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Dietary Cation–Anion Difference and Tetany Index of Timothy Forage Fertilized with Liquid Swine Manure

^a Agric. and Agri-Food Canada, Soils and Crops Res. and Dev. Cent., 2560 Hochelaga Blvd., Québec, QC, Canada G1V 2J3
^b Département de phytologie, Faculté des sciences de l'agriculture et de l'alimentation, Université Laval, Québec, QC, Canada G1K 7P4

^* Corresponding author (pelletiers{at}agr.gc.ca).

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Incidence of metabolic disorders increases when dairy cows (Bos taurus) are fed forages that have a high dietary cation-anion difference (DCAD) (>250 mmol_c kg^–1 dry matter, DM) or high grass tetany (GT) index (>2.2), both associated with high forage K concentration, often caused by applications of liquid swine manure (LSM). We determined how DCAD and GT index of timothy (Phleum pratense L.), grown on two soils with different K availability, were affected by mineral or LSM fertilization. Experimental treatments were: unfertilized control, mineral fertilizer, raw LSM, and liquid fractions of four treated LSM types (decanted, filtered, anaerobically digested, and flocculated), applied in spring and after the first of two harvests each year. Forage DCAD was lowest (–108 mmol_c kg^–1DM) with the flocculated LSM due to its higher Cl content. Forage DCAD with other LSM types was similar to that with mineral fertilizer. Forage GT indices with LSM and mineral fertilizer were higher than that of the unfertilized control but still within an acceptable range for cows. The DCAD and GT index were greater on soils with high K availability. From spring growth to summer regrowth, these values decreased for soils with low K availability and increased for soils with high K availability. Compared with mineral fertilizer, LSM applied to timothy did not increase the risk of metabolic disorders for dairy cows; a Cl-enriched LSM can substantially decrease DCAD and lower the risk of milk fever.

Abbreviations: ANOVA, analysis of variance • DCAD, dietary cation–anion difference • DM, dry matter • GT, grass tetany • LSM, liquid swine manure • PCA, principal component analysis • SEM, standard error of the mean

Dietary Cation–Anion Difference and Tetany Index of Timothy Forage Fertilized with Liquid Swine Manure

^a Agric. and Agri-Food Canada, Soils and Crops Res. and Dev. Cent., 2560 Hochelaga Blvd., Québec, QC, Canada G1V 2J3
^b Département de phytologie, Faculté des sciences de l'agriculture et de l'alimentation, Université Laval, Québec, QC, Canada G1K 7P4

^* Corresponding author (pelletiers{at}agr.gc.ca).

Received for publication April 3, 2007.
Incidence of metabolic disorders increases when dairy cows (Bos taurus) are fed forages that have a high dietary cation-anion difference (DCAD) (>250 mmol_c kg^–1 dry matter, DM) or high grass tetany (GT) index (>2.2), both associated with high forage K concentration, often caused by applications of liquid swine manure (LSM). We determined how DCAD and GT index of timothy (Phleum pratense L.), grown on two soils with different K availability, were affected by mineral or LSM fertilization. Experimental treatments were: unfertilized control, mineral fertilizer, raw LSM, and liquid fractions of four treated LSM types (decanted, filtered, anaerobically digested, and flocculated), applied in spring and after the first of two harvests each year. Forage DCAD was lowest (–108 mmol_c kg^–1DM) with the flocculated LSM due to its higher Cl content. Forage DCAD with other LSM types was similar to that with mineral fertilizer. Forage GT indices with LSM and mineral fertilizer were higher than that of the unfertilized control but still within an acceptable range for cows. The DCAD and GT index were greater on soils with high K availability. From spring growth to summer regrowth, these values decreased for soils with low K availability and increased for soils with high K availability. Compared with mineral fertilizer, LSM applied to timothy did not increase the risk of metabolic disorders for dairy cows; a Cl-enriched LSM can substantially decrease DCAD and lower the risk of milk fever.

Abbreviations: ANOVA, analysis of variance • DCAD, dietary cation–anion difference • DM, dry matter • GT, grass tetany • LSM, liquid swine manure • PCA, principal component analysis • SEM, standard error of the mean

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
HYPOCALCAEMIA (milk fever) and hypomagnesaemia (grass tetany) are two metabolic disorders of concern to the dairy industry. These disorders usually occur in early-lactating cows that have not received an adequate supply of Ca and Mg from rations or through reserve mobilization during lactation (Goff and Horst, 1997; Jefferson et al., 2001). The risk of a cow developing milk fever or grass tetany can be related to the mineral composition of their rations. The dietary cation–anion difference (DCAD) of a ration, which is a parameter related to hypocalcaemia incidence, can be calculated using three common equations:

[1]

[2]

[3]

where DCAD is expressed in mmol_c kg^–1 of DM.

