Annual Genetic Trends Research Articles

Longevity and reproductive traits in Angus cattle: Genetic parameters, predicted and realized genetic change

The objectives of this study were to estimate genetic parameters for longevity and reproductive and to evaluate their likely consequences on selection. We used calving records of 10,517 Aberdeen Angus cows, born between 1975 and 2012, with first calving in spring, from bulls with 5 or more daughters, herds with 25 or more observations, and pertaining to contemporary groups of 5 or more cows. Longevity variables were length of productive life (LPL) and stayability at 5 years (ST5); the reproductive variables were days to first calving (days1), calving success at second parity (CS2), and success of having the first three consecutive calvings (S3). CS2, S3 and ST5 were defined as binary, and days1 and LPL as continuous variables. A multi-trait, threshold-linear model was used, including contemporary group effects (herd-year of birth; days1 also included management group), age at first calving (covariate), and the genetic effect of the animal. Given the parameters, five strategies were explored to predict annual genetic progress: selection of 5% or 25% of progeny tested males, with progeny groups of 5 or 15 daughters (no selection in females), and mass selection of 75% in females (no selection in males). Annual realized genetic trends and correlated responses when selecting for ST5, CS2 or S3 were also calculated. The estimates (mean ± standard deviation a posteriori) of heritability for longevity traits were 0.08±0.03 for LPL and 0.11±0.05 for ST5; for reproductive traits, estimations were 0.08±0.02 for days1, 0.23±0.04 for S3, and 0.24±0.04 for CS2. The genetic correlation between LPL and ST5 was favourable and large (0.79); and were also favourable and large for reproductive characteristics (negative, -0.66 for days1-S3 and -0.73 for days1-CS2, and positive, +0.83 for S3-CS2). Correlations between longevity and reproduction were variable, from not different from zero (days1 with ST5 and LPL) to medium (+0.45 for ST5-S3). Realized annual genetic trends indicated small but significant favourable changes for ST5 and LPL, and unfavorable for days1, CS2 and S3. Correlated responses were, in general, also favourable, although less than the progress achieved by direct selection. There are wide possibilities for genetic improvement in these characteristics.

Genetic parameters, phenotypic and genetic trends of litter size on different breeds of goats in Egypt.

Data of 475 goats (242 Zaraibi, 84 Baladi, and 149 Damascus) kept at Sakha Farm, belonging to Animal Production Research Institute (APRI), Ministry of Agriculture, Dokki, Cairo, Egypt, from the period of 2011 to 2017 were used to estimate direct (additive) and maternal genetic effects for litter size at birth (LSB). Three animal models were used. Model 1 includes the fixed effects of breed, season, year of kidding, age of doe, and direct genetic effect. Model 2 is similar to model 1 beside the permanent environmental effect. Model 3 is similar to model 2 and includes the maternal genetic, covariance between direct and maternal genetic effects. The effects of breed, season, year of kidding, and age of doe were significant on LSB. Heritability estimates for LSB are 0.19±0.050, 0.19±0.160, and 0.06±0.007, as estimated from models 1, 2, and 3, respectively. Maternal heritability estimate using model 3 was 0.05±0.006. The removal of additive genetic maternal effect and covariance between direct and maternal effects from the model increased heritability of direct genetic effect by 0.13. Annual phenotypic trends for LSB in Zaraibi, Baladi, and Damascus goat breeds are negative. Annual genetic trends for LSB for the three breeds of goats are positive, significant, and being 0.10±0.01, 0.25±0.02, and 0.01±0.001 litter/year for Zaraibi, Baladi, and Damascus, respectively. The present results indicated that selection for LSB will take a long time. The speed and efficiency of selection is expected to increase by use of molecular markers in selection.

