Kg For Weaning Weight Research Articles

Estimating inbreeding depression for growth and reproductive traits using pedigree and genomic methods in Argentinean Brangus cattle.

Inbreeding depression reduces the mean phenotypic value of important traits in livestock populations. The goal of this work was to estimate the level of inbreeding and inbreeding depression for growth and reproductive traits in Argentinean Brangus cattle, in order to obtain a diagnosis and monitor breed management. Data comprised 359,257 (from which 1,990 were genotyped for 40,678 single nucleotide polymorphisms [SNPs]) animals with phenotypic records for at least one of three growth traits: birth weight (BW), weaning weight (WW), and finishing weight (FW). For scrotal circumference (SC), 52,399 phenotypic records (of which 256 had genotype) were available. There were 530,938 animals in pedigree. Three methods to estimate inbreeding coefficients were used. Pedigree-based inbreeding coefficients were estimated accounting for missing parents. Inbreeding coefficients combining genotyped and nongenotyped animal information were also computed from matrix H of the single-step approach. Genomic inbreeding coefficients were estimated using homozygous segments obtained from a Hidden Markov model (HMM) approach. Inbreeding depression was estimated from the regression of the phenotype on inbreeding coefficients in a multiple-trait mixed model framework, either for the whole dataset or for the dataset of genotyped animals. All traits were unfavorably affected by inbreeding depression. A 10% increase in pedigree-based or combined inbreeding would result in a reduction of 0.34 to 0.39 kg in BW, 2.77 to 3.28 kg in WW, and 0.23 cm in SC. For FW, a 10% increase in pedigree-based, genomic, or combined inbreeding would result in a decrease of 8.05 to 11.57 kg. Genomic inbreeding based on the HMM was able to capture inbreeding depression, even in such a compressed genotyped dataset.

91 Assessing Variability of Herd Sire Economic Value for Commercial Operations

Abstract Number of calves (n = 596) and weaning calf value (n = 574) from natural service, multi-sire breeding groups were evaluated in a crossbred research herd. Sires and dams that were F1 crosses of Angus (A) and Nellore (N) were mated annually during 60 to 90-day breeding seasons to produce spring-born calves in 2009–2015. Numbers of sires used annually varied from 5 to 9; numbers of females exposed per bull ranged from 14 to 22 across years. Bulls were pastured together throughout the year as well as breeding seasons. Sires were identified based on calf DNA genotyping. Calf number, birth date, birth weight, weaning weight, and economic value were determined per bull annually. Calf value was based on weaning weight and reported prices for respective weaning dates. Calf prices were calculated separately for steers and heifers relative to 22.7 kg (50 lb) increments for corresponding weight class and year. Mixed model analyses were conducted that included fixed categorical effects of calf birth year, type of F1 sire (A-sired vs. N-sired), sire nested within type, calf sex, and the interaction of F1 sire type with calf sex. Covariates of Julian birth date and calf weaning age were included for birth weight and weaning weight, respectively. Large differences in calf numbers and performance (P < 0.05) were observed. Weaned calves produced annually per sire ranged from 0 to 48. Average annual calf performance per sire ranged from 28.4 to 50.8 kg for birth weight and 146.5 to 249.0 kg for weaning weight. Annual economic value per sire ranged from $0 to $30,870 when considering half of each calf’s value as attributed to the sire. Commercial producers should consider potential sire variability for calf numbers, birth date distribution, and ratio of female-to-male calves in combination with calf performance for economic assessments.

