G. 2003. Fatty acids in forages. I. Factors affecting concentrations. Can. J. Anim. Sci. 83: 501-511. When forages represent a high proportion of ruminant diets they provide a significant quantity of fatty acids (FA). Effects of growth stage, fertilization, conservation method, growth period, species, and cultivar on forage FA were determined in four experiments. Concentrations of C16:0, C18:2, C18:3, and total FA (TFA) in timothy (Phleum pratense L.) decreased (P < 0.01), respectively, by 15, 16, 31, and 23% between stem elongation and early flowering. Nitrogen fertilization (120 vs. 0 kg N ha -1 ) caused an increase (P < 0.01) of 18% of C16:0, 12% of C18:2, 40% of C18:3, and 26% of TFA concentrations. Phosphorus was not deficient and P fertilization (45 vs. 0 kg P ha -1 ) had no significant effect on timothy FA concentrations. Wilting and drying decreased (P < 0.01) timothy C18:2, C18:3, and TFA concentrations. Concentrations of C18:2, C18:3, and TFA were higher in summer regrowth than in spring growth, primarily in orchardgrass (Dactylis glomerata L.) and timothy (P < 0.01). Significant variation for all FA concentrations was observed among 12 species (P < 0.05); on average, the C18:3, C18:2, and C16:0 accounted for 88% of TFA in studied species. Timothy was the only species in which the difference among cultivars was simultaneously significant (P < 0.05) for concentrations of C18:2, C18:3, and TFA. Among the grasses, an annual ryegrass (Lolium multiflorum Lam.) cultivar had the highest C18:3 concentration (20.6 mg g -1 DM) whereas a timothy cultivar had the lowest (7.3 mg g -1 DM) (P < 0.05). Among legumes, a white clover (Trifolium repens L.) cultivar had the highest C18:3 concentration (16.5 mg g -1 DM) whereas an alfalfa (Medicago sativa L.) cultivar had the lowest (6.0 mg g -1 DM) (P < 0.05). Polyunsaturated FA concentrations in forages can be increased by harvesting timothy at an early stage of development and as fresh grass, by increasing N fertilization of timothy, and by choosing species with higher FA concentrations such as white clover and annual ryegrass. a causé une augmentation (P < 0,01) de 18% du C16:0, 12% du C18:2, 40% du C18:3 et 26% des AGT. Le P n'étant pas défici-taire, la fertilisation en P (45 vs. 0 kg P ha -1 ) n'a pas eu d'effet sur les concentrations en AG de la fléole. Les concentrations en C18:2, C18:3 et AGT de la fléole ont diminué (P < 0.01) avec le préfanage et le séchage. Les concentrations en C18:2, C18:3 et AGT étaient plus élevées en croissance d'été qu'en croissance de printemps et ce, surtout chez le dactyle (Dactylis glomerata L.) et la fléole (P < 0,01). Une variation significative entre 12 espèces a été observée pour tous les AG (P < 0,05); en moyenne, les C18:3, C18:2 et C16:0 représentaient 88% des AGT chez les espèces étudiées. La fléole était la seule espèce où la variation entre cultivars était significative à la fois pour le C18:2, le C18:3 et les AGT (P < 0,05). Chez les graminées, un cultivar de ray-grass annuel (Lolium multiflorum Lam.) avait la plus forte (...