Genetic and environmental analysis of female calf survival in the Israel Holstein cattle population

The objectives were to estimate the effects of various environmental factors on female calf survival of Israeli Holsteins, to estimate the economic value of calf survival under Israeli conditions, to estimate the genetic and environmental variance components for calf and cow survival using the individual animal model, to perform GWAS analyses of survival to first calving and herd life after first calving, to estimate the genetic and environmental trends for calf survival since 1985, to estimate genetic correlations of calf survival with the traits included in the current Israeli breeding index, and to estimate the consequences of inclusion of calf survival in the national selection index. Mean calf survival rate of Israeli Holsteins from 2001 through 2008 was 0.85, and the mean economic value of survival to first calving was $526. Birth month, gestation length, dystocia, and twin birth significantly affected calf survival rate. Dystocia and twin birth each reduced survival rate by 0.034. Survival rate was highest for calves born in October and lowest for calves born in February. The difference between these months was 3.4%. Maximum survival was at a gestation length of 276 d, the mean gestation length for this population. Survival rate was reduced to 0.76 for calves born after a gestation length of 260 d. The individual animal model was applied for all the genetic analyses. Heritability for calf survival to first calving, as estimated by REML, was 0.009, whereas heritability of herd life from first calving was 0.15. The complete data set for genetic analysis of survival to first calving included 1,235,815 calves born between 1985 and 2017. Annual genetic and phenotypic trends for calf survival were 0.019 and 0.015%, respectively. Correlations of transmitting abilities of 226 sires born since 2010 for calf survival with the traits included in the Israeli breeding index were significant only for the maternal effects of dystocia and stillbirth. The GWAS analysis was based on the transmitting abilities of 1,493 bulls with genotypes and reliabilities >0.5 for calf survival and cow herd life. There were 7 single nucleotide polymorphisms with coefficients of determination >0.03 for calf survival and 12 single nucleotide polymorphisms with coefficients of determination >0.05 for cow survival. There was no overlap between the genome-wide significant markers for the GWAS analyses of calf survival and cow herd life. This corresponds to the conclusion from the REML results and the low correlations between the sire evaluations that the genetic control of the 2 traits are not similar. Inclusion of calf survival in the Israeli breeding would result in a 0.5% increase in calf survival over 10 yr but reduce progress for the other traits by 8%.

Genetic Improvement of Some Productive Traits in Zaraibi Goats

The objective of this study was to evaluate the genetic improvement in Zaraibi goats herd raised on El-serw research station located in the north eastern part of Nile Delta, Egypt. The station belongs to Animal Production Research Institute (APRI). Some body weights at different ages were included in genetic and environmental trends. These weights were 4-month weight (4M), 6-month weight (6M), and 12-month weight (12M). Data and pedigree information were collected from 1988 until 2018. The least square means of body weights at 4M, 6M and 12M were 12.14±0.02, 15.49±0.02 and 24.08±0.04 kg, respectively. Year of birth, season, gender of kid, parity of dam and type of birth significantly (P<0.01) affect growth traits. Genetic parameters were estimated using a multi-trait animal model program (MTDFREML). The same previous fixed effects were included in this analysis regarding the animal as random effects. The heritability of the studied body weights tend to increase as age increases. That is inversely matched with the environmental proportion of total variance which was found to be 0.72, 0.66 and 0.62 for M4, M6 and M12, respectively. The heritability value was estimated as 0.28 for 4M. Genetic trends were obtained as the regression of the predicted breeding values on years of birth and Environmental trends were obtained as the regression of year constants on years of birth. The annual genetic change trends were positive and significant for 4M, 6M and 12M (0.091, 0.121 and 0.158 kg/year, respectively) and the annual phenotypic change trends were (0.020, 0.045, 0.117 kg/year, respectively). Genetic trends for M12 trait were higher than those for other traits in this study. Genetic and environment correlations between 4 month body weight and other growth traits were positive. Negative environmental trends indicates poor management system for the flock during studied period. Weight at 12 months of age has the highest heritability in studied body weights and suggested to be selection criteria to improve yearling weight for Zaraibi goat.

Genetic, Phenotypic and Environmental Trend for Milk Yield and Production Efficiency Traits in Gir Cattle

