In a 3-year experiment on a sward of S. 23 perennial ryegrass 21 rates of nitrogen fertilizer ranging from 0 to 897 kg/ha were applied annually on plots cut three, five or ten times per year. The cutting dates within each frequency were decided on the basis of herbage growth stage. Four-parameter exponential curves fitted to the herbage yield data show that the pattern of response to nitrogen application in the five cuts per year treatment was markedly similar to that reported for a previous experiment (Reid, 1970). Alterations in the cutting frequency affected the pattern of dry-matter yield response to nitrogen, but not that of crude-protein yield response. The combined effects of cutting frequency and nitrogen rate are illustrated by response surfaces fitted to the dry-matter yield results using an extension of the equation for the curves fitted to the individual frequency results. These surfaces show that as the number of cuts per year was increased the total yield and the response to nitrogen decreased, but the response was maintained to an increasingly high nitrogen rate. The practical implications of the results are discussed in relation to intensive grazing managements for dairy cows.

Diurnal changes in number of protozoa were examined in two wethers fed once and twice daily with 0·4 kg of concentrate and 0·4 kg of hay per day. The number of protozoa varied from 4·8 × 105 to 12·5 × 105 cells/ml of rumen fluid, depending on the feeding frequency and time of the day. Entodinia formed 96·3%, Holotricha 2·0%, Diplodinia 1·3%, and Ophryoscolex 0·4% of the total counts. All taxonomic groups of protozoa reached maximum concentration immediately before feeding and decreased by about 60·80% during 4·12 h after feeding. Larger decreases occurred in animals fed once daily.

Rumen fluid volume varied from 3·12 to 4·47 l but in different ways due to feeding frequency. Diurnal patterns of dilution rate of rumen fluid were the same in animals fed once and twice daily, showing the decrease from 0·98 1/h at 09·00 h to 0·311/h at 01·00 h. It is suggested that some factors other than dilution rate may be responsible for the decrease of protozoa after feeding.

A stepwise adaptation was carried out on eight sheep through diets containing 10, 24, 44, 60 to a final diet containing 71% maize meal and molasses. The numbers of protozoa in the rumen increased in proportion to amount of readily fermentable carbohydrate fed, up to and including the 60% grain and molasses diet, while the numbers of total culturable bacteria remained essentially constant. However, the proportions of amylolytic and lactate-utilizing bacteria increased, and there was an orderly shift from acid-sensitive to more acid-tolerant species, particularly amongst the lactate-utilizers in response to the gradual decrease in the ruminal pH. Up to this stage the protozoa probably controlled the rate of fermentation by engulfing starch grains and bacteria and were thus able to maintain the pH of the rumen above 5·5. Lactic acid appeared only transiently and the peak values tended to diminish as adptation progressed.

The first day the final diet was fed the ruminal pH decreased to 5·4 or below for several hours. Within 7 days the number of protozoa had decreased by 50–80% and the number of total culturable bacteria increased sharply. Conditions in the rumen became unstable: peak values of D- and L- laotic acid increased by ca. 0·5 HIM, the acetate/propionate ratio decreased to ca. 2 and peak glucose concentration increased t o 3·2–9·5 mM. One animal refused all food for 1 day. Acid-tolerant species of lactate-utilizing bacteria multiplied rapidly in response to the increased production of ruminal lactic acid and the ratio of amylolytics to lactate-utilizers decreased from a mean of 10·7 to 3·6. This controlled the increase in lactic acid and the decrease in ruminal pH, allowing the ciliate protozoa to proliferate and regain control of the fermentation.

The types of cellulolytic bacteria did not change during the experiment. Despite their acid sensitivity, the number of cellulolytic bacteria per gram of ingesta was of the same order after 54 days on the 71% grain and molasses diet (0·5–13·3 × 107) as on the initial high roughage diet (3·2–7·6 × 107).

Three sheep which bloated showed no marked chemical or microbiological differences from the non-bloating animals.

A study of the fractionation of nitrogen isotopes in the diet by cattle is described and the results discussed.

