Peter D Johnstone

Peter D Johnstone
AgResearch

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113
Publications
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Publications

Publications (113)
Article
Full-text available
This study evaluated the effect of early weaning (EW) of artificially-reared lambs using a restricted milk replacer (MR) feeding and step-down weaning system on the short- and long-term effects on growth, feed intake, selected blood metabolites and hormones, body composition and small intestine development. Mixed-sex twin-born 2-5 d old lambs were...
Article
Fire is known to cause severe and protracted reductions in some invertebrate communities. Amphipods are prone to desiccation and, therefore, litter removal through fire could be expected to have a significant adverse impact on their populations. We aimed to determine the temporal and spatial response patterns in density of amphipods following seaso...
Article
This study aimed to evaluate intake, body growth, and the development of the rumen, mammary gland, and immune system in Holstein Friesian calves reared for 100 d on the commercially available feed FiberStart (conserved alfalfa, Medicago sativa; Fiber Fresh Feeds Ltd., Reporoa, New Zealand)and fed calf milk replacer (CMR)for either 56 or 91 d. Eight...
Article
The objectives of this study were to determine factors affecting lamb birth weight (BWT) and differences between BWT of the largest and smallest littermates (BWTD) and to assess the relative importance of BWT and BWTD on lamb survival and growth to weaning. Records from twin (n = 5369) or triplet (n = 1664) litters born on pasture were utilised. Br...
Article
Full-text available
We hypothesised that cocaine- and amphetamine-regulated transcript (CARTPT) would be differentially expressed in ewes with differing ovulation rates. Expression of mRNA for CARTPT, as well as LHCGR, FSHR, CYP19A1 and CYP17A1 was determined in antral follicles >1 mm in diameter collected during the follicular phase in ewes heterozygous for the Booro...
Article
A ewe that is mated as a juvenile (producing a lamb at 1year of age) will produce an average of only 0.6 lambs to weaning, compared to an average of 1.2 lambs in adult ewes. Understanding the underlying causes of this low reproductive efficiency and designing methods to improve or mitigate these effects could potentially increase adoption of mating...
Article
The activin pathway has been postulated to be involved in regulation of multiple reproductive processes important for survival of the conceptus. These processes include luteinisation of the follicular cells and thus function of the corpus luteum, early embryo development, and uterine function including implantation of the conceptus. Therefore, the...
Article
To determine the ability of sheep to mobilise their body reserves after being deprived of feed prior to transport for slaughter. A total of 240 3 and 4 year-old cull ewes were held off pasture for 0, 9, 18 or 30 hours (n=60 per group) then transported 1 hour by road, unloaded and washed, held in lairage for 3 hours then slaughtered. Blood samples w...
Article
1. Invertebrate biodiversity was investigated in 55 domestic gardens in the city of Dunedin in southern New Zealand. The influence of habitat types within the gardens (lawns, open beds, and closed canopy beds) on invertebrate community structure was investigated by pitfall trapping. Species richness and diversity of Coleoptera, the proportion of na...
Article
The aim of this study was to determine if single nucleotide polymorphisms (SNPs) in the leptin receptor (LEPR) gene associated with delayed onset of puberty are associated with changes in other reproductive traits in adult ewes. The ovulation rate of ewes homozygous for the SNPs was ~15% lower (PPLEPR SNPs than their wild-type or heterozygous conte...
Article
This study was conducted to investigate the effect of attaining puberty in the first year of life on future reproductive performance in ewes. Records were collected from 2091 ewes born between 2005 and 2009. In the first breeding season of life, receptivity to the ram was monitored to determine whether ewe lambs attained puberty or not. Ewes were t...
Article
Full-text available
Attainment of puberty is a key developmental event influenced by genetic and environmental factors. In examining age of attainment of puberty, we observed closely related rams from the Davisdale line whose daughters differed in age at which they attained puberty. A candidate gene approach was used to identify mutations that may underlie these obser...
Article
Partial neutralization of bone morphogenetic protein 15 (BMP15) bioactivity by immunization is known to increase ovulation rate in sheep. However, it remains uncertain whether BMP15 vaccination would be a suitable procedure for increasing lambing rate. The aim of this study was to compare the efficacy of a BMP15 vaccination treatment on lamb produc...
