Showing papers in "The Journal of Agricultural Science in 1985"

Number of kernels in wheat crops and the influence of solar radiation and temperature

Abstract: The number of kernels per m2 (K) in well managed and watered wheat crops was studied using results of experiments in Mexico and Australia in which short spring wheat cultivars were subjected to independent variation in radiation, largely via artificial shading, and in temperature. Also crops subjected to differences in weather (year), sowing date and location within Mexico, revealed responses to the natural and simultaneous variation which occurs in radiation and temperature. Responses in K were interpreted in terms of spike dry weight at anthesis (g/m2) and number of kernels per unit of spike weight.K was linearly and most closely related to incident solar radiation in the 30 days or so preceding anthesis, herein termed the spike growth period; for the cultivar Yecora 70 with full ground cover the slope was 19 kernels/MJ. This response seemed largely due to a linear response of crop growth rate to intercepted solar radiation. The proportion of dry weight increase partitioned to the spike increased somewhat with reduced radiation. Also increasing temperature in the range 14–22 °C during this period reduced K (slope approximately 4% per CC at 15 °C). The cause appeared to be lower spike dry weight due to accelerated development. The number of kernels per unit spike weight at anthesis was little affected by radiation or temperature, and averaged 78±2/g for the cultivar Yecora 70.With natural variation in radiation and temperature, K was closely and linearly correlated with the ratio of mean daily incident or intercepted radiation to mean temperature above 4·5 °C in the 30 days preceding anthesis. As this ratio, termed the photothermal quotient, increased from 0·5 to 2·0 MJ/m2/day/degree, K increased from 70 to 196 × 102/m2. These responses of K to weather, sowing date and location were closely associated with variation in spike dry weight.It was concluded that the ratio of solar radiation to temperature could be very useful for estimating K in wheat crop models. Also the analysis of K determination in terms of spike dry weight appeared promising, and suggests that wheat physiologists should place greater emphasis on the growth period immediately before anthesis.

An empirical model relating crop yield to weed and crop density and a statistical comparison with other models

Abstract: A hyperbolic model relating crop yield to weed density is extended to include crop density as a further variable. Other models were obtained from published sources, eight being originally applied to yield of above-ground biomass and six to marketable yield. Data were obtained from a field experiment in which spring wheat and spring barley were planted either in monoculture or together and at a range of densities. Further data were obtained from a published experiment on Sinapis alba and barley grown in containers. The models were fitted to data using maximum likelihood estimation. Comparisons of residual sums of squares showed that for the wheat and barley field experiment biomass yield and marketable yield were sufficiently described by a three-parameter model. The Baeumer & de Wit (1968) equation proposed for replacement series experimental designs is considered reasonable for the analysis of field additive designs provided the parameters are interpreted in agronomic terms. For the Sinapis alba and barley experiment more complex models could be justified.

Influence of caecectomy on digestibility of amino acids by roosters fed distillers’ dried grains with solubles

Abstract: Several laboratories are currently using the rapid excreta collection assay desoribed by Sibbald (1979), or a modification thereof, to measure digestibility of amino acids (AA) in feedingstuffs for poultry. The use of faecal or excreta collection assays to measure utilization of dietary AA has been frequently questioned because of the unknown effects of gut micro-organisms on AA excretion. These effects may be large with swine (Holmes et al. 1974) and thus many researchers have used ileal digesta collection to measure AA digestibility with pigs (Zebrowska, 1978). The question on significance of microbial effects is less clear with poultry. Some studies with germ-free chicks suggested that influence of the hindgut microflora on digestibility of protein and AA was significant (Salter & Coates, 1971; Elwell & Soares, 1975), whereas others indicated that these effects were small and probably negligible (Salter, Coates & Hewitt, 1974; Salter & Fulford, 1974). More recently, Parsons, Potter, Brown, Wilkins & Bliss (1982) concluded that microbial fermentation in the hindgut may have a significant effect on AA excretion by poultry, but to a much lesser extent than swine.

The relative resistance to escape of leaf and stem particles from the rumen of cattle and sheep

Abstract: In a study of the effect of animal species on the threshold particle size leaving the rumen, two grasses cut at two stages of growth and one mature legume were separated into leaf and stem fractions and fed to cattle and sheep. Samples of rumen digesta and faeces were used to determine the validity of using a 1·18 mm porosity screen to separate the rumen particles into large and small pools when studying escape of particles from the rumen. Samples of rumen digesta and faeces were collected for the determination of particle size by wet sieving and the calculation of resistance of particles to passage from the rumen relative to small particles retained on a 0·15 mm sieve.Particles 0·5 mm had a mean relative resistance to passage of 2·0 and 2·6 for cattle and sheep respectively, compared with resistance values of between 10·9 and 31·2 for particles between 1·18 and 2·36 mm. It is suggested that there is no justification for using different threshold particle sizes for sheep and cattle and that a 1·18 mm sieve may be used to divide the rumen contents of both cattle and sheep into two pools of particles with high and low relative resistance to passage from the rumen.