Compared with the diet, urine had a lower ratio of 15N to 14N, but faeces, blood and milk all had a higher ratio.

It is argued that the use of natural 15N as a tracer in grazed ecosystems is more complicated than was at first thought.

Chemical imposition of water leachable germination inhibition was attempted as a means of overcoming wheat seedling wilting after insufficient rainfall. Effective inhibition in aqueous solutions was imposed by abscisic acid, coumarin and by two ethylene releasing preparations, Ethrel and Alsol. Germination inhibition caused by the latter two compounds was found to be associated with effects of the carriers, other than pH, and was not a result of ethylene gas liberation. As evidenced by tetrazolium staining the dormant seed possessed respiratory activity, and imposed germination inhibition, even to the extent of 75%, was not lethal. Rainfall simulation effected by 30 h H2O leaching with a 200 mm precipitation equivalent was ineffective for reversal of germination inhibition caused by abscisic acid and Alsol, limitedly effective in the case of Ethrel, while the coumarin-induced inhibition was relieved to a greater extent.

Sixty-four weaned Awassi ewe lambs were used in the present study to estimate age at puberty and to investigate whether early breeding from such ewe lambs is possible. After weaning at 4 months old ewe lambs were divided at random into two experimental groups. One group, designated as moderate, was fed to attain 40 kg live weight at 12 months of age, while the other (high) was planned to reach 50 kg at the same age. Fertile rams were run with the ewe lambs at 6 months of age. Twenty ewe lambs, 10 from each treatment, were slaughtered and their ovaries were examined for the presence of corpora lutea and largest follicles.

The overall age at first oestrus was found to be 293 days. Ewe lambs of the high nutritional treatment reached puberty earlier than those of the moderate one (274 v. 312 days). Likewise, single-born lambs reached puberty earlier than twin-born ones (273 v. 312 days). Treatment differences explained 16·5% while type of birth explained 16·3% of the total variance in age at first oestrus. Ewe lambs of the high nutritional treatment experienced more heats than those of the moderate one. Simple correlation coefficients between age at first oestrus and date of birth, daily gain and live weight at puberty were 0·21, 0·09 and 0·75, respectively. Results indicated that ovulation may not occur during the first and second oestrus. From 44 ewe lambs only 12, 10 from the moderate and 2 from the high treatment, lambed 13 viable lambs. Reasons for such a low conception rate (27·3%) are discussed.

The effects of lodging on the seed yield of S. 23 and S. 24 perennial ryegrass were investigated in a series of field experiments from 1973 to 1976. Natural lodging severely reduced seed yield in all years as a result of a decrease in the number of seeds per unit area. Controlled lodging at different stages of crop growth produced more variable results, indicating that lodging may affect both pollination and seed development. Disturbance of the crop during anthesis in order to aid pollination did not improve seed yields, possibly as a result of damage incurred.

S. 24 perennial ryegrass harvested in June, and subsequently in September from the same sward was conserved by rapid freezing. The digestion of the carbohydrate and protein components of the two diets was investigated, using sheep fitted with re-entrant cannulae at the proximal duodenum and terminal ileum and consuming daily 950 g of herbage dry matter.

The higher content of soluble carbohydrate and the lower content of protein in the spring-cut herbage compared with the autumn cut, led to a more efficient fermentation in the rumen with a higher yield of volatile fatty acids per mole of substrate degraded, a proportionately higher yield of propionic acid and a substantially greater net gain of protein between mouth and duodenum on the spring cut herbage. Consequently, the quantity and composition of the amino acids entering the small intestine, or being absorbed therein, were not significantly different, despite the higher protein content noted on the autumn herbage.

The total energy absorbed was markedly higher for the spring herbage (11·2 MJ/kg D.M.) compared with the autumn herbage (9·5) and the energy absorbed as protein from the two diets comprised 20 and 26% of total energy absorbed respectively.

The possible causal mechanisms within the rumen, and the subsequent effect of these on nutrient supply are discussed in relation to the well-established higher efficiency of use of metabolizable energy (ME) of spring-cut herbage compared with autumn cut herbage of similar apparent energy digestibility.

