Genetic parameters and genotype x environment interaction for feed efficiency traits in steers fed grower and finisher diets

Development and validation of a model for early prediction of residual feed intake in beef cattle using plasma biomarkers

Identification of plasma biomarkers for feed efficiency in growing beef cattle offers a promising opportunity for developing prediction models to improve precision feeding strategies. However, these models must accurately predict feed efficiency at early stages of fattening. Our study aimed to evaluate the reliability of candidate biomarkers previously identified in late-fattening cattle when analysed during early fattening stages and to develop diet-specific prediction equations for residual feed intake (RFI). From a total of 364 Charolais bulls across seven cohorts, we selected 64 animals with extreme RFI values. The animals were fed either a corn‑ or grass-silage diets. These animals were chosen from four out of the available seven cohorts. Animals from three cohorts (24 high-RFI and 24 low-RFI, having a mean RFI difference of 1.48 kg/d) were used for biomarker confirmation and prediction model training. Animals from a fourth cohort (8 high-RFI and 8 low-RFI, having a mean RFI difference of 0.98 kg/d) were used for model external validation. Blood samples were collected at the beginning of the feed efficiency test (333 ± 20 days), and plasma underwent targeted metabolomic for 630 metabolites, natural abundance of 15N (δ15N), insulin, and IGF-1 analysis. Seven previously identified plasma biomarkers for RFI in late-fattening beef cattle still kept their capability for discriminating low and high RFI animals when analysed during early fattening stages (P < 0.05). Among these confirmed biomarkers, five were common for both grass- and corn-fed animals (creatinine, β-alanine, triglyceride TG18:0_34:2, symmetric dimethyl-arginine and phosphatidylcholine PC aa C30:2) while two were diet-specific (IGF-1 for grass silage-based diet, and isoleucine for corn silage-based diet. No new plasma biomarkers of RFI were identified at early-fattening stages (false discovery rate  > 0.05). Prediction models were developed based on seven confirmed RFI biomarkers analysed during early-fattening. Two logistic regression models incorporating creatinine and either IGF-1 (for grass silage-based diet) or PC aa C30:2 (for corn silage-based diet) effectively distinguished between high- and low-RFI animals with high sensitivity and specificity (area under the curve > 0.80). The biomarkers used in the models showed moderate to high repeatability between early and late fattening stages (0.45 < r < 0.65). The models were successfully externally validated, with more than 85% of animals from the fourth cohort correctly classified. Once validated in larger cohorts and utilising cost-effective and rapid analytical methods, these models could support precision feeding and breeding programmes, aiming to reduce the cost of raising beef cattle.

Genotype-by-environment interactions for feed efficiency traits in Nellore cattle based on bi-trait reaction norm models

BACKGROUND

Selecting animals for feed efficiency directly impacts the profitability of the beef cattle industry, which contributes to minimizing the environmental footprint of beef production. Genetic and environmental factors influence animal feed efficiency, leading to phenotypic variability when exposed to different environmental conditions (i.e., temperature and nutritional level). Thus, our aim was to assess potential genotype-by-environment (G × E) interactions for dry matter intake (DMI) and residual feed intake (RFI) in Nellore cattle (Bos taurus indicus) based on bi-trait reaction norm models (RN) and evaluate the genetic association between RFI and DMI across different environmental gradient (EG) levels. For this, we used phenotypic information on 12,958 animals (young bulls and heifers) for DMI and RFI recorded during 158 feed efficiency trials.

RESULTS

The heritability estimates for DMI and RFI across EG ranged from 0.26 to 0.54 and from 0.07 to 0.41, respectively. The average genetic correlations (± standard deviation) across EG for DMI and RFI were 0.83 ± 0.19 and 0.81 ± 0.21, respectively, with the lowest genetic correlation estimates observed between extreme EG levels (low vs. high) i.e. 0.22 for RFI and 0.26 for DMI, indicating the presence of G × E interactions. The genetic correlation between RFI and DMI across EG levels decreased as the EG became more favorable and ranged from 0.79 (lowest EG) to 0.52 (highest EG). Based on the estimated breeding values from extreme EG levels (low vs. high), we observed a moderate Spearman correlation of 0.61 (RFI) and 0.55 (DMI) and a selection coincidence of 53.3% and 40.0% for RFI and DMI, respectively.

