number of branches per plant, and grain weight from side branches decreased with increase in plant density from 74 to 111, 222, and 444 thousand plants per hectare. Grain yield per hectare decreased by 38, 51, and 72% respectively with the increases in plant population, but yield of total dry matter per hectare showed a significant increase with density. Crop growth rate increased with increasing leaf area, which in turn increased with increasing plant density. Relative growth rate, however, decreased with rising population. Over the range of the densities studied grain yield was positively related to number of side branches but negatively related to dry-matter production, leaf area duration and percentage of light intercepted. The proportion of dry matter accumulated in the pods and side branches decreased with increase in population, whereas the proportion accumulated in the main stem increased. Light seems to be the major factor controlling grain yield in this variety of soya bean, low light intensity under the plant leading to a reduction in the number of side branches, number of pods per plant and number of nodes with pods.

Growing wether sheep in metabolism cages were fed a low phosphorus diet (0–7 g P/day) and providing 16 g N/day supplemented with either urea phosphate, monoammonium phosphate or dicalcium phosphate and with appropriate additions of urea to give equivalent additional intakes of phosphorus (1–75 g P/day) and nitrogen (4–6 g N/day).

All three sources of phosphorus and nitrogen resulted in similar and significantly improved phosphorus and nitrogen retentions. There were also very similar effects on urine outputs of phosphorus and nitrogen and on the concentrations of phosphorus and urea in the blood of the sheep.