Biomedical subjects

D J Garrick

Publications and source records attributed to D J Garrick.

18 recordsLinked to original sources

PubMed2006

Weaning weight inheritance in environments classified by maternal body weight change.

In good environments, cow intake is sufficient for their own growth and for milk production to support their calf. In poor environments, cows lose BW or may reduce milk supply to maintain themselves. Heritability for direct genetic and maternal components of weaning weight as well as the correlations between these components might be expected to vary according to these circumstances. The purpose of this study was to estimate heritability and genetic correlations for the direct genetic and maternal components of weaning weight classified in 2 environments according to maternal BW gain and to identify whether a single heritability estimate is appropriate for the differing environments experienced by cows from year to year. Data used in this analysis was obtained from the Red Angus Association of America and consisted of 96,064 cow BW observations and 27,534 calf weaning weight observations. A dam's change in BW from one year to the next was used to classify each calf's weaning weight into 1 of 2 environmental groups, those being good or poor. Best linear unbiased estimates of the change in cow BW with age were obtained from analysis of cow BW using a repeatability model. If the phenotypic change in cow BW exceeded this average BW change, the calf's weaning weight associated with the end of this time frame was classified as having been observed in a good environment. If not, the calf's corresponding weaning weight was classified as having occurred in a poorer than average environment. Heritability estimates of 0.24 +/- 0.03, 0.24 +/- 0.03, 0.13 +/- 0.02, and 0.14 +/- 0.02 were obtained for weaning weight good direct, poor direct, good maternal, and poor maternal, respectively. Correlations between direct genetic and maternal weaning weight components in the good and poor environments were -0.47 +/- 0.08 and -0.20 +/- 0.09, respectively. These variance components are not sufficiently distinct to warrant accounting for dam nutritional environment in national cattle evaluation.

Aging↗

PubMed2006

'Ovar-Mhc' - ovine major histocompatibility complex: structure and gene polymorphisms.

The major histocompatibility complex (MHC) in sheep, Ovar-Mhc, is poorly characterised, when compared to other domestic animals. However, its basic structure is similar to that of other mammals, comprising class I, II and III regions. Currently, there is evidence for the existence of four class I loci. The class II region is better characterised, with evidence of one DRA, four DRB (one coding and three non-coding), one DQA1, two DQA2, and one each of the DQB1, DQB2, DNA, DOB, DYA, DYB, DMA, and DMB genes in the region. The class III region is the least characterised, with the known presence of complement cascade (C4, C2 and Bf), TNFalpha and CYP21 genes. Products of the class I and II genes, MHC molecules, play a pivotal role in antigen presentation required for eliciting immune responses against invading pathogens. Several studies have focused on polymorphisms of Ovar-Mhc genes and their association with disease resistance. However, more research emphasis is needed on characterising the remaining Ovar-Mhc genes and developing simplified and cost-effective methods to score gene polymorphisms. Haplotype screening, employing multiple markers rather than single genes, would be more meaningful in MHC-disease association studies, as it is well known that most of the MHC loci are tightly linked, exhibiting very little recombination. This review summarises the current knowledge of the structure of Ovar-Mhc and polymorphisms of genes located in the complex.

Animals↗

PubMed2006

Maternal effects on docility in Limousin cattle.

