Discipline: mastitis; Keywords: SCC, herd testing, rotary parlour, antimicrobial sensitivity, systematic extension and training, summer rise in SCC, year effect.
In a survey among dairy farmers in 2017, it was found that routine evaluation of cows, groups and/or herds for SCC was relatively low at 67% for cows and groups and 53% for whole herd testing. The majority of high SCC cows are however treated. Only 1% of dairy farmers reported to clip or flame udders. Approximately 50% of dairy farms pre-dip, lower than in some other parts of the world and approximately a third of producers either do not strip or wipe and/ or do not use gloves. Timing between individual steps of the milking routine was erratic within and between most of the dairy farms visited. Allowing for an ideal stimulation time of between 60 to 120 seconds, only 11.1% of rotary and 18.2% of other parlours were in this range. The average bulk milk SCC was 287 000 cells per mℓ and were similar across management types and regions. About two-thirds of farmers routinely identify cows with an elevated SCC, either by testing individual cows and/or groups. Of these, two-thirds consider cows with a SCC of more than 500 000 cells per ml eligible for treatment. The mastitis incidence of 31.8% was higher than the median of 20% to 25% seen elsewhere in the world and ranged from 3.5% to 93%. Milk samples for culture and microbial identification were collected on 29.2% of farms and 20.2% requested antimicrobial sensitivity, which is lower than world standards.
In this study, the majority of dairy farmers reported treating mastitis with intra-mammary antibiotics (86.3%), of which half also use injectable antibiotics (49.3%). One-fifth of the farmers reported using antibiotics in an off-label manner (including higher dosage, shorter treatment intervals and/or an extended duration of treatment), and not always doing so under the supervision of a veterinarian. The efficacy of using of injectable antibiotics, at 49.3%, must be questioned. The results of management procedures to control mastitis are disturbing. In addition, dairy farmers’ attitudes toward mastitis are alarming, with only a third testifying that they had sufficient knowledge of the condition. There certainly is a need for systematic extension and training as mastitis is costing the industry millions.
Dairy farms often experience a summer through autumn rise in SCC with some farms affected more than others. In a study, two groups of cows, referred to as high heat (HH) and low heat (LH) were established. When tested, HH and LH cows were responsible for 78% and 50% of the increase in SCC in summer respectively, and therefore it was concluded that season is a risk factor in the causal pathway towards summer rise in SCC. This was substantiated when the temperature-humidity index (THI) model was used, which showed that HH and LL cows produced 92% and 24% of the increase in SCC’s when transitioning from THI conditions below 65 to those above 70. When compared to the Central region, EC, KZN and WC had an increasing risk of producing more somatic cells in this context, with some farms having a very high number of HH cows of more than 70%, and these farms is expected to experience a more drastic summer rise in SCC.
In a large study on National Milk Recording Scheme cows, results showed that SCC increased with lactation number; 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. With regard to province, cows in North West, KZN and the Free State had significantly higher SCC than 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. The highest SCC’s were recorded in autumn. Breed effect was very small and the influence could have been skewed because of unequal numbers.
The value of these 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 should be addressed by farmers.
Meissner, H. H., 2021. Summary of Research Progress with Mastitis 2015 to 2021. Milk SA, Pretoria.