Effects of Cryopreservation on Bull Spermatozoa Distribution in Morphometrically Distinct Subpopulations

Assisted sperm morphometry analysis (ASMA) was used in this study to determine the effects of cryopreservation on bull spermatozoa distribution in morphometrically distinct subpopulations. Ejaculates were collected from five bulls and were divided. One portion was diluted at 30 degrees C in a skim milk-egg yolk medium, containing glycerol. A microscope slide was prepared from single extended sperm samples prior to freezing. The remainder of each sample was frozen in nitrogen vapours. After thawing, sperm smears were prepared as described above. All slides were air dried and stained with Hemacolor. The sperm-head dimensions for a minimum of 200 sperm heads were analysed from each sample by means of the Sperm-Class Analyser (SCA), and the mean measurements recorded. Our results showed that applying the ASMA technology and multivariate cluster analyses, it was possible to determine that three separate subpopulations of spermatozoa with different morphometric characteristics coexist in bull ejaculates (large, average and small spermatozoa). The mean values of each sperm head dimension among the three subpopulations of spermatozoa were significantly different (p < 0.001). Besides, there were significant (p < 0.001) differences in the distribution of these three sperm subpopulations between fresh and thawed samples. Thus, the percentage of representation of the subpopulation that includes those spermatozoa whose dimensions are the biggest, decreased from 52.06% in extended fresh samples to 15.51% in the thawed ones. Contrarily, the percent of representation of the subpopulation containing the smallest spermatozoa, increased from 8.70% in extended fresh samples to 34.04% in the thawed ones. In conclusion, the present study confirms the heterogeneity of sperm head dimensions in bull semen, heterogeneity that vary through the cryopreservation procedure.     

Multivariate Cluster Analysis Regression Procedures as Tools to Identify Motile Sperm Subpopulations in Rabbit Semen and to Predict Semen Fertility and Litter Size

Computerized motility analysis (CASA) shows that four separate subpopulations of spermatozoa with different motility characteristics co-exist in rabbit ejaculates. There were significant (p < 0.01) differences in the distribution of these subpopulations among separate genetic lines, total sperm abnormalities and the percentage of altered acrosomes. Furthermore, logistic and linear multivariate regressions among several parameters of rabbit semen quality analysis were tested for use as predictive tools for the fertilizing ability of a specific artificial insemination semen sample. Logistic regression analysis rendered two mathematical, significant (p < 0.01) models: one between sperm viability and conception rate and the other between total sperm abnormalities and conception rate. Multiple linear regression analyses also yielded some significant relationships between both fertility (p < 0.001) and litter size (p < 0.05), with respect to some semen characteristics. Our results support the hypothesis that the predictive in vivo fertility use of the standard rabbit semen quality analysis coupled with a CASA determination could be reasonably achieved by applying linear and logistic regression analyses among several parameters of rabbit semen quality analysis.     

A review of farm level modelling approaches for mitigating greenhouse gas emissions from ruminant livestock systems

Ruminant livestock systems contribute to global warming through the emission of nitrous oxide (N₂O), methane (CH₄) and carbon dioxide (CO₂). This paper discusses a general framework for a whole-farm approach to develop cost-effective GHG mitigation strategies. A dairy farm is a complex system with different interacting components. Generally, whole-farm approaches distinguish at least an animal component and a soil–crop component. Whole-farm models should be able to give an accurate representation of the internal cycling of materials and its constituents as well as the exchange between the farming system and its environment. The paper gives an overview of current whole-farm models that are able to simulate GHG emissions for dairy farms. These models are DairySim, FarmGHG, SIMS_DAIRY and FarmSim. All models are able to calculate CH₄ and N₂O emissions, but differences appear in the ability to calculate CO₂ emissions, economics and other parameters. The effects of selected mitigation strategies are demonstrated with some of the models. It is concluded that a whole-farm approach is a powerful tool for the development of cost-effective GHG mitigation options as it reveals relevant interactions between farm components. Model calculations underlined the relationship between farm gate N surplus and GHG emissions, and thus the possibility to use N surpluses as an indicator for GHG emissions.     

Long-term fate of nitrogen uptake in catch crops

The long-term effects of undersowing a ryegrass catch crop in cereals was analysed with the FASSET simulation model. The model was tested on a 28-year field experiment with ryegrass catch crops in spring barley. The experiment included treatments with nitrogen (N) fertiliser rates, catch crop use and timing of tillage. The modelled effects of these treatments generally agreed with observations on crop production, soil carbon, soil nitrogen and nitrate leaching. Both the observations and the simulations predicted a yield increase of 7 kg N ha⁻¹ and an increase in nitrate leaching of 13 kg N ha⁻¹ due to a prehistory of 24 years with continuous use of catch crops compared to a prehistory without catch crops.

