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The Effect of Pre-Fast Diet and Transport on Nitrogen Metabolism of Calves¹

U.S. Department of Agriculture, Bushland, TX 79012 and El Reno, OK 73036 and Texas A&M Center, Amarillo 79106

Abstract

Two trials were conducted to determine the effects of transport stress and pre-transport diet on N losses, blood chemistry and ruminal variables of steers. In each trial, 16 crossbred steers (261 kg avg weight) were assigned to four groups in a 2 x 2 factorial arrangement of treatments. Treatments consisted of either transported or non-transported groups and two pre-transport dietary regimens (alfalfa hay or a 50% concentrate diet fed for 3 d before fasting). The alfalfa hay contained 14.6% crude protein (CP) and had a calculated metabolizable energy (ME) content of 1.92 mcal/kg. The 50% concentrate diet contained 15.5% CP and had a calculated ME content of 2.23 mcal/kg. Steers in the transport group were transported for 13 h in trial 1 and 46 h in trial 2, while the remaining steers were not transported. Both groups were withheld from feed and water during the observation periods. Urine and feces were collected and blood samples were obtained at intervals during the observation periods. Transport increased (P<.05) urinary and total N excretion and nonevaporative water losses compared with fasting alone. Calves fed the 50% concentrate diet had lower N and nonevaporative water losses than calves fed hay, probably due to lower pre-fast N and water intakes. Ruminal total volatile fatty acid (VFA) concentrations and molar proportions of propionate and butyrate declined (P<.05) with time in all groups, while molar proportions of acetate and minor VFA increased. Results of these trials indicate transportation stress can cause a significant increase in total N excretion and nonevaporative water loss compared with feed and water deprivation alone. Losses of N and water were lower in calves fed a 50% concentrate diet rather than hay for 3 d before the fasting period, probably because of lower pre-fast N and water intakes.

¹ Contribution from USDA, Agr. Res. Serv., in cooperation with the Texas Agr. Exp. Sta., Texas A&M Univ., College Station 77843.

² USDA-ARS, Conservation and Production Res. Lab., P.O. Drawer 10, Bushland, TX 79012.

³ USDA-ARS, Livestock and Forages Res. Lab., P.O. Box 1199, El Reno, OK 73036.

⁴ Texas A&M Res. and Ext. Center, 6500 Amarillo Blvd. West, Amarillo 79016.

⁵ Mention of a specific product or piece of equipment does not constitute an endorsement by the USDA or the Texas Agr. Exp. Sta. and does not imply their approval to the exclusion of other products that may be suitable.