The mammary gland is controlled at two levels in the body. The genetically controlled pattern of parental investment during lactation is modified by nutritional status and signalled to the mammary gland by the endocrine system (see Peaker 1989). The response to this strategic control of the rate of milk secretion is modulated by a tactical control mechanism operating within each mammary gland. The local intramammary mechanism responds to changes in the frequency or completeness of milk removal and acts to match the rate of milk secretion to the rate of milk removal by the young or, in dairy animals, by the milker. It is the local control of milk secretion by milk removal which has been uncovered in recent years, following the realization of the physiological significance of unilateral effects of frequent milking in goats (Linzell & Peaker 1971) and cows (Morag 1973) that is the subject of this brief review.

Six soil series differed in water-soluble, exchangeable and nonexchangeable K. Significant positive relationships were observed between exchangeable K and water-soluble K. A highly significant positive relationship was found between the K saturation of the cation exchange complex and water-soluble K in the individual soil series, and when the six series were pooled; K saturation, therefore, may predict water-soluble K in a range of tropical soils. Potassium desorbed in 35 min by electroultrafiltration (EUF) may serve as a measure of exchangeable K in predominantly kaolinitic tropical soils. In soils with appreciable amounts of mica, longer K extraction by EUF (up to 70 min) may indicate the reserves of nonexchangeable K.

The nature and availability of phosphorus in long-term fertilized pasture soils was investigated in a series of field trials, which included liming, N fertilizer and cultivation and involved monitoring plant P uptake and changes in topsoil (0–7·5 cm) P fractions for 2 years (1982–83). Liming increased soil organic P mineralization. This was indicated by significant decreases in extractable organic P and concomitant increases in microbial biomass P in the limed soils, although these changes in soil P had no significant effect on pasture yield and P uptake. On the other hand, N fertilizer increased pasture yield and P uptake but had little effect on the amounts of P in the different soil P fractions. In the cultivated soils, increases in plant-available inorganic P were attributed to the release of P during decomposition of plant residues, while the maintenance of fallow conditions decreased amounts of microbial P in these soils.

A series of experiments examining the influences of size and spacing of planted potato tubers (‘seed’ tubers) on tuber yields was conducted at four sites in the UK in 1982–84. A new approach to data analysis was used to estimate the optimum tuber planting density for different ware grades. The optimum density, which maximized returns, decreased with increasing seed tuber weight and ratio of seed-tuber cost to ware value and with lower than average total tuber yields. Changing the required ware grade from 40–65 mm to 40–80 mm had a minimal effect on the optimum tuber planting density.

Optimum tuber planting densities were lower than in published recommendations but this disparity appeared to be accounted for by differences in the number of stems produced by each planted tuber. There was some evidence that, with lower seed-tuber weights, the optimum planting density differed with site and that at optimum economic densities small and medium seed tubers outyielded large seed tubers.

A study of 76 F1 hybrids involving four sources of cytoplasmic male sterility and 19 male-fertility restorers indicated great diversity among the cytoplasms for total soluble solids. The exploitation of cytoplasms other than milo is recommended for breeding programmes aimed at high total soluble solids content. Most of the Indian restorers showed significant positive general combining ability (GCA) effects, whereas exotic restorers showed negative GCA effects for total soluble solids content.

A balance experiment was carried out using four young lactating goats in a Latin square design, fed with perennial ryegrass (Lolium perenne) from plots that had received 377 kg K/ha (diet 1); 63 kg K plus 377 kg Na/ha (diet 2); 188 kg K plus 188 kg Na/ha (diet 3) or no fertilizer (control diet 4).

The apparent availability of Mg was high in all the grass diets (0·355–0·469); it was significantly depressed (P < 0·05) when the intake of K was high (diet 1); but was not significantly different when a high intake of K was accompanied by a high intake of Na (diet 3).

There was a significantly lower (P < 0·05) apparent availability of Na in diet 4 and a significantly higher (P < 0·05) apparent availability of K in diet 3. There were no significant differences in the apparent availability of Ca.

The plasma Mg concentration was not significantly affected by any dietary treatment but did decrease temporarily when diets were changed.

