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Abstract: Milk production and reproductive performance were monitored in 14 spring calving dairy herds in the south of Ireland between 1990 and 2003. In these herds, the average pedigree index for milk yield increased by 25kg per year from 1990 to 2001, while the average proportion of Holstein-Friesian genes in the cows increased from 8% in 1990 to 63% in 2001. Over this period, milk production per cow increased by 54 kg/year, while replacement rate increased from 16% in 1990 to 27% in 2003. To evaluate the farm-level financial implications of associated changes in calving pattern, milk production and replacement rate, data from the 14 spring-calving herds were included in the Moorepark Dairy System Model for each of the 14years. Two milk production scenarios were investigated, which included EU milk quota applied at farm level (S1) and no milk quota (S2). The influence of variation in milk price, cull cow value, replacement heifer cost and replacement rate were modelled using stochastic budgeting. In S1 there was a significant linear increase (P <0.05) in margin per cow (€10.8), margin per kg of milk produced (0.13cent) and net farm profit (€546) over the 14-year period. Similarly in S2 there was a significant linear increase in margin/cow (€11.3), margin/kg (0.14 cent) and farm profit (€1089) over the 14-year period. However, the analysis showed that if reproductive performance, calving spread and replacement rate could have been maintained at 1990 levels for each of the 14years then the increase per cow, per kg of milk and farm profit per year would have been €22.1, 0.31 cent and €1341 for S1, and €22.8, 0.32 cent and €2183 for S2, respectively. Stochastic analysis showed that farm profit was most sensitive to changes in milk price, followed by replacement rate. [Copyright &y& Elsevier]

Abstract: The data presented in this review show that past selection for increased milk production in Ireland over a 14-year period (1990 to 2003) resulted in increases in milk production per cow but has been accompanied by undesirable side effects in reproduction and survival. Economic analysis in a EU milk quota scenario over this period showed that only 41% of the potential improvement in farm profit was achieved because of impaired reproductive performance. Strain comparison studies show that genetic selection for increased phenotypic milk production, which is generally accompanied with increased proportion of North American Holstein Friesian genes, was associated with increased milk production per cow, lower body condition score, greater milk production response to concentrate supplementation at pasture and reduced fertility and survival. The lower reproductive performance observed with cows selected solely for high milk production was associated with lower energy balance in early lactation, greater partitioning of additional nutrients towards milk production, inability to achieve desired grass intake from pasture and decreased plasma glucose and insulin like growth factor-1 concentrations. The existence of genotype by environment interactions suggests that germplasm selected in the future should be from within the management system in which it is to be used, and based on a selection index that combines production and other traits of economic importance. [Copyright &y& Elsevier]