Gaëtan F. Tremblay

Opportunities for, and limitations of, near infrared reflectance spectroscopy applications in soil analysis: A review

Near infrared reflectance spectroscopy (NIRS) is a cost- and time-effective and environmentally friendly technique that could be an alternative to conventional soil analysis methods. In this review, we focussed on factors that hamper the potential application of NIRS in soil analysis. The reported studies differed in many aspects, including sample preparation, reference methods, spectrum acquisition and pre-treatments, and regression methods. The most significant opportunities provided by NIRS in soil analysis include its potential use in situ, the determination of various biological, chemical, and physical properties using a single spectrum per sample, and an estimated reduction of analytical cost of at least 50%. Contradictory results among studies on NIRS utilisation in soil analysis are partly related to variations in sample preparation and reference methods. The following calibration statistics appear to be most appropriate for comparing NIRS performance across soil attributes: (i) coefficient of det...

Improving the nutritive value of timothy through management and breeding

Timothy (Phleum pratense L.) is a widely grown fo rage 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 ...

Yield and nutritive value of the spring growth of an ageing timothy sward

The decline in productivity of forage grasses with age since establishment has been recognised for several years, but this yield reduction and its consequences on nutritive value have not been studied in timothy (Phleum pratense L.). Our objective was to characterize the dry matter (DM) yield and nutritive value during spring growth of an ageing timothy sward grown under non-limiting N conditions. A timothy sward, seeded in 1998, was harvested at four developmental stages (stem elongation, early heading, late heading, and early flowering) during spring growth from 1999 to 2005. The average DM yield observed in production years 5, 6, and 7 was 43% of that measured in the first 4 production years when timothy was harvested at stem elongation or early heading, 52% when harvested at late heading, and 74% when harvested at early flowering. The yield potential of timothy during spring growth decreased with ageing at a rate of 0.66 and 0.91 Mg DM ha-1 yr-1 with harvests at early and late heading, respectively. T...

Effects of nonstructural carbohydrate concentration in alfalfa on fermentation and microbial protein synthesis in continuous culture

Insufficient readily fermentable energy combined with extensive degradation of proteins in alfalfa (Medicago sativa L.) may result in poor forage N utilization by ruminants. Using the inherent genetic variability and differences between harvests, our objective was to compare the effect of contrasting concentrations of nonstructural carbohydrates (NSC) in alfalfa on rumen fermentation and microbial protein synthesis. Individual genotypes of the alfalfa cultivar AC Caribou grown near Québec City, Québec, Canada, were harvested at the vegetative and early flowering stages, dried at 55 degrees C, ground, and analyzed for soluble carbohydrates (fructose + sucrose + glucose + pinitol) and starch. Approximately 20 genotypes having, respectively, the highest and lowest NSC concentrations were pooled to constitute 2 contrasted 1-kg forage samples. Samples of high- (17.9% DM) and low- (7.4% DM) NSC alfalfa were respectively allocated to separate dual-flow fermenters in a completely randomized design with 3 replications. Rumen inoculum was obtained from 4 ruminally fistulated cows in early lactation that were fed a TMR with a 50:50 forage to concentrate ratio. A 10-d incubation period was used, with the first 6 d serving as an adaptation period followed by 4 d of sampling with solid and liquid dilution rates in the fermenters set at approximately 2.0 and 4.3%/h, respectively. High versus low NSC concentration in alfalfa significantly enhanced the apparent digestibility of OM (59.1% for high-NSC alfalfa vs. 54.4% for low-NSC alfalfa) and DM (60.0 vs. 54.3%) and the true digestibility of DM (74.1 vs. 64.7%). Increasing NSC concentration in alfalfa (high vs. low) significantly decreased ruminal pH (6.85 vs. 7.08) and NH(3)-N concentration (26.0 vs. 33.6 mg/dL) and increased total VFA concentration (94.9 vs. 83.0mM). Molar proportions of acetate, isobutyrate, and isovalerate significantly decreased, whereas molar proportions of propionate and butyrate significantly increased with high-NSC alfalfa, resulting in a more glucogenic fermentation. More importantly, microbial N flow (263 vs. 230 mg/d) and bacterial N efficiency (41.1 vs. 29.6% of available N), measured using (15)N as a microbial marker, both significantly increased with the high-NSC alfalfa. These results indicate that increasing the concentration of NSC in alfalfa promotes a glucogenic fermentation and enhances microbial N synthesis in the rumen.

Leaf and stem dry matter digestibility and ruminal undegradable proteins of alfalfa cultivars

Increased dry matter digestibility and ruminal undegradable protein (RUP) concentration are traits highly ranked to improve the nutritive value of forage legumes. Whole-plant, leaf, and stem samples of 27 alfalfa cultivars grown in eastern Canada were analysed for total nitrogen (TN), in vitro RUP, and in vitro dry matter digestibility (IVDMD). The objectives were to determine if significant variation exists among these cultivars, and to establish the relationship between nutritive value parameters of leaves and stems, and those of whole plants. Cultivars were seeded in triplicate on 2 consecutive years and evaluated during the 2 subsequent production years with two harvests per year. There were significant differences among cultivars in IVDMD of stems and plants in spring growth and summer regrowth. Cultivar differences in leaf IVDMD were significant only in spring growth, but this variation was negligible in practical terms. Cultivars with high forage IVDMD also had high stem IVDMD and this relationship...