Prevention of milk fever begins 3 to 4 wk before calving, when nonlactating dairy cows should be fed a ration with a DCAD of around –50 mmol_c kg^–1 DM when calculated using Eq. [3] (Goff and Horst, 2003). If anionic salts, like those based on CaCl₂ or MgCl₂, are being added to the ration to lower its DCAD, the initial DCAD 3 value should be no more than 250 mmol_c kg^–1 DM (Horst et al., 1997) to avoid excessive amounts of anionic salts that reduce DM intake.

The risk of grass tetany occurring can be determined by the GT index:

[4]

The occurrence of grass tetany is greatly increased in cattle grazing forages with a GT index higher than 2.2 (Jefferson et al., 2001). Supplementing rations with Ca or Mg is not as effective at lowering the risk of milk fever or grass tetany as reducing dietary K (Horst et al., 1997; Jefferson et al., 2001). In a previous study that examined the effect of N fertilization and growth stage at harvest on timothy DCAD, Pelletier et al. (2006) found that forage K concentration was the main determinant of forage DCAD.

Forage K concentration can be reduced by growing forages on soils with low to medium K availability (Pelletier et al., 2007). On intensively-managed livestock farms, however, soils tend to be rich in K (Kayser and Isselstein, 2005) due, in part, to long-term applications of inorganic fertilizers and animal manure (Murphy et al., 2005). The LSM is often high in minerals other than K, including anions, and LSM treatments can affect the mineral composition of the initial manure (Chantigny et al., 2007; Parent et al., 2007). Liquid swine manure can supply essential nutrients to grasslands (Chantigny et al., 2007) and may provide an alternative to mineral fertilizers. To reduce adverse environmental effects of LSM applications, manure can undergo mechanical, chemical, or biological treatments that modify its mineral content and availability (Chantigny et al., 2007). Anaerobic digestion and flocculation systems to treat LSM are already commercially available. Decanting of LSM can be easily made on farm by avoiding mixing of the manure while pumping the liquid fraction out of the upper part of storage tank. Some filtration systems are currently available on the market (Møller et al., 2000). Effects of these treated LSM on timothy forage DCAD and GT index have not previously been determined.

Forage mineral concentrations and DCAD can be affected by soil K availability and values differ between spring growth and summer regrowth (Pelletier et al., 2007). However, it is not known how growth period and soil K availability affect the mineral concentration, DCAD, and GT index of forage fertilized with LSM.

The objective of this study was to determine the effects of raw and treated LSM on the mineral composition, DCAD, and GT index of timothy grown on two soils with different K availability and harvested twice during the growing season.

	MATERIALS AND METHODS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Study Sites and Experimental Setup
The study sites and experimental setup were part of a larger experiment described in detail by Chantigny et al. (2007). Timothy (cv. Champ) was sown in 2000 on a sandy loam soil (mixed, frigid, Typic Dystrochrept) at Saint-David-de-Lévis (46°48' N; 71°23' W) and on a loam soil (mixed, frigid, Typic Humaquept) at Saint-Lambert-de-Lévis, QC, Canada (46°05' N; 71°02' W). In 2001 and 2002, seven fertilizer treatments were applied to 7 by 3-m plots: four pretreated LSM (decanted, filtered, digested, and flocculated), one raw LSM, one mineral fertilizer, and one unfertilized control.

Raw LSM was obtained during the winters of 2001 and 2002 from a commercial finishing swine (Sus scrofa) operation. Part of the collected LSM was transferred into a batch anaerobic digester. After standing for 1 mo in the batch digester, anaerobically digested LSM was transferred into a 1-m³ plastic container and labeled "digested LSM". The rest of the collected LSM was stored for 6 wk in four 1-m³ plastic containers. After this period, the upper half of the raw LSM was pumped out of two plastic containers and transferred to an empty 1-m³ container. This material was labeled "decanted LSM" and represents the clarified fraction of raw LSM after the natural settling of solids. Manure from a third plastic container was strained through a bed of wood shavings and sawdust. The filtrate was collected in a plastic container and labeled "filtered LSM". A fifth LSM type was obtained from another commercial finishing swine operation. This manure was chemically treated with a CaCl₂–based coagulant to remove solids, and 1 m³ of the liquid fraction was collected in a plastic container and labeled "flocculated LSM." Selected characteristics of LSM are presented in Table 1 .

