Genetic variance and covariance components for carbon dioxide production and postweaning traits in Angus cattle.

This experiment investigated phenotypic and genetic relationships between carbon dioxide production, methane emission, feed intake, and postweaning traits in Angus cattle. Respiration chamber data on 1096 young bulls and heifers from 2 performance recording research herds of Angus cattle were analyzed to provide phenotypic and genetic parameters for carbon dioxide production rate (CPR; n = 425, mean 3,010 ± SD 589 g/d) and methane production rate (MPR; n = 1,096, mean 132.8 ± SD 25.2 g/d) and their relationships with dry matter intake (DMI; n = 1,096, mean 6.15 ± SD 1.33 kg/d), body weight (BW) and body composition traits. Heritability estimates were moderate to high for CPR (0.53 [SE 0.17]), MPR (0.31 [SE 0.07]), DMI (0.49 [SE 0.08]), yearling BW (0.46 [SE 0.08]), and scanned rib fat depth (0.42 [SE 0.07]). There was a strong phenotypic (0.83 [SE 0.02]) and genetic (0.75 [SE 0.10]) correlation between CPR and MPR. The correlations obtained for DMI with CPR and with MPR were high, both phenotypically (rp) and genetically (rg) (rp: 0.85 [SE 0.01] and 0.71 [SE 0.02]; rg (0.95 [SE 0.03] and 0.83 [SE 0.05], respectively). Yearling BW was strongly correlated phenotypically (rp ≥ 0.60) and genetically (rg > 0.80) with CPR, MPR, and DMI, whereas scanned rib fat was weakly correlated phenotypically (rp < 0.20) and genetically (rg ≤ 0.20) with CPR, MPR, and DMI. The strong correlation between both CPR and MPR with DMI confirms their potential use as proxies for DMI in situations where direct DMI recording is not possible such as on pasture.

Methods and consequences of including reduction in greenhouse gas emission in beef cattle multiple-trait selection.

BACKGROUND: Societal pressures exist to reduce greenhouse gas (GHG) emissions from farm animals, especially in beef cattle. Both total GHG and GHG emissions per unit of product decrease as productivity increases. Limitations of previous studies on GHG emissions are that they generally describe feed intake inadequately, assess the consequences of selection on particular traits only, or examine consequences for only part of the production chain. Here, we examine GHG emissions for the whole production chain, with the estimated cost of carbon included as an extra cost on traits in the breeding objective of the production system. METHODS: We examined an example beef production system where economic merit was measured from weaning to slaughter. The estimated cost of the carbon dioxide equivalent (CO2-e) associated with feed intake change is included in the economic values calculated for the breeding objective traits and comes in addition to the cost of the feed associated with trait change. GHG emission effects on the production system are accumulated over the breeding objective traits, and the reduction in GHG emissions is evaluated, for different carbon prices, both for the individual animal and the production system. RESULTS: Multiple-trait selection in beef cattle can reduce total GHG and GHG emissions per unit of product while increasing economic performance if the cost of feed in the breeding objective is high. When carbon price was $10, $20, $30 and $40/ton CO2-e, selection decreased total GHG emissions by 1.1, 1.6, 2.1 and 2.6% per generation, respectively. When the cost of feed for the breeding objective was low, selection reduced total GHG emissions only if carbon price was high (~ $80/ton CO2-e). Ignoring the costs of GHG emissions when feed cost was low substantially increased emissions (e.g. 4.4% per generation or ~ 8.8% in 10 years). CONCLUSIONS: The ability to reduce GHG emissions in beef cattle depends on the cost of feed in the breeding objective of the production system. Multiple-trait selection will reduce emissions, while improving economic performance, if the cost of feed in the breeding objective is high. If it is low, greater growth will be favoured, leading to an increase in GHG emissions that may be undesirable.

Cellular development in muscle differs between Angus steers from low and high muscle score selection lines1.

