Genetics of milking characteristics in dairy cows

Abstract

Genetic selection for milking speed is feasible. The existence of a correlation structure between milking speed and milk yield, however, necessitates a selection strategy to increase milking speed with no repercussion on genetic merit for milk yield. Residual milking duration (RMD) and residual milking duration including somatic cell score (RMDS), defined as the residuals from a regression model of milking duration on milk yield or milk yield plus somatic cell score (SCS) have been advocated. The objective of this study was to undertake a first ever genetic analysis of these novel traits. Data on electronically recorded milking duration and other milking characteristics from 235 005 test-day records on 74 608 cows in 1075 Irish dairy herds were available. Variance components for the milking characteristic traits were estimated using animal linear mixed models and covariances with other performance traits, including udder-related type traits, were estimated using sire models. The heritability of milking duration, RMD and RMDS was 0.20, 0.22 and 0.18, respectively. There were little differences in the heritability of RMD or RMDS when defined using genetic regression. The genetic standard deviation of RMDS defined on the phenotypic or genetic level was 36.8 s and 37.6 s, respectively, clearly indicating considerable exploitable genetic variation in milking duration independent of both milk yield and SCS. The genetic correlation between phenotypically derived RMDS and milk yield was favourable (20.43), but RMDS was unfavourably genetically correlated with SCS (20.30); the genetic correlations with both traits when RMDS was defined at a genetic level were zero. RMDS defined at the phenotypic level was negatively (i.e. unfavourable) genetically correlated (20.35; s.e. 5 0.15) with mastitis; however, when defined using genetic regression, shorter RMDS was not associated with greater expected incidence of mastitis. RMDS, defined at the genetic level, is a useful heritable trait with ample genetic variation for inclusion in a national breeding strategy without influencing genetic gain in either milk yield or udder health.

Analysis of milking characteristics in New Zealand dairy cows

“…Clearly, variations in milking characteristics between animals exist; however, to be useful for animal breeding genetic correlations and heritabilities, these variations require examination. The estimate of heritability in this study (0.27) is consistent with previous heritability estimates for electronically recorded milking duration, which vary from 0.11 to 0.30 (Zwald et al, 2005;Gray et al, 2011;Samoré et al, 2011;Berry et al, 2013b). Residual milking characteristics (RMD, RMF, and RMDS) can be useful for evaluating animals or groups of animals for their milking speed, irrespective of milk yield.…”

“…Residual milking characteristics (RMD, RMF, and RMDS) can be useful for evaluating animals or groups of animals for their milking speed, irrespective of milk yield. The moderate values of heritability (0.27-0.31) for residual milking characteristics were similar to the 0.18 to 0.22 reported by Berry et al (2013b) and indicate that these measures could be used in a selective breeding program to improve milking efficiency. The results of the current study indicate that this can be achieved without affecting milk yield because the genetic correlations of milk yield with RMD, RMF, and RMDS were almost zero.…”

“…Furthermore, European research has indicated that selection for average milk flow may lead to poorer udder health (Bahr et al, 1995;Gäde et al, 2007). Similarly, Berry et al (2013b) reported a genetic correlation of −0.30 between both RMD and RMDS and SCS. Somatic cell count data in the present study were only available as a composite of morning and afternoon and, therefore, were not suitable for the calculation of phenotypic and genetic correlations.…”

The potential of Fourier transform infrared spectroscopy of milk samples to predict energy intake and efficiency in dairy cows

“…No heritability estimates for REI predicted from milk FTIR exist in the literature. The genetic variance of REI can, however, be calculated as shown above (Berry et al, 2013b), where (co)variance components refer to the additive genetic (co)variance components estimated in this study, σ = variance, and EI = energy intake, MY = milk yield, FY = fat yield, PY = protein yield, LW = live weight, and BCS = body condition score. The phe-notypic variance for REI was calculated using the same approach but substituting phenotypic (co)variance components for the genetic (co)variance components.…”

Cross-sectional analyses of a national database to determine if superior genetic merit translates to superior dairy cow performance

“…Test-day milking duration data were obtained using Tru-Test electronic milk-recording meters in herds that performed "do-it yourself" milk-recording; details of the methodology for calculating milking duration are explained by Berry et al (2013a). Only milking duration data on 430,351 cow-lactations from 154,267 cows in 3,109 herds captured during the first 305 d of lactation were used.…”