Chemical Analyses
Manure
For each field application of manure, a 2-L composite sample was collected from each LSM type for analysis. The LSM samples were homogenized with a Polytron (Model PT 3100, Kinematica AG, Littau-Lucerne, Switzerland) and pH was measured by direct reading with a standard glass electrode. Dry matter content was determined as the weight of materials remaining after drying 100 mL of homogenized LSM at 55°C for 96 h. Total C concentration was measured in the homogenized LSM with an automated combustion C analyzer (Model Formacs, Skalar Analytical, De Breda, the Netherlands).

Potassium, Ca, Mg, N, and P concentrations of the various LSM types were extracted by acid digestion modified from Isaac and Johnson (1976). Briefly, 1 to 3 mL of LSM were mixed with 1.5 mL of a H₂SO₄– SeO₃ solution and 2 mL of H₂O₂ (30% v/v) in a 100-mL digester tube and let to react on the bench until foaming ceased. The tubes were then placed on a block digester set at 100°C for 30 min to evaporate the water. The block digester was set at 400°C and the tubes were let to react for 40 min once the digester set point was reached. The tubes were cooled to room temperature and the mixture was diluted to 100 mL with deionized water. A PerkinElmer 3300 atomic absorption spectrometer (PerkinElmer, Überlingen, Germany) was used to determine K by flame emission, and Ca and Mg by atomic absorption. Total N and P in acid digests were measured with an automated continuous-flow injection analyzer (Model QuikChem 8000 FIA, Zellweger Analytics, Inc., Lachat Instruments, Milwaukee, WI) as previously described by Pelletier et al. (2007).

Finally, Cl and SO₄^2– were extracted by mixing 5 mL of the LSM sample with 20 mL of distilled water for 30 min; extracts were centrifuged at 32 570 x g for 10 min and filtered, and Cl and SO₄^2– concentrations were determined in the supernatant by chromatography as previously described by Pelletier et al. (2007).

Plant
Phosphorus, K, and Mg in ground forage samples were extracted using a method adapted from Isaac and Johnson (1976). Chloride was extracted using a method adapted from Liu (1998) and the extraction of S followed a method adapted from Mills and Jones (1996). These modified extraction procedures are described in more detail in Pelletier et al. (2007). Sodium and Ca were extracted by dry ashing (Miller, 1998).

Sulfur in plant digests was analyzed using a turbidimetric method installed on an automated continuous-flow injection analyzer as previously described in Pelletier et al. (2007). Concentrations of K, Ca, Mg, Na, and P were measured in plant extracts as described above for LSM extracts, with Na determined by atomic absorption. Chloride was measured by chromatography with a ASII HC column (Model DX 500, Dionex Corporation, Sunnyvale, CA). The DCAD 1, 2, and 3 were calculated with Eq. [1], Eq. [2], and Eq. [3], respectively, and the GT index was calculated with Eq. [4], with each element expressed in mmol_c kg^–1 DM (g kg^–1 DM x 1000 x valence/atomic weight).

Statistical Analyses
The experimental design was a split-plot with locations as main plots and fertilizer treatments as subplots. There were four replicates at each location. Production years and replicates within locations were considered to be random effects and harvests within years were considered to be repeated measurements; data were analyzed using the Mixed Procedure (Littell et al., 1996) with the Repeated option of SAS (SAS Institute, 1999). Sources of variation are presented in Table 3 . Statistical significance was postulated at P 0.05. Least square means and standard error of the means (SEM) were calculated. Principal component analysis (PCA) was used to describe relationships among variates related to DCAD and GT index and was performed on the least square means using the correlation matrix method for each harvest average (SAS Institute, 1999) to give equal weight to all variates. The contribution of each variate to a principal component axis can be seen from its loadings (Fig. 1 and 2 ).

View larger version (14K): [in this window] [in a new window]   Fig. 1. Diagrams of the first two principal components (PC) loadings (A, variates) and scores (B, fertilizer treatments) calculated for spring growth. Values are based on the average of two locations, Saint-Lambert-de-Lévis (loam soil) and Saint-David-de-Lévis (sandy loam soil), and 2 yr, 2001 and 2002.