The effects of carbohydrate supplements on ruminal concentrations of ammonia in animals given diets of grass silage

Abstract: Chamberlain, D. G., Thomas, P. C., Wilson, W., Newbold, J., Macdonald, J. C. (1985). The effects of carbohydrate supplements on ruminal concentrations of ammonia in animals given diets of grass silage. Journal of Agricultural Science, 104 (2), 331-340.

The cellulase content of 15 species of entodiniomorphid protozoa, mixed bacteria and plant debris isolated from the ovine rumen.

Abstract: The cellulolytic activity of cell-free extracts of 15 species of entodiniomorphid protozoa grown in vitro and under two conditions in vitrohas been measured using six different assays with substrates varying in complexity from carboxymethylcellulose to microcrystalline cellulose. Although there were differences between the assays, the highest activities were found in Eudiplodinium maggii, Epidinium ecaudatum caudatum and Ostracodinium obtusum bilobum with little or no activity in five Entodiniumspp. There was no consistent effect of growth conditions on cellulase content although with protozoa grown in vitro those grown on grass alone tended to contain more cellulase than those grown on starch and grass.A survey of methods for the release of cellulase from other rumen fractions was made and mild treatment with ultrasound of the fraction suspended in water gave the maximal release of enzyme with the highest specific activity. Using this method 62% of the total rumen cellulase was found in the protozoal fraction and 27% was associated with the plant debris in a normal sheep, fed on hay and oats, with an A-type protozoal population.

Effects of chronic environmental heat stress on blood flow and nutrient uptake of the gravid bovine uterus and foetus

Abstract: To evaluate the effects of chronic environmental heat stress during mid-gestation on gravid uterine and foetal metabolism, mature Hereford cows were assigned to control (n = 8) or heat stress (n = 5) treatments beginning on day 100 of gestation. Uterine and umbilical blood flows were estimated by the steady-state diffusion procedure on day 169 ± 4 of gestation. Oxygen (O2), glucose, lactate, α-amino nitrogen and urea nitrogen concentrations were determined for uterine and umbilical blood samples collected during this procedure. Foetuses and foetal fluids were collected on day 174±4.Uterine and umbilical blood flows were reduced and foetal weight also was less for heat-stressed than for control cows. In addition, foetal liver weight as a proportion of foetal weight and total foetal liver RNA and protein were less for heat-stressed cows. Uterine and umbilical arterial–venous concentration differences in metabolites were similar between the two groups. Uterine, foetal and utero-placental uptake or secretion rates of the metabolites measured in this study were reduced in the heat-stressed cows, primarily because of differences in blood flow. Thus, chronic heat stress during mid-gestation had an adverse effect on foetal development resulting, at least in part, from decreased uterine and umbilical blood flows, which led to a reduction in uterine, utero-placental and foetal nutrient uptake or secretion rates.

The effects of dietary starch and fibre on the in vitro rates of lipolysis and hydrogenation by sheep rumen digesta

Abstract: The objective of this work was to investigate the effects of changing proportions of readily fermentable carbohydrate and fibre in the diet on the rates of lipolysis and fatty acid hydrogenation by sheep rumen digesta. Three experiments were carried out using rumen-fistulated Romney wethers. In the first experiment rumen digesta from one sheep on a high-fibre diet was incubated in vitro with [1–14C]linoleic acid and 0, 0·1, 0·2 and 0·5% sucrose. It was found that sucrose increased the rate of hydrogenation of linoleic acid by up to 40%.In the second experiment five rumen-fistulated Romney wethers were fed five diets according to a latin-square experimental design. These diets had decreasing proportions of fibre (42·8–19·5%) and increasing proportions of starch (12·2–35·7%). Lipolysis and hydrogenation rates decreased significantly with decreasing fibre content which was reflected in the amounts of stearic and octadecenoic acids in the rumen digesta.In the third experiment sheep were fed the high-fibre diet used in the first experiment and the rumen digesta incubated in the presence of 0, 0·15, 0·45, 0·75 and 1·50% starch. Lipolysis rates increased but no effect of added starch on hydrogenation was observed.It was concluded that the short-term addition of energy to the rumen digesta increases lipolysis and hydrogenation rates. However, long-term replacement of fibre by starch results in a reduction of these rates.

