Residual feed intake in beef cattle and its association with carcass traits, ruminal solid-fraction bacteria, and epithelium gene expression

Background: Residual feed intake(RFI) describes an animal’s feed efficiency independent of growth performance.The objective of this study was to determine differences in growth performance, carcass traits, major bacteria attached to ruminal solids-fraction, and ruminal epithelium gene expression between the most-efficient and the least-efficient beef cattle. One-hundred and forty-nine Red Angus cattle were allocated to three contemporary groups according to sex and herd origin. Animals were fed a finishing diet in confinement for 70 d to determine the RFI category for each. Within each group, the two most-efficient(n = 6; RFI coefficient =-2.69 ± 0.58 kg dry matter intake(DMI)/d) and the two least-efficient animals(n = 6; RFI coefficient = 3.08 ± 0.55 kg DMI/d) were selected. Immediately after slaughter, ruminal solids-fraction and ruminal epithelium were collected for bacteria relative abundance and epithelial gene expression analyses, respectively, using real-time PCR.Results: The most-efficient animals consumed less feed(P = 0.01; 5.03 kg less DMI/d) compared with the leastefficient animals. No differences(P > 0.10) in initial body weight(BW), final BW, and average daily gain(ADG) were observed between the two RFI classes. There were no significant RFI × sex effects(P > 0.10) on growth performance.Compared with the least-efficient group, hot carcass weight(HCW), ribeye area(REA), and kidney, pelvic, and heart fat(KPH) were greater(P ≤ 0.05) in the most-efficient cattle. No RFI × sex effect(P > 0.10) for carcass traits was detected between RFI groups. Of the 10 bacterial species evaluated, the most-efficient compared with least efficient cattle had greater(P ≤ 0.05) relative abundance of Eubacterium ruminantium, Fibrobacter succinogenes, and Megasphaera elsdenii, and lower(P ≤ 0.05) Succinimonas amylolytica and total bacterial density. No RFI × sex effect on ruminal bacteria was detected between RFI groups. Of the 34 genes evaluated in ruminal epithelium, the mostefficient cattle had greater(P ≤ 0.05) abundance of genes involved in VFA absorption, metabolism, ketogenesis, and immune/inflammation-response. The RFI × sex interactions indicated that responses in gene expression between RFI groups were due to differences in sex. Steers in the most-efficient compared with least-efficient group had greater(P ≤ 0.05) expression of SLC9 A1, HIF1 A, and ACO2. The most-efficient compared with least-efficient heifers had greater(P ≤ 0.05) m RNA expression of BDH1 and lower expression(P ≤ 0.05) of SLC9 A2 and PDHA1.Conclusions: The present study revealed that greater feed efficiency in beef cattle is associated with differences in bacterial species and transcriptional adaptations in the ruminal epithelium that might enhance nutrient delivery and utilization by tissues. The lack of RFI × sex interaction for growth performance and carcass traits indicates that sex may not play a major role in improving these phenotypes in superior RFI beef cattle. However, it is important to note that this result should not be considered a solid biomarker of efficient beef cattle prior to further examination due to the limited number of heifers compared with steers used in the study.

Effects of Molasses-Urea Supplementation on Weight Gain,Ruminal Fermentation and Major Microbe Populations of Winter-Grazing Sheep in Inner Mongolia

The present experiment was conducted to determine the effects of Molasses-Urea Supplementation （MUS） on weight gain, ruminal fermentation and major microbial populations in sheep on a winter grazing regime in Inner Mongolia. Total 40 sheep, allowed free consumption of MUS after grazing, served as a treatment group, while 30 sheep, fed only by pasture grazing, served as a control group. Ruminal fermentation parameters, consisted of pH, Bacterial Crude Protein （BCP） and ammonia nitrogen （NH3-N） were measured. In addition, numbers of five symbiotic bacteria were investigated. The results showed as follows： the average daily weight gain, concentration of NH3-N and numbers of protozoa were significantly higher （p〈0.05） in the treatment group than those in the control group. Contrastingly, no significant difference was found in BCP concentration and pH between the two groups. At the end of the experiment, the populations of Selenomonas ruminantium, Anaerovibrio lipolytica, Fibrobacter succinogenes, Ruminococcus flaveciens and Ruminococcus albus in the treatment group were significantly higher than those of the control group （p〈0.05）. These results demonstrated that greater weight gain could be induced during winter in Inner Mongolia by improved nutritional status through promotion of microbial populations using urea and sugar.

