High Estimated Breeding Values Research Articles

Analysis of copy number variations in Holstein cows identify potential mechanisms contributing to differences in residual feed intake

Genomic structural variation is an important and abundant source of genetic and phenotypic variation. In this study, we performed an initial analysis of copy number variations (CNVs) using BovineHD SNP genotyping data from 147 Holstein cows identified as having high or low feed efficiency as estimated by residual feed intake (RFI). We detected 443 candidate CNV regions (CNVRs) that represent 18.4Mb (0.6%) of the genome. To investigate the functional impacts of CNVs, we created two groups of 30 individual animals with extremely low or high estimated breeding values (EBVs) for RFI, and referred to these groups as low intake (LI; more efficient) or high intake (HI; less efficient), respectively. We identified 240 (~9.0Mb) and 274 (~10.2Mb) CNVRs from LI and HI groups, respectively. Approximately 30-40% of the CNVRs were specific to the LI group or HI group of animals. The 240 LI CNVRs overlapped with 137 Ensembl genes. Network analyses indicated that the LI-specific genes were predominantly enriched for those functioning in the inflammatory response and immunity. By contrast, the 274 HI CNVRs contained 177 Ensembl genes. Network analyses indicated that the HI-specific genes were particularly involved in the cell cycle, and organ and bone development. These results relate CNVs to two key variables, namely immune response and organ and bone development. The data indicate that greater feed efficiency relates more closely to immune response, whereas cattle with reduced feed efficiency may have a greater capacity for organ and bone development.

Relationship between litters per sow per year sire breeding values and sire progeny means for farrowing rate, removal parity and lifetime born alive

The objective of this study was to determine the relationship between individual sire estimated breeding values (EBV) for litters/sow/year (LSY) and sire progeny means for farrowing rate (FR), removal parity and lifetime born alive (LTBA). Genetic parameters and breeding values were estimated using ASREML. The heritability estimate for LSY was 0.11. When all sires with 10 or more daughters with records were included in the analysis, Spearman rank correlations between the sire's LSY EBV and the sires' daughter means for FR, removal parity and LTBA were 0.49, 0.23 and 0.25 (p < 0.01). The sire EBV for LSY was favourably correlated with sires' daughter means for all three traits. This provides evidence that selecting sires with high EBV for LSY could improve herd FR, removal parity and LTBA. By including LSY as part of the selection criterion, the LTBA may be indirectly improved. The positive genetic correlation between LTBA and LSY may be a result of the improved longevity of sows with greater LSY compared with sows with lower LSY. The relationships between LSY and FR, removal parity and LTBA are strongly supported by the correlations between the sire progeny means for each trait and the sire LSY EBV.

Genotyping strategies for genomic selection in small dairy cattle populations

This study evaluated different female-selective genotyping strategies to increase the predictive accuracy of genomic breeding values (GBVs) in populations that have a limited number of sires with a large number of progeny. A simulated dairy population was utilized to address the aims of the study. The following selection strategies were used: random selection, two-tailed selection by yield deviations, two-tailed selection by breeding value, top yield deviation selection and top breeding value selection. For comparison, two other strategies, genotyping of sires and pedigree indexes from traditional genetic evaluation, were included in the analysis. Two scenarios were simulated, low heritability (h2 = 0.10) and medium heritability (h2 = 0.30). GBVs were estimated using the Bayesian Lasso. The accuracy of predicted GBVs using the two-tailed strategies was better than the accuracy obtained using other strategies (0.50 and 0.63 for the two-tailed selection by yield deviations strategy and 0.48 and 0.63 for the two-tailed selection by breeding values strategy in low- and medium-heritability scenarios, respectively, using 1000 genotyped cows). When 996 genotyped bulls were used as the training population, the sire’ strategy led to accuracies of 0.48 and 0.55 for low- and medium-heritability traits, respectively. The Random strategies required larger training populations to outperform the accuracies of the pedigree index; however, selecting females from the top of the yield deviations or breeding values of the population did not improve accuracy relative to that of the pedigree index. Bias was found for all genotyping strategies considered, although the Top strategies produced the most biased predictions. Strategies that involve genotyping cows can be implemented in breeding programs that have a limited number of sires with a reliable progeny test. The results of this study showed that females that exhibited upper and lower extreme values within the distribution of yield deviations may be included as training population to increase reliability in small reference populations. The strategies that selected only the females that had high estimated breeding values or yield deviations produced suboptimal results.