Bolinder, M. A., Angers, D. A., Bélanger, G., Michaud, R. et Laverdière, M. R. 2002. Root biomass and shoot to root ratios of perennial forage crops in eastern Canada. Can. J. Plant Sci. 82: 731-737. Shoot to root ratios (S:R) at peak standing crop are commonly used to estimate the annual crop residue C inputs to the soil from the root biomass left in the soil at harvest. However, root biomass has often been neglected in field studies and estimates of S:R for many commonly grown forage species are not available. Our objective was to determine root biomass and S:R of seven perennial grass species and two perennial legume species under eastern Canadian soil and climatic conditions. Root biomass in three soil layers (0-15, 15-30 and 30-45 cm) was measured shortly after the second harvest in the first (1995) and second (1996) year of production. Two harvests of aboveground DM were taken each year. The total root biomass (0-45 cm) in the second year of production (average of 1437 g m -2 ) was twice that measured in the first year of production (average of 683 g m -2 ). This temporal variation was mainly explained by the increase of root biomass in the 0-to 15-cm layer. The proportion of total root biomass (0-45 cm) in the 0-to 15-cm layer increased from 54 to 71% while that in the 15-to 30-cm layer decreased from 37 to 21%; the proportion of roots in the 30-to 45-cm layer remained constant at about 10% in both years. The S:R of alfalfa for the 0-15 cm depth was significantly higher than that for most of the grasses. No significant difference in S:R was observed among grass species. Recognizing that S:R may vary with locations and climatic conditions, our results suggest that average S:R of about 1.30 (values ranged from 1.01 to 1.72) in the first production year and 0.60 (values ranged from 0.43 to 0.87) in the second production year could be used as a first approximation to estimate the amount of root biomass left in the soil to a depth of 45 cm from forage crops in eastern Canada. The S:R of forage crops, particularly grasses, were lower than those of annual crops such as small-grain cereals and corn. Le rapport biomasse aérienne : biomasse racinaire (BA:BR) mesuré lorsque les cultures sont à maturité est souvent utilisé pour estimer les apports annuels de C laissés dans le sol par la BR des plantes. Cependant, la BR a souvent été négligée dans les études au champ et il n'existe pas d'estimé du rapport BA:BR pour plusieurs espèces de plantes fourragères. Notre objectif était de déterminer la BR au champ et le rapport BA:BR pour différentes espèces de plantes fourragères pérennes sous les conditions climatiques et édaphiques de l'est du Canada. Des mesures de la BR ont été effectuées pour trois couches de sol (0-15, 15-30 et 30-45 cm) et ce, pendant deux années consécutives (la première et la deuxième année de production) quelques jours après la deuxième coupe pour sept espèces de graminées et deux de légumineuses. Une variation importante dans la BR a été observée entre la première et la deuxième année de producti...

Alfalfa (Medicago sativa L.) cut at sundown has been shown to contain greater concentration of total nonstructural carbohydrates (TNC) than that cut at sunup. Fourteen multiparous (8 ruminally cannulated) and 2 primiparous lactating dairy cows were randomly assigned to 2 treatments in a crossover design (2 periods of 24 d) to investigate the effects of alfalfa daytime cutting management on ruminal metabolism, nutrient digestibility, N balance, and milk yield. Half of each alfalfa field (total of 3 fields) was cut at sundown (PM) after a sunny day, whereas the second half was cut at sunup (AM) on the following day. Both PM and AM cuts were field-wilted and harvested as baleage (531 +/- 15.0 g of dry matter/kg of fresh matter). Bales (PM and AM) were ranked according to their concentrations of TNC, paired, and each pair of PM and AM baleages was then assigned to each experimental day (total of 48 d). The difference in TNC concentration between PM and AM baleages fed during the 10 d of data and sample collection varied from -10 to 50 g/kg of dry matter. Each pair of baleage was fed ad libitum to cows once daily with no concentrate. Ruminal molar proportion of acetate and total volatile fatty acid concentration were greater in animals fed the AM baleage, whereas the proportion of valerate was greater with PM baleage; no other significant changes in ruminal molar proportions of volatile fatty acids were observed between forage treatments. Digestible organic matter intake, organic matter digestibility, and plasma Lys concentration were significantly greater in cows fed PM alfalfa, suggesting that more nutrients were available for milk synthesis. Significantly lower body weight gain and retained N as a proportion of N intake were observed in cows fed PM alfalfa, thus suggesting that nutrients were channeled to milk synthesis rather than to body reserves. Intake of dry matter (+1.0 kg/d), and yields of milk (+1.0 kg/d), milk fat (+70 g/d), and milk protein (+40 g/d) were significantly greater in cows fed PM vs. AM alfalfa. Concentration of milk urea N and excretion of urea N as a proportion of total urinary N were significantly reduced, and milk N efficiency was increased when feeding PM vs. AM alfalfa, indicating an improvement in N utilization. Increasing the TNC concentration of alfalfa by shifting forage cutting from sunup to sundown improved N utilization and milk production in late-lactation dairy cows.

