Abstract
To increase intramuscular fat accumulation, Japanese Black cattle are commonly fed a high-grain diet from 10 to 30 months of age although it can result in the abnormal accumulation of organic acids in the rumen. We explored the effect of long-term high-concentrate diet feeding on ruminal pH and fermentation, and its effect on the rumen bacterial community in Japanese Black beef cattle during a 20-month fattening period. Nine castrated and fistulated Japanese Black beef cattle were housed with free access to food and water throughout the study period (10-30 months of age). The fattening stages included Early, Middle, and Late stages (10-14, 15-22, and 23-30 months of age, respectively). Cattle were fed high-concentrate diets for the experimental cattle during fattening. The body weight of the cattle was 439 ± 7.6, 561 ± 11.6, and 712 ± 18.5 kg (mean ± SE) during the Early, Middle, and Late stages, respectively. Ruminal pH was measured continuously during the final 7 days of each stage, and rumen fluid and blood samples were collected on day 4 (fourth day during the final 7 days of the pH measurements). The 24-h mean ruminal pH during the Late stage was significantly lower than that during the Early stage. Total volatile fatty acid (VFA) during the Late stage was significantly lower than during the Early and Middle stages, but no changes were noted in individual VFA components. The lactic acid concentration during the Late stage was significantly higher than that during the Early and Middle stages. The bacterial richness indices decreased significantly during the Late stage in accordance with the 24-h mean ruminal pH. Among the 35 bacterial operational taxonomic units (OTUs) shared by all samples, the relative abundances of OTU8 (Family Ruminococcaceae) and OTU26 (Genus Butyrivibrio) were positively correlated with the 24-h mean ruminal pH. Total VFA concentration was negatively correlated with OTU167 (Genus Intestinimonas), and lactic acid concentration was correlated positively with OTU167 and OTU238 (Family Lachnospiraceae). These results suggested that long-term high-grain diet feeding gradually lowers ruminal pH and total VFA production during the Late fattening stage. However, the ruminal bacterial community adapted to feeding management and the lower pH during the Late stage by preserving their diversity or altering their richness, composition, and function, to enhance lactic acid production in Japanese Black beef cattle.
Highlights
A high-grain based diet is essential for beef and dairy cattle, to maximize growth, productivity, and high-quality meat or milk
Nutrient adequacy rates of dry matter (DM) and total digestible nutrient (TDN), calculated based on the total consumption amounts of concentrate diet and forage, during the Late stage were significantly lower than during the Early and Middle stages (P < 0.05), while that of neutral detergent fiber (NDF) was significantly higher during the Middle stage compared with the Early stage, and during the Late stage versus the Early and Middle stages (P < 0.05; Table 1)
The 24-h mean pH value during the Early and Middle stages (6.22 and 6.06, respectively) were similar level compared with the subacute ruminal acidosis (SARA) challenge model for 2 days (5.94 and 5.81; [26]), for 1 week (6.10; [3]) and mid-term for 6 weeks (5.97; [4]) in Holstein cattle studies, Japanese Black cattle presented more severe depression of ruminal pH (5.73) during the Late stage in the present study
Summary
A high-grain based diet is essential for beef and dairy cattle, to maximize growth, productivity, and high-quality meat or milk. The ruminal bacterial community and ruminal pH can adapt to and influence each other [3], and the effects of short- (days) and mid-term (weeks) SARA and RA challenges have been explored previously [3, 4, 5, 6]. The ruminal bacterial community has similar proportions between the phyla Firmicutes and Bacteroidetes under a high-forage diet with higher ruminal pH [3, 7, 8]. Grain-based SARA challenge induces death or lysis of Gram-negative bacteria, such as Bacteroidetes and Proteobacteria, and eventually the proportion of Firmicutes increases with severely low ruminal pH [3, 7, 8]
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