Novelty traits to improve cow-calf efficiency in climate smart beef production systems

[摘要] The objective of this study was to identify novelty traits as possible selection criteria toimprove cow-calf efficiency and to describe cow efficiency in extensive systems thatwill support climate smart beef production. The traits investigated were calf weaningweight as trait of the dam and kilogram calf weaned per Large Stock Unit (KgC/LSU);the latter trait being a measure (value) that expresses performance (calf weaningweight) per constant unit, viz. per LSU. This may be a useful breeding objective/goalto increase production efficiency, which may reduce the carbon footprint of extensivecow-calf production systems. No reference could be found in the literature whereKgC/LSU or weaning weight as trait of the dam were considered as breedingobjectives. Therefore it was decided to investigate the novelty traits proposed aboveas measures of cow- calf efficiency.The investigation using breed averages of 30 beef and dual purpose breeds found thatKgC/LSU was independent of cow weight and the next step was to do a genetic analyses on breed level to estimate the genetic parameters for this trait and its genetic correlations with other traits of relevance.For the purpose of the studies reported later, breed frame size specific equations weredeveloped to estimate LSU units, using published information. The differences in LSUunits between animals of the same body weight, but with different frame sizes is basedon the principle that there are differences in the voluntary feed intake between suchanimals, although they have the same body weight.A Bonsmara (most numerous breed in South Africa) dataset, comprising of 34 884complete cow-calf records for the first three parities was used to investigate KgC/LSUand calf weaning weight (1<205), both as traits of the dam, as breeding objectives toimprove efficiency in extensive cow-calf production systems. A number of models wereevaluated and the simplest models with improved (smaller) log likelihood values wasused. Heritability estimates of KgC/LSU, K205 and dam weight (OW) were 0.26±0.02,0.11 ±0.01 and 0.45±0.02 respectively. Genetic correlations of 0.39±0.03 betweenKgC/LSU and 1<205, 0.17±0.02 between OW and 1<205 and -0.83±0.01 between OWand KgC/LSU were found. The very high negative genetic correlation (-0.83) betweenKgC/LSU and OW suggests that direct selection for KgC/LSU will decrease damweight. On the contrary selection for K205 will result in a slight increase in OW, sincethe correlation between the two is only +0.17. Of interest is the moderate positivecorrelation between K205 and KgC/LSU of +0.38, indicating that selection for weaningweight as trait of the dam may increase cow efficiency, albeit that cow weight willpossibly show a small increase as well. It therefore seems that selection or KgC/LSUwill have the same defects as other ratio traits. A more effective alternative will be acow efficiency index which include OW and K205 but with a restriction on OW. Arestricted selection index will therefore restrict increases in OW (and implicitly LSU).The relationship between the novel traits and conventional pre-weaning traits werealso investigated, where the conventional traits were the weaning weight of the dam(OWW) and the average weaning weight of her three calves (ACWW). The EstimatedBreeding Values (EBV's) for the different traits were used to run a Pearson correlationanalysis and this correlation was used as approximation of the genetic correlation.Heritability estimates for ACWW and OWW were 0.81±0.02 and 0.26±0.03respectively. The correlations between K205 and KgC/LSU; ACWW and OWW are 0.42, 0.52 and 0.42 respectively; that between KgC/LSU and ACWW and DWW are0.24 and 0.08 respectively; whereas that between ACWW and DWW is 0.54. The lowcorrelation of 0.08 between DWW and KgC/LSU indicates that KgC/LSU isindependent of the weaning weight of the dam. This result suggests that an alternativeapproach to selection or selection practices may be needed to increase the efficiencyof beef cattle in climate smart agriculture.The investigation on the novel traits were extended to three diverse breeds namelythe Afrikaner (indigenous Bos taurus africanis), Angus (British Bos taurus) andCharolais (European Bos taurus), with 6 104, 7 581 and 2 291 complete cow-calfrecords respectively, using the same approach as with the Bonsmara. Theheritabilities for KgC/LSU were 0.52, 0.24 and 0.21 for the Afrikaner, Angus andCharolais respectively and that for K205 0.40, 0.17 and 0.13 respectively. In manycases the genetic correlations could not be estimated. There were major differencesin the nature of the relationship between KgC/LSU and K205 between the Angus andthe Charolais, the latter indicated a strong negative correlation (-0.75) and the Angusa strong positive correlation (+0.84). These results support the findings on theBonsmara, namely that a cow efficiency index may be a more effective alternative,with minimal to no defects.The cow efficiency in crossbreeding systems as defined by KgC/LSU was alsoinvestigated, using the results of an extensive crossbreeding experiment. The resultswas obtained by crossing the Brahman (B), Charolais (C), Hereford (H) andSimmentaler (S) as sire line breeds on the Afrikaner (A) and F1 the genotypes as damlines. Crossbreeding with the A as dam line increased the KgC/LSU on average by12.8 kg (11 .6 %), with the CA calf producing on average the most KgC/LSU (anincrease of 15.5%). In the case of F1 cows, cow productivity of as high as 46% abovethat of the pure A was achieved. From this study it is clear that cow productivity canbe increased without additional herd costs to the farmer through properly designedcrossbreeding systems, thereby promoting climate smart beef production systems andreducing the carbon footprint of beef production. The fact that there are largedifferences in the KgC/LSU between certain genotypes, points to genetic differencesand holds the potential for improvement through selection and the use ofcomplementarity between breeds.An effective way to reduce the carbon footprint from beef production and to supportclimate smart production, is to reduce the cattle numbers and increase the productionper animal. This study attempted to identify novelty traits as possible selection criteriato improve cow-calf efficiency in extensive systems, as well as the quantification ofcrossbreeding results to demonstrate the effect of appropriate crossbreeding on cowefficiency.The first recommendation is to investigate possible selection criteria to increase theweaning weight of calves in relation to a cow LSU unit in extensive beef productionsystems. The combination of calf weight as a trait of the dam and dam weight in aselection index might be a feasible option. Another alternative could be to use therelationship between weight of calf produced and the estimated feed inputs requiredto sustain the cow and allowing her to provide for the calf. Normally, the traits in aselection index are weighed with their economic value. However, in this case the traitscan even be assigned weights that can be linked to carbon footprints or credits(sequestration) and not only economic weights.This study demonstrated that the correct use of crossbreeding can improve cowefficiency substantially. However, the commercial beef producers in South Africa facethe problem of choosing a breeding bull from bulls of different breeds, without havinga tool to compare the breeding potential of these bulls directly. Within breed EBV's areavailable, but cannot be used by commercial breeders to compare bulls across breeds.The second recommendation is therefore to consider the development of breedconversion factors that can be used to convert EBV's between breeds to the samescale.

[发布机构] University of the Free State