Article
Full-text available
Sheep with a heterozygous inactivating mutation in the bone morphogenetic protein 15 (BMP15) gene experience an increased ovulation rate during either a natural oestrous cycle or a cycle in which exogenous FSH and eCG (gonadotrophins) are given to induce multiple ovulations. The primary aim of these studies was to determine whether ewes immunised a...
Article
Sheep lines with mutations in single genes that have major effects on ovulation rate have been very useful in gaining a better understanding of pathways important in controlling follicular development and ovulation rate. To date however, all known mutations are in the transforming growth factor beta (TGFB) superfamily. Ovulation rates were measured...
Article
Full-text available
A common question that arises when considering the results from a well-designed sampling programme for a rare or invasive species is: ‘Sampling has failed to detect a species that could have been present, so can we calculate the probability that it truly was absent during the sampling period?’ Noting that this invokes a Bayesian view of ‘probabilit...
Article
Soils are the substrate at the base of any grazing or cropping system providing plants with nutrients, water and physical support, a habitat for beneficial organisms and a physical base on which animals stand. A change or a loss of any one of these soil services has the potential to impact on plant growth and persistence. The findings of two ongoin...
Article
Full-text available
Altering the influence of the testicles of male lambs is used to manipulate growth and body composition. To determine the effects on carcass weight and consequently returns to farmers, an analysis was undertaken from studies in the scientific literature in which animals were slaughtered at the same time. Each dataset was treated as if it were a ran...
Article
Full-text available
This paper summarises progress in a field-based study exploring the phosphorus (P) requirements of high producing perennial ryegrass (Lolium perenne) and tall fescue (Festuca arundinacea)-based pastures, where the constraints to pasture growth and associated P uptake imposed by low nitrogen (N) availability and soil moisture over summer-autumn and...
Article
There are recognised benefits to managing fisheries by individual transferable quotas (ITQs), but ITQs may increase incentives to discard fish.Trawl data from government-observed trawlers in the New Zealand hoki fishery were used to predict catches of unobserved vessels. These predictions were compared with the catches unobserved vessels reported....
Technical Report
Full-text available
The invertebrate fauna of tussock grassland in New Zealand has not been well studied, and the effect of burning on the biodiversity of the ecosystem is poorly understood by land managers. The impacts of burning on two tussock grassland invertebrate communities in Otago, New Zealand, were investigated between 1998 and 2006. At each site, three repli...
Conference Paper
Full-text available
The impacts of burning on two tussock grassland invertebrate communities in the southern South Island of New Zealand were investigated between 1998 and 2006. At each site three replicate 1-ha plots of either unburned (control), spring- or late summer-burns were quantitatively sampled. Pre- and post-burn sampling compared invertebrate densities and...
Article
Full-text available
Facial eczema disease (FE) is a hepato-mycotoxicosis caused by sporidesmin, leading to secondary photosensitisation in severely affected sheep and cattle. Two genetic lines of Romney are maintained by selection for resistance and susceptibility to FE. Five groups of 8 animals, each group composed of 4 animals from each line, were artificially chall...
Article
Full-text available
A series of laboratory experiments was carried out with the main objective of contributing to the development of biosafety testing methods for transgenic plants or plants produced by other novel technologies. The adult stage of a New Zealand native weevil, Nicaeana cervina (Broun) (Coleoptera: Curculionidae: Entiminae), was used as a test insect as...
Article
To test the efficacy of a commercially available and an experimental vaccine against Johne's disease in young red deer (Cervus elaphus), using experimental challenge with live virulent Mycobacterium avium subsp paratuberculosis (M. ptb), measure injection-site reactions, and assess the effects of vaccination and challenge on results of subsequent s...
Article
Full-text available
The parasitoid, Microctonus aethiopoides Loan (Hymenoptera: Braconidae) was introduced into New Zealand in 1982 to control the alfalfa pest, Sitona discoideus Gyllenhal (Coleoptera: Curculionidae). Studies have shown that a number of nontarget weevil species are attacked in the field by this parasitoid. A field study was carried out to investigate...
