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Effect of Anabolic Agents on Nitrogen-Retention of Calves¹

Institute for Animal Nutrition Research², Wageningen, The Netherlands

Abstract

Nitrogen balance studies with a total number of 64 Friesian bull calves were carried out to compare the effectiveness of a number of agents with a possible anabolic effect on nitrogen-retention. The animals, housed individually in balance units, were fed a liquid milk replacer diet.

When treated at 11 or 12 weeks of age, the maximum of the cumulative response for N-retention was found as for live weight gain, at 4 to 5 weeks after treatment in most cases. The relative effectiveness of the agents in improving N-retention correlates well with their effectiveness in promoting growth. The mean effects per calf were as follows:

• 120 mg DES led to an extra N-retention of 210 and 218 g after 29 days in two experiments, respectively.
  
• 20 mg estradiol/200 mg testosterone led in two experiments to an extra N-retention of 136 and 240 g after 28 and 24 days, respectively.
  
• 20 mg estradiol led to an extra N-retention of 188 and 153 g after 24 and 38 days, respectively.
  
• 20 mg estradiol/140 mg trenbolone led to an extra N-retention of 551 g after 38 days.
  
• Zeranol, testosterone, progesterone and trenbolone, when administered alone, did not lead to a significant response in N-retention.
  

In normal veal calves the percentage of digested feed protein converted into body protein gradually decreases from 70% to less than 40% during the growing period. By administration of the most effective anabolic agent tested (20 mg estradiol/140 mg trenbolone) the percentage of digested protein converted into body protein was over an experimental period of 38 days increased from 39% in the control to 58% in the treated group.

¹ Presented during the 65th Annual Meeting of the American Society of Animal Science at the session on International Animal Agriculture, Lincoln, Nebraska, July 31, 1973.

² LOB, Haarweg 8, Wageningen