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Timothy Hay with a Low Dietary Cation-Anion Difference Improves Calcium Homeostasis in Periparturient Holstein Cows

G. B. Penner^*, G. F. Tremblay, T. Dow and M. Oba^*,1

^* Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta, T6G 2P5, Canada
Agriculture and Agri-Food Canada, Soils and Crops Research and Development Centre, Québec, Québec, G1V 2J3, Canada
Alberta Agriculture and Food, Lethbridge, Alberta, T1J 4V6, Canada

¹ Corresponding author: masahito.oba{at}afhe.ualberta.ca

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
The current study was undertaken to evaluate the effects of feeding timothy (Phleum pratense L.) hay differing in dietary cation-anion difference (DCAD) on the capability of cows to maintain calcium homeostasis around parturition. We hypothesized that feeding low-DCAD timothy hay during the prepartum period would induce a mild metabolic acidosis prepartum and improve calcium homeostasis postpartum with no effect on dry matter intake. Forty-one dry pregnant Holstein cows entering their second lactation or greater were used in a randomized complete block design. Timothy hay was obtained from an established timothy stand under a pivot irrigation system. Low-DCAD timothy hay was produced by fertilizing the area between the second and third pivot towers at a rate of 224 kg of CaCl₂/ha, and control timothy hay (high DCAD) was grown on the area between the fourth and fifth pivot towers of the same field. The chloride concentration was 1.07 and 0.15% on a dry matter (DM) basis, and the DCAD was 1.2 and 21.6 mEq/100 g of DM for the low- and high-DCAD timothy hay, respectively. Experimental diets, containing timothy hay at 63% of dietary DM, were fed ad libitum starting 30 d before the expected calving date. The DCAD values were 1.6 vs. 14.5 mEq/100 g of DM for the low- and high-DCAD timothy-based diets, respectively. At the beginning of the study, urine pH and blood bicarbonate concentration averaged 8.22 ± 0.06 and 28.5 ± 0.3 mM, respectively. The low-DCAD timothy diet decreased urine pH compared with the high-DCAD timothy diet on d 21 (7.75 vs. 8.31), d 14 (7.69 vs. 8.22), and d 7 (7.50 vs. 8.19) before calving, and it also decreased the prepartum blood bicarbonate concentration by 2 mM. In addition, cows fed the low-DCAD timothy diet had greater blood ionized calcium concentration prepartum (1.22 vs. 1.19 mM), greater blood ionized calcium concentration at 0 and 8 h after calving, and similar prepartum dry matter intake. These results indicate that timothy hay differing in DCAD affects the acid-base balance of periparturient dairy cows, and that low-DCAD timothy hay improves calcium homeostasis postpartum with no negative effect on dry matter intake.

Key Words: dairy cow • dietary cation-anion difference • calcium homeostasis • hypocalcemia

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
Parturient paresis is a metabolic disorder caused by the inability of a cow to meet the calcium demands of colostrum production via dietary calcium absorption, bone calcium mobilization, and renal calcium resorption. The resulting hypocalcemic condition affects the health and profitability of transition dairy cows. In a controlled research setting, prevalence rates for clinical hypocalcemia ranged between 13 and 20%, with an additional 20 and 53% experiencing subclinical hypocalcemia, for cows fed prepartum diets containing a DCAD of –7 and +30 mEq/100 g of DM, respectively (Joyce et al., 1997). Block (1984) conducted a 2-yr crossover study in which cows were fed a prepartum diet containing DCAD of either 3.3 mEq/100 g or –1.3 mEq/100 g of DM and reported no incidence of milk fever for cows fed the low-DCAD diet, whereas feeding the positive DCAD diet resulted in an incidence of milk fever of nearly 50%. Further, cows fed the prepartum diet containing a DCAD of –1.3 mEq/100 g produced nearly 500 kg more milk per lactation than cows receiving the diet containing a DCAD of 3.3 mEq/100 g. As such, reducing the prevalence of hypocalcemia has the potential to improve both animal health and productivity.

