At Shika in a subhumid environment of Nigeria, a 3-year study was carried out to select newly developed groundnut varieties for use in crop–livestock production systems. The study examined 11 groundnut varieties. Emergence time, plant stands at full emergence, forage and seed yields and yield components were examined. Whole plant samples were analysed for crude protein (CP) content. Varieties ICGV 87123 gave the lowest forage yield and cultivar M517-80I, the highest, with seven varieties recording forage yields above 5 t/ha. The CP content of forage was lowest (14·8%) for variety M576-80I and highest (21·6%) for variety M554-76. Mean seed yield (over 3 years) varied significantly from 0·73 to 1·68 t/ha. Only two varieties had mean seed yield >1 t/ha. The relationship between seed and forage yields was positive and significant (r = 0·529, P < 0·006). Varieties RMP 12, 88-80I and M517–80 were most promising for both forage and seed production.

Morphophysiological characters, designated as descriptors by the International Union for the Protection of New Varieties of Plants (UPOV) and the International Plant Genetic Resources Institute (IPGRI), and allozyme variation were used to study genetic diversity among four cabbage (Brassica oleracea L. var. capitata L.) open pollinated (OP) populations. The morphological and physiological characters, and gene frequencies among OP populations were analysed by using cluster (CA) and principal component analysis (PCA). Both methods gave the same clustering of OP populations. The relationships found among OP populations by analysing UPOV descriptors (30 characters) and IPGRI descriptors (30+14 characters) were similar. The relationships among OP populations obtained from gene frequencies were not similar to those obtained from morphophysiological characters, but two of the four OP populations were clustered together by both categories of data. The biggest correlation between the relationships among OP populations obtained from morphophysiological characters and those obtained from gene frequencies was r = −0·44 and r =−0·38 given by PCA and CA respectively. The importance of each character or allele with respect to the relationships among OP populations were also detected by PCA.

A field experiment was conducted for 2 years (1993–95) at Central Institute of Medicinal and Aromatic Plants, Field Station, Bangalore, India to evaluate the nitrification inhibitors, benzotriazole, o-nitrophenol, m-nitroaniline and dicyandiamide in a perennial aromatic grass, Java citronella. Citronella responded to applications of high doses of nitrogen (300 kg N/ha/year). The interaction between N doses and nitrification inhibitors was significant. Nitrification inhibitors performed better at the highest N dose (450 kg N/ha/year) and the increase in the essential oil yields was to an extent of 27·3 to 34·6% when compared with ‘N alone’ treatment. The nitrification inhibitors also increased the apparent N recoveries by citronella considerably. The oil content in the herb and its quality were not affected by the treatments. The nitrification inhibitors increased citronella yields and improved N economy.

Field experiments were conducted during two successive seasons in the Agricultural Research Center, Giza, Egypt (a clay loam soil), to study the effects of phosphorus fertilization (addition at rates of 44 and 74kg of P2O5/ha) and foliar application of zinc (at 0·0 and 40ppm of Zn applied twice, 75 and 90 days after planting) and calcium (at 0·0, 20, 40, and 60ppm of Ca applied twice, 80 and 95 days after planting) on seed, protein and oil yields and oil properties of the Egyptian cotton cultivar Giza 75. Application of P at the high rate and spraying plants with zinc and calcium at any concentration increased cottonseed yield/ha, seed index, seed oil content, oil and protein yields/ha, seed oil unsaponifiable matter, and total unsaturated fatty acids (oleic and linoleic). Conversely, decreases in oil acid value, saponification value and total saturated fatty acids occurred. The seed protein and oil refractive index tended to increase when the high P rate and Zn were applied. Seed protein content tended to decrease slightly with Ca application. Regardless of the slight decrease in protein content as a result of Ca application, the yield of protein increased, due to the fact that there was an obvious increase in seed yield which counterbalanced the negative effect of the decrease in protein content. The highest Ca concentration (60ppm) gave the highest values of cottonseed yield/ha, seed index, seed oil and protein yields/ha and oil unsaponifiable matter, followed by the concentration of 40ppm. The concentration of 40ppm gave the lowest total saturated fatty acids. The effect of Ca concentrations on oil refractive index was very limited.

