Diagnosing the silent repro threat: Subclinical metritisThe economic impact of one form of metritis versus others is hard to decipher since we are all still trying to come to a consensus about defining each condition the same way. We can all agree that collectively, all forms of metritis adversely impact reproductive performance and subsequently are very costly to dairy producers. In a Farm Report article a few months ago I discussed how confusing the lingo is when discussing metritis and subclinical forms of the disease. Nearly every veterinarian/researcher/dairy producer you ask will define them differently. As a review, we should adopt the following definitions outlined by Sheldon et al. (2006) which were published in the respected reproductive journal, Theriogenology:

Puerperal metritis – acute systemic illness (fever, loss of appetite and milk production) due to infection of the uterus with bacteria, usually within 10 days after calving.

Pyometra – the accumulation of pus in the body of the uterus in the presence of a persistent corpus luteum and a closed cervix.

Clinical endometritis – characterized by presence of vaginal discharge of >50% pus, 21 days or more after calving, and not accompanied by systemic signs.

Subclinical endometritis or metritis – inflammation of the lining of the uterus in the absence of pus-filled vaginal discharge.

The subclinical form of metritis, hereafter referred to as SM, is the toughest to diagnose since no outward signs are exhibited; no fever or vaginal discharge. The gold standard for its diagnosis is uterine cytology to determine presence of polymorphonuclear (PMN) cells, which are immune cells that act as a line of defense when inflammation occurs. If there are greater than 8% PMN cells found, the animal would be considered to have SM. Unfortunately, this method does not provide an on-farm diagnosis that immediately can be treated and requires the cytological evaluation in the lab of a veterinary clinic. 

During the spring of 2010, one of our Advanced Dairy Management students, Leanna Scholten, conducted a research project that evaluated different methods for diagnosing SM in Miner Institute’s herd with the hopes that an on-farm method or a combination of these methods might be used to accurately diagnose SM when compared to the cytological determination. A total of 29 animals between 21 and 40 days in milk were examined and found to have no signs of clinical endometritis: No vaginal discharge containing > 50% pus as determined by vaginoscopy and vaginal palpation. These animals were then evaluated for SM by using the following methods:

• Vaginal discharge assessment by vaginal speculum or vaginal palpation – presence of any pus < 50% of discharge would indicate presence of SM.

• Rectal palpation – cervical size assessed and palpation of fluid: An animal with a cervix >1.5 inches in diameter and/or has fluid present in a uterine horn may have SM. Size of the cervix may vary due to the number of calves a cow has delivered, however the cervix of a healthy animal will usually return to a size <1.5 inches after uterine involution.

• Uterine lavage – an infusion pipette used to deliver 20 cc of phosphate buffer saline into the uterus. After uterus massaged transrectally for 5-10 seconds, 2 cc of fluid aspirated using a syringe attached to the end of the infusion pipette. Fluid smeared onto a slide and stained using a modified Wright Giemsa stain then evaluated for cytology using a microscope to determine presence of PMNs.

• Cytobrush – an embryo transfer gun was modified to attach a cytobrush (see picture). The cytobrush was able to be retracted inside the ET gun when being passed through the cervix. Once inside the uterus, the cytobrush was extended beyond the ET gun and brushed gently against the uterine wall approximately ¼ turn, retracted back into the gun and removed from the cow. The brush was smeared across a microscope slide and stained to determine presence of PMN cells.

In this study, 6 out of the 29 animals were diagnosed with SM as determined by the cytobrush technique. The visual assessment of vaginal discharge from using a speculum or vaginal palpation accurately diagnosed 2 of the 6 cases and inaccurately concluded false positive for 3 cows. Half of the SM cases were accurately detected using the rectal palpation assessment; however, 8 cows were considered false positives. We determined from this study that none of the methods we evaluated, nor combinations of these methods, was a reliable on-farm diagnostic tool for assessing SM. The cytobrush was the most useful technique for assessing SM; however, it is difficult to recommend this tool as a routine method for screening cows for SM since the cost/benefit ratio is unknown. To my knowledge, cytobrushes designed for use in dairy cattle are not commercially available. From a research standpoint, I think the cytobrush will provide a useful tool for assessing uterine health as we conduct transition cow studies.

Editor's note: This article first appeared in the October 2011 issue of the Miner Institute's Farm Report.