Is there a relationship between genetic merit and enteric @entity577 emission rate of lactating Holstein-Friesian dairy XXXX ?

@entity577 @entity578 @entity291 @entity894
UNASSIGNED: The present study was undertaken to examine the effect of @entity291 genetic merit on enteric @entity577 ( @entity578 ) emission rate. The study used a data set from 32 respiration calorimeter studies undertaken at this Institute between 1992 and 2010, with all studies involving lactating Holstein-Friesian dairy @entity291 . @entity291 genetic merit was defined as either @entity894 ( @entity894 ) or profitable lifetime index (PLI), with these two United Kingdom genetic indexes expressing the expected improvement in profit associated with an individual @entity291 , compared with the population average. While @entity894 is based solely on milk production, PLI includes milk production and a number of other functional traits including health, fertility and longevity. The data set had a large range in @entity894 (n=736 records, -  30 to +  63) and PLI (n=548 records, -  131 to +  184), days in milk (18 to 354), energy corrected milk yield (16.0 to 45.6 kg/day) and @entity578 emission (138 to 598 g/day). The effect of @entity291 genetic merit ( @entity894 or PLI) was evaluated using ANOVA and linear mixed modelling techniques after removing the effects of a number of animal and diet factors. The ANOVA was undertaken by dividing each data set of @entity894 and PLI into three sub-groups ( @entity894 :  15, PLI:  67) with these being categorised as low, medium and high genetic merit. Within the @entity894 and PLI data sets there was no significant differences among the three sub-groups in terms of @entity578 emission per kg feed intake or per kg energy corrected milk yield, or @entity578 energy (CH4-E) output as a proportion of energy intake. Linear regression using the whole @entity894 and PLI data sets also demonstrated that there was no significant relationship between either @entity894 or PLI, and @entity578 emission per kg of feed intake or @entity578 -E output as a proportion of energy intake. These results indicate that @entity291 genetic merit ( @entity894 or PLI) has little effect on enteric @entity578 emissions as a proportion of feed intake. Instead enteric @entity578 production may mainly relate to total feed intake and dietary nutrient composition.
