D. R. Stevens

Introduction, production, and persistence of five grass species in dry hill country

Abstract Three trials to evaluate new grass cultivars, were attempted on a north-facing aspect in North Canterbury, New Zealand, between late March 1980 and early May 1982. The difficulty of establishing new pastures in this steep dry hill country resulted in the failure of the first two trials. The third trial used spaced transplants to evaluate ‘Grasslands. Wana’ cocksfoot (Dactylis glomerata L.), ‘Grasslands Maru’ phalaris (Phalaris aquatica L.), and ‘Grasslands Matua’ prairie grass (Bromus willdenowii Kunth). Wana was the most productive, Matua was intermediate, and Maru phalaris was the least productive. Survival was poor, however, and the role of new pastures in improving this extremely dry hill country must take second place to grazing management.

Introduction, production, and persistence of five grass species in dry hill country: 8. Summary and conclusions

The production and persistence of five oversown grass species and resident pasture, were measured between 1979 and 1987 at six New Zealand sites, under several fertiliser (phosphate and/ or nitrogen (N)) and summer grazing severity treatments. ‘Grasslands Nui’ ryegrass (Lolium perenne L.), ‘Grasslands Wana’ cocksfoot (Dactylis glomerata L.) (‘Grasslands Apanui’ at Tekapo), ‘Grasslands Maru’ phalaris (Phalaris aquatica L.), ‘Grasslands Matua’ prairie grass (Bromus willdenowii Kunth), and ‘Grasslands Roa’ tall fescue (Festuca arundinacea Schreb.), established successfully at most sites. Findlay-Wilkinson analysis of annual total herbage accumulation (THA) of four sites, found that Maru production was above average and resident production was below average. Variation in THA between sites and years was related to variation in annual rainfall (621–1484 mm/ year). Wana was the most persistent grass at all sites (60% of THA after 4–6 years), followed by Nui (51% of THA after 4–6 years). Maru was only pe...

Introduction, production, and persistence of five grass species in dry hill country: 1. Introduction, site descriptions, and general methods

Ryegrass (Lolium perenne L.), cocksfoot (Dactylis glomerata L.), phalaris (Phalaris aquatica L.), prairie grass (Bromus willdenowii Kunth), and tall fescue (Festuca arundinacea Schreb.), vary in their production and persistence during dry conditions. Improved cultivars of these species have been released but not yet evaluated for use in dry hill country, which is typically uncultivatable and of low nitrogen and phosphate fertility. This study tested the production and persistence of these cultivars in a co-ordinated series of experiments on six dry and marginally dry hill country sites of New Zealand for up to 6 years. Fertiliser inputs and summer grazing management treatments determined the adaptability of the new. cultivars to contrasting management strategies. During this time summer rainfall was average at four sites, and below average at two sites. Winter rainfall was average at three sites, and below average at three sites.

Implications of grass–clover interactions in dairy pastures for forage value indexing systems. 5. Southland

ABSTRACT The implementation and monitoring of the treatments in the core experiment (eight perennial ryegrass cultivars grown under four combinations of plus/minus clover and high/low nitrogen (N)) at a dryland Waikato site is described. The N x clover interaction was significant in 10 of the 17 seasonal or total annual herbage accumulation (HA) data sets available, caused by substantially lower annual HA in the low N minus clover treatment compared with all other treatments. Five significant scaling-type clover × cultivar interactions in HA were evident. In all cases, HA was greater in plus clover than minus clover treatments, but more so for some cultivars than others. However, the interactions were not consistent across seasons, and different cultivars or phenotypic contrast groups were involved in many cases. The hypothesis that relative HA rankings of ryegrass cultivars do not differ when ryegrass is grown in monoculture versus mixtures with white clover is supported.

Reduced ovulation rate, failure to be mated and fertilization failure/embryo loss are the underlying causes of poor reproductive performance in juvenile ewes

A ewe that is mated as a juvenile (producing a lamb at 1 year 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 juvenile ewes. In Experiment 1, 2 Cohorts of ewes, born a year apart, were mated in order to lamb at 1 and 2 years of age and the performance of the ewes at each age was compared. Onset of puberty, mating by the fertile ram, ovulation rate, early pregnancy (day 30-35) litter size, number of lambs born and number of lambs weaned were measured. In juvenile ewes, by day 35 of pregnancy, 43% of ova had failed to become a viable embryo and this early loss was the largest contributor to the poor reproductive performance observed. Compared with young adult ewes, ovulation rate was lower (p<0.001), fewer ova were exposed to sperm (p<0.001) and fertilization failure/embryo loss was increased (p<0.001) in juveniles. In Experiment 2, the early pregnancy litter size of juveniles was shown to be greater (p<0.001) in those ewes with a greater ovulation rate (p<0.001). Attaining puberty prior to introduction of the fertile ram was associated with an increased pregnancy rate (p<0.001). In juvenile ewes, failure to mate with the ram, lower ovulation rate and increased fertilisation failure/embryo loss underlie their poor reproductive performance.