Genetic evaluation of weaning weight and udder score in Nellore cattle

The aim of this study was to estimate genetic parameters for weaning weight (WW) and udder score (US) of 186,151 Nellore animals raised in extensive systems. The (co)variance components and estimated breeding values (EBVs) were obtained by two-trait analyses using Bayesian inference. The maternal effect (ME) was expressed as the maternal additive genetic variance of the calf's weaning weight (WW). The direct heritabilities were 0.13 ± 0.012 and 0.23 ± 0.012 for WW and US, respectively. The maternal heritability was 0.11 ± 0.012 for WW. The genetic correlations between WW and US (0.48 ± 0.053), WW and ME (0.41 ± 0.067), and US and ME (0.31 ± 0.041) were positive and moderate. Cows with maternal udder scores (US_M) 3 and 4 showed higher EBVs for ME (2.58 ± 0.070 and 2.88 ± 0.214, respectively) and their progeny had higher EBVs for WW (4.58 ± 0.058 and 5.07 ± 0.168) and US (0.20 ± 0.001 and 0.26 ± 0.005). The genetic trends demonstrate genetic progress in the selection program over the years, with values of 0.19 kg and 0.01 points for WW and US, respectively. The genetic trend in ME was 0.04 kg for WW. In addition, a positive genetic correlation was observed between these traits, as well between the traits and ME, i.e., selection would result in positive genetic gains. The use of US_M may help improve body weight and udder quality in the progeny. Furthermore, the trends indicate that the selection adopted on the farms has been effective in promoting genetic progress.

Genetic Evaluation of Some Productive Traits in Maraz Goats

This study was carriedout at the private project of Maraz goats at Bamerny sub-district/Amadiya district /Duhok governorate/Kurdistan Region of Iraq, and consists of 71 does, 8 bucks, as well as 234, 171 and 162 kids at birth, weaning and six month of age, respectively during two kidding seasons (2015-2016) and (2016- 2017). Milk traits consist of 121 records of each daily (DMY), total (TMY), pre-weaning (PRMY), peak milk yield (PKMY) and time to peak (TPMY), and 120 records of post weaning milk yield (POMY). Animal Model Program for single trait was used to predict the breeding value (PBV) and the real producing ability (RPA) for animals depending on one trait and then these values were ranked in descending order for each sex for selection. Rank correlation was calculated between estimates for both kid body weights and milk yield traits. The average breeding values for sires, dams, male kids and female kids were 0.1322, 0.0845, 0.0369 and 0.0247 kg for birth weight and 0.9877, 0.6804, 2.0072 and -0.6406 kg for weaning weight and 1.4295, 2.0184, 3.0952 and -1.0623 kg for six-month weight, respectively. Rank correlation coefficient (P≤0.001) between the breeding value estimates of birth weight and each of weaning weight and six-month weight were 0.36 and 0.28, respectively and between weaning weight and six-month weight was 0.84. Also the average RPA of 71 dams was estimated depending on their kid body weights at birth, weaning and six-months old were 0.0784, 3.7027 and 4.9492 kg, respectively. Also rank correlations coefficient were estimated between real producing ability of birth weight and each of weaning weight and six-month weight were 0.37 and 0.26, respectively and between weaning weight and SMWT was 0.81. In addition, the average producing ability were estimated for 71 Maraz does depending on their (DMY), (TMY), (PRMY), (PRMY), (PKMY) and (TPMY) were 0.0312, - 7.0378, -3.6234, -2.4199, 0.0477 and 0.2724 kg, respectively. Also rank correlations between real producing ability of all milk traits have been estimated and it was significant except between TPMY and each DMY, PRMY and PKMY, the significant correlation between RPA of milk traits assist to select the best animals and improve the herd genetically.

Effect of agro-ecological zone, season of birth and sex on pre-weaning performance of Nguni calves in Limpopo Province, South Africa

