Metabolic imprinting in Nellore calves and its effects on physiological processes and quantitative and qualitative aspects of carcass and meat.

Abstract

Creep-feeding is a nutritional management used to provide food supplement to suckling calves in a private trough, which only allows calf access. Its purpose is to obtain heavier individuals at weaning, improve the carcass for slaughter, providing rest for the cow. In addition, it can be a determining factor in improving the calf's health and, consequently, animal welfare. Despite being a widespread technology with demonstrated effects on bovine performance, there are no studies that have evaluated the effect of creep-feeding on gene expression and metabolism in Nellore cattle, the most important genetic group of Brazilian beef herd. Thus, this study will aim to characterize and identify differences in expressed genes and proteins (transcriptome and proteome, respectively), biological processes and enriched metabolic pathways, as well as metabolite levels (metabolome), in the Longissimus thoracis muscle (LT) and/or or in the blood of non-supplemented Nellore calves or those supplemented with an energy and protein diet in the cow-calf phase (creep-feeding) and reared and finished on pasture in a intensively or extensively way. Ninety-six male Nelore calves, offspring of four different bulls, with approximately 60 days old, and with an initial body weight (BW) of 75 kg, will be used. The trial period will be divided into two phases: Phase 1 - cow-calf (240 days); Phase 2 - rearing and finishing (679 days), totaling 919 days. The design used will be completely randomized blocks in a 2x2 factorial scheme, with factor 1 being the type of supplementation in the suckling (mineral salt - MS vs. creep-feeding) and factor 2 nutritional strategies in rearing and finishing (intensive vs. extensive). The treatments will be: T1 or creep intensive - CI) calves on pasture receiving creep-feeding (5 g/kg BW) from day 60 to 240 (180 days) in Phase 1 and energetic protein supplement (10 g/kg BW) in Phase 2; T2 or creep extensive - CE) calves on pasture receiving creep-feeding (5 g/kg BW) from day 60 to 240 (180 days) in Phase 1 and protein supplement (1 g/kg BW) in the dry season, MS (ad libitum) in the rainy, protein supplement (1 g/kg BW) in the dry season and energetic protein supplement (3 g/kg BW) in autumn in Phase 2; T3 or without creep intensive - WI) calves on pasture receiving MS (ad libitum) from day 60 to 240 (180 days) in Phase 1 and energetic protein supplement (10 g/kg BW) in Phase 2; and T4 or without creep extensive - WE) calves on pasture receiving MS (ad libitum) from day 60 to 240 (180 days) in Phase 1 and protein supplement (1 g/kg BW) in the dry season, MS (ad libitum) in the rainy, protein supplement (1 g/kg BW) in the dry season and energetic protein supplement (3 g/kg BW) in the autumn in Phase 2. Weighings, carcass ultrasonography (US) and collection of muscle biopsies and blood samples will be carried out at the beginning of supplementation, at weaning and close to slaughter. In the US will be measured: rib eye area (REA); backfat thickness (BT); backfat thickness in the picanha; marbling score (MS); and ratio (ratio between width and length of the LT muscle). The collected tissues will be used for the quantification of biochemical markers related to energy metabolism and the stressor and immune systems, as well as for transcriptome (RNA-Seq) and proteome (Label-free LC-MS/MS shotgun) analyses. After slaughter, samples (steaks) will be collected from the LT between the 12th and 13th ribs of the left half-carcass, from which the following will be determined: REA, BT, MS, intramuscular fat content (IMF), mineral and fat acid profile, predominant type of muscle fiber, color, shear force at seven and 14 days of maturation (FC7 and FC14), water loss due to thawing and cooking, and water retention capacity. One of these samples will be used for the analysis of the metabolome, which will be performed using the nuclear magnetic resonance (NMR) technique. (AU)