Genetic and environmental trends in landrace beef breeds and the effect on cow productivity

[摘要] Since the implementation of breeding values in South Africa during 1994 it is still unknownhow many breeders actually utilize breeding values in selection decisions; and whether thebreeds that promote the use of breeding values have actually made any genetic improvement or if this observed improvement was due to better management and/or more favorable environments.Climate change will have a negative effect on livestock production environments and matching the genotype with the production environment will become important. The selection of animals and genotypes that are better adapted to the anticipated environment, will ensure sustainable production. In South Africa the indigenous Sanga and Sanga derived breeds can form the basis for increased productivity and product quality. It is also anticipated that these breed types will increasingly be used as dam lines, as they mostly have smaller frames with lower feed requirements, good maternal abilities, low birth weights and mortalities. The data available on the INTERGIS (Integrated Registration and Genetic InformationSystem) was used to do a genetic evaluation for the Landrace beef breeds in South Africa.These breeds are the Afrikaner, Bonsmara, Drakensberger and Nguni (regulations of the Animal Improvement Act, Act 62 of 1998) and are all Sanga or Sanga derived breeds.A complete pedigree and data set was extracted from the INTERGIS for each of the breedsand data validation procedures were carried out as part of the routine editing procedures priorto the BLUP genetic evaluation analyses. The genetic models developed by the ARC for the routine genetic evaluation of beef breeds in 2010, were used in this study. The phenotypic-, genetic- and environmental trends were calculated for the four breeds. The total number of weaning weights and mature cow weights (the first weight after 4 years of age) are summarized below.(See table in PDF full text.)Genetic, phenotypic and environmental trends for a 25 year period from 1980 to 2005 formature cow weight, first three inter-calving periods and age at first calving was estimated; and birth- and weaning weight trends from 1985 to 2010 for the Afrikaner, Bonsmara andDrakensberger breeds. In the case of the Ng uni the period started in 1988, due to limited data from only a few state owned herds prior to 1988. The reason for this apparent discrepancy is to ensure that the same year of birth groups is compared due to the time lag that exist between the measurements of the different traits.Cow efficiency was defined as kg calf weaned per large stock unit (KgC/LSU) mated, andestimated and averaged per year of birth. Frames size specific equations were used tocalculate the LSU for different weights of lactating cows. The predicted calving percentagewas calculated from inter-calving period using an equation from the literature. This trait did not form part of the genetic analyses. Trends in this trait were estimated using data recorded between 1980 and 2013. The phenotypic, genetic and environmental trends for weaning weight, mature cow weight and inter calving period are discussed here, where applicable, since these are the traits that contribute to the estimation of cow efficiency.In the case of the Afrikaner, the phenotypic, direct genetic and maternal trends for weaningweight were +818g, +277g and +84g per year respectively. There was also a totalimprovement of 12kg in the environmental trend, indicating a possible improvement inmanagement. For mature cow weight the phenotypic trend first decreased by 3.5kg per year between 1980 and 1988, thereafter it increased by 4.3kg per year between 1989 and 1995, and then stabilized. No definite changes were observed in the genetic and environmental trends for mature cow weight. It seems that the breeding strategy followed by the Afrikaner breeders managed to increase calf weaning weight genetically by +7.0kg, while limiting the increase in mature cow weight. With inter-calving period there was a phenotypic decrease of 0.79 days per year. The genetic trend was so small that it can be ignored for all practical purposes. Initially cow efficiency (KgC/LSU) decreased, but since 1987 it has increased. The phenotype for weaning weight has increased by +20.4kg, whereas that for mature cow weight has decreased by -8.3kg. This increase in calf weaning weight with a concomitant decrease in mature cow weight and inter calving period (which was used to estimate calving percentage) resulted in an increase of 18.3% in cow productivity. This is the highest percentage increase for all the breeds studied.In the case of the Bonsmara, the phenotypic trend for weaning weight initially increased by671g per year until 1999 where after it decreased by 1829 per year until 2010. The directgenetic, maternal and environmental trends for weaning weight were +4679, +142g and-346g per year respectively. There may be many reasons for the latter trend, including poorer adaptation due to the diminishing influence of Afrikaner genes in the Bonsmara, or the decrease in number of breeders from 510 to 353 resulting in different environments. In respect of mature cow weight both the phenotypic and genetic trends increased by 700g and 6389 per year respectively. From 1989 until 2000 there was no change in the environmental trend. The phenotypic trend for inter calving period decreased by 0. 