There were no significant effects on mineral concentrations in the milk.

Determinate varieties of Vicia faba are smaller and may require higher plant population densities than their conventional indeterminate counterparts to attain high yields. This hypothesis was examined at the University of Nottingham farm at Sutton Bonington, UK, and at INRA, Dijon, France in 1986 and 1987. The determinate varieties Ticol and TP667 and indeterminate M5.1 and Maris Bead were sown in the spring to give a range of densities of 10–100 plants/m2.

Yields generally increased as population density increased. The optimum density for determinate varieties was higher than for indeterminate varieties. Indeterminate varieties yielded more than determinate varieties at all plant densities, perhaps because of their larger canopy. Seed yields were affected by year and location. Greater yields were associated with heavier seeds and more seeds per pod.

Although several yield components, when expressed per unit area, were significantly correlated with seed yield, their coefficients of determination were never very large. This confirmed the plasticity of yield in field beans.

Two steers totally nourished by intragastric infusion of volatile fatty acids and casein were given an abomasal infusion of a microbial protein preparation (Pruteen) at eight rates with a purine input ranging from 0 to 170 mmol/day over 11 successive 5-day periods. The urinary excretion of purine derivatives relative to the purine input was measured. Negligible amounts of xanthine plus hypoxanthine were present in the urine. The relative contributions of allantoin and uric acid to the total excretion were not affected by the rate of purine infusion. Total purine derivative excretion (uric acid and allantoin) was linearly correlated with purine input. Recovery in the urine of the infused purines was 0·77. It is suggested that utilization of exogenous purines may only occur in the intestinal mucosa and that the remaining purines may be completely converted, before entering the liver, to uric acid and allantoin, which are subsequently eliminated by the renal and extrarenal routes. The differences between cattle and sheep in excretion of purine derivatives, and the implications of these differences for the use of purine excretion values in order to estimate microbial protein supply to the ruminant, are discussed.

Ten dairy cows were allocated into three groups according to milk productivity (four high, four intermediate and two dry cows, respectively). Heat production and heart rate, but not rectal temperature, were significantly different (P < 0·05) between groups. Heat production increased during feeding in the morning and in the afternoon and reached a peak 3 h later. Minimum heat production was observed in the early morning before feeding. The diurnal pattern for heart rate reflected that of heat production. These results suggest that cooling dairy cows during hot summer days is most effective at feeding time and 3 h afterwards.

The effects of shade (50% of ambient light transmission) on the quality of established swards of buffalo grass (Stenotaphrum secundatum) and kikuyu grass (Pennisetum clandestinum) were examined at Wollongbar Research Station, northern New South Wales. Sarlon cloth was used to shade plots of the two species, after cutting to 8 cm, from November 1985 to March 1986. Herbage was harvested from shaded and adjacent unshaded plots for chemical analyses and for feeding as dry chaff to penned sheep at the University of Queensland research farm at Mt Cotton.

Shade markedly decreased the voluntary feed intake (VI) of P. dandestinum by 30·7% over the two harvests while VI of S. secundatum was not significantly affected. Shade had no effect on the in vitro and in vivo digestibility of P. clandestinum herbage but marginally increased that of S. secundatum. These shade effects resulted in a 14·2% increase for S. secundatum and a 34% decrease for P. clandestinum in the intake of digestible dry matter of shaded compared with unshaded herbage.

The reduced VI of the shade-grown herbage of P. clandestinum was associated with a higher proportion of stem (21 v. 8% for unshaded herbage), a lower proportion of leaf (48 v. 54%), and a lower concentration of total nonstructural carbohydrates (TNC) (0.9 v. 2.1%). In S. secundatum, there were similar, but smaller, changes in proportion of stem and TNC percentage in shade-grown herbage but, in contrast to P. clandestinum, these potential detriments to VI were offset by an increase in proportion of leaf and a decrease in the proportion of dead material. Average moisture content of shaded herbage (76%) was higher than that of unshaded herbage (70%). Nitrogen and potassium concentrations in plant tissue were higher in the shaded herbage.