The first lactation records of 1450 Gir cattle progeny of 290 dams and 41 sires maintained over the period from 1987 to 2010 at Cattle Breeding Farm, Junagadh Agricultural University, Junagadh, Gujarat were used to estimate the phenotypic, genetic and environmental trends of traits viz. first lactation total milk yield (FLTMY), first lactation total milk yield per day of first calving interval (FLTMY/FCI), first lactation total milk yield per day of first lactation length (FLTMY/FLL). The phenotypic trends were estimated as: 90.70 ± 6.44 kg, 0.24 ± 0.01 kg and 0.32 ± 0.02 kg for FLTMY, FLTMY/FCI and FLTMY/FLL respectively. The genetic trends were compared by five methods as Smith method1 (SM1), Smith method 2(SM2), Powell and Freeman method 1 (PM1), Powell and Freeman method 2 (PM2) and BLUP. The annual genetic trends for FLTMY were found to be positive by SM1 (2.88 ± 39.58 kg), PM1 (2.21 ± 37.34 kg) and BLUP (9.17 ± 1.94 kg). The annual genetic trends for FLMY/FCI were positive by SM1 (0.43 ± 0.03 kg), SM2 (2.69 ± 0.03 kg), PM1 (0.38 ± 0.02 kg) and PM2 (2.06 ± 0.02kg) while negative by BLUP (-0.05 ± 0.01 kg). The annual genetic trends for FLMY/FLL were found to be positive by SM1 (0.51 ± 0.06 kg) and PM1 (0.45 ± 0.03 kg) methods while negative by SM2 (-2.37 ± 0.05 kg), PM2 (-1.79 ± 0.03 kg) and BLUP (-0.06 ± 0.01 kg). However, the estimates obtained by BLUP method had the lowest standard errors and were more reliable compared to other methods.

The influence of ram on litter size in Suffolk sheep

The proportion of variance for service ram effects was estimated for number lambs born and weaned. The database with 11,311 lambings in purebred Suffolk was used. The basic model equation for the analysis of variance of litter size contained effects of ewe´s age at lambing, contemporary group of ewes at lambing, ewe´s permanent environmental effect and ewe´s direct additive genetic effect. The other models were extended by contemporary group of ewes during mating (harem), and additive genetic and permanent environmental effect of service ram. Variance components were estimated by the Gibbs sampling method. The proportions of variance for the service ram effect for number of lambs born and weaned were 4.1 % and 2.6 %. The annual genetic trends were 0.4 % of lambs born and 0.2 % of lambs weaned for female fertility. Male contribution on litter size was 0.2 % of lambs born and 0.1 % of lambs weaned. The results demonstrated that service rams in Suffolk sheep have low influence on litter size of their mates.

Genetic trend estimates for milk yield production and fertility traits of the Girolando cattle in Brazil

Annual genetic trends and selection differentials for 305-day milk yield (305MY), age at first calving (AFC), and first calving interval (FCI) were estimated by four selection paths [sires of bulls (SB), dams of bulls (DB), sires of cows (SC), and dams of cows (DC)] for Girolando dairy cattle in Brazil. A total of 12,739 lactation records were obtained from the Brazilian Girolando Breeders Association with cows calving in the period from 2000 to 2011. Two periods were involved: the first, from 1979 to 1996, corresponding to the formation and expansion of the herd, and second, from 1997 to 2007, characterized by the implementation of the breeding program of the Girolando breed. The whole period from 1979 to 2007 was also considered. The Wombat program was used to fit an animal model for the analyses. Estimated breeding values were extracted to calculate genetic trends for the four selection paths. Greater significant estimates of annual genetic changes for 305MY were obtained for the SC and SB paths, being both during the second period. The greatest annual genetic change estimates for 305MY were 43.06 and 101.97milk/yr for SC and DB, respectively, during the second period. A favorable genetic response was found for the SB and SC paths for AFC, averaging −4.24 (second period) and −0.32day/yr, respectively. For FCI, this effect was from 0.04 to 0.18 range for all paths. When all selection paths were combined, estimated annual genetic changes for 305MY and AFC were 7.40milk/yr and −0.13day/yr. Therefore, the results of this study showed that a well-designed genetic program has a positive impact on 305MY and AFC and a little or without impact on FCI in Girolando cattle over a 28-yr period.

Estimation of genetic parameters and trends for milk fat and protein percentages in Iranian Holsteins using random regression test day model

Abstract. The aim of the present study was to estimate the genetic parameters and trends for fat and protein percentages of milk in Iranian Holsteins calving between 2001 and 2010 using the random regression test day model. Data set included 505 160 test day records that were collected by the Animal Breeding Centre of Iran. The Legendre polynomial functions of orders (5, 5) and (5, 6) were chosen to fit the additive genetic and permanent environmental effects of fat and protein percentages, respectively. Estimated heritabilities ranged from 0.053 to 0.232 and 0.111 to 0.259 for fat and protein percentages, respectively. The averages of estimated breeding values were −8.61 and −3.15 and annual genetic trends were −0.74 kg and −0.64 kg for fat and protein percentages, respectively. Negative genetic trends for fat and protein percentages are likely the result of major emphasis on milk yield in the breeding plan of Iranian Holsteins.