The objective of this study was to quantify the role of maternal effects on docility in Limousin cattle. Docility scores were obtained at weaning while animals were restrained in a squeeze chute. Scores 1 through 6 represented a docile to aggressive temperament, respectively, and were provided by the North American Limousin Foundation. Observations with unknown age of dam, contemporary groups containing less than 10 observations, contemporary groups with no variation, and single-sire contemporary groups were removed, leaving 21,932 observations. A 2-generation pedigree file compiled from animals with observations contained 49,459 animals. Fixed effects were weaning contemporary group and age of dam (2, > or =3 yr). Six animal models encompassed combinations of random factors: direct genetic, maternal genetic, and maternal permanent environmental effects. The model D was the most basic, containing direct genetic and residual effects, and it resembled the method currently used by the North American Limousin Foundation for genetic evaluation of docility. Maternal genetic or permanent environmental effects were separately added to the model D, denoted as models DM and DC, respectively. Model DMC contained all random factors. Models DM-Zero and DMC-Zero were equivalent to models DM and DMC, respectively, but with zero direct-maternal genetic covariance. Direct heritability estimates were moderate for all models (0.29 +/- 0.02 to 0.38 +/- 0.03). Maternal heritability estimates were low, ranging from 0.01 +/- 0.01 (DM-Zero) to 0.05 +/- 0.02 (DM). Negative direct-maternal genetic correlations of -0.41 +/- 0.09 and -0.55 +/- 0.09 were estimated for models DM and DMC, respectively. The proportion of phenotypic variance accounted for by maternal permanent environmental effects was 0.03 +/- 0.01, 0.04 +/- 0.01, and 0.02 +/- 0.01 for models DC, DMC, and DMC-Zero, respectively. Likelihood ratio tests indicated that model DMC best fit the data. Although maternal genetic and maternal permanent environmental effects were significant, they accounted for only 8% (model DMC) of the phenotypic variance, and a Spearman rank correlation of 0.99 between models D and DMC showed sires did not rank differently with or without inclusion of these effects. Given these results, inclusion of maternal effects to the genetic evaluation of docility in Limousin cattle does not seem warranted.

Aggression↗

PubMed2006

Ovar-Mhc--ovine major histocompatibility complex: role in genetic resistance to diseases.

Research on the structure of the ovine major histocompatibility complex (MHC), Ovar-Mhc, and its association with resistance to various diseases in sheep has received increasing attention during recent years. The term 'resistance' is used to denote the capacity of an animal to defend itself against disease or to withstand the effects of a harmful environmental agent. The Ovar-Mhc is poorly characterised when compared to MHCs of other domestic animals. However, its basic structure is similar to that of other animals, comprising Class I, II and III regions. Products of the Class I and II genes, the histocompatibility molecules, are of paramount importance as these present antigens to T-lymphocytes, thereby eliciting immune responses. Several studies have been conducted in sheep on the involvement of MHC genes/antigens in genetic resistance to diseases, the majority being concerned with gastrointestinal nematodes. Studies on resistance to footrot, Johne's disease and bovine leukaemia virus (BLV)-induced leukaemogenesis have also been reported. Genes of all three regions were implicated in the disease association studies. In addition to disease resistance, Ovar-Mhc genes have been found to be associated with traits such as marbling and birthweight. The use of genetic markers from within the Ovar-Mhc may be useful, via marker-assisted selection, for increasing resistance to various diseases provided they do not impact negatively on other economically-important traits. This review summarises current knowledge of the role of Ovar-Mhc in genetic resistance to diseases in sheep.

Animals↗

PubMed2006

Predicting breeding values and accuracies from group in comparison to individual observations.

Individual observations are routinely used in livestock evaluations. In some cases, pooled data representing the joint but not individual performance of a group of animals may be available. For example, pooled feed intake may be measured on a pen of livestock. The usual mixed model approach to genetic evaluation can still be applied as an exact method in this setting, provided incidence and residual variance-covariance matrices are suitably modified to account for the pooling. Approximate evaluations may be achieved by treating average performance as if it pertained to each individual in the pool. Theoretical accuracies can be obtained as a function of elements of the inverse coefficient matrix. A 3-generation data set representing 1,000 animals with feed intake observations from 49 sires and 200 maternal grand sires was simulated with heritability of 0.34. Individual records were pooled to represent circumstances in which animals with records were collectively measured. Animals were allocated into pens at random, by sire, or by maternal grand sire. Simulation was replicated with unique fixed effects for each pen. Following evaluation from each method, the empirical accuracy or product-moment correlation between true (simulated) and estimated merit could be quantified. The analysis of individual observations resulted in empirical accuracy of 0.63 for animals on test and 0.77 for their sires. Pooling the observations in pens of 2, 4, or 12 animals reduced empirical accuracies for animals on test to 0.50, 0.41, and 0.21 when pooling was at random and 0.53, 0.47, and 0.34 when pooling was by sire. Simulating a fixed pen effect representing 10% phenotypic variation, but ignoring that effect in the evaluation minimally reduced empirical accuracies to 0.52, 0.46, and 0.33 when pooling by sire. Theoretical accuracies were in close agreement with empirical accuracies when the exact method was used. The approximate method that treated averages of pooled data as if they were individually observed overstated accuracy and should not be used. Selection on the basis of pooled observations can be almost as effective as using individual observations when pool sizes are small. The exact method to account for pooled data is no more complex than conventional procedures.