Twelve genotypes of cauliflower were grown in two seasons from six seedling propagation treatments in three sequential sowings. There was a high genotypic component of variation for curd weight, indicating that this character can be improved by breeding. A large genotype × environment interaction included genotypic differences in stability to the environment, notably in the self-compatible genotypes. Mean curd weight and stability of genotypes to the environment for this trait were uncorrelated, indicating that high weight and high stability could be bred into a single variety.

In these experiments lodging not only decreased the number of seeds harvested, but also had an effect in determining which spikelets on the ear set most seed. These data have also shown that many more seeds are set than are harvested, even when the crop is not lodged. It is suggested that there is a lack of assimilate supply to fill the developing seeds, some of which abort, allowing the remainder to attain a viable seed weight. Mechanical support of the crop may increase the assimilate supply to the seed thus allowing seed further up the ear and spikelet to develop fully.

Three cultivars of P. vulgaris, tested 39 and 69 days after planting, differed in the extent to which nitrogen (C2H2) fixation and nodule development were affected by plant density.

At the 39-day harvest the climbing cultivar P590 declined in fixation from 15·1 μmol C2H4 produced/plant/h at 8·5 plants/m2, to only 4·2 μmol C2H4 produced/plant/h at 41·5 plants/m2; while the prostrate P498 showed consistently high fixation from 8·5 to 41·5 plants/m2. Variation in nitrogen fixation could be explained largely by change in nodule weight, though specific nodule activity (SNA) was affected, particularly in the cultivar P590. Since the percentage soluble carbohydrate in nodules of two varieties increased at certain planting densities while SNA decreased, some nodule dysfunction is possible.

Density changes affected leaf, root and stem development in all cultivars, leaves on the lower nodes being most severely affected.

At the 69-day harvest two varieties were advanced in filling the pods and showed poor nodulation and limited fixation, even at the widest plant spacings, while nodulation and nitrogen (C2H2) fixation in the third variety, which had just flowered, showed optima similar to the earlier harvest.

The effect on sward production of grazing by sheep during different periods of the winter and the effect of different dates of ceasing grazing in late winter-early spring were measured in field experiments by cuts during the spring and summer and by botanical analysis.

Winter and early spring grazing reduced herbage yield in April, May and June, but not subsequently. Nitrogenous fertilizer applied when grazing ceased approximately counterbalanced the reduction in yield due to grazing. The grazing treatments had little or no effect on botanical composition. The size of the reduction in yield due to grazing was such that it might reasonably be explained in terms of the date on which grazing ceased and the amount of photosynthetic tissue left at that date. The amount of yield added during a given period in the spring appeared to be very greatly affected by the amount of photosynthetic tissue present at the beginning of that period and it is suggested that this is a partially hidden cost of winter and early spring grazing which should be more fully researched.

The 32 combinations of applying or not applying nitrogenous fertilizer on five dates, with 6-week intervals between dates, during one treatment year were compared in three field experiments with Italian ryegrass (Lolium mvltiflorum). Phosphorus (P)and potassium (K) were applied at a uniform, high rate to all plots. All plots were harvested, by cutting, five times during the treatment year and once in May of the subsequent year.

Dry-matter yields and dry-matter yield responses to N were lower at the September and October harvests than at the May, June and July harvests. Where no N was applied 6 weeks before a harvest, N applied 12 weeks before that harvest generally increased yields of dry matter, N, P and K. On the other hand, where N was applied 6 weeks before a harvest, N applied 12 weeks before that harvest tended not to increase dry-matter yield and tended to reduce P and K yields. Applying 420 kg N/ha/year compared with nil approximately trebled the amounts of dry matter, P and K harvested in the treatment year. At the May harvest in the subsequent year dry-matter yield was increased by N applied in the treatment year, for all five application dates, although the previous autumn there had been no positive residual effect of the early applications. Apparent recovery of N was low compared with that recorded with Italian ryegrass in Cambridge. The content of N, as well as P and K, in herbage in May was reduced by the application of N the previous year. In the 1972 experiment the proportion of ‘stem’ in the harvested produce was markedly increased by N application. The size of this effect may have been associated with the rather small amount of soil N available. Applied N increased the number of tillers in the sward, but this effect appeared to be rather short-lived. A major reason for the positive effect of applied N on dry-matter yield, including the positive residual effect, appeared to be the increase in leaf blade length and probably sheath length due to N.

