The effect of intramammary infection with coagulase-negative staphylococci in early lactating heifers on milk yield throughout first lactation revisited

Abstract

The objective of this study was to further scrutinize the previously found positive association between intramammary infection (IMI) caused by coagulase-negative staphylococci (CNS) in early lactating heifers and test-day daily milk yield (MY) throughout first lactation, with a specific focus on the effect of the heifers' genetically determined milk production levels and the incidence of clinical mastitis. Two precise longitudinal data sets were analyzed using a series of statistical models including potential confounding and intermediate variables. The final database included the IMI status at calving, composite milk somatic cell count (SCC) and MY records at test day up to 285 d in milk (DIM), farmer-recorded clinical mastitis (CM) cases between 14 and 285 DIM, estimated new IMI incidence based on a SCC threshold of 100,000 cells/mL between 14 and 285 DIM, DIM, average 305-d MY at the herd level, and the heifers' genetic merit for MY from 240 dairy heifers from 29 dairy herds. Seventy-one (29.6%) early lactating heifers were noninfected, 108 heifers (45.0%) were CNS infected, and 61 heifers (25.4%) were infected with any major pathogen. The positive effect of CNS IMI in early lactation on test-day MY was estimated at 1.32 kg/d using a first basic mixed regression model. Correcting for the confounder genetic merit for MY reduced this effect to 1.17 kg. Interestingly, taking into account the confounding effect of herd resulted in an increase of the estimate from 1.32 to 2.2 kg/d. The positive effect of CNS IMI in early lactation on MY after correcting the model for both confounders was estimated at 2.05 kg/d. Heifers infected with CNS in the first DIM tended to have fewer CM cases throughout lactation compared with the noninfected herd mates. Including the intermediate variable CM in the model explained 0.16 kg/d of the corrected effect of 2.05 kg/d. Inclusion of test-day SCC, another intermediate variable, however, increased the estimate by 0.11 kg/d. With an appropriate correction for several confounders and biologically understood intermediate variables such as CM, test-day SCC, and new IMI based on SCC threshold of 100,000 cells/mL, an unexplained test-day MY difference between CNS-infected and noninfected heifers of 2.0 kg/d remained.

Factors associated with intramammary infection in dairy cows caused by coagulase-negative staphylococci, Staphylococcus aureus, Streptococcus uberis, Streptococcus dysgalactiae, Corynebacterium bovis, or Escherichia coli

“…The positive association between milk yield and mastitis in dairy cows has been reported previously (Heringstad et al, 2003;Koivula et al, 2005;Negussie et al, 2008;Oltenacu and Broom, 2010). An IMI caused by CNS, in particular, has been associated with high milk production; some researchers have even suggested that CNS IMI could positively affect milk production (Piepers et al, 2010(Piepers et al, , 2013. However, decreases in milk production due to mastitis is an established phenomenon (Seegers et al, 2003;Hertl et al, 2014;Detilleux et al, 2015).…”

Technical note: A pilot study using a mouse mastitis model to study differences between bovine associated coagulase-negative staphylococci

“…The development and validation of molecular identification techniques specifically for bovine-associated CNS were the basis to eliminate this confusion (Zadoks and Watts, 2009). Whereas older studies dealt with CNS as one homogenous and coherent group (Schukken et al, 2009;Piepers et al, 2010;Piepers et al, 2013), more recent studies addressed the CNS species separately, revealing heterogeneous characteristics between them (Avall-Jääskeläinen et al, 2013). In essence, 12 CNS species are frequently isolated from bovine milk.…”

<b>Impact of subclinical mastitis on milk yield and economic return of dairy cows</b>

“…as it was part of the selection criteria. The magnitude of the difference, as well as the significantly higher total neutrophils, total macrophages, total lymphocytes, and total phagocytes was consistent with expectations, similar to other studies (PILLAI et al, 2001;DOSOGNE et al, 2003; SCHWARZ et al, 2011a,b;PILLA et al, 2012;PILLA et al, 2013). SCHWARZ et al (2011b) showed that PMNL in milk samples with SCC values < 6.25×10 3 cells/mL were rare (mean proportion = 15%).…”

“…Some studies reported a significant negative effect of mastitis caused by CNS on milk yield (GROHN et al, 2004;LEITNER et al, 2006). In contrast, a recent study (PIEPERS et al, 2013) found a higher daily milk yield from heifers with subclinical CNS IMI (2.0 kg/d), as compared to non-infected heifers. It has been suggested that this might be attributed to a protective effect of the current CNS infection against a subsequent infection caused by a major pathogen (PIEPERS et al, 2013).…”

“…However, studies comparing contralateral mammary quarters of the same cow could be an alternative approach, since they are anatomically isolated and have similar milk yield when they are healthy (GONCALVES et al, 2016 for MC can be a disadvantage as the process is susceptible to contamination. Furthermore, traditional methods using MC can be labor-intensive and it may take up to 2-7 days to reach a diagnosis (BARREIRO et al, 2010).The milk leukocyte differential (MLD) has been investigated for potential in diagnosis of mastitis (DULIN; PAAPE; WEINLAND, 1982;KELLY et al, 2000;PILLAI et al, 2001;DOSOGNE et al, 2003; SCHWARZ et al, 2011a,b;PILLA et al, 2012;PILLA et al, 2013).The MLD can detect changes in proportions of cell types in milk independently of the SCC, which could provide information about inflammatory processes in quarters otherwise considered healthy (PILLA et al, 2012). This information could be useful when control programs for milk pathogens are being applied (PILLA et al, 2013).…”