Two field experiments at Canterbury, New Zealand during 1991–93 investigated the effect of the timing of ploughing a 4-year-old ryegrass/white clover pasture and the effect of two winter cover crops on subsequent N mineralization, nitrate leaching and growth and N uptake of the following wheat crops.

Net N mineralization of organic N (of plant and soil origin) increased with increased fallow period between ploughing and leaching. The total amount of N accumulated in the profile by the start of winter ranged from 107 to 131 and from 42 to 45 kg N/ha for fallow treatments started in March and May respectively. Winter wheat (planted in May) had no effect on mineral N contents by the start of winter, whereas greenfeed (GF) oats (planted in March) significantly reduced the mineral N content in one year.

Cumulative leaching losses over the first winter after ploughing-in pasture varied markedly between years in relation to rainfall amount and distribution. Leaching losses were greater from the March fallow (72–106 kg N/ha) than the May fallow treatments (8–52 kg N/ha). Winter wheat did not reduce leaching losses in either year. GF oats did not reduce losses in 1991/92, but losses in 1992/93, when major drainage events occurred late in the winter, were only c. 40% of those under fallow.

Incorporation of a large amount (> 7 t/ha dry matter) of pasture or GF oat residue in spring depressed yield and total N uptake of the following spring wheat, largely due to net N immobilization which could be overcome by the application of fertilizer N.

First-year treatments had very little residual effect in the second year. Leaching losses over the second winter (mean 142 kg N/ha) were largely unaffected by the extent of first year leaching losses. Second year leaching losses were greater than first year losses, probably due to the greater amount of mineral N at depth in the soil before the start of the second winter.

Changes in the stolon carbohydrate contents (water-soluble and total non-structural) of four white clover populations were measured at the beginning and end of winter. Three of the populations were of Swiss origin - two of these were from high-altitude pastures, and the other from a valley location. Grasslands Huia was measured as a control variety. Levels of both types of carbohydrate declined during the winter in all populations. The Swiss populations from high altitudes contained the highest levels of both carbohydrate types.

An artificial freezing test was carried out on stolon segments collected from a range of clover populations (including the two high-altitude Swiss clovers) growing in field plots in January, and values of ‘lethal dose 50’ (LD50) were calculated. The two Swiss populations had the lowest LD50 values, indicating a greater intrinsic tolerance to freezing in those plants than in the other populations (of lowland temperate origin).

One of the Swiss populations, Ac3785, was grown under two temperature regimes and short daylength to determine whether its tolerance to freezing increased with time. Significant increases in tolerance occurred after 8 days at 2 °C, but plants grown at 8 °C showed no change in tolerance even after 30 days.

The results suggest that (i) stolon carbohydrate content is an important factor in the overwintering of white clover, (ii) there is a considerable amount of genetic variation in cold tolerance within white clover, (iii) artificial freezing tests can provide a method of predicting the survival of clover stolons during winter and (iv) the cold hardiness of white clover increases with time spent at temperatures near 0 °C under short daylengths.

Winter non-leguminous cover crops are included in crop rotations to decrease nitrate (NO3-N) leaching and increase soil organic matter. This study examined the effect of incorporating a mature cover crop on subsequent N transformations. A field trial containing a winter cover crop of Merced rye and a fallow control was established in December 1991 in Salinas, California. The rye was grown for 16 weeks, so that plants had headed and were senescing, resulting in residue which was difficult to incorporate and slow to decompose. Frequent sampling of the surface soil (0–15 cm) showed that net mineralizable N (anaerobic incubation) rapidly increased, then decreased shortly after tillage in both treatments, but that sustained increases in net mineralizable N and microbial biomass N in the cover-cropped soils did not occur until after irrigation, 20 days after incorporation. Soil NO3-N was significantly reduced compared to winter-fallow soil at that time. A 15N experiment examined the fate of N fertilizer, applied in cylinders at a rate of 12 kg 15N/ha at lettuce planting, and measured in the soil, microbial biomass and lettuce plants after 32 days. In the cover-cropped soil, 59% of the 15N was recovered in the microbial biomass, compared to 21% in the winter-bare soil. The dry weight, total N and 15N content of the lettuce in the cover-cropped cylinders were significantly lower; 28 v. 39% of applied 15N was recovered in the lettuce in the cover-cropped and winter-bare soils, respectively. At harvest, the N content of the lettuce in the cover-cropped soil remained lower, and microbial biomass N was higher than in winter-bare soils. These data indicate that delayed cover crop incorporation resulted in net microbial immobilization which extended into the period of high crop demand and reduced N availability to the crop.