Lowering the DCAD of prepartum diets has been shown to improve calcium homeostasis during the periparturient period. Diets containing anionic salts or an acidifying agent cause a compensated metabolic acidosis improving parathyroid hormone (PTH) sensitivity, increasing 1,25-dihydroxyvitamin D [1,25-(OH)₂ D] concentration per unit of PTH (Goff et al., 1991; Block, 1994), and improving renal resorption, osteoclastic mobilization, and intestinal absorption of calcium (Horst et al., 1997). Selection of forage species and fertilization with chloride may be a possible alternative to decrease the DCAD. Recently, Tremblay et al. (2006) evaluated the DCAD of 5 cool-season grasses grown on various soils and reported that timothy hay had the lowest DCAD due to low potassium concentration. Subsequent studies have consistently demonstrated that the DCAD of timothy hay can be further reduced when it is fertilized with various sources of chloride (Oba et al., 2007; Pelletier et al., 2007, 2008). However, data are limiting on whether timothy hay with a low DCAD can improve the cow’s ability to maintain calcium homeostasis around parturition.

Feeding anionic salts or acidifying agents often decreases DMI predisposing animals to other disorders such as displaced abomasum and ketosis. Charbonneau et al. (2006a) conducted a meta-analysis encompassing 22 published studies and reported a positive linear relationship between the DCAD calculated as (Na⁺ + K⁺) –(Cl^– + 0.6 S^2–) and DMI (P < 0.01; R² = 0.66). However, a recent study (Charbonneau et al., 2008) comparing a control diet (DCAD = 29.6 mEq/100 g of DM), a diet containing timothy hay with a low DCAD (–2.4 mEq/ 100 g of DM), and the control diet supplemented with HCl (–1.9 mEq/100 g of DM) suggests that the methods to decrease the DCAD (hay vs. HCl supplement) may have an impact on DMI. In that study, feeding cows with the low-DCAD timothy hay diet did not decrease DMI relative to the control; however, feeding cows with the HCl-supplemented diet tended to decrease DMI relative to the low-DCAD timothy hay diet. Thus, further research is warranted to investigate the effect of low-DCAD forages on DMI.

The objective of the current study was to evaluate the effects of feeding timothy (Phleum pratense L.) hay differing in DCAD on DMI and the capability of cows to maintain calcium homeostasis around parturition.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
This experiment was conducted between October 2006 and February 2007 at the University of Alberta Dairy Research and Technology Centre (Edmonton, Alberta, Canada). All procedures were approved by the Faculty Animal Policy and Welfare Committee at the University of Alberta and were performed according to the guidelines of the Canadian Council of Animal Care (Ottawa, Ontario, Canada).

Experimental Design and Dietary Treatments
Timothy hay was obtained from an established timothy stand under a pivot irrigation system near Leth-bridge (Alberta, Canada). Soil K content of the field was 486 kg/ha. The field was fertilized with 112 kg of N/ha as urea, and 39 kg of P/ha as monoammonium phosphate on April 15, 2006. In addition, anhydrous calcium chloride was applied using a fertilizer broadcaster to the area between the second and third pivot towers at a rate of 224 kg/ha (143 kg of Cl/ha) on April 15 to produce the low-DCAD timothy hay. Control timothy hay (high-DCAD) was grown on the area between the fourth and fifth pivot towers of the same field. The hay was harvested on July 8 as small rectangular bales weighing approximately 27 kg each, transported to the University of Alberta (Edmonton, Alberta, Canada), and stored in a covered shelter. The nutrient and mineral composition of the low-DCAD and high-DCAD timothy hay fed during the animal study (n = 4; samples were collected twice weekly and composited monthly) are listed in Table 1.

Body weight and BCS were determined at the start of the study for each cow. An initial spot sample of urine was collected on the enrollment day and thereafter urine samples were collected twice weekly at 1100 h via manual stimulation or voluntary urination. Frequent sample collection was designed to obtain samples collected on d –21, –14, and –7 relative to parturition. Urinary pH was determined immediately using a portable pH meter (Accumet AP61, Fisher Scientific, Pitts-burgh, PA). The pH meter was calibrated daily using standard buffers 4 and 7.

