Genetic parameters of calving ease in dairy cattle using threshold and linear models

Abstract

Genetic parameters of direct and maternal effects for calving ease (CE) in Portuguese dairy cattle were estimated applying a threshold model (TM) and three linear models (LM) using 320,953 CE records. In LM, CE scores were directly used as dependent variables (LM1) or were transformed into values on an underlying continuous liability scale (average and maximum values for LM2 and LM3, respectively). The estimate of heritability for direct effects was lower on linear models (0.04-0.05) than in TM (0.09). Furthermore, direct heritability was higher than maternal heritability, ranging between 0.04-0.09 and 0.01-0.02, respectively. The genetic correlation between direct and maternal effects was negative in all models, ranging between -0.75 and -0.82. We investigated the association between bulls estimated breeding values (EBV) attained by TM and three LM, for 2223 bulls. Results show that all correlations were higher than 0.95 and slightly greater correlations were observed for direct effects than for maternal effects. Particular emphasis was given to individual differences between EBV ranking lists. The average difference between rank positions of TM and the three LM ranged from 64 to 122. Therefore, the selection of breeding animals is influenced by the model's choice. Even with clear theoretical advantages in analysing categorical data, perhaps due to its more recent implementation, TM has not yet achieved the popularity of LM. The results of this work show that TM ranking list is more in accordance with LM2 than with LM1 or LM3. Therefore, with linear models, CE should be considered as average liability value instead of usual numerical score or maximum liability. ARTICLE HISTORY

112. Genetic and environmental influences on maternal calving difficulty in South African Holstein cattle

“…In some cases, calving difficulty is scored on a scale of up to 5, unlike the binary measurement used in the current study. Analysis of calving ease with linear models has been found to yield additive genetic variance estimates that are consistently smaller than those obtained with threshold models (Silvestre et al, 2019). A low repeatability estimate of 0.04±0.04 was observed for MCD across the first three parities, which is comparable to those reported in Iranian Holstein cows (Ghiasi et al, 2014).…”

“…Dystocia is also a welfare problem, as it causes pain and injury to the cow, which directly leads to poor cow welfare (Abdela and Ahmed, 2016). Furthermore, calving-related infections indirectly affect human health, as they require increased use of antibiotics, which contaminate the cow's milk, leading to possible microbial resistance (Silvestre et al, 2019).…”

Assessment of the genetic parameters and breeding value of bulls-producers of the Ukrainian black speckled milky breed by the main characteristics

“…The obtained estimates of heritability coefficients are close to those obtained by other researchers, in particular, Stefani et al (2021), although the heritability of milk yield at 305 days of lactation in this controlled study was higher (0.33 vs. 0.15). The use of a mixed linear threshold model allowed for a higher heritability coefficient for calving difficulty (0.1787) than when using linear models (Tomka, 2018;Silvestre et al, 2019), which allowed increasing the reliability of estimates of the breeding value of breeding bulls based on this feature. The decrease in milk yield for 305 days of lactation due to the difficult calving of cows is consistent with the data of other authors (Stefani et al, 2021).…”

“…Calving difficulty is expressed in points on 3-7-point scales (Tomka, 2018). In general, the difficulty of calving is characterised by low heritability -from 0.04 to 0.20 (Alam et al, 2017;Silvestre et al, 2019;Probo et al, 2022). Genetic assessment of calving difficulty is performed using a linear or threshold model.…”

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“…Calving difficulty is expressed in points on 3-7-point scales (Tomka, 2018). In general, the difficulty of calving is characterised by low heritability -from 0.04 to 0.20 (Alam et al, 2017;Silvestre et al, 2019;Probo et al, 2022). Genetic assessment of calving difficulty is performed using a linear or threshold model.…”