Alfalfa (Medicago sativa L.) cut at sundown (p.m.) has been shown to have a greater concentration of total nonstructural carbohydrates (TNC) than when cut at sunup (a.m.). Eight ruminally cannulated Holstein cows that were part of a larger lactation trial were used in a crossover design (24-d periods) to investigate the effects of alfalfa cutting time on digestibility and omasal flow of nutrients. Alfalfa was cut at sundown or sunup, field-wilted, and harvested as baleage (530 +/- 15.0 g of dry matter/kg of fresh matter). The difference in TNC concentration between p.m. and a.m. alfalfa within each pair of bales fed daily during the 10 d of data and sample collection varied from -10 to 50 g/ kg of dry matter. Each pair of bales was fed for ad libitum intake to cows once daily with no concentrate. During the 3 d of omasal sampling, intake (+0.8 kg/d) and omasal flow of organic matter (OM; +0.42 kg/d) tended to be greater when cows were fed p.m. vs. a.m. alfalfa, but no differences were found for ruminal and postruminal digestion of this nutrient. Similarly, N apparently digested ruminally and postruminally did not differ when feeding p.m. vs. a.m. alfalfa. However, N truly digested in the rumen, as a proportion of N intake, was significantly greater in cows fed p.m. (79%) vs. a.m. alfalfa (74%), thus suggesting that longer wilting time of alfalfa cut at sundown increased forage proteolysis. Supply of rumen-degradable protein did not change (2,716 g/d) when averaged across treatments, whereas omasal flow of non-NH(3) nonbacterial N was significantly decreased (-29 g/d) when feeding p.m. vs. a.m. alfalfa. Omasal flow of total bacterial non-NH(3)-N (NAN) increased (+21 g/d) significantly when cows were fed p.m. vs. a.m. alfalfa possibly because bacteria from cows fed p.m. alfalfa captured significantly more NH(3) than those from cows fed a.m. alfalfa. Therefore, greater availability of fermentable energy as TNC appears to increase the capacity of microbes to uptake NH(3)-N and convert it to microbial protein. Enhanced OM intake can also explain the observed increase in bacterial protein synthesis with p.m. alfalfa. Efficiency of bacterial protein synthesis, expressed on a fermented OM basis or as grams of bacterial NAN per gram of rumen-degradable N, did not differ between p.m. and a.m. alfalfa. Conversely, bacterial efficiency, as grams of bacterial NAN per gram of N intake, was significantly increased when cows were fed p.m. baleage. No significant difference between forage treatments was found for the omasal flow of total AA from omasal true digesta, suggesting no benefit of daytime cutting management on the passage of total AA to the lower gastrointestinal tract. Enhancing energy intake and TNC concentration of alfalfa by shifting forage cutting from sunup to sundown increased protein synthesis and NH(3) uptake by ruminal bacteria indicating an improvement in N utilization.

R. 2006. Winter damage to perennial forage crops in eastern Canada: Causes, mitigation, and prediction. Can. J. Plant Sci. 86: 33-47. Harsh winter climate results in frequent losses of stands and yield reduction in many forage-growing areas of Canada and other parts of the world. Climatic conditions and crop management both affect the winter survival of perennial forage crops. In this review, we present the main causes of winter damage in eastern Canada and we discuss crop management practices that help mitigate the risks of losses. Predictive tools available to assess the risks of winter damage both spatially and temporally are also presented. Our understanding of the causes of winter damage and of the plant adaptation mechanisms to winter stresses, particularly the role of N and C organic reserves, has improved. Forage species commonly grown in eastern Canada differ in their tolerance to subfreezing temperatures and to anoxia caused by the presence of ice on fields. Some improvement in winter hardiness of forage legume species has been achieved through breeding in eastern Canada but new technologies based on laboratory freezing tests and the identification of molecular markers may facilitate the future development of winter-hardy cultivars. Crop management practices required for good winter survival are now better defined, particularly those involving cutting management and the interval between harvests. Simulation models and climatic indices derived from our current knowledge of the causes of winter damage provide general indications on the risk of winter damage but their degree of precision and accuracy is still not satisfactory. Further improvements in winter survival require a more thorough understanding of the different causes of winter damage and, primarily, of their complex interactions with genetic, climatic, and management factors.