The study was conducted to determine the effect of agro-ecological zone, season of birth and sex on Nguni calves’ pre-weaning performance. Production indices such as birth weight (BW), weaning weight (WW), pre-weaning average daily gain (P-ADG) and pre-weaning gain (P-WG) were assessed in the different agro-ecological zones. Herd records on performance of 826 Nguni calves’ from nine Nguni herds representing different agro-ecological zones: arid zone (n = 217); semi-arid zone (n = 296); dry sub-humid zone (n = 118) and humid zone (n = 195) were used for the analysis of pre-weaning calf performance. General linear model (GLM) procedure of SAS (2013) was used to analyse data, whereas mean separation was conducted using Tukey’s HSD test. Agro-ecological zone had a great influence (P < 0.01) on performance levels arising from pasture conditions which were dependent on rain, temperature, topography and soil type. Fluctuations in WW, P-ADG and P-WG performance across agro-ecological zones depicted the sensitivity of Nguni calves’ to postnatal stress. Calves’ in humid zone had higher performance with 121.21 kg for WW, 96.83 kg for P-WG and 0.477 kg/day for P-ADG. The lowest WW (114.51 kg), P-WG (89.98 kg) and P-ADG (0.438 kg/day) were observed in arid zone. Male calves were heavier at weaning (128.18 kg), P-ADG (0.503 kg/day) and total gain (103.03 kg); however, similar BW of 25 kg was observed for both male and female calves. Season had a significant (P < 0.05) effect on BW, P-ADG and P-WG. The P-ADG was 0.461 kg/day for calves born in summer and 0.449 kg/day for calves born in winter season. Calves born in summer gained 94.69 kg and calves born in winter gained 92.10 kg. Summer calves gained 2.59 kg more than winter calves. Summer heifer calves performed poorly whilst summer male calves outperformed heifer calves in terms of WW, P-WG and P-ADG. Pre-weaned calves in humid zone outperformed all calves in other agro-ecological zones. It was concluded that acceptable levels of growth are achievable from Nguni cattle under the different agro-ecological zones of Limpopo province, South Africa.

Effect of inbreeding and individual increase in inbreeding on growth in Nilagiri and Sandyno breeds of sheep

SummaryIndividual increase in inbreeding coefficients (ΔFi) has been recommended as an alternate measure of inbreeding. It can account for the differences in pedigree knowledge of individual animals and avoids overestimation due to increased number of known generations. The effect of inbreeding (F) and equivalent inbreeding (EF) calculated fromΔFi, on growth traits were studied in Nilagiri and Sandyno flocks of sheep. The study was based on data maintained at the Sheep Breeding Research Station, Sandynallah. The pedigree information and equivalent number of generations were less in Sandyno compared with Nilagiri sheep. The average F and EF for the Nilagiri population were 2.17 and 2.44, respectively and the corresponding values for Sandyno sheep were 0.83 and 0.84, respectively. The trend of inbreeding over years in both the populations indicated that EF was higher during earlier generations when pedigree information was shallow. Among the significant effects of inbreeding, the depression in growth per 1 percent increase in inbreeding ranged from 0.04 kg in weaning weight to 0.10 kg in yearling weight. In general, more traits were affected by inbreeding in Nilagiri sheep, in which greater regression of growth traits was noticed with F compared with EF. Higher values of EF than F in earlier generations in both the populations indicate that EF avoided the potential overestimation of inbreeding coefficient during recent generations. In the Sandyno population, the magnitude of depression noticed among growth traits with significant effects of inbreeding was higher. The differences in response to F and EF noticed in the two populations and possible causes for the trait wise differences in response to F and EF are appropriately discussed.

Some Environmental Factors Affecting Birth Weight, Weaning Weight and Daily Live Weight Gain of Holstein Calves

The present study was conducted to determine some environmental factors affecting birth weight, weaning weight and daily live weight gain of Holstein calves of a livestock facility in Izmir, Turkey. The data on 2091 calves born between the years 2005-2010 were used to assess the relevant parameters. Effects of calving year, calving month, calf gender and the interaction between calving year and calving month on calves’ birth weights were highly significant. The overall mean of birth weights was 39.6±0.15 kg. In addition, effects of calving year, calving month, gender, birth weight, weaning age, calving year x calving month, calving year x gender and calving year x calving month x gender interactions on weaning weight (WW) and daily live weight gain (DLWG) were highly significant. The overall means of WW and DLWG were respectively found to be 79.7±0.20 kg and 525±2.5 g. A one kilogram increase in birth weight resulted in an increase of 0.89 kg in weaning weight and a decrease of 1.26 g in daily live weight gain. Prenatal temperature-humidity index (THI) affected birth weight of calves (R2=0.67). Increasing THI from 50 to 80 resulted in 3.8 kg decrease in birth weight.

Environmental factors and ram influence litter size, birth, and weaning weight in Saint Croix hair sheep under semi-arid conditions in Mexico.