The aim of the experiment was to determine the importance of liquid digested sewage sludge (‘sewage sludge’) as a source of phosphorus leaching from sandy soils in the UK. The sewage sludge was applied to uncropped loamy sand and sandy loam monolith lysimeters (1·2 m deep) annually for 3 years. The application rate was sufficient to supply approximately 60 kg P/ha annually. An application equivalent to four times this amount was also applied to two other loamy sand lysimeters to test the effects of excessive amounts. Total P (TP), total dissolved P (TDP) and molybdate-reactive P (MRP) concentrations were measured in the drainage water and were compared with leaching from untreated control soils.

After two sewage sludge applications, Olsen's extractable P content of the topsoil had increased: a P surplus of c. 100 kg/ha was required to raise the topsoil concentration by 5 mg/kg. Sewage sludge applications at the lower rate did not increase P concentrations in the drainage. Phosphorus concentrations were generally small and were, as an average of both soil types and nil and lower rate sludge applications, 12, 20 and 34 μg/l for MRP, TDP and TP respectively. Phosphorus leaching losses from the higher rate (excessively large sewage sludge applications) were more variable but not significantly (P > 0·05) different from the other treatments. Average concentrations were 9, 23 and 50 μg/l for MRP, TDP and TP respectively. Leaching from sludge biosolid applications at operational rates to sandy soils moderately well supplied with P is not a major P loss pathway.

The effects of different plant arrangements (conventional single rows v. paired rows at a standard density of 55–67 thousand three-bud setts/ha) with different intercropped green manuring strategies with Sesbania aculeata (none v. ploughed in after 4 and 6 weeks) and with different amounts of nitrogen (N) fertilizers (0,75 and 150kg/ha) were studied in sugarcane crops planted after wheat or mustard and in its first ratoon. The yield of millable cane from the planted sugarcane was not affected by intercropped green manuring or plant arrangement but was increased by fertilizer N after both wheat and mustard. The residues from the green manuring and fertilizer N both increased the yield of the following crop of ratoon sugarcane by 9–10% with the residues increasing the numbers and length of millable canes and the fertilizer N the number, girth and weight of the millable canes. None of the treatments affected the quality of cane juice in either the planted cane or the ratoon crop. Residues from the green manures and the N fertilizer treatments increased the organic carbon content and available N in the soils.

Heat tolerance of groundnut (Arachis hypogaea L.) was evaluated under field conditions using physiological traits identified in a yield model [crop growth rate (C), reproductive duration (Dr) and partitioning (p)]. In 1991, 625 diverse genotypes were initially screened under irrigation during the hottest months (February to May). Subsequent tests consisted of 16 contrasting genotypes selected based on a combination of high pod yield and partitioning coefficient of >0· 50. Large variation was observed among the 625 genotypes for pod yield and physiological traits. C was a powerful factor influencing pod yield. Eight genotypes combining high pod yield and a partitioning coefficient greater than 0·6 were identified. These included two released cultivars (55–437 and 796) in the Sahel. Correlations between seasons were significant for p (r=0·84), but non-significant for pod yield (r=0·40), C (r=0·39), and Dr (0·36). Date of sowing and genotypes had significant effects on pod yield and C, but were slight on p and Dr. Pod yield of most genotypes declined by more than 50% when flowering and pod formation occurred when maximum temperatures averaged 40°C. The results revealed that estimates of p would be a more reliable selection criterion for identification of genotypes tolerant to heat than yield. Further research is suggested to maximize crop growth rate and partitioning of genotypes growing under supra-optimal temperatures.

Forty-eight high genetic merit Holstein/Friesian dairy cows with Predicted Transmitting Abilities for milk fat plus protein yield, calculated using 1995 as the base year (PTA95 fat plus protein), of 40·0 kg, were used in an eight treatment, two period (period length = 8 weeks) change-over design experiment. Diets were offered ad libitum in the form of a complete diet. Treatments comprised a high and medium feed value silage, with concentrates being incorporated into the diet at proportional inclusion rates of 0·10, 0·30, 0·50 and 0·70 of total dry matter with the high feed value silage, and at 0·32, 0·48, 0·64 and 0·80 of total dry matter with the medium feed value silage. The high feed value silage was produced from a primary regrowth herbage (regrowth interval of 33 days) which was wilted prior to ensiling, while the medium feed value silage was produced from a primary growth herbage harvested on 9 June 1995. The high and medium feed value silages had estimated metabolizable energy concentrations of 12·4 and 11·3 MJ/kg DM respectively. Animals commenced treatments after a mean post calving interval of 26 days.