CONCLUSIONS

Our results show evidence of G × E interactions on feed efficiency traits in Nellore cattle, especially in feeding trials with an average daily gain (ADG) that is far from the expected of 1 kg/day, thus increasing reranking of animals.

Genetic association between feed efficiency, growth, scrotal circumference, and carcass traits in Guzerat cattle

The objective of this study was to estimate the genetic parameters for feed efficiency-related traits and their genetic correlations with growth, male fertility, and carcass traits using multi-trait analysis in Guzerat cattle. Further, it aimed to predict the direct and correlated responses for feed efficiency traits when selection was applied for growth, male fertility, and carcass traits. The evaluated traits were adjusted weight at 120 (W120), 210 (W210), 365 (W365), and 450 days of age (W450), adjusted scrotal circumference at 365 days of age (SC365) and at 450 days of age (SC450), scrotal circumference, ribeye area (REA), backfat thickness (BFT), rump fat thickness (RFT), residual feed intake (RFI), and dry matter intake (DMI). The genetic parameters were obtained by the restricted maximum likelihood method (REML), using an animal model in multi-trait analyses. The heritability estimates for W120, W210, W365, W450, SC365, and SC450 varied from low to high (0.17 to 0.39). The carcass traits, REA, BFT, and RFT, displayed low to moderate heritability estimates, 0.27, 0.10, and 0.31, respectively. The heritability estimates for RFI (0.15) and DMI (0.23) were low and moderate, respectively. The RFI showed low genetic correlations with growth traits, ranging from - 0.07 to 0.22, from 0.03 to 0.05 for scrotal circumference, and from - 0.35 to 0.16 for carcass, except for DMI, which ranged from 0.42 to 0.46. The RFI and DMI presented enough additive genetic variability to be used as selection criteria in Guzerat breed genetic improvement program. Additionally, the response to selection for RFI would be higher when selection is performed directly for this trait. The selection for residual feed intake would not promote unfavorable correlated responses for scrotal circumference, carcass (yield and finish), and growth traits. Therefore, the selection for more efficient animals would not compromise the productive, reproductive, and carcass performance, contributing to reduce the production costs, increasing the profitability and sustainability of beef cattle production in tropical areas.

Methane and carbon dioxide emissions and grazed forage intake from pregnant beef heifers previously classified for residual feed intake under drylot conditions

The objectives of this study were to quantify the effect of post-weaning residual feed intake (RFI) on subsequent grazed forage intake, methane (CH4), and carbon dioxide (CO2) emissions. Beef heifers classified for RFI adjusted for off-test backfat (RFIfat; 55 high and 56 low) at 9 mo of age were monitored 7 mo later for CH4 and CO2 emissions using the GreenFeed Emissions Monitoring system. About 56 of these heifers were also monitored as high and low RFIfat groups using open-path Fourier-transform infrared spectroscopy (OP-FTIR). Heifers were dosed with 1 kg of C32-labelled pellets once daily for 15 d, with twice daily fecal sampling the last 8 d to determine individual grazed forage intake using the n-alkane method. Low RFIfat pregnant heifers consumed less forage (10.25 vs. 10.81 kg dry matter d−1; P < 0.001), and emitted less daily CH4 (238.7 vs. 250.7 g d−1; P = 0.009) and CO2 (7578 vs. 8041 g d−1; P < 0.001) compared with high RFIfat animals. Results from the OP-FTIR further confirmed that low RFIfat heifers emitted 6.3% less (g d−1; P = 0.006) CH4 compared with their high RFIfat cohorts. Thus, selection for low RFIfat will decrease daily CH4 and CO2 emissions from beef cattle.