Efficiency of genomic selection in a purebred pig male line

Stochastic simulation was used to compare the efficiency of 3 pig breeding schemes based on either traditional genetic evaluation or genomic evaluation. The simulated population contained 1,050 female and 50 male breeding animals. It was selected for 10 yr for a synthetic breeding goal that included 2 traits with equal economic weights and heritabilities of 0.2 or 0.4. The reference breeding scheme, named BLUP-AM, was based on the phenotyping of all candidates (13,770 animals/yr) for Trait 1 and of relatives from 10% of the litters (270 animals/yr) for Trait 2 and on BLUP-Animal Model genetic evaluations. Under the first alternative scenario, named GE-1TP, selection was based on genomic breeding values (GBV) estimated with one training population (TP) made up of candidate relatives phenotyped for both traits, with a size increasing from 1,000 to 3,430 over time. Under the second alternative scenario, named GE-2TP, the GBV for Trait 2 were estimated using a TP identical to that of GE-1TP, but the GBV for Trait 1 were estimated using a large TP made up of candidates that increased in number from 13,770 to 55,080 over time. Over the simulated period, both genomic breeding schemes generated 39 to 58% more accurate EBV for Trait 2 than the reference scheme, resulting in 78 to 128% (GE-1TP) and 63 to 84% (GE-2TP) greater average annual genetic trends for this trait. For Trait 1, GE-1TP was 18 to 24% less accurate than BLUP-AM, reducing average annual genetic trends by 27 to 44%. By contrast, GE-2TP generated 35 to 43% more accurate EBV and 8 to 22% greater average annual genetic trends for Trait 1 than the reference scheme. Consequently, GE-2TP was 27 to 33% more efficient in improving the global breeding goal than BLUP-AM whereas GE-1TP was globally as efficient as the reference scheme. Both genomic schemes reduced the inbreeding rate, the greatest decrease being observed for GE-2TP (-49 to -60% compared with BLUP-AM). In conclusion, genomic selection could substantially and durably improve the efficiency of pig breeding schemes in terms of reliability, genetic trends, and inbreeding rate without any need to modify their current structure. Even though it only generates a small TP, limited annual phenotyping capacity for traits currently only recorded on relatives would not be prohibitive. A large TP is, however, required to outperform the current schemes for traits recorded on the candidates in the latter.

Genetic and environmental trends in the long-term dairy cattle genetic improvement programmes in the central tropical highlands of Ethiopia.

A total of 1979 lactation records from 550 selected crossbred dairy cows that born between 1974 and 2005 were used to estimate annual genetic and environmental trends in milk production and reproduction traits at Holetta Agricultural Research Center, Ethiopia. Annual genetic and environmental trends were estimated by regressing BLUP estimated breeding value on year of birth. Variance components and genetic parameters were estimated using univariate analysis of individual animal model based on restricted maximum likelihood procedures. Annual genetic trends were -3.384 days, -8.00 kg and -5.96 kg, -0.26 months, -0.29 months and -0.88 days, for lactation length (LL), lactation milk yield (LMY), adjusted 305 milk yield (305-days MY), age at puberty (APU), age at first calving (AFC) and calving interval (CI), respectively. Environmental trends for LMY was positive (6.717 kg) and was in the desired direction. Heritability estimates were 0.14, 0.44, 0.39, 0.38, 0.40 and 0.17 for LL, LMY, 305-d MY, APU, AFC and CI, respectively. Negative genetic trends in all milk production traits reflect ineffective selection program and/or lack of using sires that have positive breeding values. The result from the environmental trends shows substantial improvement in the management practices over time. Contrasting directions in genetic and environmental trends reflect ineffective breeding objectives. This warrants reconsideration of the existing breeding program in the country. Key words: Genetic trends, environmental trends, genetic parameters, breeding objectives, variance components.