View larger version (14K): [in this window] [in a new window]   Fig. 2. Diagrams of the first two principal components (PC) loadings (A, variates) and scores (B, fertilizer treatments) calculated for summer regrowth. Values are based on the average of two locations, Saint-Lambert-de-Lévis (loam soil) and Saint-David-de-Lévis (sandy loam soil), and 2 yr, 2001 and 2002.

	RESULTS AND DISCUSSION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

The target DCAD value of a ration, when calculated using Eq. [3], should not be lower than –50 mmol_c kg^–1 DM because depressed feed intake becomes a concern (Sanchez and Beede, 2004). On the other hand, if the forage DCAD 3 is higher than 250 mmol_c kg^–1 DM, it is difficult to add enough anionic salts to lower the ration DCAD to the recommended value without experiencing palatability problems (Horst et al., 1997). The forage DCAD 1 was, on average, 16% higher than the DCAD 3 (Table 4). It is therefore reasonable to hypothesize that when calculated with Eq. [1], the DCAD of a ration fed to nonlactating dairy cows should be 16% higher than with Eq. [3]. Therefore, the target DCAD 1 value of a ration should not be lower than –42 mmol_c kg^–1 DM (–50 mmol_c kg^–1 DM + 16% of 50 mmol_c kg^–1 DM) and should not exceed 290 mmol_c kg^–1 DM (250 mmol_c kg^–1 DM + 16% of 250 mmol_c kg^–1 DM).

Forage DCAD 1 and Mineral Composition
Fertilization
None of the fertilizer treatments allowed the production of forage with a DCAD 1 (hereafter called DCAD) around –42 mmol_c kg^–1 DM (Table 4). The flocculated LSM was the only fertilizer treatment that decreased forage DCAD to below 290 mmol_c kg^–1 DM; this occurred only in summer regrowth on the loam soil (significant interaction Locations x Harvests, Table 3). The DCAD of forage fertilized with flocculated LSM ranged from 225 to 326 mmol_c kg^–1 DM. Forage DCAD decreases with advancing maturity (Pelletier et al., 2006). Therefore, timothy fertilized with flocculated LSM and harvested later than the early heading stage, as in this study, would likely have a DCAD lower than 290 mmol_c kg^–1 DM.

Averaged across locations, harvests, and years, the DCAD with the flocculated LSM was 27% lower than with the other LSM types (Table 4). This result is attributed to the larger amount of Cl supplied with the flocculated LSM (50 kg ha^–1) compared with the other LSM types (21 kg ha^–1) (Table 2), which led to higher forage Cl concentrations (Table 4). For each location and harvest, Cl concentration in forage fertilized with flocculated LSM was significantly higher than in the unfertilized control forage, and significantly higher than in forages fertilized with the other LSM types (Table 4). These results agree with those of Pelletier et al. (2007) who found that increasing mineral Cl fertilization from 0 to 240 kg ha^–1 increased Cl concentration (+8.5 g Cl kg^–1 DM) and decreased DCAD (–190 mmol_c kg^–1 DM) in timothy forage. The PCA diagrams confirm that forage Cl concentration was inversely related to DCAD for both spring growth (Fig. 1A) and summer regrowth (Fig. 2A), and that this contrast between forage Cl concentration and DCAD was to a large extent determined by the flocculated LSM treatment and the unfertilized control. For both harvests, all fertilizer treatments were separate from the unfertilized control on the PCA diagrams, and the flocculated LSM treatment was distinct from the other fertilizer treatments (Fig. 1B and 2B).

In spring growth, forage K concentration was inversely related to DCAD (Fig. 1A), indicating that a high forage K concentration led to a low forage DCAD. This result is unexpected because the DCAD generally increases with increasing forage K concentration (Tremblay et al., 2006; Pelletier et al., 2007). In the present study, high forage K concentration was usually associated with high Cl concentration (Table 4; Fig. 1A and 2A), as both forage Cl and K concentrations increased with the flocculated LSM and decreased with the unfertilized control. The impact of the forage Cl concentration on DCAD was therefore greater than that of forage K concentration, probably because differences in forage Cl concentration among treatments for a given harvest (1.88–10.24 g kg^–1 DM) were greater than differences in forage K concentration (19.7–27.9 g kg^–1 DM).

