Effects of monensin of mammary gland function during late lactation in crossbred holstein cattle

Abstract

Fourteen, non-pregnant, late lactating crossbred Holstein cattle, approximately 270 days postpartum, were divided into two groups of 7 animals each. Animals in the treated group were given sodium monensin orally in a slow-release capsule. Animals in both groups were fed with similar diet ration to maintain milk production and body score at 2.5. Rice straw was fed as a source of dietary fiber throughout the experimental period. After monensin administration, the higher concentration of ruminal propionate (P<0.05) and the lower concentration of acetate (P<0.05) were apparent in comparison to pretreatment period. The ratio of acetate to propionate concentration decreased significantly after monensin administration (P<0.05), while in the control group the ratio value was maintained throughout the period of experiment. Monensin did not influence on the concentration of ruminal butyrate and valerate. The concentrations of milk allantom between the control group and the monensin treated group were not different. The allantoin excretion was low in animals treated with monensin (P<0.05). The plasma concentration of glucose, arteriovenous concentration difference and mammary gland uptake of glucose remained constant in both groups. Milk yield in the control group declined during lactation advance to the later stage of lactation. An increase in the milk yield was not apparent during monensin administration. There was a positive change in milk yield in the first 2 weeks after monensin administration. Milk compositions for lactose, fat and protein in either control or monensin treated groups did not change throughout the experimental periods. It can be concluded that the role of monensin can change the ruminal fermentation pattern. Monensin could not increase milk yield in the late lactating period. The positive responses in milk yield after monensin administration do not depend on the plasma concentration of glucose and the uptake of glucose by the mammary gland. The glucogenic theory' could not use to explain the positive effect of milk production in the first 2 week after monensin administration.