Genetic analysis of growth rate and Kleiber ratio in Zandi sheep

Genetic parameters for average daily gain from birth to weaning (ADGa), birth to 6 months (ADGb), weaning to 6 months (ADGc), weaning to yearling age (ADGd), and corresponding Kleiber ratios (KRa, KRb, KRc, and KRd) were estimated by using records of 3,533 Zandi lambs, descendent of 163 sires and 1265 dams, born between 1991 and 2005 at the Zandi Sheep Breeding Station at Khojir National Park, Tehran, Iran. A derivative-free algorithm combined with a series of six single-trait linear animal models was used to estimate phenotypic variance and its direct, maternal, and residual components. In addition, bivariate analyses were done to estimate (co)variance components between traits. Estimates of direct heritability (h ² ) were 0.11, 0.15, 0.09, 0.10, 0.10, 0.10, 0.06, and 0.07 for ADGa, ADGb, ADGc, ADGd, KRa, KRb, KRc, and KRd, respectively, thereby indicating the presence of low additive genetic variation for growth rate and Kleiber ratio in this population of Zandi sheep. Maternal genetic component was found to be significant on ADGa and KRa and contributed 3% and 5%, respectively, in total phenotypic variance of ADGa and KRa. A widespread range of genetic correlations among traits studied was observed. Except for negative genetic correlations between ADGa and KRc, ADGa and KRd, and between KRa and KRc, in other cases, genetic correlations were positive and moderate to very high. Phenotypic correlations ranged from −0.49 (ADGa/KRd) to 0.94 (ADGc/KRc). These results indicate that selecting for improved growth rate or Kleiber ratio in Zandi sheep would generate a relatively slow genetic progress.     

The importance of haplotype length and heritability using genomic selection in dairy cattle

Reliabilities for genomic estimated breeding values (GEBV) were investigated by simulation for a typical dairy cattle breeding setting. Scenarios were simulated with different heritabilites ( h ²) and for different haplotype sizes, and seven generations with only genotypes were generated to investigate reliability of GEBV over time. A genome with 5000 single nucleotide polymorphisms (SNP) at distances of 0.1 cM and 50 quantitative trait loci (QTL) was simulated, and a Bayesian variable selection model was implemented to predict GEBV. Highest reliabilities were obtained for 10 SNP haplotypes. At optimal haplotype size, reliabilities in generation 1 without phenotypes ranged from 0.80 for h ² = 0.02 to 0.93 for h ² = 0.30, and in the seventh generation without phenotypes ranged from 0.69 for h ² = 0.02 to 0.86 for h ² = 0.30. Reliabilities of GEBV were found sufficiently high to implement dairy selection schemes without progeny testing in which case a data time-lag of two to three generations may be present. Reliabilities were also relatively high for low heritable traits, implying that genomic selection could be especially beneficial to improve the selection on, e.g. health and fertility.     

Growth, weaning performance and blood indicators of humoral immunity in Holstein calves fed supplemental flavonoids

The primary objective was to test the hypothesis that flavonoids mediate immune response and affect calf performance. Twenty Holstein calves [7 ± 2 days age; 41.4 ± 0.7 kg body weight (BW)] were randomly assigned to four treatments of (i) no; (ii) low (7.3 × 10⁻⁵ g/kg BW); (iii) medium (7.3 × 10⁻⁴ g/kg BW); and (iv) high (3.6 × 10⁻³ g/kg BW) doses of flavonoids intake in a completely randomized design. Calves received the treatments as a tablet until weaning or a daily intake of 680 g starter. After weaning, calves received no supplemental flavonoids and monitored until 120 days of age. The flavonoids were extracted from propolis. Treatments did not affect body length, wither height and the severity of scours. At week 5 of age, BW was higher when calves fed the high compared to the low dose of flavonoids. At week 6, calves fed the high dose of flavonoids had higher BW than those fed no or low doses of flavonoids. The serum immunoglobulin G (IgG) concentrations remained lower at the first 3 weeks of the experiment when calves received the low but not the high doses of flavonoids. At week 4, both medium and low doses of flavonoids moderated serum IgG. At week 8, the medium and high but not the low doses of flavonoids lowered serum IgG. At week 6, calves fed high and medium flavonoids doses had lower blood immunoglobulin M (IgM) than control calves. Results suggest that flavonoids affect the humoral immune response and can improve growth in young calves. This response depended on calf age. Future studies are needed to further evaluate the premise that dietary forages or the main source of flavonoids are helpful for a less stressful weaning in the modern calf raising.     