Blood was collected on the enrollment day and thereafter twice weekly (Tuesday and Friday) corresponding to urine collection. Cows nearing parturition were observed hourly to collect blood samples immediately following parturition (0 h), and at 4, 8, 12, 16, 20, 24, 48, and 72 h following parturition. Blood from coccygeal vessels was drawn into 2 vacutainer tubes; one containing Li heparin (Fisher Scientific Co., Nepean, On-tario, Canada) and the other containing Na heparin (Fisher Scientific Co.). Whole blood in tubes containing Li heparin was immediately analyzed for pH and concentrations of Na, K, ionized Ca (iCa), and bicarbonate using an auto analyzer (GEM Premier 3000, Instrumentation Laboratory Ltd., Richmond Hill, Ontario, Canada). The blood in Na heparin tubes was immediately placed on ice and centrifuged within 30 min at 3,000 x g and 4°C for 20 min. Following centrifugation, the plasma was harvested and stored at –20°C. Plasma samples collected on the enrollment day, and at h 0, 8, 16, 24, and 72 following parturition were analyzed for PTH and 1,25-(OH)₂ D concentrations by the Diagnostic Centre for Population Animal Health (Lansing, MI). The 1,25-(OH)₂ D concentration in plasma samples were analyzed using a DiaSorin 1,25-(OH)₂ D RIA Kit (DiaSorin, Stillwater, MN). Briefly, 1,25-(OH)₂ D was extracted and purified from plasma using C18OH and "Extra Clean" cartridges (DiaSorin). Following extraction, the sample was assayed using a polyclonal antibody specific for 1,25-(OH)₂ D₂ and 1,25-(OH)₂ D₃, which avoids cross contamination with other vitamin D metabolites. The sample, antibody, and tracer were incubated for 2 h at 20°C followed by incubation with a second antibody to form a precipitating complex. After centrifugation and decantation, the bound fraction remaining in the pellet was counted in a gamma counter. Values were calculated directly from a standard curve of known concentrations. Intact PTH was measured using a 2-site immunoradiometric assay (Diagnostic Systems Laboratory, Webster, TX) that has been previously validated (Diagnostic Center for Population and Animal Health, Lansing, MI).

Statistical Analysis
Statistical analysis was conducted independently for prepartum and postpartum data. Preliminary statistical analysis determined that parity differences were not detectable between cows entering their third or greater lactation. Thus, for statistical analysis, cows were classed under 2 categories; 1) cows entering their second lactation, and 2) cows entering their third or greater lactation. The parity classification was used to group cows with similar susceptibility to hypocalcemia. Furthermore, data were analyzed to determine if initial values for DMI, urine pH, blood pH, blood iCa, plasma 1,25-(OH)₂ D, and plasma PTH were different between treatments. Statistical analysis revealed that initial treatment means for the previously mentioned variables were not different and therefore covariates were not used in subsequent analyses.

All data were analyzed using the PROC MIXED procedure of SAS (version 9.1.3; SAS Institute Inc., Cary, NC) accounting for repeated measures with the random effect of cow nested in the parity class and the fixed effects of treatment and parity class. The prepartum repeated measures were week and day relative to parturition for DMI and blood parameters, respectively, and the postpartum repeated measure was hour relative to parturition. Various covariance error structures were tested for each dependent variable and the one that yielded the lowest Akaike’s and Bayesian information criterion values was used. All data were analyzed for the main effects of treatment, parity class, time, and their interactions.

Postpartum data were also analyzed using the PROC MIXED procedure of SAS (version 9.1.3, SAS Institute Inc.) with hour relative to parturition as a regression variable to further characterize the response to timothy hay differing in DCAD. Linear effects for treatment, hour, parity, and their interactions and quadratic effects for hour, and the quadratic interactions between hour x treatment, hour x parity class, and hour x treatment x parity class were tested.

The change in blood iCa concentration following parturition was evaluated by comparing the nadir concentration to the prepartum baseline concentration. For this calculation, the nadir value observed postpartum was used and the baseline value was calculated by averaging the blood iCa concentrations for d –21, –14, and –7. Days –21, –14, and –7 relative to parturition were used for the baseline calculation because they did not differ over time. These data were analyzed using the PROC MIXED procedure of SAS (version 9.1.3; SAS Institute Inc.) with the fixed effects of treatment and parity class and the random effect of cow nested in parity class. Data were analyzed for the main effects of treatment, parity class, and the interaction between treatment and parity class.

For all statistical analyses mentioned above, differences were considered significant when P < 0.05 and trends are discussed when P < 0.10.

	RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
Low- and High-DCAD Timothy Hay
Timothy hay fertilized with CaCl₂ had a greater K concentration (nearly 16%) than timothy hay not fertilized with CaCl₂ (Table 1), but this slightly greater K concentration was offset by a much greater Cl concentration (86% increase). Thus, the marginal increase in K concentration and the large increase in Cl concentration for timothy hay fertilized with CaCl₂ resulted in a lower DCAD than timothy hay not fertilized with CaCl₂ (1.2 vs. 21.6 mEq/100 g of DM).

Prepartum
The actual days for prepartum blood and urine collection were (mean ± SD) –29.1 ± 0.7, –20.5 ± 0.2, –13.7 ± 0.2, and –6.6 ± 0.2 d relative to parturition. These collection days were close to the targeted days of –30, –21, –14, and –7 d relative to parturition, respectively.