This study was conducted to evaluate the effects of season, year of lambing, parity, and the effect of ram on litter size, birth, and weaning weight through 8years. Data of 4078 lambs sired by 21 rams and 1072 ewes were analyzed by a lineal model. There was a significant effect (P < 0.05) of lambing number on litter size and birth weight, but not on weaning weight (P > 0.05). For litter size, the lowest numbers were obtained on the first lambing ewes (1.21 ± 0.03) and the highest ones inewes starting from the fourth lambing (1.69 ± 0.04). Lowest body weights were found in lambs born from first lambing ewes (3.01 ± 0.1kg) and the highest ones in lambs born from the second (3.14 ± 0.1) to the fifth (3.15 ± 0.2) lambing ewes. The lambing breeding season had a significant effect on weaning weight: the highest weaning weights were recorded in lambs born in spring (12.70 ± 0.20kg) and the lowest ones in those born in summer (11.93 ± 0.20kg). Lambing year had a significant effect (P < 0.05) on litter size and weaning weight, since the values of both traits improved through the years. Effect of ram was significant (P < 0.05) for each of the traits considered: there were differences up to one lamb per litter, also differences up to 1.5kg for birth weight and up to 6.5kg for weaning weight among rams. In conclusion, these results indicate that environmental conditions are important source of variation in litter size, birth, and weaning weight in hair sheep under semi-arid climate.

Genetic grouping strategies in selection efficiency of composite beef cattle ( × ).

The inclusion of genetic groups in sire evaluation has been widely used to represent genetic differences among animals not accounted for by the absence of parentage data. However, the definition of these groups is still arbitrary, and studies assessing the effects of genetic grouping strategies on the selection efficiency are rare. Therefore, the aim in this study was to compare genetic grouping strategies for animals with unknown parentage in prediction of breeding values (EBV). The total of 179,302 records of weaning weight (WW), 29,825 records of scrotal circumference (SC), and 70,302 records of muscling score (MUSC) from Montana Tropical animals, a Brazilian composite beef cattle population, were used. Genetic grouping strategies involving year of birth, sex of the unknown parent, birth farm, breed composition, and their combinations were evaluated. Estimated breeding values were predicted for each approach simulating a loss of genealogy data. Thereafter, these EBV were compared to those obtained in an analysis involving a real relationship matrix to estimate selection efficiency and correlations between EBV and animal rankings. The analysis model included the fixed effects of contemporary groups and class of the dam age at calving, the covariates of additive and nonadditive genetic effects, and age, and the additive genetic effect of animal as random effects. A second model also included the fixed effects of genetic group. The use of genetic groups resulted in means of selection efficiency and correlation of 70.4 to 97.1% and 0.51 to 0.94 for WW, 85.8 to 98.8% and 0.82 to 0.98 for SC, and 85.1 to 98.6% and 0.74 to 0.97 for MUSC, respectively. High selection efficiencies were observed for year of birth and breed composition strategies. The maximum absolute difference in annual genetic gain estimated through the use of complete genealogy and genetic groups were 0.38 kg for WW, 0.02 cm for SC, and 0.01 for MUSC, with lower differences obtained when year of birth was adopted as a genetic group criterion. Grouping strategy must consider selection decisions and the number of genetic groups formed, in the way that genetic groups represent the genetic differences in population and allow an adequate prediction of EBV.

Breeding objectives and economic values for traits of low input family-based beef cattle production system in the State of Rio Grande do Sul

The objectives of this study were to define breeding objectives and derive economic weights for production traits in family-based beef cattle systems, assess the sensitivity of these weights to changes in market and husbandry indicators and estimate the expected genetic changes in the selection criteria proposed. Based on data from the production systems, farms revenues and expenses, obtained from interviews and meetings with producers, a bioeconomic model was derived, relating biological traits of animals with the financial result of the production system based on calf-crop, selling male calves and culling cows for finishing. Traits considered in the model as breeding goals were weaning rate, weaning weight and cow weight. The economic weights, obtained by the partial derivative of the bioeconomic model with respect to the trait in question, assessed on the average value of the remaining traits, were R$ 73.21% for weaning rate, R$ 17.07/kg for weaning weight and R$ 4.75/kg for cow weight. An index for joint selection of these three criteria would allocate 89.5% of importance to weaning rate, 6.9% for weaning weight and 3.6% for cow weight. In this way, for every R$ 100.00 of genetic gain in this index, there would be an increase of 1.4% in weaning rate, but with reduction of 0.004 kg in weaning weight and 0.665 kg in cow weight due to negative genetic association between these traits. The proposed index and the relative importance identified for the economic traits can guide the selection decisions of smallholders, both in the choice of their animals and in the acquisition of bulls, cumulatively increasing the productivity of their herds.

