Altering dietary crude protein levels had no effect on the performance of cereal-fed Holstein bulls
Take Home Message: There is no advantage to feeding above 120 g/kg crude protein (fresh weight basis) in the diet of finishing bull beef animals on performance or carcass classification, but will increase rearing costs (p/kg gain).
Finishing Holstein bulls on rations comprising different levels of crude protein had no effect on animal performance.
“There were no significant difference between the treatments,” said Harper Adams University College’s Simon Marsh, who shared the results of a trial, which set out to determine the effect of feeding barley-based rations containing (fresh weight basis) 120, 140 or 160g/kg dietary CP on the performance of cereal fed 280kg Holstein bulls through to slaughter, with delegates at this year’s British Society of Animal Science’s annual conference.
“The highest slaughter and carcass weights were achieved by the bulls fed the 120g/kg CP ration, but this was not statistically significant,” he added.
Suggestions that feeding a higher protein ration could increase slaughter weight, or help produce leaner carcasses, were not proven by the results of this trial. The excess protein from the 140 and 160g/kg CP diets would have to be converted to urea by the rumen micro-organisms, absorbed across the rumen wall and excreted in the urine.
“This will demand energy that would otherwise be used for growth. The bulls reared on the 120g/kg CP recorded the highest carcass value and lowest feed cost per kilogram of LWG. From the experiment it can be concluded that increasing the protein content of the ration above 120g/kg CP for 280kg bulls does not improve physical or financial performance,” explained Mr Marsh.
He added that it is common practice to give cereal fed bulls a 160g/kg crude protein (CP) diet to 250kg live weight, dropping to 140g/kg CP from 250kg to slaughter. The majority of intensively fed beef cattle are fed home- mix rations based on rolled barley with a protein concentrate or ‘protein rich’ straights, such as rapeseed meal and soya bean meal. In this latter situation higher protein rations will have increased ration costs.
The university’s trial involved a group of 48 Holstein bulls, each weighing 280kg, were reared through to slaughter on a cereal beef system and fed ad-lib diets containing either 120, 140 or 160g/kg dietary CP. The 120g/kg CP ration contained rolled barley, soyabean meal, rapeseed meal, molassed sugar beet pulp, molasses, and minerals. The 140 and 160 g/kg CP diets were formulated with 140 and 200g/kg soyabean meal and rapeseed meal replacing an equal quantity of barley. The cattle were housed in straw-bedded pens and were selected for slaughter at EUROP fat class 3.
“And overall the bulls recorded performance that either achieved or exceeded recognised targets for cereal beef production,” said Mr Marsh. “There were no significant differences in animal performance between the treatments. The bulls fed the 120g/kg CP ration recorded the highest daily and total feed intake and the worst FCR.”
The FCRs (kg feed: kg LWG) appear to be relatively high compared to the target of 5:1 for cereal beef production. “But it must be noted that the trial did not include the period of growth from 120kg to 280kg. During this rearing phase Holstein bulls at Harper Adams typically record a DLWG of 1.75kg with an FCR of 3.2,” he added.
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