Relationship between nutrition and reproduction in beef cattle

The primary nutrient consideration for optimum reproductive performance in beef cattle is energy. Low energy intake delays the onset of puberty in heifers and bulls. Heifers should reach approximately 66 per cent of mature body weight by 14 to 15 months of age and be bred 30 days prior to breeding the main cow herd. Body conditioning scores (BCS) (1 = emaciated, 9 = obese) should be used to evaluate pregnant cows entering their third trimester. Cows should calve with body conditioning score 5 to 7. Forage quality and environmental factors influence maximum dry matter intake and nutrient requirements and must be considered in the clinical setting. Crude protein dietary content should be 11 to 12 per cent for lactating beef cattle. Mineral (calcium, phosphorus, magnesium, potassium, sulfur, sodium, chloride) nutrition is not a major cause of decreased reproductive performance in beef cattle. Trace mineral deficiencies (particularly selenium, copper, and zinc) can cause decreased reproductive performance. Diagnosis of these trace mineral deficiencies can be confirmed by elemental analysis of blood or tissues.     

Direct and maternal variances and covariances and maternal phenotypic effects on preweaning growth of beef cattle

Birth weights (BW) and weaning weights (WW) of 4,423 non-creep-fed Hereford calves were used to estimate direct and maternal sources of variation and maternal phenotypic effects (fm). Seventeen different (co)variances among relatives were estimated through Henderson's Method III and restricted estimated maximum likelihood procedures. Direct and maternal (co)variances and fm were evaluated by multiple regression procedures. Estimates of h2 for BW and WW were .28 and .28 respectively, by the paternal half-sib procedure and .45 and .88, respectively, based on full-sibs. Repeatability estimates were .21 for BW and .30 for WW. Heritabilities based on regression of offspring on dam and offspring on sire were .45 and .21 for BW and .28 and .06 for WW, respectively. Negative correlations were found between solutions for additive genetic direct and additive maternal effects (rG). Estimates of rG ranged from -.86 to -1.05 for BW and from -.57 to -.79 for WW. Estimates of heritability for direct effects (h2o), for maternal effects (h2m) and for total additive genetic effects (h2T) were .16 to .27, .18 to .63 and -.02 to .05 for BW and .26 to .32, .27 to .67 and .10 to .20 for WW. Dominance affected both direct and maternal effects for BW and WW. Values of -.15 (BW) and -.25 (WW) were found for fm (path coefficient between the maternal phenotypes of dam and daughter). These results indicated that selection response would be decreased due to the negative genetic correlation between direct and maternal effects.     

Association between cow reproduction and calf growth traits and ELISA scores for paratuberculosis in a multibreed herd of beef cattle

The objective of this research was to assess the association between 4 cow reproductive and weight traits, and 2 preweaning calf traits and ELISA scores for paratuberculosis (0 = negative, 1 = suspect, 2 = weak-positive, and 3 = positive) in a multibreed herd of cows ranging from 100% Angus (A) to 100% Brahman (B). Cow data were 624 gestation lengths (GL), 358 records of time open (TO), 605 calving intervals (CI), and 1240 weight changes from November to weaning in September (WC) from 502 purebred and crossbred cows. Calf data consisted of 956 birth weights (BWT), and 923 weaning weights adjusted to 205 d of age (WW205) from 956 purebred and crossbred calves. Traits were analyzed individually using multibreed mixed models that assumed homogeneity of variances across breed groups. Covariances among random effects were assumed to be zero. Fixed effects were year, age of cow, sex of calf, year × age of cow interaction (except WC), age of cow × sex of calf interaction (only for WC), and covariates for B fraction of sire and cow, heterosis of cow and calf, and ELISA score. Random effects were sire (except for TO and CI), dam, and residual. Regression estimates of cow and calf traits on ELISA scores indicated that lower cow fertility (longer TO), lower ability of cows to maintain weight (negative WC), lower calf BWT, and lower calf WW205 were associated with higher cow ELISA scores. Further research on the effects of subclinical paratuberculosis in beef cattle at regional and national levels seems advisable considering the large potential economic cost of this disease.     

澳大利亚2019年肉牛产业发展分析与借鉴

澳大利亚是世界上牛肉出口大国之一,肉牛产业是其重要的支柱产业。我国是澳大利亚重要的牛肉出口国之一,随着我国与澳大利亚自由贸易协议的签订及实施,近几年我国对澳大利亚的牛肉进口量持续快速攀升,2019年跃居澳大利亚牛肉出口国第一位。本文收集汇总了澳大利亚官方发布的相关数据,对2019年澳大利亚肉牛产业发展现状、贸易情况进行追踪,通过分析以期为我国肉牛产业持续健康发展提出借鉴。     

Estimates of repeatability and heritability of horn fly resistance in beef cattle.

