Cowan, R. T.

Fulkerson, W. J.

McLachlan, B.

Ternouth, J.

Verrall, R. G.

University of Queensland eSpace

Asian-Aus. J. Anim. Sci. 13 Supplement July 2000 A: 529-532 
 
Variations in Dietary Nutrients and Blood Metabolites in Dairy Cows During 
the Peri-Parturient Period in Sub-Tropical Australia 
 
B. P. McLachlan1,2, R. T. Cowan1, J. H. Ternouth2, W. J. Fulkerson3 and R. Verrall4 
1 Australian Tropical Dairy Institute, University of Queensland, Gatton, Qld. 4345 
2  School of Animal Studies, University of Queensland, Gatton, Qld. 4345 
3 NSW Agriculture, Wollongbar Agricultural Institute, Wollongbar, NSW 2477 
4 School of Veterinary Science, University of Queensland, Pinjarra Hills, Qld. 4069 
 
ABSTRACT: Twenty-three commercial dairies were surveyed to investigate the variation in urine pH and body condition scores 
prepartum as well as post-partum plasma metabolites in dairy cows grazing in sub-tropical Australia.  The electrolyte content and 
calculated Dietary Cation Anion Difference (DCAD) were determined on a range of feeds fed to dry cows during the prepartum 
period.  The electrolyte content of the main forages was extremely variable across farms in both potassium (1.19 to 4.53% K) and 
DCAD (-24 to +502 meq/kg DM).   The average chloride content was surprisingly high (1.48%), and possibly contributed to the low 
DCAD content. Supplementary hay and corn silage were lower in both K% and DCAD with farms averaging 1.18% and +37 meq/kg 
DM respectively. Urine pH varied between farms (5.73 to 8.43), and 83.6% of individual cows had alkaline urine (pH>7.0). There 
was substantial variation between farms in plasma ionised calcium, total calcium, phosphorus, beta-hydroxybutyrate and body 
condition score in the periparturient cow. High incidences of sub-clinical hypocalcaemia (28.4% within 24 hours post-partum) 
suggest that the diet DCAD in the prepartum diet needs to be lowered. 
 
Key Words: Subclinical hypocalcaemia, Dairy Cows, Dietary Potassium, DCAD 
 
INTRODUCTION 
Excess dietary sodium and potassium intake 
during the three weeks prepartum predisposes cows to 
clinical and subclinical hypocalcaemia (Goff and Horst 
1997a).  Both electrolytes will increase the dietary 
cation anionic difference (DCAD), resulting in a rise in 
blood alkalinity and urine pH (Goff and Horst 1997a). 
High DCAD diets lead to a reduction in calcium 
mobilisation and absorption (Goff and Horst 1997a; 
Leclerc and Block 1989).  Particularly large amounts 
of calcium (Ca) are required for the production of 
colostrum and milk during the peri-parturient period 
and if the Ca is not replaced through bone resorption 
and intestinal absorption, severe hypocalcaemia may 
occur. 
Feeding anions (sulfate and chloride salts), to 
reduce the DCAD to –10 meq/ kg DM during the 
prepartum period will cause a mild acidosis, which 
releases the hormones needed for Ca mobilisation and 
absorption (Joyce et al., 1997).  A decrease in the 
severity of the decline in plasma Ca during the peri-
parturient period has been reported when feeding these 
negative DCAD diets (Leclerc and Block, 1989; Oetzel 
et al., 1988).   Additional benefits include increased 
milk yield (Daniels et al., 1990) and improved 
reproductive performance, lower incidence of ketosis, 
and retained placenta (Daniel et al., 1990; Oetzel et al., 
1988), and mastitis (Horst and Goff 1997a). 
Hypocalcaemia is also associated with inappetence, 
hence increased mobilisation of body fat during the 
periparturient period. Little data is available on the 
electrolyte and DCAD contents in feeds consumed by 
dry cows and their associated effect on sub-clinical 
hypocalcaemia under sub-tropical pasture grazing 
systems. This paper reports on the variation in dietary 
nutrients fed to dairy cows from commercial dairies in 
sub-tropical Australia during the prepartum period. In  
 
 
addition, blood metabolite levels immediately 
following parturition were investigated in these cows. 
 
