Covariance functions and random regression models for cow weight in beef cattle

Data from the first four cycles of the Germplasm Evaluation program at the U.S. Meat Animal Research Center were used to evaluate weights of Angus, Hereford, and F1 cows produced by crosses of 22 sire and 2 dam (Angus and Hereford) breeds. Four weights per year were available for cows from 2 through 8 yr of age (AY) with age in months (AM). Weights (n = 61,798) were analyzed with REML using covariance function-random regression models (CF-RRM), with regression on orthogonal (Legendre) polynomials of AM. Models included fixed regression on AM and effects of cow line, age in years, season of measurement, and their interactions; year of birth; and pregnancy-lactation codes. Random parts of the models fitted RRM coefficients for additive (a) and permanent environmental (c) effects. Estimates of CF were used to estimate covariances among all ages. Temporary environmental effects were modeled to account for heterogeneity of variance by AY. Quadratic fixed regression was sufficient to model population trajectory and was fitted in all analyses. Other models varied order of fit and rank of coefficients for a and c. A parsimonious model included linear and quartic regression coefficients for a and c, respectively. A reduced cubic order sufficed for c. Estimates of all variances increased with age. Estimates for older ages disagreed with estimates using traditional bivariate models. Plots of covariances for c were smooth for intermediate, but erratic for extreme ages. Heritability estimates ranged from 0.38 (36 mo) to 0.78 (94 mo), with fluctuations especially for extreme ages. Estimates of genetic correlations were high for most pairs of ages, with the lowest estimate (0.70) between extreme ages (19 and 103 mo). Results suggest that although cow weights do not fit a repeatability model with constant variances as well as CF-RRM, a repeatability model might be an acceptable approximation for prediction of additive genetic effects.     

Antimicrobial resistance in beef and dairy cattle production

Observational studies of cattle production systems usually find that cattle from conventional dairies harbor a higher prevalence of antimicrobial resistant (AMR) enteric bacteria compared to organic dairies or beef-cow operations; given that dairies usually use more antimicrobials, this result is not unexpected. Experimental studies have usually verified that application of antimicrobials leads to at least a transient expansion of AMR bacterial populations in treated cattle. Nevertheless, on dairy farms the majority of antibiotics are used to treat mastitis and yet AMR remains relatively low in mastitis pathogens. Other studies have shown no correlation between antimicrobial use and prevalence of AMR bacteria including documented cases where the prevalence of AMR bacteria is non-responsive to antimicrobial applications or remains relatively high in the absence of antimicrobial use or any other obvious selective pressures. Thus, there are multi-factorial events and pressures that influence AMR bacterial populations in cattle production systems. We introduce a heuristic model that illustrates how repeated antimicrobial selection pressure can increase the probability of genetic linkage between AMR genes and niche- or growth-specific fitness traits. This linkage allows persistence of AMR bacteria at the herd level because subpopulations of AMR bacteria are able to reside long-term within the host animals even in the absence of antimicrobial selection pressure. This model highlights the need for multiple approaches to manage herd health so that the total amount of antimicrobials is limited in a manner that meets animal welfare and public health needs while reducing costs for producers and consumers over the long-term.     

Crossbreeding cattle in beef production programmes in Kenya

Data collected on a privately owned ranch located in the Machakos District of Kenya at approximately 2 degrees latitude south of the equator at an elevation varying from 1,675 to 2,000 m were analysed on five breed groups of cows: (1) purebred Boran, (2) 1/2 Charolais-1/2 Boran (1/2 C-1/2 B), (3) 3/4 Boran-1/4 Charolais (3/4 B-1/4 C), (4) 1/2 Ayrshire-1/2 Boran (1/2 A-1/2 B) and (5) 1/2 Santa Gertrudis-1/2 Boran (1/2 SG-1/2 B). The maternal traits evaluated included age at first calving, calving interval, calf weight at weaning and cow productivity index (calf weight weaned annually per cow calving). Mean cow productivity index for all cows was 192 kg; for purebred Boran, 174 kg; for 1/2 C-1/2 B, 200 kg; for 3/4 B-1/4 C, 191 kg; for 1/2 A-1/2 B, 210 kg; and for 1/2 SG-1/2 B, 185 kg. Cow breed groups 1/2 C-1/2 B, 3/4 B-1/4 C, 1/2 A-1/2 B and 1/2 SG-1/2 B exceeded (P less than 0.01) purebred Boran by 14.9, 9.8, 20.7 and 6.3%, respectively, in cow productivity index.     