Relationship between estimated breeding value for somatic cell count and prevalence of intramammary infection in dairy goats

AIM: The objective of the study was to determine if dairy goats selected as having either Low or High estimated breeding values for somatic cell count (EBV SCC) would differ in prevalence of intramammary infection (IMI). METHODS: The EBV SCC for all does in two dairy goat herds were calculated based on the three or four herd test results for somatic cell count (SCC) from the preceding lactations. Within each herd does were categorised into six age groups (i.e. 2, 3, 4, 5, 6 and >6 years old) and ranked on EBV SCC. Approximately the top (High group; n=149) and bottom (Low group; n=148) 12.5% of the does within each age group within each herd had milk samples collected from each gland on one calendar day for subsequent microbiology. The presence of any IMI or IMI due to a major pathogen at goat level was modelled using a GLM with a binomial link function. RESULTS: There was no difference between the High and Low groups in terms of age, days in milk at the time of sampling or in the proportion of the Saanen breed. Mean EBV SCC was –1.0 (SD 0.4) vs 0.8 (SD 0.4) for the Low and High groups, respectively, and there was no overlap in EBV SCC between groups. Goats in the Low group had lower prevalence of any IMI than those in the High group (0.67 (95% CI=0.58–0.76) vs 0.81 (95% CI=0.74–0.88); p=0.002). Goats in the High group were 8.4 (95% CI=1.9–38.0) times more likely to have IMI due to a major pathogen infection than goats in the Low group (p=0.006). CONCLUSIONS: Does with a high EBV SCC had a higher prevalence of any IMI and were more likely to have an IMI dueto a major pathogen than does with a low EBV SCC. Thus selection for EBV SCC is likely to result in a lower SCC and also lower prevalence of IMI.

Genomic regions showing copy number variations associate with resistance or susceptibility to gastrointestinal nematodes in Angus cattle

Genomic structural variation is an important and abundant source of genetic and phenotypic variation. We previously reported an initial analysis of copy number variations (CNVs) in Angus cattle selected for resistance or susceptibility to gastrointestinal nematodes. In this study, we performed a large-scale analysis of CNVs using SNP genotyping data from 472 animals of the same population. We detected 811 candidate CNV regions, which represent 141.8Mb (~4.7%) of the genome. To investigate the functional impacts of CNVs, we created 2 groups of 100 individual animals with extremely low or high estimated breeding values of eggs per gram of feces and referred to these groups as parasite resistant (PR) or parasite susceptible (PS), respectively. We identified 297 (~51Mb) and 282 (~48Mb) CNV regions from PR and PS groups, respectively. Approximately 60% of the CNV regions were specific to the PS group or PR group of animals. Selected PR- or PS-specific CNVs were further experimentally validated by quantitative PCR. A total of 297 PR CNV regions overlapped with 437 Ensembl genes enriched in immunity and defense, like WC1 gene which uniquely expresses on gamma/delta T cells in cattle. Network analyses indicated that the PR-specific genes were predominantly involved in gastrointestinal disease, immunological disease, inflammatory response, cell-to-cell signaling and interaction, lymphoid tissue development, and cell death. By contrast, the 282 PS CNV regions contained 473 Ensembl genes which are overrepresented in environmental interactions. Network analyses indicated that the PS-specific genes were particularly enriched for inflammatory response, immune cell trafficking, metabolic disease, cell cycle, and cellular organization and movement.

ESR1 and ESR2 gene markers are not associated with number of piglets born alive in Italian Large White sows

Many studies have reported that markers in the estrogen receptor 1 (ESR1) and estrogen receptor 2 (ESR2) genes are associated with litter size in pigs, even if inconsistent results have been obtained in different populations. We analysed the ESR1 Pvu II and the ESR2 AF164957:c.949G>A polymorphisms in Italian Large White (ITLW) sows to evaluate if these markers are associated with number of piglets born alive at first litter (NBA1). First, both polymorphisms were genotyped by selective genotyping in a total of 440 sows chosen according to the extreme and divergent estimated breeding value (EBV) for NBA1 (220 sows with low EBV and 220 sows with high EBV). For the ESR1 polymorphism, no allele and genotype frequency differences were observed between the two groups (allele A=0.62 and allele B=0.38 in both two groups). For the ESR2 polymorphism, a trend of different allele frequency between the two tails was identified (P=0.052). However, no significant association between the same ESR2 marker and EBV NBA1 was detected analyzing 1772 ITLW sows (allele A=0.59 and allele G=0.41). As the two investigated polymorphisms were not associated with NBA1 EBVs, they seem not useful for marker assisted selection to improve this trait in the ITLW breed.