Irrespective of silage feed value, total dry matter intake and milk yield tended to increase with increasing proportion of concentrate in the diet. Milk protein concentrations increased to concentrate inputs of 0·50 and 0·64 of total DM with the high and medium feed value silages respectively, but decreased at the highest concentrate inclusion rates. Milk fat concentrations tended to decrease at higher concentrate inclusion rates. The milk yield responses to increasing proportion of concentrate in the diet have been described by a pair of significantly different equations: Y = 34·2−11·9×0·0101x and Y = 34·2−28·5×0·0101x for the high and medium feed value silages respectively (where Y = milk yield (kg/day) and x = concentrate proportion in the diet on a dry matter basis). Similarly, milk fat and milk protein yields for the two silage types have been described by pairs of significantly different equations. Using these milk yield response equations, it can be calculated that at a concentrate proportion in the diet of 0·32 total dry matter, an additional 3·7 kg of milk per day would be produced by offering the high, rather than the medium feed value silage, while at a concentrate proportion of 0·70 total dry matter, the milk yield benefit associated with the high feed value silage was reduced to 0·6 kg per day. Similarly, total dry matter intakes for animals offered the high feed value silage were 7·4 and 0·8 kg per day greater than for animals offered the medium feed value silage, at concentrate proportions in the diet of 0·32 and 0·70 total dry matter, respectively. These responses indicate that at low concentrate inclusion rates in the diet, silage feed value has a major influence on animal performance, while at higher concentrate inclusion rates, the importance of silage feed value is reduced.

Two studies were undertaken to evaluate the effects of cellulase and endoxylanase enzymes on the chemical composition and the fermentation characteristics of grass silage, using the gas production technique. Perennial ryegrass was ensiled in 1 litre glass containers for 90 days with cellulase (0·2 g/kg grass on fresh weight basis) and endoxylanase in the concentrations of 0·05 g/kg grass (Endox 0·05) and 0·2 g/kg grass (Endox 0·2). Subsequently, dried samples, ground through a 1 mm screen, were used in chemical analysis and gas production measurements. In Expt 1, the enzyme treatment significantly decreased silage NDF (P < 0·001), ADF (P < 0·001) and acetic acid (P < 0·01) concentrations and increased lactic acid (P < 0·001) production. In Expt 2, lower concentrations of NDF (P < 0·001) and ADF (P < 0·001) in treated silages resulted in increased sugar concentration (P < 0·001). In this experiment, butyric acid was detected. Addition of cellulase and Endox 0·05 enzymes did not alter silage digestibility. In both studies, cellulase and Endox 0·2 treatments tended to increase the rate of gas production within 10 hours of inoculation with rumen fluid whereas Endox 0·05 had no effect. The volume of gas produced was however greater for the untreated silage than for the enzyme-treated silage samples after 48 h of incubation. The strategy of applying cellulase and endoxylanase to the herbage in the ensiling process proved to be effective in modifying the chemical composition and increasing sugar concentration and the rate of gas production of the silages. Further research on the factors determining enzyme effectiveness is therefore suggested to elucidate the mechanisms leading to higher utilization of the released sugars.

Experiments were conducted in Nigeria to evaluate the optimum plant population density for okra (Abelmoschus esculentus) sown in monoculture or intercropped with cassava (Manihot esculenta). The crops were sown as late and early season crops in 1997 and 1998. Okra was sown at varied spacings to achieve final plant densities of 25000, 35000 and 50000 plants/ha in both monoculture and mixed stands. Intercropping had no significant effect on okra phenology (time to vegetative growth, flowering and fruiting). However, it significantly reduced weed growth by 25–45% and nematode infection in okra by 36%, and kept the canopy environment of cassava cooler by 3·0–4·4°C and more moist by 5–10g/kg, compared with monoculture. The durations of vegetative and reproductive growth and the weed-control ability of okra in both cropping systems were influenced by population density. Okra sown at 50000 plants/ha took the longest time to reach specific phenological stages, controlled weeds best and gave the highest fresh pod yields in both seasons. There was little increase in pod yields between 35000 and 50000 plants/ha in mixed stands in late season sown crops. The growth and tuber yield of cassava were not significantly affected by intercropping and okra population density.