Numbers of nitrate-reducing bacteria in the rumen as estimated by competitive polymerase chain reaction

Cell numbers of known species of nitrate- and nitrite-reducing bacteria, Selenomonas ruminantium, Veillonella parvula and Wollinella succinogenes , in the rumen of goats (25–30 kg) were estimated by competitive polymerase chain reaction (PCR). The number of S. ruminantium was the largest of the three species examined, and tended to be greater in goats fed a high-concentrate diet (5.6 × 10⁷ cells/mL rumen fluid) than in goats fed a high-roughage diet (1.3 × 10⁷ cells/mL). The number of V. parvula tended to be greater when goats were fed a high-roughage diet (6.7 × 10³/mL) than when fed a high-concentrate diet (3.2 × 10³/mL). The number of W. succinogenes was below the detectable level (< 1.0 × 10²/mL) when a high-concentrate diet was fed, but was significantly increased by feeding a high-roughage diet (1.6 × 10³/mL). Addition of potassium nitrate (6 g/day) to the high-concentrate diet tended to increase V. parvula , and significantly increased W. succinogenes , indicating that these two bacteria can be increased by feeding a diet containing nitrate.     

Direct and maternal (co)variance components, genetic parameters, and annual trends for growth traits of Makooei sheep in Iran

Genetic parameters and genetic trends for birth weight (BW), weaning weight (WW), 6-month weight (6MW), and yearling weight (YW) traits were estimated by using records of 5,634 Makooei lambs, descendants of 289 sires and 1,726 dams, born between 1996 and 2009 at the Makooei sheep breeding station, West Azerbaijan, Iran. The (co)variance components were estimated with different animal models using a restricted maximum likelihood procedure and the most appropriate model for each trait was determined by Akaike’s Information Criterion. Breeding values of animals were predicted with best linear unbiased prediction methodology under multi-trait animal models and genetic trends were estimated by regression mean breeding values on birth year. The most appropriate model for BW was a model including direct and maternal genetic effects, regardless of their covariance. The model for WW and 6MW included direct additive genetic effects. The model for YW included direct genetic effects only. Direct heritabilities based on the best model were estimated 0.15?±?0.04, 0.16?±?0.03, 0.21?±?0.04, and 0.22?±?0.06 for BW, WW, 6MW, and YW, respectively, and maternal heritability obtained 0.08?±?0.02 for BW. Genetic correlations among the traits were positive and varied from 0.28 for BW–YW to 0.66 for BW–WW and phenotypic correlations were generally lower than the genetic correlations. Genetic trends were 8.1?±?2, 67.4?±?5, 38.7?±?4, and 47.6?±?6 g per year for BW, WW, 6MW, and YW, respectively.     

Ovarian Structure in Mice Lines Selected for Weight

Selection for body weight at 49 day of age ( s and h , downward selected lines; s' and h' , upward selected lines) affected reproductive traits in CF1 mice lines. The objective of this study was to compare ovarian structures in females of these lines, as well as in unselected controls (Line t ). The number of ovarian follicles ( N ), follicle diameter (FD), number of corpora lutea (CL), litter size (LS), and body weight ( W ), were recorded. There were significant differences among lines for N , FD, CL, LS and W ; means values for the lines with the greatest difference for post-pubertal females were: N _s  = 19.3 and N _s'  = 32.7; FD _h'   = 161.7 and FD _s'  = 178.2; CL _h  = 10.3 and CL _s'  = 21.9; LS _s  = 6.0 and LS _h'  = 11.1; W _h  = 18.9 and W _s'  = 32.4. There were also differences between positive lines; Line s' had a higher proportion of large follicles in pre-pubertal females, a greater capacity to convert these follicles into CL, but a lower capacity to maintain embryos until term than Line h' . For negative lines, Line h apparently had a reduced incidence of embryonic loss when compared with Line s . In conclusion, selection for body weight modified ovarian structure, as well as reproductive efficiency.     

