Sodium discharge from dairies in California has been identified as an important contributor to soil and water pollution. The Waste Discharge Requirements General Order For Existing Milk Cow Dairies (2007) aims to minimize the amount of fixed solids, including Na, that are discharged from dairies, aiming to maximise the useable lifespan of water resources. As sodium bicarbonate (SB) contains 270 g/kg Na, SB supplementation can substantially increase Na discharge from dairies. The aim of this study was to determine the effects of SB and a potentially alternative buffer that does not contribute to Na discharge and related negative impacts on soil and water quality, (i.e., calcium magnesium carbonate (CMC)), on the performance of high producing California dairy cows. This could help establish if CMC could substitute for SB while maintaining potential benefits of SB. It is well known that SB is a rumen buffer, but research indicates that its benefits are limited mainly to corn silage-based diets. Californian dairies use a wide range of forages, and tend not to base their diets solely or mainly on corn silage. Therefore, typical Californian lactation diets do not always conform to those reported in research publications involving SB. In addition, research parameters such as milk yield, DM intake and dietary ADF often differ substantially between reported studies and conditions present on commercial California dairies, and results are therefore not always practically applicable. Apart from its rumen buffering capacity, SB also has an influence on dietary cation anion difference (DCAD), and can therefore elicit a response via a change in blood acid base balance of cows. The experiment was a Latin square design with 3 treatments (i.e., control (C), SB and CMC), 3 pens of ~310 early lactation cows each, and 3 periods of 28 d. Sodium bicarbonate supplemented cows had elevated milk fat proportion, but a reduced milk yield, resulting in similar milk fat yield between SB supplemented and C cows. Based on a tendency for elevated faecal and in vitro rumen fluid pH, SB had a buffering effect on the gastrointestinal tract GIT, most likely in the rumen. However, it is likely that the difference in DCAD between the C and SB diets played a role in affecting milk yield and milk fat proportion, and a high intake of Na may have been the cause for a reduction in milk yield resulting in passive increase in milk fat proportion. There were no differences between C and CMC treatments, except for an elevated faecal pH of CMC cows. As CMC is not generally soluble at normal rumen pH, buffering likely occurred in the abomasum and small and large intestines. However, a lack of difference in productivity indicates that the buffering effect on the hindgut was not physiologically required. While there were no productive benefits of SB use, it likely substantially increased Na discharge, resulting in an increase in soil and water sodicity and the associated deterioration in soil and water quality. While CMC did not improve productivity or efficiency of cows, it also did not increase Na discharge from the dairy and therefore did not contribute to soil or water sodicity. It can be concluded that SB or CMC supplementation is not advisable for diets and conditions comparable to those present in this study, i.e., high producing dairy cows fed a diet with ‘normal’ aNDF levels and relatively low proportions of corn silage and starch (334.0, 104.0 and 160.3 g/kg DM, respectively, in our study). Copyright
Dissertation (MSc(Agric))--University of Pretoria, 2012.