Effects of diet type on nutrient utilization and energy balance in drylot heifers

Authors: BABER, J - Texas A&M University; WICKERSHAM, T - Texas A&M University; SAWYER, J - Texas A&M University; Freetly, Harvey; Brown-Brandl, Tami; Hales Paxton, Kristin

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2020
Publication Date: 1/13/2020
Citation: Baber, J.R., Wickersham, T.A., Sawyer, J.E., Freetly, H.C., Brown-Brandl, T.M., Hales, K.E. 2020. Effects of diet type on nutrient utilization and energy balance in drylot heifers. Journal of Animal Science. 98(1):1-8. https://doi.org/10.1093/jas/skaa006.
DOI: https://doi.org/10.1093/jas/skaa006

Interpretive Summary: Feeding cattle in intensified settings allows cow-calf producers to decrease their reliance on grazed forage and utilize alternative feedstuffs. During times of intense management, diet type may alter energy utilization. Fourteen pregnant heifers were used in an experiment to determine effects of diet type on nutrient and energy utilization. Heifers were randomly assigned to 1 of 2 treatments, a forage diet or a concentrate diet, and individually fed to meet energy requirements for maintenance and conceptus growth. Feeding concentrate-based rather than forage-based diets increased energy retained by the cattle, without changing body condition score. However, feeding the diets based on concentrate grain increased energy retention as fat and carbohydrate within the body. Thus, feeding heifers concentrate-based diets in a drylot should be used with caution if excessive fat deposition is a concern.

Technical Abstract: Feeding cattle in intensified settings allows cow-calf producers to decrease their reliance on grazed forage and utilize alternative feedstuffs. During times of intense management, diet type may alter energy utilization. Fourteen pregnant MARC III heifers (405 ± 44 kg BW) were used in a 180 d experiment to determine effects of diet type on nutrient and energy utilization. Heifers were randomly assigned to 1 of 2 treatments, a forage diet (FOR; 2.10 Mcal metabolizable energy [ME]/kg; 95.75% forage) or a concentrate diet (CONC; 2.94 Mcal ME/kg; 71% concentrate), and individually fed to meet maintenance energy requirements (0.135 Mcal ME/kg BW0.75). The CONC diet contained dry-rolled corn, corn stalks (10.16 cm grind size), soybean meal, corn silage (approximately 45% corn grain; stored in a plastic bag), dicalcium phosphate, urea, and a premix pellet; FOR contained alfalfa hay (harvested at mid-bloom), corn silage, dicalcium phosphate and a premix pellet. Measurements of energy intake and digestibility were measured over a 4-d period on d 116, 172 and 235 of gestation. Using portable headbox calorimeters, measurements of O2, CO2, and CH4 gases were collected over a period of 24 h. Data were analyzed in a completely randomized design with diet as fixed effect. Dry matter and organic matter digestibility were greater for CONC than FOR (P < 0.01). Intake of gross energy (GE) and digestible energy (DE) were greater for FOR (P < 0.01), but by design, ME intake was not different between treatments (P = 0.26). Energy lost as methane (% of GE intake) was not different between treatments (P = 0.49). The ratio of ME to DE was greater for CONC (86.8 vs 82.8; P = 0.01) than FOR. Heat production relative to ME was not different between treatments (P = 0.85). Maternal tissue energy did not differ and was 1.2 Mcal/d for CONC and 0.9 Mcal/d for FOR (P = 0.73). Greater nitrogen (N) consumption was observed for FOR (192.2 g/d) than CONC (134.0 g/d; P < 0.01), and retained N was greater for FOR than CONC (P < 0.01) on d 116 and 235 of gestation. Neither concentrate-based or forage-based diets affected body condition score (P = 0.26). Heifers fed concentrate-based diets retained more energy in part because they had larger calves, but this energy was not recovered in maternal tissue.