Case study: The effect of inbreeding on the production and reproduction traits in the Elsenburg Dormer sheep stud

Data of the Elsenburg Dormer sheep stud, which was kept closed since inception, were collected over a period of 62 years (1941–2002). The breed is a composite, resulting from a cross of Dorset Horn rams with South African Mutton Merino ewes. These data were analysed to quantify the increase in actual level of inbreeding and to investigate the effect of inbreeding on phenotypic values, genetic parameters and estimated breeding values. After editing 11954 pedigree, 11721 birth weight (BW) and survival, 9205 weaning weight (WW) and 7504 reproduction records were available for analysis. The mean level of inbreeding ( F) of all animals over all years was 16%; 14% for dams and 16% for sires. Mean, minimum and maximum F for the lambs in 1997 (when 3 rams from outside were introduced) were 22%, 21% and 24% respectively. Estimates of inbreeding depression for individual inbreeding of 1% were − 0.006 kg for birth and − 0.093 kg for weaning weight respectively. These were the only estimates that were significantly ( P < 0.01) different from zero. No significant effects of inbreeding on the other traits were found. There were virtually no differences in the genetic parameters estimated when fitting the two models (inclusion or exclusion of inbreeding coefficients as covariates). Estimates of the phenotypic variance differed slightly for WW between the two models. Ranking of animals were studied for weaning weight when the two models were considered. The high correlation coefficients (0.990) indicate that the use of inbreeding coefficients did not cause important changes in ranking of animals and sires for WW. It was concluded that slow inbreeding (rate of inbreeding of approximately 1.53% per generation over 19 generations) allows natural selection to operate and to remove the less fit animals. At any given mean level of F, less inbreeding depression would then be expected among the individuals who accumulated the inbreeding over a larger number of generations. Nevertheless, inbreeding coefficients should be considered when mating decisions are made, to limit the possible deleterious effects of inbreeding on productive and reproductive traits and to detect animals “resilient to” higher levels of inbreeding.

Some reproductive and growth traits of crossbred genotypes produced by crossing local sheep breeds of Kivircik x White Karaman and Chios x White Karaman in steppe conditions

Abstract. The aim of this study was to investigate some production traits of crossbred genotypes produced for lamb production by crossing local sheep breeds of Kivircik (K) x White Karaman (W) and Chios (C) x White Karaman in steppe conditions. W breed is raised in steppe conditions while K and C breeds are raised in Mediterranean climate conditions in Turkey. A total of 340 ewes was used through 3 years. The litter size for W, KWF1 and CWF1 ewes were 1.26, 1.19 and 1.52 (P&lt;0.05), respectively. The least squares means of W, KW F2, KW B1, CW F2 and CW B1 lambs were 91.2, 95.7, 95.6, 87.3 and 94.2 % for survival rate at weaning (90 days); 4.4, 4.3, 4.1, 4.2 and 4.1 kg for birth weight; 21.1, 20.3, 19.6, 20.3 and 19.9 kg for weaning weight; 31.9, 29.4, 30.3, 30.5 and 30.1 kg for 180 day weight, respectively. The differences among genotypes for survival rates and growth performance of lambs were not statistically significant (P&gt;0.05). The results indicated that Chios crossbred ewes had the highest reproductive performance while all genotypes had similar performance in terms of survival and growth of lambs in steppe conditions.

