Consistency of feed efficiency ranking and mechanisms associated with inter-animal variation among growing calves

Compilations and updates on residual feed intake in sheep

The increasing global demand for food and the strong effect of climate change have forced animal science to advance regarding new methods of selection in search of more efficient animals in production systems. Feed consumption represents more than 70% of the costs of sheep farms, and more efficient animals can increase the farmers' profitability. One of the main measures of feed efficiency is estimated residual feed intake (RFI), created in 1963 by Robert Koch for estimation in cattle and later adapted for sheep. Animals with negative RFI values (RFI-) are more efficient than animals with positive values (RFI+), with influence on the variables of performance, carcass quality and production of enteric gases. The RFI is the most common and accepted metric of the feed efficiency trait for genetic selection, since it is independent of growth traits, unlike the feed conversion ratio. The purpose of this review article was to present updated literature information on the relationship of RFI estimates with performance measures, molecular markers, greenhouse gas production and feed efficiency, the technical aspects and physiological basis of metabolic in sheep.

Estimating the heritability of nitrogen and carbon isotopes in the tail hair of beef cattle

BACKGROUND

The natural abundance of nitrogen (δ15N) and carbon (δ13C) isotopes in animal tissues are used to estimate an animal's efficiency in nitrogen utilization, and their feed conversion efficiency, especially in tropical grazing systems with prolonged protein restriction. It is postulated that selection for improving these two characteristics (δ15N and δ13C) would assist the optimisation of the adaptation in ever-changing environments, particularly in response to climate change. The aim of this study was to determine the heritability of δ15N and δ13C in the tail hair of tropically adapted beef cattle to validate their inclusion in genetic breeding programs.

METHODS

In total, 492 steers from two breeds, Brahman (n = 268) and Droughtmaster (n = 224) were used in this study. These steers were managed in two mixed breed contemporary groups across two years (year of weaning): steers weaned in 2019 (n = 250) and 2020 (n = 242). Samples of tail switch hair representing hair segments grown during the dry season were collected and analysed for δ15N and δ13C with isotope-ratio mass spectrometry. Heritability and variance components were estimated in a univariate multibreed (and single breed) animal model in WOMBAT and ASReml using three generations of full pedigree.

RESULTS

The estimated heritability of both traits was significantly different from 0, i.e. 0.43 ± 0.14 and 0.41 ± 0.15 for δ15N and δ13C, respectively. These traits had favourable moderate to high genetic and phenotypic correlations (- 0.78 ± 0.16 and - 0.40 ± 0.04, respectively). The study also provides informative single-breed results in spite of the limited sample size, with estimated heritability values of 0.37 ± 0.19 and 0.19 ± 0.17 for δ15N and δ13C in Brahman, and 0.36 ± 0.21 and 0.46 ± 0.22 for δ15N and δ13C in Droughtmaster, respectively.

CONCLUSIONS

The findings of this study show, for the first time, that the natural abundances of both nitrogen and carbon isotopes in the tail hair in cattle may be moderately heritable. With further research and validation, tail hair isotopes can become a practical tool for the large-scale selection of more efficient cattle.

Factors important for bull purchasing decisions and management in extensive rangeland production systems of New Mexico: a producer survey

There were 463,000 head of beef cows in New Mexico as of January 1, 2021 (NASS, 2020), down roughly 4% from 2020 (NASS, 2019). Frequent drought often results in herd reduction and loss of valuable genetic progress. Bull selection is critical due to their influence on herd development. A survey was conducted to identify traits important to bull selection in New Mexico. Surveys were collected digitally (n = 83) and via the mail (n = 74). Responses were largely by cow/calf producers averaging 57 ± 1 years old with 24 ± 1 years' experience. Survey respondents represented 4,384,296 acres of private owned, private leased, and leased public rangeland and irrigated pasture meadow in New Mexico and surrounding states. Average cow/calf operation size was 294 ± 39 head and average bull herd size was 21 ± 3 head. Average price paid for a bull in the past 2 years was $3,981 ± 213. Physical characteristics, individual bull performance information, and genetic information are all important traits to New Mexico bull buyers; however, most producers (56%) indicated that structural soundness was the most important factor influencing their selection decisions. Amongst expected progeny differences (EPDs), New Mexico producers consider the calving ease direct (CED) and birth weight (BW) EPDS to be most important (40% and 35%, respectively). Producers also indicated that multitrait selection indexes used by the American Angus Association were important to their selection decisions, with the beef value ($B) and weaned calf value ($W) indexes being cited most often (35% and 31%, respectively). Elements important to bull purchase include the bull's sale preview (87%), body condition score (86%), feed efficiency/average daily gain information (85%), and actual scrotal circumference (82%). Following purchase of a new bull, most (60%) keep the bull separate from the cow herd until the following breeding season, while the remaining 40% of producers turn newly purchased bulls out within 30 days of purchase. Sixty eight percent of producers evaluate semen quality annually or prior to the start of the breeding season. Interestingly, 39% of producers indicated they used reproductive technologies like artificial insemination and synchronization of estrus while most (80%) test for trichomoniasis. The primary factor influencing culling decisions is age, followed by soundness and fertility.