The prepartum BW and BCS of cows fed the low-DCAD and high-DCAD treatments were not different and averaged 724 kg and 3.27 BCS respectively (Table 3). Prepartum DMI was not affected by dietary treatment (P = 0.37; Table 3) but it was affected by week relative to parturition (P < 0.01; Figure 1). Average DMI across treatments was 11.3, 11.2, and 9.2 kg/d for wk –3, –2, and –1 relative to parturition, respectively; for both treatment groups of cows, DMI decreased by an average of 18% during the week before calving. Mean urine pH over the entire prepartum period was nearly 0.5 pH units lower for cows fed low-DCAD timothy than cows fed high-DCAD timothy hay (Table 3). Furthermore, there was a treatment x day interaction for urine pH. Feeding low-DCAD timothy hay decreased urinary pH from 8.16 ± 0.08 on d –30 to 7.50 ± 0.08 on d –7 relative to parturition; however, feeding high-DCAD timothy hay had no effect on urinary pH with values of 8.27 ± 0.08 and 8.19 ± 0.09 on d –30 and –7, respectively (Figure 2). Blood pH was not affected by treatment, day relative to parturition, or parity class, although an interaction between parity class and day relative to parturition was detected (P < 0.05). The interaction was a result of cows entering their third or greater lactation having a decrease in blood pH from trial initiation to d –7, whereas cows entering their second lactation had no change in their blood pH values during the same time (data not shown). Blood bicarbonate concentration was 7% lower for cows fed low-DCAD timothy hay than for cows fed high-DCAD timothy hay (Table 3). Furthermore, there was a tendency (P = 0.07) for a treatment x day interaction for blood bicarbonate concentration; the low-DCAD treatment tended to reduce blood bicarbonate concentrations as the calving date approached, whereas the high-DCAD treatment did not affect blood bicarbonate concentrations (data not shown). The prepartum concentration of blood iCa was greater for cows fed low-DCAD timothy diet when compared with cows fed high-DCAD timothy diet (1.22 vs. 1.19 mM, respectively; P = 0.01). Blood iCa concentration increased slightly from the initial concentration of 1.18 mM on d –30 to 1.21 mM for d –21 and reached a plateau thereafter (week; P < 0.01, data not shown). An interaction between parity class and day relative to parturition was detected for blood iCa concentration where cows entering their third or greater lactation initially had lower blood iCa concentration than cows entering their second lactation (1.16 vs. 1.20 mM, respectively) but had similar blood iCa concentrations on d –21, –14, and –7 relative to parturition (data not shown).

View larger version (13K): [in this window] [in a new window]   Figure 1. The DMI of cows fed the low- or high-DCAD timothy diet for 30 d before the expected calving date. Weeks with uncommon letters are significantly different (P < 0.05).

View larger version (16K): [in this window] [in a new window]   Figure 2. The treatment x day interaction for prepartum urine pH in cows fed the low- or the high-DCAD timothy diet for 30 d before their expected calving date. All data points with uncommon letters are significantly different (P < 0.05).

View larger version (17K): [in this window] [in a new window]   Figure 3. The quadratic hour x treatment interaction for postpartum blood ionized calcium (iCa) concentration in cows fed the low- or high-DCAD timothy diet for 30 d before the expected calving date. All data points with uncommon letters are significantly different (P < 0.05).

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

In the current study, feeding the low-DCAD timothy diet reduced the metabolic alkalosis prepartum as indicated by decreased urinary pH and blood bicarbonate concentration when compared with feeding the high-DCAD timothy diet. Previous studies also reported that low or negative DCAD diets induce metabolic acidosis as indicated by reduced urine pH and blood bicarbonate concentration (Goff and Horst, 1998; Moore et al., 2000; Roche et al., 2003). However, the degree of metabolic acidosis in the previously mentioned studies was greater than in the current study. Metabolic acidosis increases the tissue responsiveness to PTH, increasing the synthesis of 1,25-(OH)₂ D, and thus improving the ability to increase plasma Ca through mobilization, resorption, and absorption (Horst et al., 1997). Correspondingly, we observed a greater concentration of iCa prepartum for cows fed the low-DCAD timothy diet when compared with cows fed the high-DCAD timothy diet. Greater blood iCa concentration has been consistently reported when cows are fed diets containing a low or negative DCAD (Tucker et al., 1992; Moore et al., 2000). In the current study, the blood iCa concentration following parturition also tended to be greater for cows fed the low-DCAD timothy hay than cows fed the high-DCAD timothy hay as indicated by a quadratic hour x treatment interaction. These data indicate improved iCa homeostasis immediately after parturition for cows fed low-DCAD over cows fed high-DCAD timothy diets.

