Economic Values for Perennial Ryegrass Traits in New Zealand Dairy Farm Systems

Perennial ryegrass (Lolium perenne L.) is the main species used in dairy pastures throughout New Zealand. There are approximately 30 perennial ryegrass cultivars sold commercially in New Zealand, but currently there is no evaluation system which allows farmers to compare the potential impact of different cultivars on the profitability of their farm business. Such an economic evaluation system requires information on performance values (PV) for cultivars which quantifies their performance with respect to the major productivity traits (herbage accumulation (HA, kg DM/ha), nutritive value and persistence) relative to a genetic base, and economic values (EV, Doyle and Elliott 1983) which estimate the additional profit resulting from each unit change in the trait of interest (Equation 1). Economic value = Δ operating profit/Δ trait of interest (1) This paper describes a system modelling approach developed to estimate EV for seasonal HA of pasture in the major dairying regions of New Zealand. This information is used in the DairyNZ Forage Value Index system (www.dairynzfvi.co.nz) which is being developed to include information on all three productivity traits for commercially available ryegrass cultivars

Development of a Forage Evaluation System for Perennial Ryegrass Cultivar and Endophyte Combinations in New Zealand Dairy Systems

An economic index for perennial ryegrass (Lolium perenne L.) cultivars is a relatively new concept, although recently introduced in Ireland (McEvoy et al. 2011). By contrast, in dairy cattle breeding, the concept of an economic index rating animals and economic values underlying that index is well entrenched (Philipson et al. 1994; Veerkamp, 1998). Historically, forage evaluation data for individual cultivars were either displayed using absolute numbers for seasonal dry matter production within a season or across all seasons with a notation to indicate statistical differences, or percentage values where a reference cultivar is 100. The adoption of an economic index and routine evaluation approach for perennial ryegrass provides a method to identify traits of economic importance to focus plant breeding efforts better and to provide clarity for farmers around predicting cultivars that will maximise farm profit. It also allows for routine tracking of genetic gain of individual traits and the economic index. In this paper, the economic based forage evaluation techniques now used in New Zealand for perennial ryegrass cultivar/endophyte combinations are presented

“Everything You Always Wanted to Know about Sex (but Were Afraid to Ask)” in Leishmania after Two Decades of Laboratory and Field Analyses

Leishmaniases remain a major public health problem today (350 million people at risk, 12 million infected, and 2 million new infections per year). Despite the considerable progress in cellular and molecular biology and in evolutionary genetics since 1990, the debate on the population structure and reproductive mode of Leishmania is far from being settled and therefore deserves further investigation. Two major hypotheses coexist: clonality versus sexuality. However, because of the lack of clear evidence (experimental or biological confirmation) of sexuality in Leishmania parasites, until today it has been suggested and even accepted that Leishmania species were mainly clonal with infrequent genetic recombination (see [1] for review). Two recent publications, one on Leishmania major (an in vitro experimental study) and one on Leishmania braziliensis (a population genetics analysis), once again have challenged the hypothesis of clonal reproduction. Indeed, the first study experimentally evidenced genetic recombination and proposed that Leishmania parasites are capable of having a sexual cycle consistent with meiotic processes inside the insect vector. The second investigation, based on population genetics studies, showed strong homozygosities, an observation that is incompatible with a predominantly clonal mode of reproduction at an ecological time scale (∼20–500 generations). These studies highlight the need to advance the knowledge of Leishmania biology. In this paper, we first review the reasons stimulating the continued debate and then detail the next essential steps to be taken to clarify the Leishmania reproduction model. Finally, we widen the discussion to other Trypanosomatidae and show that the progress in Leishmania biology can improve our knowledge of the evolutionary genetics of American and African trypanosomes

Spatio-temporal development of forests - Current trends in field methods and models

