The interacting effects of genotype and density on the yield of dry matter by mature shoots were examined at Oxford, England. There were six hybrids, either pure dent or flint × dent crosses, together with two open-pollinated flint varieties of very early maturity. Over a range of 15 densities (5·0–30·8 plants/m2) for all the genotypes the relationship between the yield of the shoot and density can be adequately described by the reciprocal equation 1/w = A + Bp, where w = weight per plant, p = number of plants per unit area and A and B are constants for any particular set of conditions. Values of both 1/B (asymptotic yields) and 1/A (weight per plant at very low densities) were dependent upon the genotype. In a regression analysis between 1/w and p, the variance of 1/w was over 40 times as great at high as at low densities and a weighted analysis was necessary. Some hybrids approached maximal yields at 5 plants/m2, whereas others required a density of 10–15 plants/m2. The possible reasons for these interactions are discussed and improvements in experimental design suggested.

Eighteen varieties of safflower were studied in a randomized block design with five replications. Data on fourteen quantitative characters were recorded. Appreciable variability was displayed by all characters, especially yield and number of heads/plant. The heritability estimates ranged between 65 and 98%.

Seed (achene) yield gave a significant positive genotypic correlation with number of seeds/head, head width, bract width and oil content. The 100-seed weight was significantly negatively correlated with the number of seeds/head and plant height at maturity. The genotypic correlations between yield/plant and four other traits were partitioned into direct and indirect effects. The highest direct positive contribution to yield was given by plant height, which had also a positive indirect effect via number of heads. The direct effect of the number of heads/plant was negative and the indirect effect via head width was positive.

The technique of visual appraisal of intact sides of beef was used on most of the carcasses previously described in Parts I and II of this series. Tests of discrimination and consistency were carried out for each of the judges taking part, and their assessments were compared with the results of subsequent dissection of the carcasses.

It was found that visual appraisal of the subcutaneous fat content of a carcass was very good, especially with the aid of photographic standards, though a curious tendency to match the standards consistently to carcasses of a higher proportion of fat than those used for the photographs themselves was apparent. This did not materially affect the use that can be made of visual judgements in predicting fat content and it was found that expert judgement alone is capable of predictive accuracy roughly equal to that obtained from simple measurements, though not as good as that obtained by partial dissection, as described in Part II. Equations are given for the prediction of carcass composition, using visual appraisal in combination with other variables.

The appraisal of conformation was not so successful; reasons for this are advanced, and suggestions made for future improvement.

The growth and yield of five highland varieties of tropical maize were studied. Grain yields were between 4·7 and 8·8 t/ha. Crop growth rates (C) increased to a maximum of between 25 and 35 g/m2/day at silking and then declined. Grain growth rates (maximum 21 g/m2/day) exceeded current C during most of the grain-filling period.

After silking, when C exceeded grain growth rate, dry matter accumulated in the stem and husk, resulting in an increase of from 200 to 600 g/m2. Later, as grain growth rate increased and exceeded current C, some of this accumulated material was incorporated into the grain, and stem weight decreased. A comparison of the dry weight changes after flowering in these varieties with those reported for a hybrid that yielded 12 t grain/ha indicates that the smaller yield of the Mexican varieties was associated with smaller grain growth rates and the incorporation into the grain of a smaller fraction of the dry weight produced after flowering. These results suggest that the capacity of the grain ‘sink’ to utilize assimilates limited yields in the tropical varieties.

The growth and yield of three tropical varieties of maize were studied at two elevations in Mexico: Poza Rica (60m) and Tlaltizapan (940m). Grain yields were between 3·5 and 8·5 t/ha. The growing period was longer and the crop produced more dry weight and yield at Tlaltizapan than at Poza Rica. Crop growth rates (C) increased to a maximum of about 35 g/m2/day at both sites and then declined. Grain growth rates (maximum 35 g/m2/day) exceeded current C during most of the grain filling period. After silking when C exceeded grain growth, dry matter accumulated in the stem. Later as grain growth increased and exceeded C, some of the accumulated material was incorporated into the grain and stem weight decreased. The dry weight increase after flowering was similar at the two sites, but the grain yield at Tlaltiapan was larger because a larger proportion of the dry weight increase was incorporated into the grain than at Poza Rica. The results indicate that at both sites grain ‘sink’ capacity was limiting yield.