CNV detection and their association with growth, efficiency and carcass traits in Santa Inês sheep

Copy number variations (CNV) are an important source of genetic variation. CNV has been increasingly studied and frequently associated with diseases and productive traits in livestock animals. However, CNV-based genome-wide association studies (GWAS) in Santa Inês sheep, one of the principal sheep breeds in Brazil, have not yet been reported. Thus, the aim of this study was to investigate the association between CNV and growth, efficiency and carcass traits in sheep. The Illumina OvineSNP50 BeadChip array was used to detect CNV in 491 Santa Inês individuals. Then, CNV-based GWAS was performed with a linear mixed model approach considering a genomic relationship matrix, for ten traits: (1) growth: body weight at three (W3) and six (W6) months of age; (2) efficiency: residual feed intake (RFI) and feed efficiency (FE) and (3) carcass: external carcass length (ECL), leg length (LL), carcass yield (CY), commercial cuts weight (CCW), loin eye area (LEA) and subcutaneous fat thickness (SFT). We identified 1,167 autosomal CNV in 438 sheep, with 294 non-redundant CNV, ranging from 21.8 to 861.9 kb, merged into 216 distinct copy number variation regions (CNVRs). One significant CNV segment (p_FDR -value<0.05) in OAR3 was associated with CY, while another significant CNV in OAR6 was associated with RFI. Additionally, another 5 CNV segments were considered relevant for investigation in the future studies. The significant segments overlapped 4 QTLs and spanned 8 genes, including the SPAST, TGFA and ADGRL3 genes, involved in cell differentiation and energy metabolism. Therefore, the results of the present study increase knowledge about CNV in sheep, their possible impacts on productive traits, and provide information for future investigations, being especially useful for those interested in structural variations in the sheep genome.

Relationships among feed efficiency traits across production segments and production cycles in cattle

Understanding the relationships between feed efficiency traits measured in different stages of production is necessary to improve feed efficiency across the beef value chain. The objective of this study was to evaluate relationships among feed efficiency traits measured as growing heifers and breeding females and in their progeny in three full production cycles, and relationships of dam residual feed intake (RFI) with lifetime and lifecycle cow efficiency traits. Data were collected on 160 mixed-breed heifers from 240 d of age to weaning of their third progeny, and postweaning performance of progeny until harvest in experiments initiated in 1953, 1954, 1959, 1964, 1969, and 1974. Individual feed offered was recorded daily, and feed refusals measured every 28 d. Milk yield was measured at 14-d intervals throughout lactation by machine or hand milking. Females and progeny were weighed at 28-d intervals and progeny were harvested at a constant endpoint of live grade or age depending upon the experiment. Feed efficiency traits of RFI and residual BW gain (RG) were computed as the residual from linear regression for developing heifers, dams (RFI and residual energy-corrected milk [RECM]), and postweaning progeny. Feed:gain ratio (FCR) was computed for developing heifers and postweaning progeny, and feed:milk energy ratio (FME) was computed for dams. Various measures of cow efficiency were calculated on either a life cycle or lifetime basis using ratios of progeny and dam weight outputs to progeny and dam feed inputs. Pearson correlations were computed among traits adjusted for a random year-breed-diet group effect. Heifer RFI (0.74) and RG (-0.32) were correlated (P ≤ 0.05) with dam RFI in parity 1 only, but were not correlated (P > 0.05) with dam RECM in any parity. Heifer RFI was correlated (P ≤ 0.05) with progeny RFI (0.17) in parity 3 only. Heifer FCR was not correlated with dam FME or progeny FCR in any parity. Dam RFI was weakly correlated (r = 0.25 to 0.36; P ≤ 0.05) among parities, whereas dam FME and RECM were strongly correlated (r = 0.49 to 0.72; P ≤ 0.05) among parities. Dam RFI in parity 1 and 2 was weakly correlated (r = -0.20 to -0.33; P ≤ 0.05) with cow efficiency ratios that included dam weight as an output, whereas dam RFI in parity 3 was not correlated with any cow efficiency ratio. In conclusion, feed efficiency traits were poorly correlated across production segments, but moderately repeatable across production cycles.

