Methane emissions from beef cattle grazing on semi-natural upland and improved lowland grasslands.

In ruminants, methane (CH4) is a by-product of digestion and contributes significantly to the greenhouse gas emissions attributed to agriculture. Grazed grass is a relatively cheap and nutritious feed but herbage species and nutritional quality vary between pastures, with management, land type and season all potentially impacting on animal performance and CH4 production. The objective of this study was to evaluate performance and compare CH4 emissions from cattle of dairy and beef origin grazing two grassland ecosystems: lowland improved grassland (LG) and upland semi-natural grassland (UG). Forty-eight spring-born beef cattle (24 Holstein-Friesian steers, 14 Charolais crossbred steers and 10 Charolais crossbred heifers of 407 (s.d. 29), 469 (s.d. 36) and 422 (s.d. 50) kg BW, respectively), were distributed across two balanced groups that grazed the UG and LG sites from 1 June to 29 September at stocking rates (number of animals per hectare) of 1.4 and 6.7, respectively. Methane emissions and feed dry matter (DM) intake were estimated by the SF6 tracer and n-alkane techniques, respectively, and BW was recorded across three experimental periods that reflected the progression of the grazing season. Overall, cattle grazed on UG had significantly lower (P<0.001) mean daily DM intake (8.68 v. 9.55 kg/day), CH4 emissions (176 v. 202 g/day) and BW gain (BWG; 0.73 v. 1.08 kg/day) than the cattle grazed on LG but there was no difference (P>0.05) in CH4 emissions per unit of feed intake when expressed either on a DM basis (20.7 and 21.6 g CH4 per kg DM intake for UG and LG, respectively) or as a percentage of the gross energy intake (6.0% v. 6.5% for UG and LG, respectively). However, cattle grazing UG had significantly (P<0.001) greater mean daily CH4 emissions than those grazing LG when expressed relative to BWG (261 v. 197 g CH4/kg, respectively). The greater DM intake and BWG of cattle grazing LG than UG reflected the poorer nutritive value of the UG grassland. Although absolute rates of CH4 emissions (g/day) were lower from cattle grazing UG than LG, cattle grazing UG would be expected to take longer to reach an acceptable finishing weight, thereby potentially off-setting this apparent advantage. Methane emissions constitute an adverse environmental impact of grazing by cattle but the contribution of cattle to ecosystem management (i.e. promoting biodiversity) should also be considered when evaluating the usefulness of different breeds for grazing semi-natural or unimproved grassland.

The role of arbuscular mycorrhizal fungi in the transfer of nutrients between white clover and perennial ryegrass.

A glasshouse experiment was conducted in which 15N was used as a tracer applied as (15NH4)2SO4 to donor plants of white clover and perennial ryegrass. Nitrogen transfer via hyphae of arbuscular mycorrhizal fungi (AMF) or by other routes was studied by separating the root systems of the two plant species, as donors and receivers, when growing in the same pot, with selective mesh barriers of varying pore sizes in the presence and absence of AMF. Inoculation with AMF increased DM production and nitrogen (N) yield of clover plants. Transfer of 15N occurred between white clover and grass plants but was independent of AMF. Pore size of the mesh barriers controlled the degree of 15N enrichment in the grass, suggesting that transfer was mediated by mass flow and/or diffusion. Additional experiments showed that grass roots could pass through pores of 60-microm diameter, and hyphal links could not be detected by autoradiography, thus supporting the conclusions of the tracer experiment.

Uptake of Zn by arbuscular mycorrhizal white clover from Zn-contaminated soil.

