Growth, feed digestibility and carcass characteristics of male dairy calves infused with growth hormone-releasing factor and/or actively immunized against somatostatin

One week after weaning, 16 animals were immunized (IMM) against human-globu lin (hG-IMM) and 16 against SRIF conjugated to hG (SRIF-IMM) in Freund's co mplete adjuvant. Subsequent boosters in Found's incomplete adjuvant were ma de on days 14, 25, 56 and 73 of the experimental period. On day 79, half of the animals within each immunization treatment were infused continuously w ith human GRF(1-29)NH2 (3.33 ng min(-1) kg(-1) BW) and the other half with saline over a 32-day period. GRF increased (P = 0.01) body weight gain by 1 2%, whereas SRIF immunization decreased (P = 0.01) weight gain by 7.5% duri ng the infusion period (days 79-111). However. the effect of SRIF immunizat ion on growth rate was not significant (P > 0.10) when considered over the entire duration of the experiment (days 0-111). Feed intake, feed efficienc y, carcass characteristics, nutrient digestibility, nitrogen retention and metabolizability of energy were not affected (P > 0.10) by SRIF immunizatio n or GRF infusion. However, GRF infusion increased pancreatic activity of a mylase (P < 0.05). In conclusion, GRF, unlike SRIF immunization, could be u sed to improve growth performance of fast-growing corn-fed bull calves.