The growth of okra and cassava were better with early than late season sowing, irrespective of okra population density or cropping system. This appears to have been due mainly to the effect of temperature and rainfall differences between the seasons. The substantial variation in the weather during the two seasons also had greater effect in monoculture than mixed stands. It is concluded that when rainfall is limiting, okra could be intercropped with cassava using population density up to 35000 plants/ha to allow the vegetable to develop and to maximize pod yield under the relatively dry conditions. The optimum target suggested is 50000–60000 plants/ha during the wet periods.

There is the potential for arsenic to enter the human food chain via ingestion by grazing animals. Data on the transfer of arsenic to ruminants have been too sparse to allow the development of dynamic models to predict changes in the arsenic contents of different tissues following ingestion. A study is described during which a group of 6-month-old lambs were given a single oral administration of 73AsCl3. Subsequently, concentrations of 73As in the tissues of groups of lambs slaughtered at intervals over a period of 181 days were determined. A true absorption coefficient of 0·46±0·055 (mean±S.E.) was determined which is considerably lower than expected from previous studies of non-ruminant animals which demonstrate complete absorption for inorganic arsenic. The resultant data were used to develop a compartment model to describe arsenic behaviour in sheep tissues. The derived model accounted for 80 % (n = 100) of the observed variation in the data. The model predicts that arsenic concentrations in tissues rapidly (< 40 days) reach equilibrium with the dietary intake level. Equilibrium transfer coefficient values (the ratio of the arsenic concentration in a tissue to the daily dietary intake of arsenic) for the important food-chain tissues were calculated as: (2·5±0·67)×10−3 days/kg for muscle, (9·1±1·96)×10−3 days/kg for liver and (1·1±0·14)×10−2 days/kg for kidney.

Previous studies have demonstrated that protein sources which are primarily degraded in the rumen such as rapeseed meal or soyabean meal may be as effective as a less rumen degradable protein source such as fishmeal in supporting higher levels of animal performance in young steers fed on grass silage. However, the response to type of protein supplement is likely to be influenced by the composition of the basal diet. This study has examined the effect of supplementing silages prepared from early (EH) and late (LH) harvested grass with two protein sources of differing rumen degradability, rapeseed meal (RSM) and fishmeal (FM) or a mixture of the two (M), thus creating eight experimental diets of LH, LHRSM, LHFM, LHM, EH, EHRSM, EHFM and EHM. Silage was offered ad libitum and supplements were included at 100 g fresh weight/kg silage DM intake. The RSM and M diets were made isonitrogenous with FM diets by the addition of urea. Animals remained on diets for 18 weeks and liveweights were monitored for a further 13 weeks while the animals were at pasture. Dry matter (DM) intakes and liveweight gains were higher with EH than with LH silage (P < 0·001). Response to type of protein supplement was dependent on silage quality. On LH silage, higher intakes were noted on FM and M (82·4 and 82·8 g DM/unit metabolic liveweight/day, respectively) relative to silage only (75·8 g DM/unit metabolic liveweight/day) and this contributed towards higher liveweight gains (P < 0·01). Liveweight gains tended to be higher on LH silage supplemented with FM compared to RSM (0·76 v. 0·67 kg/day, respectively, P = 0·08). In comparison, on EH silage, relative to EH unsupplemented, the intake was highest on M (89·2 v. 96·6 g DM/unit metabolic liveweight/day), but liveweight gains were not significantly different between supplements. On turnout to pasture, those animals fed on silage alone exhibited compensatory growth (P < 0·025) with the result that those fed on LH silage only grew faster and achieved the same liveweight after 13 weeks at grass as those supplemented with RSM or M. There was a tendency for those fed on FM to maintain an advantage in liveweight after the period at pasture. On EH silage, at the end of the grazing period no significant differences in liveweight existed between the different supplements and on average were 23 kg heavier than EH silage unsupplemented. In conclusion, silage type (stage of harvest and quality) and protein supplementation influenced animal performance. On late harvest and poorer digestibility silage, there was some indication that feeding fishmeal was better than rapeseed but this was less evident on early harvest and higher digestibility silage. However, considering the price differential between these two supplements and small difference in animal performance it is concluded that rapeseed meal is as effective as fishmeal when used as a protein supplement for growing cattle fed on grass silage.