Variation in development of wheat and barley in response to sowing date and variety

Abstract: A number of commercial varieties and advanced breeding lines of wheat and of barley were each sown successively in the field from early in September until late in February in 3 or 2 years. Shoot apex development was monitored throughout the growing season and the dates at which the double ridge stage and the terminal spikelet stage were attained are reported. There was considerable variation in the date at which these stages occurred, associated both with variety and date of sowing. When sown early, spring wheat varieties and the winter wheat, Fenman, developed more rapidly than the other winter wheats, but the difference disappeared in sowings made in the middle of October or later. Spring barley developed more quickly than winter barley and the difference persisted until sowings made in mid-November.Length of the longest leaf sheath, number of emerged leaves on the main shoot and the time when stem elongation began (‘ear at 1 cm’), plant characters used to assess the stage for various agronomic treatments, were measured in parallel with apex development. The relationships between number of emerged leaves and the length of the longest leaf sheath and stage of development were found to vary with sowing date. The stage ‘ear at 1 cm’ provided a good guide to shoot apex development. Stem length and number of elongated internodes varied with date of sowing. Some of the variation in number of emerged leaves at a given stage and in the final number of elongated internodes was found to be correlated with total number of leaves on the main shoot. The form of analysis used indicated that sowing date may have important effects, via its effect on the number of leaves on the main shoot, on the duration of ear growth in wheat and barley and on the duration of ear formation in barley.

Boran cattle maintained by chemoprophylaxis under trypanosomiasis risk

Abstract: Reproductive performance, mortality, growth, and culling and replacement rates based on 20000 calving records were evaluated for grade Boran beef cattle maintained with trypanocidal drugs in an area of high trypanosomiasis risk in Tanzania. Under ranching conditions, over a 10-year period in this area of high Glossina morsitans morsitans, G. pallidipes and G. brevipalpis challenge, a calving interval of 15·9 months, pre-weaning mortality of 8%, annual cow mortality of 5·8% and 8-month weaning weight of 133·5 kg resulted in a herd productivity of 96 kg of weaner calf per cow per year. The proportion of heifers required as replacements (45%) and the generation interval (6·9 years) indicated scope for implementation of selection programmes on growth traits. The level of productivity achieved compared favourably with major data sets recently analysed from pure Boran cattle under trypanosomiasis-free ranching conditions in Kenya, and from trypanotolerant N'Dama cattle in West Africa. These results indicate the possibility of improving livestock production in tsetse-infested areas by the rational use of chemoprophylaxis as an integral part of management. Year, season, cow age, calf sex and location on ranch had significant effects on practically all the traits of calving interval, pre-weaning mortality and growth, and cow productivity. Superior performance where bush clearance and tsetse fly control had taken place suggests that economic evaluation of these interventions should be attempted. The season of calving had a major effect on productivity. Cows of 5–8 years of age were the most productive, as were animals producing male calves, features well recognized in beef cattle production. An average of 4·4 treatments with Samorin, a prophylactic, and 0·6 treatments with Berenil, a therapeutic, were required per year. The number of treatments varied from year to year and by area, being greater in the south of the ranch where the tsetse challenge was considered higher. However, the age and season of calving had little effect on the number of treatments required. Despite such extensive use of trypanocidal drugs, there was no indication that drug resistance had developed or evidence that repeated inoculation of Samorin had affected productivity. Grading-up of small East African Zebu cattle to Boran over an 8-year period allowed annual comparison of birth weights, pre-weaning growth and weaning weights of two groups of calves, one having a higher level of Boran genes (varying from 12 to 6% higher annually) than the other. Those with the higher level of Boran genes performed better by 3·3% for all attributes studied, but as the percentage difference in Boran genes decreased, so did this difference. In an environment improved through bush clearance and tsetse fly control, the calves with higher levels of Boran genes were superior, but this superiority was not expressed in the unimproved environment.

Heavy metal uptake from contaminated soils by six varieties of lettuce (Lactuca sativa L.)

Abstract: A replicated pot experiment is described in which six lettuce varieties were grown in four contaminated soils of different Cd, Cu, Pb and Zn concentrations. Webb's Wonderful absorbed least and All Year Round absorbed most Cd and Zn from all four soils. Uptake of both metals by all six varieties increased with increasing soil contents and leaf Cd and Zn concentrations were positively and significantly correlated. There was little evidence for a varietal control of the absorption of Pb and none for Cu, but a significant positive correlation between leaf Cu and Pb concentrations was observed.

Fat partitioning in British Friesian cows: the influence of physiological state on dissected body composition

Abstract: The influence of physiological state (pregnant, lactating, dry) on body composition and fat partitioning in Friesian cows has been examined. A total of 20 cows, four per physiological state, were slaughtered and their left half carcasses dissected into individual muscles, bones and fat depots. All body parts, including the internal organs and fat depots, were weighed at slaughter.Muscle tissue and the internal organs showed some weight changes, consistent with a redistribution of tissue towards the udder and gut, and mobilization of muscle, but the major changes in weight associated with changing physiological state occurred in total body fat.Intermuscular fat made the greatest absolute contribution to changing fat weight, but subcutaneous fat showed the greatest proportional change with changing physiological state. The order of depletion of fat depots during fat loss was approximately the reverse of the order of development found during developmental growth.The distribution of subcutaneous fat between seven defined regions of the carcass was not affected by differences in total fatness in different physiological states. This, and the high correlation found between fat depth and total body fatness, confirms the view that measures of subcutaneous fat depth, e.g. by ultrasonics, should be useful predictors of the energy status of cows in varying physiological states.