Animals↗

PubMed2005

Phenotypic relationships between hair whorl characteristics and spermatozoal attributes in Holstein bulls.

The objective of this study was to characterize facial whorl characteristics in Holstein stud bulls (n = 485) and to investigate their association with measures of semen quantity and quality. Bulls had 1 (n = 454), 2 (n = 21) or no facial hair whorls (n = 5). Some 39% of bulls had whorls in the middle of their forehead, whereas 43% had whorls very low down on their forehead. Spiral whorls were present on 77% of bulls while 22% had elongated whorls. Abnormally shaped whorls were found more often on bulls with low whorls (27% versus 17%, P = 0.01) than on bulls with high or middle whorls. Semen production data were obtained from the AI center database to provide a representative sample of each sires most recent semen production characteristics. The number of semen collections per bull averaged 38 with a range of 1 (n = 9) to 272 (n = 1). The average number of days between collections was 5 but varied from 1 to 425 days. Average age of bulls at first recorded collection was 679 days and ranged from 307 to 4555 days. There were no significant differences between black and white bulls in semen quality or quantity. Semen quality over the summer months was reduced in comparison to the winter months. Age of the bull at time of collection had no effect on any of the semen quality traits. Older bulls had larger scrotal circumference and produced more semen (P > 0.01). Bulls with whorls located in the center of the forehead were not significantly different in semen quality or quantity for the 10 traits considered when compared to bulls with whorls located outside the center. In contrast to previous research findings with Angus cattle, semen attributes were not significantly different between bulls characterized with round (or spiral) epicenters and those with abnormally shaped whorls. The difference between the two studies may be due to the fact that Angus bulls have a higher percentage of abnormal elongated whorls compared to Holsteins.

Animals↗

PubMed2005

Emerging technologies for identifying superior dairy cows in New Zealand.

The performance of animals is determined by the interaction of their genes with environmental circumstances. Accordingly, animals exhibiting superior performance are not necessarily the animals with the best genes nor are they the best choice of parents. Statistical analyses of production records for repeated traits, e.g. lactation yields and reproductive performance, show that part of the variation in performance among animals in the same herd and year is due to genetic differences, and the remainder is due to so-called residual or environmental factors that are not passed on to offspring. These within-herd environmental factors can be partitioned into a component that affects performance throughout an animal's lifetime, and a part that is unique to each observation. The process of animal evaluation from pedigree and performance records partitions the superiority of each cow into these three components. Reliable assessment of the genetic merit of bulls has required progeny testing, and for cows has required observation of their own individual performance. Selection on the genetic or breeding value component has systematically improved animal performance over recent decades, but has been limited by the age at which assessments of genetic merit are available. Emerging molecular technologies can read DNA sequences or measure RNA expression and have allowed the identification of a number of chromosome regions, and a few specific genes in those regions, that influence economic performance. This information allows better characterisation of the relationships between animals and more accurate predictions of genetic merit in bulls without progeny information and in cows that have yet to produce their own performance record. At some stage, enough genes responsible for variation in performance will be identified to allow faster genetic progress through selection of animals at young ages and therefore more rapid turnover of the generations. Mechanisms that modify gene expression have been identified and these may ultimately allow animals to be selected at an early age for lifetime productivity, accounting for processes that modify gene expression and lead to differences in performance that are not reflected by DNA sequence information. This review describes the status of these emerging technologies and their likely role in the improvement of dairy cattle.

Animals↗

PubMed2005

Changes in inbreeding of U.S. Herefords during the twentieth century.

