@article{dhakal_tiezzi_clay_maltecca_2015, title={Inferring causal relationships between reproductive and metabolic health disorders and production traits in first-lactation US Holsteins using recursive models}, volume={98}, ISSN={["1525-3198"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84925299358&partnerID=MN8TOARS}, DOI={10.3168/jds.2014-8448}, abstractNote={Health disorders in dairy cows have a substantial effect on the profitability of a dairy enterprise because of loss in milk sales, culling of unhealthy cows, and replacement costs. Complex relationships exist between health disorders and production traits. Understanding the causal structures among these traits may help us disentangle these complex relationships. The principal objective of this study was to use producer-recorded data to explore phenotypic and genetic relationships among reproductive and metabolic health disorders and production traits in first-lactation US Holsteins. A total of 77,004 first-lactation daughters' records of 2,183 sires were analyzed using recursive models. Health data contained information on reproductive health disorders [retained placenta (RP); metritis (METR)] and metabolic health disorders [ketosis (KETO); displaced abomasum (DA)]. Production traits included mean milk yield (MY) from early lactation (mean MY from 6 to 60 d in milk and from 61 to 120 d in milk), peak milk yield (PMY), day in milk of peak milk yield (PeakD), and lactation persistency (LP). Three different sets of traits were analyzed in which recursive effects from each health disorder on culling, recursive effects of one health disorder on another health disorder and on MY, and recursive effects of each health disorder on production traits, including PeakD, PMY, and LP, were assumed. Different recursive Gaussian-threshold and threshold models were implemented in a Bayesian framework. Estimates of the structural coefficients obtained between health disorders and culling were positive; on the liability scale, the structural coefficients ranged from 0.929 to 1.590, confirming that the presence of a health disorder increased culling. Positive recursive effects of RP to METR (0.117) and of KETO to DA (0.122) were estimated, whereas recursive effects from health disorders to production traits were negligible in all cases. Heritability estimates of health disorders ranged from 0.023 to 0.114, in accordance with previous studies. Similarly, genetic correlations obtained between health disorders were moderate. The results obtained suggest that reproductive and metabolic health disorder and culling due to metabolic and reproductive diseases have strong causal relationships. Based on these results, we concluded that a health disorder (either reproductive or metabolic) occurring in early lactation has a moderate causal effect on the reproductive or metabolic health disorder occurring in later lactation. In addition, direct, indirect, and overall effects of reproductive and metabolic health disorders on milk yields for cows that avoid culling are weak.}, number={4}, journal={JOURNAL OF DAIRY SCIENCE}, publisher={Elsevier}, author={Dhakal, K. and Tiezzi, F. and Clay, J. S. and Maltecca, C.}, year={2015}, month={Apr}, pages={2713–2726} }
 @article{dhakal_tiezzi_clay_maltecca_2015, title={Short communication: Genomic selection for hoof lesions in first-parity US Holsteins}, volume={98}, ISSN={["1525-3198"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84928093134&partnerID=MN8TOARS}, DOI={10.3168/jds.2014-8830}, abstractNote={Hoof lesions contributing to lameness are crucial economic factors that hinder the profitability of dairy enterprises. Producer-recorded hoof lesions data of US Holsteins were categorized into infectious (abscess, digital and interdigital dermatitis, heel erosion, and foot rot) and noninfectious (korn, corkscrew, sole and toe ulcer, sole hemorrhage, white line separation, fissures, thin soles, and upper leg lesions) categories of hoof lesions. Pedigree- and genomic-based univariate analyses were conducted to estimate the variance components and heritability of infectious and noninfectious hoof lesions. A threshold sire model was used with fixed effects of year-seasons and random effects of herd and sire. For genomic-based analysis, a single-step procedure was conducted, incorporating H matrix to estimate genomic variance components and heritability for hoof lesions. The pedigree-based analysis produced heritability estimates of 0.11 (±0.05) for infectious hoof lesions and 0.08 (±0.05) for noninfectious hoof lesions. The single-step genomic analysis produced heritability estimates of 0.14 (±0.06) for infectious hoof lesions and 0.12 (±0.08) for noninfectious hoof lesions. Approximated genetic correlations between hoof lesion traits and hoof type traits along with productive life and net merit were all low and ranged between -0.25 and 0.14. Sire reliabilities increased, on average, by 0.24 and 0.18 for infectious and noninfectious hoof lesions, respectively, with incorporation of genomic data.}, number={5}, journal={JOURNAL OF DAIRY SCIENCE}, author={Dhakal, K. and Tiezzi, F. and Clay, J. S. and Maltecca, C.}, year={2015}, month={May}, pages={3502–3507} }
 @article{dhakal_maltecca_cassady_baloche_williams_washburn_2013, title={Calf birth weight, gestation length, calving ease, and neonatal calf mortality in Holstein, Jersey, and crossbred cows in a pasture system}, volume={96}, ISSN={["0022-0302"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84871620780&partnerID=MN8TOARS}, DOI={10.3168/jds.2012-5817}, abstractNote={Holstein (HH), Jersey (JJ), and crosses of these breeds were mated to HH or JJ bulls to form purebreds, reciprocal crosses, backcrosses, and other crosses in a rotational mating system. The herd was located at the Center for Environmental Farming Systems in Goldsboro, North Carolina. Data for calf birth weight (CBW), calving ease (0 for unassisted, n=1,135, and 1 for assisted, n=96), and neonatal calf mortality (0 for alive, n=1,150, and 1 for abortions recorded after mid-gestation, stillborn, and dead within 48 h, n=81) of calves (n=1,231) were recorded over 9 calving seasons from 2003 through 2011. Gestation length (GL) was calculated as the number of days from last insemination to calving. Linear mixed models for CBW and GL included fixed effects of sex, parity (first vs. later parities), twin status, and 6 genetic groups: HH, JJ, reciprocal F(1) crosses (HJ, JH), crosses >50% Holsteins (HX) and crosses >50% Jerseys (JX), where sire breed is listed first. The CBW model also included GL as a covariate. Logistic regression for calving ease and neonatal calf mortality included fixed effects of sex, parity, and genetic group. Genetic groups were replaced by linear regression using percentage of HH genes as coefficients on the above models and included as covariates to determine various genetic effects. Year and dam were included as random effects in all models. Female calves (27.57±0.54 kg), twins (26.39±1.0 kg), and calves born to first-parity cows (27.67±0.56 kg) had lower CBW than respective male calves (29.53±0.53 kg), single births (30.71±0.19 kg), or calves born to multiparous cows (29.43±0.52 kg). Differences in genetic groups were observed for CBW and GL. Increased HH percentage in the calf increased CBW (+9.3±0.57 kg for HH vs. JJ calves), and increased HH percentage in the dams increased CBW (+1.71±0.53 kg for calves from HH dams vs. JJ dams); JH calves weighed 1.33 kg more than reciprocal HJ calves. Shorter GL was observed for twin births (272.6±1.1 d), female calves (273.9±0.6 d), and for first-parity dams (273.8±0.6 d). Direct genetic effects of HH alleles shortened GL (-3.5±0.7 d), whereas maternal HH alleles increased GL (2.7±0.6 d). Female calves had lower odds ratio (0.32, confidence interval=0.10-0.99) for neonatal calf mortality in second and later parities than did male calves. Maternal heterosis in crossbred primiparous dams was associated with reduced calf mortality.}, number={1}, journal={JOURNAL OF DAIRY SCIENCE}, author={Dhakal, K. and Maltecca, C. and Cassady, J. P. and Baloche, G. and Williams, C. M. and Washburn, S. P.}, year={2013}, month={Jan}, pages={690–698} }