The higher yielding capacity and maintenance of nutritive quality of shaded S. secundatum compared with shaded P. clandestinum indicates the potential usefulness of S. secundatum for plantation agriculture.

Wheat straw (WS), paddy straw (PS), farmyard manure (FYM) and water hyacinth (Eichhornia crassipes) compost (WHC) were applied at four rates and on four dates before transplanting to the rice cultivar Ratna, in a pot experiment at Kharagpur, India in the wet (first crop) and dry (second crop) seasons of 1985/86. Grain yield of the first crop increased significantly with increasing rates of FYM and WHC up to the equivalent of 15 t/ha but, with the application of WS and PS, the yield was greatest at 10 t/ha and decreased at 15 t/ha. On the other hand, yield increased appreciably when WS and PS were applied up to 30 days before transplanting (DBT) but, with FYM and WHC, such increases were less pronounced. The effect of higher rates (10 and 15 t/ha) was more pronounced with early application of organic materials (20 and 30 DBT). Residual soil fertility estimated by organic carbon and available N, P and K increased under all the organic materials, which favourably influenced growth and yield of the second crop grown without supplementary fertilization. The residual effect of increasing rates of WS and PS in increasing grain yield was significantly higher than with FYM and WHC.

The effects of year of birth, age of dam, sex of calf, month of birth and weaning age on weaning weights of Mashona calves on six commercial farms in Zimbabwe were estimated by least squares procedures from data of 6365 calves born 1977–85. The least squares mean weight at 205 days among farms ranged from 123 to 159 kg while the linear regression coefficients of weight on age ranged from 0·31 to 0·46 kg. Adjustment for weaning age by the average daily gain from birth to weaning failed to remove the dependence of adjusted weight on age. Sex was the most important source of variation and the mean difference between male and female calves was 12·9 kg. Sex difference was markedly influenced by herd production rate, being greater in herds of above average production.

Weights of calves of 3-, 4- and > 11-year-old dams deviated from those of dams aged 5–10 years (mature) by 14·5, 8·5 and 2·9 kg, respectively. Herd mean influenced the difference between 3-year-old and mature dams, the difference increasing as herd mean declined. Herd-year specific factors seem more appropriate for sex and 3-year-old dams and an annual crop of > 50 calves would confer an advantage to herd-specific over general adjustment factors. On the basis of equality of variances within subclasses, multiplicative factors were superior to additive factors for sex of calf and month of birth; both types of adjustment were suitable for age of dam.

The effects on flower drop and pod set of applications of either the auxin 4-choloroindole, the cytokinin 6-benzylaminopurine (BAP) or gibberellic acid (GA3) to every flower, 1 day before or 1 day after tripping, were studied in broad bean plants grown in a glasshouse in 1988. Control plants shed most of their flowers; pods that did set originated primarily from flowers at proximal positions on the raceme. Most pods set on the lower part of the reproductive portion of the control plants. Chloroindole and GA3 application before tripping had no significant effect on pod-set pattern. However, GA3 applied after tripping significantly enhanced pod set at proximal flowers by 21% but inter-raceme pod set was not significantly altered. Chloroindole applied after tripping significantly increased pod set, particularly at proximal flower positions on the raceme; this treatment increased inter-raceme pod set but the increase was significant only for the basal four racemes and racemes 11, 12 and 13. Application of BAP before or after tripping resulted in almost complete pod set on all racemes; but greater flower drop was observed on the uppermost five racemes of plants treated after tripping than on corresponding racemes of plants treated before tripping. The effects of BAP, chloroindole or GA3 treatment were not due to changes in the synchrony of flower opening. An adequate supply of a cytokinin appeared to be necessary at or before pollination to initiate changes in reproductive organs to prepare them to become net attractors of assimilates from other plant parts. Auxin and gibberellin were only effective in promoting fruit set 24 h after tripping. An adequate supply of auxin, and perhaps of gibberellin, in balance with cytokinin appears to be required after pollination to maintain the flow of adequate assimilates to enable further pod development and for maturation to proceed.

