Growth curves of carcass traits obtained by ultrasonography in three lines of Nellore cattle selected for body weight

Effects of different maternal nutrition approaches on weight gain and on adipose and muscle tissue development of young bulls in the rearing phase

This study evaluated the effects of prenatal nutrition on body weight (BW), average daily gain (ADG), rump fat thickness (RFT), backfat thickness (BFT), ribeye area (REA), muscle cell area (MCA), and the number of cells in REA (NCREA) of young Nellore bulls during the rearing period. After pregnancy confirmation (30 days of pregnancy), 126 Nellore cows were separated into three prenatal nutritional treatments (NP (control; 0.03% of BW), only mineral supplementation; PP (0.3% of BW), protein-energy supplementation in the final third; and FP (0.3% of BW) protein-energy supplementation during the entire pregnancy). After calving, all animals were submitted to the same environmental conditions (sanitary and nutritional) and the different supplementation protocols ceased. The males (63 bulls) were evaluated during the entire rearing phase (210 ± 28 days to 540 ± 28 days of age) to weight gain (BW and ADG), carcass characteristics (RFT, BFT, and REA), and for histological assessments (MCA and NCREA; 7 animals per treatment randomly selected). All phenotypes were subjected to an analysis of variance. The different prenatal stimuli had no effect on BFT, RFT, MCA, and NCREA (P > 0.05); however, prenatal nutrition influenced BW of the animals during the rearing phase (P < 0.01) and showed a tendency on ADG (P = 0.09) and REA (P = 0.08). In conclusion, the offspring from FP treatment showed greater BW during the rearing phase in comparison to the NP group. This is related to a greater protein offered in prenatal nutrition, increasing muscle development during the gestational period.

Genetic association among feeding behavior, feed efficiency, and growth traits in growing indicine cattle

This study aimed to estimate genetic parameters, including genomic data, for feeding behavior, feed efficiency, and growth traits in Nellore cattle. The following feeding behavior traits were studied (861 animals with records): time spent at the feed bunk (TF), duration of one feeding event (FD), frequency of visits to the bunk (FF), feeding rate (FR), and dry matter intake (DMI) per visit (DMIv). The feed efficiency traits (1,543 animals with records) included residual feed intake (RFI), residual weight gain (RWG), and feed conversion (FC). The growth traits studied were average daily gain (ADG, n = 1,543 animals) and selection (postweaning) weight (WSel, n = 9,549 animals). The (co)variance components were estimated by the maximum restricted likelihood method, fitting animal models that did (single-step genomic best linear unbiased prediction) or did not include (best linear unbiased prediction) genomic information in two-trait analyses. The direct responses to selection were calculated for the feed efficiency traits, ADG, and WSel, as well as the correlated responses in feed efficiency and growth by direct selection for shorter TF. The estimated heritabilities were 0.51 ± 0.06, 0.35 ± 0.06, 0.27 ± 0.07, 0.34 ± 0.06, and 0.33 ± 0.06 for TF, FD, FF, FR, and DMIv, respectively. In general, TF and FD showed positive genetic correlations with all feed efficiency traits (RFI, RWG, and FC), ADG, DMI, and WSel. Additionally, TF showed high and positive genetic and phenotypic correlations with RFI (0.71 ± 0.10 and 0.46 ± 0.02, respectively) and DMI (0.56 ± 0.09 and 0.48 ± 0.03), and medium to weak genetic correlations with growth (0.32 ± 0.11 with ADG and 0.14 ± 0.09 with WSel). The results suggest that TF is a strong indicator trait of feed efficiency, which exhibits high heritability and a weak positive genetic correlation with growth. In a context of a selection index, the inclusion of TF to select animals for shorter TF may accelerate the genetic gain in feed efficiency by reducing RFI but with zero or slightly negative genetic gain in growth traits.

The phenotypic relationship between residual intake and gain and other feed efficiency traits in Nellore cattle

This study aimed to compare feed efficiency measures of Nellore beef cattle on different residual intake and gain (RIG) classes. We used data from 610 animals weighing on average 236.33 kg and average of 283 days of age from feedlot performance tests carried out between 2005 and 2012. Animals were grouped based on RIG into three different classes: high RIG (> mean + 0.5 standard deviation (SD), most efficient; n = 193), medium RIG (mean ± 0.5 SD; n = 235), and low RIG (< mean - 0.5 SD, least efficient; n = 182). Residual feed intake (RFI), residual gain (RG), feed conversion ratio (FCR), feed efficiency (FE), relative growth rate (RGR), and Kleiber ratio (KR) of animals in each RIG class were compared by Tukey test at 1% of probability. Phenotypic correlations between variables were evaluated as well. Animals on high RIG class showed lower dry matter intake (P < 0.01) and higher average daily gain (P < 0.01) than low RIG animals. Consequently, high RIG animals had lower FCR (P < 0.01) and higher FE (P < 0.01) than those animals in low RIG class. The most efficient animals based on RIG were also the most efficient animals based on RG and RFI. RIG was negatively correlated to dry matter intake (P < 0.01) and FCR (P < 0.01), and a positive correlation was found between RIG and FE (P < 0.01). Therefore, RIG appears to be a good parameter to select animals with reduced dry matter intake and high productive performance.

Phenotypic and Genetic Correlations of Feed Efficiency Traits with Growth and Carcass Traits in Nellore Cattle Selected for Postweaning Weight

This study evaluated phenotypic (r_ph) and genetic correlations (r_g) between 8 feed efficiency traits and other traits of economic interest including weight at selection (WS), loin-eye area (LEA), backfat thickness (BF), and rump fat thickness (RF) in Nellore cattle. Feed efficiency traits were gain:feed, residual feed intake (RFI), residual feed intake adjusted for backfat thickness (RFI_b) and for backfat and rump fat thickness (RFI_sf), residual body weight gain (RG), residual intake and body weight gain (RIG), and residual intake and body weight gain using RFI_b (RIG_b) and RFI_sf (RIG_sf). The variance components were estimated by the restricted maximum likelihood method using a two-trait animal model. The heritability estimates (h²) were 0.14, 0.24, 0.20, 0.22, 0.19, 0.15, 0.11 and 0.11 for gain:feed, RFI, RFI_b, RFI_sf, RG, RIG, RIG_b and RIG_sf, respectively. All r_ph values between traits were close to zero, except for the correlation of feed efficiency traits with dry matter intake and average daily gain. High r_g values were observed for the correlation of dry matter intake, average daily gain and metabolic weight with WS and hip height (>0.61) and low to medium values (0.15 to 0.48) with the carcass traits (LEA, BF, RF). Among the feed efficiency traits, RG showed the highest r_g with WS and hip height (0.34 and 0.25) and the lowest r_g with subcutaneous fat thickness (-0.17 to 0.18). The r_g values of RFI, RFI_b and RFI_sf with WS (0.17, 0.23 and 0.22), BF (0.37, 0.33 and 0.33) and RF (0.30, 0.31 and 0.32) were unfavorable. The r_g values of gain:feed, RIG, RIG_b and RIG_sf with WS were low and favorable (0.07 to 0.22), while medium and unfavorable (-0.22 to -0.45) correlations were observed with fat thickness. The inclusion of subcutaneous fat thickness in the models used to calculate RFI did not reduce the r_g between these traits. Selecting animals for higher feed efficiency will result in little or no genetic change in growth and will decrease subcutaneous fat thickness in the carcass.