68 days per year with no clear genetic change. Despite the genetic and phenotypic increase in mature cow weight, cow efficiency improved although the LSU for cows increased from 1.34 in 1980 to 1.45 in 2013. The reason for this is that inter calving period decreased by 16.9 days and this decrease offset the higher maintenance requirements associated with the heavier cows and cow productivity still improved by 10%. The breed is cautioned about the increase in mature cow weight. In the case of the Drakensberger the phenotypic and maternal genetic trends for weaningweight do not show any change, whereas there is an increase of 248g per year in the directgenetic trend. The environmental trend for weaning weight first decreased (-1.05kg/year) and then increased (+0.725g/year) from 2000. The trends in weaning weight are antagonistic and variable. This could be an indication of the variable and harsh environments (e.g. cold spells) in which the breeds was kept over the period of the study. There was no phenotypic change in mature cow weight. In contrast to no phenotypic trend, there was a positive genetic trend for mature cow weight of 603g per year and a negative environmental trend for mature cow weigh of 1. 76kg per year from 1980 to 1994, thereafter it increased with 2.68kg per year until 2005. For inter-calving period there was a phenotypic decrease of 1.36 days per year. The genetic trend showed a small decrease of 0.07 days per year. Cow efficiency increased over time although there was a slight decrease from 1996 to 2004. This was due to a decrease in weaning weights and a lower calving percentage (longer inter-calving period) during the same period. Inter calving period decreased drastically by 34 days over the period of study and the net result is an increase in cow productivity of 14.2%. All the phenotypic changes in the Nguni were non-significant or negative (in the case of intercalving period this is favourable), except for cow efficiency. The phenotype for mature cow weight decreased by 1.02kg per year. All the genetic changes were negligible. It is common knowledge that the Nguni breed does not have uniform breeding strategies that is followed by most of the breeders. It is therefore not surprising that no genetic change was observed in respect of the Nguni. The improvement in cow efficiency was possible due to an improvement in inter-calving period of 1.08 days per year or 19.4 days over the period. The improvement in estimated calving percentage managed to increase cow efficiency by 10.4%, which is similar to the increase in the cow efficiency of the Bonsmara.Possible reasons for the differences in the phenotypic and genetic changes between breeds are, (1) changes in the production environment, production region and production system, e.g. Nguni cattle are currently farmed with in areas that were traditionally regarded as unsuitable for cattle farming, (2) relative emphasis on pre-weaning and post weaning traits and (3) effects of climate change on the availability of nutritional needs. From this study it would appear that some breeds will have to reconsider their breeding strategies.An issue of concern is that there were no detectable genetic change for inter-calving period in all the breeds. It is therefore recommended that the genetic improvement of fertility in beef cattle in South Africa be researched properly and that the appropriate breeding technology to handle fertility be developed or refined. The decrease in the phenotype for inter-calving period observed in this study can be a result of many factors including but not limited to; better record keeping both on the farm and by the Society, management decisions such as culling cows that do not reconceive regularly or within a specified period of time and stringent application of breed standards in respect of fertility.This study demonstrated what happened genetically in South Africa's Landrace breeds over the past years and what the current levels of productivity are in these breeds. It alsodemonstrated that cow productivity improved in all the breeds. Improving productivity is thekey to reducing the environmental impact of beef production and to provide sufficient animal protein to satisfy the growing demand. It is foreseen that Land race breeds may become more important in South Africa as a consequence of climate change that will result in more challenging environments. It is therefore recommended that economic selection indices be developed that includes both post weaning growth traits and cow productivity for South Africa's Landrace breeds.It is recommended that studies similar to this one is carried out for all the major beef breeds in South Africa. This will give an indication of the genetic changes that occurred in the different breeds and breed types in South Africa and how this affected cow productivity. This is of particular interest in the case of breeds where genetic material is imported regularly.

[发布机构] University of the Free State