A new method to estimate residual feed intake in dairy cattle using time series data

In dairy, the usual way to measure feed efficiency is through the residual feed intake (RFI) method. However, this method is, in its classical form, a linear regression, which, by construction, does not take into account the evolution of the RFI components across time, inducing approximations in the results. We present here a new approach that incorporates the dynamic dimension of the data. Using a multitrait random regression model, the correlations between milk, live weight, DM intake (DMI) and body condition score (BCS) were investigated across the lactation. In addition, at each time point, by a matrix regression on the variance-covariance matrix and on the animal effects from the three predictor traits, a predicted animal effect for intake was estimated, which, by difference with the actual animal effect for intake, gave a RFI estimation. This model was tested on historical data from the Aarhus University experimental farm (1 469 lactations out of 740 cows). Correlations between animal effects were positive and high for milk and DMI and for weight and DMI, with a maximum mid-lactation, stable across time at around 0.4 for weight and BCS, and slowly decreasing along the lactation for milk and weight, DMI and BCS, and milk and BCS. At the Legendre polynomial coefficient scale, the correlations were estimated with a high accuracy (averaged SE of 0.04, min = 0.02, max = 0.05). The predicted animal effect for intake was always extremely highly correlated with the milk production and highly correlated with BW for the most part of the lactation, but only slightly correlated with BCS, with the correlation becoming negative in the second half of the lactation. The estimated RFI possessed all the characteristics of a classical RFI, with a mean at zero at each time point and a phenotypic independence from its predictors. The correlation between the averaged RFI over the lactation and RFI at each time point was always positive and above 0.5, and maximum mid-lactation (>0.9). The model performed reasonably well in the presence of missing data. This approach allows a dynamic estimation of the traits, free from all time-related issues inherent to the traditional RFI methodology, and can easily be adapted and used in a genetic or genomic selection context.

The repeatability of feed intake and feed efficiency in beef cattle offered high-concentrate, grass silage and pasture-based diets

Breeding values for feed intake and feed efficiency in beef cattle are generally derived indoors on high-concentrate (HC) diets. Within temperate regions of north-western Europe, however, the majority of a growing beef animal's lifetime dietary intake comes from grazed grass and grass silage. Using 97 growing beef cattle, the objective of the current study was to assess the repeatability of both feed intake and feed efficiency across 3 successive dietary test periods comprising grass silage plus concentrates (S+C), grazed grass (GRZ) and a HC diet. Individual DM intake (DMI), DMI/kg BW and feed efficiency-related parameters, residual feed intake (RFI) and gain to feed ratio (G : F) were assessed. There was a significant correlation for DMI between the S+C and GRZ periods (r = 0.32; P < 0.01) as well as between the S+C and HC periods (r = 0.41; P < 0.001), whereas there was no association for DMI between the GRZ and HC periods. There was a significant correlation for DMI/kg BW between the S+C and GRZ periods (r = 0.33; P < 0.01) and between the S+C and HC periods (r = 0.40; P < 0.001), but there was no association for the trait between the GRZ and HC periods. There was a significant correlation for RFI between the S+C and GRZ periods (r = 0.25; P < 0.05) as well as between S+C and HC periods (r = 0.25; P < 0.05), whereas there was no association for RFI between the GRZ and HC periods. Gain to feed ratio was not correlated between any of the test periods. A secondary aspect of the study demonstrated that traits recorded in the GRZ period relating to grazing bite rate, the number of daily grazing bouts and ruminating bouts were associated with DMI (r = 0.28 to 0.42; P < 0.05 - 0.001), DMI/kg BW (r = 0.36 to 0.45; P < 0.01 - 0.001) and RFI (r = 0.31 to 0.42; P < 0.05 - 0.001). Additionally, the number of ruminating boli produced per day and per ruminating bout were associated with G : F (r = 0.28 and 0.26, respectively; P < 0.05). Results from this study demonstrate that evaluating animals for both feed intake and feed efficiency indoors on HC diets may not reflect their phenotypic performance when consuming conserved forage-based diets indoors or when grazing pasture.

