Effect of Saccharomyces cerevisiae fermentation product (XP) on energetic efficiency of diet fed to high producing dairy cows during the hot season

Abstract Text: The objective was to test whether Saccharomyces cerevisiae fermentation product (XP, Diamond V, Cedar Rapids, IA) could compensate for lower energy density in diets by increasing digestive efficiency. Forty-two multiparous Israeli-Holstein dairy cows were divided into 2 treatment groups according to milk production, parity, DIM and BW. Treatments consisted of: (i) Control – a common Israeli diet contained 1.78 Mcal NE_L/kg DM; (ii) XP – diet contained 1.75 Mcal NE_L/kg DM and supplemented with 50 g XP/cow/day. Diets were isonitrogenous and consisted of the same ingredients. The study was conducted for 14 wk during the typical hot season. Milk yield, DMI, rumination time and lying time were recorded daily, and milk components were measured weekly. Rumen and blood samples were taken at the 12^th wk of the study: -2, 0, 2 and 4 h relative to feeding time for rumen pH, VFA and ammonia, and plasma glucose and urea. Data were analyzed using the PROC MIXED model of SAS. Milk yields tended to be higher (P<0.1) in control than in XP group, and FCM (4%) yields and milk components percentages and yields were similar between treatments. No treatment effect was observed for daily rumination and resting time. The energy intake was lower (48.9 and 50.5 Mcal/d, respectively; P < 0.05), and DMI tended to be lower (P<0.1) in cows supplemented with XP than in control cows. Energy in milk per energy consumed tended to be higher (P < 0.1) in cows supplemented with XP, and resulted in similar feed efficiency (milk, ECM or FCM/DMI). Plasma glucose concentrations were higher in cows supplemented with XP than in control cows (66.2 and 63.8 mg/dL, respectively; P<0.05). Plasma urea concentrations were 15% lower (P<0.001), and rumen ammonia concentrations were also lower in cows supplemented with XP than in control cows (125.8 and 157.2 µg/ml, respectively; P<0.001). Rumen pH was higher in cows supplemented with XP than in the control group (6.76 and 6.57, respectively; P<0.05). Rumen propionic, butyric and total VFA concentrations were higher (P<0.05) in control cows than cows supplemented with XP, whereas the acetic/propionic ratio tended to be higher (P< 0.1) in cows supplemented with XP. In conclusion, supplementation of 50 g XP/d to dairy cows fed a lower energy diet increased energy availability, potentially through improved ruminal nitrogen metabolism, and increased supply of glucose for milk production.

Keywords: energetic efficiency, XP, nitrogen metabolism