Contribution of Binomial Variation, Technician, Herds, and Cows to Observations Between Cow Variance of Conception Rates
1965; Elsevier BV; Volume: 48; Issue: 1 Linguagem: Inglês
10.3168/jds.s0022-0302(65)88165-6
ISSN1529-9066
Autores Tópico(s)Animal Behavior and Welfare Studies
ResumoA method of estimating between cow variance of conception rates and the contribution of sampling variance due to the binomial distribution of the data is presented.The total variance of conception rate, expressed as a proportion, was 0.22954, and the components of variance were ~r'-'~ technicians 0.00120, (r~ herds 0.00291, (r-~c cows 0.02238, ~r-', binomial variation 0.20305.Sampling variation accounted for 88.5% of the variation between cows, 43.5% of the variation between herds, and 11.3% of the variation between technicians.The interpretation of conception rate data in the light of this high sampling variation is discussed.In New Zealand dairying is seasonal.Cows calve in tile late winter and e'~rly spring, so that their period of maximum production cointides with the spring and early summer flush of pasture growth.Under such conditions, where cows have to calve at yearly intervals, high reproductive efficiency is essential.In this paper estimates have been obtained of some of the major factors affecting variations in fertility in an artificial breeding service. DATA AND METHODSArtificial Breeding in New Zealand is organized to fit in with the seasonal nature of dairying.Herds are organized into technician croups, each technician servicing approximately 20 herds and a total of 1,200 cows, over a period of 7 wk in the spring months.Coneeption rate data was obtained for 50 such technician groups in the Auckland province, in each or' the spring mating seasons of 1958 and 1961.There were 1,035 herds {.ontaining 59,778 cows in the 1958, and 973 herds containing 58,934 cows in the 1961 analysis.All herds used semen on the same day as collection, az~d, apart from breed, farmers had no choice in the bulls to be used in their herds.Under these conditions, semen supplied to each herd }lad the salne fertilizing capacity.Seven weeks after the end of the mating season farmers are circularized with a list or' their cows apparently in calf to A.B.They enter return dates on these forms.Conception rates are obtained from these data, a successful
Referência(s)