Genetic parameters and genome-wide association study regarding feed efficiency and slaughter traits in Charolais cows

Residual energy intake (REI) on two successive diets (hay and maize based) and slaughter traits, including visceral organs, were phenotyped in 584 adult purebred Charolais cows. To investigate the relationships between these traits and their genetic determinism, we first estimated the genetic parameters, including correlations, using REML modeling under WOMBAT software. The animals were then genotyped on the BovineSNP50 SNPchip before being imputed to the 600K density and genome wide association study was performed with GCTA software. We found low heritability for REI (h2 = 0.12 in each of the diet phases). Although the phenotypic correlation between the two diet phases was moderate (0.36), the genetic correlation was high (0.83), indicating a common genetic determinism for feed efficiency regardless of the diet. Correlations between REI and slaughter traits were negative regarding muscle-related traits and positive for fat-related traits, indicating that efficient animals generally had a more muscular carcass. It was also seen that feed efficiency was genetically and phenotypically correlated with smaller organs when expressed as a proportion of their empty body weight. From the GWAS analysis, seven QTLs were found to be associated with a trait at the genome-wide level of significance and 18 others at the chromosome-wide level. One important QTL was detected in BTA 2, reflecting the essential effect of the myostatin gene on both carcass composition and relative organ weight. Three QTLs were detected for REI during the maize diet phase on BTA 13, 19, and 28, the latter being significant at the genome-wide level. The QTLs on BTA 19 mapped into the TANC2 gene and the QTLs on BTA 28 into the KIF1BP gene, which are both known to interact with the same protein (KIF1A). However, no obvious functional link between these genes and feed efficiency could be made. Among the other QTLs detected, one association on BTA 4 with liver proportion mapped to the candidate gene WASL, which has previously been shown to be differentially expressed in liver cells and linked to feed restriction or cancer development. No QTLs were found to be common between feed efficiency and any slaughter traits.

Genetic parameters for feed efficiency in Romane rams and responses to single-generation selection

Feeding costs represent one of the highest expenditures in animal production systems. Breeding efficient animals that express their growth potential while eating less is therefore a major objective for breeders. We estimated the genetic parameters for feed intake, feed efficiency traits (residual feed intake (RFI) and feed conversion ratio (FCR)), growth and body composition traits in the Romane meat sheep breed. In these traits, selection responses to single-generation divergent selection on RFI were evaluated. From 2009 to 2016, a total of 951 male lambs were tested for 8 weeks starting from 3 months of age. They were weighed at the beginning and at the end of the testing period. Backfat thickness and muscle depth were recorded at the end of the testing period through ultrasound measurements. Feed intake was continuously recorded over the testing period using the automatic concentrate feeders. The heritability of RFI was estimated at 0.45 ± 0.08, which was higher than the heritability of FCR (0.30 ± 0.08). No significant genetic correlations were observed between RFI and growth traits. A favourable low negative genetic correlation was estimated between RFI and muscle depth (-0.30 ± 0.15), though additional data are needed to confirm these results. The selection of low RFI sires based on their breeding values led to the production of lambs eating significantly less concentrate (3% decrease in the average daily feed intake), but with the same growth as lambs from sires selected based on high RFI breeding values. We concluded that in meat sheep, RFI is a heritable trait that is genetically independent of post-weaning growth and body composition traits. A one-generation divergent selection based on RFI breeding values highlighted that substantial gains in feeding costs can be expected in selection schemes for meat sheep breeds.

The effect of breed and diet type on the global transcriptome of hepatic tissue in beef cattle divergent for feed efficiency

Background

Feed efficiency is an important economic and environmental trait in beef production, which can be measured in terms of residual feed intake (RFI). Cattle selected for low-RFI (feed efficient) have similar production levels but decreased feed intake, while also emitting less methane. RFI is difficult and expensive to measure and is not widely adopted in beef production systems. However, development of DNA-based biomarkers for RFI may facilitate its adoption in genomic-assisted breeding programmes. Cattle have been shown to re-rank in terms of RFI across diets and age, while also RFI varies by breed. Therefore, we used RNA-Seq technology to investigate the hepatic transcriptome of RFI-divergent Charolais (CH) and Holstein-Friesian (HF) steers across three dietary phases to identify genes and biological pathways associated with RFI regardless of diet or breed.

Results

Residual feed intake was measured during a high-concentrate phase, a zero-grazed grass phase and a final high-concentrate phase. In total, 322 and 33 differentially expressed genes (DEGs) were identified across all diets for CH and HF steers, respectively. Three genes, GADD45G, HP and MID1IP1, were differentially expressed in CH when both the high-concentrate zero-grazed grass diet were offered. Two canonical pathways were enriched across all diets for CH steers. These canonical pathways were related to immune function.

