Evaluation of genetic trends for traits of economic importance in South African Holstein cattle

Discipline: genetic evaluation; 

Genetic evaluation for the South African dairy industry has kept pace with global advances in statistical methodology. Increasingly accurate estimated breeding values (EBVs), produced routinely in the past two or three decades, have aided selection decisions. This has been coupled with an increase in the number of traits officially recorded and for which EBVs are calculated. Currently, EBVs are routinely published for more than 20 traits for the major dairy breeds. It is, however, important to monitor genetic trends from time to time to understand whether the dairy industry in general and a particular breed specifically are moving forward.  

The current study, therefore, was conducted to assess the genetic trends realized for traits of economic importance in the South African Holstein population, for the period from 1983 to 2008. Performance and pedigree data of 1231930 animals were used to calculate EBVs for these traits by a multi-trait animal model. The resulting EBVs in turn were used to compute annual mean rates of genetic change.

It was quite alarming to find that genetic trends for milk yield have decreased by approximately 57% during the decade from 1990 to 2000 and have reached stasis in 2005 - 2007. Calving interval and somatic cell count also deteriorated over much or all of the period investigated. It should be recognized that a comparatively small number of farmers participate in milk recording, which may affect the representativeness of the sample of animals used in the analysis. Nevertheless, given the widespread availability of genetic evaluations for these traits and the potential for selection to implement favourable genetic trends, development of strategies to improve the South African Holstein appears to be urgently needed.

Reference

Ramatsoma, N.I., Banga, C.B., MacNeil, M.D. & Maiwashe, A., 2014. Evaluation of genetic trends for traits of economic importance in South African Holstein cattle. S.Afr. J. Anim. Sci. 44, 85 – 89. 

Since the results of the Ramatsoma study are quite alarming, it was decided to investigate further and Dr Bernice Mostert of Stud Book did a further analysis on 1181008 animals from 2870 farms. Two important differences between the data sets of Dr Mostert and of Ms Ramatsoma are that Dr Mostert’s data included primarily herds of stud animals whereas that of Ms Ramatsoma also included a comparatively large proportion commercial animals, and secondly the time frame used by Dr Mostert was from 1983 to 2011 with base year 2005, whereas Ms Ramatsoma used 1983 to 2009 with base year 2001. The model methodology also differed somewhat, which makes direct comparison difficult. Nevertheless, the interpretations of the two studies were the opposite.                                   

As a result, further opinions were obtained, that of respectively Dr Michiel Scholtz of the ARC and Prof Frikkie Neser of the UFS. Dr Scholtz’ opinion was that a shortcoming in both studies was that environmental and phenotypic trends were not reported, which would have provided a clearer picture. Prof Neser expressed the opinion that the Holstein breed (stud and commercial) has made considerable progress in milk yield, fat and protein, but may have gone backwards in terms of SCC, calving interval and longevity.    

Interestingly, Dr Mostert also used two so-called bio-economical indices, namely the Holstein Merit Index (HMI), with most weight on Protein Yield and the Fluid Milk Index (FMI), with most weight on Milk Yield. Other components of the indices are Functional Herd Life, Daughter Fertility, Udder, Udder Health, Frame Size and Feet & Legs. These indices are expressed in Rand and indicate an animal’s superiority or inferiority relative to that of the base cows. These were the results of extensive simulation processes taking all possible factors contributing towards dairy herd productivity into account. Not only are biological aspects (such as production parameters, reproduction and herd life) considered, but also management costs (time and direct costs) related to treatment and prevention of conditions negatively affecting production efficiency. It is based on current economic tendencies with regards to milk pricing, feed prices, veterinary costs related to treatment, labour costs and management costs in South African production systems and the local economic environment. 

The trends of these bio-economical indices indicate sound improvement over many years in all traits that contribute to economical production of the SA Holstein breed. However, the size of the sample and the fact that it is based primarily on stud animals must be taken into account. It is evident that this type of investigations are regularly required and from larger and more representative numbers.