纤维素酶在肉牛生产中的研究与应用

自从1906年纤维素酶首次在蜗牛的消化液中被发现以来，纤维酶的研究就受到动物营养界的普遍关注。进入上世纪90年代，世界能源的匮乏促使纤维素酶的研究重点转向开辟新能源方面。反刍动物日粮以粗饲料为主，但是我国目前优质牧草的缺口很大，因而极大地限制了     

超敏蛋白复合酶在肉牛生产中的应用

[目的]试验将超敏蛋白复合酶添加于肉牛生产中的母牛繁育和肉牛育肥环节,研究其应用效果。[方法]试验选择平均怀孕45 d左右的同批次怀孕母牛28头,随机均分为试验A1组和对照A2组,选择育肥青年牛78头,随机均分为试验B1组和对照B2组。对照A2组和B2组按照原来的饲料配方饲喂,试验A1组和B1组在原有的基础上添加精饲料1‰的超敏蛋白复合酶进行饲喂。[结果]试验结果表明,怀孕母牛的试验组相较于对照组产活仔数多1头,出生均重差为7.58 kg, 60日龄断奶均重差为12.55 kg;育肥青年牛的试验组相较于对照组增重大幅提升,育肥期平均增重差为84 kg。[结论]超敏蛋白复合酶在肉牛生产的母牛繁育、青年牛育肥方面均表现出卓越成效,经济效益明显提高。     

HACCP模式在肉牛安全生产中的应用

HACCP是迄今为止食品安全生产方面最有效、最科学的质量管理方法之一。本文根据HACCP的技术规程,对肉牛生产的各流程进行分析,确定了肉牛生产过程中的关键控制点,并提出了控制措施。     

大豆皮在奶牛、肉牛和猪饲养中的应用(2)

3大豆皮对奶牛和肉牛的饲用价值用大豆皮替代奶牛混合精料中的燕麦或玉米并不会使产奶量和产奶效率下降(Kung和Lin,1997;Kohlm eier,1996)。Owen等(1984)在3个独立的奶牛试验中用大豆皮代替21%￣50%的混合谷物,产奶量、产奶效率未受显著影响。在后来的研究中(Nakam ura和Owen,1     

Genetic antagonism between body weight and milk production in beef cattle

Korean cattle have an unusually short suckling period (4 mo) due to poor milking ability, and this is a hindrance to growth of calves. Therefore, Korean cattle breeders have shown interest in genetic improvement of milking ability. In this study, body weight (birth weight, weaning weight, and yearling weight) and five daily milk yields by period in Korean cattle (Hanwoo) were analyzed using a two-trait sire and maternal grandsire mixed model. The milk yields used were actually measured at sequential intervals from 1 to 4 mo after calving. Posterior means of the parameters were estimated using Gibbs sampling. Heritability estimates (0.25 to 0.26) for daily milk yield at weaning were larger than those with other periods. Genetic impact on daily milk yield, especially at weaning, was emphasized in order to lengthen the suckling period of Korean cattle. Genetic correlation estimates between BW and daily milk yield were all negative (-0.08 to -0.16 for birth weight, -0.04 to -0.21 for weaning weight, and -0.12 to -0.19 for yearling weight), whereas environmental correlation estimates were all positive (0.20 to 0.39 for birth weight, 0.34 to 0.51 for weaning weight, and 0.30 to 0.45 for yearling weight). The negative estimates of genetic correlation between weight and milk yield implied genetic antagonism between direct and maternal effects for weaning weight of beef cattle.     