This study assessed cellular characteristics of longissimus lumborum (LL) and semitendinosus (ST) muscles in steers genetically selected for low (Low) or high (High) muscling using live muscle scoring, and High steers with 1 copy of the loss-of-function 821 del11 MSTN allele (HighHet). We hypothesized High and HighHet have altered muscle cellular characteristics and mechanisms influencing muscling compared with Low steers. Angus steers 25 mo old comprising 14 High, 19 Low, and 11 HighHet were backgrounded to 20 mo of age, grain finished for 150 d, and then slaughtered. Body and carcass weights did not differ due to muscling line (P = 0.46). Weight of LL was 16% greater (P = 0.004) and total protein in LL was 18% greater (P = 0.012) in HighHet than Low steers. ST weight in HighHet was 10% and 13% greater than in High and Low steers (P = 0.007), respectively, and of total ST protein 12% and 17% greater in HighHet than High or Low (P = 0.002). Cross-sectional area (CSA) of LL was greater in HighHet than in High and greater in High than in Low (85.0 vs. 77.0 vs. 70.4 cm2, P < 0.001). Apparent number of myofibers and myofibers per unit CSA did not differ between the muscling lines in LL (P = 0.14) or ST (P = 0.47). Myofiber CSA was greater in the ST of Low than of High and HighHet for type 1 (36% and 31% respectively, P = 0.005) and 2A (22% and 25%, P < 0.001). HighHet steers had greater area of glycolytic (type 2X) relative to more oxidative myofiber types within LL (P = 0.02; 11% and 43% more than High and Low, respectively) and ST (P < 0.001; 27% and 75%). Concentration of RNA in LL was 13% and 10% greater (P = 0.005) in High than in Low and HighHet, respectively, and total amount of RNA in LL was 22% greater in High and 20% greater in HighHet than in Low (P < 0.001). The LL of High steers had less protein to RNA (P = 0.03; 57.4 vs. 65.6) and more RNA to DNA (P = 0.007; 9.03 vs. 7.83) than Low. HighHet steers had 11% more DNA in ST than High (P = 0.04) and 19% more RNA in ST than Low (P = 0.012). The shift towards glycolytic myofibers was consistent with loadings in a principal component that explained 39% of the variation in LL and 38% in ST. Overall, these findings show that selection for increased muscling using live cattle muscle scoring, and 1 copy of the 821 del11 MSTN allele, results in more glycolytic muscle. They also suggest that increased muscling of the High compared with Low steers may be associated with increased translational capacity in the LL.

Genetic variation in residual feed intake is associated with body composition, behavior, rumen, heat production, hematology, and immune competence traits in Angus cattle1.

This experiment was to evaluate a suite of biological traits likely to be associated with genetic variation in residual feed intake (RFI) in Angus cattle. Twenty nine steers and 30 heifers bred to be divergent in postweaning RFI (RFIp) and that differed in midparent RFIp-EBV (RFIp-EBVmp) by more than 2 kg DMI/d were used in this study. A 1-unit (1 kg DM/d) decrease in RFIp-EBVmp was accompanied by a 0.08 kg (SE = 0.03; P < 0.05) increase in ADG, a 0.58 kg/d (0.17; P < 0.01) decrease in DMI, a 0.89 kg/kg (0.22; P < 0.001) decrease in FCR, and a 0.62 kg/d (0.12; P < 0.001) decrease in feedlot RFI (RFIf). Ultrasonically scanned depths of subcutaneous fat at the rib and rump sites, measured at the start and end of the RFI test, all had strong positive correlations with RFIp-EBVmp, DMI, and RFIf (all r values ≥0.5 and P < 0.001). Variation in RFIp-EBVmp was significantly correlated (P < 0.05) with flight speed (r = -0.32), number of visits to feed bins (r = 0.45), and visits to exhaled-emission monitors (r = -0.27), as well as the concentrations of propionate (r = -0.32) and valerate (r = -0.31) in rumen fluid, white blood cell (r = -0.51), lymphocyte (r = -0.43), and neutrophil (r = -0.31) counts in blood. RFIp-EBVmp was also correlated with the cellular immune response to vaccination (r = 0.25; P < 0.1) and heat production in fasted cattle (r = -0.46; P < 0.001). Traits that explained significant variation (P < 0.05) in DMI over the RFI test were midtest metabolic-BW (44.7%), rib fat depth at the end of test (an additional 18%), number of feeder visits (additional 5.7%), apparent digestibility of the ration by animals (additional 2.4%) and white blood-cell count (2.1%), and the cellular immune response to vaccine injection (additional 1.1%; P < 0.1), leaving ~23% of the variation in DMI unexplained. The same traits (BW excluded) explained 33%, 12%, 3.6%, 3.7%, and 3.1%, and together explained 57% of the variation in RFIf. This experiment showed that genetic variation in RFI was accompanied by variation in estimated body composition, behavior, rumen, fasted heat production, hematology, and immune competence traits, and that variation in feedlot DMI and RFIf was due to differences in BW, scanned fatness, and many other factors in these cattle fed ad libitum and able to display any innate differences in appetite, temperament, feeding behavior, and activity.

Relationships among carbon dioxide, feed intake, and feed efficiency traits in ad libitum fed beef cattle.