Alfalfa (Medicago sativa L.), an important forage crop that is also a potential biofuel crop, has advantages of high yield, high lignocellulose concentration in stems, and has low input costs. In this study, we investigated population structure and linkage disequilibrium (LD) patterns in a tetraploid alfalfa breeding population using genome-wide simple sequence repeat (SSR) markers and identifi ed markers related to yield and cell wall composition by association mapping. No obvious population structure was found in our alfalfa breeding population, which could be due to the relatively narrow genetic base of the founders and/or due to two generations of random mating. We found signifi cant LD (p < 0.001) between 61.5% of SSR marker pairs separated by less than 1 Mbp. The observed large extent of LD could be explained by the effect of bottlenecking and selection or the high mutation rates of SSR markers. Total marker heterozygosity was positively related to biomass yield in each of fi ve environments, but no relationship was noted for stem composition traits. Of a total of 312 nonrare (frequency >10%) alleles across the 71 SSR markers, 15 showed strong association (p < 0.005) with yield in at least one of fi ve environments, and most of the 15 alleles were identifi ed in multiple environments. Only one allele showed strong association with acid detergent fi ber (ADF) and one allele with acid detergent lignin (ADL). Alleles associated with traits could be directly applied in a breeding program using marker-assisted selection. However, based on our estimated LD level, we would need about 1000 markers to explore the whole alfalfa genome for association between markers and traits.

2001. Improving the nutritive value of timothy through management and breeding. Can. J. Plant Sci. 81: 577-585. Timothy (Phleum pratense L.) is a widely grown forage grass species in cool and humid regions of the world including northeastern and northwestern North America, Nordic countries, Russia, and Japan. The nutritive value of timothy decreases with time, phenological development, and increasing forage yield. This review paper summarizes methods of controlling or improving the nutritive value of timothy through management practices and genetic selection, while keeping in mind the importance of forage yield. Consequently, the nutritive value of timothy is considered in relation to the accumulation of forage yield. The ecophysiological basis for the decrease in nutritive value with increasing forage yield during a growth cycle is presented with the assumption that the forage is made of two components: metabolic and structural. The decrease in the proportion of the metabolic component with increasing forage yield reduces the nutritive value of timothy. The nutritive value is also affected by the N concentration of the metabolic component, and by the digestibility of the structural component. Harvest dates, growing seasons, N fertilization, and cultivars have an indirect effect on the nutritive value of timothy through increased forage yield and the change in the proportion of the metabolic and structural components, but they also have a direct effect on each component. The results presented demonstrate the possibility of dissociating yield and nutritive value by plant breeding and, therefore, to improve the nutritive value of timothy while maintaining forage yield. Nord, les pays scandinaves, la Russie, et le Japon. La valeur nutritive de la fléole des prés diminue avec le temps, le développement phénologique, et l'accumulation de rendement. Cet article de synthèse présente des façons de contrôler ou d'améliorer la valeur nutritive de la fléole des prés par la régie et la sélection génétique sans toutefois négliger l'importance du rendement. Ainsi, la valeur nutritive de la fléole des prés est considérée en relation avec l'accumulation du rendement fourrager. La base écophysiologique de la diminution de la valeur nutritive avec l'augmentation du rendement durant un cycle de croissance est présentée en faisant l'hypothèse que la biomasse aérienne est formée de deux composantes: métabolique et structurale. La diminution de la proportion de la composante métabolique avec l'augmentation du rendement réduit la valeur nutritive. La valeur nutritive est aussi affectée par la teneur en azote de la composante métabolique, et par la digestibilité de la composante structurale. Les dates de coupe, la saison de croissance, la fertilisation azotée et les cultivars ont un effet indirect sur la valeur nutritive de la fléole des prés via une augmentation du rendement et un changement de la proportion des composantes métaboliques et structurales, mais ils ont de plus un effet direct sur chacune de ces deux dernières composantes...

Freezing tolerance is a determinant factor of persistence of alfalfa (Medicago sativa L.) grown in northern climates. Selection for winter hardiness in field nurseries is difficult because of the unpredictability of the occurrence of test winters allowing the identification of hardy genotypes. A method of selection entirely performed indoor in growth chambers and walk‐in freezers has been applied for the identification of genotypes with superior freezing tolerance. Using that approach, cultivars recommended for growth in eastern Canada have been submitted to cycles of recurrent selection to generate populations potentially more tolerant to freezing (TF). Subsequent determination of the freezing tolerance of populations recurrently selected using plants acclimated to natural hardening conditions in an unheated greenhouse revealed a progressive increase in response to this selection approach. Field assessment of TF populations also showed better survival and forage yield than original cultivars at sites that experienced severe winter conditions. At stressed sites, a significant proportion of the variance in the yields of the populations was explained by freezing tolerance potential. Our results show that major increases in freezing tolerance (between 3 and 5°C) of alfalfa and better survival to severe winter conditions in the field can be achieved by screening for freezing tolerance under indoor growing conditions and intercrossing the selected plants.