Effects of Selective Dry Cow Treatment on Intramammary Infection Risk after Calving, Cure Risk during the Dry Period, and Antibiotic Use at Drying-Off: A Systematic Review and Meta-Analysis of Current Literature (2000–2021)

The objectives of this paper were (i) to perform a systematic review of the literature over the last 21 yr and (ii) to evaluate the efficacy of selective dry cow treatment (SDCT) vs. blanket dry cow treatment (BDCT) in dairy cows regarding the risk of intramammary infection (IMI) after calving, new IMI risk after calving, cure risk during the dry period, and a reduction in antibiotic use at drying-off by meta-analysis. The systematic search was carried out using the databases PubMed, CAB Direct, and ScienceDirect. A meta-analytical assessment was performed for each outcome of interest using random-effects models, and the relative risk (RR) for IMI and cure or the pooled proportion for antibiotic use was calculated. The final number of included studies was n = 3 for IMI risk after calving and n = 5 for new IMI risk after calving, cure risk during the dry period, and antibiotic use. The RR levels for IMI (RR, 95% confidence interval [CI]: 1.02, 0.94–1.11; p = 0.592), new IMI (RR, 95% CI: 1.06, 0.94–1.20; p = 0.994), and cure (RR, 95% CI: 1.00, 0.97–1.02; p = 0.661) did not differ significantly between SDCT and BDCT. Substantial heterogeneity was observed between the trials regarding the pooled proportion of antibiotic use within the SDCT groups (I2 = 97.7%; p < 0.001). This meta-analysis provides evidence that SDCT seems to be an adequate alternative to BDCT regarding udder health with a simultaneous reduction in antibiotic use. Limitations might arise because of the small number of studies included.

62 Feeding Chicory-plantain Silage and Se-yeast to Lactating Ewes Subjected to Intramammary Infection: Effect on the Immune System

The objective was to test the effect on the immune status by feeding a combination of chicory-plantain and Se-yeast in lactating ewes subjected to intramammary infection (IMI) with 2×107CFU of Strep uberis in both glands. For the purpose we enrolled 28 Polypay lactating sheep from a prior study where they were randomly allocated to receive chicory (CS) or grass (GC) silage and either 3.6 mg of Se/day as Se-yeast (DiaMune, Diamond V) (Y) or isoenergetic-isonitrogenous alfalfa meal (C) for 2 months. For the present study, ewes were kept on the original dietary regiment except the CT group received a chicory-plantain silage(50% each). Blood was collected prior to and for 10 days after IMI for a complete blood count(VetScan HM5), leukocytes migration, and rectal temperature (RT). Data were analyzed using GLIMMIX (SAS)with time, silage type, and Se and their interactions as the fixed effects and ewe as random effect with significance declared at P ≤ 0.05. RT was lower in chicory vs. grass before IMI and Se limited the RT increase after IMI. Total WBC levels tended (P = 0.06) to increase in animals fed with Se after IMI, which was driven by a larger number of lymphocytes. Hematocrit, red blood cells, and hemoglobin were strongly decreased by IMI. The mean cell volume was overall larger in ewes fed with chicory-plantain silage while mean cell hemoglobin was larger in animal fed with grass silage. The platelet distribution width was affected by silage*Se interaction due to a positive effect by Se in grass-fed but negative in chicory-plantain-fed ewes. Migration of neutrophils was larger in animals fed with chicory-plantain before IMI but similar between groups after IMI. Overall, these findings indicate that Se supplementation can increase lymphocytes with no effect on neutrophils while activity of neutrophils is positively affected by feeding chicory-plantain silage.

64 Feeding Chicory-plantain Silage and Se-yeast on Lactating Ewe Subjected to Intramammary Infection: Effect on Performance and Milk Quality

Our objective was to test the effect on milk yield and quality of feeding a combination of chicory-plantain and Se-yeast in lactating ewes subjected to intramammary infection (IMI). For this purpose, we enrolled 28 Polypay ewes from a prior study where they received chicory (CS) or grass (GC) silage and supplemented with 3.6 mg of Se/day as Se-yeast (DiaMune, Diamond V) (Y) or not (C) for 2 months. For the present study, ewes were kept on the original dietary regiment except the CS group received a chicory-plantain silage (50% each). Ewes were milked twice daily and milk was collected for analysis of components and somatic cell count (SCC). IMI was induced by injecting 2×107 CFU of Strep. uberis in both glands. Data were analyzed using GLIMMIX (SAS) with time, silage, and Se and their interactions as the fixed effects and ewe as random effect with significance declared P ≤ 0.05. SCC increased 8-fold 24h post-IMI and remained at that level until the end of the experiment with higher values pre-IMI in GC-Y animals but no difference post-IMI. Milk yield drastically decreased post-IMI but was not affected by treatments. Protein, fat, solids, amount of de novo fatty acids, and amount of C16:0 were larger in milk of ewes fed chicory-plantain compared to grass silage. Supplementation of Se had minor effect on milk components with a tendency (P = 0.07) to decrease fat, solids, and amount of de novo fatty acids. Amounts of C18:0, C18:1, and preformed fatty acids in milk were increased by Se supplementation in ewes fed grass while decreased in ewes fed chicory. The use of Strep. uberis was effective in inducing IMI in ewes with chicory-plantain improving several milk components while Se supplementation had minor effects. The combination of chicory and Se did not improve the response to IMI.

Intramammary Immunisation Provides Short Term Protection Against Mannheimia haemolytica Mastitis in Sheep

Mastitis affects both dairy and meat/wool sheep industries with losses due to reductions in milk quality and quantity, increased treatment costs and restricted lamb growth. Effective vaccines would be important tools for mastitis control. However, the development of vaccines against mastitis has proved challenging due to the failure to target protective immunity to the mammary gland. In order to target responses to the mammary gland, this study tested whether local administration directly into the gland through the teat canal or in the udder skin confers protection against an intramammary infection. In this study, we tested a vaccine that confers protection against respiratory disease caused by Mannheimia haemolytica to determine if it also protects against intramammary infection by the same organism. No evidence of protection was observed in animals that received a subcutaneous immunisation in the udder skin, however, intramammary immunisation provided almost complete protection against an experimental challenge administered 7 days post immunisation but not if the challenge was delivered 14 days post immunisation. To investigate further the nature of this variation in response, the somatic cell count and concentration of cytokines Interleukin-1β, Interleukin-10 and Interleukin-17A was determined in milk over the course of each study. Intramammary immunisation induced an inflammatory response within the mammary gland, characterised by increases in SCC and in the production of cytokines IL-1β, IL-10, and IL-17A. This response was similar to that observed in un-vaccinated control animals post challenge. The SCC and cytokine levels had returned to levels comparable with un-vaccinated controls prior to challenge at both 7 and 14 days post immunisation. The transient nature of the protective effect is consistent with the priming of an innate antibacterial response within the mammary gland which provides protection against challenge at 7 days but is diminished by 14 days post-vaccination. Further studies are planned to determine the nature of the innate immune mechanisms associated with the protective effect described here to determine whether it may be exploited to improve ruminant udder health.