Genetic diversity in the U.S. Hereford population was characterized by examining the level and rate of inbreeding and effective population size. Pedigree records for 20,624,418 animals were obtained from the American Hereford Association, of which 96.1% had both parents identified. Inbreeding coefficients were computed and mean inbreeding (Fx) calculated by year from 1900 to 2001. Inbreeding increased rapidly between 1900 and 1945. From 1946, inbreeding increased linearly to a maximum of 11.5% in 1966. Throughout the 1970s and 1980s, mean inbreeding decreased to mid-century levels. Several alternatives were investigated to explain this decline. The average relationship between prominent sires fell from 20 to 12% during the time that the level of inbreeding decreased, which reflects an increase in the popularity of certain less fashionable sire lines that would have temporarily decreased inbreeding. Pedigrees were constructed for animals born after 1990. This subsample of animals with no missing ancestors in at least 12 generations did not exhibit a decrease in inbreeding. Missing ancestral information therefore contributed to the apparent decline. One cause of missing ancestry results from outcrossing to imported animals. The effect of missing ancestry was investigated by simulating the missing ancestors. In 2001, Fx was 9.8%, and approximately 95% of individuals were inbred. The maximal inbreeding coefficient was 76%. The annual change in mean inbreeding (DeltaFx) was estimated for Herefords born during five time periods from 1946 to 2001, where inbreeding was changing at different linear rates. The DeltaFx for the most recent generation (1990 to 2001) was 0.12%/yr. Assuming a generation interval of 4.88 yr, the estimated effective population size was 85. This study provides a benchmark of current genetic diversity in the Hereford population. Results indicate that inbreeding is accumulating linearly and below critical levels. Increases in the adoption of reproductive technologies could decrease genetic diversity, and in the future, we may need to consider strategies to minimize inbreeding.

Animal Husbandry↗

PubMed2000

Profitabilities of some mating systems for dairy herds in New Zealand.

The aim of this study was to evaluate the profitability of dairy herds under three mating systems involving the Holstein-Friesian, Jersey, and Ayrshire breeds. Mating systems were straight breeding and rotational cross-breeding using two or three breeds. A deterministic model was developed to simulate the nutritional, biological, and economic performance of dairy herds under New Zealand conditions. Expected performances per cow were obtained using estimates of breed group and heterosis effects, age effects, and age distribution in the herd. Requirements for dry matter in feed were estimated per cow for maintenance, lactation, pregnancy, and growth of the replacements. Stocking rate was calculated by assuming 12,000 kg of dry matter utilized annually per hectare. Productivity per hectare was calculated as performance per cow multiplied by stocking rate. Profitability was the difference between income (sale of milk and salvage value of animals) and costs (related to the number of cows in the herd and the land area farmed). Under current market values for milk and meat, all of the rotational crossbred herds showed superior profitability to the straightbred herds (Holstein-Friesian x Jersey, NZ$505/ha; Holstein-Friesian x Jersey x Ayrshire NZ$493/ha; Jersey x Ayrshire, NZ$466/ha; Holstein-Friesian x Ayrshire, NZ$430/ha; Jersey, NZ$430/ha; Holstein-Friesian, NZ$398/ha; and Ayrshire, NZ$338/ha). Changes in the value for fat relative to protein affected profitability more significantly in herds using the Jersey breed, and changes in the value for meat affected profitabiity more significantly in herds using the Holstein-Friesian and Ayrshire breeds. Results suggested that, under New Zealand conditions, the use of rotational crossbreeding systems could increase profitability of dairy herds under the conceivable market conditions.

Animals↗

PubMed2000

Possible effects of 25 years of selection and crossbreeding on the genetic merit and productivity of New Zealand dairy cattle.

