Interaction between residual feed intake and thermal environment on performance, nitrogen balance, ingestive behavior and carcass yield of dorper lambs

Residual feed intake (RFI) is a nutritional variable used in genetic improvement programs, the relationship between the environment and the availability of energy and protein in the diet has not yet been explored. Thus, the aim was to evaluate interactions between RFI and thermal environment on performance, nitrogen balance, ingestive behavior and carcass yield of Dorper lambs receiving diets containing different concentrate levels. Dorper lambs (male, n = 64, 17.83 ± 2.43 kg and 110 ± 10 days of age) were confined individually for 40 days for RFI classification. Lambs were separated into positive RFI (n = 30) and negative RFI (n = 30) and remained confined for another 60 days. The animals were distributed in a randomized block design, with a 2 × 2 × 3 factorial scheme, with 2 confinement environments (full sun or shade), 2 groups of feed efficiency (RFI positive or RFI negative) and three diets containing different concentrate levels (30, 45 and 60%), with 5 replications in each treatment. Isolated effects of concentrate level were observed for dry matter intake and digestibility, feeding, rumination, idle and chewing times, feeding efficiency, ingested, excreted and absorbed nitrogen, and on cooling losses, hot and cold carcass yield (P < 0.05). There was an effect of environment × concentrate interaction on performance, retained nitrogen and nitrogen balance (P < 0.05). There was an effect of RFI × environment interaction on the dry matter rumination efficiency, hot and cold carcass weight (P < 0.05). Under experimental conditions, RFI did not influence the productive performance of Dorper lambs. Interactions between environment and diet indicate better performance for Dorper lamb confined in the shade and receiving a higher proportion of concentrate. Animals with negative RFI show better performance and carcass weight when confined in shade, while animals with positive RFI showed better responses to these variables when confined in full sun.

Genetic and phenotypic parameters for feed efficiency and component traits in American mink

Feed cost is the largest expense of mink production systems, and, therefore, improvement of feed efficiency (FE) through selection for high feed-efficient mink is a practical way to increase the mink industry's sustainability. In this study, we estimated the heritability, phenotypic, and genetic correlations for different FE measures and component traits, including harvest weight (HW), harvest length (HL), final body length (FBL), final body weight (FBW), average daily gain (ADG), daily feed intake (DFI), feed conversion ratio (FCR), residual feed intake (RFI), residual gain (RG), residual intake and gain (RIG), and Kleiber ratio (KR), using data from 2,288 American mink (for HW and HL), and 1,038 to 1,906 American mink (for other traits). Significance (P < 0.05) of fixed effects (farm, sex, and color type), a covariate (age of animal), and random effects (additive genetic, maternal, and common litter) were evaluated through univariate models implemented in ASReml-R version 4. Genetic parameters were estimated via fitting a set of bivariate models using ASReml-R version 4. Estimates of heritabilities (±SE) were 0.28 ± 0.06, 0.23 ± 0.06, 0.28 ± 0.10, 0.27 ± 0.11, 0.25 ± 0.09, 0.26 ± 0.09, 0.20 ± 0.09, 0.23 ± 0.09, 0.21 ± 0.10, 0.25 ± 0.10, and 0.26 ± 0.10 for HW, HL, FBL, FBW, ADG, DFI, FCR, RFI, RG, RIG, and KR, respectively. RIG had favorable genetic correlations with DFI (-0.62 ± 0.24) and ADG (0.58 ± 0.21), and nonsignificant (P > 0.05) genetic correlations with FBW (0.14 ± 0.31) and FBL (-0.15 ± 0.31). These results revealed that RIG might be a superior trait as it guarantees reduced feed intake with faster-growing mink yet with no negative impacts on body weight and length. In addition, the strong positive genetic correlations (±SE) between KR with component traits (0.88 ± 0.11 with FBW, 0.68 ± 0.17 with FBL, and 0.97 ± 0.02 with ADG) suggested KR as an applicable indirect measure of FE for improvement of component traits as it did not require the individual feed intake to be measured. Overall, our results confirmed the possibility of including FE traits in mink breeding programs to effectively select feed-efficient animals.

Grazing beef cows identified as efficient using a nutrition model partition more energy to lactation

Context The efficiency of the cow–calf sector could be enhanced by matching cow biological type to the production environment; however, methods to estimate the biological efficiency of grazing beef cows are not available. Aims This study utilised a mathematical nutrition model for ranking beef cows for estimated biological efficiency, determining energetic efficiency and evaluate relationships with other production traits. Methods Cow live weight, calf birth and weaning weight, calf birth and weaning date, and forage nutritive value of hay and pasture were collected for 69 Brangus crossbred beef cows over a complete production cycle. The Cattle Value Discovery System for Beef Cow (CVDSbc) model was used to compute metabolisable energy required (MER) for the cow, and energy efficiency index (EEI) was computed as the ratio of MER to calf weaning weight. Pearson correlation coefficients were computed among performance traits. During late lactation and gestation, low (n=8) and high (n=8) EEI cows were individually fed ad libitum for 44 and 32 days, respectively, then fed 0.5× the estimated metabolisable energy required for maintenance for 7 days (gestation experiment only). Apparent nutrient digestibility, heat production, and milk yield were measured. Key results EEI was strongly negatively correlated (P&lt;0.05) with model predicted peak milk (−0.62) and calf weaning weight (−0.65), but moderately correlated (P&lt;0.05) with cow live weight (0.46). Dry matter intake was not different (P&gt;0.75) between low and high EEI cows even though low EEI cows weighed less (P&lt;0.05) during late lactation and gestation experiments. Low EEI cows tended to have greater efficiency of metabolisable energy use for maintenance and gain (P&lt;0.10), and EEI was negatively correlated (P&lt;0.05) with the efficiency of metabolisable energy use for maintenance (−0.56) and gain (−0.57). Conclusion The CVDSbc model identified cows that weaned heavier calves due to greater dry matter intake of cows relative to live weight allowing more energy apportioned towards lactation, and more efficient use of metabolisable energy for maintenance and gain. Implications Energy efficiency index might provide a logical assessment of biological efficiency of beef cows in grazing production systems.