Fifteen hundred Thornber 808 and 909 female chicks were reared for 126 days from day-old on conventional diets or on diets with 200 g field beans/kg. From 127 to 490 days they were offered a control diet or diets with 100 or 200 g field beans/kg. When the diets fed from 127 to 490 days contained 0 or 200 g field beans/kg their food intakes were 45·4 and 44·6 kg/bird and they laid 235 and 233 eggs, respectively. The differences were not significant. Efficiency of food conversion to egg mass was significantly reduced from 0·310 to 0·303 when beans were increased from 100 to 200 g/kg of diet and mean egg weight was significantly reduced from 58·9 to 57·6 g when beans were included at 200 g/kg of diet in the 127- to 490-day period.

The effects of various stimuli on the secretion of urea and ammonia in gastric juice were examined in sheep with innervated pouches in the fundic and pyloric regions of the abomasum.

Histamine, pentagastrin and feeding increased the rate of secretion and acidity of fundic juice, but had little or no effect on the concentration of urea and ammonia. The increased output of gastric juice meant that more urea and ammonia entered the abomasum in the secretions. The rate of secretion of pyloric juice was also increased by histamine and feeding, and there was an indication that histamine increased the concentration of urea + ammonia in the secretions after a period of starvation.

Intravenous injections of urea increased the concentration of ammonia in abomasal liquor. This was due in part to higher levels of ammonia in ruminal liquor passing to the abomasum, and to higher concentrations of urea + ammonia in gastric juice. The concentration of urea + ammonia in fundic juice was 45·0±1·1% of the plasma urea level, and 60·4±1·5% in the pyloric secretions.

The major nitrogenous components of gastric juice were determined in sheep with innervated pouches in the fundic and pyloric regions of the abomasum.

Fundic secretions contained mean levels of 36–55 mg total-N/100 ml in the fluid fraction, and pyloric secretions contained 38–70 mg/100 ml. Of this, 65–76% and 75–91% could be attributed to protein, in the fundic and pyloric secretions respectively. Tungstic acid was found to be the most suitable precipitant of proteins in the gastric juice.

Dissolved mucin accounted for 2–16% of the total-N in the fluid fraction of the fundic secretions, and for 6–14% in the pyloric secretions. Urea + ammonia contributed 2·8–13·4% of the total-N.

The daily output of nitrogen by the fundic region of the abomasum, including that contributed by the cellular debris and visible mucus, was calculated at 0·46–2·4 g. The comparable values for the pyloric region varied between 0·05 and 0·37 g N/day.

The electrophoretic patterns of the abomasal secretions were similar to those reported for human gastric juice.

The common use of range by different types of animals may be more efficient than separate grazing by each type in that they may be complementary in their utilization of forage. Also, under certain pasture and range conditions the danger of permanent damage by over-grazing can be critical. This paper presents a method of assessing the optimum carrying capacity of range under single or common use subject to constraints on the level of utilization of forage plants. The joint optimum carrying capacity for the animal types may vary as the management objective varies between maximum profit, maximum animal gain or maximum utilization of forage, all subject to the same protection against over-grazing.

In simulated swards of perennial ryegrass the production of aerial tillers, in which the growing point has been raised some distance above ground level by internode extension, depended upon the genotype and management. In both genotypes studied decreasing the height of defoliation from 10 to 2·5 cm nearly halved the incidence of aerial tillering, while the presence of a mulch of chopped straw at the base of the sward more than doubled the occurrence of these tillers. The effects of management are also discussed in relation to herbage production. The differences between the genotypes in the degree of aerial tillering suggests that selection for reduced aerial tillering may be of benefit.

Six spring varieties of oats were sown in a glasshouse in winter and in spring. The grain was analysed for oil, protein and kernel content and 1000-grain weight, and the maturation period was measured.

Oil content varied from 2·4 to 7·9% and protein content from 7·9 to 16·3%. Varietal differences in oil content between varieties were recognized and these were maintained at both sowing dates.

Winter sowing, in comparison with spring sowing, resulted in an increase in oil and kernel content and 1000-grain weight, and a decrease in protein content. The increased oil content was partly due to increased kernel content, while the decrease in protein content was partly due to changes in 1000-grain weight.

The maturation period was not affected by sowing date, but was positively correlated with oil content. Oil and protein content were not negatively correlated, and there were indications that it may be possible to select varieties which will produce grain high in both oil and protein.