A deterministic model was developed to evaluate the concurrent effects of selection and crossbreeding on the rate of genetic gain and productivity of New Zealand dairy cattle over 25 yr. Selection was based on an index, which included estimated breeding values for mature cow live weight and lactation yields of milk, fat, and protein. Mating strategies involving Holstein-Friesian, Jersey, and Ayrshire breeds were evaluated. Effects of heterosis and age were included to calculate live weight and yields of milk, fat, and protein per cow. Feed requirements were estimated for maintenance, lactation, and pregnancy and for replacement heifers. Stocking rate was calculated by assuming 12,000 kg of dry matter annually utilized per hectare. Upgrading to either Jersey or Holstein-Friesian increased the number of potential bull mothers and resulted in genetic gains of 0.27 genetic standard deviations/yr for both options. Rotational crossbreeding of Holstein-Friesian x Jersey decreased the number of potential bull mothers and resulted in a genetic gain of 0.24 genetic standard deviations/yr. Upgrading to Jersey resulted in the least increase in milk (5%) and the greatest increase in fat (16%) and protein (27%) per hectare with a small decrease in stocking rate (0.4%). Upgrading to Holstein-Friesian reduced the stocking rate by 11% and increased production of milk, fat, and protein per hectare by 10, 8, and 21%, respectively. Rotational crossbreeding of Holstein-Friesian x Jersey resulted in greater production per hectare than the intermediate production between upgrading to Jersey and upgrading to Holstein-Friesian. Crossbreeding can be used in combination with selection to exploit the effects of heterosis while maintaining genetic diversity to cover changes in market conditions.

Animals↗

PubMed2000

Effects of selection and crossbreeding strategies on industry profit in the New Zealand dairy industry.

The effects of selection and crossbreeding on the New Zealand dairy industry net income were evaluated with a deterministic model over a 25 yr planning horizon. Several mating strategies involving Holstein-Friesian, Jersey and Ayrshire cattle were evaluated. These strategies were straight breeding, upgrading to Holstein-Friesian, upgrading to Jersey, upgrading to Ayrshire, use of the best bulls irrespective of breed and two- and three-breed rotational crossbreeding. Industry productions of milk, fat, protein, and lactose were calculated assuming that 12,000 kg of dry matter per hectare was utilized from 1,224,911 hectares of pasture. Profitability was the difference between income (international sale of whole milk powder, casein, butter, and beef from salvage animals) and costs (farm expenses, milk collection, manufacture, and marketing). Casein and whole milk powder were valued at NZ$8.345 and NZ$3.306/ per kilogram, respectively, over 25 yr. Butter was valued at NZ$2.995/kilogram for base year production levels and NZ$0.45/kilogram for marginal increases in production. Upgrading to Holstein-Friesian resulted in the highest industry net income (NZ$1119 million) followed by straight breeding (NZ$1086 million) and two-breed rotational Holstein-Friesian x Jersey (NZ$1076 million). However, if the marginal value of extra butter production was assumed equal to the average base value, then upgrading to Jersey resulted in the highest industry net income (NZ$1185 million) followed by two-breed rotational Holstein-Friesian x Jersey (NZ$1177 million) and use of the best bulls (NZ$1173 million). Future costs and prices of dairy products have major impact on mating strategies.

Animals↗

PubMed1999

Short communication: quantitative trait loci analysis on 17 nonproduction traits in the New Zealand dairy population.

Seven New Zealand Holstein-Friesian families and two Jersey families, a total of 274 sires, were analyzed in a granddaughter design for marker-quantitative trait loci associations. For 17 nonproduction traits (management, size, and conformation traits), an across-family analysis was undertaken using multimarker regression procedures. Threshold levels were set empirically by permuting the data. A quantitative trait locus for stature was identified on chromosome 14, which was significant at the 15% experimentwise level (suggestive linkage). The quantitative trait locus was identified to be segregating in three of the nine families.

Animals↗

PubMed1998

Genetic and economic responses for within-family marker-assisted selection in dairy cattle breeding schemes.