A range of scenarios was constructed to evaluate the fate of the reduced nitrate leaching on crop N uptake, N leaching, gaseous emissions and change in soil organic N, and how this fate interacts with soils and climate and management. These scenarios showed that 22–30% of the reduced nitrate leaching was subsequently leached during the following decades after termination of catch crop use. Between 35 and 40% of the reduced nitrate leaching was harvested in cereals. The exact distribution depended primarily on the soil texture. The scenarios showed that effects of catch crops should be evaluated on the long-term rather than consider short-term effects only.     

PCR-based markers to differentiate the mitochondrial genomes of petaloid and male fertile carrot (Daucus carota L.)

Cytoplasmic male sterility (CMS) is essential for the development of highly adapted and uniform hybrid varieties of carrot and other crops. The most widely used type of CMS in carrot is petaloidy, in which the stamens are replaced by petals or bract-like structures. We have developed a series of mitochondria-specific PCR markers to distinguish cytoplasms inducing petaloidy (Sp) and male-fertility (N). The markers target the atp1,atp6, atp9, orfB (atp8), nad6 and cob loci from the mitochondrial genomes of a diverse collection of male fertile and petaloid carrots. We report 14 primer pairs that amplify marker fragments from either Sp or N cytoplasms and three primer pairs that amplify fragments with length polymorphism. The amplification products span sites of insertions, deletions or recombinations adjacent to or within the coding regions of the targeted genes. The markers reported here are useful tools to identify the type of cytoplasm in cultivated carrot and to evaluate variation in the mitochondrial genomes within the genus Daucus. This revised version was published online in August 2006 with corrections to the Cover Date.     

Crop nitrogen demand and canopy area expansion in winter wheat during vegetative growth

The effect of nitrogen (N) on crop growth and productivity is mediated through effects on both light interception (green crop area) and radiation use efficiency (RUE). The effects of N nutrition on these factors were studied using data on green area index (GAI), above-ground dry matter and N uptake from growth analysis measurements in winter wheat from a number of experiments in Denmark with different application rates of N. Only measurements taken prior to anthesis were used in the statistical analyses. The N uptake was found to be proportional to GAI, and to have an additional curvilinear response to dry matter implying decreasing N concentration with increasing dry matter. This supports the hypothesis that nitrogen is associated with both the green surfaces of the crop canopy and with the dry matter component. A model of GAI expansion is presented incorporating three limiting factors: an exponential increase in GAI in thermal time, a minimum leaf area ratio, and a minimum ratio of GAI to N content in above-ground dry matter. This simple function has potential to be used as a tool for targeting timing and rates of N fertilisation in relation to a desired development of GAI. Such N application strategies should also consider the nitrogen nutrition index (NNI), which was defined based on the relationship between N uptake and both GAI and dry matter. The response of RUE to NNI showed a curvilinear response with a tendency for saturation at high NNI. The design of N application strategies should therefore ensure that low NNI is avoided during the most productive periods in the growing season.     

Genotypes of Perennial Ryegrass (Lolium perenne L.) with High Anther-Culture Response through Hybridization

Anther-culture response in Lolium perenne was studied in the hybrid populations from three responsive diploid parent clones to obtain genotypes with superior anther-culture response through hybridization. Genetic variation for anther-culture response was significant both within and between the four hybrid families and their parents. A reciprocal effect was indicated for embryo formation and regeneration percentages for one of the cross combinations. Among 55 hybrid clones tested in two environments, 6 clones were identified with an anther-culture response level superior to their parents. While the parents produced one green plant or less per 100 anthers, these superior clones produced from 11 to 59 green plants/100 anthers, mainly as the result of improved embryo formation and improved percentages of regenerated plants being green. A significant correlation (r = 0.397^**) was observed between embryo formation and percentage of green plants. The results are discussed with regard to the possible transfer of anther-culture response to non-responsive breeding material through hybridization.     

A polycross pattern formula

Summary A formula defining a polycross pattern is introduced. The pattern appears to be a special latin square in which every clone has any one other clone as a neighbour and just once in each of the four directions North, South, East, and West, presenting an ideal polycross pattern. The formula holds good for n clones when n+1 is a prime.     

A completely balanced polycross design

Summary A polycross design for n² replicates of n distinct clones is introduced. The design consists of n distinct n x n polycross patterns, provided n+1 is a prime number.The design is completely balanced in that it has the following properties with respect to nearest neighbours: In anyone of the four main directions, North, South, East, and West, every clone has any other clone as a nearest neighbour exactly n times, while no clone has itself as a nearest neighbour. In any of the four intermediate directions, NorthEast, SouthEast, SouthWest, and NorthWest, every clone has any other clone as a nearest neighbour exactly n–2 times, and itself as a nearest neighbour exactly n–1 times.     

Segregation of Isozyme Marker Loci Amongst Androgenetic Plants of Lolium perenne L.

The segregation of isozyme markers has been examined in the green and albino androgentic progenies of two plants of Lolium perenne. Overall the pooled data for the loci PG1/2 and GOT/2 does not deviate from expectation, but there is considerable heterogeneity between families and between green and albino plants. Specific alleles predominate in the different progeny sets. The results may be accounted for by possible linked loci affecting anther culture response or of linked lethal genes.