Lactation Response of Dairy Cows Receiving Bovine Somatotropin and Fed Rations Varying in Crude Protein and Undegradable Intake Protein

Our experiment evaluated lactation and metabolic responses of Holstein cows injected with somidobove (recombinant bST) and fed one of four isocaloric rations containing either 14 (low) or 17% (high) CP and undegradable intake protein of 33 (low) or 40% (high) of CP. Multiparous cows (n = 37) in early lactation, averaging 37 kg/d of milk, received somidobove (640mg per injection) at 28-d intervals for 112 d and one of four protein rations: low-low, low-high, high-low, and high-high. Nine other multiparous controls were fed low-low ration with no somidobove. On the low-low ration, somidobove significantly increased milk yield by 2.3 kg/d, but not 3.5% FCM (1.7 kg/d), in-takes of DM or CP, or milk composition. Milk and 3.5% FCM increased by 1.7 and 2.1 kg/d in cows fed high undegradable intake protein but there was no effect on milk composition, BW, or DM intake. Ration CP had no effect on production variables in cows receiving somidobove. Serum urea was higher in cows fed high CP rations; undegradable intake protein was without effect. Plasma leucine was higher in cows fed high undegradable intake protein. Administration of somidobove to cows fed low-low rations reduced plasma methionine, serum albumin, hemoglobin, and albumin:globulin ratio. Milk production of high producing dairy cows receiving somidobove may be limited by the amount of protein available at the small intestine.