Genetic parameters of finish time in Korean Thoroughbred racehorses

This study was conducted to estimate the annual genetic and environmental trends of Thoroughbred racehorses. A total of 208,043 records collected from horses that raced at Gwacheon racecourse were analyzed. The average generation intervals of the sires of offspring and the dams of offspring were 10.82 and 10.31years, respectively. The effects of the contemporary groups accounted for more than approximately 44% of the total variation in finish time and were the most important environmental effects in the genetic evaluation model. The range of estimated heritabilities and repeatabilities were from 0.06 to 0.30 and from 0.31 to 0.59, respectively. The estimate of heritability was highest at the racing distance of 1000m (0.30), and decreased as the racing distance increased. Of the total variance components, the proportion of variance due to the jockey was from 0.02 to 0.06, and it was larger in longer distance races than in shorter ones. According to the results, racehorses accounted for 94.8%, and the jockey for only 5.2%, of finish time. As the racing distance increased, the percent contribution of the jockey also tended to increase. The phenotypic and environmental improvements were −2.140 and −1.492s over 16years studied, respectively. On the other hand, genetic gains in racing performance of home-produced and imported racehorses in the same period were −0.459 and −0.369s, respectively. The genetic improvement of racehorses in racing performance was very consistent, resulting in average gains of −0.029 and −0.031s per year in home-produced and imported racehorses, respectively.

Seleção para peso pós-desmama em um rebanho Gir. 1. Resposta direta e correlacionada em 21 anos de seleção

A seleção para peso pós-desmama tem sido aplicada em um rebanho Gir (80 vacas, seis touros) desde 1976, e um rebanho Nelore Controle, NeC (60 vacas, quatro touros), tem sido mantido para avaliação da mudança ambiental. O critério de seleção dos machos foi o peso aos 378 dias (P378), obtido em prova de ganho de peso, e o das fêmeas, o peso aos 550 dias (P550) em recria a pasto. A média dos diferenciais de seleção efetivos dos pais foi, respectivamente, 19,5 e 1,8 kg para Gir e NeC, correspondendo a 0,72 e 0,07 unidades de desvio-padrão (u.d.p.). A média dos diferenciais de seleção efetivos acumulados dos pais, na progênie de 2001, foi 83,7 e 7,2 kg para Gir e NeC, correspondendo a 3,17 e 0,29 u.d.p. O intervalo de geração médio no rebanho Gir foi 5,65 anos e no NeC 5,0 anos e o coeficiente de geração médio individual na progênie de 2001 atingiu 4,25 (Gir) e 4,65 (NeC) gerações de seleção. As estimativas de tendência genética no rebanho Gir, obtidas por quadrados mínimos, foram PN = 0,16; P210 = 0,81 kg/ano; GPRE = 3,02 g/dia/ano; P378 = 2,88; P550 = 2,80 kg/ano; G112 = 11,2 g/dia/ano, AM = 0,003 e AF = 0,004 m/ano. Com base no modelo misto, as estimativas para essas características foram menores (0,03 e 0,28 kg/ano; 1,15 g/dia/ano; 1,45 e 1,07 kg/ano; 3,73 g/dia/ano; 0,003 e 0,002 m/ano). As estimativas de herdabilidade realizadas para P378 e P550 foram 0,69 e 0,64, respectivamente. Os resultados indicaram que a seleção para peso pós-desmama, com base na informação de desempenho individual, promoveu respostas genéticas significativas tanto nas características sob seleção direta quanto nas respostas correlacionadas em características de crescimento da fase pré e pós-desmama no rebanho Gir.

Estimates of genetic parameters and genetic trends for live weight and fleece traits in Menz sheep