Rumen biohydrogenation of dietary polyunsaturated fatty acids (PUFA) is a significant limitation on any attempt to manipulate the PUFA content of ruminant products (meat or milk). This study examined rumen biohydrogenation of PUFA, the effects of PUFA on other aspects of rumen metabolism and fatty acid flow to and digestion in the small intestine of steers fed on different sources of lipid. Animals were fed ad libitum on grass silage and one of four concentrates (60:40 forage:concentrate on a dry matter basis) containing differing sources of lipid: megalac (rich in C16:0; M), linseed (rich in C18:3n-3; L), fish oil (rich in C20:5n-3 and C22:6n-3; FO) and a mixture of linseed/fish oil (LFO). Diets were formulated so that total dietary oil intake was approximately 60 g/kg of the DM intake, approximately half of which was from the experimental test oil. Rumen NH3-N (P = 0·09) and total VFA concentrations (P = 0·007) were higher on L, FO and LFO compared to M. Dry matter intakes did not differ across treatments and averaged 7·2 kg/day. Intake and flow of fatty acids to the duodenum was 323, 438, 344 and 381 (S.E.M. 9·1; P < 0·001) and 432, 489, 412 and 465 (S.E.M. 18·5; P < 0·1) g/day for M, L, FO and LFO, respectively. Biohydrogenation of C18:1n-9 was lower than all the other unsaturated fatty acids and it was lower of FO and LFO compared to M and L, on average 66·1 and 72·2 %, respectively. Biohydrogenation of C18:2n-6 averaged 89·8 % across treatments and was lower (P < 0·05) on M compared to L and FO. Biohydrogenation of C18:3n-3 averaged 92·1 % across treatments and was lowest on M (88·8 %) and highest on L and LFO (94·3 %). Biohydrogenation of C20:5n-3 and C22:6n-3 averaged approximately 91 and 89 % across the treatments, respectively. Small intestinal digestibilities of all fatty acids were high. In conclusion, feeding different sources of lipid with different fatty acid composition had significant effects on rumen function. The PUFA in whole linseed were only partially protected from biohydrogenation by the seed coat and in contrast to previous reports the C20 PUFA in fish oil were biohydrogenated to a large extent.

In order to compare the growth potential of buds of two contrasting cultivars of white clover (Trifolium repens L.) (cv. AberHerald and Grasslands Huia) during the winter–early spring period, we adapted a method to assess the potential for activity of shoot buds and root primordia. The growth potential was evaluated following the excision of individual stolon nodes sampled in the field, from experimental plots located in the eastern part of France. Two populations of nodes were sampled: (i) the youngest node emerged from the apical bud (node 1), (ii) the third node behind the apex (node 3). The excised nodes were placed in controlled conditions and the outgrowth of axillary buds and roots was recorded every day for a week. The study demonstrated a seasonal influence on the potential for activity of axillary buds and root primordia, particularly for buds at node 3. The proportion of potentially active shoot and root buds was less than 50% at the end of March, and then increased from end of March to reach 80% in April. The data indicated a genetic variation in potential for outgrowth during winter. AberHerald had a higher percentage of potentially active buds than Huia during winter, irrespective of the node position. Moreover AberHerald buds had faster rates of outgrowth than Huia buds. Differences between cultivars in winter survival and potential for growth in spring were linked to identified cultivars' differences in developmental characteristics of buds.