Fibrous root growth and water use of sugar beet

Abstract: Development of the fibrous root system of sugar beet was studied by washing soil samples taken from field experiments through the growing season. At the beginning of June the root system was still poorly developed but during June there was rapid proliferation. In the top 70 cm there was only little further increase in root density after the end of June. Below 70 cm root density increased up to the end of August. Throughout the season fibrous root density decreased with depth. Despite the origin of the lateral roots from two grooves on the storage root, fibrous root distributions at each depth around individual plants were essentially uniform from mid-June onwards. In the absence of nitrogen fertilizer, fibrous root development exceeded that of a crop given fertilizer, particularly at depths greater than 50 cm early in the season. The maximum value of root density was 2·8 cm/cm3 soil recorded in the top 10 cm in mid-September. Compared with published data for other crops, the sugar-beet root system was sparser than that of winter wheat or maize but denser than that of a soya bean or cassava.Soil water content was measured with a neutron probe. Inflows to roots were calculated from soil water content changes in different soil layers. In the top 30 cm, inflows ranged up to 10·8 μl water/cm root.day and were up to five times higher than published inflows for winter wheat. At 30–100 cm sugar beet and winter wheat inflows were generally similar. The 0–30 and 30–120 cm layers contributed about 80 and 20% respectively of the total water use by sugar beet while no uptake was recorded below 110 cm. Previous studies have shown that sugar beet often takes up water from soil deeper than 110 cm, although it is not unknown for the depth of water removal to be restricted.

Water stress and time of floral initiation in pearl millet

Abstract: The interaction of water stress and time from sowing to floral initiation was investigated in the field with pearl millet hybrid BJ 104. Extended daylength was used to delay panicle initiation (PI) and flowering (FL) of crops exposed to single periods of mid-season drought. Growth, yield and yield components were related to the number of days for PI and FL in both irrigated and water-stressed treatments. Delay in PI resulted in more leaves and tillers per plant, and greater leaf area, height and total dry matter. Grain yield, however, was not affected resulting in lower ‘harvest index’. There was, however, an increase in the grain yield of main shoots which was offset by a proportional decrease in the grain yield of tillers. Water stress effects were dependent on the physiological stage of the crop at which stress occurred, as a result of the photoperiod treatments. Water stress prior to panicle initiation did not affect the grain yield of the main shoot but increased tiller grain yield, resulting in a higher total (crop) grain yield. Water stress during panicle development reduced the grain yield on the main shoot but this loss was compensated by the grain from the increased number of tiller panicles which reached flowering. Water stress during flowering and grain filling reduced grain yields of both main shoot and tillers, making this the most sensitive stage. Photoperiodic control of floral initiation can provide an escape mechanism to avoid the coincidence of mid-season water stress with sensitive periods of growth.

Endogenous faecal loss of phosphorus in growing lambs and the calculation of phosphorus requirements.

Abstract: SUMMARY The endogenous faecal loss of P has been investigated in growing lambs given diets either grossly deficient, moderately deficient or just adequate in P. This loss was found to increase in direct relation to the increased P intake, in spite of the high P requirements of the deficient animals, which suggests that some increased loss with increased P intake is inevitable. Results throw doubt on the validity of the assumption made by the Agricultural Research Council (1980) in their calculations of P requirements, that the endogenous faecal loss of P is maintained at a constant level equal to that which occurs at zero P intake, until requirements are met. Even on the diet which was, according to Agricultural Research Council (1980) recommendations, just adequate in P, lambs were unable to retain the expected amount of P commensurate with their growth. This inability to retain P was not due to a failure of P absorption, since the efficiency of absorption from this diet was higher than the value used by the Agricultural Research Council (1980) in their calculations. Rather, it must have been due to an inevitable endogenous faecal loss of P that was considerably higher than the value assumed by the Agricultural Research Council (1980). It is suggested that in future the value of endogenous faecal loss used in calculations of P requirements is the minimum one that allows a particular requirement to be achieved.