In two experiments frozen heather (Calluna vulgaris, L. Hull), which contained 85–90% of the current season's shoots, was offered ad libitum to castrated male sheep. In one experiment, heather harvested in July, September, November and March was offered to six sheep per harvest, D.M. digestibility fell from 55.9% in July to 41.9% in March, with the greatest decline occurring after flower development in August. There were no significant changes with season in voluntary intakes, which were low, ranging from 29 to 39 g D.M./kg W0.75/day. Apart from the July harvest, intakes of digestible D.M. were insufficient to maintain the sheep. The apparent digestibility of N(14·3–42·2%) and plasma urea N values (5–6 mg/100 ml) were low and undigested N of dietary origin in the faeces was high (25–45%). Sheep offered the September, November and March harvests were in considerable negative apparent balances of N and it was calculated that the sheep were in a negative balance of truly digested N. In a second ex-periment, heather harvested in August from pioneer, building and mature stands was offered to six sheep per harvest. There were no significant differences between stands in voluntary intake and digestibility.

Four young females of four ruminant species, namely cow, buffalo, sheep and goat were used to study the utilization of sun-cured berseem hay (20·6% CP) fed in long form during a 28-day experimental period. Voluntary intake of hay was estimated during the last 10 days and digestibility of feed nutrients and nitrogen balance during the last 6 days.

The digestibility coefficients of dry matter (D.M.), organic matter (OM), crude protein (CP), crude fibre (CF), ether extract (EE) and nitrogen-free extract were higher for sheep and goat than for cow and buffalo but such differences were significant for D.M., OM and CP only. The daily D.M. intake was 3·56, 3·17, 0·92 and 0·63 kg/animal and 82·5, 81·2, 70·4 and 65·1 g/kg W0.75 in buffalo, cow, sheep and goat, respectively, but intake of total digestible nutrients (TDN) relative to metabolic body size was similar for all species.

Buffalo was superior to the other three species and cow to sheep and goat in ability to retain nitrogen. Berseem hay fed ad libitum supported a daily gain of 742, 500, 71 and 31 g in young female buffaloes, cows, sheep and goats, respectively. Digestible CP values of 13·33, 13·47, 15·38 and 15·01% and TDN values of 59·8, 57·6, 70·4 and 77·6% were obtained for cow, buffalo, sheep and goat, respectively.

The quantity of in vitro digested cell wall was determined in the separated leaf and stem of Digitaria decumbens (pangola grass) fertilized at three different levels of nitrogen and cut after two different periods of regrowth. The treatment means ranged from 39·6 to 41·5 g digested cell wall per 100 g forage organic matter in leaf, and from 37·5 to 41·6 g in stem. For both leaf and stem the lowest mean amounts of digested cell wall were associated with the highest levels of fertilizer and the longer periods of regrowth. The results for nitrogen fertilizer were consistent with those from previous in vivo digestibility experiments, but when the effect of the total cell wall on digested cell wall was taken into account there were inconsistencies. The previous in vivo digestibility data were used in conjunction with the present results in support of a view that interpretation of digestibility data for grasses is best made by reference to a constant digested cell wall of 39·5 g/100 g forage organic matter.

A method of including urea into whole grains is described. The whole grains were found to absorb completely a saturated solution of urea.

The method gave the different cereals examined (barley, oats, wheat and maize) a homogeneouis distribution of urea and increased the voluntary intake of whole grains by lambs. The evolution of NH3 in the rumen liquor was slightly slower when urea was absorbed into the grains than when it was included as urea crystals. The N content in the urea-treated grain was not changed after 6 months of storage.

A field experiment was made on a sandy clay loam soil during the rainy seasons of 1967 and 1968 to study the relative efficiency of urea, N-serve treated urea, AM-fertilizer, IBDU fertilizer and nitrogen-enriched coal for the rice variety IR-8. Nitrogen-enriched coal supplied very little nitrogen to rice. All other materials were superior to urea. Largest yield of rough rice and nitrogen uptake was obtained with IBDU. The yield of rough rice given by AM-fertilizer was equal to that with IBDU in 1968; in that year both AM-fertilizer and N-serve treated urea supplied as much N to the crop as IBDU. Yield of straw showed no significant difference between these three materials in either year. Ammoniacal and nitrate nitrogen in soil at flowering and at harvest of the rice was most in plots receiving IBDU followed by those receiving AM-fertilizer, N-serve treated urea and urea. Mineral nitrogen in plots receiving N-enriched coal was only slightly more than in control plots.

In order to assess the potential value of milk conductivity sensors for the detection of subclinical mastitis, measurements have been made manually on quarter foremilk samples for 10–74 days from 44 cows in two herds. Some measurements were also made of quarter cell counts and yields but the true status of the cows was established by bacteriological examination near the end of each run.