White clover genotypes selected for frost tolerance and susceptibility were pair-crossed in various combinations with unselected genotypes of Grasslands Huia. Progeny lines and parent genotypes were artificially frosted at −8°C and scored for percentage of leaves damaged. Progeny from crosses between frost-tolerant genotypes were less damaged by frost than progeny from crosses involving either susceptible genotypes or unselected Grasslands Huia genotypes. Heritability estimates for frost tolerance or susceptibility were high, ranging from 0·75 to 0·93, depending on method of calculation. Removal of leaf-size effects from scores of frost damage reduced heritability estimates to 0·54–0·73. It was concluded that, because heritability for frost tolerance was high, selection for this character and incorporation of frost tolerance into agronomically suitable but frost-sensitive cultivars by breeding would be successful.

Compositional analysis of feeds and other materials by near-infrared reflectance (NIR) has been proposed as a cheap and rapid alternative to traditional wet chemical methods. A theoretical basis for NIR measurements is needed and may be obtained from the study of artificial mixtures of pure chemicals.

Mixtures of lactose, casein and sodium oleate, in widely differing concentrations, were analysed by NIR. Principal component analysis was used to study the variations between spectra, and multiple linear regressions gave predictors of sample compositions from the spectra. Optical densities at most combinations of wavelengths gave good predictions of sample compositions because there was much less unexplained variation between NIR spectra than would occur between natural samples.

The voluntary food intake, in vivo digestibility and site of nutrient digestion was measured in 12 Polled Dorset ram lambs, from 6 to 24 weeks of age, offered clover hay. Lambs were weaned at 6 weeks of age. Six were fitted with a permanent T-shaped cannula in the abomasum and a temporary rumen catheter during the periods of digesta flow measurement.

Surgical modification of lambs did not influence intake (g/kg live weight (W) per day), in vivo digestibility or marker retention time in the rumen. However, intact lambs grew significantly faster than cannulated lambs (139 v. 109g/day, P < 0·05) apparently because of an overall higher cumulative intake over the whole experimental period rather than any change in efficiency of use of nutrients or maintenance requirement.

Relative to live weight, intake increased rapidly until c. 10 weeks of age and remained relatively constant at c. 37 g DM/kg W per day for the remainder of the experiment. Age had no effect on in vivo digestibility of organic matter (OM) or neutral detergent fibre (NDF) (average 0·69).

The proportion of digestible organic matter apparently digested in the rumen (DOMADR) decreased from 0·63 to 0·47 between 8 and 24 weeks of age whilst intake between these measurement periods increased. Nonammonia N (NAN) flow past the abomasum was similar at all ages in relation to digestible organic matter intake (55·1 g NAN/kg DOMI) but was higher at 16 and 24 weeks of age than at 8 and 12 weeks of age, respectively, in relation to organic matter apparently digested in the rumen (OMADR) (116 and 85 g NAN/kg OMADR, respectively, P < 0·05).

Fractional outflow rate of digesta markers from the rumen, when estimated from abomasal digesta, was significantly higher than when estimated from faeces (103Ru-p 0·121 v. 0·09; 51Cr-EDTA 0·169 v. 0·111/h; P > 0·05).

It was concluded that cannulation did not affect intake and digestion characteristics in these young lambs. The changes in the site of nutrient digestion as the animals aged may have been due to agerelated changes in digestive function but appeared to be associated with the increase in intake that occurred between measurement periods of the cannulated lambs.

seventeen maize (Zea mays L.) genotypes (unimproved local varieties, improved open-pollinated composites, hybrids and F1 varietal crosses) were compared on a 1–5 scale for taste when eaten as boiled green maize. Significant differences were obtained between and within genotypic groups. Differences within the open-pollinated composites and the varietal crosses were highly significant. Using mean score ratings as an index for selection, the three genotypes TZB, BN59 × 1K8149SR-BC2 and TZESR-W × 1K8149SR-BC2 were identified as having the best taste, with mean scores of 3·6, 4·3 and 3·5, respectively.