Soil erosion in south Somerset

Abstract: Local soil erosion has long been a problem on very fine sandy and silty soils in south Somerset. Some 40 fields in arable use were chosen randomly and monitored monthly for erosion in the winter of 1982–3. Erosion was measured along fixed traverses and then compared with soil attributes, site factors and cultivation practices. Winter cereals were worst affected with a third of the fields having soil losses in excess of 4 m3/ha. There was least erosion on bare ploughed ground and moderate losses on cash root crops. Soil type, organic-carbon content, clay content, drill direction, wheeling density and slope all affected soil loss in winter cereal fields.Erosion did not assume serious proportions until a combination of soil surface conditions and soil wetness allowed run-off to form rills. Only moderate falls of rain were then needed for widespread removal of soil. Preventative measures include grassing slope convexities, more grass in the rotation to improve soil organic matter and structure, avoiding wheelings, drilling across the slope and keeping headland widths to a minimum.

The effects of direct drilling, shallow cultivation and ploughing on some soil physical properties in a long-term experiment on spring barley

Abstract: Physical measurements were made on the soil of a long-term cultivation experiment comparing direct drilling, tine cultivation and mouldboard ploughing for spring barley to investigate possible reasons for differences in yield. The soil was a typical argillio brown earth, approximately 90 cm of sandy clay loam topsoil and clay loam subsoil overlying magnesian limestone. For the three periods 1971–4, 1975–7 and 1978–80 the mean grain yields were marginally lower after direct drilling than after shallow cultivation or ploughing. There was an average decline in yield of 1·33 t/ha from the first to the last period, the decline being greater for direct drilling than the other two tillage systems. Although the surface horizon (0–5 cm) of direct-drilled soil had a higher content of organic matter than the ploughed, this did not increase the stability of the aggregates. Slaking tests had shown the soil to be inherently unstable and likely to suffer from structural problems. After the first 3 years bulk density of direct-drilled soil (0–15 cm) increased markedly to ca. l·5 g/cm8 and then remained relatively stable. In the ploughed soil, density increased steadily over the period to an average value of co. 1·45 g/cm8. Tine cultivation to 7–8 cm reduced cone resistance values in the surface compared with direct-drilled soil but below 15 cm there were no significant differences. Ploughing gave significantly lower values than direct drilling to a depth of 30 cm. Measurements of pore sizes in direct-drilled and ploughed soil were highly variable with few significant differences. Mean air capacity values (1978–80) tended to be lower in direct-drilled than in ploughed topsoil particularly for plots direct drilled after 7 years of deep tine cultivation. A limited number of root measurements in 1978 and 1980 showed that the length of root per unit of ground area was much less after direct drilling than after ploughing. Shallow cultivation, surprisingly, gave most root with a greater proportion of the root system below 20 cm than in the other two treatments. The classification of this soil according to its suitability for direct drilling cereals is discussed.

Dietary phosphorus depletion in sheep: effects on plasma inorganic phosphorus, calcium, l,25-(OH)2-Vit.D3 and alkaline phosphatase and on gastrointestinal P and Ga balances

Abstract: Experiments were carried out to study the effects of dietary P depletion on plasma concentrations of inorganic P (P1), calcium, 1,25-(OH)2-Vit.D3 and alkaline phosphatase, and to investigate the effects of P depletion, in comparison with P repletion, on intestinal flow and net disappearance of Ca and P in sheep. The animals were adapted to an experimental diet of pellets and chopped straw providing between 0·91 and 1·04 g P/day for depletion. They were repleted by single infusions of phosphate into the duodenum raising total P supply to about 4·1 g/day. During P depletion plasma P1, concentrations decreased significantly whereas those of Ca increased. The development of hypercalcaemia is discussed with respect to intestinal absorption and bone accretion and resorption. Plasma 1,25-(OH)2-Vit.D3 and alkaline phosphatase were not affected by P depletion.In P depletion the flow through the gastrointestinal tract of total P contained in the digesta and faecal P excretion were significantly reduced and the P balance was slightly negative. Calcium net absorption from the gut was also reduced. Daily flow of total P and P1, contained in the particle-free intestinal fluid was markedly lower in P depletion as compared with P repletion. The percentage of net disappearance from the small intestines of total P and P1, in the particle-free fluid was 57 and 70 % in the depleted state and 79 and 93% in the repleted state.

The effect of variation in phosphorus intake on salivary phosphorus secretion, net intestinal phosphorus absorption and faecal endogenous phosphorus excretion in sheep

Abstract: Mature sheep fitted with rumen and duodenal cannulae, and fed a pelleted hay diet, were given supplementary phosphorus by continuous infusion into the rumen and the effects on salivary phosphorus secretion, net intestinal phosphorus absorption and faecal endogenous phosphorus excretion were studied. In control periods little phosphorus was excreted in the urine and little increase was seen in response to supplementation, the faeces being the major pathway for excretion. Increasing phosphorus intake led to an increase in net intestinal phosphorus absorption, a rise in plasma phosphate concentration, an increase in salivary phosphorus secretion and an increase in faecal endogenous phosphorus excretion. Overall net intestinal absorptive efficiency for phosphorus did, however, decrease as intake rose so that changes in faecal endogenous phosphorus excretion were in part due to increased salivary phosphorus secretion and in part to a reduction in overall absorptive efficiency. The significance of these changes in relation to the control of phosphorus balance in ruminants is discussed.