Field and glasshouse studies were conducted in Durango, Mexico in 1987 and in East Lansing, Michigan, USA in 1989, respectively, to determine the effects of moisture deficits upon N-use efficiency (NUE), N partitioning and remobilization, and N harvest index (NHI) in edible beans (Phaseolus vulgaris L.). Four indeterminate, semi-prostrate genotypes adapted to the semi-arid high plains of Mexico, Pinto Nacional-1, Durango 222, L1213–2 and Bayo Madero, were used in the field study and Pinto Nacional-1 and Bayo Madero were used in the glasshouse study. A Xerosol Haplic soil was used in the field study and a Spinks loamy sand in the glasshouse study. A moisture deficit was induced by use of temporary rainshelters in the field and curtailment of water in the glasshouse. Plants were sampled periodically and subdivided into leaves, stems, pods and flowers, and roots (in the glasshouse study only) for determination of dry weight and total N content. Water-use efficiency was determined in the glasshouse study. A moderate moisture deficit (drought intensity index 0·41) reduced yield by 41% in comparison with non-stressed yield (from 134·3 down to 79·2 g/m2) and resulted in a greater percentage of seed-N derived from N that had been redistributed from the leaf, indicating that N partitioning was not impaired by this degree of stress. In contrast, N remobilization was greatly reduced by a more severe moisture deficit (drought intensity index 0·92), which resulted in yield losses of 92% (from 2·19 down to 0·17 g/pot). These results suggest that N remobilization may be an important drought adaptation strategy under moderate or intermittent moisture deficits. Severe moisture deficits reduced NHI, harvest index (HI), NUE and water-use efficiency (WUE) when WUE was expressed as seed dry weight per litre water used. Genotypic variability was observed for NHI, HI and NUE.

A 4-year field experiment was conducted from 1986 to 1989 in Niger to determine the effects of pre- and post-harvest tillage and rotation of pearl millet (Pennisetum glaucum (L). R. Br.) and cowpea (Vigna unguiculata (L.) Walp.) on crop yield, crop water use and soil fertility on a sandy soil. Presowing tillage increased grain and crop residue yields over the traditional system of no tillage. Post-harvest tillage resulted in lower yields than pre-sowing tillage during the last 2 years of the experiment. Millet-cowpea rotation increased yield and there were no important tillage × rotation interactions. Crop water use was similar for a dry and a wet year, but less water was held in the profile after the harvest of cowpea. Compared to pre-sowing tillage and no tillage, post-harvest tillage increased the amount of water conserved until the next season. In all treatment combinations, soil organic matter and total N content both declined on average by 62%, and soil pH (KCI) decreased from 4·6 to 4·3.

Slurry pH is of great importance for the regulation of ammonia volatilization from livestock slurry, and therefore more knowledge of the buffer system controlling pH is urgently needed for modelling ammonia losses from stored and surface-applied slurry. The composition of 17 different Danish cattle, pig and biogas plant-digested slurries was studied. The results were used to describe the main buffer components in the slurries, and to discover the most important chemical components necessary for modelling slurry pH. The results showed that the pH of slurry was mainly controlled by the species NH4+/NH3, CO2/HCO3-/CO32- and CH3COOH/CH3COO-, and that ion pair formation did not change the ionic balance significantly. There were only trace amounts of Ca2+, Mg2+ and inorganic phosphates in solution due to precipitation of CaCO3 (calcite) and MgNH4PO4.6H2O (struvite). Measured electrical conductivities were found to be strongly correlated with the calculated ionic strength.