A randomised block glasshouse pot experiment compared the growth and Zn uptake of mycorrhizal and nonmycorrhizal white clover plants grown in a sterile soil/sand mixture containing 25 mg Zn kg(-1) to which five application rates of Zn (as ZnSO4) from 0 to 400 mg kg(-1) were made. Two mycorrhizal inocula infected roots from the field and from clover trap cultures, were compared. Mycorrhizal infection (ranging from 33% to 46% of total root length) and Zn application had little effect on plant growth. Increasing Zn application rate led to increased uptake of Zn in roots and shoots (especially roots), but the increases were significantly greater in non-mycorrhizal controls than in mycorrhizal treatments. In contrast, P uptake was higher in mycorrhizal than in non-mycorrhizal plants. Plants that received trap culture inoculum had significantly lower Zn uptake than those that received field inoculum. The results indicate that mycorrhizal infection may have exerted some protective effect against plant Zn accumulation at the range of soil Zn concentrations studied and may have immobilised Zn in or near the roots to some extent. However, this mycorrhizal effect cannot be explained simply by tissue dilution, hyphal sequestration or root immobilisation of Zn.

Energy intake in early infancy and childhood fatness.

OBJECTIVE: To investigate whether aspects of infant energy intake are related to fatness in early childhood. DESIGN: Longitudinal investigation of infants studied at 12 weeks and 2-3.5 y. SUBJECTS: 20 healthy infants, breast-fed or formula-fed, from the general population. MEASUREMENTS: Milk volume intake (MVI) by deuterium turnover, estimated energy intake, weaning status and body composition in infancy, body composition in childhood. RESULTS: MVI was not related to infant skinfolds or percentage fat. Weaning was inversely related to MVI (P < 0.04) at 12 weeks, and inversely related to skinfolds (P = 0.055) and fat mass (P = 0.020) in childhood. MVI and total energy intake were not related to childhood fatness. CONCLUSIONS: Early weaning was associated with a moderate reduction in childhood fatness. Two possible mechanisms are discussed. However, early infant energy intake was not an important determinant of later fatness in this population.

Investigation of the relationship between infant temperament and later body composition.

OBJECTIVE: To investigate the ability of maternally-rated infant temperament to predict fatness and activity patterns in early childhood. DESIGN: Longitudinal investigation of infants studied at 12 weeks and followed up at 2-3.5 y of age. SUBJECTS: Thirty healthy full-term infants from the general population. MEASUREMENTS: Body composition, behavioural activity and temperament at 12 weeks; anthropometry, body composition, diet and behavioural activity at follow-up. RESULTS: Infant temperament predicted later behaviour and fatness. Easily soothable infants had leaner childhood skinfold thicknesses (P < 0.02) and were more active in childhood (P < 0.025). Infant distress was also related to childhood diet composition. CONCLUSIONS: Infant temperament can predict later body composition and behaviour. Both energy intake and energy expenditure may be mechanisms by which the relationship develops.

The relationship between components of infant energy expenditure and childhood body fatness.

OBJECTIVE: To investigate whether any component of infant energy expenditure is related to fatness in early childhood, and whether infant fatness is related to childhood variables. DESIGN: Longitudinal investigation of infants studied at 12 weeks and followed up at 2.5 to 3.5 years of age. SUBJECTS: 30 healthy full-term infants selected from the general population. MEASUREMENTS: Sleeping metabolic rate, total energy expenditure, anthropometry and behaviour at 12 weeks; anthropometry, body composition and behaviour in follow-up. RESULTS: Energy expenditure at 12 weeks (minimal metabolism, total energy expenditure, energy expended on physical activity, behaviour) showed no relationship with later fatness. Infant fatness (skinfold thicknesses and percentage fat) showed in contrast a strong relationship with childhood fatness. Infant fatness also predicted childhood behaviour. CONCLUSIONS: These data do not support the theory that reduced energy expenditure in early infancy is related to later fatness. However, infant fatness influences both later fatness and activity patterns.

The influence of expanding leaves and the reproductive stem apex on apical dominance in Lolium multiflorum.

In vegetative plants of Lolium multiflorum removal of the two youngest emerging leaves resulted in increased expansion of basal tiller buds. A similar release of inhibition of tiller buds took place if the floriferous apex was removed. The surgical procedures did not affect the response. Under conditions of N-deficiency total tiller number was reduced but on removal of the apex the deficient plants showed an increased initial rate of tiller bud expansion. Apical dominance during the vegetative stage of growth in this grass was apparently due to the expanding leaves in the vegetative apex, but in the flowering plant the control was exerted by the inflorescence or the elongating stem.