Menz sheep are indigenous to the highlands of Ethiopia, and highly valued for their meat and wool production. The area is characterized as a low input mixed barley-sheep production system. In 1998, a selection experiment was set up to evaluate the response of Menz sheep to selection for yearling live weight (WT12) and greasy fleece weight (GFW) combined in an economic index. In this paper, we report the results of this breeding program obtained between 1998 and 2003. Average annual genetic selection responses for WT12 and GFW were 1.506 and 0.043 kg in the selected flock and 0.392 and −0.008 kg in the control flock. Annual genetic trends in the selected flock, estimated by regressing BLUP estimated breeding values on year of birth, were 0.495 ± 0.053 kg for WT12, 0.012 ± 0.002 kg for GFW, and Birr 5.53 ± 0.55 for the aggregate breeding value (1 Ethiopian Birr = 0.115 USD). Corresponding values for the control flock were 0.276 ± 0.065 kg, 0.003 ± 0.002 kg and Birr 2.93 ± 0.69. Correlated responses in birth weight (WT0), weaning weight (WT3), 6-month weight (WT6) and staple length (STPL) in the selected flock were 0.038 ± 0.005 kg, 0.271 ± 0.03 kg, 0.388 ± 0.039 kg and 0.011 ± 0.017 cm, respectively. Heritabilities, estimated by fitting a multitrait individual animal model were 0.464 ± 0.014, 0.477 ± 0.016, 0.514 ± 0.017, 0.559 ± 0.019, 0.393 ± 0.016 and 0.339 ± 0.014 for WT0, WT3, WT6, WT12, GFW and staple length (STPL), respectively. Phenotypic and genetic correlations between all traits were positive, except for STPL and WT12. Estimates of genetic parameters and observed genetic trends confirm that selective breeding can lead to significant genetic improvement in Menz sheep.

Selection Responses for Clinical Mastitis and Protein Yield in Two Norwegian Dairy Cattle Selection Experiments

Inferences from two dairy cattle selection experiments, in which sires were selected from external sources, were drawn by using an animal model to analyze data from the entire population. The first selection experiment was carried out in the period from 1978 to 1989 and included groups selected for high milk production (HMP) and low milk production (LMP). Each year, the highest ranking proven sires for milk production, from the most recent group of Norwegian Dairy Cattle (NRF) test bulls, were selected and mated to the cows in the HMP group. A group of sires with low milk production indices from progeny testing in 1978 and 1979 were used as sires in the LMP group during the entire experiment. The second selection experiment, which started in 1989, included one high protein yield (HPY) group and one low clinical mastitis (LCM) group. The highest ranking proven NRF sires for protein yield and mastitis resistance were selected each year from the most recent group of progeny tested bulls and used as sires in the HPY and LCM groups, respectively. Genetic trends for protein yield were positive (as expected) for HMP and HPY cows, and negative for LMP and LCM cows. Estimates of annual genetic trends for clinical mastitis were +0.23, −0.02, +0.04, and −0.91% per year for HMP, LMP, HPY, and LCM cows, respectively. The difference in genetic trend of clinical mastitis between HMP and HPY groups, both selected for increased milk production, reflects the gradual change in the NRF breeding objective towards more weight on health relative to milk over the last 20 yr. After four cow generations, the genetic difference in mastitis between HMP and LMP group cows was 3.1% clinical mastitis, a correlated response to selection for increased milk production. The genetic difference between LCM and HPY cows of 8.6% clinical mastitis after three cow generations is mainly a result of direct selection against clinical mastitis in the LCM group. In the NRF population, an approximately flat genetic trend for clinical mastitis was found for cows born from 1976 to 1990, whereas cows born after 1990 showed a genetic improvement equivalent to a reduction of 0.19% clinical mastitis per year. The results show that it is possible to obtain considerable selection response for clinical mastitis, and that selection for increased milk production will result in an unfavorable correlated increase in mastitis incidence, if mastitis is ignored in the breeding program.

Estimativas de (Co)Variâncias e Tendências Genéticas para Pesos em um Rebanho Canchim

Os objetivos deste trabalho foram obter estimativas de (co)variâncias e estimar a tendência genética para os pesos ao nascimento (PN), à desmama (PD) e a um ano de idade (P12) em um rebanho da raça Canchim. Foram utilizados dados de 6.517 animais, nascidos de 1953 a 1996, para estimar os valores genéticos pelo método da máxima verossimilhança restrita livre de derivadas, empregando-se um modelo que incluiu os efeitos fixos de grupo de contemporâneos (ano/época de nascimento/sexo do bezerro) e a covariável idade da vaca ao parto (efeitos linear e quadrático) e os efeitos aleatórios genéticos direto e materno e de ambiente permanente. Foram estimadas tendências genéticas para os efeitos aditivos diretos, maternos e do total maternal, pela regressão ponderada das médias anuais (ou de gerações) dos valores genéticos diretos, maternos e do total maternal sobre o ano de nascimento (ou geração) dos animais. As estimativas de herdabilidade direta foram iguais a 0,39; 0,48; e 0,63 para PN, PD e P12, respectivamente, enquanto as estimativas de herdabilidade materna foram, na mesma ordem, 0,03; 0,04; e 0,05, respectivamente. As tendências genéticas diretas anuais foram iguais a 0,046; 1,336; e 1,619 kg para PN, PD e P12, respectivamente, representando cerca de 0,13; 0,66; e 0,75% das médias do rebanho. Por geração, as tendências foram, na mesma ordem, 0,269; 7,715; e 9,599 kg, respectivamente. As tendências genéticas maternas e do total maternal foram, em geral, lineares e positivas. Os resultados mostraram que os critérios de seleção utilizados resultaram em progresso genético para PN, PD e P12, contudo, o progresso obtido ficou bem aquém do possível.

