Roberto Luiz Teodoro

Lactation curve in Guzera breed

The objectives of this work were to identify the mathematical functions that better fitted the milk production of Guzera breed cows, to evaluate the effects of the environmental factors on the lactation curve format and to estimate the genetic parameters for the milk production and for the dependable components of the lactation curve format. A total of 1130 lactations from 583 Guzera breed cows, daughters of 165 bulls, with production over the period from 1983 to 1997 were used. The models y = a n e -cn, y = a - cn + ln (n), y=a -cn e y =a e-c n were the ones that best fitted the milk production of the cows. By the analysis of variance, it was observed that the effects of cow herd, calving year and cow age at calving influenced the total milk production, initial milk production and milk decline production rate characteristics. The coefficients of heritability and repeatability estimates were obtained by means of one and two characteristic analyses. The animal selection, based only on the of the lactation curve format, would be of low efficiency.

Genome wide scan for quantitative trait loci affecting tick resistance in cattle (Bos taurus × Bos indicus).

BackgroundIn tropical countries, losses caused by bovine tick Rhipicephalus (Boophilus) microplus infestation have a tremendous economic impact on cattle production systems. Genetic variation between Bos taurus and Bos indicus to tick resistance and molecular biology tools might allow for the identification of molecular markers linked to resistance traits that could be used as an auxiliary tool in selection programs. The objective of this work was to identify QTL associated with tick resistance/susceptibility in a bovine F2 population derived from the Gyr (Bos indicus) × Holstein (Bos taurus) cross.ResultsThrough a whole genome scan with microsatellite markers, we were able to map six genomic regions associated with bovine tick resistance. For most QTL, we have found that depending on the tick evaluation season (dry and rainy) different sets of genes could be involved in the resistance mechanism. We identified dry season specific QTL on BTA 2 and 10, rainy season specific QTL on BTA 5, 11 and 27. We also found a highly significant genome wide QTL for both dry and rainy seasons in the central region of BTA 23.ConclusionsThe experimental F2 population derived from Gyr × Holstein cross successfully allowed the identification of six highly significant QTL associated with tick resistance in cattle. QTL located on BTA 23 might be related with the bovine histocompatibility complex. Further investigation of these QTL will help to isolate candidate genes involved with tick resistance in cattle.

On the Search for Markers of Tick Resistance in Bovines

Genetic differences in susceptibility to ticks (Rhipicephalus (Boophilus) microplus) are considerable in bovines. Here, mapping, association and gene expression approaches were employed to further advance our understanding of the molecular basis of tick resistance. A B. taurus x B. indicus F2 population was developed by Embrapa and 382 individuals were measured for parasitic load. Scanning of all chromosomes is in progress. Quantitative trait loci (QTL) for tick load were mapped to chromosomes 4, 5, 7, 10, 14, 18 and 23 out of the 20 chromosomes scanned and were dependent on the season in which the phenotype was scored. In the candidate gene approach, females from the genetic groups Nelore (NE--184), Canchim x Nelore (CN--153), Aberdeen Angus x Nelore (AN--123) and Simmental x Nelore (SN--120) were evaluated under natural infestation. Microsatellite markers close to the genes for interleukin 2 (IL2), interleukin 4 (IL4) and interferon gamma (IFNG) were analysed. Tick counts were associated with the marker for interleukin 4 (P < 0.05) in three genetic groups. Differences in cytokine mRNA levels of naive versus infested Nelore calves as well as between resistant versus susceptible cows from NE, CN and AN genetic groups were also investigated. Comparison of cytokines from infested and naïve animals showed downregulation of IL2. When resistant cows were compared to susceptible animals, IL8 was downregulated. These results reinforce the multiloci nature of tick resistance and the need to consider QTL and environment interactions.