Growth, feed intake and maternal performance of Angus heifers selected for high or low growth and milk production

Weight of calf weaned per cow that incorporates both growth and maternal component traits is an important determinant of profitability for cow–calf production systems. In New Zealand, there is little objective information available on the performance of progeny from bulls selected for either growth or maternal ability when compared under similar pastoral farming conditions. The present experiment produced 84 Angus heifers sired by Angus bulls divergently selected for high (Hi-Gr) or low (Lo-Gr) estimated breeding value (EBV) 600-day weight or high (Hi-Milk) or low (Lo-Milk) 200-day maternal EBV. Each heifer had their liveweight gain from weaning to just before first calving, herbage intake from pasture using the n-alkane method, and maternal performance (calf production after first and second parity) assessed. Liveweights of heifers born to Hi-Gr bulls were generally greater than for all other lines, while there was no difference between Lo-Gr and either of the maternal lines. There was no difference (P &gt; 0.05) in herbage intake between the different genetic lines when measured at Days 310 (days of age from birth) and 880. At Day 400, the Lo-Milk selection line had higher (P &lt; 0.05) intakes than the Hi-Milk, Hi-Gr and Lo-Gr lines. Calves born to the Lo-Gr heifers at the first parity were lighter while the birth weights of calves born at the second parity calving were similar for all the selection lines. Calf weaning weight was lowest (P &lt; 0.05) after both the first and second parity weaning for the Lo-Milk sired heifers. The Lo-Milk heifers produced the least milk at Day 50 during their first lactation while the Hi-Milk heifers produced the most. This experiment confirms that for beef cattle, producers who wish to select bulls to use in their herds based on either high growth rate or high milk EBV, the resultant progeny will outperform those that are average or below average for those particular traits.

Effects of growth path, sire type, calving time and sex on growth and carcass characteristics of beef cattle in the agricultural area of Western Australia

Growth, carcass characteristics and meat quality of the steer and heifer progeny of autumn (AC: March–April) and winter (WC: June–July) calving cows following weaning in January in each of 3 years (2003–05) were measured. The cows were mated to sires with a high estimated breeding value for either retail beef yield (RBY), intramuscular fat (IMF) or both RBY and IMF. After weaning, the progeny entered one of three growth paths until slaughter at an average steer liveweight of 500 kg: (i) fast – fast growth from weaning on a high concentrate feedlot diet; (ii) slow – slow growth from weaning (~0.6 kg/day) to 400 kg liveweight followed by growth at over 1 kg/day on high quality pasture; or (iii) comp. – 10% weaning weight loss, immediately after weaning followed by compensatory or rapid growth of over 1 kg/day on high quality pasture. Steers on the fast growth path had higher (P &lt; 0.001) P8 fat thickness than those on the slow or comp. growth paths whereas heifers on the fast growth path only had higher (P &lt; 0.001) P8 fat thickness than those on the slow growth path. Animals on the fast growth treatment had higher (P &lt; 0.001) levels of IMF% than the slow animals which were higher (P &lt; 0.001) than the comp. growth treatment. AUS-MEAT and US marbling scores were not different among growth paths. Animals finished on the fast growth path had a lower (P &lt; 0.001) RBY% than those on either the slow or comp. growth paths. The RBY-sired progeny had higher (P &lt; 0.001) finishing liveweight and hot standard carcass weight than either RBY and IMF or IMF-sired animals. IMF-sired progeny had higher (P &lt; 0.01) rib fat thickness than either RBY or RBY- and IMF-sired animals. There was also a similar trend for P8 fat thickness but the effects were not significant. The RBY-sired animals had lower AUS-MEAT marbling scores (P &lt; 0.01), US marbling scores (P &lt; 0.001) and levels of IMF% (P &lt; 0.01) than either of the other two sire treatments. RBY-sired animals also had higher (P &lt; 0.001) estimated RBY% than those from the IMF sires while those by RBY and IMF sires were intermediate and not significantly different from either. Calving time had little influence on most carcass characteristics. However, WC animals tended to be fatter and have higher marbling scores than AC animals. The IMF% was higher (P &lt; 0.01) in WC animals from RBY and IMF sires than in the corresponding AC animals. Heifers had lighter slaughter liveweight, carcass weight, were fatter and had higher marbling scores than steers. Heifers also had lower (P &lt; 0.001) RBY% than the steers. Ossification scores for heifers were higher (P &lt; 0.001) than for steers by ~30 units in AC calves and by 20 units in WC calves. The results of this experiment confirm the effectiveness of using sires with high estimated breeding value for the required characteristics in producing the desired improvements in the progeny. The absence of any interactions of sire type with growth path indicates that differences between sire types will be similar regardless of environmental conditions. Animals raised on a faster growth path after weaning produce carcasses with more fat and more IMF% than those grown on slower growth paths.