Horn fly population density on 215 beef cows representing seven breed groups and 51 sires was used to obtain estimates of repeatability (rXX) and heritability (h2) for resistance to the horn fly (Haematobia irritans [L.] Diptera: Muscidae). Total horn fly densities were determined weekly on each cow beginning in May and ending in late October or early November of 1988, 1989, and 1990. No insecticides were used on cattle in this study. Estimates of h2 for horn fly resistance (low horn fly number per cow) were obtained by the paternal half-sib method (4 sigma 2S) and as twice the intrasire regression of offspring on dam (2bDD/S). Variance component estimates were obtained using a completely nested ANOVA that included overall mean, breed, sire/breed, cow/sire, and residual error. One hundred twenty-six daughter-dam pairs were available for regression analysis. In a preliminary analysis, the within-breed regression was nonsignificant (P greater than .05), implying that the regression was the same for all breeds; therefore, breed was deleted from the model. The regression model included an overall mean, year, and the intrasire regression of daughter on dam (bDD/S). The estimate of rXX was .47 +/- .02. Estimates of h2 were .78 +/- .16 and .59 +/- .10 from the 4 sigma 2S and 2bDD/S methods, respectively. Similar estimates of rXX and h2 were obtained when each observation of horn fly number per cow (x) was transformed to both log10 (x) and square root of x. These estimates suggest the possibility of selection procedures as an environmentally safe alternative to the use of chemical control.     

Genome-wide association studies of female reproduction in tropically adapted beef cattle

The genetics of reproduction is poorly understood because the heritabilities of traits currently recorded are low. To elucidate the genetics underlying reproduction in beef cattle, we performed a genome-wide association study using the bovine SNP50 chip in 2 tropically adapted beef cattle breeds, Brahman and Tropical Composite. Here we present the results for 3 female reproduction traits: 1) age at puberty, defined as age in days at first observed corpus luteum (CL) after frequent ovarian ultrasound scans (AGECL); 2) the postpartum anestrous interval, measured as the number of days from calving to first ovulation postpartum (first rebreeding interval, PPAI); and 3) the occurrence of the first postpartum ovulation before weaning in the first rebreeding period (PW), defined from PPAI. In addition, correlated traits such as BW, height, serum IGF1 concentration, condition score, and fatness were also examined. In the Brahman and Tropical Composite cattle, 169 [false positive rate (FPR) = 0.262] and 84 (FPR = 0.581) SNP, respectively, were significant (P < 0.001) for AGECL. In Brahman, 41% of these significant markers mapped to a single chromosomal region on BTA14. In Tropical Composites, 16% of these significant markers were located on BTA5. For PPAI, 66 (FPR = 0.67) and 113 (FPR = 0.432) SNP were significant (P < 0.001) in Brahman and Tropical Composite, respectively, whereas for PW, 68 (FPR = 0.64) and 113 (FPR = 0.432) SNP were significant (P < 0.01). In Tropical Composites, the largest concentration of PPAI markers were located on BTA5 [19% (PPAI) and 23% (PW)], and BTA16 [17% (PPAI) and 18% (PW)]. In Brahman cattle, the largest concentration of markers for postpartum anestrus was located on BTA3 (14% for PPAI and PW) and BTA14 (17% PPAI). Very few of the significant markers for female reproduction traits for the Brahman and Tropical Composite breeds were located in the same chromosomal regions. However, fatness and BW traits as well as serum IGF1 concentration were found to be associated with similar genome regions within and between breeds. Clusters of SNP associated with multiple traits were located on BTA14 in Brahman and BTA5 in Tropical Composites.     

Estimates of genetic parameters for live animal ultrasound, actual carcass data, and growth traits in beef cattle

Growth and carcass measurements were made on 2,411 Hereford steers slaughtered at a constant weight from a designed reference sire program involving 137 sires. A second data set consisted of ultrasound measures of backfat (USFAT) and longissimus muscle area (USREA) from 3,482 yearling Hereford cattle representing 441 sires. Restricted maximum likelihood procedures were used to estimate genetic parameters among carcass traits and live animal weight traits from these two separate data sets. Heritability estimates for the slaughter weight constant steer carcass backfat (FAT) and longissimus muscle area (REA) were .49 and .46, respectively. In addition, FAT had a negative genetic correlation with REA (-.37), weaning weight (-.28), and yearling weight (-.13) but positive with marbling (.19) and carcass weight (.36). Marbling was moderately heritable (.35) and highly correlated with total postweaning average daily gain (.54) and feedlot relative growth rate (.62). Heritability estimates for weight constant USFAT and USREA were .26 and .25, respectively. The genetic correlation between weight constant USFAT and USREA was positive (.39), indicating that in these young animals USFAT does not seem to be an indication of maturity. Mean USFAT measures and variability were small (.48 +/- .17 cm, n = 3,482). Results indicate that carcass fat on slaughter steers and ultrasound measures of backfat on young breeding animals may have different relationships with growth and muscling. These relationships need to be explored before wide scale selection based on ultrasound is implemented.     

