肉牛剩余采食量的概念和实践应用

剩余采食量(RFI)是实际采食量与预测采食量的差值,是衡量肉牛饲料效率的新指标。文章简要介绍了RFI的概念、测定方法、应用RFI的益处,以及影响肉牛RFI的一些生理因素,包括采食量、消化率、体组织代谢、活动量、体温调节等。最后,文章讨论了RFI在肉牛生产实践中的应用。     

Genetic relationships between feed efficiency in growing males and beef cow performance

Most studies on feed efficiency in beef cattle have focused on performance in young animals despite the contribution of the cow herd to overall profitability of beef production systems. The objective of this study was to quantify, using a large data set, the genetic covariances between feed efficiency in growing animals measured in a performance-test station, and beef cow performance including fertility, survival, calving traits, BW, maternal weaning weight, cow price, and cull cow carcass characteristics in commercial herds. Feed efficiency data were available on 2,605 purebred bulls from 1 test station. Records on cow performance were available on up to 94,936 crossbred beef cows. Genetic covariances were estimated using animal and animal-dam linear mixed models. Results showed that selection for feed efficiency, defined as feed conversion ratio (FCR) or residual BW gain (RG), improved maternal weaning weight as evidenced by the respective genetic correlations of -0.61 and 0.57. Despite residual feed intake (RFI) being phenotypically independent of BW, a negative genetic correlation existed between RFI and cow BW (-0.23; although the SE of 0.31 was large). None of the feed efficiency traits were correlated with fertility, calving difficulty, or perinatal mortality. However, genetic correlations estimated between age at first calving and FCR (-0.55 ± 0.14), Kleiber ratio (0.33 ± 0.15), RFI (-0.29 ± 0.14), residual BW gain (0.36 ± 0.15), and relative growth rate (0.37 ± 0.15) all suggest that selection for improved efficiency may delay the age at first calving, and we speculate, using information from other studies, that this may be due to a delay in the onset of puberty. Results from this study, based on the estimated genetic correlations, suggest that selection for improved feed efficiency will have no deleterious effect on cow performance traits with the exception of delaying the age at first calving.     

Prevotella copri,a potential indicator for high feed efficiency in western steers

There has been a great interest to identify a microbial marker that can be used to predict feed efficiency of beef cattle. Such a marker, specifically one that would allow an early identification of animals with high feed efficiency for future breeding efforts, would facilitate increasing the profitability of cattle operations and simultaneously render them more sustainable by reducing their methane footprint. The work presented here suggests that Prevotella copri might be an ideal microbial marker for identifying beef cattle with high feed efficiency early in their life span and in the production cycle. Developing more refined quantification techniques that allow correlation of P. copri to feed efficiency of beef cattle that can be applied by lay people in the field holds great promise to improve the economy of cattle operations while simultaneously reducing their environmental impact by mitigating methane production from enteric fermentation.     

EM发酵玉米秸秆和青贮玉米秸秆对奶牛生产性能的对比试验

本试验应用EM发酵玉米秸秆和青贮玉米秸秆饲喂奶牛,以观察两种方法处理的玉米秸秆对奶牛生产性能及经济效益的影响效果。结果表明,用EM发酵的玉米秸秆饲喂奶牛较青贮玉米秸秆饲喂奶牛,每天每头奶牛采食量提高1.03%,平均产奶量提高2.02%,经济效益提高0.13元;EM原液发酵的玉米秸秆和青贮玉米秸秆1∶1混合饲喂奶牛,每天每头奶牛采食量、平均产奶量、经济效益分别比饲喂青贮玉米秸秆的奶牛提高2.85%、2.99%和1.15元。     

尿素糖浆饲料舔块在养牛生产中的应用效果

[目的]甘肃省的饲料资源现状是粗饲料资源丰富,蛋白质饲料相对不足,为了解决草食畜养殖过程中蛋白质饲料不足的问题,[方法]通过对育肥牛、奶牛、牦牛等补饲尿素糖浆饲料舔块,增加蛋白质采食量,[结果]显示,采食尿素糖浆饲料舔块后,育肥牛日增重增加,奶牛产奶量提高,繁殖母牛怀孕率提高,读牛初生重提高.[结论]补饲一定数量的尿素糖浆饲料舔块,在粗放饲养和低精饲料条件下生产性能明显提高.     