Energy requirements for maintenance and growth were estimated by comparative slaughter in Omani male lambs during the hot summer months (July–October: maximum temperature, 48 °C). Weaned lambs (n = 10 per diet) were fed one of three totally mixed, 160 g CP/kg DM diets that contained 600, 400 or 200 g rhodesgrass hay/kg for low (9·98 MJ/kg, medium (10·3 MJ/kg) and high (11·4 MJ/kg) energy contents, respectively. All diets were balanced to meet the minimum nutritional needs for maximum growth. The trial lasted for 113–114 days. The purpose of having three diets was to induce a broad spectrum of growth rates that could be used in regression analysis (tested for linear, quadratic and exponential effects). Metabolizable energy (ME) intake was regressed on live weight (LW), empty body weight, tissue energy and tissue protein gain and vice versa. Coefficients of determinations were not significantly improved by quadratic or logarithmic regressions over linear relationships. Geometric mean regressions were used to control further biases due to major axis dependence when Y is regressed on X or vice versa. Based on tissue energy gain, the best estimates of ME required for maintenance (MEm) and gain (MEg) were 526 kJ/kg LW0·75/d and 42·1 kJ/kg LW0·75/g LW gain, respectively. Net energy values for maintenance (NEm) and gain (NEg) were 278 kJ/kg LW0·75/d and 20·6 kJ/kg LW0·75/g LW gain, respectively. These equations predicted MEm and NEm requirements that were similar to or slightly greater than those established by the US National Research Council (1985) and the UK Agricultural and Food Research Council (1993) for growing male lambs. The MEg and NEg requirements were substantially greater (by 43–89%) in this respect. Efficiency values were calculated as net energy available for maintenance or gain divided by the metabolizable energy available for maintenance or gain. The efficiency of metabolizable energy used for maintenance and gain was 0·50 and 0·52, respectively, and did not appear to be much different from values for other breeds of sheep in temperate climates. Dietary energy concentrations did not affect the efficiency of energy deposition. The data suggest that Omani sheep in hot climates have greater NEg requirements, and consequently MEg requirements, than other breeds of sheep in temperate climates.

A summer lamb finishing experiment at Palmerston North, New Zealand compared the performance and health of weaned lambs grazing Aries HD or Yatsyn 1 perennial ryegrass (Lolium perenne). Aries HD ryegrass was originally selected for increased digestibility over summer and early autumn. Two groups of Romney×Suffolk lambs (15 per group) were rotationally grazed on each cultivar in a leader-follower sequence to assess both the nutritive value of the pastures and the alkaloid challenge imposed by the respective cultivar/endophyte (Neotyphodium lolii) associations. Herbage from leader pastures contained a higher content of ryegrass (600 v. 474±27·3 g/kg, P < 0·001) and a lower content of dead material (355 v. 479±34·2 g/kg, P < 0·001) than follower pastures. The in vitro organic matter digestibility coefficient of leader pastures was greater (0·62 v. 0·55±0·024, P < 0·05) and the neutral detergent fibre content lower (592 v. 631±11·4 g/kg, P < 0·005) than follower pastures. Consequently, the leader lambs had faster liveweight gains (92 v. 53±10·6 g/day, P < 0·0005) than the follower lambs. Aries HD and Yatsyn 1 cultivars were similar in sward composition, in vitro organic matter digestibility, neutral detergent fibre content and nitrogen content. Lambs grazing Aries HD had a higher herbage intake in late January than lambs grazing Yatsyn 1 pasture (0·95 v. 0·85±0·023 kg OM/day, P < 0·005). Overall, the liveweight gains of lambs grazing Aries HD and Yatsyn 1 were similar (71 v. 73±10·6 g/day, P > 0·7).

Grazing sequence and cultivar did not affect the concentrations of lolitrem B and peramine from herbage cut to ground level. However, serum prolactin concentration, which can indicate ergovaline intoxication, was lower in lambs grazing follower swards (181 v. 120±18·0 ng/ml, P < 0·005). Ergovaline concentration in Aries HD herbage was about half the concentration detected in Yatsyn 1 herbage (0·25 v. 0·49±0·050 mg/kg, P < 0·001). In addition, respiration rate, which can be an indicator of heat stress, was higher in lambs grazing Yatsyn 1 than Aries HD (77 v. 74±1·1 breaths per minute, P < 0·005). All lambs on all treatments had clinical ryegrass staggers from 10 February to 9 March. Lambs were removed from the experiment on 9 March. Both grazing sequence and cultivar affected the severity of ryegrass staggers. Staggers score was highest in Yatsyn 1 followers (4·4) and lowest in Aries HD leaders (3·1). Both grazing sequence and cultivar affected the alkaloid challenge imposed on lambs, resulting in differences in staggers severity, heat stress and performance of the lambs over the summer and autumn period.