Estimation of direct and maternal (co)variance components for growth traits in Australian Simmental beef cattle

SUMMARY: Field data on weight recordings provided by the Australian Simmental Breeders Association was analysed. From a data set of 64,962 animals, which had either birth (BW), weaning (WW), yearling (YW), or final weight (FW) records a subset of 17 herds comprising 18,083 animals was used to obtain uni- and bivariate estimates of variance components. This subset had to be subdivided into six further subsets, called group herds. The models used allowed for additive genetic, maternal genetic, and permanent environmental effects and for a covariance between additive direct and maternal genetic effects. Estimates were pooled across group herds. The results for BW, WW, YW, FW were .33, .35, .37, and .30, respectively, for heritabilities and .074, .18, and .11 for maternal heritabilities (not estimated for FW). Significant correlations between direct and maternal genetic effects (rAM) existed for WW and YW in the magnitude of -.39 and -.22. However, further research is needed due to the problems associated with the estimation of r(AM) . ZUSAMMENFASSUNG: Sch?tzung direkter und maternaler (Ko)Varianz-Komponenten für Wachstumsmerkmale bei australischem Fleckvieh Gegenstand der Untersuchung waren im Feld erhobene Gewichte, die von der Australischen Simmental Breeders Association bereitgestellt worden waren. Aus einer Datei von 64.962 Tieren, die entweder ein Geburtsgewicht (GG), ein Absetzgewicht (AG), ein J?hrlingsgewicht (JG) oder ein Endgewicht (EG) aufwiesen, wurde ein Teildatensatz von 18.083 Tieren extrahiert und einer uni- und bivariaten Sch?tzung von Varianzkomponenten unterzogen. Diese Datei mu?te weiterhin in sechs verschiedene Dateien aufgeteilt werden; diese wurden Gruppenherden genannt. Die verwendeten Modelle erlaubten additiv-genetische, maternal-genetische und permanente Umwelteffekte sowie das Vorhandensein einer Kovarianz zwischen additiv-genetischem und maternal-genetischem Effekt. Die Sch?tzwerte wurden über die Gruppenherden gepoolt. Die Ergebnisse in der Reihenfolge GG, AG, JG und EG waren 0,33, 0,35, 0,37 und 0,30 für die Heritabilit?ten sowie 0,074, 0,18 und 0,11 für die maternalen Heritabilit?ten (nicht gesch?tzt für EG). Signifikante Korrelationen zwischen direktem und maternal-genetischem Effekt (r(AM) ) existierten für AG und JG in der Gr??enordnung von -0,39 und -0,22. Trotz dieses Ergebnisses sind weitere Untersuchungen n?tig, weil die Sch?tzung von r(AM) problematisch ist.     

Estimates of heritabilities and correlations of traits associated with pelvic area in beef cattle

Pelvic measurements, cow weights and cow ages were obtained on 703 Angus- and Hereford-sired cows from five Louisiana Agricultural Experiment Station herds. Cows were either purebred or crossbred, ranging in age from 1 to 14 yr, and sired by 52 Angus and 63 Hereford bulls. All pelvic measurements were obtained via the rectum by the same technician. Paternal half-sib heritability estimates and genetic (rG) and phenotypic (rP) correlations were computed for pelvic height (PH), pelvic width (PW), pelvic area (PA-I; the product of PH X PW), the ratio of PH to PW and cow weight (CW). Pelvic area was also calculated as an ellipse using the formula PA-II = pi (PH/2)(PW/2). Mean PA-I was 298.5 cm2 while PA-II averaged 234.4 cm2. The pooled heritability estimate for PA-I was .68 +/- .34, indicating that pelvic area is a highly heritable trait and should respond to selection. The estimate for PA-II was similar (.66 +/- .34). The heritability of PW was higher than for PH or PA-I. The heritability of CW was .57 +/- .34 and CW was positively correlated (rG2 = .47 and rP = .40) with PA-I. Direct selection for PA-I was estimated to yield a response of 12.2 cm2 in one generation with a correlated response for CW of 12.5 kg. If change in CW was held at zero using a restricted selection index, about 90% as much increase in PA-I was estimated compared with ignoring CW in the index. Therefore, selection for increased pelvic area can be accomplished without causing large increases in cow size. This should aid in reducing calving difficulty.     

