This study was undertaken to investigate the environmental factors affecting
production, fertility and health traits of dairy cows and to estimate the genetic
parameters and ( co )variance components of these traits and associations among
them. Production traits studied were Milk yield (MY), Fat yield (FY) and Protein
yield(PY). Fertility traits were Calving interval (CI), Days to first service (DTFS),
Days open (DO), Number of services per conception (NSPC) and Conception to
first service (CTFS). Health traits were Mastitis and Lameness. Data were from
Livestock Services UK (LSUK) LTD.
Range of values for the traits, across data sets were 6182-7888kg, 24 l308kg and 201-256kg for MY, FY and PY respectively. Mean lactation length
ranged from 300-320 days and mean calving age from 29-65 months. Average
values for traits, across data sets, were 396-407 days, 81-90 days, 101-107 days, 1.4-1.6 and 60-68% for CI, DTFS, DO, NSPC and CTFS respectively. Incidence of mastitis and lameness across all herds was 0.8-2.0% and in data sets with only herds where mastitis and/or lameness were recorded was 9.0-10.0% and 5-6% respectively.
Breed (British-Holstein vs Holstein-Friesian) affected milk yield and CI. No
effect of breed was detected on mastitis or lameness. Lactation number had an
effect on production traits, CI, DTFS and DO. Yields were low in early lactations
(1-2), increased from lactation 2-5 and declined thereafter. Intervals for fertility
traits were longer in early lactations and shortened with the increase in lactation
number. No effect of lactation number was noted on mastitis, but it affected
lameness. There was an effect of lactation length on production traits and mastitis
but it did not affect lameness. Calving age affected production traits in all data sets and differences were higher in heifers than in data sets with lactation > 1 and in all lactations. Among fertility traits, CI was the only trait affected by calving age in all data sets; DTFS, DO and NSPC were affected in some data sets. Mastitis and lameness were affected by calving age.
A large number of records were eliminated during data editing because of
incomplete or missing information, missing pedigree information or problems
associated with pedigree information. Heritabilities of production traits were high
in lactation 1 (0.38-0.52) and moderate (0.22-0.35) in lactation> 1. Repeatabilities of these traits were high (0.62-0.92). Genetic correlations among production traits were moderate to strong (0.38-0.92) and phenotypic correlations were high (0.62-0.92). Heritability of fertility traits were low and these ranged from zero to 0.14 and repeatabilities were also low (0 to 0.19). Genetic correlations among fertility traits were close to 1. For bivariate analyses of CTFS with other fertility traits estimates were similar in sign but higher in magnitude in a threshold model than in a model where CTFS was treated as a continuous trait. Heritability of mastitis and lameness when treated as continuous traits was low (<0.01-0.03); when the traits were treated as binary with underlying logistic distribution heritabilities ranged from 0.14-0.23 and when analysed as binary traits with standard normal distribution heritabilities ranged from 0.07-0.14.
Most of the genetic correlations between production and fertility traits were
favourable (-0.12 to -0.36). The genetic correlation between production and
mastitis was positive and unfavourable (0.28-0.51). Whereas, between production
traits and lameness correlations were favourable and ranged from -0.28 to -0.63.