Milk residues and performance of lactating dairy cows administered high doses of monensin

Milk residues and performance were evaluated in lactating cows that were fed up to 10 times the recommended dose of monensin. Following an acclimatization period of 14 d, during which cows were fed a standard lactating cow total mixed ration containing 24 ppm monensin, 18 lactating Holstein dairy cows were grouped according to the level of feed intake and then randomly assigned within each group to 1 of 3 challenge rations delivering 72, 144, and 240 ppm monensin. Outcome measurements included individual cow daily feed intakes, daily milk production, body weights, and monensin residues in composite milk samples from each cow. There were no detectable monensin residues (< 0.005 microg/mL) in any of the milk samples collected. Lactating cows receiving a dose of 72 ppm monensin exhibited up to a 20% reduction in dry matter intake, and a 5% to 15% drop in milk production from the pre-challenge period. Cows receiving doses of 144 and 240 ppm monensin exhibited rapid decreases in feed intake of up to 50% by the 2nd d and milk production losses of up to 20% and 30%, respectively, within 4 d. Lactating cows receiving up to 4865 mg monensin per day had no detectable monensin residues (< 0.005 microg/mL) in any of the milk samples collected. Results of this study confirm that food products derived from lactating dairy cattle receiving monensin at recommended levels are safe for human consumption.     

Grass silage intake, rumen and blood variables, ultrasonic and body measurements, feeding behavior, and activity in pregnant beef heifers differing in phenotypic residual feed intake

The objectives of this study were to quantify the phenotypic variation in residual feed intake (RFI) in pregnant beef heifers offered a grass silage diet and to characterize their productivity. Seventy-three pregnant (mean gestation d 198, SD = 27 d) Simmental and Simmental × Holstein-Friesian heifers (mean initial BW 548, SD = 47.5 kg) were offered grass silage ad libitum. Heifer DMI, BW, BCS, skeletal measurements, ultrasonic fat and muscle depth, visual muscularity score, rumen fermentation, total tract digestibility, blood metabolite and hematology variables, feeding, and activity behavior were measured during an 84-d feed intake study. After parturition calf birth weight, calving difficulty, cow serum IgG, hematology variables, and calf humoral immune status were measured. In a subset of cows (n = 28), DMI, milk yield and various body composition variables were also measured approximately 3 wk postpartum. Phenotypic RFI was calculated for each animal as the difference between actual DMI and expected DMI. Expected DMI was computed for each animal by regressing average daily DMI on conceptus-adjusted mean BW(0.75) and conceptus-adjusted ADG over an 84-d period. Within breed, heifers were ranked by RFI into low (efficient), medium, and high (inefficient) groups by dividing them into thirds. Heifers with high RFI had 8.8 and 17.1% greater (P < 0.001) DMI than medium and low RFI groups, respectively. The RFI groups did not differ in ADG or BW (P > 0.05). Residual feed intake was positively correlated with DMI (r = 0.85) but not with feed conversion ratio, ADG, or BW. The RFI groups did not differ (P > 0.05) in skeletal size, BCS, ultrasonic fat depth, total tract digestibility, calf birth weight, calving difficulty, serum IgG concentrations, or milk yield. Visual muscularity scores, initial test and postpartum ultrasonic muscle depth were negatively correlated with RFI (P < 0.05). Including mean ultrasonic muscle depth into the base RFI regression model increased its R(2) (0.29 to 0.38). Pearson rank correlation between RFI and muscle-adjusted RFI was 0.93. The results show that efficient RFI heifers consumed less feed without any compromise in growth, body composition, or maternal traits measured.     

