Impacts of providing a protein/energy supplement to mid-gestation beef heifers grazing fall native range pastures

• Grant number: 24/20430-4
• Support Opportunities: Scholarships abroad - Research Internship - Scientific Initiation
• Start date: March 09, 2025
• End date: July 08, 2025
• Field of knowledge: Agronomical Sciences - Animal Husbandry - Animal Production
• Principal Investigator: Miguel Henrique de Almeida Santana
• Grantee: Antonio Rodrigues Ferreira Braga
• Supervisor: Carl Robertson Dahlen
• Host Institution: Faculdade de Zootecnia e Engenharia de Alimentos (FZEA). Universidade de São Paulo (USP). Pirassununga , SP, Brazil
• Institution abroad: North Dakota State University (NDSU), United States
• Associated to the scholarship: 24/10252-1 - Different supplementation strategies during rearing and their effects on the development of the reproductive tract and the response to puberty induction in Nelore heifers, BP.IC

Abstract

First calf-heifers require greater dietary energy during pregnancy compared with mature cows because of the nutritional demands for pregnancy maintenance, fetal growth and development, lactation, and continued growth of the pregnant heifer. In scenarios where forage availability is limited, providing energy in the form of corn or corn byproducts on low-quality range can aid in enhancing animal performance, optimizing forage utilization, and bridging the gap for the increasing nutritional demands of the pregnant female. The goal of this project is to determine the impacts of providing supplemental protein/energy during mid-gestation on fall pasture on hormone/metabolite profiles of the dam and on the calf being gestated. Formulating strategies aimed at maximizing animal performance and enhancing forage digestibility in pregnant beef heifers, with a particular focus on translating effects to the offspring. For the experiment, Angus-based heifers (n = 120, 13 to 14 months of age) were selected in May of 2024. Heifers were bred to sexed male semen from a single sire and managed on a single pasture through the first trimester of pregnancy (89 ± 5 days), at which point heifers were moved to a single, stockpiled forage pasture until the end of the second trimester of pregnancy (180 ± 5 days). At 89 ± 5 days of pregnancy, heifers pregnant with female fetuses were assigned to receive 1 of 2 dietary treatments: (1) full access to grazing on fall pasture (Control, n = 25), or (2) full grazing access plus a protein/energy supplement delivered to target gains of 0.45 kg/hd/day (Supplement, n = 25). Heifers will remain on their respective treatments until 180 ± 5 days of pregnancy, at which point all heifers will be managed on a common diet in preparation for calving. Blood samples were collected from heifers at breeding, day 89, and will be collected at day 135, day180, at calving, from calves at birth and at pasture turnout to be analyzed for hormone and metabolite responses to treatments (Nonesterified fatty acid - NEFA, Blood Urea Nitrogen - BUN, glucose, insulin, and insulin-like growth factor 1 - IGF-1). These samples are integral for evaluating the metabolic and endocrine environments of the dam and calf. This effort stands to elevate overall herd performance, profitability, and success of beef herds.