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.

Selection criteria for feed efficiency-related traits and their association with growth, reproductive and carcass traits in Nelore cattle

Context Livestock feed costs have a higher impact on the profitability of beef production systems and are directly related to feed efficiency. However, these traits are hard and have high costs to measure, reducing the availability of phenotypic records and reliability of genetic evaluations. Thus, the use of genomic information can increase the robustness of genetic studies that address them. Aims The aim of the present study was to estimate genetic parameters for feed efficiency, growth, reproductive and carcass traits in Nelore cattle and the correlated response among them, using genomic information. Methods Residual feed intake (RFI), dry-matter intake, feed conversion ratio, feed efficiency (FE), residual average daily gain (RG), residual feed intake and average daily gain (RIG), birthweight, weight at 120, 240, 365 and 450 days of age, scrotal circumference at 365 and 450 days of age, rib-eye area, backfat thickness and rump fat thickness were evaluated. The genetic parameters were estimated using the single-step genomic best linear unbiased prediction approach. Key results The FE-related traits showed low to moderate heritability ranging from 0.07 to 0.23. Feed efficiency-related traits showed low genetic correlations with reproductive (–0.24 to 0.27), carcass (–0.17 to 0.27) and growth (–0.19 to 0.24) traits, except for growth with dry-matter intake (0.32–0.56) and weight at 365 days of age with FE (–0.40). Conclusions The selection to improve growth, reproductive and carcass traits would not change RFI, RG and RIG. The choice of the most adequate selection criterion depends on the production system, that is, RFI might be used for low-input beef cattle systems, and RIG would be used for more intensive and without-any-dietary-restrictions beef cattle systems. Implications The estimates of heritability and genetic correlations suggest that genetic selection for feed efficiency using RFI, RG and RIG in Nellore cattle leads to higher genetic gain than does that using FE and feed conversion ratio without affecting other profitability traits.

Selection strategies for beef cow size and condition

Context The present work was motivated by beef breeder concerns that selection for high growth and low fat in steers and low mature weight in cows will lead to cows that have low body condition and, therefore, productivity. Aims The aim of this was to partition cow weight into size (associated with height) and condition (variation net of height) and test whether the trait net weight is a worthy addition to breeding programs. Methods Angus cows (5901) were measured as heifers (4889) and at pre-calving and weaning of their first and second calf (minimum 2690) for weight, height and body condition traits (condition score, ultrasound eye-muscle area, P8 and rib fat depth, and intramuscular fat percentage). A novel trait was developed by fitting height as a covariate to weight, with the residuals termed net weight. Key results Net weight was both heritable and genetically correlated with cow condition score and ultrasound measures. However, despite having a lower heritability, condition score was a more effective measure for genetic improvement of cow condition. Conclusions A measure of cow condition should be included in genetic evaluation programs but net weight is unlikely to be that measure. Implications Condition score should be recorded at the time of mature cow weight for breeding programs.

Selection for lower residual feed intake in mice is accompanied by increased body fatness and lower activity but not lower metabolic rate

Context Mice bred to be genetically different in feed efficiency were used in this experiment designed to help improve our knowledge of the biological basis of variation in feed efficiency between individual animals. Aims This experiment used mice to explore the metabolic basis of genetic variation in feed efficiency in the growing animal. Methods Mice bred to differ in residual feed intake (RFI) recorded over a postweaning test were used. After 11 generations of divergent selection, mice in groups were tested for RFI from 6 to 8, 8 to 10, and 10 to 12 weeks of age, and measured for traits describing the ability to digest feed, body composition, protein turnover, basal and resting metabolic rate, and level of activity. Key results Compared with the low-RFI (high efficiency) line mice, high-RFI mice consumed 28% more feed per day over their RFI-test, were no heavier, were leaner (16% less total fat per unit of bodyweight), did not differ in the fractional synthesis rate of protein in skeletal muscle or in liver, and had similar basal metabolic rates at 33°C. On an energy basis, the selection lines did not differ in energy retained in body tissue gain, which represented only 1.8% of metabolisable energy intake. The remaining 98.2% was lost as heat. Of the processes measured contributing to the higher feed intake by the high-RFI mice, 47% of the extra feed consumed was lost in faeces and urine, activity was 84% higher and accounted for 24%, the cost of protein gain was 6% higher and accounted for 2%, and the energy cost of digesting and absorbing the extra feed consumed and basal heat production could have accounted for 11 and 15% each. Conclusions Selection for low RFI (high efficiency) in mice was accompanied by an increase in body fat, an improvement in the process of digestion, a lower rate of protein turnover and a much lower level of activity. Selection did not result in major change in basal metabolic rate. Implications This experiment with mice provided new information on the biological basis of genetic differences in feed efficiency. The experiment investigated the relative importance of major energy-consuming metabolic processes and was able to quantify the responses in protein turnover and level of activity, being responses in energy-consuming processes that have proven difficult to quantitatively demonstrate in large farm animals.