MATERIALS AND METHODS 
Three hundred and twenty four peri-parturient 
cows across 23 herds were selected from a range of 
feeding systems from September 1998 through to April 
1999. The majority of cows selected were of the 
Holstein-Friesian breed.  Twenty-one herds 
participated in a herd recording system. Thirteen herds 
fed 3–6 kg/cow/d of concentrates, with the remaining 
ten herds feeding 0–2 kg/cow/d concentrates during the 
3-week prepartum period. A total of ten herds (110 
cows) incorporated anionic salts into the grain mix and 
this was fed as a single feed, once per day. 
Samples of pasture, forage and concentrate mix 
were periodically sampled on each farm, dried and 
analysed for potassium (K), sodium (Na), chloride (Cl) 
and sulphur (S). The dietary DCAD on all feeds were 
calculated. DCAD was defined as the summation in 
milliequivalents of the cations, Na and K, minus the 
summation of the anions, Cl and S, expressed as 
meq/kg DM. 
Blood was sampled from the tail vein within 24 
hours of calving from a total of 271 cows.  Blood was 
collected in lithium heparin vials, centrifuged, 
refrigerated and measured for plasma ionised calcium 
(ICa). The plasma was then frozen at –200C and later 
analysed for plasma total Ca, magnesium (Mg), 
phosphorus (P), potassium (K), sodium (Na) and beta-
hydroxy butyrate (BHB).  Urine pH was measured and 
body condition score (BCS) was estimated on 
individual cows prior to calving. BCS was estimated 
using a scale between 1 and 5. 
Simple descriptive statistics were calculated 
across farms for feed nutrients. Analysis of variance 
Asian-Aus. J. Anim. Sci. 13 Supplement July 2000 A: 529-532 
 
was carried out on all animal parameters and means 
and standard errors for each farm were derived. 
RESULTS 
 
Dietary cations and anions measured in forage 
and supplementary feeds fed during the prepartum 
period are shown in Table 1. The main forage source 
(MFS) was pasture, hay or silage, which supplied the 
bulk of the diet. Supplementary forage (SF) consisted 
of hay and/or corn silage given in addition to the main 
forage source.  All nutrients analysed in the forage 
varied widely between farms with much higher levels 
being recorded in the MFS compared to SF.  Potassium 
averaged 2.65% in the MFS, reaching a high of 4.53% 
on one farm.  Potassium was lower in SF with an 
average of 1.18% across farms.  Sodium content was 
generally low in all forage but did reach higher levels 
(0.4 – 0.6%) in some plant species.  Chloride content 
was much higher than sulphur and contributed more to 
the anionic content in the forage. DCAD content varied 
between farms with the average for the MFS being 
higher than SF (+168 and +37 meq/kg DM 
respectively).   Individual forage samples ranged from 
–161 to +502 meq/kg DM. 
Molasses was high in chloride and sulphur 
(0.90% S; 2.90% Cl and –547meq/kg DM).  Anionic 
salts were fed on ten farms to supply between –852 and 
–3030 meq/cow/d.  Three farms provided molasses, 
which supplied –370 to –1326 meq/cow/d.   Anionic 
salts provided a source of supplementary sulphur, 
which was fed at high levels (32-55 g/cow/d) on some 
farms. 
Plasma metabolites, urine pH and body 
condition score (BCS) were summarised to present the 
minimum and maximum for both farms and for all 
cows (Table 2). Urine pH varied greatly between farms 
(P<0.001). Mean urine pH was alkaline at pH 7.71, 
with 83.6% of cows with urine pH greater than 7.0 
(Figure1). Mean BCS was 3.47, however variation did 
exist between farms (P<0.001) with three farms falling 
below 3.0.  ICa and total Ca were different between 
farms with ICa being the most variable (p<0.001). Sub-
clinical hypocalcaemia was evident with 28.4% of all 
cows experiencing plasma ICa levels below a defined 
concentration of 1.0 mmol/l (Figure 2).  The number of 
cows reaching clinical levels (≤0.7 mmol ICa/l) was 
extremely low (3.7%) with a maximum recording of 
17.6% on one farm.  Total Ca followed a similar 
pattern with 32.5% of cows reaching sub-clinical levels 
below 2.0 mmol/l. Phosphorus was variable for farms 
(p<0.001), with 32.1% of all cows falling outside the 
normal range (1.13-2.25 mmol/l). Plasma Mg, Na and 
BHB concentrations were variable between farms 
(P<0.001), unlike plasma K. 
 
