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To determine the effect of prepubertal immunization against GnRH on the development of sexual and social behavior of Friesian bulls, 90 calves were randomly assigned to five treatments: 1) [I.sub.2], immunized against GnRH at 2 and boosted at 2.5, 4, and 7.5 mo of age, n = 2 x 10; 2) [I.sub.4], immunized against GnRH at 4 and boosted at 4.5 and 7.5 mo of age, n = 2 x 10; 3) [I.sub.7.5], immunized against GnRH at 7.5 and boosted at 8 mo of age n = 2 x 10; 4) S, steers castrated at 2 mo of age, n = 10; and 5) B, intact bulls, n = 2 x 10. Blood samples were collected initially every 2, then every 3 wk. Plasma was analyzed for anti-GnRH titers and plasma testosterone concentration. Sexual and agonistic behavior, male-male mounting, and damage to paddocks was assessed throughout the experiment. All immunized calves developed antibodies against GnRH (32.3 [+ or -] 2.0% bound at a 1:10 plasma:PBS-BSA dilution, 14 d after first boost). Plasma testosterone concentrations were < 1 ng/mL for all immunized animals until 11 mo of age, when they increased to levels found in intact bulls at 14 mo of age. At slaughter, testes and seminal vesicle weights were 38.3 and 31.6% lighter, respectively, for all immunized treatments compared to B. There were no significant differences between [I.sub.2], [I.sub.4], and [I.sub.7.5] in any of the sexual or agonistic behavior tests. Bulls scored higher than steers in all sexual behavior tests. Immunized bulls scored lower than bulls in sexual behavior tests from 10 to 17 mo of age. The proportion of immunized animals that serviced an estrous cow was lower than the proportion of intact bulls at 10, 12.5, 14, and 17 mo of age. Immunized animals scored lower than bulls in bull challenge tests at 8.5, 11.5, 13, 14.5, and 17 mo of age. Paddock damage by animals on the three immunization treatments was lower than that by bulls from 7 to 14.5 mo of age, as were leg wear scores (an indicator of male-male mounting behavior) from 9 to 14 mo of age. There was no difference in sexual behavior between immunized bulls ([I.sub.2], [I.sub.4], and [I.sub.7.5]) and bulls while held in lairage pens for 16 h before slaughter, but all treatment groups scored higher than steers. There was a similar trend for agonistic behavior, although [I.sub.4] bulls were no different from steers. Prepubertal immunization against GnRH at 2, 4, and 7.5 mo of age impaired testes function and affected the development of social and sexual behavior of young bulls. Key Words: Immunization, GnRH, Bulls, Steers, Behavior, Testosterone

Despite the clear importance of drinking water, calves are not always provided water on farm for the first few weeks of life. The main objective of this study was to investigate the effects of water provision (access or no access) and milk allowance (high or low) on the behavior and growth rate of calves. Fifty mixed-breed calves were each assigned to 1 of 4 treatments: (1) water and high (10 L/d) milk allowance (n = 13), (2) no water and high milk allowance (n = 12), (3) water and low (5 L/d) milk allowance (n = 12), or (4) no water and low milk allowance (n = 13). Visits to the water trough, water intake, milk drinking behavior (visits and drinking speed), proportion of observations eating hay and calf starter, and lying behavior were recorded from when the calves were, on average, 5 d of age (standard deviation: 2 d) for 4 consecutive weeks. Calves were weighed weekly. Some calves began to visit the water trough from the start of the recording period, as early as 4 d of age, and water intake increased with age for all calves that had access to it. This increase was greater for calves provided a high milk allowance. Water intake increased with ambient temperature, which highlights the importance of providing drinking water in warm conditions. Overall, calves spent a greater proportion of observations eating hay and calf starter with age. The provision of drinking water was associated with a greater proportion of observations eating hay but less eating calf starter. The increase in the proportion of observations eating calf starter with age was greater for calves on a low milk allowance than of those provided a high milk allowance; this is likely due to calves on a low milk allowance searching for nutrients and energy. Calves on a high milk allowance grew faster and spent more time lying compared with calves with a low milk allowance, thus suggesting greater satiety of well-fed calves. Our results suggest that calves should have free access to drinking water from birth and that access to drinking water may aid in hay (fiber) intake and possibly rumen development. [ABSTRACT FROM AUTHOR]