A simple mathematical model is shown to provide reasonably good predictions of time series data on ammonia loss from three experiments on slurry stores. The model produces predictions of changes in the distribution of ammonia with depth. Experimental evidence suggests that ammonia concentrations above a critical value appear to destroy the viability of Cryptosporidium oocysts. Using this criterion, the model predicts that, even under the most favourable circumstances, oocysts are unlikely to remain viable in slurry stores except in the top few centimetres. The effect of stirring the slurry is considered.

Data on ovulation rate and numbers of ova and transferable embryos recovered from superovulated cattle and sheep were analysed using generalized linear models, quasi-likelihood, restricted maximum likelihood (REML) and generalized linear mixed models (GLMMS). The data pertained to the operation of nucleus breeding schemes in cattle and the commercial application of embryo transfer in sheep.

Results of the analyses showed that generalized linear models involving Poisson and Binomial distributions were inappropriate because of over-dispersion, and that analyses using quasi-likelihood to model negative binomial and β-binomial distributions were more suitable. Factors identified as important in determining the results in cattle were the number of previous superovulations (a higher proportion of transferable embryos were obtained in the initial flush compared to subsequent recoveries in two out of three sets of data), the donor (significant in all analyses with repeated recoveries) and its mate (significant in some analyses). In sheep, the use of pFSH or hMG for superovulation increased embryo yields above those obtained with PMSG + GnRH. Analyses of a further data set for sheep showed the effect of breed was ambiguous.

The effects of donors and their mates were treated as random effects in analyses involving REML and GLMMS. Results showed that the repeatability of the number of transferable embryos produced per donor ranged between 0·13 and 0·23 in three sets of data and was significant in all cases. In these analyses the variance among mates was not significantly different from zero.

The results of analyses were used to develop a random generator to simulate the numbers of ova and embryos recovered from a cow following superovulation. By sampling from negative binomial distributions where the scale factor used for each cow was a normally distributed deviate, distributions were obtained which had the same mean, variance and repeatability as those observed.

The evaluation of n-alkane concentrations in herbage and faeces is the basis of a methodology that yields precise estimates of herbage intake. Established chemical analysis procedures for the determination of n-alkane concentrations in herbage and faecal samples involve an elaborate sequence of steps utilizing n-hexane as solvent for both the liquid-liquid extraction of n-alkanes from the sample and the solid-phase separation of n-alkanes in the extract. Composites of herbage and faecal samples from studies with sheep provided the experimental material used to evaluate a series of modifications which would simplify and reduce the workload involved in the chemical analysis. The results show that a less hazardous chemical, n-heptane, can replace n-hexane at all stages of the analytical procedure. They also show that evaporation of the sample extract and redissolving it prior to the separation of the n-alkanes, using a silica gel column, is unnecessary and that the volume of solvent used can be reduced. Procedures for saponification of samples prior to extraction can also be simplified as the process can be run overnight involving a slow build-up of temperature to 90 °C. The gain in precision from processing samples in duplicate was negligible and it would be more appropriate to invest extra efforts on an increased number of experimental animals. The results snowed that the workload and cost of using the n-alkane technique to estimate herbage intake can be reduced substantially.

Herbage intake estimation, using the n-alkane technique, requires the determination of the ratio of ‘dosed’ to ‘natural’ n-alkane concentrations in faeces. The present study was designed to evaluate the accuracy and precision of intake estimates based on the analysis of pooled samples of total daily faecal output and those derived from rectal grab samples.