Animals selected for postweaning weight gain rate have similar maintenance energy requirements regardless of their residual feed intake classification

Data of comparative slaughter were used to determine Nellore bulls' net energy requirements classified as efficient or inefficient according to residual feed intake (RFI) and selection lines (SL). Sixty-seven Nellore bulls from the selected (SE) and control (CO) lines of the selection program for postweaning weight gain were used. The animals underwent digestibility trials before being submitted to the finishing trial. Sixteen bulls were slaughtered at the beginning of the finishing trial, and their body composition was used as the baseline for the remaining animals. For body composition determinations, whole empty body components were weighed, ground, and subsampled for chemical analyses. Initial body composition was determined with equations developed from the baseline group using shrunk body weight, fat, and protein. The low RFI (LRFI) and CO animals had a lower dry matter (DMI) and nutrient intake (P < 0.05) than high RFI (HRFI) and SE animals, without alterations in digestibility coefficients (P > 0.05). During the finishing trial, DMI remained lower for LRFI and CO animals. Growth performance was similar between RFI classes, except for empty body weight gain that tended to be higher for LRFI than HRFI (P = 0.091). The SE animals had less fat content on the empty body (P = 0.005) than CO. Carcasses tended to be leaner for LRFI than HRFI (P = 0.080) and for SE than CO (P = 0.066) animals. LRFI animals retained more energy (P = 0.049) and had lower heat production (HP; P = 0.033) than the HRFI ones. Retained energy was not influenced by SL (P = 0.165), but HP tended to be higher for SE when compared to CO (P = 0.075) animals. Net energy requirement for maintenance (NEm) was lower for LRFI than HRFI (P = 0.009), and higher for SE than CO (P = 0.046) animals. There was an interaction tendency between RFI and SL (P = 0.063), suggesting that NEm was lower for LRFI+CO than HRFI+CO (P = 0.006), with no differences for SE (P = 0.527) animals. The efficiency of ME utilization for maintenance (km) of LRFI and HRFI animals were 62.6% and 58.4%, respectively, and for SE and CO were 59.0% and 62.1%, respectively. The breeding program for postweaning weight has not improved feed efficiency over the years, with RFI classification not being a promising selection tool for SE animals. Classification based on RFI seems to be useful in animals that have not undergone the breeding program, with LRFI animals having lower energy requirements than the HRFI ones.

Characterization of feeding behavior traits in steers with divergent residual feed intake consuming a high-concentrate diet

The objective of this study was to examine the differences in feeding behavior patterns of steers with divergent phenotypes for residual feed intake (RFI). Three trials were conducted with 508 Angus-based composite crossbred steers (body weight [BW] = 309 ± 57 kg) fed a high-concentrate diet in pens equipped with electronic feed bunks (GrowSafe System). Initial and final carcass ultrasound measurements (intra-muscular fat, backfat depth, and rib-eye area) were collected on days 0 and 70, and BW measured at 14-d intervals. Individual dry matter intake (DMI) and feeding behavior traits were collected for 70 d, and RFI calculated as the residual from the regression of DMI on average daily gain (ADG) and mid-test BW0.75. Steers were ranked by RFI and assigned to low-, medium-, and high-RFI classes based on ± 0.5 SD from the mean RFI within the trial. The feeding behavior traits evaluated in this study included frequency and duration of bunk visit (BV) and meal events, head-down (HD) duration, mean meal length, time-to-bunk interval, the maximum nonfeeding interval, and the day-to-day variation of these traits, defined as the root mean squared error (RMSE) from linear regression of each trait on the day of trial. Additionally, three ratio traits were evaluated: BV events per meal, HD duration per BV event, and HD duration per meal event. Low-RFI (feed-efficient) steers consumed 16% less (P < 0.01) DMI, while BW and ADG were not different compared with high-RFI steers. Low-RFI steers had 18% fewer and 21% shorter (P < 0.01) BV events, and 11% fewer and 13% shorter (P < 0.01) meal events per day compared with high-RFI steers. Furthermore, low-RFI steers exhibited less (P < 0.05) day-to-day variance in DMI, as well as in frequency and duration of BV and meal events and HD duration compared with high-RFI steers. Differences in feeding behavior traits due to RFI were minimally affected by covariate adjustment for DMI, indicating that steers with divergent RFI have distinct feeding behavior patterns that are largely independent of differences in DMI. These results suggest that feeding behavior traits may be useful biomarkers for the prediction of feed efficiency in beef cattle.