We present a critical review of current trends in research of spatio-temporal development of forests. The paper addresses (1) field methods for the development of spatially-explicit models of forest dynamics and their integration in models of forest dynamics, (2) strengths and limitations of traditional patch models versus spatially-explicit, individual-based models, and (3) the potential for moment-based methods in the analysis of forest dynamics. These topics are discussed with reference to their potential for solving open questions in the studies of forest dynamics. The study of spatio-temporal processes provides a link between pattern and process in plant communities, and plays a crucial role in understanding ecosystem dynamics. In the last decade, the development of spatially-explicit, individual-based models shifted the focus of forest dynamics modelling from the dynamics of discrete patches to the interactions among individual organisms, thus encapsulating the theory of "neighbourhood" dynamics. In turn, the stochastic properties and the complexity of spatially-explicit, individual-based models gave rise to the development of a new suite of so-called moment-based models. These new models describe the dynamics of individuals and of pairs of individuals in terms of their densities, thus directly capturing second-order information on spatial structure. So far, this approach has not been applied to forests; we indicate extensions needed for such applications. Moment-based models may be an important complement to spatially explicit individual-based models in developing a general spatial theory of forest dynamics. However, both kinds of models currently focus on fine scales, whereas a critical issue in forest dynamics is to understand the interaction of fine-scale processes with coarser-scale disturbances. To obtain a more complete picture of forest dynamics, the relevant links and interactions between fine-, intermediate-, and coarse-scale processes ought to be identified. Intensive links between modelling work and field studies designed across different scales are a promising means to create a new perspective on forest dynamics

Liveweight and body condition change through pregnancy as a predictor of ewe litter size

Knowledge of litter size allows for the preferential feeding of pregnant ewes with higher nutritional requirements and/or differential lambing supervision. The possibility of predicting ewe litter size from liveweight and body condition change over pregnancy was examined. The live weight and GR estimate (calibrated with ultrasound measurement) of 247 Corrie dale ewes (average liveweight 64.4kg) was recorded on five occasions during pregnancy. Litter size was determined at lambing. The prediction of litter size of a 50:50 division of the flock, (average lamb drop 1.44) on joining weight (1.52:1.36) was improved by using liveweight 6 weeks prior to the start of lambing (1.28:1.60) or liveweight/GR deviations at day 140 (1.16:1.72). A second flock (average lamb drop 1.60) produced similar results, where the division was based on predicted lamb drop, although divisions six weeks prior to lambing (1.33:1.78) and liveweight/GR deviations at day 140 (1.31:1.77) were slightly less accurate. Useful accuracy in separating single and twin bearing ewes was achievable based on liveweight and GR measurements prior to lambing. Ewes bearing twin lambs were 4.3kg heavier than single bearing ewes at the end of pregnancy but some of this difference (2.6kg) existed at joining. Non pregnant ewes lost weight (1.7kg) over pregnancy and single and twin bearing ewes gained 5.7 and 7.4kg respectively. GR declined by 4.1, 3.3 and 4.7 in non pregnant, single and twin bearing ewes respectively. For each kg increase in liveweight change during pregnancy GR increased by 0.72mm for both single and twin bearing ewes. Changes in liveweight and GR from day 100 to 140 showed similar trends. Although differences in GR adjusted liveweight between single and twin bearing ewes, 140 days after ram introduction, was smaller than reported conceptus weights would suggest, separation of the flock on this basis provided a satisfactory level of accuracy

Comparative nutrition and energy metabolism of young red deer (Cervus elaphus) and red x elk hybrid deer

