We set out in a study at UCD's Lyons Research Farm to measure the production and metabolic response of increasing levels of by-products in the diet of dairy cows at grass.
Given the increasing focus on the environment, we also wanted to assess what effects, if any, these feeds have on the excretion of nitrogen and phosphorus relative to cereal and soyabean meal based diets.
This study, which was funded by Department of Agriculture through the Research Stimulus Fund, was carried out during April-June 2014 and involved 48 early-mid lactation spring calving cows.
The trial lasted 70 days and cows were offered one of four concentrates types, fed at 6kg/cow/day through the milk parlour along with grazed grass.
All feeds were fed as pellets of good physical quality.
Treatment 1 (BP35) acted as the control with high levels of barley and soyabean meal and 35pc by-products, Treatment 2 (BP55) had lower levels of barley and soyabean meal and 55pc byproducts,
Treatment 3 (BP75) had reduced levels again of barley and soyabean meal and 75pc byproducts and the last treatment, Treatment 4 (BP95) did not contain any barley or soyabean meal and therefore was composed of by-products only.
SHs, DDGs, PKE were included in the concentrates in equal proportions.
Animals were grazed as a single group and were offered fresh allocations of pasture twice daily (20 kg DM/day) to ensure that grass intakes were not restricted.
Concentrates were formulated to be 16pc crude protein and energy levels decreased slightly from BP35 to BP95 (0.95 to 0.92 UFL). Corn distillers was used as the source of DDG.
On a daily basis, milk yield was recorded and grass was measured and sampled.
Weekly, milk samples were taken for composition and quality analysis (fat, protein, casein, lactose, SCC) and cows were weighed and body condition was also scored weekly.
Rumen samples were analysed for pH and other rumen parameters such as volatile fatty acids and ammonia.
Such measurements provide a good indication of rumen health.
As the study was conducted in early-mid lactation, blood samples were also taken on a weekly basis, to measure indicators of energy balance such as NEFAs, BHBs and glucose.
Different concentrate feeds can influence grass intake, so grass consumption was also measured during the experiment.
In addition, excretion of nitrogen and phosphorus were measured to see what impact, if any, feeding these by-products would have on nutrient excretion through urine and faeces.
Methane would also be an important consideration but wasn't measured here.
The study demonstrated that there was no effect of concentrate offered on any parameter measured in the study.
Intake of dry matter (DM - grass and total DM), milk production and composition (milk yield, fat, protein, lactose, casein, SCC), cow BCS and body weight, rumen and blood parameters were not affected by dietary treatment.
Equally, nitrogen and phosphorus excretion were unaffected by diet.
As feed costs represent a large proportion of the total costs of milk production, value for money is very important.
At the time of this study, the cost differential between BP35 (high cereal, soyabean concentrate) vs BP95 (all by-product concentrate) was approximately €20/tonne.
This offers the opportunity for cost saving at farm level considering that the lower cost ration (BP95) did not have any negative impact on performance.
This is particularly relevant when margins at farm level are under pressure.
The results from this study demonstrate that increasing the inclusion levels of DDG, SH and PKE in the concentrate of pasture fed dairy cows is possible without negatively impacting on milk production, rumen health, the metabolic status of the dairy cow or excretion of nitrogen and phosphorus.
Just as importantly, this study shows that barley can be fed at reasonably high levels to cows at grass without having a negative impact on performance because cows fed BP35, which contained 6kg of barley at 45pc inclusion, consumed nearly 3kg of barley.
Karina Pierce lectures in dairy production at UCD