Genetic trends for milk, fat and protein in the Zimbabwean Holstein-Friesian population from 1973 to 1994

Abstract. Genetic trends based on 30 395 records with parities 1 to 8 were estimated using average information restricted maximum likelihood algorithm (AIREML), which had overall mean, herd, month of calving, year of birth, parity and linear and quadratic effects of days in milk. Due to changes in the Zimbabwean milk recording system data set was split into records of cows born from 1973 to 1989 and the other from 1987 to 1994. The first data set was further split into even numbered herds (EVNH73) and odd numbered herds (ODNH73), due to computational limitations. The highest milk production was from May to August. Peak milk production was observed in parity 4. The heritabilities for FCM (0.22 to 0.26), fat percent (0.24 to 0.28) and protein percent (0.21) were comparable to literature values. The annual genetic trends of FCM ranged from 8.36 kg to 13.2 kg, fat per cent ranged from 0.0 % to −0.008 % and protein per cent was −0.003 % in the three data sets. Genetic trends for milk yield, fat and protein yield were also positive but overally lower than in most other countries. The positive genetic trends obtained for milk, fat and protein yields imply that some progress has been made in increasing the milk production despite the relatively small population and significant restrictions. There is need to develop a selection index to improve milk yield and milk composition.

Estimativas de parâmetros genéticos e de tendências fenotípica , genética e de ambiente de algumas características produtivas da raça Gir Leiteiro

Os objetivos do estudo foram estimar os parâmetros genéticos e as tendências fenotípica, genética e de ambiente para produção de leite (PL), duração da lactação (DL), produção de gordura (PG) e porcentagem de gordura (CG) no leite, na raça Gir, utilizando análises uni e bivariadas sob o método da máxima verossimilhança restrita, por meio de algorítmo livre de derivadas (MTDFREML), ajustando modelos-animal. O modelo matemático adotado para as quatro características produtivas incluiu os efeitos fixos de rebanho-ano de parto, época de parto e idade ao parto como covariável (linear e quadrática) e, além do resíduo, os efeitos aleatórios de animal e ambiente permanente. Por meio de análises bivariadas, as estimativas de herdabilidade foram, respectivamente: PL e DL, 0,21 e 0,11; PL e PG, 0,22 e 0,21; PL e CG, 0,19 e 0,12. As estimativas de repetibilidade foram PL, 0,51; DL, 0,32; PG, 0,47; e CG, 0,13. As correlações fenotípicas, genéticas e de ambiente foram, respectivamente: para PL e DL, 0,62, 0,76 e 0,57; para PL e PG, 0,93, 0,97 e 0,91; para PL e CG, -0,02, -0,11 e -0,01. As estimativas das mudanças anuais fenotípica, genética e de ambiente para as características produtivas estudadas foram, respectivamente: para PL, 66,93± 7,06 (P&lt;0,01), 10,46± 1,08 (P&lt;0,01) e 56,47 kg/ano na população de vacas, e 29,63± 14,34 (P&lt;0,05), 19,29± 5,27 (P&lt;0,01) e 10,34 kg/ano na população de touros; para DL, -0,16± 0,31 (P&gt;0,05), 0,21± 0,09 (P&lt;0,05) e -0,37 dias/ano na população de vacas, e -0,69± 0,44 (P&gt;0,05), -0,10± 0,28 (P&gt;0,05) e -0,59 dias/ano na população de touros; para PG, 3,53± 0,58 (P&lt;0,01), 0,40± 0,09 (P&lt;0,01) e 3,13 kg/ano na população de vacas, e 1,37± 0,95 (P&gt;0,05), 0,47± 0,29 (P&gt;0,05) e 0,90 kg/ano na população de touros; para CG no leite, 0,039± 0,014 (P&lt;0,05), 0,001± 0,001 (P&gt;0,05) e 0,038 %/ano na população de vacas, e 0,010± 0,011 (P&gt;0,05), 0,000± 0,003 (P&gt;0,05) e 0,010 %/ano na população de touros.