For uninfected cows, conductivities of the four quarters tended to move in parallel from day to day whereas for infected cows there were usually substantial departures from parallelism. A statistic which is a measure of departure from parallelism is the quarter × day interaction mean square (I.M.S.), the magnitude of which was used to discriminate between infected and uninfected cows. Using conductivity data obtained at the time of the bacteriological examination, I.M.S. correctly identified all 19 un-infected cows and 24 out of 25 infected cows, the single misclassified cow being only mildly infected. The procedure was further tested on data obtained from one of the herds a year later. In this case, using the I.M.S. limits established the year before, 14 out of 18 infected cows were correctly identified, the four failures being only mildly infected. With nine uninfected cows, there were three false positives but these cows were all pregnant and had been lactating for 44 weeks. Although special limits may have to be set for cows in late lactation, two of these animals had been infected during the lactation, so that conductivity changes may reflect past damage to the udder.

The same data used to set I.M.S. limits were also examined in simpler ways that required little or no calculation. These were ‘differential conductivity’ (the quarter with the highest conductivity divided by the value for the lowest), ‘absolute conductivity’, ‘mixed conductivity’ (mixed foremilk from all four glands) and ‘out-of-balance conductivity’ (the product of the conductivities of the fore quarters divided by the product of the hind quarters or vice versa). These methods of analysis were all less sensitive than the I.M.S. test for parallelism. Differential conductivity, absolute conductivity and mixed conductivity all detected severe cases but missed more mild cases. Out-of-balance conductivity was much less satisfactory because it missed some severe cases.

Nitrification of aqueous ammonia, and its uptake by grass, are slower when the amount of NH3-N injected per unit length of slit is increased and as a result crop yield is spread more evenly over the growing season. Measurements of the amounts of NH4-, NO3- and NO2-N in the soil, made at intervals from February until October, and computed diagrams showing their distribution in soil under grass, are presented. We conclude that, at average current rates of application, most of the aqueous ammonia used for grass in England and Wales is probably not applied along the injection slit in sufficient quantity to allow it to persist throughout the summer.

Several models have been proposed in the literature relating gain per animal (Ya) and stocking rate (x) from grazing experiments. Results from an experiment in which tropical pasture species were grazed continuously by beef cattle at a number of stocking rates (Jones, 1974) were used to examine this relation. A simple linear model of the form y = a − bxfitted the data well. Production per hectare (Yh) was related to stocking rate by yh = ax − bx2.

Stocking rate for maximum gain per hectare (the optimum stocking rate) on each pasture could be calculated from the linear regression by a/2b.

Data from a number of stocking rate experiments in tropical and temperate environments were examined to see if this relation held for a wider range of stocking rates and pasture types. Results were expressed on a common basis by calculating the optimum stocking rate and relating ratios of gain to ratios of stocking rate relative to that at the optimum.

For gain per animal, the overall relation obtained: Ya = l·999–0·999x (r = –0·992; P < 0·001; n = 114) did not differ significantly from the expected linear relation: y = 2−x. Linearity was established over the range 0·18–2·0 times the optimum stocking rate. At rates greater than twice the optimum, animal gain was negative. When expressed as gain per hectare (Yh) the quadratic equation Yh = 2x − x2 gave a good fit to the data over this range.

It is suggested that, since the relation between production per animal and stocking rate (animals/ha) remains linear over a wide range of stocking rates, two rates of stocking (with replication) may be adequate for grazing experiments and these would not have to span the optimum stocking rate in order to predict gain at the optimum stocking rate.

Winter bean crops, mainly of the variety Throws MS, were surveyed for proportions of cross-bred seed, using hilum colour as a genetic marker. In 1971 a significantly greater proportion of cross-breds was detected in random samples taken from the centre than in similar samples from the border of three fields and from the total of all seven fields. An hypothesis is proposed that pod setting at the centre was limited more than at the border by a factor such as plant competition and chocolate spot at a time when selfing was enforced due to a general lack of bee visitation, or else inbred embryos aborted more under the stress of disease in the centre. No differences between centre and border were found in 1972 except for a greater proportion of cross-breds from the border of a Maris Beagle field and this only applied to parent plants of certain genotypes.

Significant differences were also found between fields and between seasons. There was a significant regression of percentage selfing on field size but there was no evidence that bees failed to penetrate to the centre of large fields.

Implications for variety development, testing and purity are discussed.