Elk (Cervus elaphus spp) are widely used as a terminal sire in the New Zealand deer industry because elk red deer crosses are heavier at 12 months of age than pure-bred red deer (Cervus elaphus) and therefore better fit market demands. However, it is unclear whether nutritional requirements differ between genotypes. A series of experiments compared young (4 - 12 months) red deer and red deer-elk cross (hybrids) in various aspects of their nutrition. Single genotype groups (10-15) of red deer and hybrid weaner stags were offered one of four pasture allowances (2 to 12 kg DM/head/day) on a rotationally grazed mixed ryegrass - white clover pasture system for 9 weeks in winter (June-July), spring (October-December) and summer (February - March). Stags were weighed and given a new allocation of pasture weekly. Pre-grazing pasture mass ranged from 800 kg DM/ha for low pasture allowances to 4500kg DM/ha for higher allowances. Winter live-weight gain was low (40-80 g/day), relatively unaffected by pasture allowance and similar for both genotypes. In spring however, hybrids gained live-weight on average 100 g/day more than red deer across all pasture allowances and the response to additional pasture allowance was large (110 g/day at 2kg DM/head/day to 300 g/day at 9.5 kg DM/head/day). At the highest pasture allowance, hybrids grew faster (350 g/day) than red deer (250 g/day), although red deer were able to achieve this live-weight gain when offered less pasture (4 vs 12 kg DM/head/day, respectively). Summer live-weight gain was lower for both genotypes and responded less to increases in pasture allowance than during spring. A second experiment compared the live-weight gain of both genotypes at ad lib feeding in an indoor environment where intake could be accurately measured. A group of red deer (n =15) and a group of hybrid (n =15) weaner stags were housed indoors during winter (3 June - 27 August) and spring (16 October - 16 December) and fed a pelleted grain based ration ad lib. Mean daily intake for each group (kg DM/head/day) was calculated as the difference between feed offered and feed refused. Hybrids had a significantly higher (P< 0.05) absolute DM intake compared with red deer in both seasons, although when expressed on a metabolic body weight basis, there was no difference between genotypes irrespective of season. Live-weight gain during winter did not differ significantly between genotypes regardless of whether it was expressed on an absolute or metabolic weight basis. Spring live-weight gain, expressed both on an absolute and metabolic live-weight basis, was significantly higher for hybrids compared with red deer (P<0.05). Red deer and hybrids increased their feed intake from winter to spring by 20% and 24% respectively on a metabolic body weight basis. Although the difference between genotypes in their seasonal increase in intake was relatively small there was a large difference in their pattern of live-weight gain. Red deer exhibited a 34% and hybrids a 76% seasonal increase in live-weight gain expressed on a metabolic live-weight basis from winter to spring. These results indicate the greater rate of live-weight gain displayed by hybrids compared with red deer was not associated with a greater ad lib intake (expressed on a metabolic body weight basis) and the seasonal increase in live-weight gain is greater for hybrids than for red deer. A further experiment estimated the energy requirement for maintenance of both genotypes. Five deer of each genotype were housed in separate pens (3.5m²) during winter (3 June - 27 August) and spring (16 October - 16 December) and randomly assigned to one of 5 feeding levels (0.5, 0.6, 0.7, 0.8, or 0.9 times estimated ad lib intake of l.5 and l.7 kg DM/head/day during the winter and 3.0 and 3.3 kg DM/head/day during the spring for red deer and hybrids, respectively. Maintenance requirement was determined by regression analysis of live-weight gain on ME intake. Although there was no seasonal effect on the live weight gain response to intake there was a significant genotype effect. To maintain live weight during either season, hybrids required a higher ME intake (0.52 MJ ME/W0.75/day compared with red deer 0.41 MJ ME/W0.75/day). The rate of increase in live weight gain to increasing intake declined as intake increased and more so for red deer than hybrids. The final experiment in the series involved individually housed deer and aimed to more precisely determine differences in maintenance requirement and examine the difference in composition of gain between genotypes. In addition, in vivo apparent DM digestibility was measured in both genotypes. Red deer (n=7) and hybrid weaner stags (n=7) were housed in individual pens for a period of 8 weeks in both winter (July - August) and spring (November - December) and offered one of 7 feeding levels which ranged from maintenance to ad lib. During each 8 week experimental period, live weight gain, apparent digestibility and feed intake were measured. Immediately prior to, and at the conclusion of each 8 week period body composition was estimated using computer-assisted topography (CT scan). In winter, there was no significant difference in the live weight gain response to intake although red deer tended to have a higher (44 vs 55 MJ/kg) requirement for gain than hybrids. In spring, red deer had a lower requirement for maintenance (0.35 vs 0.47 MJ ME/W0.75/day) but a greater requirement for live weight gain (64 vs 35 MJ/kg) than hybrids. In spring, mean ad lib intake was about 30% higher than in winter and was greater for hybrids than for red deer. Energy retention in whole body (kJ/W0.75/day) did not differ between genotypes in either winter or spring but both the energy requirement for zero energy balance (0.59 vs 0.48 MJ ME/W0.75/day) and the efficiency of utilisation (0.37 vs 0.24) was greater in spring than in winter. The disparity between live weight gain and whole body weight gain may have been due to differences in gut fill. There was no significant difference between genotypes in relative growth coefficients for lean, bone or adipose tissue in whole body. However hybrids tended to have a higher winter and lower spring growth coefficient for fat compared with red deer. Growth coefficients for adipose, lean and bone, respectively were 0.983, 1.063 and 1.026 for winter and 1.02, 0.708 and 1.727 for spring. At the same whole body weight, deer in October had less adipose tissue than in August. It is unclear whether this represents a strategy for rapid spring growth or is an artefact of experimental protocol. Apparent dry matter digestibility (DMD) did not differ between genotypes but was higher by between 7 and 15 percentage units in winter compared with spring. Unexpectedly, digestibility was positively correlated with intake. Digestibility increased by 2.6 percentage units for every 10g DM/W0.75/day increase in either season in one group and 4.1 and 2.1 percentage units for deer in winter and spring respectively in another group. Errors in faecal collection were discounted as causes of the unexpected result