The influence of plane of nutrition and diet composition on the performance of dairy cows

Abstract: Summary Seventy-six first-calf cows (heifers), 32 second·calf cows and 39 adult cows participated in a trial in which three diets composed of 60:40, 75:25, 90:10 proportions of compound to hay (hay dry-matter digestibility 0·6) were given for the first 36 weeks of lactation in amounts to provide daily an estimated 125, 156 MJ and ad libitum digestible energy (DE) for heifers, and 156, 187 MJ and ad libitum DE for the other parities. The ad libitum intakes were 150 and 200 MJ DE daily for heifers and for older cows respectively. Greater compound content of the diet and larger daily allowance of DE were associated with increased occurrence of mastitis and lameness but not digestive upsets. Dry·matter (D.M.) digestibility was increased with a greater proportion of compound in the diet but was not affected by the amount consumed or stage of lactation. Milk yield and live·weight change were increased linearly and additively by a greater intake of digestible dry matter and by a greater proportion of compound in the diet, throughout the lactation save for no effect of diet composition on live·weight change in early lactation. On equal feed intakes older cows gave more milk and lost more live weight than heifers in early lactation but not thereafter; responses to additional feed were equal for all parities studied. Milk fat concentration was reduced both by increased allowance and by the high compound diet. Milk solids·not·fat (SNF) concentration was not affected by the treatments. Yield of milk fat was not affected by amount eaten and was reduced by the 90:10 diet. Yields of SNF and milk energy were increased by amount eaten and by increased compound in the diet. Thirty-two primiparous cows continued on their experimental treatments without interruption to the end of the second lactation. In the second lactation the effects on yields of milk, milk energy, and SNF were magnified indicating a cumulative effect from lactation to lactation. Little cumulative effect was observed on either milk fat yield, or concentrations of fat and SNF in milk. More generous feeding was associated with reduced milk output/unit D.M. consumed in the first but not the second lactation. More generous feeding improved live·weight change less in the second than in the first lactation. No cumulative effects over two lactations were observed consequent upon variation in diet composition.

Allometric changes during growth in rabbits

Abstract: Differential growth from 1 to 20 weeks of age was studied on 320 rabbits from two lines (New Zealand White and California) and both sexes by means of the allometric equation log y = log a + b log x. Regression lines were fitted to the evolution of organs (blood, skin, thymus, heart–lungs, liver, kidneys and alimentary tract), carcass, tissues (bone, lean and fat) and anatomic components (head, breast and ribs, loin, abdominal wall, fore and hind legs) relative to empty body weight; stomach, caecum and intestines relative to alimentary tract; bone and lean groups relative to total bone and lean and fat depots relative to total fat.The convenience for a correct description of relative growth of determining both the quantitative growth, in order to apply the allometric equation only to the real growth period of each component, and the possible existence of allometric changes, is discussed.The results for each component are presented and discussed. There were no significant differences due to line, and sex had a significant influence (P < 0·001) only on the relative growths of total fat, lean content in the loin and hypodermic fat. All the components, with the exception only of thymus, presented a change in their allometric coefficients. These changes for most components, except fat depots, were concentrated in a small interval of time (4–8 weeks of age) between weaning and the inflexion point of the body weight growth curve.

Some factors limiting the growth and yield of winter wheat and their variation in two seasons