Wether lambs maintained in individual metabolism crates, offered fresh herbage ad libitumand dosed daily with 120 mg of n-dotriacontane (C32), were used. Actual intake was recorded daily and samples of total faecal output were retained either for individual analysis or to produce 6-day composites by pooling representative amounts of material from each day's faecal output. Different pooling strategies were evaluated: a constant volume of fresh faecal material from each day or a constant weight (or constant volume) of dried and ground material from each day's faecal output. In addition, daily rectal grab samples, obtained at the same time each day, were pooled using a constant daily volume of fresh faeces. Herbage intake was estimated using the ratios of faecal concentrations of n-hentriacontane (C31) or n-tritriacontane (C33) relative to that for C32.

Similar patterns of effects were observed for intake estimates derived from the C31: C32 and C33:C32 n-alkane ratios for the different faecal sample types. Comparisons based on intake estimates derived from the use of the C33: C32 ratio showed that there were no significant differences between actual intake and estimates based either on the mean of daily samples or on the different composites of total daily faecal output. Intake estimates based on the analysis of composites of total daily faecal output were consistently lower (c. 3%) than those based on the analysis of daily faecal samples. A difference of this magnitude is expected, based on the algebraic relationship between the mean of a ratio of two variables (e.g. faecal concentrations of C33 and C32) and the ratio of the corresponding means. Intake estimates derived from the use of rectal grab samples, taken 3 h after the daily dose was given, yielded a proportionate overestimation of actual intake of 0·06 (P < 0·10). No significant differences were detected in the precision of intake estimates derived either from individual daily samples, composites of total daily faecal output, or composites of rectal grab samples, although the latter yielded the lowest precision.

It is concluded that faecal samples can be pooled on a gravimetric or a volumetric basis over several days with negligible loss in precision of intake estimates. Such pooling greatly reduces the workload and costs involved in using the n-alkane technique. Sampling and analytical errors associated with t e technique were found to be very small, and the processing of faecal samples in duplicate would result in a negligible increase in the precision of intake estimates. The need for further evaluation of rectal grab sampling under grazing conditions is highlighted.

The idea that the addition of compound feed to grass at ensilage can result in adequate preservation of the crop without the need for an acid additive, and that less compound feed would then need to be given when the silage is subsequently fed, was tested with dairy cows. Two diets were compared: (1) a conventional grass silage, to which acid had been added at the time of ensiling, plus concentrates supplied at the time of feeding, and (2) grass silage, to which a compound feed had been added at the time of ensiling, plus a lower rate of concentrates. Each diet was fed to 12 lactating cows for 82 days.

The total intake of dry matter was 17·3 kg per cow per day on diet 1 and 18·3 kg on diet 2. Daily milk yields per cow were 24·5 and 26·1 kg, respectively, with similar milk composition. The estimated diet costs per kg of milk were 9·3 p on (1) and 8·3 p on (2). It is concluded that the addition of compound feed to grass at ensilage is worth considering on dairy farms as an alternative to conventional grass silage, but that a more comprehensive study is needed.

Low, medium and high planes of nutrition were imposed on Friesian calves from 1 to 13 weeks of age (Period 1) and factorially arranged with low and high planes of nutrition in the 13–25 week period (Period 2). In the final (residual) period, from 25 weeks to slaughter, all animals were given the same high plane diet comprising 3·5 kg of concentrates and grass silage ad libitum. The different planes of nutrition were achieved by offering restricted allowances of milk replacer or concentrates with grass silage ad libitum. Representative animals were slaughtered at 1, 13 and 25 weeks of age while the remaining animals were slaughtered at mean liveweights of 503 and 553 kg. Over 2 years, a total of 120 Friesian steers were taken through to the final slaughter point, with 60 additional animals being slaughtered at interim stages. The animals were housed in non-bedded accommodation throughout the study and the calves were born in January of each year. The ME intake of the low plane animals in Period 1 was 0·55 that of the high plane animals and produced liveweight (LW), empty body (EBW), carcass (CW), non-carcass (NCW) and alimentary tract (ALW) weight gains which were 0·60, 0·46, 0·47, 0·44 and 0·55 of the gains of the high plane animals. In Period 2 the low plane animals had ME intakes which were 0·69 of the high plane animals and produced proportional gains of 0·57, 0·48, 0·45, 0·51 and 0·56 respectively. Previously restricted animals had higher rates of gain subsequently and the indices for weight compensation by the final slaughter point in LW, EBW, CW, NCW and ALW for the low plane treatments in Period 1 were 0·72, 0·82, 0·89, 0·73 and 0·97 while indices for low v. high in Period 2 were 0·82, 0·82, 0·79, 0·86 and 0·95. With lower plane animals, food intakes/liveweight0·75 were significantly higher during the compensating period. Calves which had been restricted in either of the early periods had significantly improved food conversion efficiency during the compensating period but lifetime food efficiency was not affected by plane of nutrition in early life.