The effect of herbage allowance and milk intake upon herbage intake and performance was investigated using 48 Hereford × Friesian calves purchased at 10–12 days of age and reared on reconstituted milk substitute. Groups of 24 calves were fed low (L) or high (H) daily quantities of milk normally associated with 240-day lactation yields of 1000 or 2000 kg. Six calves on each milk treatment were allocated to four daily herbage allowances during the grazing season. These were 20, 40, 60 or 80 g/kg herbage dry matter/kg live weight.

There was no effect of herbage allowance before day 95; thereafter both herbage intake and live-weight gain of the L20 and H20 groups were depressed. The effect was greatest for the L calves. Additional milk consumption reduced herbage intake at all herbage allowances. Milk intake influenced the extent to which calves were buffered from the effects of a low herbage allowance.

The paper reports on a study, conducted in four successive seasons, of sexual development and breeding activity in females of the Iceland breed, the only breed of sheep kept in the country. The ewe lambs normally attained puberty in their first year of life, on average at 7 months of age, with marked individual variation in both age and body weight at first oestrus. Ewe lambs always showed oestrus on average slightly later than mature ewes (2–9 years), the mean date of onset of the breeding season of the latter being 8 December, however, with considerable individual variation. Furthermore, ewe lambs had a shorter breeding season (1–4 months) than ewes (4–6 months) and they appeared to experience more silent heats resulting in less regular cyclic activity. There seemed to be a minor increase in the duration of the oestrous cycle with age and ewe lambs clearly exhibited shorter oestrus (heat) than ewes. With seasonal breeding activity ranging from November to May the mid-breeding season occurs some 4–7 weeks after the shortest day.

In experiments over 3 years (1974–6) cow slurry in the range 0–112·5 t/ha and ammonium nitrate in the range 0–120 kg N/ha were applied to field plots factorially to test the effects on the yield and quality of spring barley grain.

In 1974 slurry application markedly improved the grain yield (cv. Golden Promise) at each rate of inorganic N and increased grain size. Applying N fertilizer with more than 37·5 t slurry/ha reduced grain yield below the maximum. Grain with the highest crude protein content (15·1 %) was obtained from a combination of slurry and inorganic N. The residual effects of the slurry treatments gave satisfactory grain yields in 1975 without additional fertilizer.

Grain yields (cvs Julia and Abacus) in other experiments carried out on a different soil type in 1975 and 1976 were approximately half those obtained in 1974, due in part to drought conditions. The pattern of the results was similar. Heaviest grain yields were harvested from plots receiving 70 t slurry/ha with no additional N.

From gel filtration studies it has been found that more than 50% of organic phosphorus dissolved in pig slurry is contained in compounds of high molecular weight. Various ions, e.g. calcium, copper, orthophosphate, are bound by these compounds. From the purine and pyrimidine base composition and resistance to acid and alkali treatment it follows that these organic compounds probably are complexes derived from polydeoxyribonucleotides (DNA).

The effect of drying pig slurry at various temperatures (0–100 °C) on the solubility of phosphorus, calcium and copper after redispersion of the dried slurry was investigated. The solubility of organic phosphorus was not affected by drying and redispersion in water, but the amount of phosphorus contained in dissolved organic molecules of high molecular weight decreased on drying at higher temperatures. The solubility of copper was also not affected by heat treatment. The solubility of inorganic phosphorus is mainly related to the solubility constants of mineral phosphates. On the other hand the total solubility of the cations involved is determined by complex formation.