大豆皮在奶牛、肉牛和猪饲养中的应用(1)

前言大豆作为蛋白质来源已有五千多年的历史。中国首先提倡种植大豆,本世纪初传入美国。起初,人们主要关心大豆的含油量,提出油以后的大豆粕和大豆皮仅仅是副产品。不久,大豆粕中蛋白质的优异品质被人们所认识。从此,大豆粕成了猪、鸡日粮中补充蛋白质的主要来源。大豆加工时可     

Cumulative discounted expressions of dairy and beef traits in cattle production systems

Gene-flow methodology was used to calculate the cumulative discounted expressions (CDE) for annual/lactation, replacement heifer, cull cow, birth, yearling, and slaughter traits in alternative cattle production systems. Generic equations were presented and parameters representing dairy-beef production systems in Ireland and Brazil were inputted. Cumulative discounted expressions using input parameters from a hypothetical purebred dairy production system with poor cow longevity were also calculated. Cumulative discounted expressions were calculated assuming either an initial purebred or crossbred mating within each production system. Absolute and relative differences in CDE existed among trait categories across the three alternative production systems investigated. For example, the CDE of beef-related traits accruing from an initial purebred mating ranged from 0.42 to 0.75 CDE of an annual/lactation trait across the three contrasting systems investigated which differed in various input parameters. Such variation may alter the relative emphasis of traits on overall profitability thereby contributing to genotype by environment interactions. The results of this study highlight the necessity to consider auxiliary traits in sire selection over and above those representing the principal intended use of the sire. This was particularly so for integrated dairy-beef cattle production systems.     

Evaluation of intensive vs extensive systems of beef production and the effect of level of beef cow milk production on postweaning performance

Charolais-sired calves from three groups of beef cows, similar in growth potential and mature size but different in genetic potential for milk production (5.6, 7.7, 9.0 kg/d; low, medium, and high, respectively), were allotted to two beef production systems each year for 3 yr. At weaning, calves in an intensive (Int) system went directly into the feedlot for finishing (236 d); calves in an extensive (Ext) system were wintered on corn residues (195 d), grazed pasture (115 d) and then were finished (122 d). Postweaning effects of increased weaning weight due to increased level of milk were small and not affected by growing-finishing system. Only the steer calves from the low milk-producing cows showed evidence (P less than .01) of compensatory growth postweaning in response to reduced levels of milk during the suckling phase. Cattle from the Ext system were heavier (P less than .01) before (388 vs 233 kg) and after (595 vs 531 kg) the finishing phase than Int system cattle. During finishing, cattle from the Ext system made more rapid gains (1.70 vs 1.36 kg/d) and consumed more feed (12.4 vs 8.5 kg/d, 2.52 vs 2.19% of average BW) but were less efficient (.137 vs .160, gain/feed) than cattle from the Int system (P less than .05). Extensive systems of beef production produced more total kilograms of beef per animal but they were 196 d older at slaughter.     

Estimation of effective population size using bivariate discrete distributions for modeling family size in beef cattle

The effects of heat processing (roasting and steeping) on nitrogen (N) fractionations, ruminal degradation and intestinal digestibility of N and amino acids (AA) in two Iranian whole soybean cultivars (Sahar and Williams) were determined using two ruminally fistulated and two intestinally cannulated Holstein steers by nylon bag techniques. The seeds were roasted at 140 to 145 °C using a drum roaster. A fraction of the seeds were cooled immediately and the rest were held in isolated barrels for 45 min (steeping). The non-protein N (NPN) and buffer soluble N (BSN) fractions in heat processed soybeans were found to be reduced significantly (P < 0.01) compared to raw seeds. Soluble (a) and insoluble potentially degradable (b) fractions of N, showed a similar pattern in raw and heat processed soybeans (in both cultivars), but rate of degradation (c) was reduced dramatically in heat processed seeds (67 and 70% in Sahar and Williams cultivars, respectively). The ruminal degradability of N and AA of heat processed soybeans was reduced significantly (P < 0.001) compared to raw seeds. However, among the individual AA some variation was found. Intestinal digestibility of N and AA (total and individual) was improved significantly (P < 0.001) by roasting (16.9 and 12.3% for N and total AA, respectively) and steep-roasting (25.0 and 18.5% for N and total AA, respectively). Intestinal digestibility of N or AA, measured with or without ruminal pre-incubation, was the same. Total tract disappearance of N was not significantly different between raw and roasted seeds. Total tract disappearance of total AA was higher for raw than roasted seeds, due to higher protein degradability of raw seeds. Roasting and steep-roasting were effective methods of changing the site of digestion from rumen to small intestine and therefore the amount of digestible undegraded AA in the small intestine can be increased. There was no significant difference between the two soybean cultivars with respect to N and total AA ruminal degradability, intestinal digestibility and total tract disappearance. The interaction between cultivar and heat processing was also not significantly different.     

