Effects of increased dietary sugar and reduced rumen-undegradable protein during the transition period on production, metabolic, and immune parameters in dairy cows

Optimizing carbohydrate and protein fractions in transition dairy cow diets is critical for maintaining rumen function, health, and productivity. Although rations should be rich in starch and undegraded protein for high-yielding cows, this study examined the effects of reducing dietary starch and rumen-undegradable protein while increasing sugar and rumen-degradable protein (isocaloric and isonitrogenous) on milk yield, milk composition, and selected blood metabolic and immune parameters in transition dairy cows. Forty Holstein dairy cows, approximately 210 days pregnant, were divided into two groups, each consisting of 20 cows. The control (C) group was fed a standard ration, while the animals in the treatment group (T) were fed a ration containing reduced bypass protein content and increased sugar content. Weekly blood samples were collected throughout the study period. Following parturition, milk yield and milk composition were monitored regularly. In addition, feed intake was recorded and monitored during the study. Blood glucose concentration increased in the treatment group during the prepartum, parturition, and postpartum periods (P=0.0266, P=0.0307, P=0.0089). While IgG levels increased throughout the study (P<0.0001), NEFA levels decreased during the parturition and postpartum period. Additionally, Blood ürea nitrogen (BUN) levels decreased after parturition (P=0.0421). Milk yield was similar between the treatment and control groups. Postpartum feed consumption (P=0.0011) and milk fat (P=0.0017) were higher in the treatment group. In conclusion, increasing dietary sugar and reducing rumen-undegradable protein during the transition period improved indicators of energy metabolism, enhanced immune status, promoted feed intake, and increased milk fat content. This nutritional strategy may support metabolic health and productive performance in transition dairy cows.