Effect of divergence in residual feed intake on expression of lipid metabolism-related genes in the liver of meat-type ducks1

Lipid metabolism is considered one of the important factors affecting residual feed intake (RFI). However, the relationship between RFI and expression of lipid metabolism-related genes is unknown in meat-type ducks. To address this issue, a total of 1,000 male meat-type ducks with similar body weight were randomly selected to measure body weight gain and feed intake from 21 to 42 d of age to estimate RFI. The 8 greatest- (high RFI [HRFI]) and lowest- (low RFI [LRFI]) ranking birds were then selected for the present study. Relative expressions of key genes, namely sirtuin 1 (Sirt1), forkhead box O1 (Foxo1), peroxisome proliferator-activated receptor gamma (PPARγ), sterol regulatory element-binding transcription factor 1c (SREBP-1c), fas cell surface death receptor (FAS), acetyl-CoA carboxylase alpha (ACC), carnitine palmitoyltransferase 1A (CPT1A), and acyl-CoA oxidase 1 (ACOX1), were then determined in the HRFI and LRFI ducks by quantitative PCR. The results showed that RFI, feed conversion ratio (FCR), and average daily feed intake (ADFI) were significantly lower (P < 0.05) in LRFI ducks than in HRFI ducks. In addition, expression of Sirt1, Foxo1, CPT1A, and ACOX1 were significantly higher in LRFI ducks than in HRFI ducks (P < 0.05), whereas PPARγ and FAS expression levels were significantly lower in LRFI ducks than in HRFI ducks (P < 0.01). Correlation analysis showed that Sirt1, CPT1A, and ACOX1 expressions were significantly negatively correlated with FCR (r = -0.81 to -0.93; P < 0.01), whereas PPARγ and FAS expressions were significantly positively correlated with FCR (r = 0.74 to 0.87; P < 0.01). PPARγ expression was significantly positively correlated with RFI (r = 0.83; P < 0.01), whereas CPT1A and ACOX1 expressions were significantly negatively correlated with RFI (r = -0.84 to -0.89; P < 0.01). Sirt1 mRNA expression was positively correlated with Foxo1, CPT1A, and ACOX1 mRNA expression (r = 0.78 to 0.92; P < 0.01). Association of Foxo1 with CPT1A and ACOX1 was positive (r = 0.88 to 0.96; P < 0.01). These results suggest that genes related to fatty acid oxidation are upregulated in the liver of ducks with high feed efficiency, while genes associated with lipid synthesis are downregulated. Furthermore, the inclusion of lipid metabolism-related genes in future breeding programs might be beneficial for selecting ducks with greater feed efficiency phenotype.

FABP4 gene has a very large effect on feed efficiency in lactating Israeli Holstein cows

Improving feed efficiency (FE) is a major goal for the livestock industry. Previously, we have identified 48 SNP markers distributed over 32 genes significantly associated with residual feed intake (RFI) in Israeli Holstein male calves, the most significant of which are located in the bovine FABP4 gene. In the present study, we tested associations of eight of the FABP4 markers with RFI and feed conversion ratio (FCR), along with milk composition and feeding behavioral traits, in 114 lactating Israeli Holstein cows. Large allele effects were found, along with large contributions of FABP4 markers to the phenotypic variation [mean contribution of all significant markers (P < 0.05), 15.4 and 12.0% for RFI and FCR, respectively] and genotypic variation [means of all significant markers (P < 0.05), 75.7 and 32.4% in RFI and FCR, respectively]. However, the association of all significant FABP4 markers with FE and milk content traits was found in opposite directions, such that improved FE was accompanied by decreased milk content. Hence, before inclusion in breeding programs, the gain in FE must be economically balanced with the loss in milk contents. On the other hand, these findings imply that in any current improvement program concentrated on milk traits alone, without taking into account the effect on FE, the progress in milk composition is probably accompanied by deterioration of FE. These results, if confirmed in other populations and breeds, set FABP4 as a prime candidate in any marker-assisted selection program targeting FE as a whole and RFI in particular.