In vitro ruminal undegradable proteins of alfalfa cultivars

The quality of alfalfa would be greatly improved by an increase in its ruminal undegradable protein (RUP) concentration. Protein degradation rate (PDR), in vitro dry matter digestibility (IVDMD), leaf weight ratio (LWR), dry matter yield (DMY), total nitrogen (TN), in vitro RUP (expressed on both TN, RUP-TN, and dry matter basis, RUP-DM), acid detergent fiber (ADF), and neutral detergent fiber (NDF) concentrations were determined in 27 alfalfa cultivars. Cultivars were seeded in triplicate on 2 consecutive years and evaluated during the 2 subsequent production years with two harvests per year. Protein degradation rate and RUP-TN were determined using a ruminal inhibitor in vitro system. Data were averaged for spring growth, summer regrowth, and both harvests across 2 production years. Each of the three data sets was analyzed by ANOVA followed by a principal component analysis (PCA) on the ANOVA means. For the four-harvest data, cultivar differences were highly significant (P < 0.001) for all variates exce...

The effects of growth temperature on digestibility and fibre concentration of seven temperate grass species

Abstract The effects of growth temperature on digestibility and fibre concentration of seven grass species: Kentucky bluegrass (Poa pratensis L), timothy (Phleum pratense L), meadow foxtail (Alopecurus pratensis L), perennial ryegrass (Lolium perenne L), red fescue (Festuca rubra L), tufted hair-grass (Deschampsia caespitosa L (PB)) and meadow fescue (Festuca pratensis Huds) were investigated in growth chamber and greenhouse experiments. Seedlings from each grass species were established in a greenhouse and then transferred at five weeks of age to three growth chambers with day/night temperatures of 9/5, 13/9 and 17/13°C, respectively. Three pots of each species from each temperature treatment, and from the greenhouse control, were harvested weekly for three weeks. The rate of decline of in vitro true digestibility (IVTD) and in vitro cell wall digestibility (IVCWD) increased with increasing temperature for all species. Each degree of increase in temperature decreased the IVTD by an average of 0.22 g kg−1 dry matter (DM) day−1 between 9 and 13°C, and by 0.35 g kg−1 DM day−1 between 13 and 17°C. On average, the neutral detergent fibre (NDF) increased at a rate of 0.78 g kg−1 DM day−1 for each degree increase in temperature between 9 and 17°C. The effects of temperature were less for perennial ryegrass and meadow fescue than for the other species. Perennial ryegrass was consistently ranked as highest in digestibility, followed by meadow fescue; tufted hair-grass had the lowest digestibility. The rate of decline in digestibility was slower for perennial ryegrass and meadow fescue than for the other species.

Proteolysis in alfalfa silages made from different cultivars

During silage fermentation, proteolysis reduces the nutritional value of N, particularly in alfalfa. This study evaluated the proteolysis of 27 alfalfa cultivars seeded in triplicate in 2 consecutive years. Forage from each plot was wilted to a targeted dry matter (DM) content of 250 g kg–1 and ensiled in laboratory silos. Minisilos were made with spring growth and summer regrowth in the first year of production for the first seeding, and with the first 2 yr of production for the second seeding, giving 3 harvest years altogether. Concentrations of NPN, NH3, FAA, DM, TN, and pH were measured in silages, whereas RUP concentration was evaluated in forages. Low NPN concentration indicates low proteolysis during silage fermentation. Spring growth and summer regrowth were analyzed separately by ANOVA as a completely randomized block design replicated over 3 harvest years. A principal component analysis was then performed on the ANOVA means. Silage DM was used as covariate when it was deemed appropriate. There w...

Protein fractions and ruminal undegradable proteins in alfalfa

The relationship between protein fractions of the Cornell Net Carbohydrate and Protein System (CNCPS) and in vitro ruminal undegradable protein (RUP) concentration was studied using variability among 14 genotypes and 27 cultivars of alfalfa harvested at early bloom in the spring growth. Significant differences in soluble N concentration (fraction A + B1), degradable true protein fractions (fractions B2 and B3), and in vitro RUP concentration were found among genotypes but not among cultivars. Correla tions between in vitro RUP values and fractions A + B1 and B2 were significant for genotypes ( r = -0.77 and r = 0.78) and cultivars ( r = -0.72 and r = 0.64). Protein fractions of the CNCPS should be considered as an alternative laboratory method for in vitro RUP to screen alfalfa genotypes for breeding purposes. Key words:

Mehlich 3 extractable nutrients as determined by near-infrared reflectance spectroscopy

Near-infrared reflectance spectroscopy (NIRS) is a cost-effective and environmentally friendly technique of soil analysis that is particularly advantageous in intensive soil sampling and soil nutrient management as well. This study evaluated the potential of NIRS for predicting P, K, Ca, Mg, Cu, Zn, Mn, Fe, and Al extracted by Mehlich 3. We used 150 air-dried samples collected from a 15-ha site dominated by Orthic Humic Gleysol and Gleyed Dystric Brunisol soils. Calibration equations were developed using modified partial least squares regression. The accuracy of NIRS prediction was evaluated using the coefficient of determination (R2), the ratio of performance deviation (RPD), and the ratio of error range (RER). Reliable calibrations were found for Ca, Cu, and Mg (R2 ≥ 0.7, RPD ≥ 1.75, and RER ≥ 8). Less-reliable calibrations were found for Al, Fe, K, Mn, P, and Zn (R2 < 0.7, RPD < 1.75, and RER < 8). In the validation with independent samples, acceptable regression coefficients (i.e., 0.8 ≤ slope ≤ 1.2) ...