In a study of two coarse wool breeds (Awassi and Karadi) and their reciprocal crosses, data were obtained on the mean fibre length, mean fibre diameter, fibre type ratio, medullation and on the effect of some environmental factors on these traits. Reciprocal crosses showed intermediate values, in growth rate of fibres, percentages of fibre types and medullation, between those of the parental breeds. Sex exhibited a significant effect at weaning only, on fibre length. Heterosis in fibre length, at the two ages, was small and negative. Maternal influence on fibre length was small and not significant. Fibre length in Karadi sheep showed the highest frequency of bimodal distribution whereas Awassi showed the lowest. Awassi × Karadi was closer to Karadi and Karadi × Awassi had greater affinity to Awassi in the frequency of samples showing bimodal distribution.

Reciprocal crosses had larger diameter, at weaning, than those of the parental breeds. At 1 year of age they assumed an intermediate position between the pure bred parents.

At weaning, the two reciprocal crosses showed a highly significant heterosis in fibre diameter; its value decreased with advancing age and it showed no significant effect at 1 year of age.

Maternal influence on fibre diameter was very small and not significant.

Karadi × Awassi and Karadi samples had the highest percentage of samples showing bimodal distribution of fibre diameter.

Samples with bimodal distribution of both length and diameter, indicating two coats, had the highest frequency in Karadi followed by Karadi × Awassi; Awassi showed the lowest value.

Percentages of fine, coarse and kemp fibres were significantly affected by breed and age of dam. Type of birth showed a significant effect only on percentage of coarse fibres.

Karadi wool might be more suitable for carpet manufacturing. It excelled the other groups in the bimodal distribution of both length and diameter as well as in medullation. Cross-breeding increased the bimodality of fibre distribution.

Exotic accessions of Phaseolus vulgaris selected for seedling cold tolerance by Austin & Maclean (1972) in a test in controlled environments were grown in a field experiment at Wellesbourne in 1974. Yields of up to 4·;7 t/ha at a plant density of 34 plants/m2 were obtained. In 1975, six selected accessions were grown at 21 plants/m2 at six different sites. Mean site yields ranged from 1·0 to 3·1 t/ha. The six accessions all had better emergence and higher yields than two commercial cultivars used as controls. The genotype × site interactions for yield (and for yield components) were small. The variation in yield between accessions (from 2·0 to 2·5 t/ha) was smaller than the variation in yield between sites. Variation in yield components tended to be additive between sites, and compensatory between accessions. There was a negative correlation between crude protein content and yield across accessions; the correlation between protein content and yield across sites was not significant. Accessions differed significantly in the amount of green leaf still attached to plants at harvest. This variation was not related to maturity as judged by moisture content of the seed. There was a negative correlation across accessions between the weight of leaf per plant at harvest and harvest index (the ratio of seed weight to stem weight).

The results of 80 calorimetric experiments with sheep and cattle, mostly conducted in Scotland, were analysed using a generalization of the Mitscherlich equation R = B(l–exp(–pG))–l, where R is daily energy retention and G daily gross energy intake, both scaled by dividing by the fasting metabolism. The relations between gross energy and metabolizable energy were also examined. Methods of fitting the Mitscherlich equation and the errors associated with it are presented.

It is shown that the gross energy of the organic matter of feed can be estimated from proximate principles with an error of ±2·3% (coefficient of variation) and that provided different classes of feed are distinguished, the metabolizable energy of organic matter can be estimated from gross energy and crude fibre content with an error of ±6·9%. Parameters of the primary equation made with cattle agreed with those made with sheep and there was no evidence of non-proportionality of responses on substitution of feeds in mixtures.

The efficiency of utilization of gross energy for maintenance and for body gain of energy was related to the metabolizability of gross energy and, in addition, to fibre or to protein content. Prediction equations are presented which describe these relationships.

It is shown that the primary equation can be manipulated to express a number of biological concepts and that its two parameters B and p can be simply derived from estimates of the two efficiency terms for maintenance and production.

The results are discussed in relation to the design of feeding systems for ruminant animals and to the derivation of optima in their feeding.