Direct and maternal (co)variance components and genetic parameters for growth and reproductive traits in the Boran cattle in Kenya

Direct and maternal (co)variance components and genetic parameters were estimated for growth and reproductive traits in the Kenya Boran cattle fitting univariate animal models. Data consisted of records on 4502 animals from 81 sires and 1010 dams collected between 1989 and 2004. The average number of progeny per sire was 56. Direct heritability estimates for growth traits were 0.34, 0.12, 0.19, 0.08 and 0.14 for birth weight (BW), weaning weight (WW), 12-month weight (12W), 18-month weight (18W) and 24-month weight (24W), respectively. Maternal heritability increased from 0.14 at weaning to 0.34 at 12 months of age but reduced to 0.11 at 24 months of age. The maternal permanent environmental effect contributed 16%, 4% and 10% of the total phenotypic variance for WW, 12W and 18W, respectively. Direct-maternal genetic correlations were negative ranging from −0.14 to −0.58. The heritability estimates for reproductive traits were 0.04, 0.00, 0.15, 0.00 and 0.00 for age at first calving (AFC), calving interval in the first, second, and third parity, and pooled calving interval. Selection for growth traits should be practiced with caution since this may lead to a reduction in reproduction efficiency, and direct selection for reproductive traits may be hampered by their low heritability.     

Genetic evaluation of growth in farmers’ flocks of Madras Red sheep under long-term selection in a group breeding scheme

The Network Project on Sheep Improvement (NWPSI)–Madras Red field unit is a group breeding scheme involving 198 farmers’ flocks of Madras Red sheep in which selection for growth traits and rotation of rams have been practised for over two decades. Growth data collected from these flocks were used to evaluate the performance and understand the direct and expected responses to selection based on genetic parameters. The body weight at birth (BW), weaning weight (WW), 6-month weight (6W), 9-month weight (9W), 12-month weight (YW), pre-weaning average daily gain (ADG1, birth to 3 months), post-weaning ADG2 (3–6 months), ADG3 (6–9 months), ADG4 (9–12 months) and ADG5 (3–12 months) were 2.67, 10.05, 14.56, 18.36, 21.36, 80.13, 49.05, 43.00, 34.21 and 41.18 g, respectively. Univariate analyses were carried out using animal and sire models to estimate variance components. Heritability obtained from animal model for BW was 0.36 and the values for other body weight traits were almost unity. Heritability estimate for pre-weaning ADG1 was 0.31. Very high genetic variability was observed in spite of long-term selection and this sustenance of variability is one of the main advantages of a group breeding scheme, combining several flocks of smaller size. An increasing genetic and phenotypic trend was noticed for almost all the traits studied. The expected responses calculated based on genetic parameters also indicated scope for improvement.     

Genetic and phenotypic parameters and annual trends for growth and fertility traits of Charolais and Hereford beef cattle breeds in Kenya

This study estimated genetic and phenotypic parameters and annual trends for growth and fertility traits of Charolais and Hereford cattle in Kenya. Traits considered were birth weight (BW, kg), pre-weaning average daily gain (ADG, kg/day) and weaning weight (WW, kg); calving interval (CI, days) and age at first calving (AFC, days). Direct heritability estimates for growth traits were 0.36 and 0.21; 0.25 and 0.10; 0.23 and 0.13 for BW, ADG and WW in Charolais and Hereford, respectively. Maternal heritability estimates were 0.11 and 0.01; 0.18 and 0.00; 0.17 and 0.17 for BW, ADG and WW in Charolais and Hereford, respectively. Direct-maternal genetic correlations ranged between −0.46 and 1.00; −0.51 and −1.00; −0.47 and −0.39 for BW, ADG and WW in Charolais and Hereford, respectively. Genetic correlations ranged from −0.99 to unity and −1.00 to unity for growth and fertility traits respectively. Prospects for improvement of growth and fertility traits exist.     

