Spring grazing managements which allowed some early inflorescence development, followed by hard grazing in order to remove the reproductive stems (designated ‘late control’), were compared with a conventional close grazing strategy (‘early control’) in three paddock-scale complete randomized block studies with dairy cows grazing perennial ryegrass/white clover pastures during consecutive years (1990–1993) in Palmerston North, New Zealand. Experiment 1 was designed to evaluate the timing of late control, Expt 2 to investigate the most suitable intensity of control, and Expt 3 tested different practical approaches to carrying out the late control management.

Late control generated an average herbage production increase of 24% (750 kg DM/ha) in October and November (spring) and 22% (950 kg DM/ha) from January to April (summer–autumn) compared with the conventional management. The increase in herbage accumulation during spring was a consequence of greater perennial ryegrass reproductive development. Increased summer–autumn herbage accumulation after late control management was attributed to enhanced tillering activity and accumulation of perennial ryegrass. Effects on white clover production were inconsistent. Experiment 3 compared the effects of two practical late control strategies, involving either a short period of rapid rotational grazing or a simulation of increased stocking rate normally associated with forage conservation, on the milk production and forage intake of groups of cows in self-contained farmlet systems. During the control period, the reproductive state of the sward caused a small decrease in herbage digestibility. However, the extra herbage produced subsequently did not differ in digestibility from that produced on the conventionally managed sward and resulted in an increase of around 11·5% in total milk solids yield (fat, protein and lactose) per cow, particularly towards the end of the season (March and April).

The late control spring grazing management strategy is a viable option for dairy farmers. It should coincide with the time of anthesis of ryegrass plants (late November–early December), and is more effectively achieved when forage conservation practices are used to augment grazing pressure in the grazed area of the farm.

This experiment examined the effects of immunizing against ACTH (adrenocorticotrophic hormone) and GnRH (hypothalamic peptide gonadotrophic releasing hormone) on growth and carcase composition of entire ram lambs from 6 to 35 weeks of age. There were four experimental groups (each of 17 animals) in a 2×2 factorial design: (1) a non-immunized control group, (2) immunized against ACTH, (3) immunized against GnRH and (4) immunized against both antigens. After booster injections, experimental lambs exhibited antibody titres to the two antigens presented, resulting in significantly lower cortisol and testosterone levels (P<0·001) in peripheral blood. The fall in blood cortisol levels in response to ACTH immunization was later matched by a similar decline in control animals to a point where they were not different.

In GnRH-immunized animals, antibodies disrupted the pituitary-gonadal axis, thereby impacting severely on testes development in growing lambs to the degree that by day 119 their testes were smaller than at the commencement of the experiment. Towards the end of the growth phase of the animals, GnRH-immunized lambs had significantly lower body weights at day 189 (P<0·05) and day 204 (P<0·01) while ACTH-immune lambs were not different in weight from control animals. Also, GnRH-immunized lambs were found to have greater GR measurement (P<0·05). Although ACTH immunization was capable of lowering cortisol for a brief period during the current experiment, the results were variable and detrimental to the efficacy of the immuno-castration vaccine (GnRH).

Two field trials were conducted in the 1999 and 2000 cropping seasons to determine the effect of planting date and host plant resistance on grain mould and anthracnose, and host plant resistance with fungicides on anthracnose of sorghum in the Nigerian northern Guinea Savanna. Three sorghum varieties were used [SAMSORG 40 (ICSV 111), SAMSORG 4 (KSV 4) (both early maturing and susceptible to anthracnose) and SAMSORG 14 (KSV 8) (medium maturing and resistant to anthracnose)]. Results show that early planting in June and the first 2 weeks of July predisposed susceptible varieties to high level of anthracnose while planting in June predisposed SAMSORG 40 and SAMSORG 4 to high levels of grain mould but gave highest grain yield for the three varieties. The resistant variety SAMSORG 14 was resistant to both anthracnose and grain mould irrespective of planting date. Foliar application with benomyl controlled anthracnose and gave highest yields when combined with seed treatment using metalaxyl+carboxin+furathiocarb (MCF). However, seed treatment alone with MCF did not control anthracnose.

