Lower CP concentration reduced feed intake and milk production, but partitioning of energy and ME ‘efficiency’ remained the same
Take Home Message: Reducing dietary CP had no effect on efficiency of ME use, but lowered methane emissions
Reducing dietary CP concentration significantly decreased feed intake and milk production, but had no effects on energy partitioning between milk and body tissue or efficiency of ME used for lactation. That was the finding of a study, carried out by a team of scientists at Hillsborough’s AFBI, to evaluate the effects of dietary crude protein (CP) concentration on energetic efficiency and methane emission in lactating dairy cows.
“And we also found that increasing dietary CP concentration from 120g/kgDM to 150g/kgDM significantly reduced methane emission as a proportion of DM intake and milk yield, but further increasing dietary CP concentration to 180g/kgDM had no effect,” AFBI’s Tianhai Yan told delegates at this year’s British Society of Animal Science annual conference.
He and his team conducted a series of studies to examine the effects of dietary protein source and concentration on milk production, energy and nitrogen (N) utilisation efficiencies and fertility in dairy cows.
Trials involved 47 first and 40 multi-lactation Holstein dairy cows fed diets with varying concentration of CP concentrations – 180g/kgDM,150g/kgDM and 120g/kgDM in mixed diets containing 450g/kgDM of forage and 550g/kgDM of concentrates.
Concentrate supplements consisted of different proportions of the same ingredients (barley, wheat, sugar beet pulp, citrus pulp, soya bean meal, rapeseed meal and molasses).
During early (70 to 90 days), mid (150 to 170 days) and late (230 to 250 days) lactation, the same four cows and four heifers from each treatment were transferred to metabolism units for eight days with measurements of feed intake and faeces and urine outputs during the final six days.
Immediately following completion of digestibility measurements, all cows were transferred to indirect respiration calorimeter chambers for three days with gaseous exchange measured during the final two days.
Live weight was recorded at the beginning and end of these measurements and milk yield and fat, protein and lactose concentrations in milk were measured daily.
“And we found that there was no significant difference in live weight or fat, protein or lactose concentration in milk between the three dietary treatments,” said Dr Yan. “But increasing dietary CP concentration significantly increased DM intake and milk yield.”
Faecal energy output was lower with low compared to medium CP diets, but there was no significant difference between medium and high CP diets. Dietary CP concentration had no significant effect on methane energy output (MJ/d), energy balance or energy partitioning between milk and body tissue (milk energy/ME intake and energy balance/ME intake).
“And there was no significant difference in the efficiency of ME use for lactation between the three diets, when using ME requirements for maintenance,” added Dr Yan. “Increasing dietary CP concentration significantly reduced methane emission as a proportion of DM intake and milk output, but the differences between medium and high CP diets were not significant.”
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