Marker-assisted selection schemes that utilize information about quantitative trait loci to preselect progeny test bulls within a family are the most practical application of quantitative trait loci results in the short-term. Technical difficulties exist for across-family marker-assisted selection using BLUP procedures. Two within-family marker-assisted selection schemes were evaluated genetically and economically using stochastic simulation for a locus that explained 5% of phenotypic variance. The genetic and economic impacts of variation in the number of offspring per bull-dam were evaluated. The top down marker-assisted selection scheme identifies sires that are heterozygous for the locus based on the granddaughter design and uses the quantitative trait locus information in the preselection of grandsons entering progeny testing. The bottom up marker-assisted selection scheme identifies sires heterozygous for a quantitative trait locus based on the daughter design and uses the information in the preselection of sons entering progeny testing. The top down scheme with one progeny per bull-dam reduced the rate of genetic gain compared with that from a breeding scheme that ignored knowledge of the quantitative trait locus. The top down scheme with reproductive performance of 3 or 40 progeny per bull-dam increased genetic gain by 1 to 2%. The bottom up scheme increased the rate of genetic gain by 1.5, 3.5, and 5% for 1, 3, and 40 progeny per bull-dam, respectively. When the top down scheme was used on the maternal path and the bottom up scheme on the paternal path, increases were 9% with 40 progeny per bull-dam. The use of reproductive technologies on bull-dams is imperative to prevent gains from marker-assisted selection being eroded by the loss in polygenic selection differential that results when more bull-dams are required to enable preselection of sons using markers.

Animals↗

PubMed1997

Effect of live weight and differing economic values on responses to selection for milk fat, protein, volume, and live weight.

Five traits of major economic importance in the New Zealand dairy industry are milk volume, milk fat, milk protein, live weight, and survival. This study evaluated the impact of live weight as a trait in the selection objectives for the New Zealand dairy industry. Live weight of the lactating cow is an important measure because it reflects feeding costs via maintenance feed and salvage values of cows to be culled. In addition, selection responses were evaluated for differing relative economic values for milk protein and milk fat, and selection indexes that included or excluded phenotypic and genotypic correlations between traits were compared. Inclusion of live weight, with a negative economic value in a four-trait selection index with milk, milk fat, and protein resulted in higher economic response. Protein response to selection was not more than 2% when the relative economic value for the ratio of protein to milk fat exceeded 5:1 in a two-trait model; however, milk fat response decreased by over 10%. When a negative relative economic value was assigned to milk fat, economic returns were lower because of lower milk fat responses and the lack of higher protein responses compared with the same ratio for relative economic value but a positive weight for milk fat. Accounting for phenotypic and genetic correlations in deriving selection index weight improved economic response 5%.

Animals↗

PubMed1996

Correction for amino acid loss during acid hydrolysis of a purified protein.

Hydrolyzing a protein in acid for a single hydrolysis interval, normally 24 h, will lead to inaccurate estimates of the amino acid composition of that protein due to an effect of the time of hydrolysis on peptide bond cleavage and amino acid degradation. The simultaneous yield and decay of amino acids during the hydrolysis of a protein can be described by a compartmental model with parameters for the hydrolysis and loss rates specific to each amino acid in a protein. The amino acid composition of the protein prior to hydrolysis can be determined by nonlinear regression of data derived from multiple hydrolysis intervals. In the present study egg-white lysozyme was hydrolyzed in 6 M HCl using 18 hydrolysis intervals (range, 2-141 h) using the conventional duplicate hydrolyses/interval system. Hydrolysis and loss rates were determined for each amino acid. Increasing the number of hydrolysis intervals prior to the maximum point on the hydrolysis curve, and including an hydrolysis interval greater than 100 h increased the accuracy with which the hydrolysis and loss rates were estimated. Most of the amino acids underwent some degree of loss during hydrolysis. Of particular note was the loss rate for cysteic acid, which was greater than that found for serine which is commonly regarded as an acid-labile amino acid. The determined amino acid composition of the protein, based on the nonlinear regression of the data from four different series of hydrolysis intervals, was compared with the known amino acid composition (sequencing). Using the routine duplicate sampling system, a nonlinear regression including 10 hydrolysis intervals (2, 6, 10, 14, 18, 22, 26, 30, 60, and 141 h) resulted in a mean amino acid recovery of 100% (range, 94-110%) and provided an acceptable compromise between accuracy and the cost of analysis.

Amino Acids↗

PubMed1989

Variance heterogeneity in direct and maternal weight traits by sex and percent purebred for Simmental-sired calves.

