Genetic parameters for milk yield and faecal nematode egg count in Saanen does

Results of two herd tests per lactation (each comprising daily milk yield and yield of fat and protein (FP)) and faecal nematode egg counts (FEC) on Saanen does in Northland, New Zealand, were recorded during the lactations of 1991/92 to 1996/97. The data were used to estimate genetic parameters for milk yield and FP, and for FEC. A total of 4738 records from 1161 does, the daughters of 53 sires, were available. Restricted maximum likelihood procedures with an animal model were used for analyses. Overall, daily yields of milk and FP were 1.40 litres and 0.091 kg (average concentration 64.4 g/litre). Among the five age classes of doe, milk yield ranged from 0.93 to 1.80 litres, while FP ranged from 0.061 to 0.117 kg. Geometric mean FECs ranged from 974 to 1241 eggs/g faeces among does of different ages, and from 748 to 3093 eggs/g among years (lactations). There was a curvilinear relationship between all three traits and days in milk, with declining yields and FEC as lactation progressed. The heritabilities (h(2)) for milk yield and FP averaged 0.23 +/- 0.04 and 0.27 +/- 0.04, respectively, with corresponding repeatability (r) values of 0.26 +/- 0.03 and 0.27 +/- 0.03. Estimates of h(2) for log, (FEC+100) across years were 0.09 +/- 0.05 (mid lactation) and 0.06 +/- 0.04 (late lactation), with corresponding r values of 0.09 +/- 0.06 and 0.15 +/- 0.04. The genetic correlation between milk yield and FP was 0.87 +/- 0.03, and those between FEC and milk yield or FP were -0.21 +/- 0.26 and -0.17 +/- 0.24, respectively. Phenotypic correlations between milk yield and FP, FEC and milk yield, and FEC and FP averaged 0.88 +/- 0.01, -0.07 +/- 0.03, and -0.07 +/- 0.03, respectively.