Protein in Heifer Rations

Calves (0-6weeks) should receive the majority of their nutrition from milk; this is what they are most efficient at utilising at this point and are eating limited quantities of starter, therefore, look at providing high quality, digestible milk replacer made up of milk proteins (these are digested most efficiently by the calf) and a high energy supply to ensure protein is used for tissue growth. In the pre-weaning period we are not only looking to grow the calf and develop its rumen but internal development too. Calves on an elevated plain of pre-weaning nutrition in the first 60 days of life had a positive carry-over effect on pre-pubertal follicular growth and that an increased post-weaning plane of nutrition had a positive effect on reproductive tract development (Bruinjé et al., 2019). A good quality starter such as Start ‘n’ wean should be available from birth; offered a small amount at first and refreshed daily to maintain palatability. As with milk replacer, the source of the protein in a starter has an impact of digestibility levels, easily digestible proteins such as Hypro Soya Bean Meal will mean more efficient use and limit waste protein. E. K. Miller-Cushon et al., 2014 found that calves
preferred a high energy high protein starter, with calves having highest intakes of Hypro Soya Bean Meal and wheat meal, concluding that to promote early intake of starter feed, ingredients of the starter should include these highly ranked ingredients.

Calves have no capacity to produce their own protein, all of the protein requirements must come from the diet. Pre-weaning is the period of highest growth and protein requirements are going to be the highest here than any other period, 5.5g protein/kg of body weight needed to gain 1kg/ day (NRC, 2001). It is also, however, the period of lowest dry matter intake in kg but highest % of BW which brings about the need for a reasonably high protein diet, 18.3% in the TOTAL diet is recommended. Energy is frequently more limiting to growth in calf diets than protein, based on the National Research Council’s calf sub-model and considerable recent published research, Progressive Dairy (2020).

NRC guidelines (2001) state that 18.3% overall is sufficient in pre-weaned calves, when milk replacer protein level is an optimal 22-24%. Zanton and A H Heinrichs, 2007 found that Dietary CP concentrations of 18.9% for milkfed calves were found to maximize gross N efficiency. Additionally, the published research shows that 18% CP (as-fed basis) is optimum for calf starters fed to calves from birth to approximately two months of age. Feeding high levels of protein result in more nitrogen being excreted in the urine in animals fed high protein starter (Albino et al., 2015). Therefore, it is recommended that calves are fed a high quality 18-20% (Start‘n’Wean or Heifer600) starter feed made up of digestible proteins and a good quality milk replacer, plus ad-lib straw for this period.

Post-weaning heifers have the capacity to produce their own protein, and the substrates need to be provided to allow them to do this. Protein utilisation is not as efficient as it was a few months ago and N efficiency drops from almost 90% in new-borns to 30% at breeding weight, their growth becomes slower and more sustained. Dry matter intakes increase relative to energy and protein requirements. Protein requirements drop to 2.9g/kg of body weight (NRC 2001) and demand for protein significantly drops at 140kg. The NRC (2001) state that 12-14% crude protein in heifer diets is optimal and G. I. Zanton and A. J. Heinrichs (2007) also found that Dietary CP concentrations of 14.2% for weaned heifers maximized gross nitrogen efficiency. Heifer diets should start at 16% in the total diet and reduce to 14% in the first six months.

When protein is oversupplied more Nitrogen is excreted in the urine in animals fed high protein starter, (Albino et al., (2015). In the Zanton & Heinrichs., (2007) trial the groups of
heifers consuming five diets of varying protein levels had the same dry matter intake, dry matter digestibility and gained nearly one kilogram per day, the high protein groups did not
gain more. The response in gross N efficiency to additional N intake was not different between diet groups; rather, the absolute level obtainable differed. There are also other points to bear in mind, there are several negative environmental impacts to oversupply of protein and with targets for reducing emissions at the forefront of many farming operations. Also to consider are cost implications to feeding excess protein when it is not needed and wasted; consider streamline operations and cutting excess protein. The efficiency of utilisation is also not at its optimal. Furthermore, researchers determined that when feeding high levels of high-protein milk replacer, performance was not improved by feeding more protein in the starter (Progressive Dairy, 2020).

• Starter diets of 16-18% crude protein appear to yield the best effects when on milk and weaning diets should be
  between 16-18% in the total diet
• Once calves reach 100-120kg begin to drop protein levels
• Calf starter should contain Hypro Soya Bean Meal and wheatmeal at a high level to ensure high energy and highly digestible protein sources.

• Begin at 16% in the total diet and drop to 14% in the first six months. There is no evidence to suggest any extra protein yields additional benefits
• Diets don’t need a huge amount of changing once set, however, it is important to keep on top of changes in
  silage and be mindful of energy density in the overall diet
• Monitor growth where possible; physical weighing is the gold standard but weigh bands do provide a good
  alternative
• Bear in mind when taking information from abroad raw material supply isn’t the same, they have access to certain protein sources that we don’t, however, our milk powder portfolio is far superior, bear this in mind when
  making decisions on milk powder and feed.