Heat stress, potentially affecting both the health of animals and the yield and composition of milk, occurs frequently in tropical, sub-tropical and temperate regions. A simulated acute heat stress experiment was conducted in controlled-climate chambers and milk samples collected before, during and after the heat challenge. Milk lipid composition, surveyed using LC-MS, showed significant changes in triacylglycerol (TAG) and polar lipid profiles. Heat stress (temperature-humidity index up to 84) was associated with a reduction in TAG groups containing short- and medium-chain fatty acids and a concomitant increase in those containing long-chain fatty acids. The abundance of five polar lipid classes including phosphatidylethanolamine, phosphatidylserine, phosphatidylcholine, lysophosphatidylcholine and glucosylceramide, was found to be significantly reduced during heat stress. Lysophosphatidylcholine, showing the greatest reduction in concentration, also displayed a differential response between heat tolerant and heat susceptible cows during heat stress. This phospholipid could be used as a heat stress biomarker for dairy cattle. Changes in TAG profile caused by heat stress are expected to modify the physical properties of milk fat, whereas the reduction of phospholipids may affect the nutritional value of milk. The results are discussed in relation to animal metabolism adaptation in the event of acute heat stress.

Italian ryegrass (Lolium multiflorum Lam.) is one of the most important temperate forage grasses on a global basis. The present study estimated trait variance, inter-trait correlation and broad-sense heritability (H2) for herbage yield, nutritive values and morphological characteristics of Italian ryegrass, and analysed associations between these traits and single nucleotide polymorphism (SNP) markers. A field-based, spaced-plant nursery experiment was conducted to assess 960 genotypes from seven cultivars and breeding lines, in a randomised complete block design with four replicates. Significant correlations, broad ranges of variation and significant genotypic variance components were identified for 18 measured phenotypic traits. Moderate H2 estimates (0.36–0.52) were obtained for nutritive values, compared with low to high H2 estimates (0.20–0.69) for yield over five cuttings, and moderate to high H2 estimates (0.40–0.78) for morphological traits. Within- and among-cultivar variation ranged from 40.0% to 95.1% and 4.9% to 60.0%, respectively, depending on different traits. Association analysis identified 65 significant SNP–trait gene associations involving multiple genomic regions, which warrant further validation. The implications of trait correlation and heritability for selection and improvement are discussed.

The genus Lolium (ryegrasses) exhibits substantial variation between species for annual-perennial growth habit. The genetic bases of this trait, and other characters that are differentiated between taxa, have been investigated through molecular genetic marker-based mapping of an interspecific mapping population derived from pair-wise crossing of single genotypes from Lincoln, a long-lived cultivar of perennial ryegrass, and Andrea, a cultivar of annual-type Italian ryegrass. The Andrea 1246 and Lincoln 1133 parental maps contained 122 loci on eight linkage groups (LGs), and 169 loci on seven LGs, respectively. A total of 10 phenotypic traits were measured, including annuality-perenniality index, date of head emergence, number of spikes per plant, number of spikelets per spike, number of floret per spike, flag leaf length, flag leaf width, spike length, stem length, and extent of regrowth. A total of 31 putative quantitative trait loci (QTLs) were detected. Regions of significance were identified on Andrea 1246 LGs 1, 2, 3 and 6. An annuality-perenniality index QTL on LG2 accounted for 30% of trait-specific phenotypic variance (V p ). In addition, LG2 contained coincident QTLs for the number of spikes per plant and head emergence date traits. The Lincoln 1133 genetic map displayed QTL-containing regions of significance on LGs 1, 4, 5 and 7, accounting individually for 10-22% of V p . QTLs identified in this study provide potential targets for ryegrass breeding in order to improve vegetative yield, persistence and seed yield.