Relationships of feedlot feed efficiency, performance, and feeding behavior with metabolic rate, methane production, and energy partitioning in beef cattle

Residual feed intake (RFI) is the difference between the actual and expected feed intake of an animal based on its BW and growth rate over a specified period. The biological mechanisms underlying the variation in feed efficiency in animals with similar BW and growth rate are not well understood. This study determined the relationship of feedlot feed efficiency, performance, and feeding behavior with digestion and energy partitioning of 27 steers. The steers were selected from a total of 306 animals based on their RFI following feedlot tests at the University of Alberta Kinsella Research Station. Selected steers were ranked into high RFI (RFI > 0.5 SD above the mean, n = 11), medium RFI (RFI +/- 0.5 SD above and below the mean, n = 8), and low RFI (RFI < -0.5 SD below the mean, n = 8). The respective BW +/- SD for the RFI groups were 495.6 +/- 12.7, 529.1 +/- 18.6, and 501.2 +/- 15.5 kg. Digestibility and calorimetry trials were performed on a corn-or barley-based concentrate diet in yr 1 and 2, respectively, at 2.5 x maintenance requirements. Mean DMI (g/kg of BW(0.75)) during the measurements for high-, medium-, and low-RFI groups, respectively, were 82.7 +/- 2.0, 78.8 +/- 2.6, and 81.8 +/- 2.5 and did not differ (P > 0.10). Residual feed intake was correlated with daily methane production and energy lost as methane (r = 0.44; P < 0.05). Methane production was 28 and 24% less in low-RFI animals compared with high- and medium-RFI animals, respectively. Residual feed intake tended to be associated (P < 0.10) with apparent digestibilities of DM (r = -0.33) and CP (r = -0.34). The RFI of steers was correlated with DE (r = -0.41; P < 0.05), ME (r = -0.44; P < 0.05), heat production (HP; r = 0.68; P < 0.001), and retained energy (RE; r = -0.67; P < 0.001; energy values are expressed in kcal/kg of BW(0.75)). Feedlot partial efficiency of growth was correlated (P < 0.01) with methane production (r = -0.55), DE (r = 0.46), ME (r = 0.49), HP (r = -0.50), and RE (r = 0.62). With the exception of HP (r = 0.37; P < 0.05), feed conversion ratio was unrelated to the traits considered in the study. Feeding duration was correlated (P < 0.01) with apparent digestibility of DM (r = -0.55), CP (r = -0.47), methane production (r = 0.51), DE (r = -0.52), ME (r = -0.55), and RE (r = -0.60). These results have practical implications for the selection of animals that eat less at a similar BW and growth rate and for the environmental sustainability of beef production.     

Drinking frequency effects on the performance of cattle: a systematic review

This study used a systematic literature review methodology to determine whether there is evidence that drinking frequency has effects on cattle performance, what performance responses to drinking frequency are documented and how performance responses vary according to environmental and animal factors. Electronic databases were searched for English language articles with original data on at least one performance attribute (e.g. water intake, feed intake, live weight) of cattle in response to voluntary drinking frequency or controlled access periods to water. Sixteen experiments on dairy cows and 12 experiments on beef cattle were retrieved from the literature. For beef cattle, all experiments reported reduced water and feed intake with access to water once every second and/or third day compared with once‐daily access. Median reductions of 15% and 25% in water intake and 16% and 9% in feed intake were found across experiments respectively. Live weight responses of beef cattle to access to water were limited and yielded positive, negative and no effects. For dairy cows, most experiments reported reduced water intake, milk yield and milk fat content with access to water twice or once daily compared with controls (ad libitum or ad libitum except at the dairy). Median reductions of 13% and 12% in water intake, 2% and 1% in milk yield and 1% and 2% in milk fat content were found across experiments respectively. Water availability effects on feed intake and live weight were very limited for dairy cows and yielded positive, neutral and negative effects. Season, climate, experiment conditions, animal class and animal genotype were identified to potentially influence intake responses of cattle. The review highlights a number of important gaps in the literature where future work is required to better understand the optimum drinking frequency of cattle and implications of water availability on health, welfare and performance.     