Polymorphisms in the 5′ Upstream Region of the CXCR1 Chemokine Receptor Gene, and Their Association with Somatic Cell Score in Holstein Cattle in Canada

Identification of regulatory elements in 5′ regions of chemokine genes is fundamental for understanding chemokine gene expression in response to infection diseases. The CXCR1 receptor is expressed on the surface of neutrophils and interacts primarily with CXCL8 (IL-8), the most potent chemoattractant for neutrophils. The aim of this study was to characterize the 5′ upstream region (2.1kb) of the bovine CXCR1 chemokine receptor gene for polymorphism content and to identify in silico potential transcription-factor binding sites. The 5′ flanking region was found by mining the NCBI GenBank (www.ncbi.nlm.nih.gov/). A DNA sequence from the whole genome shotgun sequence project with reference number AC150887.4 contained the CXCR1 5′ flanking sequence. Computer analysis revealed potential binding sites for the transcription factors nuclear factor κB (NF-κB), binding factor GATA-1, barbiturate inducible element (Barbie), nuclear factor of activated T-cells, and activator protein 1. Polymorphism discovery in this region was conducted by constructing an inclusive DNA pool including 2 phenotypic extreme groups, 20 bulls with high estimated breeding values (EBV) for somatic cell score (SCS), and 20 bulls with low EBV for SCS. Independent amplicons along the 5′ flanking region of bovine CXCR1 were generated for polymorphism discovery by sequencing. Three novel single nucleotide polymorphisms (SNP), CXCR1c.−344T>C, CXCR1c.−1768T>A, and CXCR1c.−1830A>G, and a previously identified SNP in the coding region, CXCR1c.777G>C, were identified. The 4 SNP were genotyped in Canadian Holstein bulls (n = 338) using tetra-primer amplification refractory mutation system (ARMS)-PCR. Average allele substitution effects were estimated to investigate associations between the 4 SNP and EBV for SCS in first, second, and third and later lactations. Multiple trait analysis revealed that the SNP CXCR1c.−1768T>A was associated with EBV for SCS in the first and second lactations and over all 3 lactations. Haplotype analysis substantiated this association with EBV for SCS in the first lactation. Given the location of SNP CXCR1c.−1768T>A and the surrounding potential binding recognition sequences for NF-κB, GATA-1, and Barbie transcription-factors, this SNP may be implicated in gene regulation and warrants further research.

Genetic and phenotypic parameters of lactations longer than 305 days (extended lactations)

Test-day milk yield and somatic cell count data over extended lactation (lactation to 540–600 days) were analysed considering part lactations as different traits and fitting random regression (RR) models. Data on Australian Jersey and Holstein Friesian (HF) were used to demonstrate the shape of the lactation curve and data on HF were used for genetic study. Test-day data from about 100 000 cows that calved between 1998 and 2005 were used for this study. In all analyses, a sire model was used.When part lactations were considered as different traits, protein yield early in the lactation (e.g. first 2 months) had a genetic correlation of about 0.8 with protein yield produced after 300 days of lactation. Genetic correlations between lactation stages that are adjacent to each other were high (0.9 or more) within parity. Across parities, genetic correlations were high for both protein and milk yield if they are within the same stage of lactation. Phenotypic correlations were lower than genetic correlations. Heritability of milk-yield traits estimated from the RR model varied from 0.15 at the beginning of the lactation to as high as 0.37 by the 4th month of lactation. All genetic correlations between different days in milk were positive, with the highest correlations between adjacent days in milk and decreasing correlations with increasing time-span. The pattern of genetic correlations between milk yield in the second 300 days (301 to 600 days of lactation) do not markedly differ from the pattern in the first 300 days of lactation. The lowest estimated genetic correlation was 0.15 between milk yield on days 45 and 525 of lactation. The result from this study shows thatprogeny of bulls with high estimated breeding values for yield traits and those that produce at a relatively high level in the first few months are the most likely candidates for use in herds favouring extended lactations.

Whole-body protein metabolism and energy expenditure in sheep selected for divergent wool production when fed above or below maintenance

Rates of whole-body protein turnover and energy expenditure were measured in two groups of wethers differing in estimated breeding values (EBVs) for wool growth, but with similar EBVs for fibre diameter and liveweight (LW). The sheep were offered a pelleted diet at 1.2 times their metabolisable energy (ME) requirement for maintenance (1.2 M) followed by either 0.8 M or 1.8 M for 5 weeks. In the 5th week, whole-body protein metabolism was estimated by using intravenous injection of 15N-glycine (g N/day) and whole-body energy expenditure rate (EE) was predicted by the CO2 entry rate technique using intravenous injection of NaH13CO3. The higher N intake (8.7 v. 20.4 g N/day, P &lt; 0.001) was associated with a higher whole-body protein flux (22.1 v. 34.2 g N/day, P &lt; 0.001), and a higher whole-body protein synthesis rate (17.0 v. 25.5 g N/day, P &lt; 0.001) and protein degradation rate (15.9 v. 20.7 g N/day, P &lt; 0.001). Irrespective of feeding levels, sheep with high-fleece EBVs (F+) synthesised and degraded more body protein N (g N/day) than sheep with low-fleece EBVs (F–), and F+ sheep also retained more ingested protein N (P &lt; 0.05) in wool and body tissue than F– sheep, but the significant differences due to genotypes disappeared when whole-body protein flux, synthesis and degradation were expressed as g N/kg LW0.75.day (metabolic weight). Estimates of EE were lower when the sheep were offered 0.8 M than when offered 1.8 M (5.85 v. 7.68 MJ/day, P &lt; 0.001) and were higher in F+ than in F– sheep (6.95 v. 6.58 MJ/day; P &lt; 0.05), but F+ sheep had a significantly lower (P &lt; 0.05) EE (MJ/kg LW0.75.day) than F– sheep. F+ animals also retained more energy in wool and wool-free body tissue than F– animals (P &lt; 0.05). The present study indicates that genetic selection for wool growth has resulted in increased efficiency of dietary protein and energy use for wool production and body-tissue growth in these sheep. Furthermore, there is no ‘trade off’ between deposition of nutrients in the body and wool in sheep with high EBVs for wool growth.