Genetic parameter of birth and weaning weights for Friesian calves by using an animal model

Abstract. Birth and weaning weights of 556 Friesian calves by 41 sires out of 318 different dams over a 11 years period were obtained from a herd of Friesian in Sakha Experimental Farm, Ministry of Agriculture, Egypt were used. The records were analyzed by Multiple Trait Likelihood Method (MTDFREML) by using a repeatability animal model (BOLDMAN et al., 1995). Convergence was attained after 699 iterations. The fixed effects included in the model were season and year of calving, parity and sex and the random effects were direct and maternal genetic, permanent maternal environmental and error. Direct heritability estimates for birth weight (BW) and weaning weight (WW) are 0.28 and 0.13, respectively, while, maternal heritability estimates for the same traits are 0.14 and 0.06, respectively. Repeatability estimates are 0.75 and 0.15 for BW and WW, respectively. Phenotypic and genetic correlations are 0.89 and 0.80, respectively. Estimates of calve breeding values ranged from −3.12 to 4.11 kg for BW and ranged from −4.10 to 5.11 kg for WW. Sire breeding values ranged from −3.40 to 2.99 kg for BW and ranged from −2.50 to 4.47 kg for WW. Dam breeding values ranged from −6.80 to 5.54 kg for BW and ranged from -6.10 to 6.39 kg for WW.

Early growth performance of Bos taurus × Bos indicus cattle crosses in Ethiopia: estimation of individual crossbreeding effects

SummaryIn an effort to estimate breed differences, heterotic and recombination effects, a total of 4957 birth weight (BWT), 4245 weaning weight (WWT) and 3330 yearling weight (YWT) records collected from 38 crossbred and three purebred genotypes generated from crossing Friesian (F), Jersey (J) and Simmental (S) with the Boran (Bo), Barca (Ba) and Horro (Ho) (Bos indicus) breeds in Ethiopia were used. Differences between genotypes were significant (p &lt; 0.01) for all traits. Genetic group mean values adjusted for environmental effects ranged from 20 to 30 kg for BWT, 88 to 114 kg for WWT, 122 to 157 kg for YWT and 358 to 492 g for preweaning average daily gain (ADG). The breed additive effect of F as a deviation from the Bo was significant (p &lt; 0.01) and positive for all traits. Relative to the Bo mean, the additional breed additive contributions of the F breed on BWT, WWT, ADG and YWT were 39.3, 16.5, 9.3 and 10.3%, respectively. However, the breed additive effects of the Ho and J breeds were significantly (p &lt; 0.01) negative for all traits. The heterotic effects were significantly negative (p &lt; 0.01) for BWT for all F and S crosses, but positive (p &lt; 0.01) on all other traits for all types of crosses. The average heterosis estimated within the F, J and S breeds were: −2.1 ± 0.6, 0.2 ± 0.6 (p &gt; 0.05) and −2.3 ± 0.6 kg for BWT, 8.82.1, 11.8 ± 2.3 and 13.7 ± 2.4 kg for WWT, 60.4 ± 11.3, 64.8 ± 12.3 and 90.6 ± 12.7 g for ADG, and 19.8 ± 2.6, 19.5 ± 2.8 and 20.8 ± 2.9 kg for YWT, respectively. The recombination effects were significant (p &lt; 0.01) for the majority of crosses for all traits. The estimates of the recombination loss were negative in all traits, except for BWT. The average recombination effects estimated within the F, J and S breeds were: 2.6 ± 0.8, 2.9 ± 0.9 and 2.4 ± 1.0 kg for BWT, −13.6 ± 3.2, −4.2 ± 3.4 (p &gt; 0.05) and −16.0 ± 4.0 kg for WWT, −88.0 ± 17.1, −39.4 ± 18.4 and −102.2 ± 21.3 g for ADG, and −14.4 ± 4.0, −0.1 ± 4.4 (p &gt; 0.05) and −17.5 ± 4.9 kg for YWT, respectively. It could be concluded that the breed differences, heterotic and recombination effects seem to be important genetic factors affecting early growth performances in the breed crosses tested.

Evaluation of maternal performance of daughters from high and low milk EPD sires.