日粮阴阳离子平衡在奶牛生产中应用的研究进展

日粮中的阴、阳离子对奶牛的正常生产和健康有着重要的意义,它们不仅影响奶牛体液的酸碱平衡和渗透压、机体的代谢活动及多项生理指标,而且在奶牛不同的生理阶段,适宜的日粮阴阳离子平衡能提高奶牛的采食量、生产性能,还能有效预防奶牛的产后瘫痪等疾病。作者现就日粮阴阳离子平衡(dietary cation anion balance,DCAB)在奶牛上的应用进行综述,为生产实践中合理应用提供一定的理论基础。     

Association of residual feed intake with abundance of ruminal bacteria and biopolymer hydrolyzing enzyme activities during the peripartal period and early lactation in Holstein dairy cows

Background: Residual feed intake(RFI) in dairy cattle typically calculated at peak lactation is a measure of feed efficiency independent of milk production level. The objective of this study was to evaluate differences in ruminal bacteria, biopolymer hydrolyzing enzyme activities, and overall performance between the most-and the leastefficient dairy cows during the peripartal period. Twenty multiparous Holstein dairy cows with daily ad libitum access to a total mixed ration from d-10 to d 60 relative to the calving date were used. Cows were classified into most-efficient(i.e. with low RFI, n = 10) and least-efficient(i.e. with high RFI, n = 10) based on a linear regression model involving dry matter intake(DMI), fat-corrected milk(FCM), changes in body weight(BW), and metabolic BW.Results: The most-efficient cows had ~ 2.6 kg/d lower DMI at wk 4, 6, 7, and 8 compared with the least-efficient cows. In addition, the most-efficient cows had greater relative abundance of total ruminal bacterial community during the peripartal period. Compared with the least-efficient cows, the most-efficient cows had 4-fold greater relative abundance of Succinivibrio dextrinosolvens at d-10 and d 10 around parturition and tended to have greater abundance of Fibrobacter succinogenes and Megaspheara elsdenii. In contrast, the relative abundance of Butyrivibrio proteoclasticus and Streptococcus bovis was lower and Succinimonas amylolytica and Prevotella bryantii tended to be lower in the most-efficient cows around calving. During the peripartal period, the most-efficient cows had lower enzymatic activities of cellulase, amylase, and protease compared with the least-efficient cows.Conclusions: The results suggest that shifts in ruminal bacteria and digestive enzyme activities during the peripartal period could, at least in part, be part of the mechanism associated with better feed efficiency in dairy cows.     

脂肪对奶牛采食量及瘤胃消化的影响

随着人们对脂肪营养和生理功能认识的深入,多种脂肪产品用于高产奶牛生产中,大量试验结果证明,日粮中添加脂肪对奶牛采食量和瘤胃消化具有影响,作者综述了日粮脂肪在瘤胃内的代谢、日粮中添加脂肪对脂肪酸、干物质、碳水化合物、粗纤维和粗蛋白质采食量和瘤胃消化影响的研究进展。     

牛甲烷排放量的估测

反刍动物甲烷排放量的研究主要是根据能量转化过程中甲烷能量损失量来确定饲料的代谢能和能量需要。但由于甲烷是温室气体的一种来源,其排放量的增加致使全球气温升高。因此,近些年来国内外学者对反刍动物甲烷排放量的估测越来越重视。研究方法大多根据反刍动物甲烷排放量的实测结果,运用统计方法建立甲烷排放量的估测模型。本文重点介绍中国农业大学以瘤胃瘘管阉牛作为试验动物,用大型自控呼吸测热室持续测定不同日粮在全消化道内甲烷排放量所得出的估测模型。根据《奶牛营养需要和饲料成分》(2007)中现有参数,选用上述估测模型进行甲烷排放量的估测。其中,由于我国存栏产奶奶牛的平均产奶量较低,故估测的甲烷排放量为96.29 kg/(头.a)。但日产奶量为20 kg/头的奶牛其甲烷排放量估测值为114.6 kg/(头.a)。此外,本文还利用上述模型对我国肉牛、役牛和牦牛的甲烷排放量作了初步估测。     

牛粪好氧堆肥处理技术

随着我国肉（奶）牛养殖的规模化、集约化发展,牛粪高效、安全的利用成为当前发展现代农业和环境保护急需解决的重要问题。本文对照牛粪发酵参数,重点介绍了牛粪堆肥发酵的控制和调节,以及堆肥产物的质量评判标准,旨在为该领域的研究提供理论参考。     

