Soya has long been the ’go-to’ product to supply rumen-bypass protein in dairy cow diets, but as the dairy industry faces continued scrutiny about the use of the product, alternatives are being seriously considered.
One of these alternatives is rapeseed, which has been shown in a recent study at the University of Nottingham to produce higher milk yields, at a lower cost and with a reduced impact on the environment.
Professor Phil Garnsworthy, of the University of Nottingham, says soya increasingly has a ‘bad press’.
“Soya has a high carbon footprint; much higher than other protein sources, and there are growing concerns about genetically modified crops.
“Rapeseed meal could be an alternative; it has a lower carbon footprint and is home-grown, meaning nitrogen is recycled locally.
“However, it does have a relatively low level of digestible undegraded protein [DUP], which is why soya with its higher DUP content has been traditionally used in rations.”
The trial at Nottingham used 44 early lactation, high yielding Holstein Friesians, with an average yield of 11,000 litres/cow. The cows were individually fed an ad lib, partial mix ration, with concentrates fed at milking at a rate of 0.45kg per litre over 32 litres.
Each diet was fed for 28 days, during which time the cows had access to the university’s robots, with the average number of visits standing at 3.2 per day.
The control diet included soyabean meal as the main source of DUP, while ‘test diet one’ used heat-treated rapeseed expeller (NovaPro) plus wheat distillers grain, and ’test diet two’ contained the heat-treated rapeseed expeller and a rumen protein supplement (SoyPass).
All the rations were based on the same mix of grass, maize and wholecrop silages.
Prof Garnsworthy explains the results showed an increase in dry matter intake of 1kg when the cows were fed the test diets compared to the control diet, and milk yields for the cows fed the test diets were 1.6kg greater than those fed the control diet.
He says: “We do not think we changed the diet composition that much to have had that big an impact on dry matter intake. And we think it was a milk yield response that explained the DMI increase; the cows were producing more milk, so they ate more.”
There was very little difference in milk constituents, but milk ureas were lower.
Prof Garnsworthy says: “The milk urea drop was interesting as we were actually putting more urea into the diet. This response suggests the test diets were capturing more rumen degradable protein.”
Prof Garnsworthy adds he would speculate that the improved yield was down to improved amino acid balance in the test diets.
“Several essential amino acids were higher in the test diet, compared to the control diet, and we think this may have stimulated milk yield.”
The price of NovaPro is currently about 14 per cent below that of soyabean, resulting in a rumen by-pass protein cost of 15.5p/100g DUP compared to 17.3p/100g DUP. (Prices correct as of February 2019 and based on 29-tonne tipped bulk loads delivered on-farm January to April within 50 miles of origin).