Although flavonoids or yeast have been used as feed additives to improve the production efficiency and health of adult cattle, little information is available on their effects on rumen fermentation in calves. The objective of this study was to investigate the effects of feed supplementation with mulberry leaf flavonoids and Candida tropicalis on performance, blood parameters, and rumen fermentation characteristics during pre-weaning and post-weaning periods. Forty-eight Holstein calves were used in a four-groups trial and were supplemented with (1) no yeast or flavonoids (CON), (2) active dry yeast (ADY; C. tropicalis, 5.0 × 10⁹ CFU/d), (3) flavonoids (FLA; 3 g/d), or (4) yeast and flavonoids (YF; C. tropicalis, 5.0 × 10⁹ CFU/d; flavonoids, 3 g/d). The feeding strategy was as follows: milk replacer was offered at 12% of body weight in two meals per calf each day at age 21 d, and a gradual weaning process was adopted at age 50 to 56 days. Data of daily feed intake, body weight, and serum and rumen fermentation parameters were obtained at 28, 42, 56, and 80 d ages, respectively. A significant time effect and interaction between treatment and time was found for average daily gain, feed efficiency, total volatile fatty acid concentration, and proportion of propionate in calves (p < 0.05). Average daily gain and feed efficiency increased during post-weaning and overall periods for calves in FLA and YF groups compared with CON and ADY groups (p < 0.05). A reduction of fecal scores with supplementation was found in FLA and YF groups (p < 0.05). Rumen fluid pH and ammonia nitrogen concentration remained constant across the groups, whereas total volatile fatty acid concentration and molar proportion of propionate significantly increased during the pre-weaning and overall periods in FLA and YF groups (p < 0.05). Calves in YF group had the highest serum concentrations of IgG and IgA during the overall period (p < 0.05). Additionally, serum β-hydroxybutyric acid concentration was higher in ADY and FLA groups during the post-weaning period (p < 0.05). Supplementation with C. tropicalis showed little effect on increasing growth performance and health compared with flavonoids alone. Meanwhile, the combination of C. tropicalis and flavonoids was not synergistic with respect to improving health and rumen fermentation compared with use of flavonoids alone in pre- and post-weaning calves (p > 0.05).

Development of alternative forage resources is of great importance to provide necessary nutrients and minimize greenhouse gas emissions in ruminant production. The aim of this study was to examine the effects of dietary supplementation of Moringa oleifera on the production performance and fecal methanogenic community in dairy cows using methyl-coenzyme M reductase α-subunit gene. Sixty-four cows were allocated to one of four treatments: basal diet without M. oleifera (control) or low (3% w/w, M3), medium (6%, M6), or high (9%, M9) supplementation with M. oleifera. This study demonstrated that different supplementation levels of Moringa oleifera in the diet achieved similar feed intake and milk production, but adding 6% of Moringa oleifera improved milk fat content. Two families, two phyla, three genera, and three species in total were identified among the four treatments. The fecal archaeal community in the control treatment was predominated by Methanobrevibacter (39.1% of the total sequence reads) followed by Methanosphaera and Methanocorpusculum at the genus level. The increased abundance of the Methanosphaera genus and Methanosphaera sp. ISO3-F5 species was induced by secondary metabolites of Moringa oleifera in the diet. Results indicated that Moringa oleifera supplementation not only improved dairy product quality but could also potentially reduce methane emissions.

Enteric methane (CH₄) emissions from young ruminants contribute to a substantial proportion of atmospheric CH₄ accumulation. Development of emission inventory and mitigation approaches needs accurate estimation of individual emission from animals under various physiological conditions and production systems. This research investigated the effect of different dietary concentrate contents on feed intake, growth performance, nutrient digestibility and CH₄ emissions of heifers at various stages, and also developed linear or non-linear prediction equations using data measured by sulphur hexafluoride tracer technique. Increasing dietary concentrate contents increased feed intake and growth rate, enhanced nutrient digestibility, and reduced enteric CH₄ emissions. Heifers at the age of 9, 12, and 15 months with an average weight of 267.7, 342.1, and 418.6 kg produced 105.2, 137.4, and 209.4 g/day of CH₄, and have an average value of CH₄ energy per gross energy intake (Y_m) 0.054, 0.064, 0.0667, respectively. Equations relating CH₄ emission values with animal and feed characteristics were developed with high determination coefficients for heifers at different growth stages. Dietary concentrate contents had significant influence on overall performance of heifers. These data can be used to develop regional or national emission inventories and mitigation approaches for heifers under various production regimes in China.