The highest DCAD occurred in forages fertilized with the digested LSM (Table 4). Forage from this fertilizer treatment had a low concentration of Cl and a high concentration of K. The other LSM types (raw, decanted, and filtered) were grouped together on the PCA diagrams at both harvests (Fig. 1B and 2B) and had similar DCAD, DM yield, and forage K and Cl concentrations (Table 4).

In spring growth, the mineral fertilizer treatment tended to be positively related with the flocculated LSM treatment in terms of forage Cl concentration (Fig. 1A). Forages from the mineral fertilizer treatment had a Cl concentration (6.98 g kg^–1 DM) close to that of the flocculated LSM treatment (8.45 g kg^–1 DM) and significantly higher than the other LSM types (2.5–4.2 g kg^–1 DM) (Table 4). The mineral fertilizer treatment included the application of 34 kg Cl ha^–1 as KCl in spring and no KCl application after the first harvest. This result likely explains why Cl concentration of forages receiving mineral fertilization was relatively high (6.98 g kg^–1 DM) in the spring but relatively low (4.48 g kg^–1 DM) in the summer regrowth (significant interaction Fertilizer treatments x Harvests, Table 3).

The unfertilized control treatment produced forages with the lowest concentrations of Cl (2.49 and 2.32 g Cl kg^–1 DM) and K (20.7 and 21.9 g K kg^–1 DM) at both harvests (Table 4). The lowest forage K concentration did not lead to the lowest DCAD. At both harvests, the DCAD of the unfertilized forage was intermediate among all treatments. This result is likely due to the very low Cl concentration of timothy in the unfertilized control compared to forage grown on plots that received a fertilizer treatment (Table 4).

A major determinant of variation among fertilizer treatments was forage DM yield. This attribute influenced the second principal component of the PCA for spring growth (Fig. 1A) and the first component for summer regrowth (Fig. 2A). Indeed, the second component of the PCA diagram in spring growth was determined by the contrast between the unfertilized control and the digested LSM treatment (Fig. 1B). For this harvest, the digested LSM treatment was associated with the highest forage DM yield (5.15 Mg ha^–1) on both soil types, while the unfertilized control produced the lowest DM yield (3.97 Mg ha^–1, Table 4). In the summer regrowth, the contrast between the unfertilized control and the flocculated LSM determined the first component of the PCA diagram (Fig. 2B). The flocculated LSM treatment produced one of the highest DM yields (2.55 Mg ha^–1) for the summer regrowth, while the unfertilized control produced the lowest DM yield (1.30 Mg ha^–1). At both harvests, the three DCAD were in opposition with DM yield in the first component of the PCA diagrams (Fig. 1A and 2A) and DCAD tended to decrease with increasing DM yield. Pelletier et al. (2006) also observed that an increase in DM yield with advancing plant maturity from stem elongation to early flowering stage decreased forage DCAD.

Locations
Forage DCAD was, on average, lower on the loam soil (349 mmol_c kg^–1 DM) than on the sandy loam soil (418 mmol_c kg^–1 DM) mainly because forage K concentration was lower on the loam soil (22.0 vs. 24.9 g kg^–1 DM, Table 4). This difference in forage K concentration between locations can be explained in large part by the low soil K availability of the loam soil (100 kg ha^–1) compared with that of the sandy loam soil (338 kg ha^–1). This effect of soil K availability on forage K concentration and DCAD has been reported previously (Pelletier et al., 2007). Forage Na concentration was more than 10 times higher on the loam soil (0.461 g kg^–1 DM) than on the sandy loam soil (0.021 g kg^–1 DM, Table 4). This could be due to the generally lower forage K concentration at this location. As suggested by Pelletier et al. (2007), a low forage K uptake would support a higher forage Na uptake to balance ionic charges within the plant. A high Na concentration has a limited effect on forage DCAD because it remains relatively low compared to the concentrations of other nutrients. However, the concomitant decrease in forage K concentration can have a major impact on DCAD because of its much greater abundance in forage.

Harvests
Differences between harvests varied with soil type (significant interaction Locations x Harvests, Table 3). On the loam soil, DCAD in summer regrowth was, on average, 53 mmol_c kg^–1 DM lower than in spring growth. In contrast, DCAD was 84 mmol_c kg^–1 DM higher in summer regrowth than in spring growth on the sandy loam soil (Table 4). These results are mainly explained by forage K concentration, which decreased on the loam soil (–2.0 g kg^–1 DM) but increased on the sandy loam soil (+3.8 g kg^–1 DM) from spring growth to summer regrowth. Forage Cl concentration was similar in both harvests. Because forage K concentration is known to be negatively related to DM yield (Pelletier et al., 2006), the increase in forage K concentration was likely due to the substantial decrease in DM yield on the sandy loam soil (–3.61 Mg ha^–1) between spring and summer harvests. On the loam soil, DM yield only slightly decreased between spring and summer harvests (–0.90 Mg ha^–1).