Conclusions

The absence of common differentially expressed genes across all dietary phases and breeds in this study supports previous reports of the re-ranking of animals in terms of RFI when offered differing diets over their lifetime. However, we have identified biological processes such as the immune response and lipid metabolism as potentially associated with RFI divergence emphasising the previously reported roles of these biological processes with respect to RFI.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5906-8) contains supplementary material, which is available to authorized users.

Feed efficiency of tropically adapted cattle when fed in winter or spring in a temperate location

Earlier work has shown that young tropically adapted cattle do not gain weight as rapidly as temperately adapted cattle during the winter in Oklahoma. The objective for this study was to determine whether efficiency of gains was also affected in tropically adapted cattle and whether efficiency was consistent over different seasons. Over 3 yr, 240 straightbred and crossbred steers (F1 and 3-way crosses) of Angus, Brahman, or Romosinuano breeding, born in Brooksville, FL, were transported to El Reno, OK in October and fed in 2 phases to determine performance, individual intake, and efficiency. Phase 1 (WIN) began in November after a 28-d recovery from shipping stress and phase 2 (SS) began in March, 28 d following completion of WIN each year. The diet for WIN was a grower diet (14% CP, 1.10 Mcal NEg/kg) and that for the SS was a feedlot diet (12.8% CP; 1.33 Mcal NEg/kg). After a 14-d adjustment to diet and facilities, intake trials were conducted over a period of 56 to 162 d for determination of intake and gain for efficiency. Body weights were recorded at approximately 14-d intervals, and initial BW, median BW, and ADG were determined from individual animal regressions of BW on days on feed. Individual daily DMI was then regressed by phase on median BW and ADG, and residuals of regression were recorded as residual feed intake (RFI). Similarly, daily gain was regressed by phase on median BW and DMI, and errors of regression were recorded as residual gain (RADG). Gain to feed (G:F) was also calculated. The statistical model to evaluate ADG, DMI, and efficiency included fixed effects of dam age (3 to 4, 5, 6 to 10, and >10 yr), harvest group (3 per year), age on test, and a nested term DT (ST × XB), where DT is the proportion tropical breeding of dam (0, 0.5, or 1), ST is the proportion tropical breeding of sire (1 or 0), and XB whether the calf was straightbred or crossbred. Year of record, sire (ST × XB), and pen were random effects. Preweaning ADG and BW increased (P < 0.05) with level of genetic tropical influence, but during the WIN, ADG and efficiency estimated by G:F and RADG declined (P < 0.05). Tropical influence had little effect on RFI during the WIN, or on most traits during SS. In general, during SS, crossbred steers gained faster and were more efficient by G:F and RADG (P < 0.05) than straightbred steers. Simple correlations, both Pearson and Spearman, between RFI in WIN and RFI in SS were 0.51 (P < 0.001), whereas that for RADG was 0.17 (P < 0.01).

Variation in residual feed intake depends on feed on offer

Two small pen trials with cattle and sheep both clearly demonstrated that while there is significant variation in residual feed intake when on high energy supply, there is negligible variation when energy supply is limited. A review of literature demonstrated that this is also the case when energy supply is limited by heat or physiological state, such as peak lactation, and in multiple species. There is little evidence of variation in efficiency of maintenance requirements, growth or lactation. Nor is there strong evidence for large variation in digestibility within breeds, despite some differences between divergent breeds. Thus, the primary source of variation in residual feed intake must be in appetite and, in variable environments, it is possible that those with greater appetite are more resilient during times of feed shortage.