Angus cattle from 2 beef cattle projects on which carbon dioxide production rate (CPR) was measured were used in this study to examine the relationships among BW, DMI, and carbon dioxide traits of beef cattle fed ad libitum on a roughage diet or a grain-based feedlot diet, and to evaluate potential proxies for DMI and feed efficiency. In both projects, the GreenFeed Emission Monitoring system, which provides multiple short-term breath measures of carbon dioxide production, was used as a tool to measure CPR. The data were from 119 Angus heifers over 15 d on a roughage diet and 326 Angus steers over 70 d on a feedlot diet. Mean (±SD) age, BW, and DMI were 372 ± 28 d, 355 ± 37 kg, and 8.1 ± 1.3 kg/d for the heifers, and 554 ± 86 d, 577 ± 69 kg, and 13.3 ± 2.0 kg/d for the steers, respectively. The corresponding mean CPR was 5760 ± 644 g/d for heifers and 8939 ± 1212 g/d for steers. Other traits studied included carbon dioxide yield (CY; CPR/DMI) and intensity (CI; CPR/BW) and 5 forms of residual carbon dioxide production (RCP), which is a measure of actual minus predicted CPR. Feed efficiency traits studied included feed conversion ratio (FCR) and residual feed intake (RFI). The relationship between CPR and DMI, and between CPR and BW was both positive and linear, for the heifers and also for the steers. For the combined heifer and steer datasets, the R2 for the relationship between CPR and BW, and between CPR and DMI was 0.82 and 0.78, respectively. The correlation between CPR and DMI (r = 0.84 for heifers; r = 0.83 for steers) was similar to that between CPR and BW (r = 0.84 for heifers; r = 0.87 for steers). Most of the carbon dioxide traits were significantly (P < 0.05) correlated with one or both feed efficiency traits. One of the RCP traits (RCPMA) was computed by maintaining metabolic BW (M) and average daily gain (A) in the formula for RFI, but substituting the DMI with CPR. The correlation (r = 0.27) between RCPMA and RFI, though significantly different from zero, was not strong enough for its use as proxy for RFI. On the other hand, a strong correlation (r = 0.73) was obtained between the CPR to gain ratio (CGR) and FCR. This indicates that, where DMI is not available, CPR could be used in its place to compute a feed efficiency trait similar to FCR, since the computation of CGR was similar to that for FCR, except that DMI was substituted with CPR in the FCR formula.

Characterization and Profiling of Liver microRNAs by RNA-sequencing in Cattle Divergently Selected for Residual Feed Intake.

MicroRNAs (miRNAs) are short non-coding RNAs that post-transcriptionally regulate expression of mRNAs in many biological pathways. Liver plays an important role in the feed efficiency of animals and high and low efficient cattle demonstrated different gene expression profiles by microarray. Here we report comprehensive miRNAs profiles by next-gen deep sequencing in Angus cattle divergently selected for residual feed intake (RFI) and identify miRNAs related to feed efficiency in beef cattle. Two microRNA libraries were constructed from pooled RNA extracted from livers of low and high RFI cattle, and sequenced by Illumina genome analyser. In total, 23,628,103 high quality short sequence reads were obtained and more than half of these reads were matched to the bovine genome (UMD 3.1). We identified 305 known bovine miRNAs. Bta-miR-143, bta-miR-30, bta-miR-122, bta-miR-378, and bta-let-7 were the top five most abundant miRNAs families expressed in liver, representing more than 63% of expressed miRNAs. We also identified 52 homologous miRNAs and 10 novel putative bovine-specific miRNAs, based on precursor sequence and the secondary structure and utilizing the miRBase (v. 21). We compared the miRNAs profile between high and low RFI animals and ranked the most differentially expressed bovine known miRNAs. Bovine miR-143 was the most abundant miRNA in the bovine liver and comprised 20% of total expressed mapped miRNAs. The most highly expressed miRNA in liver of mice and humans, miR-122, was the third most abundant in our cattle liver samples. We also identified 10 putative novel bovine-specific miRNA candidates. Differentially expressed miRNAs between high and low RFI cattle were identified with 18 miRNAs being up-regulated and 7 other miRNAs down-regulated in low RFI cattle. Our study has identified comprehensive miRNAs expressed in bovine liver. Some of the expressed miRNAs are novel in cattle. The differentially expressed miRNAs between high and low RFI give some insights into liver miRNAs regulating physiological pathways underlying variation in this measure of feed efficiency in bovines.

Characterisation of local Ghanaian chickens: growth performance evaluation based on Richards growth model and genetic size scaling.

The Richards growth model was fitted to body weight-age data of local and SASSO T44 chickens to describe their growth performance. Males had higher (P < 0.05) asymptotic mature weights than females. Within the local chicken population, birds from the savannah zone had higher (P < 0.05) asymptotic mature weights compared to forest chicken which ironically had higher body weights at hatch. Male local chicken had lower maturing rates compared to the females. Female local chicken were superior to SASSO T44 females in terms of maturing rate. On the average, local chickens took relatively longer time (78.4-83.3 days) to reach the point of inflection than the SASSO T44 population (74.2-79.8 days). However, there were no significant differences (P > 0.05) in the age at inflection among local chicken populations. The shape parameter for SASSO T44 chicken (0.053-0.370) and maturation rate for local chicken (0.177-0.198) were the most critical parameters. Scaling the body weights into degree of maturity highlighted the degree to which genotypes matured over time. Female chickens had the highest (P < 0.05) degree of maturity at all ages. The local chicken populations were also metabolically older than SASSO T44 chickens. Results of this study provide an opportunity to develop breeding strategies for local chicken by modifying either management practices or their genetic makeup to positively affect their growth and productivity.