The effectiveness of alternative fertilizer strategies to control nitrate leaching was investigated in a field experiment at IGER, Aberystwyth using simulated pastures to represent swards grazed by dairy cattle between May and October 1997, following an initial silage cut. Cut-plots with and without applications of artificial urine were used to represent the separate components of grazed pastures managed with the following nitrogen (N) fertilizer strategies: standard (fertilizer applied uniformly to all areas of the sward at a total rate of 180 kg N/ha between May and October), tactical (fertilizer rates adjusted to match the average soil mineral-N content of the pasture to that of ungrazed reference plots receiving the standard rate) and patch-avoidance (fertilizer applied at the standard rate but withheld from areas that had received urine). Calculated stocking rates derived from herbage yields indicated that 12% of the pasture would have been affected by urine up to the end of ‘grazing’ in October. The presence of urine patches increased the nitrate-N content of the 0–90 cm soil profile in October from 61 kg N/ha for ungrazed pasture to 104 kg/ha for ‘grazed’ pasture receiving the standard fertilizer rate. Although the patch-avoidance strategy was more effective than the tactical in reducing the accumulation of nitrate in soil under urine patches, they were both of limited effectiveness in reducing the content over the pasture as a whole. Profile contents in October for the simulated pastures managed with the tactical and patch-avoidance strategies were equivalent to 99 and 97 kg nitrate-N/ha, respectively. The tactical strategy achieved a 26% saving in overall fertilizer use. Under the conditions of the experiment this did not significantly reduce herbage yields. The patch-avoidance strategy reduced fertilizer use by only 3%.

The effects of dietary energy concentration on tissue composition and nitrogen metabolism were determined by comparative slaughter and nitrogen balance trials in Omani male lambs during the hot summer months (July to October; maximum temperature 48 °C). Weaned lambs (n = 10 per diet) were fed on one of three isonitrogenous (160 CP g/kg DM) diets that contained low (9·98 MJ/kg DM), medium (10·3 MJ/kg DM) and high (11·4 MJ/kg DM) metabolizable energy contents. An initial slaughter group of 10 animals was used to estimate the initial body composition. Treatment animals were slaughtered at 113–114 days. Increasing dietary energy concentrations resulted in a progressive increase in empty body, carcass and non-carcass water, protein and fat contents. Increasing dietary energy concentrations also resulted in a greater deposition of energy in carcass fat and a reduced deposition of energy in carcass protein. Dietary energy concentration did not affect the distribution of energy between protein and fat within empty body and non-carcass tissues. Ratios of energy to empty body, carcass or non-carcass weight were not affected by dietary energy concentrations and averaged 17·1, 18·2 and 15·9 MJ/kg respectively. These data indicate that more energy is required to deposit carcass tissues than non-carcass tissues. Nitrogen balance trials (feed N–faecal N–urinary N) conducted midway through the experiment indicated that dietary energy concentration had no effect on nitrogen digestibility or nitrogen retention. However, nitrogen retention determined by comparative slaughter showed that animals fed the low energy diet retained significantly less empty body nitrogen compared to animals fed the high energy diet. Thus, nitrogen retention determined by nitrogen balance trials overestimated direct measurements of nitrogen retention determined by comparative slaughter and this overestimation was greater on the low energy diet.

A statistical model of the grazing preference of sheep is presented for the evaluation of spaced plants in small plots for plant breeding purposes. Plants are located randomly to reduce the effect of external factors on diet selection, and to differentiate between discriminatory and random grazing. Consistency of discrimination among grazings and sites (Massey University, New Zealand and INIA La Estanzuela, Uruguay) was tested. The statistical design and subsequent analyses considered all sources of variation to minimize error, and to separate genetic effects from environment effects. Clonal replicates were used to enhance error-control, and hence the precision of heritability estimates, as most characters are inherited quantitatively. Post-grazing leafiness is considered the best character to select and breed for animal preference in a red clover germplasm.