Fine mapping quantitative trait loci for feed intake and feed efficiency in beef cattle

Feed intake and feed efficiency are economically important traits in beef cattle because feed is the greatest variable cost in production. Feed efficiency can be measured as feed conversion ratio (FCR, intake per unit gain) or residual feed intake (RFI, measured as DMI corrected for BW and growth rate, and sometimes a measure of body composition, usually carcass fatness, RFI(bf)). The goal of this study was to fine map QTL for these traits in beef cattle using 2,194 markers on 24 autosomes. The animals used were from 20 half-sib families originating from Angus, Charolais, and University of Alberta Hybrid bulls. A mixed model with random sire and fixed QTL effect nested within sire was used to test each location (cM) along the chromosomes. Threshold levels were determined at the chromosome and genome levels using 20,000 permutations. In total, 4 QTL exceeded the genome-wise threshold of P < 0.001, 3 exceeded at P < 0.01, 17 at P < 0.05, and 30 achieved significance at the chromosome-wise threshold level (at least P < 0.05). No QTL were detected on BTA 8, 16, and 27 above the 5% chromosome-wise significance threshold for any of the traits. Nineteen chromosomes contained RFI QTL significant at the chromosome-wise level. The RFI(bf) QTL results were generally similar to those of RFI, the positions being similar, but occasionally differing in the level of significance. Compared with RFI, fewer QTL were detected for both FCR and DMI, 12 and 4 QTL, respectively, at the genome-wise thresholds. Some chromosomes contained FCR QTL, but not RFI QTL, but all DMI QTL were on chromosomes where RFI QTL were detected. The most significant QTL for RFI was located on BTA 3 at 82 cM (P = 7.60 x 10(-5)), for FCR on BTA 24 at 59 cM (P = 0.0002), and for DMI on BTA 7 at 54 cM (P = 1.38 x 10(-5)). The RFI QTL that showed the most consistent results with previous RFI QTL mapping studies were on BTA 1, 7, 18, and 19. The identification of these QTL provides a starting point to identify genes affecting feed intake and efficiency for use in marker-assisted selection and management.     

Simulated efficiency of range beef production. I. Growth and milk production

A revised version of the Texas A&M University Beef Cattle Production Model was used to simulate the effects of growth, milk production and management system on biological and economic efficiency of beef production in a northern plains, range environment. Animals varying in genetic potential for birth weight (BWA), yearling weight (YW), mature weight (WMA) and milk production (PMA) were simulated under both a weanling system of management (weaned calves custom-fed in the feedlot) and a yearling system (calves wintered on the ranch, then custom-fed after their second summer). The yearling system of management was biologically less efficient, but economically more efficient than the weanling system due primarily to heavier slaughter weights of fed animals. The advantage of the yearling system was most apparent for smaller genotypes. Herd efficiency improved with decreased BWA and increased YW, but changed little when WMA was varied while other growth traits were held constant. Increased PMA was favored for production of live weight at weaning and for production of slaughter product when feedlot costs were high. Increased PMA was not favored when feed costs for the cow herd were high. Economic weights generated from the simulation indicated the importance of selection for rapid early growth followed by selection for lighter birth weight. While larger genotypes were generally favored in this study, optimal cow size depended on economic conditions. Larger types were more biologically efficient and more economically efficient using standard costs, but medium- and small-size cattle were more efficient when feedlot costs were high. Small cattle were least efficient when feed costs for the cow herd were high.     