Phenotypic variances for linear and transformed weight traits were partitioned into residual, direct genetic (D) and maternal genetic (M) components using REML techniques with American Simmental Association data from calves born 1969 to 1985. Variance components were estimated separately from subclasses defined by sex (male, female) and percent Simmental (50, greater than or equal to 75). The model included fixed effects of contemporary group and age-of-dam (less than 3, 3 to 5, greater than 5 yr). Additive relationships among sires and maternal grandsires were included. Results follow for a sire-maternal grandsire model for greater than or equal to 75% Simmental untransformed data based on 143,280 male and 281,805 female weaning weights (WW) representing 4,763 and 7,406 sires, respectively. Female results are bracketed. For computational simplification, 47,650 [30,909] postweaning gain (PW) records were included in the analysis only for 114,404 [182,255] calves with birth weight (BW). Phenotypic standard deviations (kg) were: BW, 4.5 [4.1]; WW, 26.9 [23.2]; and PW, 25.9 [19.9]. Heritabilities were: BWD, .40 [.45]; WWD, .32 [.39]; PWD, .26 [.32]; BWM, .13 [.15]; WWM, .20 [.16]; and PWM, .01 [.01]. These heritabilities are higher than previously used for genetic evaluations in this breed. Moderate and positive correlations .26 to .50, existed between direct effects and were similar for both sexes. Direct and maternal effects on the same trait were correlated negatively: BW, -.45 [-.31]; and WW, -.27 [-.34]. Genetic correlation between BWM and WWM was .53 [.49]. First-cross progeny exhibited less genetic and residual variation and had lower heritabilities than Simmental calves of higher percent. Correlations between sire evaluations on the subsets were consistent with those expected given a perfect genetic correlation between traits for each sex and percent Simmental. Logarithmic transformed records were no more homogeneous than untransformed records.

Analysis of Variance↗

PubMed1989

Multiple trait prediction for a type of model with heterogeneous genetic and residual covariance structures.

A restricted set of models is defined that allows for heterogeneous genetic and residual covariance structures. Multiple trait models and models with multiple random factors are included. The restriction on the model is that the correlations among genetic effects in different classes are the same. Equivalently, the genetic covariance matrices are assumed to differ between classes due to scaling. This assumption greatly reduces the number of parameters that must be specified and does not adversely affect the computational burden of a mixed model analysis. An application of the model for genetic evaluation of beef cattle is described and illustrated numerically.

Analysis of Variance↗

PubMed1984

Effects of oestradiol benzoate treatment on the reproductive performance and endocrine status of sows after lactations of 10 or 35 days.

Forty-two Landrace X Large White sows were used in 3 studies of oestradiol benzoate treatment 24 h (E1) or 48 h (E2) after piglet removal, following lactations of 10 (S) or 35 (L) days, or were untreated controls (C). For Exp. 1, oestradiol benzoate doses were 4, 16 and 64 micrograms/kg body weight; since highest mean LH peaks followed use of the 16 micrograms/kg dose, this treatment was used in later studies. Treatments for Exp. 2 were S-E1 and L-E1 (N = 3). Pregnancy rates were 1/3 and 2/3, respectively, while 10-day weaned sows tended to have longer weaning-remating intervals, shorter oestrous periods and lower post-injection oestradiol peaks. Post-treatment LH peaks were recorded from all L-E1 sows, but only one S-E1 animal. Treatments S-E2, L-E2, S-C and L-C (N = 6) were used in Exp. 3; pregnancy rates were 1/6, 6/6, 5/6 and 6/6, respectively, while peak oestradiol levels were 49.5 +/- 8.3, 74.8 +/- 15.1, 21.7 +/- 2.0 and 51.8 +/- 26.5 pg/ml, respectively. Weaning-remating intervals were extended in S-C sows (P less than 0.05), while oestradiol treatment prolonged behavioural oestrus. LH peak values were reduced after short lactations, but not affected by oestradiol treatment. Plasma prolactin concentrations at weaning were higher in sows in treatment S than in treatment L, while at the subsequent oestrus in oestradiol-treated sows they were elevated more and for longer periods than in controls. These results demonstrate that reduced gonadotrophin secretion and fertility after short lactations are not overcome by treatment with oestradiol benzoate.

Animals↗