The influence of gene-environment interactions on GHR and IGF-1 expression and their association with growth in brook charr, Salvelinus fontinalis (Mitchill)

BackgroundQuantitative reaction norm theory proposes that genotype-by-environment interaction (GxE) results from inter-individual differences of expression in adaptive suites of genes in distinct environments. However, environmental norms for actual gene suites are poorly documented. In this study, we investigated the effects of GxE interactions on levels of gene transcription and growth by documenting the impact of rearing environment (freshwater vs. saltwater), sex and genotypic (low vs. high estimated breeding value EBV) effects on the transcription level of insulin-like growth factor (IGF-1) and growth hormone receptor (GHR) in brook charr (Salvelinus fontinalis).ResultsMales grew faster than females (μ♀ = 1.20 ± 0.07 g·d-1, μ♂ = 1.46 ± 0.06 g·d-1) and high-EBV fish faster than low-EBV fish (μLOW = 0.97 ± 0.05 g·d-1, μHIGH = 1.58 ± 0.07 g·d-1; p < 0.05). However, growth was markedly lower in saltwater-reared fish than freshwater sibs (μFW = 1.52 ± 0.07 g·d-1, μSW = 1.15 ± 0.06 g·d-1), yet GHR mRNA transcription level was significantly higher in saltwater than in freshwater (μSW = 0.85 ± 0.05, μFW = 0.61 ± 0.05). The ratio of actual growth to units in assayed mRNA ('individual transcript efficiency', iTE; g·d-1·u-1) also differed among EBV groups (μLOW = 2.0 ± 0.24 g·d-1·u-1; μHIGH = 3.7 ± 0.24 g·d-1·u-1) and environments (μSW = 2.0 ± 0.25 g·d-1·u-1; μFW = 3.7 ± 0.25 g·d-1·u-1) for GHR. Males had a lower iTE for GHR than females (μ♂ = 2.4 ± 0.29 g·d-1·u-1; μ♀ = 3.1 ± 0.23 g·d-1·u-1). There was no difference in IGF-1 transcription level between environments (p > 0.7) or EBV groups (p > 0.15) but the level of IGF-1 was four times higher in males than females (μ♂ = 2.4 ± 0.11, μ♀ = 0.58 ± 0.09; p < 0.0001). We detected significant sexual differences in iTE (μ♂ = 1.3 ± 0.59 g·d-1·u-1; μ♀ = 3.9 ± 0.47 g·d-1·u-1), salinities (μSW = 2.3 ± 0.52 g·d-1·u-1; μFW = 3.7 ± 0.53 g·d-1·u-1) and EBV-groups (μLOW = 2.4 ± 0.49 g·d-1·u-1; μHIGH = 3.8 ± 0.49 g·d-1·u-1). Interaction between EBV-group and environment was detected for both GHR (p = 0.027) and IGF-1 (p = 0.019), and for iTE in the two genes (p < 0.0001; p < 0.05, respectively), where increased divergence in levels of GHR and IGF-1 transcription occurred among EBV-groups in the saltwater environment.ConclusionOur results show that both environment and sex have major impacts on the expression of mRNA for two key genes involved in the physiological pathway for growth. We also demonstrate for the first time, at least in fish, genotype-by-environment interaction at the level of individual gene transcription. This work contributes significantly to ongoing efforts towards documenting environmentally and sexually induced variance of gene activity and understanding the resulting phenotypes.