An experiment was conducted to investigate the effect of grazing legumes and ryegrass on the performance of Suffolk×Mule finishing lambs in terms of growth rate, days to finish and carcass characteristics. Replicate plots (n=2) of red clover (Trifolium pratense), lucerne (Medicago sativa), lotus (Lotus corniculatus) and perennial ryegrass (Lolium perenne) were established in May 1999 at the Institute of Grassland and Environmental Research (IGER), Aberystwyth, and maintained at a similar vegetative growth stage. From the beginning of September 1999 each forage was grazed by 10 wether lambs and 10 ewe lambs. The lambs grazed the experimental plots from weaning until they reached fat-class 3L. There was a significant decline in crude protein (CP) concentration in lucerne (−2·6 g/kg DM/day, P<0·05) and lotus (−2·5 g/kg DM/day, P<0·001) over the grazing period, while the CP concentration in red clover and ryegrass remained comparatively constant. Growth rates were highest for lambs grazing lotus compared with lambs grazing the other forages, and growth rates were significantly higher for lambs grazing red clover than for lambs grazing ryegrass. Growth rates of lambs grazing lucerne were significantly lower than lambs grazing lotus but similar to that of lambs grazing red clover and ryegrass. Lambs grazing the legume forages required significantly fewer days to finish compared with lambs grazing ryegrass. Cold carcass weight and killing out percentage were significantly higher for lambs grazing red clover compared with that for lambs grazing the other forages. Lambs grazing red clover and lucerne had significantly higher voluntary intakes, estimated using n-alkanes, than lambs grazing ryegrass, with intakes for lambs grazing lotus not significantly different. There were no treatment effects on in vivo digestibility. Levels of total protein and β-hydroxybutyrate in blood were unaffected by dietary treatment, although lambs grazing the forage legumes had significantly higher blood glucose and urea concentrations compared with lambs grazing ryegrass. Lambs grazing lotus had the highest plasma albumin. The results indicate that by grazing finishing lambs on forage legumes it is possible to increase growth rates and reduce time to finish without compromising carcass quality.

Forage degradability data from pooled forage samples were compared to those obtained from field samples using an in situ technique. Four fistulated sheep were employed as part of a Split Plot design within a 4×2 factorial (four times of incubation as plots and two forages as subplots) over a 4×4 Latin Square. The field site sample technique led to more realistic confidence limits for all parameters when modelling forage degradation and suggested the possibility of working with a single fistulated ruminant. Such a technique meets animal welfare requirements, saves experimental work and may stimulate the use of the in situ technique with simpler designs.

In previous comparative studies of buffaloes and temperate cattle, a greater increase in rectal temperature (RT) and skin temperature (ST), and a greater decrease in haematocrit (Ht) have been observed in buffaloes than in temperate cattle with an increase in ambient temperature (AT). Our series of previous experiments suggested that great changes in RT, ST and Ht are induced in buffaloes by a marked increase in blood flow from the body core to the surface, which accelerates dissipation of heat from the skin surface. On the basis of these suggestions, the present study was undertaken to compare fluctuations in RT, ST and Ht between buffaloes and tropical cattle. Fluctuations in the aforementioned parameters, particularly RT and Ht, were greater in buffaloes than in cattle. Moreover, the correlation for RT or Ht v. AT was significant for buffaloes (r=0·33 and −0·37, respectively) but not for cattle. The correlation coefficient for ST v. AT was significant in both species, but was greater in buffaloes (r=0·63) than in cattle (r=0·56). These results demonstrate that with changes in ambient temperature, RT, ST and Ht fluctuate much more in buffaloes than in tropical cattle, as found previously for temperate cattle. Therefore, the distinctive thermoregulatory responses of buffalo are confirmed as being specific to this species.

Over the last two decades, dairy cattle management in Malawi has been oriented towards increasing milk yield per animal. One consequence of this process has been reliance on Holstein Friesian bull semen from temperate regions. The aim of the current study was to evaluate the performance of Holstein Friesian cows on large-scale farms in Malawi. A data set of 60640 test-day records from Holstein Friesian cows in first, second and third lactation from three large-scale dairies in Malawi were utilized. Fixed effects of herd, year and season of calving were tested. (Co)variance components were estimated through the restricted maximum likelihood (REML) procedure. Heritability, genetic and phenotypic correlations for milk yield, lactation length, age at first calving, and calving interval were determined. In general, milk yield decreased over the years and there was significant (P<0·001) variation in milk yield between herds. The genetic base, as indicated by the genetic trend, remained almost constant in the studied period. This entails genotype by environment interaction, culminating in the additive genetic effect not expressing itself fully in the phenotype. It is therefore apparent that considerable improvement could be achieved by improving the production environment.

The effect of sward bulk density on bite mass and bite dimensions was examined in two experiments using oesphageally fisulated cows to graze microswards under field conditions. In Experiment 1 microswards of uniform sward height were hand thinned to create differences in sward bulk density. In Experiment 2 plots were sown with monocultures of a range of ryegrass cultivars selected on the basis of their contrasting sward structures to provide a range of sward bulk densities and grazed down in two consecutive strata. Both methods were successful in providing a range of microswards of different sward bulk densities. In Experiment 1 bite mass increased significantly as sward bulk density increased. In Experiment 2 bites taken from the first stratum did not differ significantly in mass due to bites being deeper in swards with low bulk density, compensating for the lower bite bulk density. However, mass of bites taken mainly from the second stratum were lower in some swards due to lower bite bulk density which was related to tiller density rather than sward bulk density. The results emphasize the importance of sward bulk density in determining bite mass and dimensions, especially for the first stratum, and of tiller density in the bulk density of bites in the lower stratum in sward depletion, the latter requiring to be studied further.

