SLOVENIAN VETERINARY RESEARCH

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Slov Vet Res 2013; 50 (2): 57-66UDC 636.2.03:616-076:637.1:618.7-07Original Scientific ArticleAssociations between the fat to protein ration inmilk, health status and reproductive performancein dairy cattleOžbalt Podpečan 1 *, Janko Mrkun 2 , Petra Zrimšek 21Savinian Veterinary Policlinic, Celjska c. 3/a, 3310 Žalec, 2Clinic for Reproduction and Horses, Veterinary Faculty, Gerbičeva 60,1000 Ljubljana, Slovenia*Corresponding author, E-mail: ozbalt.podpecan@gmail.comSummary: The aim of the present study was to evaluate pregnancy rates of 232 dairy cows in relation to fat to protein ratio(FPR) in milk, using survival analysis. Pregnancy rates of cows inseminated within 90 and 120 days postpartum in a group ofclinically healthy cows were 38 and 68 %, respectively. Lower pregnancy rates are observed in groups of cows with ketosisand reproductive disorders, 44 and 28 % for pregnancy rate within 120 days. The highest correlation between FPR and calvingto conception interval (CC) was observed between 30 and 60 days postpartum (r = 0.411, P < 0.001). Diagnostic evaluation ofFPR using ROC (receiver operating characteristics) analysis showed that FPR at 1.37 discriminates cows with CC below andabove 120 days with an accuracy of 71 %. Survival curves for the subgroups of animals with FPR below or above 1.37 differedsignificantly in the case of clinically healthy cows, where CC in subgroups were 87 ± 28 and 122 ± 42 days, respectively. Althoughsurvival curves for subgroups for cows with diseases did not differ significantly we observed longer CC in all subgroups withFPR > 1.37 than in subgroups with FPR < 1.37. In all groups pregnancy rates within 90 and 120 days were lower in subgroups withFPR > 1.37 than in subgroups with FPR < 1.37. Therefore, FPR can be used by bovine practitioners to predict fertility problemsin dairy herds.Key words: dairy cows; fat to protein ratio in milk; calving to conception interval; ROC analysis; survival analysisIntroductionIncreased fat mobilization in a period ofnegative energy balance (NEB) coupled withdecrease in dry matter and energy intake isshown in higher milk fat concentration and lowermilk protein concentration in the postpartumperiod of dairy cows (1). In the last fifteen yearsa correlation between energy balance in the earlyReceived: 1. July 2012Accepted for publication: 27 November 2012postpartum period and milk composition hasbeen reported, using different parameters suchas fat to protein ratio (FPR), protein to fat ratio,fat/lactose quotient, milk yield and milk proteinconcentration (2, 3, 4, 5). Buttchereit et al. (6)showed FPR to be a suitable indicator of the energystatus in postpartum dairy cows. FPR indicates lowenergy balance more reliably than body conditionscore (BCS) (7). A FPR threshold of 1.4 duringthe first month of lactation is commonly used byveterinary practitioners as a marker of NEB (8).FPR is also used as a diagnostic tool to estimate
58O. Podpečan, J. Mrkun, P. Zrimšeksome metabolic disorders such as subclinical andclinical ketosis (1, 7).Geishauser et al. (9) found that FPR in thefirst test milk could be useful as a predictor forsubsequent abomasal displacement. Clinicalmastitis appears most commonly in the first30 days postpartum (10). Increased incidenceof mastitis during early lactation or at peakproduction could result from a severe NEB (11,12) severity of induced E coli mastitis has beenrelated to some blood metabolite concentrationscharacteristic of NEB (13). Animals exposed tosevere NEB suffer from impaired reproductiveperformance (14, 15, 16) which can be shown asabsence of oestrus signs, delayed onset of cyclicity,failure to conceive at 1 st artificial insemination(AI) and finally in prolonged calving to conceptioninterval. Moreover, FPR was recently assessed asa predictor of calving to conception interval (CC) ofindividual cows, using fixed thresholds (17).The aim of the present study was to evaluatepractical use of milk and medical data recordsin association with reproductive performance inhigh yielding dairy cows. We evaluated pregnancyrates of dairy cows in relation to FPR in milk,using survival analysis. First, a complete receiveroperating characteristics (ROC) analysis, wasperformed to provide an index of accuracy bydemonstrating the limits of the test’s ability todiscriminate between healthy cows pregnantat day 90 (or day 120) after calving or not (18).Groups of clinically healthy cows and cows withketosis, clinical mastitis or fertility problems werecompared using Kaplan-Meier survival curves.Material and methodsAnimals and dataRecords of 232 high yielding dairy cows(Holstein-Friesian), BVD and IBR-IPV free, ina period from April 2009 to June 2010 formeda basis for the study. Cows were kept in a freestallbarn system. The basic ration was composedof hay, grass and maize silage. According to themilk yield, protein concentrate (19 % digestibleraw protein), roughly crushed maize grains andvitamin-mineral mixture were supplementedby a computerised feeding system. All cowscould access basic ration and water ad libitumduring the whole year in the stall. The voluntarywaiting period of the herd was 80 days. Theywere inseminated by a well trained inseminator.Reproduction parameters, calving to 1 st service(CFS), 1 st service to conception (FSC) and calvingto conception (CC) intervals were derived fromfarm records. All animals showing clinical signsof disease were examined and treated by bovinepractitioners using standardized protocols.Treatment data were recorded for every animalindividually. Animals were divided into 5 groupsaccording to occurrence of different diseases in thefirst 90 days post partum (p.p.) (Table 1): Group 1:clinically healthy cows; Group 2: cows with clinicalketosis (diagnose based on clinical signs and milktests with sodium nitoprosside); Group 3: cowswith clinical mastitis; Group 4: cows with fertilityproblems (included gynaecological disorders suchas retained placenta, puerperal metritis, cysticovarian disease and endometritis); Group 5: othercows.Milk sampling and analysisDaily milk yield was measured and milk sampleswere collected at regular test days performed in a30 day intervals in the post partum period at threestages: stage 1, 0 – 30 days post partum; stage2, 30 – 60 days post partum; stage 3, 60 – 90days post partum. Samples were conserved withsodium azide and sent, at outdoor temperature, toa dairy research laboratory. Protein and fat wereanalysed in milk samples using Fourier TransformInfrared Spectroscopy (CombiFoss 6000).Statistical analysisGroups of cows were compared with respect toCFS, FSC, CC, milk yield and FPR at stages 1, 2and 3, using One way analysis of variance in thecase of normal distribution of the data or Kruskal-Wallis one way analysis of variance on ranks inthe case of non-normal distribution of data. Whena significant difference among the groups wasfound, further pair-wise multiple comparisonswere performed using the Holm-Sidak method(normal data distribution) or Dunn’s method(non-normal data distribution).FPRs in stages 1, 2 and 3 were compared withineach group using One way repeated measuresanalysis of variance or Friedman repeatedmeasures analysis of variance on ranks, according
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