Discipline: mastitis; Keywords: SCC, test day records, lactation, province, season, breed, variation explained.
One of the key traits in profitable milk production is somatic cell count (SCC). It is used as a measure of udder health and management thereof in terms of cleanliness, cow health and selection is paramount. Over years, a substantial data base has accumulated from the milk recording and management system, allowing analyses from different perspectives to better understand factors influencing SCC. Some factors not normally thought of provide interesting results as shown by the author cited below.
Some 530 000 SA Holstein, Jersey and Ayrshire test day records – taken between 1 September 2016 and 31 August 2020 – were available to determine which variables have a significant influence on SCC. The variables tested were lactation number, stage of lactation, the province in which the cows were milked, year, season and breed.
The results showed that SCC increased with lactation number; by the third lactation SCC was almost double the SCC in the first lactation. The same trend was evident with stage of lactation; as lactation progressed, SCC increased, although first lactation cows tended to differ. Probably due to the stress of first calving the SCC was higher initially than in mid-lactation and then started to increase again towards late lactation. With regard to province, cows in North West, KZN and the Free State had significantly higher SCC that cows in Limpopo, Mpumalanga and Gauteng, but the effect of number of herds tested in the different provinces might have skewed the results. Other affecting factors per province include feeding and management environment, temperature and rainfall. The year 2017 showed the highest SCC (especially during winter), followed by 2018 and 2016. The lowest SCC’s were recorded in 2019. The 2017 levels were probably associated with the drought during that year. Although season played a roll, the influence of season was much smaller than the previous variables. The highest SCC’s were recorded in autumn. The breed effect was also very small and the influence could have been skewed because of unequal numbers.
The value of the results: Although highly significant, the amount of variation explained by the variables tested was only 18%. The overwhelming amount of variation (82%) is therefore attributed to management, animal health and genetics of the cow which need to be addressed by farmers.
D. Kruger, 2020. Factors that affect somatic cell count. Stockfarm no 41, November 2020.