Sun X.Z.,Agresearch Ltd. |
Waghorn G.C.,DairyNZ Ltd. |
Clark H.,Agresearch Ltd.
Animal Feed Science and Technology
Perennial ryegrass is the principal component of diets fed to ruminants in New Zealand. Selection for ryegrass improvement should incorporate measures relating to feeding value (i.e. quality × intake) for sheep and cattle. This study was designed to measure the variation in characteristics of nutritive value of three ryegrass cultivars harvested at different stages of regrowth. The cultivars were Grasslands Greenstone (Greenstone; tetraploid), Grasslands Samson (Samson; diploid) and Quartet (tetraploid). They were grown as pure swards with leafy regrowth harvested after 2, 3, 4, 5, 6 and 7 weeks for measurement of chemical composition, physical parameters (i.e. shear force and energy required for mincing), degradation kinetics and distribution of constituents between the immediately degradable (A), potentially degradable (B) and undegradable (C) fractions. Analyses showed that age of regrowth resulted in larger differences in composition and degradation kinetics than cultivar, and emphasised the need to harvest material in a similar condition to that grazed by animals. Cultivar differences were best indicated by chemical composition and ratios of crude protein (CP):neutral detergent fibre (aNDF) in the dry matter (DM), the proportion of CP in the 'A' fraction as well as degradation of DM in the 'B' fraction. The CP:aNDF ratios averaged for the three cultivars at 2, 3, 4, 5, 6, and 7 weeks were 0.82, 0.76, 0.71, 0.55, 0.48 and 0.42, respectively, with averages at weeks 5 and 6 for Greenstone, Samson and Quartet of 0.59, 0.49 and 0.48, respectively. The ratio differed between ages (P<0.001) and across cultivars (P<0.05). The DM fractional degradation rates (k) tended to decline from 0.18 to 0.12/h with maturity (P<0.05) and after weeks 5 and 6 of regrowth averaged 0.17, 0.16 and 0.14/h for the respective cultivars. Both the concentration of lignin(sa) in DM and shear force were weakly associated with regrowth and cultivar and appeared to be less important than chemical composition for indicating nutritive value of leafy ryegrass. © 2009 Elsevier B.V. All rights reserved. Source
Berry D.P.,Moorepark Dairy Production Research Center |
Kearney J.F.,Irish Cattle Breeding Federation |
Roche J.R.,DairyNZ Ltd.
There is a paucity of estimates of genetic variation for secondary sex ratio (i.e., sex ratio at birth) in dairy cattle. The objective of this study was to estimate the direct and maternal genetic variance as well as maternal permanent environmental variance for offspring sex in dairy herds. The data consisted of 77,508 births from 61,963 dams and 2,859 sires in 1,369 Irish dairy herds across the years 2003 to 2008, inclusive. Mixed models were used to estimate all parameters. Significant genetic variation in sex ratio existed, with a heritability for secondary sex ratio estimated at 0.02; the genetic standard deviation was 0.07 percentage units. No maternal genetic effects on secondary sex ratio were identified but the proportion of phenotypic variance in secondary sex ratio attributable to maternal permanent environmental effects was similar to that attributable to the additive genetic variance (i.e., 0.02). These results, therefore, suggest that the paternal (genetic) influence on secondary sex ratio is just as large as the maternal (non-genetic) influence, both of which are biologically substantial. The results from this study will be useful in generating a sample population of divergent animals for inclusion in a controlled experiment to elucidate the physiological mechanism underpinning differences in secondary sex ratio. © 2011 Elsevier Inc. Source
Burke C.R.,DairyNZ Ltd.
Society of Reproduction and Fertility supplement
The New Zealand (NZ) economy and its dairy industry are sensitive to global consumer perception of farming practices used to generate milk products because milk exports account for > 25% of national export earnings and > 90% of milk produced is exported as products. Astute management of product image and market risk is, therefore, important for the viability of the industry and country. More than 95% of milk produced in NZ comes from strictly seasonal, pasture-based systems, with associated constraints on reproductive performance. Increasing herd sizes, operational changes and genetic selection priorities have further challenged dairy farmers to achieve optimal levels of herd fertility. Reproductive management practices have developed to address the need to maintain a 365-day inter-calving interval, essentially through maximizing the number of cyclic cows during the breeding period and minimizing the duration of the seasonal calving period. Aspects of the hormonal interventions developed and routinely used to achieve these objectives have been the subject of product quality and market risk concerns forcing the industry to explore alternative ways of achieving reproductive performance goals. One approach has been to exploit the inherently high level of fertility in NZ dairy herds. This approach has seen the inclusion of fertility-related traits in the national genetic evaluation system to prevent further decline in genetic fertility. More recently, a nationally coordinated extension program has been adopted to support farmers and their advisors to identify, prioritize and improve on key management areas for incremental gains in herd reproductive performance. Advances in automation and bio-sensing are yet to make a significant impact, but remain potentially valuable additions in supporting the dairy farmer to manage the areas having the largest effects on reproductive performance. Source
Bryant R.H.,Lincoln University at Christchurch |
Gregorini P.,DairyNZ Ltd. |
Edwards G.R.,Lincoln University at Christchurch
Animal Feed Science and Technology
New Zealand dairy systems are based on Lolium perenne pastures with low nitrogen use efficiency (NUE) and high urinary N losses. Modelling attempts to provide solutions to improve NUE are limited due to lack of data on pasture N fractions under a range of management situations. The effects of N application (0 or 25. kg. N/ha), cultivar (standard and high sugar cultivars), regrowth interval (leaf appearance of 2, 3 and 4 leaf) and time of day (morning or afternoon) on chemical composition and N fractionation of L. perenne were investigated in a field study in early spring. Leaf appearance interval and time of day had the greatest influence on chemical composition and fractionation. Both fraction A (non-protein N) and water soluble carbohydrates increased by 60% between second and fourth leaf appearance (P<0.001) and by 20% between morning and afternoon (P<0.001). Total N and fractions B1 and B2 (soluble true protein) declined during the day and with leaf appearance. Addition of low fertiliser N rates did not alter N fractionation or chemical composition but improved herbage yield. The effects of using a high sugar cultivar were small and inconsistent and differences between cultivars were more closely linked with flowering date. Generally, the relative proportions of N fractions could be altered with management strategies but the overall solubility of N remained high at over 0.85. While management factors play an important role in influencing the quality of herbage and total N relative to carbohydrate, there is little scope to improve NUE by reducing the proportions of soluble N fractions. © 2012 Elsevier B.V.. Source
Walker C.G.,DairyNZ Ltd. |
Mitchell M.D.,University of Queensland
Animal Production Science
Epigenetic mechanisms, such as DNA methylation, regulate gene expression and, subsequently, phenotype, without changing the underlying DNA sequence. It is well established that the environment and nutrition can regulate methylation and, therefore, modify phenotype. In this review, regulation of DNA methylation and in particular, the influence of B-vitamin on one-carbon metabolism is outlined, and how deficiency or supplementation with B-vitamins, such as folate, can influence disease. Evidence is provided for the roles of B-vitamin in regulating reproduction and how deficiency of B-vitamin may be impacting dairy cattle fertility. Results from our laboratory provide evidence for an association between DNA methylation and gene expression in the endometrium during early pregnancy. It is, therefore, hypothesised that DNA methylation may regulate the uterine response to the embryo during early pregnancy and that aberrant DNA methylation during this time may jeopardise pregnancy success. Further research is required to establish if B-vitamin supplementation can improve reproductive success and if this effect is via changes to DNA methylation and gene expression in the endometrium, or via positive effects on oocyte and embryo development. © CSIRO 2013. Source