Identification of single nucleotide polymorphisms in the bovine CCL2, IL8, CCR2 and IL8RA genes and their association with health and production in Canadian Holsteins

The aim of this study was to identify the presence of SNPs in the chemokine genes CCL2 and IL8 and the chemokine receptor genes IL8RA and CCR2, and assess their potential contribution to variation in estimated breeding values (EBVs) for somatic cell score (SCS) and four other traits in Canadian Holstein bulls. Pools of DNA for bulls with high (H) and low (L) EBVs for SCS were used for identification of 11 SNPs. Two unreported SNPs were found in the CCL2 gene and one SNP was found in the CCR2 gene. Previously reported SNPs (three in the IL8 gene and five in the IL8RA chemokine receptor) were also identified. Two SNPs in CCL2, three in IL8, one in IL8RA and one in CCR2 were genotyped in Canadian Holstein bulls (n = 338) using tetra primer ARMS-PCR. We investigated associations of these seven polymorphisms with three production traits (milk yield, fat yield and protein yield) and one conformation trait related to mastitis (udder depth). The allele substitution effect for the CCL2 rs41255713:T>C SNP was significant at an experimental-wise level for milk yield (247.5 +/- 79.9 kg) and protein yield (7.4 +/- 2.3 kg) EBVs (P <or= 0.05). The associations of the SNPs with SCS EBVs were not significant at an experimental-wise level. However, the allele substitution effect of the CCR2 rs41257559:C>T SNP on SCS was significant at the comparison-wise level (-0.04 +/- 0.02, P = 0.05), which might indicate a possible association in support of other published studies. Lastly, we assigned CCR2 to BTA22q24, where a previously QTL for SCS was identified.

Responses of wool growth rate and body reserves to nutrition in Merino ewes: a potential biological link between production and fitness

This study examined whether the low body-fat reserves in sheep with high estimated breeding values (EBVs) for clean fleece weight (CFW) reported previously are affected by nutritional history, and second whether the effect may be related to differences in the variation in fibre diameter (CVfd). Groups of 11 20-month-old Merino ewes with high and low EBVs for CFW and for CVfd were compared in a 2 × 2 design at low bodyweight, then fed ad libitum for 100 days and re-measured. The response of wool growth rate to feed supply (WRF) was estimated as the slope of the regression against time of clean wool mass collected from mid-side patches at intervals of 30–40 days throughout the experiment. High CFW sheep had greater feed intake relative to liveweight and liveweight gain (P = 0.02), but did not differ significantly in other characteristics from low CFW sheep. High CVfd sheep had lower plasma concentrations of insulin (P = 0.02), IGF-1 (P = 0.03), and albumin (P = 0.02) throughout the study, and had less fat when in poor body condition (P = 0.02). The WRF was greater in both the high CFW (P = 0.003) and the high CVfd (P = 0.004) genotypes. When studied in poor body condition, sheep with a high WRF had lower liveweight (P &lt; 0.001), lower body condition score (P &lt; 0.001), lower plasma albumin (P &lt; 0.001), and higher plasma growth hormone (P = 0.02), but these relationships weakened or disappeared after ad libitum feeding. Sheep with high WRF also had lower plasma concentrations of insulin (P = 0.002) and IGF-1 (P = 0.008) throughout the study, which may have brought about the increased responsiveness of protein and energy metabolism to nutrition. The results indicate that genetic selection for wool characteristics can affect the responsiveness of wool growth rate to nutrient supply. Sheep that are highly responsive grow more wool when offered abundant feed, but may have lower body nutrient reserves when on limited feed.

Estimation of breeding value and genetic trend of Garut sheep and its crossbred

Crossing of Garut (GG) sheep with St. Croix sheep (HH) and Moulton Charollais (MM) resulting HG sheep (♂HH X ♀GG) and MG sheep (♂MM X ♀GG) was done by Indonesian Research Institute for Animal Production. The work continued by crossing MG and HG sheep to obtain HMG (♂HG X ♀MG) and MHG (♂MG X ♀HG) sheep. The study was continued by selection program based on phenotypic performance. Estimation of breeding value and genetic trends were done in order to study the effectiveness of selection program and to study the genetic progress of each breed. The breeding value was estimated by Best Linear Unbiased Prediction (BLUP) method using Variance Component Estimation (VCE4) software to calculate variance component and using Prediction and Estimation (PEST) to calculate Breeding Value. Genetic variations of composite sheep were generally higher than Garut sheep, represented by higher estimated heritability value. Genetic correlation of body weight at diffrent age is high, that makes selection at one age could also increase body weight at any level of age. In general of this population shows positive genetic trend, but fluctuated from year to year. Composite breed tend to have higher estimated breeding value than Garut sheep. Selection method that was practiced in this population showed in line with selection method using breeding value criteria. Key Word s: Breeding Value, Genetic, BLUP, Garut Sheep, St. Croix, Moulton Charollais