Table 1. Variation in dietary nutrients (dry matter basis) fed to dairy cows during the prepartum 
 period on commercial dairies.   Means are expressed on a farm basis. 
Variable Mean Herd  Size Minimum Maximum 
Main Forage Source (Pasture/Hay/Silage) 
     K% 2.65 23 1.19 4.53 
     Na% 0.09 23 0.04 0.32 
     S% 0.23 23 0.14 0.39 
     Cl% 1.48 23 1.06 1.92 
    DCAD*meq/kg 
DM 
+168 23 -24 +502 
Supplementary Forage (Hay/Corn Silage) 
   K% 1.18 10 0.35 2.51 
   Na% 0.07 10 0.01 0.25 
   S% 0.15 10 0.09 0.27 
   Cl% 0.73 10 0.14 1.76 
   DCAD* meq/kg 
DM 
+37 10 -123 +188 
Supplementary Anions (Anionic Salts/Molasses) 
   Meq#/cow/d -894 23 -3030 0 
   Sulphur g/cow/d 14.4 23 0 54.8 
                                                                                                 
*   Dietary Cation-Anion Difference (DCAD) = (Na+ + K+) – (Cl- + S--), expressed as meq/kg DM 
#   Milliequivalents of (Na+ + K+) (Cl- + S--), 
Asian-Aus. J. Anim. Sci. 13 Supplement July 2000 A: 529-532 
 
Table 2. Variation in urine pH and BCS (1-5) during the prepartum period and plasma metabolites within 24 hours 
post-partum . S.D. is the within farm variation. 
 
Variable 
Mean 
Sample 
Size S.D. 
FARM 
Min             Max 
COW 
Min             Max 
        
Urine pH 7.71 220 0.57 5.90 8.43 4.50 8.80 
BCS 3.47 233 0.66 1.97 4.42 1.5 5.0 
Plasma metabolites mmol/l 
ICa 1.04 271 0.14 0.80 1.15 0.39 1.30 
Total Ca 2.05 268 0.29 1.67 2.29 0.86 2.62 
Mg 1.04 251 0.16 0.93 1.15 0.65 1.80 
P 1.74 246 0.51 1.41 2.39 0.32 3.39 
K  4.55 264 0.39 4.28 4.90 3.6 6.2 
Na 144.2 265 2.45 140.7 149.0 137.0 154.0 
BHB 0.53 246 0.22 0.30 1.17 0.2 1.90 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
 
0
5
10
15
20
25
30
35
40
<0.7 0.7-0.8 0.8-0.9 0.9-1.0 1.0-1.1 1.1-1.2 1.2-1.3
Plasma Ionised Calcium mmol/l
P
er
ce
nt
ag
e 
of
 c
ow
s
Figure 1. Variation in urine pH measured in cows during 
the prepartum period (N=220). Urine pH above 
recommended levels is represented by dark shading. 
Figure 2. Variation in Plasma Ionised Calcium measured 
within 24 hours post-calving (N=271). ICa below 
recommended level is represented by dark shading. 
0
5
10
15
20
25
30
35
40
4.5-5.5
5.5-6.0
6.0-6.5
6.5-7.0
7.0-7.5
7.5-8.0
8.0-8.5
8.5-9.0
UrinepH
P
er
ce
nt
ag
e 
of
 c
ow
s
Asian-Aus. J. Anim. Sci. 13 Supplement July 2000 A: 529-532 
 
DISCUSSION 
 
The survey indicated that only a small percentage 
of cows grazing sub-tropical pastures (3.7%) reached 
critically low levels of plasma ICa (≤0.7 mmol/l) even 
though the main forage source contained 2.65% K. 
This result is in contrast to international feeding 
systems where Goff and Horst (1997a) recorded a 50% 
incidence in clinical hypocalcaemia for cows fed 2.1% 
K diets, prepartum. Lerclerc and Block (1989) noted 
that 47% of cows experienced clinical hypocalcaemia 
when fed a diet high in DCAD (+331 meq/kg DM).  
Our results are different, possibly because of the higher 
levels of chloride found in sub-tropical pastures. 
Despite the low level of clinical cases, sub-clinical 
hypocalcaemia  
 