Low, medium and high planes of nutrition were imposed on Friesian calves from 1 to 13 weeks of age (Period 1) and factorially arranged with low and high planes of nutrition in the 13–25 week period (Period 2). In the final (residual) period, from 25 weeks to slaughter, all animals were given the same high plane diet. The different planes of nutrition were achieved by offering restricted allowances of milk replacer or concentrates with roughage ad libitum. The roughage was grass hay during the milkfeeding period and grass silage thereafter. Representative animals were slaughtered at 1, 13 and 25 weeks of age while the remaining animals were slaughtered at mean liveweights of 503 and 553 kg. The ME intake of the low plane animals in Period 1 was 0·55 that of the high plane animals and produced daily accretions of protein, fat and energy in empty body which were respectively 0·43, 0·29 and 0·36 of the gains of the high plane animals. The ME intake of the low plane in Period 2 was 0·69 of the high plane and daily accretions of protein, fat and energy in empty body were 0·46, 0·59 and 0·54 of the gains of the high plane animals.

Within Period 2 compensatory protein growth was observed in both carcass and non-carcass components in response to nutritional restriction in Period 1. Compensatory protein growth was also obtained in the carcass component in the residual period as an indirect effect of nutritional restriction in Period 2.

Nutritional restriction in early life produced relatively small non-significant direct effects on body and carcass composition and while early restriction subsequent produced a considerable degree of compensatory growth, there were no significant differences in carcass measurements or chemical composition of the carcass by the final slaughter weight.

Whole-body oxygen (O2) consumption was measured continuously in pigs from the product of blood flow through the pulmonary artery and arterio-venous (AV) difference of blood O2 content across the lungs (pulmonary AV procedure). Blood flow in the pulmonary artery, a measure of cardiac output, was monitored continuously using a transit-time ultrasound flow probe surgically implanted around the artery. The O2 content of pulmonary artery blood, which represents mixed venous blood O2 aturation (SvO2) was recorded continuously by fibre-optic oximetry. The relative constancy of arterial blood oxygen saturation (SaO2), obtained by catheterization of the saphenous artery, obviated the need for continuous monitoring. Complete recovery from surgical procedures, as indicated by the absence of infection and a return to pre-surgery food intake, occurred in 3–5 days. The combination of transit-time ultrasound and fibre-optic oximetry allowed the pulmonary AV procedure to provide continuous data on the oxygen consumption of growing pigs at high temperatures.

