Genetic trend and parameter estimates for milk yield traits and kidding date in a Saanen goat herd in New Zealand

Data from a large herd of Saanen goats were analysed to investigate the genetic variation in milk production traits and kidding date (KD), and genetic relationships between them. The analysis involved 14 years of milk yield data (1991/92-2004/05), comprising 20296 herd-test records for daily milk yield (litres (L)) and milk solids yield (fat and protein (FP)) from two to four annual herd tests per individual doe, and 5 years of KD data (2000/01-2004/05) comprising a total of 3548 records. Herd size increased over the 14 years from 180 to 820 herd-tested does per season. Lactating does were managed outdoors on pasture until 1995/96. Progressively from 1996/97 part of the milking herd was moved to covered yards and, from 2001, pasture and supplements were carried year-round to all milking does and young stock in covered yards. After the herd-establishment years, there were few purchased bucks (19% since 1998), and 94% of does recorded in the milking herd were homebred. Kidding was seasonal. Does were not synchronised for mating. In 2000-04, the KD range averaged 122 days in mixed-aged does, with mainly single-sire matings. Herd-test yields and kidding data were analysed using restricted maximum likelihood, with a repeated-animal model and full relationship matrix. Single-trait heritability estimates for L, FP, and KD were 0.35 +/- 0.03, 0.30 +/- 0.03, and 0.14 +/- 0.03, respectively, and corresponding repeatabilities were 0.52 +/- 0.01, 0.47 +/- 0.01, and 0.24 +/- 0.02. The genetic correlation between FP and KD was 0.14 +/- 0.09. Genetic selection for FP over 13 years has achieved a 3.1 +/- 0.19% annual rate of progress. The consequences of later kidding from does with genetically higher daily yields are discussed, in relation to future management and selection plans.