 
(ICa<1.0 mmol/l) was detected in 28.4% of cows 
recorded in the survey and is reason for concern.  It is 
still possible that the diet DCAD fed to cows during the 
prepartum period needs to be lowered further to reduce 
sub-clinical hypocalcaemia.  
Urine pH is a good indication of the acid base 
status in blood pH. Urine pH in this study averaged 
7.71 across farms with 83.6% of cows measuring pH 
levels greater than 7.0. For successful control of 
hypocalcaemia the average pH of the urine (Holstein-
Friesian) should be between 6.0 and 6.5 (Goff and 
Horst 1997b).   The urine data suggests that the DCAD 
of the diet was not low enough to cause a metabolic 
acidosis, hence calcium mobilisation may not be 
adequate prior to calving. 
Normal ranges for plasma P, Mg, K and Na are 
(P: 1.13-2.25; Mg: 0.7-2.25; K: 3.9-5.8; Na: 132-152). 
In this survey, plasma Mg, K and Na concentrations 
fell within the normal range following parturition, 
although variation existed between farms. According to 
Oetzel et al. (1988) these blood metabolites are 
unaffected by the feeding of anionic salts pre-calving.  
Phosphorus was extremely variable between farms 
with 14.2% of cows experiencing deficient levels.  
Goff and Horst (1997a) found that plasma P 
concentration decreased at calving to 1.23 mmol/l, 
however the values were still within the normal range.  
High levels of sulfates were fed as anionic salts in 
the prepartum period and this is of concern since some 
studies have reported a polioencephalomalacia-like 
syndrome (non-responsive to thiamine) when dietary 
sulfate is raised above 0.4% (equates to 40g S in a 10 
kg DM intake).  Some farms are supplementing with 
32-55g S in one feeding in addition to forage S.   It is 
also important to note that sulfate salts are not as 
effective in acidifying the blood as are chloride salts 
(Goff and Horst 1997b).  Replacing some of the 
sulfates with chloride salts would reduce any chance of 
toxicity and improve the acidifying effects of the 
anionic salts. 
Dietary nutrients are possibly not in balance 
during the prepartum period on some farms as 
indicated by the variation in both BHB and BCS across 
farms. BHB is related to fat mobilisation, and high 
levels can be an indication that the cow is in an 
extreme negative energy balance.  Sub-clinical 
hypocalcaemia can lead to reduced nutrient intake 
postpartum and consequently an increase in fat 
mobilisation. Some herds were over conditioned with 
BCS greater than 4.0.  Excessively fat cows tend to eat 
less postpartum and mobilise more body tissues than 
thin cows (Treacher et al. 1986).  
This survey has demonstrated that large 
differences exist between farms in nutrients fed during 
the prepartum period to dairy cows. The existence of 
sub-clinical hypocalcaemia and low plasma P in some 
herds suggests that the prepartum diet needs 
modification.  
 
ACKNOWLEDGEMENTS 
 
We are appreciative of the support from both 
the dairy farmers and The University of Queensland 
Veterinarians from the Dayboro and Kenilworth 
regions. The survey would not have been possible 
without the help of staff located at Kairi, Mutdapilly, 
Wollongbar, and the Pinjarra Hills Research farms. 
Financial support was provided by the University of 
Queensland, the Dairy Research and Development 
Cooperation and the Australian Tropical Dairy 
Institute. 
REFERENCES 
 
Daniels, R. C. W., Kerr D. R. and Mulei C. M. 1990. 
Occurrence and effects of sub-clinical hypocalcaemia in 
dairy cows. Proceedings of the New Zealand Society of 
Animal Production. 50, pp. 261-263. 
Goff, J. P. and Horst R. L. 1997a. Effects of the addition of 
potassium or sodium, but not  calcium to prepartum 
rations on milk fever in dairy cows. Journal of Dairy 
Science. 80, pp. 176-186. 
Goff, J. P. and Horst R. L. 1997b. Milk fever and dietary 
potassium. Proceedings of the Cornell Nutrition 
Conference. pp. 181-189. 
Joyce, P. W., Sanchez W. K. and Goff J. P. 1997.  Effect of 
anionic salts in prepartum diets based on alfalfa. Journal 
of Dairy Science. 80, pp. 2866-2875. 
Leclerc, H. and Block E. 1989. Effects of reducing dietary 
cation-anion balance for prepartum dairy cows with 
specific reference to hypocalcemic parturient paresis. 
Canadian Journal of  Animal Science. 69, pp. 411-423. 
Oetzel, G. R., Olson J. D., Curti, C. R. and Fettman M. J. 
1988.  Ammonium chloride and ammonium sulfate for 
prevention of parturient paresis in dairy cows.  Journal of 
Dairy Science. 71,  pp. 3302-3309. 
Treacher, R. J., Reid I. M. and Roberts C. J. 1986. Effect of 
body condition on the health and performance of dairy 
cows. British Society of Animal Production. 43, pp. 1-6. 
 
Email: Bpm@warigal.uqg.uq.edu.au 
 
 


Variations in Dietary Nutrients and Blood Metabolites in Dairy Cows During the Peri-Parturient Period in Sub-Tropical Australia

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Variations in Dietary Nutrients and Blood Metabolites in Dairy Cows During the Peri-Parturient Period in Sub-Tropical Australia

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