Friesian cow experimentally treated with recombinant somatotropin(r-bST): effects on productive and reproductive parameters

Abstract

The study examined the effect of recombinant somatotropin (r-bST) on production and reproduction. Twenty cows were randomly divided in two treatment groups: r-bST (n=10), treated, starting at the eighth postpartum week by injections of r-bST every 14 days; control (n=10), untreated. Cows were milked twice a day, recording milk production. Body condition scores (BCS) were monthly determined for each cow. Blood samples were collected twice a week from jugular vein and assayed by IGF-1 immunoassay. At the fifth r-bST injection, an estrous cycle was synchronized by two intramuscular injections of 0,15 mg of PGF2a analogue (dcloprostenol; Dalmazin, Fatro, Italy) given 11 days apart and ovaries were daily examined by ultrasonography. Follicles were classified as small, medium, large. Milk yield significantly increased after r-bST treatment (P £ 0.05), remaining higher than control group. At the fourth postpartum month, BCS significantly increased in control group and at the end of the trial it was 2.30 in r-bST and 2.52 in control group (P £ 0.05). Treated cows had more serum concentration of IGF- 1 and more small and medium follicles vs control ones. The first wave dominant follicle growth was similar. The start of the second follicular wave was earlier in r-bST treated cows.