Association of the bovine major histocompatibility complex (BoLA) BoLA-DRB3 gene with fat and protein production and somatic cell score in Brazilian Gyr dairy cattle (Bos indicus)

The effect of the bovine major histocompatibility complex (BoLA) locus on animal health may be due to a direct action of its alleles on immune functions, whereas its indirect effect on production traits might be explained by the better general health conditions of more productive animals. In the present study, the BoLA-DRB3 gene was investigated in 1058 cows belonging to seven Brazilian Gyr Dairy herds (Bos indicus, Zebu cattle). A total of 37 alleles were identified, 15 of them described for the first time in a Zebu breed. A highly significant association (p < 0.02) was observed between allele *54 and a decrease (-26.1 kg) in milk protein yield and there was a significant association (p < 0.05) between this allele and lower (-26.07 kg) milk fat yield. There was also a significant association (p < 0.05) between allele *6 and decreased (-12.47 kg) milk protein and allele *7 and increased (12.72 kg) milk protein. There were also indications of association (p < 0.10) between somatic cell score (SCS) and alleles *3 (SCS increased by 0.54 units) and *31 (SCS increased by 0.46 units). The highly significant association of allele *54 with lower protein yield suggests the possible use of this allele in marker-assisted selection programs.

Aspectos genéticos e ambientais da curva de lactação de vacas da raça Guzerá

The knowledge of the genetic relationships between the parameters of lactation curve and the milk yield is important for the selection of cows and sire. The records milk yield from 583 cows of the Guzera breed, daughters of 165 sire, were used to estimate the lactation curve parameters by two mathematical models. Milk productions were obtained from the extracted base of data from National Animal Science Archive maintained by National Center for Dairy Research (Embrapa Gado de Leite). The analyses were performed by the MTDFREML system, under animal model containing herd-year-season of calving, the linear and quadratic age effects of calving, as fixed effects animal, permanent environment and error included as random effects. The estimates of genetic correlations between the total milk yield and the initial milk yield, and the rate of decline of milk yield were 0.55 and 0.86, and -0.19 and 0.38, respectively, for each mathematical model. For last two characteristics, these estimates were 0.45 and 0.75, indicating that cows with larger initial milk yield presented accentuated milk yield declines along the lactation period. The genetic correlations among 305-days yield and the parameters of model followed the same tendency, in magnitude and sign, to the one of the total milk yield. In agreement with the results, it can be inferred that the selection for the total milk yield results in increment in the initial milk yield, and in inexpressive changes in the rate of decline of the milk yield, not altering the form of the lactation curve. The rank correlations among the classifications of the predicted genetic values were high and positive (0.68 and 0.74), suggesting that the individuals with the highest genetic values for initial milk yield, would be also those with higher values for total milk yield.

Population structure of Brazilian Gyr dairy cattle

The objective of the present study was to evaluate the genetic structure of Gyr cattle selected for milk production. Files of pedigree and production were composed of 27,610 animals. The ENDOG program was used for the calculation of individual inbreeding coefficient (F) and coefficient of average relatedness (AR), effective number of animals(Ne), effective number of founders (fe) and ancestors (fa), and generation interval (GI). Individual inbreeding coefficients and average relatedness in the population were 2.82% and 2.10%, respectively. It was observed a reduction in the effective number of animals, especially after publication of the results of the first progeny test. The estimated effective number of founders was 146 and 75 for the ancestrals. Out of those, only 28 ancestors accounted for the origin of 50% of the population genes. The average generation interval was 8.41 years and it was longer for males than for females. For maintaining genetic variability in future generations, it should be invested mating strategies that reduce inbreeding and which do not use massively only some high breeding value sires.

Parâmetros genéticos entre características de leite, de peso e a idade ao primeiro parto em gado mestiço leiteiro (Bos taurus x Bos indicus)

Genetic correlations between milk production (milk, fat, protein yield lactation length in 305-d lactation), live weight (average cow live weight, growth rate between 12-24 mo) and age at first calving traits were estimated in a population of Mestico Leiteiro Brasileiro (MLB) females using REML methodology and animal model. The estimates of heritability were respectively, 0.28± 0.08, 0.30±0.11, 0.28±0.09, 0.19±0.07, 0.18±0.06, 0.42±0.10 and 0.48±0.12 for those traits. Genetic correlations between milk, fat and protein yield with cow average weight were, respectively, -0.22±0.22, -0.49±0.31, -0.22±0.23, and between milk, fat and protein yield with heifer live weight gain, -0.59±0.35, -0.73±0.44, -0.62±0.37 as well. Genetic correlations between milk yield, cow average weight and heifer live weight gain with age at first calving were, respectively, 0.05±0.18, -0.05±0.18, 0.02±0.20. The high genetic correlation between milk production and lactation length (0.93±0.02) indicated that variation of the lactation length should not be removed when selecting tropical dairy cattle.