Association between butyrate and short-chain fatty acid concentrations in gut contents and faeces in weaning piglets

The concentration and composition of short-chain fatty acids (SCFA) in gastrointestinal and faecal samples were studied in weaning pigs fed different amounts and composition dietary fibre (DF). In Trial 1 a total of 50 castrated piglets were fed five experimental diets with varying contents of citrus pectin (soluble fibre) and barley hulls (insoluble fibre) and gastrointestinal contents were collected at euthanasia 9 days after weaning. In Trial 2, 120 pair-wise penned piglets were allocated to the same experimental diets as in Trial 1 (24 piglets per treatment), and fresh faecal samples were collected 5 and 32 days after weaning.

There was no difference in the concentrations of SCFA caused by dietary treatments, but across treatments there was a correlation between concentration of SCFA and the proportion of butyrate. The correlation was lowest in the caecum (r² = 0.22, P = 0.0007) and highest in the distal colon (r² = 0.45, P = 0.0001). In faeces there was no relationship 5 days after weaning (r² = 0.004. P = 0.64) but a correlation of r² = 0.25 (P = 0.0001) 32 days after weaning. The results suggest that adaptive changes and differences between piglets in fermentative capacity immediately after weaning are associated not only with a higher concentration of SCFA but also a changed fermentation profile.     

Selection for increased weaning or yearling weight in Hereford cattle. II. Direct and correlated responses

Selection was applied from 1964 to 1978 for increased weaning weight (WWL) or yearling weight (YWL) in two Hereford lines. An Angus line was maintained as an unselected control line (CL). Each line was maintained with 50 cows and four sires each year (two sires selected each year and used for 2 yr). Primary traits measured in the lines were birth weight (BW), preweaning daily gain (WDG), weaning weight (WW), weaning conformation grade (WG), weaning condition score (WC), weaning to yearling daily gain (YDG), yearling weight (YW), yearling conformation grade (YG) and yearling condition score (YC). Averaged over two methods, estimated genetic responses/generation (in standard deviation units) in WWL and YWL were: BW, .29, .26; WDG, .17, .15; WW, .22, .19; WG, .19, .26; WC, .12, .12; YDG, -.02, .04; YW, .08, .14; YG, .19, .16; YC, -.13, -.03. The realized heritability estimates were .23 and .15 for WW and YW, respectively. The realized genetic correlation between WW and YW was .69. Progeny from crosses of selected WWL and YWL sires to Angus cows had similar feedlot and carcass performance. At the end of the study, milk yield and composition were similar for mature cows in WWL and YWL.     

The correlation between passage rate of digesta and dry matter digestibility in various stages of swine

The relationship between passage rate of digesta (PRD) and apparent faecal dry matter digestibility (DMD) was investigated in five trials. In trial 1, 2, and 3, 36 weanling (16.9 ± 3.0 kg), 24 growing (51.3 ± 8.8 kg), and 23 finishing (104.8 ± 5.2 kg) barrows were housed in metabolic crates. The beginning and end of 5-day collection periods were marked by the addition of 0.5% indigo carmine to the feed for total faeces collection and PRD determination by observing the time required for the marker to appear. In trial 4 and 5, 21 gestating gilts (215.0 ± 15.0 kg), and 19 lactating sows were individually penned. Addition of 0.5% chromic oxide to the feed enabled indirect determination of DMD and PRD. The PRD, which ranged from 12 to 80 h, was positively correlated with DMD in weanling (R² = 0.483, P < 0.001), growing (R² = 0.425, P < 0.01), and finishing (R² = 0.553, P < 0.001) pigs. Body weight and DMD were not significantly correlated in weanling (R² = 0.001, P = 0.893), growing (R² = 0.000, P = 0.995), or finishing (R² = 0.092, P = 0.156) pigs. A positive correlation between PRD, which ranged from 27 to 102 h, and DMD occurred in gestating gilts (R² = 0.231, P < 0.05), but not in lactating sows (R² = 0.014, P = 0.633). The results indicate that longer retention times of digesta improve DMD in swine. Also the results indicate the importance of PRD as a potential independent variable in digestibility assessments.     