Recently, there has been interest in the potential of using diets with a low but positive DCAD to improve Ca homeostasis around parturition. Kurosaki et al. (2007) reported that multiparous cows fed a diet containing 1.2 mEq/100 g of DM had lower urinary pH prepartum, greater serum Ca during the first 3 d following parturition, and required less treatment for hypocalcemia compared with multiparous cows fed diets containing 14.6 or 15.3 mEq/100 g of DM. As such, multiparous cows fed the 1.2 mEq/100 g of DM diet had 50% less hypocalcemia (serum Ca <5 mg/dL) than multiparous cows fed high-DCAD diets. Similarly, in the current study, we observed decreased urinary pH and blood bicarbonate concentration prepartum, improved iCa concentration postpartum, and a 48% reduction in the prevalence of subclinical hypocalcemia for cows fed the low-DCAD (1.6 mEq/100 g of DM) compared with cows fed the high-DCAD (14.5 mEq/100 g of DM) diet.

Although we saw a drastic reduction in the prevalence of subclinical hypocalcemia, 35% of the cows fed the low-DCAD timothy diet were still diagnosed with this disorder. Reported prevalence rates for hypocalcemia in cows fed low but positive DCAD diets have ranged from 11% for cows fed a diet with a DCAD of 1.2 (Kurosaki et al., 2007; serum Ca <5 mg/dL) to 50% for cows fed a diet with a DCAD value of 0 mEq/100 g of DM (Moore et al., 2000; plasma Ca <4 mg/dL). Furthermore, Moore et al. (2000) reported improvements in Ca homeostasis as the DCAD value of the diet was reduced from +15 to 0 and from 0 to –15 mEq/100 g of DM. Although diets containing a low but positive DCAD may reduce the prevalence of hypocalcemia, the prevalence could be reduced to a greater extent by reducing the DCAD further. Further research is warranted to determine the optimal DCAD that accounts for both reducing the prevalence of hypocalcemia and minimizing depression in DMI.

Much attention has been directed toward the effects of PTH and 1,25-(OH)₂ D on calcium homeostasis in dairy cows. In the current study, plasma concentrations of PTH and 1,25-(OH)₂ D did not differ between the 2 dietary treatments. The plasma concentration of PTH remained high for 24 h after calving but decreased by h 72. Further, it took approximately 16 h before plasma 1,25-(OH)₂ D reached its peak concentration. The slow response for an increase in plasma 1,25-(OH)₂ D concentration may be due in part to PTH resistance (Martig and Mayer, 1973). Supporting the notion of PTH resistance, upon simple correlation analysis, there was no relationship between plasma PTH and 1,25-(OH)₂ D concentrations, nor between plasma PTH and iCa concentrations. Consistent with previous findings (Horst et al., 1997), we observed that plasma 1,25-(OH)₂ D increased when iCa concentration was low but decreased from h 24 to 72 corresponding to an increase in iCa concentration. This corresponded to a significant but weak negative correlation between plasma 1,25-(OH)₂ D and blood iCa concentration (r2 = 0.18, P < 0.01). These results suggests that cows in the current study were responsive to circulating 1,25-(OH)₂ D in plasma but may have experienced tissue resistance to PTH.

In the current study, feeding a low-DCAD timothy diet increased the baseline blood iCa concentration and the nadir iCa concentration relative to the high-DCAD timothy diet. However, there was no difference between treatments for the extent of reduction in blood iCa concentration following parturition. We speculate that differences in tissue sensitivity to PTH between the prepartum and postpartum periods may explain why cows fed the low-DCAD timothy diet in the current study had greater prepartum blood iCa concentration but a similar decrease in postpartum blood iCa concentration. Martig and Mayer (1973) injected PTH intramuscularly before and after parturition and observed that PTH resistance was greater before parturition than following parturition. In our study, feeding a low-DCAD timothy diet decreased the prepartum blood bicarbonate concentration, an indicator of mild metabolic acidosis, but following parturition there was no difference in blood bicarbonate concentration between dietary treatments. Thus, carry-over effects of feeding the low-DCAD timothy diet on metabolic acidosis may have been minimal. The dietary treatment effect on prepartum blood iCa concentration observed in our study was in agreement with those reported by Kurosaki et al. (2007). Furthermore, in the study of Moore et al. (2000), blood samples were collected within 4 h of calving and they reported that the postpartum iCa concentration in blood decreased to a similar extent (83 and 82% of the prepartum iCa) for cows fed diets with DCAD values of +15 and 0 mEq/100 g of DM. Based on results of the current and previous studies, the postpartum improvement in blood iCa concentration for diets having a low but positive DCAD may be a response of greater prepartum blood iCa concentration rather than a greater ability to prevent a reduction in postpartum iCa blood concentration, whereas diets with a negative DCAD value seem to reduce the extent of blood iCa postpartum depression in addition to increased prepartum iCa blood concentration (Moore et al., 2000; Kurosaki et al., 2007).