On a clay loam soil, the cultivar Col 148, planted in spring 1987 at 57560 three-budded setts/ha received 0, 75, 100 and 150 kg N/ha and 0, 10, 20 and 30 t/ha fresh sulphitation press mud either separately or in combined applications, at 80% moisture. Separate applications of up to 150 kg N/ha and up to 30 t press mud/ha increased the cane biomass by 24·6% and 13·2%, respectively, whereas combined application increased it up to 38·1% more than in the control. A N concentration of 1·95–2·12% in the blades of leaves 3·6 from the top of the plant from tillering to the grand growth stage was necessary for maximum dry matter production. Sulphitation press mud enhanced uptake and availability of N and P to the crop and reduced soil pH. Application of 10 t press mud/ha saved 75 kg/ha of fertilizer N.

The response to shade in growth and nutritive quality of buffalo grass (Stenotaphrum secundatum) was compared with that of two other stoloniferous grasses, mat grass (Axonopus compressus) and kikuyu grass (Pennisetum clandestinum). The grasses were grown outdoors in Brisbane, Australia, in soil in pots over two growing seasons in 1985/86. Treatments in the first season (Expt 1) were shading at 0 (full sun), 42, 59 and 68% with moderate N (two spaced applications of 50 kg/ha) and, in the second season (Expt 2), 0 and 59% shade with high (50 kg/ha every 2 weeks) and low (5 kg/ha every 2 weeks) N.

Unusually for tropical grasses, the top yield of all species was higher under shade than in full sun, except for S. secundatum at high N in Expt 2. S. secundatum and A. compressusshowed an increase in top yield up to 68% shading whereas P. clandestinum reached a maximum at 42% shading. Shade increased shoot:root ratio and specific leaf area in all species but had little effect on leaf:stem ratio and the proportion of dead material in the tops. Stubble yield (stem bases and stolons) was reduced under shade but to a much smaller extent than root yield. S. secundatum and A. compressus had similar morphological characteristics. Their yield was lower than that of P. clandestinum in Expt 1 (autumn growth) but was similar to that of P. clandestinum in Expt 2 (summer growth). These grasses had a higher leaf:stem ratio and lower proportion of dead material in tops than P. clandestinum.

Shade generally increased herbage nutritive value through an increase in N concentration and drymatter digestibility. The latter response was somewhat variable and mostly small (1–3% units). Under shade, the general trend was towards a decrease in total nonstructural carbohydrates, cell-wall content and insoluble ash, and an increase in lignin content. A. compressus was higher in digestibility and soluble carbohydrates than the other grasses.

S. secundatum was not clearly superior in response to shade and its nutritive quality was lower than that of A. compressus.

Eight feeds were treated with seven solvents and the proportion of seven mineral elements (Ca, Mg, P, Na, K, Cu, Zn) released was assessed. Six of the feeds were from Sri Lanka (Panicum maximum ecotype Guinea A, Glyricidia maculata, Artocarpus heterophyllus, untreated and urea-treated rice straw, and rice bran) and two from the Netherlands (maize silage and wheat straw). The solvents were water, tris buffer, rumen fluid from a cow deprived of (RF -) or fed (RF +) mineral supplements, neutral detergent solution with (NDS +) or without (NDS -) EDTA, and acid detergent solution (ADS).

Both the type of feed and the solvent significantly influenced (P < 0·01) the amount of dry matter loss and the proportion of minerals released. Maize silage released over 80% of its minerals, except Cu, in water and tris buffer, probably because of the low pH (3·7) during ensiling. The other feeds differed widely in their ability to release minerals. In general, P, Na and K. were more soluble in water than Ca, Mg and Zn.

Mineral concentration in RF influenced not only the amount of minerals released, but also the extent of sorption by the feed. The latter effect was more pronounced in feeds with low mineral concentration, maize silage being no exception.

Treatment with NDS+ and ADS removed all minerals except Cu. With all feeds, 12–34% and 5–34% of the Cu remained in the ND and AD residues, respectively, indicating its association with the cell wall. Results of the NDS- treatment showed that some of the Ca and Mg may be associated with the cell wall.

Comparison of the feeds across the different solvents tested indicated that, in terms of absolute quantity of mineral released, G. maculata could be a good source of Ca, Mg, K and Cu, and that rice bran is a good source of P and Zn. The variety of rice straw tested released high amounts of Na. A. heterophyllus is rich in available Ca.