Effects of marginal selenium deficiency and winter protein supplementation on growth, reproduction and selenium status of beef cattle

Seventy-two Hereford X Simmental cows, averaging 498 kg in body weight and 5.2 yr of age, were used in a 2-yr study to ascertain if selenium (Se)-vitamin E (E) injections and winter protein supplementation would affect growth, reproduction and health of beef cattle maintained year-round on feedstuffs marginally deficient in Se (.03 to .05 mg/kg). Cows received either no injection or a mixture of 30 mg Se (as sodium selenite) and 408 IU E injected subcutaneously beginning 3 to 4 mo prepartum and at 60-d intervals throughout the 2-yr period. Calves born to Se-E treated cows were injected with 5.5 mg Se and 75 IU E/100 kg body weight at 60-d intervals beginning at 1 mo of age. Calves were born between December 30 and February 20 and cows were bred between March 20 and May 20. Cattle grazed pasture (.05 mg Se/kg) that consisted of orchardgrass, bluegrass and white clover during the fall, spring and summer. During winter (December 15 to May 2), cattle were fed corn silage (.03 mg Se/kg) supplemented with either: no protein supplement (control), soybean meal or a urea-corn mixture. Cows and calves receiving Se-E had higher (P less than .01) whole blood glutathione peroxidase (GSH-Px) activity and plasma Se concentrations than controls. Selenium-E injections reduced (P less than .05) calf death losses from 15.3% to 4.2% and slightly increased (P less than .10) adjusted calf weaning weights. Hemoglobin concentrations were higher (P less than .05) in Se-E-injected supplemented calves at 1 mo of age but not at 5 or 7 mo of age.(ABSTRACT TRUNCATED AT 250 WORDS)     

Symmetric differences squared and analysis of variance procedures for estimating genetic and environmental variances and covariances for beef cattle weaning weight: II. Estimates from a data set

Analysis of variance (ANOVA) and symmetric differences squared (SDS) methods were used to estimate additive genetic and environmental variances and covariances associated with weaning weight. The two methods were applied to 503 beef records collected over 19 yr from a relatively unselected university Angus herd. The SDS methodology was used with four models. The first model included direct (g) and maternal (gm) additive genetic effects, the genetic covariance between direct and maternal additive genetic effects (sigma ggm), permanent maternal environmental effects (m) and temporary environmental effects (e). The second model also allowed for a nonzero environmental covariance (sigma mem) between dam and offspring weaning weights. Models 3 and 4 were models 1 and 2, respectively, expanded to include a grandmaternal genetic effect (gn) and covariances sigma ggn and sigma gmgn. Two ANOVA solution sets for the parameters of model 4 were based on sire, dam, maternal grandsire, maternal grandam and phenotypic variances and offspring-dam (covOD), offspring-sire (covOS), offspring-grandam (covOGD) and offspring-maternal half-aunt or uncle (covOMH) covariances. Four ANOVA solution sets for the parameters of model 2 were based on sire, dam, within dam and maternal grandsire variances, covOD and either covOS or covOGD. Symmetric differences squared estimates of h2g and h2gm averaged .30 and .16, respectively. All SDS estimates of rho ggm (correlation between direct and maternal genetic effects) were less than -1. Estimates of sigma mem were positive. Both SDS estimates and one of the two ANOVA estimates of the grandmaternal variance were negative. The ANOVA model 4 estimates of h2g were .33. The estimates of h2gm were .44 and .39, while the estimates for rho ggm were -.88 and -.80. Both estimates of sigma mem were positive. The four ANOVA model 2 estimates of h2g and h2gm averaged .33 and .48, respectively. Three of the four estimates of rho ggm were less than -.97; the fourth was .35. Three of the four estimates of sigma mem were positive. Expectations show the extent to which SDS and ANOVA estimators were biased by nonzero grandmaternal components that were not accounted for. The extent to which dominance components bias the ANOVA estimators also is shown. Nonzero grandmaternal effects need to be taken into account in either SDS or ANOVA solution sets, or important biases occur with most of the estimators. More numerous, and generally more severe, biases occur with ANOVA estimators than with SDS estimators in solution sets that do not account for grandmaternal effects.     