Effects of formic acid and corn flour supplementation of banana pseudostem silages on nutritional quality of silage,growth,digestion,rumen fermentation and cellulolytic bacterial community of Nubian black goats

The objective of this study was to evaluate the effects of adding formic acid and corn flour supplementation to banana pseudostem silages on the nutritional quality of these silages,growth,digestion,rumen fermentation and cellulolytic bacterial community of Nubian black goats fed these silages.Banana pseudostem silage was prepared either conventionally without any additives(CON)or mixed with 0.6% formic acid(F),10% corn flour(C),or both(F+C).Four experimental diets containing 40% of the corresponding silages were designed with roughage to concentrate ratio of 50:50(dry matter(DM)basis).A total of 48 Nubian black castrated goats(body weight(BW),(22.64±1.82)kg;4-mon-old)were randomized into one of the four treatment groups with 12 replicates of one castrated goat per replicate for each treatment in a completely randomized design.Each group was fed on one of the four experimental diets for 40 days.A factorial arrangement of treatments of 2(formic acid levels:0 and 0.6%)×2(corn flour:0 and 10%)was adopted.Formic acid supplementation increased(P<0.05)average daily gain,as well as lactic acid,propionate and butyric acid and water-soluble carbohydrate concentrations,but decreased(P<0.05)the feed conversion rate,pH value,acetate/propionate ratio,and butyric acid concentration relative to the CON group.Corn flour supplementation increased(P<0.05)the apparent digestibility of crude protein,neutral detergent fiber,and non-fibrous carbohydrate and Fibrobacter succinogenes,Ruminococcus albus,and Butyrivibrio fibrisolvens populations,but decreased(P<0.05)the Ruminococcus flavefaciens population relative to the CON group.There were no F×C treatment interactions(P>0.05)for any of the other indices except for the apparent digestibility of non-fibrous carbohydrate(NFC)(P<0.05).The results demonstrated that adding 0.6% formic acid and 10% corn flour supplementation to banana pseudostem silages improved the nutritional quality of these silages and enhanced the growth performance of Nubian black castrated goats by improving apparent nutrient digestibility,and regulating ruminal fermentation and bacteria populations.

Urea transport and hydrolysis in the rumen: A review

Inefficient dietary nitrogen(N)conversion to microbial proteins,and the subsequent use by ruminants,is a major research focus across different fields.Excess bacterial ammonia(NH3)produced due to degradation or hydrolyses of N containing compounds,such as urea,leads to an inefficiency in a host’s ability to utilize nitrogen.Urea is a non-protein N containing compound used by ruminants as an ammonia source,obtained from feed and endogenous sources.It is hydrolyzed by ureases from rumen bacteria to produce NH_(3) which is used for microbial protein synthesis.However,lack of information exists regarding urea hydrolysis in ruminal bacteria,and how urea gets to hydrolysis sites.Therefore,this review describes research on sites of urea hydrolysis,urea transport routes towards these sites,the role and structure of urea transporters in rumen epithelium and bacteria,the composition of ruminal ureolytic bacteria,mechanisms behind urea hydrolysis by bacterial ureases,and factors influencing urea hydrolysis.This review explores the current knowledge on the structure and physiological role of urea transport and ureolytic bacteria,for the regulation of urea hydrolysis and recycling in ruminants.Lastly,underlying mechanisms of urea transportation in rumen bacteria and their physiological importance are currently unknown,and therefore future research should be directed to this subject.