Abstract
The objectives of this study were to 1) determine the variation of nutrient digestion, plasma metabolites and oxidative stress parameters triggered by induced subacute ruminal acidosis (SARA); and 2) evaluate the ability of pelleted beet pulp (BP) as a replacement for ground corn to alleviate SARA. Eight Holstein-Friesian cows were fed four diets during four successive17-day periods: 1) total mixed ration (TMR) containing 0% finely ground wheat (FGW) (W0); 2) TMR containing 10% FGW (W10); 3) TMR containing 20% FGW (W20); and 4) TMR containing 10% BP as a replacement for 10% ground corn (BP10). The SARA induction protocol reduced the mean ruminal pH from 6.37 to 5.94, and the minimum ruminal pH decreased from 5.99 to 5.41 from baseline to challenge period. Mean ruminal pH increased from 5.94 to 6.05, and minimum daily ruminal pH increased from 5.41 to 5.63, when BP was substituted for corn. The apparent digestibility of nutrients was not affected by the dietary treatments, except that the digestibility of neutral detergent fibre (NDF) and acid detergent fibre (ADF) was reduced in cows fed the W20 diet compared with cows fed the W0 and W10 diets, and cows fed the BP10 diet had higher NDF and ADF digestibility than the cows fed the W20 diet. Cows fed the W20 diet had a lower plasma concentration of β-hydroxybutyrate (BHBA), non-esterified fatty acids (NEFA), cholesterol, triglyceride, and total antioxidative capacity (TAC), and a higher plasma concentration of glucose, insulin, malonaldehyde (MDA), super oxygen dehydrogenises (SOD), and glutathione peroxidase (GSH-Px) than cows fed the W0 diet. Substitution of BP for corn increased concentrations of plasma BHBA and TAC, but decreased concentrations of plasma MDA. Our results indicate that reduction of fibre digestion; the concomitant increase of plasma glucose and insulin; the decrease of plasma BHBA, NEFA, cholesterol, and triglyceride; and changes of plasma oxidative stress parameters are highly related to SARA induced by W20 diets. These variables may be alternative candidates for SARA diagnosis. We also suggest that the substitution of BP for corn could reduce the risk of SARA, increase fibre digestion, and improve the antioxidant status in dairy cows.
Highlights
Subacute ruminal acidosis (SARA) is one of the most common chronic digestive disorders on intensive dairy farms, and is defined as periods of moderately depressed ruminal pH [1]
The total tract digestibility of neutral detergent fibre (NDF) and acid detergent fibre (ADF) increased in cows fed the BP10 diet compared with cows fed the W20 diet, and the results might be due to the higher ruminal pH of cows fed the diet inclusion of beet pulp (BP)
The concentrations of plasma BHBA, cholesterol and triglyceride were lower in cows fed the W20 diet throughout the daytime, and the results reveal that SARA had a significant effect on diurnal fluctuations in plasma metabolites
Summary
Subacute ruminal acidosis (SARA) is one of the most common chronic digestive disorders on intensive dairy farms, and is defined as periods of moderately depressed ruminal pH (the minimum pH varies between 5.2 and 5.6) [1]. There is continued interest in finding quick and simple indicators (e.g., plasma metabolites) as potential diagnostic tools of rumen fermentation pattern and function [6]. Plasma metabolites were often used to monitor the health and metabolic status of dairy cows, and Ametaj et al [8] indicated that dairy cows fed diets containing high rapidly fermentable carbohydrates could greatly perturb the patterns of plasma metabolites. There is limited information on the role of high-grain induced SARA on diurnal perturbations of plasma metabolites in dairy cows. It is widely accepted that oxidative stress is positively related to high grain or high starch diets of ruminant animals [9], and that high-producing dairy cows exposed to a high-starch diet are more susceptible to inadequate antioxidant status [10], resulting in a poorly functioning immune system and increased risk of rumenitis as well as laminitis. The oxidative stress index could be a general approach used in ruminant medicine in the future [11]
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