Abstract
Twenty-two Merino lambs (average weight=15.3 kg) were used to study the effects of inclusion of sodium bicarbonate in the concentrate on feed intake, digestibility, rate of passage, nitrogen balance and ruminal fermentation in vivo and in vitro. Lambs were allocated to two experimental groups receiving concentrate and 20 g/kg sodium bicarbonate (group Bic) or concentrate alone (group Control). Both groups received barley straw ad libitum. Faeces and urine were collected for 5 days to estimate digestibility, nitrogen balance and rate of passage. After slaughter (at 25 kg live weight), samples of rumen fluid were collected from each lamb to determine parameters of ruminal fermentation and to be used as inocula for batch cultures of rumen microorganisms. There were no significant differences between treatments (P>0.10) in concentrate intake, dry matter digestibility, nitrogen balance and digesta kinetics. However, straw intake was greater (P
Highlights
Fattening lambs are generally fed rations containing over 800 g kg-1 concentrate in order to achieve high levels of energy intake and daily weight gains (Normand et al, 2001)
There were no differences between treatments for any of the parameters related to the rate of passage (k1, k2, TT and total mean retention time (TMRT); P>0.10) or nitrogen balance
Dry matter intake was not significantly affected with the inclusion of bicarbonate in the diet, in agreement with the results reported by Mandebvu and Galbraith (1999) using a lower dose of sodium bicarbonate (15 g kg-1)
Summary
Fattening lambs are generally fed rations containing over 800 g kg-1 concentrate in order to achieve high levels of energy intake and daily weight gains (Normand et al, 2001) This results in reduction of the molar proportion of acetate and increase of the molar proportion of propionate (Enemark et al, 2002), which reduces methane production and enhances energy retention (Russell, 1998). Buffers can enhance ruminal environmental conditions by modulating acidity of the ruminal contents, preventing severe drops in pH (Le Ruyet and Tucker, 1992). Some salts, such as sodium bicarbonate, are routinely added to ruminant diets to buffer rumen pH, and have been widely used for fattening lambs. It has been suggested that it may improve the amount and efficiency of ruminal microbial protein synthesis, which occurs independently of changes in ruminal fluid dilution rates (Mees et al, 1985), and enhance bacterial uptake of ammonia (Newbold et al, 1988), these effects being eventually associated to a higher feed intake and a subsequent increased daily gain (Tripathi et al, 2004)
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