Abstract: Multi-factorial experiments on winter wheat cv. Hustler in autumn 1979 and 1980 sown on a clay loam soil following potatoes tested the effects of combinations of the following eight factors, each at two levels: sowing date; amount of nitrogen; division of nitrogen; timing of nitrogen; irrigation; autumn pesticide (aldicarb); summer aphicide (pirimicarb); and fungicide (carbendazim, tridemorph, maneb and captafol). The mean grain yields of all plots in 1980 and 1981 were respectively 9·6 and 8·3 t/ha; the best eight-plot means were 11·2 and 9·9 t/ha. Fungicides had the largest effect on grain yield, increasing it by 0·8 and 1·7 t/ha in 1980 and 1981, mainly by increasing grain size. Effects were greater with earlier sowing and the larger amount of nitrogen. Benefits from fungicide were well related to the control of leaf diseases, mainly Septoria spp., which became severe after anthesis. Fungicide temporarily decreased the number of saprophytic fungi on the developing ears. Aphids that appeared in autumn on plots sown in mid-September were controlled by autumn pesticide, which also prevented the spread of barley yellow dwarf virus that occurred only in 1981. Consequently, yield of early-sown plots in 1981 was increased by autumn pesticide, but only when the severe infection with leaf diseases was controlled by fungicide. Autumn pesticide decreased nematode populations. Aphid populations in summer were small and yield was unaffected by the decrease in numbers that followed application of an aphicide. Sowing on 20 or 15 September, as compared with 19 or 30 October, caused faster growth and development and greater uptake of N from the soil early in the season. Effects were smaller after April: earlier sowing increased total dry weight by 2·5–3·0 t/ha and, when leaf diseases and barley yellow dwarf virus were controlled, increased yield by 0·9-l·0t/ha. Increasing the amount of N applied by 70 kg/ha (from 105 or 80), increased yield only in 1980 and then only when fungicide was used. Extra N decreased yield in 1981 in the absence of fungicide. Extra N always increased N uptake and decreased grain size. Applying most or all of the Non 4 or 19 March instead of 15 or 23 April resulted in less uptake of N from anthesis onwards and smaller yield, especially in 1980. N in three applications instead of one had negligible effect. Trickle irrigation decreased yield slightly, despite delaying leaf senescence and increasing straw weight. Attributes of wheat on best yielding plots differed little between years. Average values were: 534 ears/m2; 40·7 grains/ear; 40·4 mg/grain; 18·8 t/ha total dry matter and 214 kg N/ha uptake by grain plus straw.

Drought resistance of hard wheat cultivars measured by a rapid chlorophyll fluorescence test

Abstract: Disks of hard wheat (Triticum durum Desf.) leaves subjected to rapid desiccation over 4 h showed noticeable changes in the shape of the in vivo chlorophyll fluorescence induction curves. In drought-sensitive varieties (such as Claridoc), water stress resulted in a strong inhibition of the slow fluorescence induction transients. In particular, the fluorescence quenching rate was markedly decreased in water-stressed leaf disks. In contrast, leaves of drought-resistant varieties (such as Aouedj) showed only minor changes in chlorophyll fluorescence. The results of this investigation suggest that the slow transient of the in vivo chlorophyll fluorescence induction phenomenon may provide a simple method for selecting drought-tolerant wheats.

Relationship of stalk morphology and chemical composition to lodging resistance in maize (Zea mays L.) in a rainforest zone

Abstract: Field and laboratory studies were carried out in 1981 and 1982 to investigate the relationship of stalk morphology and chemical composition to lodging resistance in maize in the rainforest zone of Nigeria.Morphological characters correlated with lodging were plant height, diameter and length of basal internode, thickness of rind and weight of 5 cm basal section. Lodging was negatively correlated with grain yield, and with the percentages of total nonstructural carbohydrate, protein and potassium in the stalks. Premature stalk senescence and rot were common in varieties susceptible to lodging. Lodging had no relationship with leaf area and number of days from sowing to flowering.

The digestibility by sheep and goats of five roughages offered alone or with concentrates

Abstract: The digestive efficiency, rumen fermentation pattern, nitrogen balance, water intake and urine excretion were compared using four mature vasectomized Chios rams and four Damascus goats for each of five roughages (barley, lucerne or sudax hay, barley straw and leaves and twigs of acacia) offered alone or with concentrates (1:1 ratio), at approximately the maintenance energy level. There were no species differences in the apparent digestibility of nutrients when the roughages were offered alone except for the significantly higher digestibility of dry matter, organic matter (OM), and gross energy (GE) of straw by goats. Sheep exceeded goats significantly in the digestibility of D.M., OM, GE and crude protein (CP) of lucerne hay plus concentrate and of CP when barley hay or sudax hay were supplemented with concentrate. Compared with sheep, goats tended to consume more D.M. per kg W 0·75 and drink less water and excrete less urine, but significant differences for water were obtained only with barley straw plus concentrate and for urine with barley hay and acacia. Daily protein retention (g/kg W 0·75 ) was consistently lower in goats than sheep but significant difference was obtained with acacia and with lucerne hay or straw plus concentrate. These results would suggest that Damascus goats require more protein for maintenance than sheep. Compared with sheep, goats had significantly higher rumen NH 3 ·N concentration with both acacia diets but lower with lucerne hay. Total VFA concentration tended to be higher in sheep with all diets, but significance was observed only with barley hay although rumen pH was lower (acacia diets) or similar compared with goats. The molar proportion of acetic was significantly higher in sheep than goats with barley hay plus concentrate. Goats exceeded sheep significantly in the proportion of propionic with straw, of butyric with both barley hay and sudax hay plus concentrate diets, and of isobutyric with barley hay or acacia plus concentrate; with the other diets goats tended to have higher proportions of butyric and isobutyric.

