Volume 22 • Issue 03 • 2018 major contributor to the pathogenesis , it is not clear how to avoid a reduction in voluntary intake , which occurs in some cows even in the absence of any social stressors such as group changes and by eliminating competition for bunk space by feeding cows individually ( unpublished observation ). Although overcrowding affects feeding behavior ( Olofsson , 1999 , Proudfoot et al ., 2009 ), there is no evidence that stocking rate affects metritis incidence ( Silva et al ., 2014 ). Nevertheless , it seems prudent to avoid overcrowding of dry cows , frequent group changes and mixing heifers and older cows . Hygiene plays a role in metritis prevalence , and attention should be paid to hygiene in calving pens ( Schuenemann et al ., 2011 ). Herds using straw bedding in calving pens have lower incidence of metritis than those using other forms of bedding ( Kaneene and Miller , 1994 ). Recently a multivalent vaccine has been reported to reduce risk of metritis in dairy cows ( Machado et al ., 2014 ) and is currently in clinical trials .
There is some prospect of genetic selection for reduction of metritis incidence . Some investigators have reported heritability of metritis to be as high as 0.19 and 0.26 for primiparous and second lactation cows , respectively ( Lin et al ., 1989 ). Others have reported more modest heritability , ranging from 0.02 to 0.07 ( Lyons et al ., 1991 , Zwald et al ., 2004b , a ). We have observed large differences in metritis incidence in first lactation daughters of different bulls calving in the same year in one large herd ( see Table 1 ). Polymorphisms in genes encoding toll like receptors and the leptin receptor gene have been linked to metritis incidence ( Oikonomou et al ., 2009 , Pinedo et al ., 2013 ). As this is currently an area of active research more concrete guidelines are likely to emerge .
Pyometra
Pyometra occurs as a specific postpartum condition in postpartum cows . It is characterized by the accumulation of purulent or mucopurulent exudates in the uterus in the presence of an active corpus luteum in acyclic cows . It affects about 4 % of dairy cows each lactation ( Akordor et al ., 1986 ), but its incidence may be increased by routine use of GnRH in the early postpartum period ( Etherington et al ., 1984 ). In general , ovulation is delayed in cows with significant uterine pathogen load ( Sheldon et al ., 2002 ) but if cows do ovulate in the face of ongoing uterine contamination they risk development of pyometra , as the endometrial damage may impair endogenous release of PGF2α . Traditionally T . pyogenes have been the most common bacteria isolated from cases of pyometra ( Ribeiro et al ., 2015 ) but metagenomic methods demonstrate prevalence of F . pyogenes in affected animals ( Knudsen et al ., 2015 ). A specific form of pyometra is also seen in cows infected with Tritrichomonas foetus ( BonDurant , 1997 ) and is not considered further here .
The treatment of choice for pyometra is PGF2α or its analogs ( de Kruif et al ., 1977 , Fazeli et al ., 1980 , Ott and Gustafsson , 1981 , Paisley et al ., 1986 , el-Tahawy Ael and Fahmy , 2011 ). Treatment results in luteolysis , behavioral estrus , expulsion of accumulated exudate and bacteriological clearance of the uterus in about 90 % of treated cases . Recurrence of pyometra after a single treatment occurs in 9 to 13 % of cases ( de Kruif et al ., 1977 , Fazeli et al ., 1980 ). First service conception rate of approximately 30 % or more follows treatment , but 80 % of animals may be expected to conceive within 3 to 4 inseminations ( de Kruif et al ., 1977 , Ott and Gustafsson , 1981 ).
Estrogens , in the form of estradiol cypionate of diethyl stilbestrol , have also been used for the treatment of pyometra . ( Such use is now illegal in many countries .) It should be remembered that estrogens are luteolytic in cows . The clinical response to estrogen therapy is poorer than that expected after treatment with PGF2α ( Fazeli et al ., 1980 ), and posttreatment conception results are poorer . Both a higher ( de Kruif et al ., 1977 ) and a lower ( Fazeli et al ., 1980 ) incidence of cystic ovarian disease after treatment of pyometra with estrogens relative to prostaglandins , has been reported . In one study ( Fazeli et al ., 1980 ), nitrofurazone infusion into the uterus was combined with either estradiol or prostaglandin treatment . In both cases , the use of nitrofurazone significantly depressed posttreatment conception rates . These data provide additional evidence against intrauterine infusion as a modality of treatment for bovine uterine disorders .
Endometritis
Endometritis ( sometimes referred to as subclinical endometritis ) is defined as inflammation of the endometrium . It is a local disease and is not accompanied by systemic signs . It typically occurs in clinically relevant form after 4 weeks postpartum . Endometritis requires endometrial cytology ( Gilbert et al ., 1993 , Gilbert et al ., 1998 , Gilbert et al ., 2005 , Dubuc et al ., 2010b ) or biopsy ( Bonnett et al ., 1993 ) for convincing diagnosis , but its presence can be inferred from the pH , protein or leukocyte esterase concentration of recovered uterine lavage fluid ( Cheong et al ., 2012 , Denis- Robichaud and Dubuc , 2015 ), or more simply the
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