Growth performance, feed digestibility, body composition, and feeding behavior of high- and low-residual feed intake fat-tailed lambs under moderate feed restriction

Two experiments were conducted to evaluate the effect of moderate feed restriction on productivity of lambs classified on the basis of phenotypic expression of residual feed intake (RFI). In Exp. 1, 58 fat-tailed Kurdi ram lambs (32.1 ± 4.2 kg BW) were individually fed, ad libitum, a pelleted diet (35% alfalfa hay and 65% concentrate). Feed intake and ADG were determined for a 6-wk period and 3 feed efficiency measures including RFI, G:F, and partial efficiency of maintenance (PEM) were calculated. The lambs were sorted based on RFI and the 16 highest RFI (RFI ≥ mean + 0.5 SD) and 16 lowest RFI (RFI ≤ mean - 0.5 SD) lambs were subjected to body composition (BC) and DM digestibility (DMD) analysis. Feeding behavior traits (FB) were also evaluated for 24 h using a regular 5-min interval observation method. The high- and low-RFI lambs (14 lambs/RFI group) so classified in Exp. 1 were used in Exp. 2. Half of the lambs in each RFI group were randomly selected to be fed ad libitum or 85% of ad libitum (restricted feeding), which resulted in 4 experimental groups: 1) ad libitum high-RFI, 2) feed restricted high-RFI, 3) ad libitum low-RFI, and 4) feed restricted low-RFI. The lambs were fed the same diet as Exp. 1, and growth efficiency during a 6-wk test period as well as BC, DMD, and FB were also determined in Exp. 2. In Exp. 1, the low-RFI lambs consumed 14% ( < 0.01) less feed than high-RFI lambs. Differences were also observed between high- and low-RFI groups for G:F ( = 0.01), RFI ( < 0.01), and PEM ( < 0.01) in Exp. 1, but no differences were detected between high- and low-RFI lambs for ADG ( = 0.79), DMD ( = 0.42), BC ( > 0.72), and FB ( > 0.24). In Exp.2, the restriction feeding regime negatively affected ADG ( < 0.01) and G:F ( = 0.02) in low-RFI lambs, whereas G:F ( = 0.02) and PEM ( < 0.01) were improved in high-RFI lambs under the feed restriction condition. No effects of feed restriction on DMD ( = 0.87) and BC ( > 0.05) were observed. The lambs fed at the restricted level of intake presented a greater time ( < 0.01) and rate ( = 0.01) of eating than those fed ad libitum. Although bunk visits and feeding events were decreased ( < 0.01) with feed restriction, no interaction ( > 0.05) was detected between RFI phenotype and feeding regime for FB. In summary, feeding high-RFI lambs at 85% of ad libitum level improved G:F with no effect on ADG, whereas growth performance was reduced by feeding low-RFI lambs at 85% of ad libitum. However, these changes in feed efficiency were not related to DMD, BC, or FB.

Genetic and environmental variation in methane emissions of sheep at pasture

A total of 2,600 methane (CH4) and 1,847 CO2 measurements of sheep housed for 1 h in portable accumulation chambers (PAC) were recorded at 5 sites from the Australian Sheep CRC Information Nucleus, which was set up to test leading young industry sires for an extensive range of current and novel production traits. The final validated dataset had 2,455 methane records from 2,279 animals, which were the progeny of 187 sires and 1,653 dams with 7,690 animals in the pedigree file. The protocol involved rounding up animals from pasture into a holding paddock before the first measurement on each day and then measuring in groups of up to 16 sheep over the course of the day. Methane emissions declined linearly (with different slopes for each site) with time since the sheep were drafted into the holding area. After log transformation, estimated repeatability (rpt) and heritability (h(2)) of liveweight-adjusted CH4 emissions averaged 25% and 11.7%, respectively, for a single 1-h measurement. Sire × site interactions were small and nonsignificant. Correlations between EBV for methane emissions and Sheep Genetics Australia EBV for production traits were used as approximations to genetic correlations. Apart from small positive correlations with weaning and yearling weights (r = 0.21-0.25, P < 0.05), there were no significant relationships between production trait and methane EBV (calculated from a model adjusting for liveweight by fitting separate slopes for each site). To improve accuracy, future protocols should use the mean of 2 (rpt = 39%, h(2) = 18.6%) or 3 (rpt = 48%, h(2) = 23.2%) PAC measurements. Repeat tests under different pasture conditions and time of year should also be considered, as well as protocols measuring animals directly off pasture instead of rounding them up in the morning. Reducing the time in the PAC from 1 h to 40 min would have a relatively small effect on overall accuracy and partly offset the additional time needed for more tests per animal. Field testing in PAC has the potential to provide accurate comparisons of animal and site methane emissions, with potentially lower cost/increased accuracy compared to alternatives such as SF6 tracers or open path lasers. If similar results are obtained from tests with different protocols/seasonal conditions, use of PAC measurements in a multitrait selection index with production traits could potentially reduce methane emissions from Australian sheep for the same production level.