Genotype and age effects on sheep meat production. 1. Production and growth

The growth, wool production and teeth eruption of animals from five genotypes [Poll Dorsetgrowth (PD) × Border Leicester × Merino (BLM); PDg × Merino (M); Poll Dorsetmuscling (PDm) × M; M × M; BL × M] were evaluated over the age span of 4 to 22 months of age. In total, 16 sires were used to generate the animals and these were selected for growth based on estimated breeding values (EBVs), apart from one group (PDm) which was selected for muscling based on EBVs. In total, 595 animals were slaughtered at 4, 8, 14 or 22 months of age. The birthweight of lambs born to BLM ewes was 0.6 kg heavier (P &lt; 0.001) than those born to Merino ewes, and wether lambs were 0.2 kg heavier than ewe lambs (P &lt; 0.001). The yearling weight (YWT) EBV had no effect on birthweight. There were significant (P &lt; 0.001) differences between genotypes for predicted weaning weight at 4 months of age, with a range of 10.6 kg among the groups. The PDg × BLM were the heaviest (37.8 ± 0.7 kg) and the Merino the lightest (27.3 ± 0.8 kg). Wether lambs were 2.0 kg heavier (P &lt; 0.001) than ewe lambs at weaning. The YWT EBV had no effect on weaning weight. There was a significant (P &lt; 0.001) interaction between the age at slaughter and genotype for final liveweight of each age group. The PDg × BLM were the heaviest at each age and the Merinos the lightest, and for the oldest animals, the BLM were significantly (P &lt; 0.05) heavier than PDm × M, whereas at younger ages this was not the case. The significant interaction (P &lt; 0.001) between sex and age at slaughter reflected the increasing difference in liveweight between the sexes as age at slaughter increased. There was also a significant (P &lt; 0.05) interaction between the YWT EBV and age at slaughter. The overall coefficients were –0.01, 0.14, 0.34 and 0.65 for slaughter ages 4, 8, 14 and 22 months, respectively, indicating that in young animals there was no effect of sire YWT EBV on liveweight, but as the animals aged there was an increasing effect such that progeny of sires with high sire YWT EBV were heavier. This effect was evident within all genotypes. There was a sire breed effect on fleece weight and total wool weight (P &lt; 0.001) with Merino-sired hoggets producing 0.4 kg more wool than Border Leicester-sired hoggets and 1.5 kg more than Poll Dorset-sired hoggets. There was a weak genotype effect on time to erupt the first permanent incisor, which if modelled as a proportion of Border Leicester (0, 1/4, 1/2) was significant (–34 ± 12 days, P &lt; 0.05), Border Leicester earlier than not Border Leicester. Ewe lambs took 9 days longer (P &lt; 0.05) to erupt their first permanent incisor compared with wether lambs.

Genetic and nutritional regulation of lamb growth and muscle characteristics

Combined actions of nutrition and genetic regulation of the growth rate of lambs as well as the physical, biochemical, and eating quality characteristics of their skeletal muscle were assessed in a major field experiment. Data arising were collated and integrated to consolidate findings made at the farm, animal, tissue, cellular, and gene expression levels. At the farm level, increased nutrient availability significantly increased the growth rate of crossbred lambs and increased the growth advantage resulting from the use of sires with high estimated breeding values (EBV) for growth. In contrast, the extra depth of the M. longissimus thoracis et lumborum (EMD) arising from sires with a higher EBV for this trait was constant irrespective of nutrition. Ewe liveweight and body condition were critical in determining the pre-weaning nutrition and growth of lambs, with the LOW plane of nutrition causing stunting of forelimb bones and changes to the allometric growth coefficients for carcass lean and fat. The EBV of the sire for muscling (PEMD) influenced several non-muscling traits, and interactions with nutrition suggested that on HIGH nutrition, absorbed nutrients were partitioned away from wool and fat accretion and towards protein accretion in lambs having superior muscling genetics. Expression levels of known myogenic factors in muscle, together with a suite of peptides and proteins whose identity and levels were determined by proteomic screening, contributed to improved understanding of the mechanisms underpinning nutritional and genetic regulation of skeletal muscle development. The study revealed the need for caution in the use of indirect markers of growth or composition, with their usefulness being constrained if the localisation of the response to selection is specific to parts of the carcass where the selection had initially been concentrated. As well, the possibility that much of the variation explained by potential physiological markers can be accounted for by non-invasive measures of growth and fatness currently used by Australian farmers must be considered.

Skin characteristics and skin protein composition of Merinos differing in estimated breeding values for wool growth and fed at above and below maintenance