DMI
It is well documented that feeding close-up diets of a negative DCAD value improves Ca homeostasis around parturition (Oetzel, 1991; Horst et al., 1997; Lean et al., 2006), but a negative DCAD ration often decreases DMI especially if a great amount of anionic salts are used (Tucker et al., 1992; Joyce et al., 1997; Vagnoni and Oetzel, 1998). Charbonneau et al. (2006a) recently conducted a meta-analysis encompassing 22 studies and found a positive linear relationship between the DCAD and DMI. In the current study, we did not observe a reduction in DMI with the low-DCAD relative to the high-DCAD timothy diet. Although the low-DCAD timothy hay provided a lower DCAD than the high-DCAD timothy hay, the diet based on the low-DCAD timothy hay still provided a positive DCAD (cations > anions). As a result, the metabolic acidosis in the current study for cows fed the low-DCAD timothy diet was not as severe as in previous studies using anionic supplements (Tucker et al., 1992; Goff and Horst, 1998; Vagnoni and Oetzel, 1998). It is therefore possible that the low-DCAD timothy diet did not induce metabolic acidosis severe enough to reduce DMI.

Alternatively, it is possible that the form of the DCAD supplement may influence the depression in DMI. Charbonneau et al. (2008) compared 3 diets consisting of 1) a low-DCAD diet (–2.4 mEq/100 g of DM) using only low-DCAD timothy hay, 2) a low-DCAD diet (–1.9 mEq/100 g of DM) made with a combination of low- and high-DCAD timothy hay and additional HCl, and 3) a high-DCAD diet (29.6 mEq/100 g of DM) made with the same combination of low- and high-DCAD timothy hay. These diets were fed to nonpregnant and nonlactating cows, and cows fed the low-DCAD diet had similar DMI to those fed the high-DCAD timothy diet. Cows fed the diet supplemented with HCl, however, tended (P = 0.08) to have lower DMI (9.8 kg/d) than cows fed the low-DCAD timothy hay diet (11.5 kg/d) even though the DCAD of the low-DCAD timothy diet was slightly lower than that of the HCl-supplemented diet. However, not all studies using HCl have resulted in reduced DMI (Goff and Horst, 1998). The results of the current study and those of Charbonneau et al. (2008) suggest that the form of DCAD supplement, rather than the DCAD value itself, may have an impact on DMI. However, in another study, feeding timothy silage with a low DCAD value (–2.1 mEq/100 g of DM) tended to reduce DMI when compared with the control treatment (23 mEq/ 100 g of DM; Charbonneau et al., 2006b). More data are needed to elucidate the relationship between decreased DMI and the severity of the metabolic acidosis while using different anionic supplements.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
Feeding a diet based on a low-DCAD timothy hay during the prepartum period had no effect on DMI and induced a mild but compensated metabolic acidosis, improving the ability of cows to maintain calcium homeostasis around parturition compared with feeding a diet based on a high-DCAD timothy hay. These results indicate that feeding timothy hay with a low DCAD may be one strategy to reduce hypocalcemia in periparturient dairy cows.

	ACKNOWLEDGEMENTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
The authors thank the staff of the Dairy Research and Technology Centre farm staff for general animal husbandry and the staff of the University of Alberta Metabolic Unit for assistance with timothy hay delivery. Gratitude is extended to M. A. Bal, L. McKeown, C. Silveira, and S. Vishantha-Patabendi for technical assistance. Financial support from Zen-Raku-Ren (Japanese Federation of Dairy Cooperative Associations), Advancing Canadian Agriculture and Agri-Food program of Agriculture and Food Council, and Alberta Milk are gratefully acknowledged.

Received for publication November 20, 2007. Accepted for publication January 20, 2008.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 


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