Conference Paper
Full-text available
The invertebrate fauna of tussock grassland in New Zealand has not been well studied, and the effect of burning on the biodiversity of the ecosystem is poorly understood by land managers. The impacts of burning on two tussock grassland invertebrate communities in Otago, New Zealand, were investigated between 1998 and 2006. At each site, three repli...
Article
Full-text available
Indigenous tussock grassland in New Zealand has a history of extensive pastoralism, and burning has been used to remove litter to improve establishment of aerially oversown pasture species and to promote palatable tussock growth for livestock. In recent years, considerable areas of tussock grassland have been retired from grazing and formally prote...
Article
In two pot experiments with a soil deficient in P and N, vesicular-arbuscular mycorrhizas stimulated the shoot growth of Lolium perenne L. greatest (24%) with the highest levels of applied P and/or N, and where the shoot N and P concentrations approached the normal agronomic range. It is suggested that applied N, and possibly P, resulted in mycorrh...
Article
Full-text available
Indigenous tussock grassland in New Zealand has a history of extensive pastoralism, and burning has been used to remove litter to improve establishment of aerially oversown pasture species and to promote palatable tussock growth for livestock. In recent years, considerable areas of tussock grassland have been retired from grazing and formally prote...
Article
Full-text available
The triketone chemotype of manuka, Leptospermum scoparium (Myrtaceae), is commercially important because of its antimicrobial activity. Oils from 36 individual plants on the East Cape of New Zealand all showed similar high triketone contents (>20% total triketones) with little seasonal variation. Analyses of oils from 261 individual manuka plants c...
Article
Full-text available
Bone density (BD) is an important factor in osteoporotic fracture risk in humans. However, BD is a complex trait confounded by environmental influences and polygenic inheritance. Sheep provide a potentially useful model for studying differences in BD, as they provide a means of circumventing complex environmental factors and are a similar weight to...
Article
Many incomplete block design strategies have been devised to improve the efficiency of experiments. However, the constraints imposed by these designs can be unrealistic because natural blocks may not be all the same size or there may be no conventional designs for required treatment, replication, block and plot combinations. In addition, because of...
Article
Full-text available
The principle cue entraining circannual environmental rhythms and reproductive function in red deer is photoperiod, but other factors probably play important roles in modifying seasonality. Examination of calving records of untreated, first‐calving hinds over a 10‐year period revealed year‐to‐year variation in the mean calving date. Most variation...
Conference Paper
Full-text available
INTRODUCTION Low bone mineral density (BMD) has been shown to be an important factor in osteoporotic fracture risk in humans (Hui et al., 1988 ; Cummings et al., 1990). In humans BMD is a polygenic trait dependent on the action of a number of genes. A study of BMD in sheep has not previously been reported. Sheep are potentially a valuable animal mo...
Article
Full-text available
A laboratory study of aspects of parasitoid host acceptance, suitability and physiological regulation in natural and novel host species was carried out to investigate the degree of variability encountered with different hosts and to determine the value of such observations in host range determination. The parasitoid Microctonus aethiopoides Loan wa...
Article
Full-text available
Ginseng (Panax ginseng C.A. Meyer) is a potential new crop for New Zealand. Under artificial shade, 1‐year‐old seedlings were grown in either peat‐ or soil‐based media for 4 years. At the final harvest mean root fresh weight was 55 g/plant in the peat media and 40 g/plant in the soil media. Total ginsenoside % of the 5‐year‐old roots was up to 6.9%...
Article
The aim of this study was to determine whether a predictive geometric soil-landscape model, potentially applicable to 400 000 ha of seasonally dry greywacke steeplands in New Zealand, could be created for 29 soil properties, using a very low soil sampling density. We postulated that in these deeply dissected steeplands which have relatively uniform...
Article
There has been some recent interest in sequential experiments as a means of reducing the number of animals used in comparative experiments. This paper describes sequential methods and explores their properties. Comparisons are made with fixed sample‐sized experimental designs which result from traditional power calculations. Attention is drawn to p...