Twenty castrated male sheep were selected from a commercial flock, 10 with high estimated breeding values (EBVs) (F+) and 10 with low EBVs for wool production (F–). Five of each EBV treatment were offered feed at 0.8M [0.8 times their metabolisable energy (ME) requirement for maintenance] and the other 5 were offered feed at 1.8M for 6 weeks. On the midside area of skin, the F+ group had a greater rate of clean wool growth (g/100cm2.day) and daily growth in fibre length (mm/day) than the F– group at both feeding levels (P&lt;0.05). Fibre diameter (FD) was finer for F+ than F– sheep at both feeding levels (P&lt;0.001). As the feeding level increased, FD increased (P&lt;0.001), but the ratio of fibre length growth to mean FD remained constant. The secondary follicle density in F+ sheep decreased with an increase in the feeding level (P&lt;0.01), whereas the secondary follicle density of F– sheep remained unchanged (P&gt;0.05). The ratio of secondary to primary follicles (S/P) was 21% higher (P&lt;0.01) in skin from F+ sheep than in skin from F– sheep, but this difference was not related to the feeding level. Skin thickness at the midside was thinner (P&lt;0.05) when sheep were underfed, but F+ sheep had a thicker (P&lt;0.05) skin than F– sheep. The trephine (diameter: 1.5 cm; area: 1.766 cm2)-sampled skin weight was heavier for F+ than for F– (0.339 v. 0.294 g, P&lt;0.05) but did not differ (P&gt;0.05) with the level of intake. The weight of the dermis layer was greater in F+ than F– sheep (0.231 v. 0.190 g per trephine, P&lt;0.05) and F+ sheep also tended to be more responsive to feeding level than F– sheep (interaction: P = 0.06). True protein content per 100 g wet skin did not differ between F+ and F– sheep or between feeding levels, whereas the protein content per 100 cm2 skin was significantly (P&lt;0.05) higher in F+ sheep. The concentration of collagen in skin protein (g/100 g) was lower in F+ sheep than F– sheep at both feeding levels (P&lt;0.05). Of the amino acids evaluated, significant differences occurred between F+ and F– sheep for the methionine (Met) concentration in plasma (P&lt;0.05) and in the free amino acid pool in the skin (P = 0.06). The distribution ratio of skin Met concentration to plasma Met concentration was significantly lower in the F+ sheep than F– sheep (0.77 v.1.18 kg skin/ L plasma). Results presented here indicate that skin characteristics such as skin thickness, follicle density, S/P ratio, skin weight, dermis weight, true protein or collagen content were a consequence of genetics and nutritional variation in wool growth rate, fibre length and fibre diameter. Selection for high EBVs for wool growth has resulted in animals which grow more wool at the 2 levels of feed intake provided, supported by their higher S/P ratios, higher skin and protein masses, more responsive dermides and higher efficiency of Met usage in skin tissue.

Effect of nutritional restriction and sire genotype on forelimb bone growth and carcass composition in crossbred lambs

The aim of this study was to assess the effect of low or high whole-of-life nutritional planes on bone growth, maturation, and carcass composition in lambs from sires (n = 9) with high estimated breeding values (EBVs) for post-weaning eye muscle depth (PEMD) or liveweight gain (PWWT), compared with sires of industry average for both traits. Lambs (n = 54) were killed at 8 months of age before measurement of forelimb bones, radiographic scoring, and histological measurement of growth plates, and bone ash mineral analysis. A subset of these (n = 36) had carcass composition serially assessed during growth by CAT-scan. Results reveal that the nutritional restriction imposed in this experiment caused significant restriction of skeletal growth, as reflected by shorter, thinner forelimb bones, altered limb proportions, narrowing (and in some cases permanent closure) of growth plates, and an altered bone mineral profile. CAT-scan analysis showed restriction of bone growth was similar to that of muscle growth. Progeny of high muscling (PEMD) sires showed greater muscle growth, but were possibly more susceptible to some of the skeletal effects of nutritional restriction. Greater sire EBVs for PEMD, PWWT, or fat depth were associated with narrower growth plates, suggestive of slower longitudinal bone growth and shorter adult limb length, although bone mass was not affected according to earlier CAT-scan data. Results also suggest that progeny of high PEMD or PWWT sires are earlier maturing in terms of skeletal (or at least limb) growth, although their bone mineral profile (magnesium content) was more consistent with that of physiologically less mature animals.

Influences on the loin and cellular characteristics of the m. longissimus lumborum of Australian Poll Dorset-sired lambs

Offspring of 4 Poll Dorset rams differing in eye muscle depth estimated breeding values (EBVs) were studied to determine sire, sex, and nutritional influences on cellular characteristics in the longissimus lumborum muscle. At 12 weeks of age, 62 lambs were individually fed a concentrate diet with or without protected nutrients ad libitum for 120 days while 39 lambs were grazed on improved pasture. Sire influenced the percentages of type 2A and 2B/2X myofibres, but not myofibre number or size. Progeny of the highest eye muscle depth EBV ram had less type 2A and more 2B/2X myofibres than the lowest ranking sire. At equivalent carcass weight, amount of RNA and protein in the longissimus muscle was influenced by sire, consistent with differences in eye muscle depth EBVs. Sex had little effect on muscle cellular characteristics, whereas lambs fed pasture had less type 1 myofibres than those fed concentrates and had less muscle RNA and a higher ratio of protein to RNA. The findings demonstrate differences in m. longissimus lumborum cellular characteristics in offspring of sires differing in muscle EBVs. The extent to which these differences relate to the Carwell muscle hypertrophy gene remains to be determined.