Weaning marks the shift away from the majority ofenergy from intestinal absorption of nutrients to energybeing derived from ruminal microbial fermentation andthe production of SCFA being absorbed and metabolizedby the rumen epithelium (Baldwin et al., 2004). Themajor metabolic pathway of SCFA metabolism in therumen epithelium is ketogenesis (Leighton et al., 1983).Blood BHBA was similar for both treatment groups upto d 35 (<100 μM) while they were consuming the sameminimal amounts of starter. However, blood BHBA of6WW calves increased significantly at step-down, in associationwith starter intake. The BHBA results agreewith those in some studies (Khan et al., 2011), rangingfrom 0 to 400 μM, which is lower than reported by others(Quigley and Caldwell, 1991). This sharp increasein blood BHBA is similar to results in lambs weanedduring wk 7 of life, where BHBA increased 6-fold between42 and 56 d of age (Baldwin and Jesse, 1992).Although morphological development is clearly affectedby diet, the ketogenic capacity of the rumen epitheliumhas been shown to increase with age in lambs (Laneet al., 2002). Similarly, Bush (1988) found that calveswere only at 40% the ketogenic rate of a mature ruminantat 30 d of age, despite being weaned at 28 d.By 60 d of age, calves were producing ketones at ratessimilar to that of a mature ruminant, which also agreeswith early work by Warner et al. (1956) and Tamateet al. (1961). This suggests that certain steps in rumenmaturity do not occur before 8 wk of age.
การแปล กรุณารอสักครู่..