Angus bulls (n = 24) were selected for either high or low milk EPD, but with similar growth EPD and mated within location (n = 6) at random to Angus cows. Daughters from these matings were bred to calve first at 2 yr of age to common reference sires across locations. Lactation records for 192 daughters were used to evaluate 12-h milk yield, percentage of milk fat and protein, and weaning weight of offspring. Milk production was measured four times during the lactation at regular intervals within location. Dams were separated from their calves the night before milking and milked with a portable milking machine the next morning to estimate 12-h milk yield. A sample of the milk was collected from each cow and analyzed for percentages of milk fat and protein. Data were analyzed as repeated records of the dam. Fixed effects were location, genetic line of sire, gender of calf within location, and milking period, with postpartum interval used as a covariate. Fixed effects and the random effects of sire of dam nested within line, sire of calf, and year were estimated by REML. Genetic line was an important source of variation for milk yield (P < 0.01) and percentage of milk fat (P = 0.03) but not for percentage of milk protein (P = 0.49). Location was significant for all three milk variables (P < 0.01), but the interactions between line and location were not significant. Gender of calf was significant for milk yield (P = 0.04) but not for percentage of milk fat or protein. Line (P = 0.02), location (P = 0.01), calf gender (P = 0.01), and age at weaning (P = 0.01) were significant sources of variation for weaning weight but the interaction of line and location was not (P = 0.69). The correlation coefficient between the sire's milk EPD and 12-h milk yield was significantly different from zero (r = 0.56). The difference between the least squares means for high and low lines for milk yield was 0.66 kg/12 h and the difference was 15.3 kg for weaning weight. The results indicate that there was not evidence for a genotype by environment interaction in milk production for daughters from divergent sires selected for high or low milk EPD.

The effects of maternal calving date and calving interval on growth performance of beef calves

This study was undertaken to investigate the growth performance of calves born to dams with different calving dates and calving intervals. Early calving dams produced calves with the lowest birth weights, the highest actual weaning weights and the highest pre-breeding heifer weights. The higher weaning weights of early calvers were due to higher pre-weaning average daily gains and the older age of their calves at weaning. Corrected weaning weights of calves born to dams calving at different times during the calving season were not significantly different. A one-day increase in calving interval resulted in a decrease of 0.29 ± 0.01 kg for weaning weight and a decrease of 0.54 ± 0.01 kg for heifer pre-breeding weight. It is recommended that date of calving and actual weaning weight of calves should be considered when evaluating the reproductive and productive performance of breeding cows. (South African Journal of Animal Science: 2000, 30(1): 70-76)

Effects of inbreeding and heterozygosity on preweaning traits in a closed population of Herefords under selection.

Records of five inbred lines at the Livestock and Range Research Laboratory were used to evaluate effects of inbreeding and heterozygosity on preweaning traits. Members of each line were descendants of a single founder Hereford bull. A total of 8,065 records of birth weight and 7,380 records of preweaning daily gain and weaning weight were analyzed by derivative-free REML using a model that included fixed effects of sex, combination of year and month of birth and parity of dam, with covariates for direct and maternal genetic fractions of inheritance from the genetic groups, inbreeding, and heterozygosity fractions. Heterozygosity fractions were computed for crosses between lines. The random model effects were direct and maternal genetic and uncorrelated maternal permanent environmental and temporary environmental. Direct inbreeding and heterozygosity fractions averaged .098 and .343, and maternal inbreeding and heterozygosity fractions averaged .075 and .294. Regression coefficients of traits on direct and maternal inbreeding fractions were -5.8 +/- 1.1 and -4.7 +/- 1.3 for birth weight, -.189 +/- .031 and -.252 +/- .039 for preweaning daily gain, and -44.5 +/- 6.6 and -56.1 +/- 8.4 kg for weaning weight. Estimates for direct heritability, maternal heritability, and direct-maternal genetic correlations were .37, .12, and -.01 for birth weight; .16, .25, and -.27 for daily gain; and .17, .26, and -.21 for weaning weight. Results suggest that heterosis represents recovery of accumulated inbreeding depression. Results also indicate that selection can overcome inbreeding depression and antagonism exists between direct and maternal genetic effects for preweaning traits.

