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Time to power up against acidosis By Hajer Khelil-Arfa PhD, R&D Timab Magnesium

Introduction The increase in the genetic potential of dairy cows for milk production in recent years has to led to the use of high starch diets to maximize milk production (Plaizier et al, 2008). Conversely, these diets can lead to subacute ruminal acidosis (SARA). A low ruminal pH leads to a decrease in digestive effectiveness which in turn leads to a decrease in dry matter intake, milk yield, milk fat content, fibre digestibility and many other disorders (Plaizier et al, 2008). To minimize the occurrence of ruminal acidosis, dairy nutritionists

usually choose to supplement dietary buffers, especially where feeding conditions include large amounts of readily fermentable carbohydrates. Dietary buffers may prevent depressions in rumen pH. Buffered diets allow greater dry matter intake, fibre and dry matter digestibility, and milk fat percentage for cows at risk of SARA. Different buffers and alkalizing agents can be used to buffer dairy cow diets (Table 1).


Sodium bentonite Sodium bicarbonate Sodium sesquicarbonate Calcium carbonate Postassium bicarbonate Magnesium carbonate

Sodium carbonate Magnesium oxide Potassium carbonate

TYPE Buffer





Alkalizing agents


Dietary Buffers to prevent SARA Commonly used as an exogenous buffer, sodium bicarbonate (SB) is involved in the stabilization of ruminal pH in cows that can potentially suffer from ruminal acidosis (Meschy et al, 2004). Results considering the effects of SB on rumen pH are varying in different studies. The typical response expected is an increase in pH, but there are however reports of no effects (Hu & Murphy, 2005) or even a decrease in pH. Hu and Murphy (2005), showed that effects of SB addition to the

total mixed ration (TMR) of lactating cows depends on forage type in the diet, with beneficial effects of SB being limited to corn silage based diets. Also, as a soluble buffer, sodium bicarbonate is short lived in the rumen (Van Soest, 1994) and cannot effectively buffer ongoing production of acids in the rumen. Apart from its buffering capability, dietary SB addition affects the dietary cation anion difference (DCAD) due to the Na ion. Recent research points to substantial effects of the DCAD value, defined as milliequivalents (mEq) of (Na + K- Cl)/100 g of dietary dry matter DM, on performance of lactating dairy cows. Hu and Murphy (2004) reported that milk yield and DM intake increased quadratically

with DCAD, peaking at ∼34–40 mEq/100 g DM, respectively. Blood pH and HCO3 concentrations also increased with dietary DCAD level, which points to an improved acid–base balance of the cows.

PAGE 24 MARCH/APRIL 2017 FEED COMPOUNDER -NaHCO3 )3 -2H2 0 (OH6 )-nH2 0 In the study of Rauch et al, (2012) SB supplemented cows had

lower (P<0.01) milk yield (45.2 versus 46.2 kg/d) compared to the control, and the reduced milk yield may have been related to increase intake of Na. Urine volume is partly a function of Na intake (Bannink et al, 1999), and therefore SB cows excreted more urine than control cows. If cows were not consuming enough water to compensate for this additional loss, or if there was a physiological limitation in absorption and metabolism of additional water required, there may have been a physiological shortage of fluid in the body resulting in the reduction in milk yield (Rauch et al, 2012). Furthermore, high Na excreted in animal faeces and urine can

negatively affect ground and surface water for human and livestock drinking purposes and irrigation (Berg et al., 2010), while contributing to soil degradation which results in reduced biomass yield (Mengel and Kirkby, 2001). The use of SB has shown to increase the excretion of Na, and as SB is widely used it might be viable to consider a different buffer for inclusion in lactating dairy cow rations. West et al, (1987) reported that cows offered diets containing

1.85% K2CO3 had higher rumen pH than controls postfeeding (Figure 1). Authors concluded that Potassium carbonate is a buffer comparable to 1.5 % NaHCO3; it serves also as a K supplement.

Figure 1: Postprandial response of rumen pH to buffered diets 6.8




5.6 0 2 4 6 Control 1.25% K2CO3

Hours Post Feeding 1.5% NaHCO3

8 10

1.85% K2CO3

Also, magnesium oxide and calcium carbonate or “limestone” are used as sources of minerals as well as alkalizing and buffering agents, respectively. Xin et al (1989) tested control diet against three diets containing 0.4% MgO (DM basis) with increasing reactivity rates (A, B, C). Diets contained corn silage and concentrate at a 40:60 ratio (DM). They found that all treatments had rumen pH above the control throughout the postfeeding sampling period. Rumen pH was different (P<.05) between MgO-A and MgO-C, but only MgO-C was higher than the control (Figure 2).


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