Grass Tetany Index
The forage GT index was significantly affected by the fertilizer treatments (Table 3) but was always below 2.2 (Table 4), the maximum acceptable value for cows. The risk of developing grass tetany is greatly increased above this threshold. The highest GT indices (2.1) were observed in the spring growth of forages grown on the sandy loam soil (Table 4; significant interaction Locations x Harvests, Table 3). They were associated with both high forage K concentration and low Ca and Mg concentrations. It is generally accepted that because LSM is rich in K, it increases the GT index and the incidence of grass tetany (Cherney et al., 2002). However, our results show that high GT indices were not exclusive to LSM treatments. Indeed, the mineral fertilizer treatment resulted in a forage K concentration and a GT index similar to those of the LSM treatments (Table 4) even though the amounts of K supplied by LSM were much higher than with the mineral fertilizer treatment (Table 2). Moreover, PCA diagrams of both harvests (Fig. 1 and 2) show that both flocculated LSM and mineral fertilizer treatments tended to produce forages with a high GT index; these two fertilizer treatments also tended to produce the highest forage K concentrations (Table 4). On the other hand, the low forage GT index was associated with the unfertilized control treatment (Fig. 1 and 2) which produced timothy with the lowest forage K concentration (Table 4). These results suggest that K supply played a major role in determining the GT index and that K from the inorganic source was more easily taken up by timothy than K from organic sources. Jefferson et al. (2001) also reported the major role of K concentration in the GT index of Russian wildrye [Psathyrostachys juncea (Fisch.) Nevski].

The GT indices were greater on the sandy loam soil than on the loam soil (Tables 3 and 4) due to the greater soil K availability on the sandy loam soil (338 kg ha^–1 vs. 100 kg ha^–1). This result confirms that soil K availability also principally determines the GT index. The GT index was greater in spring growth than in summer regrowth on both soils even though forage K concentration was the same or slightly less in spring growth. Forage Mg and Ca concentrations were much greater in summer regrowth than in spring growth, resulting in a reduced GT index. Forages harvested in summer are therefore less likely to cause grass tetany.

	CONCLUSIONS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
The DCAD and GT index were greater in timothy grown on the soil with high K availability than on the soil with low K availability. Timothy DCAD decreased from spring growth to summer regrowth on the soil with low K availability and increased on the soil with high K availability. The GT index was decreased on both soils from spring growth to summer regrowth.

Flocculated LSM, which had the highest Cl content of all LSM types, decreased timothy DCAD compared with the other fertilizer treatments, whereas the digested LSM tended to have the highest DCAD. In summer regrowth, DCAD was as low as 225 mmol_c kg^–1 DM in timothy fertilized with the flocculated LSM on the soil with limited K availability. This forage could be served to dry dairy cows in combination with anionic salts to prevent post-calving hypocalcaemia. The GT indices of timothy fertilized with LSM and mineral fertilizer were similar, but higher than that of the unfertilized control. Timothy fertilized with LSM, however, had GT indices acceptable for cows. Compared with mineral fertilizer, raw and treated LSM applied to timothy did not increase the risk of metabolic disorders for dairy cows; a Cl-enriched LSM can substantially decrease DCAD and lower the risk of milk fever.

	ACKNOWLEDGMENTS

 
The authors would like to acknowledge the technical assistance of Mario Laterrière, Danielle Mongrain, Catherine Pinsonneault, and Johanne Tremblay. We also acknowledge Christina McRae, of EditWorks, for structural editing of this manuscript. This study was funded by the Québec Hog Producers Federation (FPPQ), the Agriculture and Agri-Food Canada Matching Investment Initiative, and by "Action concertée FQRNT (Fond québécois de la recherche sur la nature et les technologies)—NOVALAIT inc.– MAPAQ (Ministère de l'Agriculture, des Pêcheries et de l'Alimentation du Québec) en collaboration avec Agriculture et Agroalimentaire Canada."

	NOTES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
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	REFERENCES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

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