25. A comparison of symptoms in subclinical and clinical mastitis cases in cows

Abstract

Deer farmers maintaining stag herds for velvet antler production are interested in: selection of stags for superior lifetime performance; selection of sires and dams to produce improved sons; and management of the stag herd to increase returns from velvet antler. Knowledge of genetic and phenotypic relationships between weights of velvet antler harveste+d at different ages and between winter liveweights and velvet antler weights will allow benefits from selection and some management practices to be quantified. This paper reports estimates of these relationships from a study involving some 2021 stags with two-year old velvet antler records representing 92 sire progeny groups distributed over five farms. Heritability estimates (s.e.) for velvet antler weight at successive ages from 2- to 8-year old stags ranged from 0.43 (0.09) to 0.85 (0.33). The average estimated genetic correlation between velvet weights in successive years was 0.97 (0.07) but declined to 0.76 (0.29) as the number of years between harvests increased. Phenotypic correlations were consistently lower than genetic correlations. Treating log-transformed velvet weight as a repeatable trait resulted in an estimated heritability of 0.36 (0.08) with a repeatability of 0.64 (0.08) and s.d. of 0.11 (log scale). Average velvet production in kg (Y) can be predicted from age in years (X) from the following equation: log10(Y) = −0.37 + 0.33X − 0.044X2 + 0.002X3Within a cohort of stags of the same age, heavier stags produced heavier velvet antlers, with an average genetic correlation of 0.74 (0.21) and phenotypic correlation 0.44 (0.04). The genetic correlation between liveweight of hinds at two years of age and velvet antler weight at various ages averaged 0.5 (0.19). Liveweights had high heritabilities in both sexes and at all ages with estimates ranging from 0.48 (0.36) to 0.80 (0.12). Average heritabilities across adult ages were 0.54 (0.27) and 0.62 (0.20). Ignoring sex differences, the average genetic and phenotypic correlations between successive liveweights were 0.93 (0.26) and 0.85 (0.04), respectively. The average genetic correlation between stag and hind liveweights at the same age was 0.73 (0.30). Comparing different cohorts of stags of the same age, there was no relationship between average liveweights and average velvet weights. As stags aged, the average weights of velvet antler and liveweight increased. Describing velvet antler weight in kg (y) as a non-linear function of liveweight in kg (X), the allometric equation was Y = 0.21 X1.4, indicating velvet antler weight is later maturing than liveweight.