Genetic and environmental trends in a large commercial Jersey herd in the Central Rift Valley, Kenya.

Records from a large commercial Jersey herd covering the period 1980 to 1993 were used to estimate genetic and environmental trends in production traits, fertility traits and age at first calving. The farm is located in the upper midland agroecological zone of the Central Rift Valley in Kenya. The estimated annual genetic trends were 0.8 kg (milk yield), 0.003% (butterfat per cent), 0.09 kg (butter fat yield), 0 d (calving interval), -0.001 (number of services per conception), 0.22% (conception rate) and -0.5 d (age at first calving). All the traits studied showed an environmental trend in the desired direction: 14.6 kg (milk yield), 0.029% (butterfat per cent), 1.31 kg (butterfat yield), -2.52 d (calving interval), -0.62 (number of services per conception), 0.89% (conception rate), and -17 d (age at first calving). Despite great genetic variation in the production traits, the genetic trend in all traits was very small reflecting ineffective selection, whereas the results for the environmental trends indicate a substantial improvement in the management.

Selection for postweaning growth in inbred Hereford cattle: the Fort Keogh, Montana line 1 example.

Demographic characteristics and genetic trends in birth weight and pre- and postweaning ADG were examined in a population of Hereford cattle (Line 1). Line 1 was founded largely from two paternal half-sib sires and has been selected for postweaning growth. There were pedigree records on 951 members of the base population that predated 1935, when data collection began. Numbers of records analyzed using mixed-model methodology were 4,716 birth weight, 4,427 preweaning ADG, and 3,579 postweaning ADG. Birth weight and preweaning ADG were considered to have direct and maternal genetic components. Inbreeding accumulated rapidly from 1935 to 1960 and more slowly (.22%/yr) thereafter. Any reduction in additive genetic variance due to inbreeding and selection may have been offset by a concurrent reduction in generation interval that was observed as time progressed. Expected selection differential for 365-d weight, averaged over sexes, was 31.2 kg per generation. For birth weight, annual genetic trends in direct and maternal effects were 42 +/- 3 g and 15 +/- 3 g, respectively. Annual direct and maternal genetic trends for preweaning ADG were .70 +/- .06 g/d and .63 +/- .06 g/d, respectively. Direct response in postweaning ADG was linear and equal to 5.3 +/- .6 g.d-1.yr-1. As a result, estimated breeding values of birth weight, 200-d weight, and 365-d weight increased by 3.2 kg, 14.5 kg, and 62.4 kg, respectively, from 1935 to 1989. Selection within Line 1 was effective in increasing genetic potential for growth over 13 generations. No selection plateau was observed in any of the traits examined.

Nordic dairy cattle comparison for milk production by using a mixed linear model approach

The exchange of genetic material between the dairy cattle populations in the Nordic countries is well established. Initially the following Nordic dairy cattle populations were used to perform a comparison of their genetic levels for milk production: the Norwegian Cattle (NRF), the Swedish Red and White Cattle (SRB), and the Finnish Ayrshire Cattle (FAY). A linear model, including genetic base of sire proofs and genetic group made up by breed composition and date of birth of sire as fixed effects and sire as a random effect, was applied to standardize and deregress official sire proofs. The result was expressed as Nordic transmitting ability in kg of fat- and protein-corrected milk (FPM). The overall average of Nordic proofs of sires used in the NRF population was, respectively, 72 and 151 kg FPM higher than those of sires proven in the SRB and FAY populations. A genetic comparison of the breeds gave the same general result. The annual genetic trends were 25.5, 16.7 and 30.4 kg FPM in the NRF, SRB and FAY populations. Actually, the highest selection differentials were measured for bull sires in the FAY population. Sons of foreign bull sires had an overall negative impact in the NRF population, but a positive impact in both the SRB and FAY populations.