Implications of nutritional strategies during gestation and pre- weaning for skeletal muscle composition in bovines

The productive traits of beef cattle can be defined by pre and post-natal environmental conditions. Different strategies have been used in beef cattle during gestation and pre- weaning to improve animal performance and meat quality. The intrauterine conditions modulate the skeletal muscle development and establish, at least partially, the postnatal body composition, influencing the final meat quality. Therefore, supplementation of nutrients during the fetal stages can improve the maternal metabolism to regulate the nutrient partitioning needed to supply the fetus and, consequently improve pos natal performance. In addition, supplementation of nutrients during the early weaning stage to about 250 d of age can be a strategy to specifically enhance intramuscular adipogenesis, resulting in adipocyte hypertrophy and high marbling. Thus, the current study was developed based on two experiments. The aim of the first study was to evaluate the impact of shifting urea release from rumen to the intestinal tract at late gestation on liver metabolism, and nutritional status of pregnant cows at late gestation. Twenty-four Brahman dams, pregnant from a single sire, and weighing 545 kg ± 23 kg were confined into individual pens at 174 ± 23 d of gestation, and randomly assigned into one of two dietary treatments up to 270 d of gestation: Control (CON, n = 12), consisting of a basal diet supplemented with conventional urea, where the cows were fed with diets containing 13.5 g conventional urea per kg dry matter; and PRU (PRU, n = 12), consisting of a basal diet supplemented with a urea coated to extensively prevent ruminal degradation while being intestinally digestible, where the cows were fed with diets containing 14,8 g urea protected from ruminal degradation per kg dry matter. Post-ruminal supply of urea reduced the urine levels of 3-methylhistidine (P = 0.02). There were no differences between treatments for dry matter intake (DMI; P = 0.76), total digestible nutrient (TDN) intake (P = 0.30), and in the body composition variables, such as, subcutaneous fat thickness (SFT; P = 0.72), and rib eye area (REA; P = 0.85). In addition, there were no differences between treatments for serum levels of glucose (P = 0.87), and serum levels of glucogenic (P = 0.28), ketogenic (P = 0.72), glucogenic, and ketogenic (P = 0.45) amino acids, neither for urea in urine (P = 0.51) as well as urea serum (P = 0.30). One the other hand, enriched pathways were differentiated related to carbohydrate digestion, and absorption, glycolysis, pyruvate metabolism, oxidative phosphorylation, pentose phosphate pathway, and biosynthesis of amino acids of the exclusively expressed proteins in PRU cows. Shifting urea supply from the rumen to post-ruminal compartments decreases muscle catabolism in cows during late gestation. Our findings indicate that postruminal urea supplementation for beef cows at late gestation may improve the energy metabolism to support maternal demands. In addition, the post-ruminal urea release seems to be able to trigger pathways to counterbalance the oxidative stress associated to the increase liver metabolic rate. The second study were developed to elucidate the impact of nutrient supplementation of beef female calves at pre-weaning (100–250 days of age) on intramuscular adipogenic determination. Thirty-four female calves were assigned to two experimental treatments: Control (CON, n = 17), where animals were supplemented only with mineral mixture; Supplemented (SUP, n = 17), where animals received energy-protein supplement containing minerals (5 g/kg of BW per day) of their body weight. Animals were supplemented from 100 to 250 days of age, and muscle samples were biopsied at the end of the supplementation period. Regarding the performance variables, there were no differences between treatments for initial body weight (P = 0.75). The final body weight (P = 0.07), average daily gain (P = 0.07), rib eye area (P = 0.03), and rib fat thickness (P = 0.08) were greater in SUP female calves compared with CON treatment. The number of fibro-adipogenic progenitor cells (P = 0.69) did not differ between treatments, while a greater number of intramuscular pre-adipocytes were observed in SUP than CON female calves (P = 0.01). The expression of miRNA-4429 (P = 0.20) did not differ between treatments, while the expression of miRNA-129-5p (P = 0.09) and miRNA-129-2-3p (P = 0.05) was greater in CON than SUP female calves. Our results suggest that nutrient supplementation at early postnatal stages of development enhances the commitment of fibro- adipogenic progenitor cells into the adipogenic lineages allowing to an increase in intramuscular fat deposition potential of the animals later in life. Altogether the results suggest that nutritional strategies during the fetal and pre-weaning stages improve maternal metabolism to maintain an adequate fetus’ development and enhance the number of pre-adipocytes in the skeletal muscle preparing intramuscular adipose tissue for fat deposition during the postweaning period. Keywords: Beef cattle. Creep feeding. Female calves. Marbling. Preadipocytes. Proteome. Skeletal Muscle.

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