Estimates of genetic parameters for growth traits in Kermani sheep

Birth weight (BW), weaning weight (WW), 6-month weight (W6), 9-month weight (W9) and yearling weight (YW) of Kermani lambs were used to estimate genetic parameters. The data were collected from Shahrbabak Sheep Breeding Research Station in Iran during the period of 1993-1998. The fixed effects in the model were lambing year, sex, type of birth and age of dam. Number of days between birth date and the date of obtaining measurement of each record was used as a covariate. Estimates of (co)variance components and genetic parameters were obtained by restricted maximum likelihood, using single and two-trait animal models. Based on the most appropriate fitted model, direct and maternal heritabilities of BW, WW, W6, W9 and YW were estimated to be 0.10 +/- 0.06 and 0.27 +/- 0.04, 0.22 +/- 0.09 and 0.19 +/- 0.05, 0.09 +/- 0.06 and 0.25 +/- 0.04, 0.13 +/- 0.08 and 0.18 +/- 0.05, and 0.14 +/- 0.08 and 0.14 +/- 0.06 respectively. Direct and maternal genetic correlations between the lamb weights varied between 0.66 and 0.99, and 0.11 and 0.99. The results showed that the maternal influence on lamb weights decreased with age at measurement. Ignoring maternal effects in the model caused overestimation of direct heritability. Maternal effects are significant sources of variation for growth traits and ignoring maternal effects in the model would cause inaccurate genetic evaluation of lambs.     

Metabolites of Monascus ruber in silages

A total of 233 silages were examined and found that Monascus ruber was present in 43 samples with counts between 1 × 10³ and 9 × 10⁶ colony-forming units (CFU)/g (mean: 2 × 10⁵ CFU/g). Monacolin K_L and the hydroxy acid monacolin K_A were detected by liquid chromatography-mass spectrometry in 45 and 50 of 233 samples at levels ranging from 25–15 600 and 28–65 400  μ g/kg, respectively. Citrinin was found with high-performance liquid chromatography-fluorescence detection (FLD) in 14 (6%) samples, the concentrations varied between 2.4 and 64.2  μ g/kg. The concentrations of citrinin were low and toxic effects are not anticipated. Monacolin K_A and monacolin K_L occur frequently and in considerable amounts in silages. These metabolites are believed to influence the metabolic activity of rumen anaerobic fungi resulting in a poorer digestion of crude fibre.     

(Co)variance components, genetic parameters and annual trends for calf weights in a pedigree Brahman herd under selection for three decades

A 300 cow Brahman herd kept on improved pasture was subjected to a selection and management programme based on a limited breeding season. Artificial insemination using mainly progeny tested bulls was used in part of the herd and the rest were bred in single sire herds. Of the 200 sires used during the 30 year period, 82% were homebred and selected principally for high estimated breeding value of 18-month weight. Variance components of birth (BW), weaning (205 W) and 18-month (548 W) weights of 6130 calves born 1968 through to 1997 were estimated by the Restricted Maximum Likelihood method (REML) using uni- and bivariate animal models. For each weight the animal's direct and maternal genetic and the dam's permanent environmental effects were considered random and those of sex, year and month of birth and age of cow were considered fixed, but the models differed as far as the number of significant interactions included. Adjusted least squares means for BW, 205 W and 548 W were 28, 158 and 292 kg. Phenotypic and direct and maternal genetic trends from univariate analysis were for BW: 0.156, 0.061 and −0.001 kg; for 205 W: 0.471, 0.126 and 0.044 kg; for 548 W: 1.973, 0.486 and 0.251 kg per year. Direct and maternal heritabilities from univariate analyses were for BW, 205 W and 548 W, 0.33 and 0.08; 0.07 and 0.14; 0.13 and 0.08, respectively. Genetic direct-maternal correlations for the three weights were −0.37, −0.13 and 0.49 and permanent environmental variance of the dam as proportion of phenotypic variance (c²) had values of 0.03, 0.16 and 0.01, respectively. Direct and maternal genetic correlations were for BW: 205 W, 0.64 and 0.74; for BW: 548 W, 0.35 and 0.74; and for 205 W: 548 W, 0.64 and 0.96. Future genetic work in the herd should put more emphasis on the improvement of cow efficiency for sustainable beef production on native and improved pasture.     