Article
Aims: To measure the efficacy of a pour-on formulation of moxidectin against lungworm and abomasal parasites in weaner wapiti x red deer and to compare this with its efficacy in weaner red deer. Methods: Six red and six wapiti hybrid deer, naturally infected with lungworm and gastro-intestinal parasites, were treated with pour-on moxidectin at 5...
Article
Full-text available
Six phosphate rocks (PRs), Sechura (SPR), North Carolina (NCPR), Egypt (EPR), Arad (APR), Zin (ZPR), and Nauru (NPR), were compared with single superphosphate (SSP) as annually applied P fertilisers for mown ryegrass/ white clover swards at two sites, in the central North Island (Te Kuiti) and southern South Island (Woodlands) of New Zealand over a...
Article
The effect of four drill types on the establishment of overdrilled lucerne (Medicago sativa) in a 300–800 mm rainfall tussock grassland environment in New Zealand was examined. The effect of herbicide pre‐treatment and oversowing on plant numbers was also investigated. The highest initial seedling population count was 310 seedlings m, but this numb...
Article
Comparative experiments on parasite burdens present difficulties for modelling and interpretation: data tend to have highly skewed distributions, some standard methods of testing for effects have low power, and there is a need to make allowance for dependencies among the various measurements. Randomization testing and canonical variates analysis ar...
Article
Full-text available
Forty‐six data‐sets from a series of 17 long‐term field trials measuring the effects of rates and forms of phosphate (P) fertiliser on pasture production and soil fertility in New Zealand were used to characterise the relationship between pasture dry matter (DM) yield in any year (expressed as relative yield, RY) and soil Olsen P test at the end of...
Article
Introduction of the Inverdale prolificacy gene (FecXI) could markedly improve reproductive efficiency in commercial flocks, but as homozygous carrier Inverdale ewes are infertile, it is imperative that these animals are identified at an early age and excluded from breeding stock. As the ovaries of homozygous carrier ewes are nonfunctional, there ar...
Article
Improvement of depleted grasslands can be restricted by the lack of reliable, cost effective and ecologically sound establishment techniques. This paper presents results from an experimental strip seeder drill designed to mechanically remove competing vegetation. Lucerne (Medicago sativa L.), birdsfoot trefoil (Lotus corniculatus L.), cocksfoot (Da...
Article
Full-text available
The parasitoids Microctonus hyperodae Loan and M. aethiopoides Loan have been introduced into New Zealand to control the forage pests Listronotus bonariensis (Kuschel) and Sitona discoideus Gyllenhal, respectively. Laboratory experiments were carried out to investigate the effect of host–parasitoid ratio, and exposure time on host survival, parasit...
Article
Full-text available
Triple superphosphate (TSP) and Sechura phosphate rock (SPR) were applied to developed pastures annually at 0.75 times the estimated annual pasture maintenance requirement (M) and triennially at 2.25 times M in small‐plot trials at 12 sites for 6 years. A control treatment receiving no phosphorus (P) fertiliser was also included. Pasture dry matter...
Article
The possible influence of social factors on the timing of puberty in the hind was investigated utilizing seasonally advanced (melatonin-treated) hinds and stags. Melatonin treatment of both sexes resulted in a significant advancement in the onset of pubertal ovarian activity (26 days, P < 0·001) and calving (27 days, P < 0·001) in the treated hinds...
Article
A national series of rates × forms of phosphate fertilizer trials has provided a large amount of data on patterns of response of pasture production and soil P tests to forms, rates and frequencies of P fertilizer application over time. A simple mechanistic model of P in pastoral systems has been developed in an attempt to account for the observed p...
Article
The effect of annual applications of triple superphosphate (TSP) and Sechura phosphate rock (SPR) on clover content of permanent pasture was measured at seven sites in New Zealand. Clover content as a percentage of total pasture dry matter (DM) production (% clover) increased with phosphorus (P) application rate, and the response of % clover to P i...
Article
Full-text available
The effects of annual applications at four different rates of either triple superphosphate (TSP) or Sechura phosphate rock (SPR) on the Olsen P test in soil under pasture were measured over 6 years at 13 sites in New Zealand. Averaged over the 13 sites, TSP applied at the calculated maintenance (M) rate maintained an almost constant Olsen P level t...
