@conference {41838,
	title = {Estimation of lactation persistency in crossbred grazing dairy cattle},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {65},
	year = {2005},
	month = {Jan},
	pages = {300-305},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	address = {Christchurch},
	abstract = {Lactation persistency is commonly referred to as the rate of decline in daily yield after the peak of lactation and can be measured in different ways. The objective of this study was to calculate different measures of persistency for milk traits and estimate the correlations between parameters of the lactation curve in crossbred cattle. Herd test records of milk, fat, protein and lactose from 810 first lactation cows were used to obtain individual lactation curves using a mixed model fitting six knots splines. The model included the fixed effects of contemporary group (year-calving week), sire, age at calving (linear and quadratic) and an average spline and the random effect of cow-spline interaction. All cows were in their first lactation, second cross Friesian x Jersey from a crossbreeding experiment established for quantitative trait loci identification. Persistency was measured in three different ways: P1, slope of the line fitted using linear regression of daily yield on day of lactation from day 60 to day 220; P2, the area under the lactation curve from day 121 to 180 divided by the area under the curve from day 1 to 60; and P3, the 240-day lactation yield divided by peak yield multiplied by 240. Correlations between measurements of persistency ranged from 0.24 to 0.81 and were significantly different to zero (P < 0.001). Correlations between lactation yield and measurements of persistency ranged from -0.43 to +0.33 and were significantly different to zero (P < 0.01). These results indicate that measurements of persistency are not invariant and highlight the need to calculate persistency in a more consistent way. When cows were classified for persistency P2 of fat plus protein, cows of high persistency (top 25\%), compared with cows of low persistency (bottom 25\%), had significantly (P < 0.05) more days in milk, higher total yields of milk and its components, lower peak yields, later day of peak yield and lower rate of decline in daily yield from day 60 to day 220 (P1), but similar 240-day total yield of fat and protein. Farming cows of high persistency may be an alternative to reduce farm investments in peak notes and risks of metabolic problems and reproductive failures.
KEYWORDS: lactation persistency; milk yield. },
	issn = {1176-5283},
	author = {Lopez-Villalobos N and Spelman RJ and Harris BL and Stanley G and Harcourt S}
}
@conference {41480,
	title = {Friesian Jersey crossbred trial: Generating phenotypes for the discovery of quantitative trait loci},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {64},
	year = {2004},
	month = {Jan},
	pages = {92-95},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	address = {Hamilton},
	abstract = {The breeding of improved varieties of agriculturally important species requires constant effort and innovation. The ways we in New Zealand use emerging technologies to maintain our low-cost, low-input, sustainable, pastoral agricultural systems are extremely important. When it comes to developing elite varieties and strains of ryegrass we have been, until very recently, disrupting  much to achieve little: we rely on chance to find the right combinations of traits in our breeding lineages, whether animal germplasm or plants cultivars. The use of Cisgenics{\AE}, where heritable material is moved only within a species by either traditional or modern biotechnological means offers a better way for  ryegrass breeding in line with a key principle of science and economics.},
	issn = {1176-5283},
	author = {Spelman RJ and Hooper JD and Stanley G and Kayis SA and Harcourt S}
}