Genetic relationships between calving performance and beef production traits in Piemontese cattle

The aim of the study was to obtain estimates of genetic correlations between direct and maternal calving performance of heifers and cows and beef production traits in Piemontese cattle. Beef production traits were daily gain, live fleshiness, and bone thinness measured on 1,602 young bulls tested at a central station. Live fleshiness (six traits) and bone thinness were subjectively scored by classifiers using a nine-point linear grid. Data on calving performance were calving difficulty scores (five classes from unassisted to embryotomy) routinely recorded in the farms. Calving performance of heifers and cows were considered different traits. A total of 30,763 and 80,474 calving scores in first and later parities, respectively, were used to estimate covariance components with beef traits. Data were analyzed using bivariate linear animal models, including direct genetic effects for calving performance and beef traits and maternal genetic effects only for calving performance. Due to the nature of the data structure, which involved traits measured in different environments and on different animals, covariances were estimated mostly through pedigree information. Genetic correlations of daily gain were positive with direct calving performance (0.43 in heifers and 0.50 in cows) and negative with maternal calving performance (-0.23 and -0.28 for heifers and cows, respectively). Live fleshiness traits were moderately correlated with maternal calving performance in both parities, ranging from 0.06 to 0.33. Correlations between live fleshiness traits and direct calving performance were low to moderate and positive in the first parity, but trivial in later parities. Bone thinness was negatively correlated with direct calving performance (-0.17 and -0.38 in heifers and cows, respectively), but it was positively correlated to maternal calving performance (0.31 and 0.40). Estimated residual correlations were close to zero. Results indicate that, due to the existence of antagonistic relationships between the investigated traits, specific selection strategies need to be studied.     

Effect of level of beef cow milk production on pre- and postweaning calf growth

Three groups of beef cows that were similar in growth and mature size, but different in genetic potential for level of milk provided to their calves, were studied. A procedure for fitting grafted polynomials based on calf suckling data was used to estimate the total amount of milk produced by each cow during 205-d lactations. Estimated 205-d milk production of the high milk group exceeded that of the medium and low milk groups by 186 and 561 kg, respectively. Differences in milk production of the three groups tended to increase as dams got older. The pooled, within milk-group correlation between calf gain to 205 d and milk intake was .60. Calves suckling dams with low milk production relied earlier and to a greater extent on alternative food sources of lower nutritional value than milk. Calves suckling high milk-group dams had 16.9 kg greater 205-d weaning weight than those suckling low milk-group dams, solely because of differences in maternal environment. Calves from the high milk group maintained 63% of the advantage over those in the low milk group in 205-d weight through a fairly rapid postweaning growth period to slaughter.     

Pasture intensification in beef cattle production can affect methane emission intensity