Genetic parameters for production and feeding behaviour traits in crossbred steers fed a finishing diet at different ages

Durunna, O. N., Mujibi, F. D. N., Nkrumah, D. J., Basarab, J. A., Okine, E. K., Moore, S. S. and Wang, Z. 2013. Genetic parameters for production and feeding behaviour traits in crossbred steers fed a finishing diet at different ages. Can. J. Anim. Sci. 93: 79–87. Because cattle can be raised postweaning under several feeding regimes, this study examined the consistency of phenotypic and genetic parameters of some production and feeding behaviour traits between two feeding periods that beef cattle received a finisher diet. Crossbred steers (n=851) were used for feeding trials from 2002 to 2009 where the steers received a finisher diet either during the fall–winter season (FP1) or during the winter–spring season (FP2). The steers evaluated in FP2 received a backgrounding diet in FP1. Traits examined include dry matter intake (DMI), average daily gain (ADG), gain: feed ratio (G:F), residual feed intake (RFI), and ultrasound measures of backfat thickness (UBF), rib-eye area (UREA) and marbling (UMB). Others include feeding duration (FD), headdown time (HDT) and feeding frequency (FF). As expected, there was no difference (P=0.90) between the RFI measured in the two periods. The two periods were similar for UBF (P=0.87) and UREA (P=0.25),while DMI, ADG and UMB were greater (P<0.04) in FP2 than in FP1. The FD, HDT and FF were greater (P<0.0001) in FP1 compared with FP2. Heritability estimates were calculated in FP1 and FP2, respectively, for ADG (0.38, 0.28), DMI (0.52, 0.42), RFI (0.16, 0.27), G:F (0.18, 0.33), HDT (0.35, 0.18) and FF (0.26, 0.46). More importantly, genetic correlations between FP1 and FP2 were estimated for DMI (0.61), RFI (0.65) and G:F (0.60). The results may indicate the influence of age or feeding period or both on these traits, which may suggest the need for multi-environment genetic evaluations to identify superior animals.

Triennial Lactation Symposium: Opportunities for improving milk production efficiency in dairy cattle

Increasing feed costs and the desire to improve environmental stewardship have stimulated renewed interest in improving feed efficiency of livestock, including that of US dairy herds. For instance, USDA cost projections for corn and soybean meal suggest a 20% increase over 2010 pricing for a 16% protein mixed dairy cow ration in 2011, which may lead to a reduction in cow numbers to maintain profitability of dairy production. Furthermore, an October 2010 study by The Innovation Center for US Dairy to assess the carbon footprint of fluid milk found that the efficiency of feed conversion is the single greatest factor contributing to variation in the carbon footprint because of its effects on methane release during enteric fermentation and from manure. Thus, we are conducting research in contemporary US Holsteins to identify cows most efficient at converting feed to milk in temperate climates using residual feed intake (RFI), a measure used successfully to identify the beef cattle most efficient at converting feed to gain. Residual feed intake is calculated as the difference between predicted and actual feed intake to support maintenance and production (e.g., growth in beef cattle, or milk in dairy cattle). Heritability estimates for RFI in dairy cattle reported in the literature range from 0.01 to 0.38. Selection for a decreased RFI phenotype can reduce feed intake, methane production, nutrient losses in manure, and visceral organ weights substantially in beef cattle. We have estimated RFI during early lactation (i.e., to 90 d in milk) in the Beltsville Agricultural Research Center Holstein herd and observed a mean difference of 3.7 kg/d (P < 0.0001) in actual DMI between the efficient and inefficient groups (±0.5 SD from the mean RFI of 0), with no evidence of differences (P > 0.20) in mean BW, ADG, or energy-corrected milk exhibited between the 2 groups. These results indicate promise for using RFI in dairy cattle to improve feed conversion to milk. Previous and current research on the use of RFI in lactating dairy cattle are discussed, as well as opportunities to improve production efficiency of dairy cattle using RFI for milk production.