Sodium Bicarbonate Can Increase Milk Fat Concentration in Lactating Ewes Fed Ryegrass Herbage Rich in Water-Soluble Carbohydrates

Pastures rich in water-soluble carbohydrates (WSCs) can decrease milk fat concentration in dairy ruminants, associated with rumen pH reduction. To prevent milk fat reduction, sodium bicarbonate was supplemented as a rumen buffer to sheep fed indoors on tetraploid annual ryegrass (Lolium multiflorum Lam. ssp. westervoldicum) herbage rich in WSCs (28% DM). Ten lactating Sarda ewes were assigned to the control group (CNT) or the sodium bicarbonate group (BIC; 25 g/day per ewe before ryegrass feeding). All ewes were housed indoors, machine-milked at 16:30 and 07:30, fed freshly cut ryegrass ad libitum (12:30 to 07:30 of subsequent day), and fed concentrates during milkings. Individual grass, measured with automatic feeders, and concentrate intake were recorded. Total dry matter intake (DMI) (p = 0.03), ryegrass DMI (p = 0.03), milk fat concentration in afternoon (p < 0.01) and morning (p = 0.03) milkings, and afternoon milk fat yield (p = 0.03) were higher in BIC than CNT. Milk yield was unaffected. In conclusion, sodium bicarbonate supplementation can increase milk fat concentration in ewes fed high-WSC herbage, with rapid effect on the rumen. WSC concentration should be considered when formulating rations for pasture-fed dairy sheep and, more generally, dairy ruminants.