Increasing greenhouse gas (GHG) emissions from anthropogenic activities have contributed to global warming and consequently to climate change. Among all sources of emissions, the agricultural sector accounts for just under a quarter, mainly because of the intensification of food production systems necessary to supply the growing demand of the population. As ruminal fermentation is the largest source of methane emission in the livestock industry, emission by cattle has become the focus of studies. The aim of this study was to evaluate enteric methane emission and emission intensities of Nellore cattle at different ages submitted to levels of intensification of the grazing system. Twenty-four animals per cycle (age of 21.8 and 13.1 mo in cycles 1 and 2, respectively) were randomly distributed across different grazing systems: irrigated pasture with a high stocking rate (IHS), dryland pasture with a high stocking rate (DHS), recovering dryland pasture with a moderate stocking rate (DMS), and degraded pasture with a low stocking rate (DP). Methane emission was measured using the sulfur hexafluoride technique in each season of the cycle. Intensive systems provided higher yields of good-quality forage as well as superior animal performance when compared with DP. Methane yields were different between seasons and cycles. Methane emissions per average daily weight gain and dry matter digestible intake were different between treatments. Differences in the results were observed when they were analyzed per hectare, with the highest gain yield (P = 0.0134), stocking rate, weight gain, carcass production, and total methane emission (P < 0.0001) being found for the intensive systems. There were no differences in emissions per weight gain or carcass production between production systems, while a difference was observed between cycles (P = 0.0189 and P = 0.0255, respectively), resulting in lower emission intensities for younger animals. We conclude that more intensive systems resulted in a higher kilograms production of carcass per hectare; however, animals at 19 mo of age raised in the IHS and DMS systems had a lower emission intensity in kilogram of CO₂-eq. per kilogram of carcass. Moderate intensification (DMS) using animals at about 19 mo of age might be an effective strategy to mitigate GHG emissions from Brazilian tropical pastures. Further studies are needed to understand the relationship between increasing productivity and decreasing environmental impacts, especially methane emission from ruminants.     

DDGS和其他来源的粗饲料在肉牛生产上的应用研究

两组试验用来评估当在蒸汽压片玉米（SFC）日粮中添加玉米DDGS和苜蓿干草（AH）或者玉米青贮（CS）的肉牛的胴体品质、瘤胃发酵或日粮代谢的影响。在试验1中,358头体重为353±13kg的杂交母牛被用来评估玉米DDGS和AH（或CS）对肉牛胴体品质的影响,试验日粮分为4组,分别为：SFC-CS日粮,即蒸汽压片玉米（SFC）和11%青贮料（CS）;DDGS-CS日粮,即蒸汽压片玉米（SFC）和11%青贮料（CS）以及25%DDGS;SFC-AH日粮,即蒸汽压片玉米（SFC）和6%AH;DDGS-AH日粮,即SFC和25%DDGS以及6%AH。所有的牛每天自由采食,试验时间为97d。结果显示,饲喂DDGS没有影响肉牛的平均日增重（ADG,P=0.19）、干物质采食量DMI（P=0.14）以及饲料转化率（P=0.67）。饲喂CS的肉牛要比饲喂AH的肉牛的DMI高（P=0.05）,但ADG（P=0.56）和G：F（P=0.63）没有太大差别;各处理组的肉牛热胴体重（HCW）、屠宰率、皮下脂肪厚度以及牛肉产量、质量等级的差别也不大（P〉0.20）;饲喂CS组的肉牛相对饲喂AH肉牛有降低大理石花纹评分分数的趋势。在第2个试验中,12头荷斯坦奶牛用来评估各种日粮的肉牛瘤胃发酵和日粮代谢的差异。结果显示,饲喂后14h所有处理组的肉牛瘤胃pH值低于5.8,饲喂25%的DDGS组的肉牛瘤胃的乙酸和丙酸的比率较低（P=0.02）,但瘤胃乳酸浓度要比未添加DDGS组的高（P=0.02）。饲喂25%的DDGS组的肉牛瘤胃氨气浓度有所下降（P〈0.01）。这说明当在肉牛蒸汽压片玉米日粮中添加DDGS可以提高饲料转化率。     

Systems approaches to beef cattle production systems using modeling and simulation

Systems approach techniques have been applied to modeling production systems for beef cattle from the relatively micro‐level of tissues and organs to the macro‐level of farms and geographical regions. This paper reviews the various types of beef cattle production models already in operation in order to analyze beef cattle production systems and their components. It may be theoretically possible to construct system models which describe such complex production systems and can be generally used in various genetic, nutritional, management and economic situations as well as in training, extension and educational programs. Moreover, the systems approach can assist in the organization of information and identification of knowledge gaps and thereby open an avenue to multi‐disciplinary research projects.