PSII-6 Performance based NEm requirement adjustment for heifers fed during winter months in eastern South Dakota compared to the Texas panhandle

Abstract

Crossbred beef heifers [n = 96; initial shrunk BW=238 kg (SD 21.5)] were used in a completely randomized design to evaluate climatic effects on feedlot heifer growth and efficiency. The study was conducted from November 8, 1991 to May 11, 1992. Heifers were assembled into groups at the Ruminant Nutrition Center (RNC) in Brookings, SD. One group (TX; n = 48) was shipped to New Deal, Texas and fed on slatted-concrete floors, and the second group (SD; n = 48), was shipped half-way to Texas, returned to the RNC, and fed on solid-concrete floors. Transit distance was 1,530 km. Pen was the experimental unit (6 to 8 head·pen-1); diets, health management, and implant programs were normalized across locations. The finishing diet was fed from d 33 to 185 at both locations and the energetics assessment was for the period from d 60 to 185. There were 18 d below -7.8°C and 102 d below 5°C in SD. Transit shrink, estimated empty body fat % (EBF), BW adjusted to 28% EBF (AFBW), and DMI did not differ (P ≥ 0.10). Heifer ADG was 18% greater (P < 0.05) in TX (1.40 vs. 1.16 ± 0.037 kg). Observed vs. predicted dietary energy differed (P ≤ 0.05), for NEm (0.97 vs. 0.87 ± 0.013) and NEg (0.97 vs. 0.84 ± 0.016) for TX and SD, respectively. Using calculated diet energy values based upon TX heifer performance as a reference, relative adjustments to metabolic rate were calculated. The estimated metabolic rate was elevated (P < 0.05) for SD heifers (0.077 vs. 0.101 ± 0.0031 Mcal/MBS). These results indicate that heifers fed in South Dakota had a 31% increase in metabolic rate when compared to heifers fed in the Texas panhandle. More of these types of assessments are needed to improve projection and tracking models used in precision cattle feeding.