Genetic parameters for growth traits in Mexican Nellore cattle

The aim of this study was to estimate genetic parameters for growth traits in Mexican Nellore cattle. A univariate animal model was used to estimate (co)variance components and genetic parameters. The traits evaluated were birth weight (BW), weaning weight (WW), and yearling weight (YW). Models used included the fixed effects of contemporary groups (herd, sex, year, and season of birth) and age of dam (linear and quadratic) as a covariate. They also included the animal, dam, and residual as random effects. Phenotypic means (SD) for BW, WW, and YW were 31.4 (1.6), 175 (32), and 333 (70) kg, respectively. Direct heritability, maternal heritability, and the genetic correlation between additive direct and maternal effects were 0.59, 0.17, and −0.90 for BW; 0.29, 0.17, and −0.90 for WW; and 0.24, 0.15, and −0.86 for YW, respectively. The results showed moderate direct and maternal heritabilities for the studied traits. The genetic correlations between direct and maternal effects were negative and high for all the traits indicating important tradeoffs between direct and maternal effects. There are significant possibilities for genetic progress for the growth traits studied if they are included in a breeding program considering these associations.     

Folliculogenesis and Morphometry of Oocyte and Follicle Growth in the Feline Ovary

This study was designed to describe, both quantitatively (morphometry) and qualitatively (histological differentiation), follicle and oocyte growth in the feline ovary. The ovaries of 43 cats were collected and processed for histology. The diameters of 832 follicle/oocyte pairs were measured, with and without zona pellucida (ZP), and a special emphasis was placed on the study of early folliculogenesis. Primordial, primary, secondary, pre-antral and early antral follicles were measured at 44.3, 86.2, 126.0, 155.6 and 223.8 μm in diameter respectively. A biphasic pattern of follicle and oocyte growth was observed. Before antrum formation, follicle ( x ) and oocyte ( y ) size were positively and linearly correlated ( y  = 0.500 x  + 20.01, r ² = 0.89). Antrum formation occurred when the follicle reached 160–200 μm in diameter (when oocyte was at 102 μm). After antrum formation, a decoupling was observed, a minimal increase in oocyte size contrasting with a significant follicle development ( y  = 0.001 x  + 114.39, r ² = 0.01). The pre-ovulatory follicle diameter was approximately 3500 μm and the maximal oocyte diameter was 115 μm. The ZP, absent in primordial and primary follicles, appeared at the secondary stage and reached almost 6 μm at the pre-ovulatory stage. These results suggest that (i) in feline ovary, follicle and oocyte growth pattern is similar to that observed in other mammals; (ii) the antrum forms in 160–200 μm follicles, which represents 5% of the pre-ovulatory diameter and (iii) the oocyte had achieved more than 90% of its maximal growth at the stage of antrum formation.     