Carbohydrase activity in the pancreatic tissue and small intestine mucosa of sheep fed dried-grass or ground maize-based diets

Abstract: Two groups of six sheep were fed either dried-grass or ground maize-based diets for at least 4 weeks before slaughter. Samples of the small intestinal mucosa and spancreatic tissue were assayed for a-amylase, glucoamylase, maltase and oligo-l,6-glucosidase.The pancreatic tissue contained high activities of α-amylase and much lower activities of glucoamylase, maltase and oligo-1,6-glucosidase. There was no effect of diet on the specific activities of any of these enzymes in the pancreatic tissue.The activity of α-amylase adsorbed on to the mucosa of the small intestine was greatest in the proximal region of the small intestine, the activity generally declining with increasing distance away from the pylorus. There was no diet effect on the absorbed α-amylase activity.Similar patterns of distribution along the small intestine were observed for maltase, glucoamylase and oligo-1,6-glucosidase with the highest activities in t he jejunum. There was no overall effect of diet on glucoamylase or maltase specific activities and glucoamylase total activity, although the total activities of maltase and oligo-1,6-glucosidase were significantly greater for the sheep fed the ground maize-based diet (P < 0·05).It is suggested that ruminant animals may be capable of digesting large amounts of starch in the small intestine through an adaptation in the activity of the host carbohydrases.

Nitrogen concentrations in field-grown spring barley: an examination of the usefulness of expressing concentrations on the basis of tissue water

Abstract: A study was made of growth and N concentrations of field-grown crops of spring barley (Hordeum vulgare L. cv. Georgie or Triumph). Nitrogen concentrations were calculated on the basis of both dry matter and tissue water because previous research had indicated that K concentrations expressed on the basis of tissue water were better for assessing the K status of crops. The aim was to see whether this was also the case for N. When supplies of P and K were adequate, the addition of N fertilizer stimulated growth in all crops except when sufficient N was already supplied as farmyard manure. Percentage N in dry matter declined as plants grew and was higher in plants given N than in plants grown without N, although the difference diminished with time. Nitrogen concentrations calculated on the basis of tissue water were very similar for both N-sufficient and N-deficient crops despite large differences in growth rates. Nitrogen concentrations in tissue water also declined but only until anthesis, thereafter they increased. This pre-anthesis decline was due to the increase in the amount of stem tissue which had lower N concentrations in tissue water than leaves. Similarly the post-anthesis increase in N concentrations was due to the development of the ears which had high concentrations of N in tissue water. The effects of deficiencies of P or K or water on N concentrations in tissue water of the cultivars Georgie or Julia were studied also in field experiments at Rothamsted. Lack of P and K inhibited growth of crops given 144 kg N/ha. Crops grown without N grew more slowly than those given N but their growth was not further inhibited by lack of P or K. Deficiencies of either P or K increased N concentrations calculated on the basis of tissue water in crops given 144 kg N/ha but not in crops grown without N. The increase in concentration was not due to changes in the proportions of leaves and stems but to real increases in N concentrations in leaves, stems and ears. Drought decreased growth and also resulted in higher N concentrations in tissue water. In the absence of other limiting factors, N concentrations expressed on the basis of tissue water were very similar for both N-sufficient and N-deficient crops. They increased only when growth was limited by factors other than N. The implications of this for the control of N concentrations by crops is discussed. It is concluded that N concentrations expressed on the basis of tissue water are unlikely to be useful for determining the N requirements of barley. Percentage N in dry matter might be more useful for this purpose.

Repelling foraging honeybees with alarm pheromones

Abstract: The honeybee alarm pheromones 2·heptanone and isopentyl acetate were repellent to honeybee foragers when applied to plots of oil-seed rape and field beans and to sunflower heads Their possible use to repel bees from crops before insecticide application is discussed

The effect of sulphur deficiency on the uptake and incorporation of nitrogen in ryegrass

Abstract: SUMMARY Sulphur deficiency reduced the yield and sulphur content of ryegrass at the fourth cut, while increasing the nitrogen content and N:S ratio. The distribution of the forms of nitrogen was also altered, with a decrease in the proportion of nitrogen recovered as amino acids and an increase in the concentration of asparagine. Amino acid analysis showed that the concentrations of the sulphur-containing amino acids cyst(e)ine and methionine were depressed by sulphur deficiency as well as those of arginine, histidine, lysine, glycine, leucine, serine and threonine. Sulphur deficiency, therefore, decreases the quality of crude protein found in grass, as well as reducing the yield.

Interactions between Rhizobium strains and lentil (Lens culinaris Linn.) genotypes under salt stress

Abstract: Three strains of Rhizobium able to fix nitrogen in symbiosis with lentils in saline soil were screened. Nodulation pattern, N2-fixation and grain yield were all influenced by Rhizobium strain and lentil genotype. Genotypes DL-443 and Pant L-406 were found to be more salt tolerant than others, and gave the highest grain yield.