Evaluation of management variables to advance conception and calving date of red deer (Cervus elaphus) in New Zealand venison production systems

The ability to shift the supply of New Zealand chilled venison from farmed yearling red deer stags to obtain premium prices in seasonal European markets necessitates early calving of hinds combined with high growth rates of their calves. Two studies over a three-year period evaluated three management variables that offer potential to advance calving date. Under the conditions of the studies there was no consistent evidence that the management practices of early stag introduction, early weaning and enhanced hind nutrition prior to conception (lactation) and pre-calving (third trimester of pregnancy) advanced conception date and calving date in red deer hinds. However, the nutrition effect was diminished by the difficultly in achieving the dietary contrast necessary for the targeted 5kg differentiation in hind live weight at strategic times of the year. Across all hinds there was a significant pre-mating (mid-March) live weight effect on conception day in the one year in which a 5kg difference between nutritional regimens was achieved, but the driver was live weight and not nutrition. There were significant effects of nutrition on calf growth, with the growth rates of calves weaned in mid-March significantly higher when their dams grazed a high plane of nutrition pre-conception. There were significant and consistent inverse relationships between conception day and calving date that implied variation around gestation length, with early- and late-conceiving hinds exhibiting longer and shorter gestation lengths, respectively. Across all treatments, calving date was predicted to advance by approximately 5 days for every 10-day advance in conception date. However, there was a significant carry-over effect of nutrition pre-conception on calving date, with hinds on a high plane of nutrition pre-conception exhibiting shorter (2-4 days) gestation lengths. There were also indications that hinds may manipulate gestation length in response to live weight gain pre-calving. These findings suggest that fetal growth trajectory may be the principle driver of gestation length and calving date. Although there were no direct effects of hind nutrition pre-mating on conception dates, nutrition remains an important component of the management of hinds and their calves in venison production systems. The outcomes of the 3-year program suggest that there are limited opportunities to manipulate calving date through manipulation of management variables.

Potential waterway contamination associated with wintering deer on pastures and forage crops

Abstract Two wintering systems common to deer farming in southern New Zealand were studied to determine the relative contaminant losses in overland now from pasture or forage crop grazed during winter. Contaminant concentrations (dissolved reactive phosphorus, total dissolved phosphorus, total phosphorus, particulate phosphorus, suspended sediment, ammonium‐N, nitrate+nitrite‐N, and Escherichia coli) were greater after grazing than before and generally greater from the forage crop than pasture. Dissolved reactive phosphate was an exception, being lost in similar quantities from both wintering systems. On average, all contaminants exceeded national guidelines for lowland surface water quality. Of greatest concern were Escherichia coli from the forage crop system and dissolved reactive phosphorus from both systems, as these may not be filtered by buffer strips or riparian areas and are major causes of contamination problems in the region.

Implications of grass–clover interactions in dairy pastures for forage value indexing systems. 1. Context and rationale

ABSTRACT The development of economic indexing systems for ranking cultivars of forage species requires new knowledge of factors that may influence the scaling of agronomic data collected in controlled, small-plot evaluation trials to whole farm systems. In the case of perennial ryegrass indexing, one such knowledge gap is the effect of growing clover with ryegrass on the relative rankings of different ryegrass cultivars. The objective of the investigation reported in this series was to test whether the relative yield rankings of perennial ryegrass (Lolium perenne L.) cultivars representing the range in phenotypes now available to New Zealand farmers as a result of recent breeding differed when those cultivars were grown in monocultures (as per standard protocols for cultivar yield trialling systems such as the National Forage Variety Trials) versus mixtures of grass and clover. This paper presents the rationale for the investigation by reviewing developments in perennial ryegrass breeding and evaluation in the context of grass–clover relationships in grazed pasture systems. The papers that follow report results from a multi-year, multi-site investigation comparing the yield, nutritive value and other productivity-related variables of eight perennial ryegrass cultivars grown with or without white clover (monoculture versus mixture respectively) at two levels of nitrogen fertiliser. Key considerations in the design of the experiment on which the investigation was based are discussed.

Implications of grass–clover interactions in dairy pastures for forage value indexing systems. 6. Cross-site analysis and general discussion

ABSTRACT Herbage accumulation (HA) data from four sites were combined to (1) address the hypothesis that adjustments to the New Zealand Forage Value Index to account for grass–clover interactions are not required and (2) explore the main effects of clover and nitrogen (N) fertiliser treatments on pasture productivity. In summer and autumn, pastures based on mid-season heading ryegrass cultivars consistently supported a greater clover content than pastures based on late heading cultivars. However, the cloveru2009×u2009 cultivar interaction was significant in only 2 of 17 HA data sets available for analysis. Thus, the hypothesis is supported. Compared with ryegrass monocultures, mixtures yielded an additional 2.4 (in the Low-N treatment) and 1.2 (High-N treatment) t DM/ha/year. Apparent N transfer from clover to grass was 79 (Low N) and 27 (High N) kg N/ha/year, derived from estimated N fixation efficiencies of 66 (Low N) and 50 (High N) kg N/t clover DM grown.

Effect of conception date and hind nutrition on fetal growth trajectory and gestation length of red deer (Cervus elaphus)

This study tested the hypothesis that the negative association between gestation length and conception date in red deer is mediated by nutrition. Twenty-eight pregnant red deer were randomly allocated to four groups according to a 2 × 2 factorial design, with the factors conception date (14 March, E; 28 April, L) and level of nutrition (ad libitum, H; restricted, R). Animals were housed indoors in individual pens from early winter until calving and offered daily an ad libitum pelleted ration. The daily ration was then restricted from late winter in ER (134 days post-conception) and LR (89 days post-conception) groups, so that these hinds did not experience a seasonal increase in food intake. X-Ray computed tomography scans were taken at Days 120, 150, 180 and 210 of gestation (mid–late gestation) to estimate weight of various conceptus components. Growth rate of the total fetus was significantly higher in LH than in other treatments (P 0.05) between treatments or calf sex. Birthweight was associated directly with change in hind liveweight (P = 0.03) and body condition score during the third trimester of pregnancy (P = 0.01), but was not significantly associated with gestation length (P = 0.34). Gestation length was 4.4 days longer in LR than LH hinds (P = 0.03) and was negatively associated with both food intake (P = 0.03) and LW gain (P = 0.02) during the final trimester of gestation. Feeding late-conceiving hinds an ad libitum diet of high-quality food during the third trimester of gestation maximises fetal growth and shortens gestation length.