Article
Seasonally anovular Coopworth ewes previously isolated from rams were joined with either Coopworth or Poll Dorset entire rams for 28 days from either 6 January or 3 February in each of 3 successive years. Induction of ovulation varied between years, and more ewes ovulated when exposed to rams of either breed in February. When rams were introduced i...
Article
Full-text available
Pasture herbage dry matter (DM) responses to annual applications of triple superphosphate (TSP) at 0.5, 0.75, 1.0, and 2.0 times the calculated maintenance requirement were measured in 12 field trials for 6 years. The trials were on well‐established, permanent pastures which had typical fertiliser histories and represented major pastoral soils of N...
Article
Romney ewes grazed red clover (P) or mixed red clover/ryegrass (M) pastures for about 6 months/year until mating in Year 4 (P) or 5 (M) of a 6-year study. A further group grazed ryegrass/ white clover (C) pasture continuously throughout the study. At other times all animals grazed ryegrass/white clover pasture as one mob. Ewes grazing P pasture wer...
Article
Reactive phosphate rocks (RPRs) from Sechura, Peru (SPR) and North Carolina, USA (NCPR) were compared with triple superphosphate (TSP) as phosphate (P) fertilizers for permanent grass/clover pastures in four field trials in New Zealand. Trial sites ranged in initial pH (in water) from 5.7 to 6.3 and in rainfall from 712 to 1338 mm yr−1. SPR and NCP...
Article
Soil pH was measured over 6 years in 10 field trials in which superphosphates (SPs) and reactive phosphate rocks (RPRs) were applied annually to clover/grass pastures at rates equivalent to 0, 0.5, 0,75, 1.0, and 2.0 times the estimated amounts of phosphorus (P) required for maintaining near-maximum pasture production. Over the 6-year period, soil...
Article
Full-text available
The practice of doing a single comparative trial at a particular site and extrapolating results from that site to many others, ignores the potential variability in results which may occur when the same treatments are applied in different environments. In order to overcome this difficulty with on-farm investigative developments, the concept has been...
Article
Ram lambs were selected from a total of 1206 lambs in 8 industry Coopworth ram breeding flocks. Eight rams were selected randomly (one from each flock), 8 were selected on the basis of a low live weight-adjusted ultrasonic backfat thickness (lean) and 8 for a high post-weaning growth rate (PW gain). Rams from a Coopworth line specially selected and...
Article
The five fattest and five leanest rams were selected on the basis of their liveweight-adjusted ultrasonic backfat thickness from a flock of 100 Coopworths at around 6 months of age. A total of 110 male progeny of these 10 rams were slaughtered between January and April at a mean hot carcass weight (HCW) of 17.13 kg. There were no significant differ...
Article
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A trial was carried out in unimproved tussock grassland on the East Otago Plateau of the South Island of New Zealand to investigate the impact of native broad-nosed weevils (Coleoptera: Curculionidae) feeding on survival, establishment, and yield of oversown white clover. The trial consisted of 20 sites 1 km apart where two plots were established i...
Article
Full-text available
In a series of 12 field uials located throughout New Zealand annual application of phosphate(P) fertiliser was compared with ttiennial application using rates which applied the same total amount of P over 6 years. Test materials were triple supetphosphate (TSP) and Sechura phosphate rock (SPR), both of which were applied annually at rates which pro...
Article
Proliferation of new phosphatic fertilizers with diverse chemical properties necessitates much agronomic evaluation including comparison in field experiments. If such experiments lack the power to detect real and economically important differences between fertilizers, there is a danger of inferior products entering the fertilizer market. The abilit...
Article
Full-text available
The concurrent and long-term effects of feeding high (H) and low (L) levels of nutrition from weaning to 4 years of age were measured in 188 high fecundity heterozygous Booroola Merino × Coopworth (BC) ewes (Fec Fec) and 58 low fecundity New Zealand Merino × Coopworth (MC) ewes. Following the cessation of differential feeding, all groups were graze...