This group, which is concerned with the applications of mathematics to agricultural science, was formed in 1970 and has since met at approximately yearly intervals in London for one-day meetings. The thirty-sixth meeting of the group, chaired by Dr T. R. Wheeler of The University of Reading, was held in the Kohn Centre at the Royal Society, 6 Carlton House Terrace, London on Friday, 26 March 2004 when the following papers were read.

A somewhat unpredicted effect of the 2001 Foot and Mouth crisis, has been to ‘derail the TB control programme both as regards cattle measures and the badger culling trial’ (EFRA 2003). Sadly, cattle TB is now out of control, rising by c. 20% a year, and back to 1960s levels. Unfortunately attention has focused to such an extent on badgers that many now seemingly do not understand how TB works in cattle and why annual testing and movement bans are the answer: they brought cattle TB down to tiny southwest hot-spots by the mid-1970s without any badger culling (Hancox 2000, 2002, 2003).

A 3-year study was set up to evaluate the influence of cow genetic potential for milk production and concentrate supplementation level on profitability of pasture based systems of milk production. In each of the 3 years, 96 cows were used in a three (genotype)×3 (levels of concentrate supplementation) randomized block design. Cows were categorized based on their pedigree index (PD) for milk production (PDMILK) into low (LP; PDMILK less than 100 kg), medium (MP; PDMILK 100–200 kg) and high (HP; PDMILK 200–300 kg). Concentrate supplementation levels were 376, 810 and 1540 kg per cow per lactation, identified as low (LC), medium (MC) and high (HC) concentrate respectively. Three milk production scenarios were investigated using the Moorepark Dairy Systems Model (MDSM) which included: EU milk quota applied at farm level with current costs and prices (S1), EU quota applied at farm level with projected future costs and prices (S2), and EU milk quota applied at industry level (quota purchasing possible) with projected future costs and prices (S3). The effect of variation in milk price, concentrate price and opportunity cost of land were modelled using stochastic budgeting. The results suggest that where EU milk quota is applied at farm level (S1 and S2), the optimum system of milk production is where margin per unit of output is maximized. When milk quota is applied at industry level (S3) the optimum system will be where margin per cow will be maximized. The results also suggest that the optimum system for cows with lower genetic potential for milk production is low level of concentrate supplementation, while cows with higher genetic potential for milk production is high level of concentrate supplementation.

The composition of yeast communities in the rumen of cattle was investigated using comparative DNA sequence analysis of yeast 26S rDNA genes. 26S rDNA libraries were constructed from rumen fluid (FF), rumen solid (FS) and rumen epithelium (FE). A total of 97 clones, containing a partial 26S rDNA sequence of 0·6 kb length, were sequenced and subjected to an on-line similarity search.

The 41 FF clones could be divided into five classes. The largest class was affiliated with Pezizomycotina class (85·4% of clones), and the remaining classes were related with the Urediniomycotina (2·4%), Hymenomycetes (4·9%), Ustilaginomycetes (4·9%) and Saccharomycotina (2·4%) classes. The 26 FE clones could be divided into three classes and the Saccharomycetes class (92·4% of clones) was the largest group. The remaining classes were related with either Pezizomycotina (3·8%) or Ustilaginomycetes (3·8%). The 30 FS clones were all affiliated with Saccharomycotina. Saccharomycotina were predominant in rumen epithelium and rumen solid while Pezizomycotina were predominant in rumen fluid. Yeast belonging to the Saccharomycotina class was predominant in the rumen as a whole (57%). One clone (FF34) had less than 90% similarity to any sequence in the database and was thus apparently unrelated to any previously described yeast.

A model was published by Lewis et al. (2002) to predict the mean age at first egg (AFE) for pullets of laying strains reared under non-limiting environmental conditions and exposed to a single change in photoperiod during the rearing stage. Subsequently, Lewis et al. (2003) reported the effects of two opposing changes in photoperiod, which showed that the first change appears to alter the pullet's physiological age so that it responds to the second change as though it had been given at an earlier age (if photoperiod was decreased), or later age (if photoperiod was increased) than the true chronological age. During the construction of a computer model based on these two publications, it became apparent that some of the components of the models needed adjustment. The amendments relate to (1) the standard deviation (S.D.) used for calculating the proportion of a young flock that has attained photosensitivity, (2) the equation for calculating the slope of the line relating AFE to age at transfer from one photoperiod to another, (3) the equation used for estimating the distribution of AFE as a function of the mean value, (4) the point of no return when pullets which have started spontaneous maturation in response to the current photoperiod can no longer respond to a late change in photoperiod and (5) the equations used for calculating the distribution of AFE when the trait is bimodal.