Partitioning of energy during lactation of primiparous beef cows

For a beef cow to continue in an annual production cycle, she must rebreed within 3 mo after calving. Malnutrition during this period frequently results in failure of the cow to become pregnant. The energetic needs of the cow are increased by lactation, and additional energy is required for growth of the primiparous cow. Determining energy expenditures during the first 40 to 60 d postpartum is critical to developing feed programs that will allow cows to become pregnant with a second calf. Sixty-seven balance trials were conducted on 25 MARC III cows (4-breed composite: (1/4) Hereford, (1/4) Angus, (1/4) Red Poll, and (1/4) Pinzgauer) that were between 3 and 53 d in milk. Cows' BW were 481 +/- 4 kg. Metabolizable energy intake ranged from 14.8 to 28.9 Mcal/d. Milk yields ranged from 4.7 to 13.3 kg/d. Recovered energy (RE) increased linearly with increased ME intake. Forty-seven observations were obtained with cows in negative tissue energy (TE) balance, and 20 observations were obtained with cows in positive TE balance. Estimated zero RE from regression analysis of RE on ME intake was 146 kcal of ME/kg of BW(0.75). Efficiency of conversion of ME to lactation energy (LE) was 72%. The efficiency for conversion of ME to TE and the conversion of TE to LE was 78%. Our findings suggest that, even though their milk production is lower, the overall efficiency of energy retention in young beef cows is similar to that of dairy cows.     

Review: Cost of Reproductive Diseases and Conditions in Cattle

Based on information from USDA National Animal Health Reporting System early State pilot studies and more recent national studies, the cost of reproductive diseases and conditions was estimated for beef and dairy cattle. We estimate the total yearly cost of female infertility, abortions/stillbirths, dystocia, retained placentas, and metritis/pyometra to be $441 to $502 million for beef producers and $473 to $484 million for dairy producers with an aggregate national total of approximately $1 billion annually. This loss is over six times more costly than that resulting from respiratory diseases. Three-fourths of the cost for reproductive diseases and conditions can be attributed to female infertility and dystocia and the failure to produce a healthy calf that will survive the first 24 h of life. Aggregate national costs are roughly evenly divided between beef and dairy; per cow costs are more than three times greater for dairy cows ($52.60) than for beef cows ($14.00). Approximately equal national costs are attained because there are more than three times more beef cows than dairy cows. One factor contributing to the greater cost for dairy cows is lost milk production associated with dystocia and retained placentas. Lost milk production accounts for one-third of the costs associated with reproductive diseases and conditions in dairy cattle. We conclude from this review and our resulting estimates that focusing on developing strategies to increase the probability of conception, minimize dystocia, and produce a healthy calf that survives beyond the first 24 h of birth must continue to receive high priority in both dairy and beef cattle management and research.     

Cattle selected for lower residual feed intake have reduced daily methane production

Seventy-six Angus steers chosen from breeding lines divergently selected for residual feed intake (RFI) were studied to quantify the relationship between RFI and the daily rate of methane production (MPR). A 70-d feeding test using a barley-based ration was conducted in which the voluntary DMI, feeding characteristics, and BW of steers were monitored. The estimated breeding value (EBV) for RFI (RFI(EBV)) for each steer had been calculated from 70-d RFI tests conducted on its parents. Methane production rate (g/d) was measured on each steer using SF(6) as a tracer gas in a series of 10-d measurement periods. Daily DMI of steers was lower during the methane measurement period than when methane was not being measured (11.18 vs. 11.88 kg; P = 0.001). A significant relationship existed between MPR and RFI when RFI (RFI(15d)) was estimated over the 15 d when steers were harnessed for methane collection (MPR = 13.3 x RFI(15d) + 179; r(2) = 0.12; P = 0.01). Animals expressing lower RFI had lower daily MPR. The relationship established between MPR and RFI(15d) was used to calculate a reduction in daily methane emission of 13.38 g accompanied a 1 kg/d reduction in RFI(EBV) in cattle consuming ad libitum a diet of 12.1 MJ of ME/kg. The magnitude of this emission reduction was between that predicted on the basis of intake reduction alone (18 g x d(-1) x kg of DMI(-1)) and that predicted by a model incorporating steer midtest BW and level of intake relative to maintenance (5 g x d(-1) x kg of DMI(-1)). Comparison of data from steers exhibiting the greatest (n = 10) and lowest (n = 10) RFI(15d) showed the low RFI(15d) group to not only have lower MPR (P = 0.017) but also reduced methane cost of growth (by 41.2 g of CH(4)/kg of ADG; P = 0.09). Although the opportunity to abate livestock MPR by selection against RFI seems great, RFI explained only a small proportion of the observed variation in MPR. A genotype x nutrition interaction can be anticipated, and the MPR:RFI(EBV) relationship will need to be defined over a range of diet types to account for this.