The effects of severe food restriction and of protein supplementation on the apparent digestibility of a forage were studied on 12 wethers in 1992 at INRA, Theix. Ruminal digestion of the forage cell walls was studied in a second experiment carried out on four ewes fitted with rumen and duodenal cannulas, receiving the same diets as the wethers. The animals were fed on two different hay-based diets: hay only (58 or 25 g/kg BW0·75 per day) or hay supplemented with fish meal (48 or 20 g hay with 6·5 and 3·0 g fish meal respectively per kg BW0·75). The effects of fish meal supplementation on apparent digestibility of the hay cell walls were small, + 1·8 and + 2·3 units for neutral detergent fibre (NDF) and acid detergent fibre (ADF) respectively. In contrast, NDF and ADF digestibility was respectively 4·0 and 4·7 units higher at low than at high intake. Rumen fluid volume decreased by 2·4 1 with decreasing intake, while water concentration in rumen content increased slightly from 89·8 to 91·8%. The mean retention time of the hay particles in the foreguts increased concomitantly from 39·5 to 55·1 h. This was achieved by a higher retention time to a similar extent in both slow and fast compartments. The calculated in situ degradability of NDF and ADF increased respectively by 12·1 and 13·1 units with decreasing intake. This reflected the lower fractional outflow rate recorded at low intake. If a fractional outflow rate value of 4·1%/h (as measured in high intake diets) was applied to all dietary treatments, NDF and ADF in situ degradability would be greater at low than at high intake (31·7 v. 26·6% for NDF; 27·9 v. 22·1 % for ADF), indicating a higher microbial activity in restricted diets. Interactions between intake and fish meal supply were detected for in situ degradation parameters, indicating principally a reduction of the cell wall undegraded fraction in supplemented diets when intake declined. Ruminal fermentation was modified by the dietary treatments, the acetate: propionate ratio being higher at low intake. Fish meal increased concentrations of ammonia and of isoacids in rumen liquid. The relationship between apparent digestibility and in situ degradability of plant particles is discussed.

The physiological consequences of selection for weaning weight were investigated using 14-month-old castrated male Merino lambs from lines selected for (W +) and against (W – ) weight at weaning for over 10 generations. The selection experiment commenced in 1953 and was conducted at Trangie, NSW, Australia. Lambs from these lines now differ by 42% in weight at weaning and maturity, and have a proportionately similar composition of protein, fat and ash in their bodies at similar stages of maturity. In the whole body, there were no apparent between-strain differences in protein synthesis, but W + lambs had lower (P < 0·05) rates of phenylalanine oxidation than W – lambs. In hind limb muscle, protein metabolism of W + lambs was more responsive to food intake than in W – lambs. In particular, the rate of change of protein degradation differed (P < 0·05) between the lines in response to food intake per unit liveweight with protein degradation decreasing with increased feed intake in W + lambs. W + lambs had lower (P < 0·05) rates of blood flow to, and used less (P < 0·05) oxygen per kg hind limb muscle than W— lambs. Endocrine differences between the lines included increased (P < 0·05) plasma insulin-like growth factor-I (IGF-1) concentration in W + compared to W— lambs and, from regression analysis, an indication that there was a higher (P < 0·01) response in hind limb protein gain to insulin in the W + lambs.

These results suggest that selection for weaning weight has altered the dynamics of protein metabolism in lambs, principally through alterations in protein breakdown in muscle. Moreover, they suggest that there are associated genetic differences in endocrine control of protein metabolism which involve insulin and possibly IGF-I.

Cumulative feed and water intakes and body weights of 30 growing ewe lambs of three different breeds were recorded weekly for 34 weeks between October 1990 and June 1991 at the Experimental Farm of the University of Pretoria. The results were analysed to obtain water efficiencies on both an absolute and metabolic weight gain basis. On an absolute basis, Mutton Merino sheep consumed 145% and Dorper 109% more water than Blackhead Persian sheep. On a metabolic weight gain basis, the corresponding differences were 92 and 66%, respectively. Mutton Merino and Dorper lambs also consumed 69 and 41% more water per kg feed intake than the Blackhead Persians, respectively. Weekly water consumption increased twice as much per 1 °C increase in ambient temperature in the Dorper and Mutton Merino lambs as in the Blackhead Persians. These results suggest that sheep of the Blackhead Persian, and probably also other indigenous breeds, balance their water requirements at a more economical level and would be a more appropriate choice than those breeds currently being managed in sustainable sheep production systems in areas where water availability is limited.

Sheep fitted with a ruminal and a duodenal cannula were used to study the effect of dry matter intake and the physical form of the diet on salivary P secretion and faecal endogenous P loss. At constant low P intake, changing the form of the diet had no effect on either parameter and while increasing dry matter intake did produce small changes in the partitioning of P excretion between urine and faeces it had no effect on overall endogenous P loss (faecal endogenous P + urine P) which was largely determined by P intake.