Genetic analysis of growth,visual scores,height, and carcass traits in Nelore cattle

Covariance components were estimated for growth traits (BW, birth weight; WW, weaning weight; YW, yearling weight), visual scores (BQ, breed quality; CS, conformation; MS, muscling; NS, navel; PS, finishing precocity), hip height (HH), and carcass traits (BF, backfat thickness; LMA, longissimus muscle area) measured at yearling. Genetic gains were obtained and validation models on direct and maternal effects for BW and WW were fitted. Genetic correlations of growth traits with CS, PS, MS, and HH ranged from 0.20 ± 0.01 to 0.94 ± 0.01 and were positive and low with NS (0.11 ± 0.01 to 0.20 ± 0.01) and favorable with BQ (0.14 ± 0.02 to 0.37 ± 0.02). Null to moderate genetic correlations were obtained between growth and carcass traits. Genetic gains were positive and significant, except for BW. An increase of 0.76 and 0.72 kg is expected for BW and WW, respectively, per unit increase in estimated breeding value (EBV) for direct effect and an additional 0.74 and 1.43, respectively, kg per unit increase in EBV for the maternal effect. Monitoring genetic gains for HH and NS is relevant to maintain an adequate body size and a navel morphological correction, if necessary. Simultaneous selection for growth, morphological, and carcass traits in line with improve maternal performance is a feasible strategy to increase herd productivity.     

Estimates of direct and maternal (co)variance components as well as genetic parameters of growth traits in Nellore sheep

In the present study, (co)variance components and genetic parameters in Nellore sheep were obtained by restricted maximum likelihood (REML) method using six different animal models with various combinations of direct and maternal genetic effects for birth weight (BW), weaning weight (WW), 6-month weight (6MW), 9-month weight (9MW) and 12-month weight (YW). Evaluated records of 2075 lambs descended from 69 sires and 478 dams over a period of 8 years (2007–2014) were collected from the Livestock Research Station, Palamaner, India. Lambing year, sex of lamb, season of lambing and parity of dam were the fixed effects in the model, and ewe weight was used as a covariate. Best model for each trait was determined by log-likelihood ratio test. Direct heritability for BW, WW, 6MW, 9MW and YW were 0.08, 0.03, 0.12, 0.16 and 0.10, respectively, and their corresponding maternal heritabilities were 0.07, 0.10, 0.09, 0.08 and 0.11. The proportions of maternal permanent environment variance to phenotypic variance (Pe²) were 0.07, 0.10, 0.07, 0.06 and 0.10 for BW, WW, 6MW, 9MW and YW, respectively. The estimates of direct genetic correlations among the growth traits were positive and ranged from 0.44(BW-WW) to 0.96(YW-9MW), and the estimates of phenotypic and environmental correlations were found to be lower than those of genetic correlations. Exclusion of maternal effects in the model resulted in biased estimates of genetic parameters in Nellore sheep. Hence, to implement optimum breeding strategies for improvement of traits in Nellore sheep, maternal effects should be considered.     

Estimation of genetic parameters for preweaning growth traits of Brahman cattle in Southeastern Mexico

The genetic parameters for Brahman cattle under the tropical conditions of Mexico are scarce. Therefore, heritabilities, additive direct and maternal correlations, and genetic correlations for birth weight (BW) and 205 days adjusted weaning weight (WW205) were estimated in four Brahman cattle herds in Yucatan, Mexico. Parameters were estimated fitting a bivariate animal model, with 4,531 animals in the relationship matrix, of which 2,905 had BW and 2,264 had WW205. The number of sires and dams identified for both traits were 122 and 962, respectively. Direct heritability estimates for BW and WW205 were 0.41?±?0.09 and 0.43?±?0.09, and maternal heritabilities were 0.15?±?0.07 and 0.38?±?0.08, respectively. Genetic correlations between direct additive and maternal genetic effects for BW and WW205 were ?0.41?±?0.22 and ?0.50?±?0.15, respectively. The direct genetic, maternal, and phenotypic correlations between BW and WW205 were 0.77?±?0.09, 0.61?±?0.18, and 0.35, respectively. The moderate to high genetic parameter estimates suggest that genetic improvement by selection is possible for those traits. The maternal effects and their correlation with direct effects should be taken into account to reduce bias in genetic evaluations.