Associations between maternal milk protein genotypes with preweaning calf growth traits in beef cattle

The objectives of this study were to investigate milk casein polymorphisms in dams and to determine the impacts of maternal casein genotypes on growth traits of their sucking calves. Milk samples from 433 dams of the breeds German Angus (GA) and German Simmental (GS) were typed at the milk protein loci α _s1-casein (α_s1-CN), β-casein (β-CN), α _s2-casein (α_s2-CN), and κ-casein (κ-CN) via isoelectric focusing. Associations between casein genotypes in maternal milk with growth traits of their 1,872 calves were analyzed until the age of weaning using linear mixed models, considering either genotypes of individual casein loci (model 1) or composite α _s1-β-α _s2-κ-CN genotypes within the casein cluster (model 2). Besides environmental effects such as sex, age of the dam, and calving year-season, genetic effects (breed group and maternal and paternal effects) were considered in statistical models. The composite casein genotype BBǀA2A2ǀAAǀAB (order of genes on bovine chromosome 6: α _s1-ǀβ-ǀα _s2-ǀκ-CN) was associated with greater average daily weight gains (ADG) and heavier age-adjusted weaning weights (WW) of calves (P < 0.05). The effects of composite genotypes on birth weight of calves were similar (P > 0.05; model 2). With regard to individual casein loci, greater ADG and WW were observed for calves from dams with the genotypes κ-CN BB and α _s1-CN BB, respectively (P < 0.05; model 1). Age-adjusted WW was largest for calves from dams carrying the κ-CN genotype BB (215 kg) compared with calves representing the maternal AB and AA genotypes (both 204 kg). Results from the present study suggested selectable casein genotypes due to their nutritional value of milk (value in terms of offspring performances), offering new perspectives for breeding strategies in beef cattle to improve preweaning calf performance.     

The complex relationship between welfare and reproduction in cattle

Using reproduction parameters as indicators for cattle welfare has limitations and, at best, these parameters should only be viewed as indirect indicators of welfare. On a farm level, measures such as fertility rates emphasize biological performance of the herd but fail to consider the welfare of individual animals. Even on an individual level, the relationship between reproductive effectiveness and animal welfare is complex. Good reproductive performance does not automatically signify good welfare, as domestication and targeted breeding programmes have led to prioritization of high productive and reproductive performance in most modern farm animal species. In this review, we synthesize literature regarding cattle husbandry, reproduction, welfare and their multidimensional relationships. We argue that practices such as artificial insemination or the use of sexed semen may provide potential welfare advantages as these practices reduce the risk of disease transmission and injury or enable selection of specific beneficial traits. Furthermore, they may offer a solution to current practices jeopardizing welfare, such as the management of surplus bull calves in the dairy industry. Conversely, the animals’ ability to perform natural behaviours such as oestrous expression, an aspect arguably contributing to welfare, is often limited on commercial farms; this limitation is particularly evident in housing systems such as tie stalls where movement is restricted. Moreover, common management practices such as oestrus manipulation may lead to negative attitudes in citizens who often regard naturalness as important element of animal welfare.     

Association between IGF-I, IGF-IR and GHRH gene polymorphisms and growth and carcass traits in beef cattle

Molecular biology techniques are of help in genetic improvement since they permit the identification, mapping and analysis of polymorphisms of genes encoding proteins that act on metabolic pathways involved in economically interesting traits. The somatotrophic axis, which essentially consists of growth hormone releasing hormone (GHRH), growth hormone (GH), insulin-like growth factors I and II (IGF-I and IGF-II), and their associated binding proteins and receptors (GHRHR, GHR, IGF-IR and IGF-IIR), plays a key role in the metabolism and physiology of mammalian growth. The objectives of the present study were to estimate the allele and genotype frequencies of the IGF-I/SnaBI, IGF-IR/TaqI and GHRH/HaeIII gene polymorphisms in different genetic groups of beef cattle and to determine associations between these polymorphisms and growth and carcass traits. For this purpose, genotyping was performed on 79 Nellore animals, 30 Canchim (5/8 Charolais+3/8 Zebu) animals and 275 crossbred cattle originating from the crosses of Simmental (n=30) and Angus (n=245) sires with Nellore females. In the association studies, traits of interest were analyzed using the GLM procedure of SAS and least square means of the genotypes were compared by the Tukey test. Associations of IGF-I/SnaBI genotypes with body weight and subcutaneous backfat were significant (p<0.05), and nearly significant for longissimus dorsi area (p=0.06), with the BB genotype being favorable compared to the AB genotype. No significant associations were observed between this polymorphism and weight gain or carcass yield (P>0.05). The IGF-IR/TaqI and GHRH/HaeIII polymorphisms showed no association with production traits.