Correlations among semen quality traits and scrotal circumference of sires of the Gyr breed.

Data related with semen characteristics such as volume (VOL), gross motility (TURB), motility (MOT), vigor (VIG), concentration (CONC), major defects (DMA) and minor defects (DME) from 807 semen output (CS) of 105 sires of the Gyr breed selected for milk production, and their measurements of scrotal circumference (CE) were used to study factors that affect these traits and the correlations among them. Uni and bivariate animal models that included the fixed effects of AI company, year and season of CS or CE measurement, age at CS or CE measurement, and random animal (bull) effect were used to evaluate the effects of these source of variation and the correlation between those traits. AI company and sire had a significant effect on all traits. Age affected only CE, TURB and NEMOV (= VOL x CONC x MOT). Repetabilities estimated by univariate model ranged from 0.23 for CONC to 0.70 for TURB. In general, phenotypic correlations, estimated by bivariate model were in a favorable direction. Pearson correlation between CE and all other traits ranged from -0.19 to 0.35. The recorded correlations, in general in a favorable direction, suggested that CE could be used as an elimination trait of sire to be pre-selected as a semen donor.

Estimação de parâmetros genéticos de medidas de conformação, produção de leite e idade ao primeiro parto em vacas da raça Gir Leiteiro

ABSTRACT - Data from 573 primiparous lactating Gyr cows were used to estimate the (co) variance components of the conformation traits, milk production up to 305 days of lactation (MP) and age at first calving (AFC) by REML method. These components were used to calculate heritability coefficients and genetic, phenotypic and residual correlations. The conformation measures, the heart girth (HG), croup height (CH), body length (BL), teats length (TL), teats diameter (TD) and udder height (UH) were obtained in the cows at first lactation with average age of 4.05 years. The genetic and phenotypic correlations between MP and AFC were 0.49 and 0.18 respectively. The genetic correlation between traits were MP x HG = -0.37; MP x CH = -0.62; MP x BL = -0.52; MP x TL= -0.08; MP x TD= -0.12; MP x UH = -0.69; AFC x HG = -0.05; AFC x CH = -0.37 and AFC x BL = 0.25. These estimates of genetic correlation between milk production and body size measures, in general, indicate that the selection for milk production held as a correlate response, decreasing in the cow size.

Differential expression of genes in resistant versus susceptible Gyr x Holstein cattle challenged with the tick Rhipicephalus (Boophilus) microplus.

The bovine tick Rhipicephalus (Boophilus) microplus causes major losses in cattle production systems in tropical regions. Bos indicus breeds are more resistant to ticks than B. taurus breeds. Resistance genes could be an alternative to control this parasite. We examined the pattern of gene expression of three calcium-binding-protein genes: translationally controlled tumor protein 1 (TPT1), allergen Bos d3 (S100A7), calcium channel protein transient receptor potential vanilloid 6 (TRPV6), and the cysteine proteinase inhibitor gene (CST6). These genes were selected from cDNA libraries prepared from skin biopsies taken from resistant and susceptible Gyr x Holstein F₂ animals. These biopsies were also used to study the expression level of these genes through real-time PCR analysis. The relative expression levels of the S100A7, TPT1, TRPV6, and CST6 genes were 2.01 ± 0.6, 1.32 ± 0.9, 1.53 ± 1.2, and 2.03 ± 0.7 times higher in the susceptible group, respectively. Skin lesion tissue from the susceptible animals showed significantly more mRNA transcripts of these genes in comparison with the resistant animals (P = 0.001). However, this hypersensitivity does not seem to protect the susceptible animals against tick infestation.