Lactobacillus spp. supplementation under grazing conditions: Methane and milk production responses during early lactation.

Abstract

Both in vitro and in vivo studies have shown the potential of Lactobacillus spp. to mitigate enteric methane. However, their mitigation impact on early-lactation dairy cows grazing high-pasture diets has not been studied. This study evaluated the effect of supplementing freeze-dried or liquid Lactobacillus spp. products on enteric methane emission from early lactation dairy cows offered a high forage diet. Forty spring calving Holstein Friesian dairy cows, grazing a perennial ryegrass (PRG) (Lolium perenne L.) based pasture, milked twice daily, were randomly allocated to one of the 3 treatment diets offered for 35 d: 1) CON: Control, fed a basal diet (n = 14); 2) FLA: basal diet plus freeze-dried Lactobacillus spp. (n = 13) delivering 5.0 × 10¹⁰ cfu/milking, and 3) LLA: basal diet plus Liquid Lactobacillus spp. (n = 13) delivering 5.75 × 10¹⁰ cfu/milking. The basal diet comprised 6.9 kg DM/day of a grain mix plus PRG pasture at an allowance of approximately 25 kg DM/cow per day. Covariate observations were made for the first 5 d of the 40-d experiment, before commencing treatments. During the last 5 d of the experiment, individual forage dry matter intake for each cow was estimated using the n-alkane technique, and methane emissions from individual cows were measured using the modified sulfur hexafluoride (SF₆) tracer technique. Data were analyzed using a completely randomized design based ANCOVA. Methane production (g/day), yield (g/kg DMI) and intensity (g/kg energy corrected milk) were not affected by the inclusion of either form of Lactobacillus spp. in the diet, although a numerical reduction of 6% in methane yield was observed in the FLA group, compared with the control group. Methane emissions from the CON cows were approximately 38% lower than those estimated using inventory factors. This is likely due to the low fiber concentration and low DM concentration of the PRG offered likely resulting in a high ruminal passage rate, reducing ruminal retention time and extent of fermentation. The high passage rate could have also restricted the colonization potential of supplemented Lactobacillus spp. This, combined with the large rumen volume of dairy cows and low dose rate may in part explain the limited methane mitigation. Notably, production responses to Lactobacillus spp. supplementation have been more evident in small ruminants, suggesting species-specific differences. These findings highlight the need for tailored probiotic strategies, particularly in pasture based dairy systems.