CHANGES IN BEEF CATTLE PERFORMANCE AFTER TEN YEARS OF YEARLING WEIGHT SELECTION

Selection for yearling weight, a trait with relatively high heritability, in beef cattle should lead to a significant response in a short period of time. Changes should also occur in correlated and component traits. Data from 10 yr of yearling weight selection in beef Shorthorn cattle were used to quantify the response in correlated calf and cow traits. Selection response was measured as the difference between the performance of the select line and a corresponding control line. Annual response to selection for bull and heifer calves, respectively, averaged 5.1 and 4.3 kg for yearling weight, 2.1 and 1.6 kg for weaning weight, 0.3 and 0.2 kg for birth weight, 0.016 and 0.014 kg d−1 for post-weaning average daily gain and 0.010 and 0.007 kg d−1 for preweaning average daily gain. There were no significant changes in calf survival or cow reproductive performance. Cow weights increased 4.5 kg yr−1 for 2-yr-old heifers, similar to the yearling weight response, but only 1.3 kg yr−1 for all cows because of the time delay caused by the age distribution of the breeding herd. Yearling weight increases were brought about by increases in the individuals genetic potential for gain, primarily postweaning. Response to yearling weight selection would be relatively easy to achieve for beef producers. Some additional costs would be incurred, however, and the environmental effects, which were large, would have to be monitored. Key words: Beef cattle, yearling weight, selection response, correlated response

Direct and maternal genetic effects due to the introduction of Bos taurus alleles into Brahman cattle in Florida: II. Preweaning growth traits.

Records of birth weight (BW), weaning weight (WW) and condition score (CS) from 1,467 Brahman and Brahman X Angus crossbred calves from Brahman and crossbred Brahman sires and Brahman, crossbred Brahman and Angus dams were collected at the Subtropical Agricultural Research Station, Brooksville, Florida, from 1971 to 1982. Best linear unbiased estimates (BLUE) of Brahman sire and dam group additive genetic effects (as deviations from Angus) and Brahman X Angus dam and calf group nonadditive (intralocus) genetic effects (as deviations from intralocus group genetic effects in the parental breeds) were obtained. Linear combinations of these were used to compute direct and maternal Brahman additive and Brahman X Angus nonadditive (intralocus) group genetic effects. The respective BLUE of these four effects were 5.99 +/- 2.08, -5.70 +/- 1.91, .52 +/- 1.81 and 2.85 +/- .72 kg for BW; 9.60 +/- 10.29, 8.76 +/- 9.47, 9.47 +/- 8.96 and 20.95 +/- 3.56 kg for WW; and -1.10 +/- .55, 1.64 +/- .50, 1.47 +/- .47 and .05 +/- .19 units for CS. Linear combinations of the BLUE of sire, dam and calf group genetic effects can be used to predict the genetic worth of crossbred groups composed of any combination of Brahman and Angus breeding. Nonadditive maternal group genetic effects were the most important factor for BW and WW, whereas nonadditive direct group genetic effects were the most important for CS.

Effect of preweaning nutritional management on yearling weight response in an open-herd selection program.

Records on 276 progeny were collected in the final 2 yr (1984 and 1985) of an 8-yr Hereford cattle selection project. Selection was practiced using the top sires from the American Hereford Association's National Cattle Evaluation based on yearling weight expected progeny difference. An unselected control line was maintained to monitor environmental change. One-half of each line was creep-fed during the preweaning period for the last 2 yr to evaluate genotype x environment interactions. Direct response to yearling weight selection averaged 28 +/- 8 kg. Correlated response to selection amounted to .057 +/- .028 kg/d in preweaning ADG, 14 +/- 6 kg in weaning weight, .085 +/- .033 kg/d in postweaning ADG, 4.6 +/- 1.5 cm in yearling hip height and 11.2 +/- 3.0 cm2 in yearling pelvic area. Yearling fat thickness and scrotal circumference were not significantly affected by selection. Significant effects of creep feeding were observed for yearling weight (15 +/- 3 kg), preweaning ADG (.067 +/- .012 kg/d), weaning weight (13 +/- 2 kg), yearling hip height (1.2 +/- .5 cm) and yearling fat thickness (.07 +/- .03 cm). Postweaning ADG, yearling pelvic area and yearling scrotal circumference were not affected by creep feeding. No significant genetic group x creep feeding effects were found for any of the traits analyzed, indicating calves genetically superior for growth did not gain any additional advantage from creep feeding.