Effects of plant extract supplementations or monensin on nutrient intake, digestibility, ruminal fermentation and metabolism in dairy cows

Abstract

This study aimed to evaluate the effects of diet supplementation with monensin and saponins alone or combined with essential oils (EOs) on the nutrient intake and apparent digestibility, rumen fermentation parameters, microbial population, nitrogen balance, ruminal microbial protein synthesis, blood metabolites, and milk composition, yield and fatty acid profile of mid- to late-lactating Jersey cows. Eight ruminally cannulated lactating Jersey cows (average 17.6 ± 5.5 kg/day of milk yield and 100.5 ± 26.6 days of milk (mean ± SD)) were distributed in a replicated 4 × 4 Latin square design with 21-day periods (last seven days for sampling). Treatment sequences were randomly designated to cows and consisted of: (1) CON - Control, no feed additive; (2) SAP - 16 g/cow/day of a supplement based on whole-seed fenugreek powder (variety Fenucold) standardized to diosgenin, one of the major steroidal sapogenins of fenugreek (2000 mg/kg); (3) SAPEO - SAP supplement combined with a blend of natural EOs with major components of carvacrol (2500 mg/kg), cinnamaldehyde (5600 mg/kg) and limonene (3000 mg/kg); and (4) MON - Monensin, inclusion of monensin sodium in the diet at 24 mg/kg DM. Cows fed CON showed higher dry matter, organic matter, crude protein and ether extract intakes than animals fed MON, whereas higher neutral detergent fibre intake was observed in animals fed SAPEO than those fed MON (P < 0.05). Diet and time effects were observed for ruminal pH and concentration of ruminal ammonia nitrogen (P < 0.05). Cows fed SAP showed a higher relative proportion of Fibrobacter succinogenes (P = 0.04) than animals fed MON. Cows fed CON had higher net and digestible energy intakes than animals fed MON (P < 0.05). Cows fed SAPEO showed higher albumin concentrations (P = 0.04) than those fed CON, SAP, and MON. Besides, cows fed CON showed higher urea concentrations (P = 0.04) than those fed SAP and SAPEO. Higher protein and fat levels in the milk were observed in cows fed SAPEO than animals fed MON (P < 0.05). Monensin decreased the concentrations of C4:0, C6:0, C8:0, and C18:1 cis-11 milk fatty acids (P < 0.05). Monensin decreased nutrient intake to a more energetically efficient pathway but did not alter milk production, digestibility, or rumen fermentation. Saponin supplementation associated with essential oils increases milk fat and protein contents in lactating Jersey cows compared to animals fed a monensin-supplemented diet.