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Microbial population and ruminal fermentation patterns differ according residual feed intake (RFI) classes, with possible alterations in biohydrogenation and consequently in fatty acids (FA) profile of subcutaneous fat deposition. This study aimed to evaluate FA profile of subcutaneous fat deposition in Nellore bulls classified by RFI. Data from four different trials, totaling 106 Nellore bulls (475.5 ± 77 kg of slaughter BW and 623 ± 97 d of age at slaughter), previously classified by RFI as positive (PRFI) or negative (NRFI), were used. Fatty acids profile was determined in Longissimus muscle with fat cover samples, collected immediately after boning, vacuum packed and frozen until analysis. Data were analyzed using SAS MIXED procedure, including in the model as fixed effects RFI class and age at slaughter as covariate and as random effects feeding type within trial and year of trial. Least square means were compared by the t-test, being significance determined at P ≤ 0.05 and trends at 0.05 < P ≤ 0.10. Significant difference between RFI classes was only detected for cis-vaccenic FA (C8:1 n7) (2.45 vs 2.29 g/100g; P = 0.049) and tendency for oleic FA (C18:1 n9) (34.9 vs 36.3 g/100g; P = 0.092), for PRFI and NRFI respectively. The sum of total saturated (43.4 g/ 100g), monounsaturated, and polyunsaturated (12.8 g/100g) FA, revealed a significant difference between RFI classes only for total monounsaturated FA (43.2 vs 44.8 g/100g; P = 0.046) for PRFI and NRFI respectively. This difference can be due the tendency detected between RFI classes for oleic FA, which is the monounsaturated FA in the highest concentration in the profile. Monounsaturated FA are essential in human diet because they can contribute to reduced blood cholesterol and triglyceride levels, exerting cardiovascular protection. In conclusion, NRFI Nellore animals have a better FA profile of subcutaneous fat deposition.

ContextThe body condition score (BCS) is an easily measured, fast, inexpensive, and non-invasive tool to estimate the amount of body fat and to evaluate the nutritional status of dairy cows.AimsThe aim of this study was to validate BCS in primiparous Gyr cows by using ultrasound measurements of subcutaneous fat (FT).MethodsBody weight, BCS (score of 1–9) and FT measured at five body sites (FT1–FT5) were recorded during the prepartum and postpartum periods. Linear regression of FT on BCS and Pearson’s correlations were used.Key resultsThe correlations between body weight and FT measures ranged from 0.49 to 0.63 and from 0.51 to 0.64 during the pre- and postpartum periods respectively, while the correlations between BCS and FT ranged from 0.69 to 0.82 and from 0.67 to 0.78 in the two periods. The BCS better reflected the variation in FT before and after calving than did body weight. Linear regression models were used to explore the relationship between BCS and FT measurements considering the former as the predictor variable. The coefficients of determination (R2) obtained for the prepartum variables ranged from 0.48 to 0.67. The highest R2 was obtained for the model that included FT measured in the lumbar region midway between the last rib and tuber coxae (hook; FT4) as the response variable. The R2 of the models whose response variables were obtained during the postpartum period ranged from 0.45 to 0.60. The highest R2 was observed when the pelvic region midway between the tuber coxae (hook) and tuber ischii (pin; FT2) was used as a response variable.ConclusionsThe correlations between BCS and FT validate the use of BCS obtained by visual assessment as a tool for evaluating fat reserves in Gyr dams before calving and during first lactation. Among the FT measurements, FT2 and FT4 are interesting because both are easy to measure and showed higher correlations and coefficients of determination with BCS before calving and lactation.ImplicationsThe BCS is an accessible tool for producers that requires only training of the evaluator and that is economically viable since no special equipment is needed.

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This study aimed to evaluate relationships among maternal residual feed intake (RFI) with growth performance and expression of genes involved in lipid metabolism in offspring of Nellore cattle. Fifty-three cows classified as negative or positive RFI by genomic prediction were exposed to fixed-time artificial insemination (FTAI) protocols at 2 and 3 years of age using semen from the same bull. In the first year, cows gestated under grazing conditions and nursed their calves in the feedlot. In the second year, the opposite occurred. Cows were weighed every 28 days during pregnancy and calves were weighed at birth and every 28 days until weaning. Ultrasound images were collected from the carcass of cows and calves. Muscle gene expression was evaluated in calves at birth and weaning. Data were analyzed by year considering the fixed effects of RFI class and FTAI protocol for variables measured in cows, and RFI class, FTAI protocol and sex for variables measured in calves. There was no effect of maternal RFI on calves performance in the first year. Lower expression of FABP4 gene and trend towards lower expression of SREBF1 and LPL genes were detected in samples collected after birth from calves born to negative RFI cows, indicating that adipogenesis was reduced during the fetal and neonatal period. In the second year, negative RFI cows had greater subcutaneous fat thickness than positive RFI cows, and their calves tended to be heavier at birth and to have less rump fat thickness at weaning. No significant differences in expression of genes studied were detected between cow RFI classes. Nellore cows classified as negative RFI consume less feed and produce calves whose growth potential is similar to that of calves produced by positive RFI cows.