Effects of feeding monensin to bred heifers fed in a drylot on nutrient and energy balance

Authors: HEMPHILL, COURTNEY - Texas A&M University; WICKERSHAM, TRYON - Texas A&M University; SAWYER, JASON - Texas A&M University; Brown-Brandl, Tami; Freetly, Harvey; Hales Paxton, Kristin

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/21/2017
Publication Date: 4/3/2018
Publication URL: https://handle.nal.usda.gov/10113/6472204
Citation: Hemphill, C.N., Wickersham, T.A., Sawyer, J.E., Brown-Brandl, T.M., Freetly, H.C., Hales, K.E. 2018. Effects of feeding monensin to bred heifers fed in a drylot on nutrient and energy balance. Journal of Animal Science. 96(3):1171-1180. https://doi.org/10.1093/jas/skx030.

Interpretive Summary: The objective of this study was to determine if feeding monensin would improve diet digestion, energy and nutrient balance in bred heifers receiving a limit-fed corn stalk-based diet. Sixteen pregnant heifers were used in a 161 day study. Heifers were randomly assigned to 1 of 2 treatments, no monensin or 150 miligrams of monensin each day. Dry matter intake was not different across treatments and increased to account for increasing fetal growth requirements. Dry matter, organic matter, and fiber digestion did not differ between treatments. No differences in gross energy intake were observed between the treatments, and digestible energy and metabolizable energy intakes were also not affected by monensin inclusion. Fecal, methane, urinary and heat energy losses were not different between treatments. Heifers fed monensin did produce 7% less methane per day when expressed as liters of methane produced on a metabolic body weight basis. Monensin had no effect on energy retained by the heifers. Thus, the use of monensin for heifers fed in drylot did not improve digestibility, nutrient, or energy balance.

Technical Abstract: The objective of this study was to determine if feeding monensin would improve diet digestion, energy and nitrogen balance in bred heifers receiving a limit-fed corn stalk-based diet. Sixteen pregnant Meat Animal Research Center (MARC) III composite heifers were used in a 161 d completely randomized design. Heifers were randomly assigned to 1 of 2 treatments, no monensin (CON) or 150 mg/d monensin (MON), with 8 heifers in each treatment group. Heifers were limit-fed a corn stalk-based diet at 100% of MEm requirements. Effects of monensin on energy and nitrogen balance were determined via total fecal and urine collections and open-circuit respiration calorimetry. Total fecal and urine collection occurred on d 14, 42, and 161 of monensin feeding, and calorimetry measurements were made on d 0, 3, 14, 28, 42, and 161 of monensin feeding. Dry matter intake was not different (P = 0.94) for CON and MON heifers and, by design, increased (P < 0.01) from d 14 to d 161 of the trial to account for increasing fetal growth requirements. No differences (P = 0.91) in GE intake were observed between CON and MON heifers, and DE and ME intakes did not differ (P > 0.58) with monensin inclusion. Dry matter, OM, NDF, and ADF digestion did not differ (P > 0.52) between treatments. Fecal, methane, urinary and heat energy losses were not different (P > 0.16) for MON and CON heifers. Methane production was not different between treatments when expressed as daily liters of methane (P = 0.40); however, MON heifers produced 7% less (P = 0.03) methane per day than CON heifers when expressed as liters of methane produced on a metabolic body weight basis. Furthermore, monensin had no effect (P = 0.36) on overall RE. Nitrogen intake and excretion was not different (P > 0.13) between treatment groups. Results of this experiment indicate that adding monensin to limit-fed, corn stalk-based diets may not have a large effect on the energy and nitrogen balance of confined heifers.