Energized calf milk: is it worth investing in early life nutrition?

The overall aim of heifer rearing is to produce healthy calves that grow at the desired growth rates in order to calve for the first time at 22–24 months of age. Daily liveweight gain (DLWG) has been highlighted to be a critical component of an efficient heifer rearing system (Chester-Jones et al, 2017). The desire for increased DLWGs during the pre-weaning period has resulted in the aim of feeding elevated planes of milk nutrition (~20% birth bodyweight), as this has been shown to significantly impact first lactation milk yield, calf health and feed conversion efficiency (Soberon et al, 2012). Whole milk (WM) is thought to have the optimal composition in relation to the calf 's requirements and has been used as the gold standard to compare commercial milk replacers (CMR) to. CMRs are highly variable, because of the differences in formulation balance, raw material inclusion and nutrient digestibility; these different components are discussed in detail below.

Milk feeding: where does the energy come from?

Historically, formulations of CMR have differed significantly from WM in their levels of energy, protein and minerals. Energy source is one of the major differences, and arguably one of the most critically important components of a CMR (Amado et al, 2019). CMRs generally contains high levels of lactose, whereas whole milk contains higher levels of fat.

The metabolisable energy for WM and CMR is typically 22.6 MJ/kg dry matter (DM) (5.4 Mcal ME/kg) and 19.2–19.6 MJ/kg DM (4.6-4.7 MCal ME/kg) respectively (Drackley, 2008; Amado et al, 2019; Berends et al, 2020). The differences are a result of CMRs having a higher level of lactose (42–50% vs 33–38% of DM) and lower level of fat (16–22% vs 30–40% DM) than WM. This ultimately results in a lower energy:protein ratio for traditional CMRs compared with WM. The energy in milk comes from lactose and fat, with dietary fat providing 50% of total dietary energy in WM.

Impact of higher lactose content in CMR

Higher lactose content in CMR has been linked to osmotic diarrhoea as indicated in Table 1 (Hof, 1980). The three diets were skim CMRs, containing varying amounts of lactose, fat and crude protein (CP) (diet A contained 13.8% lactose, 17.2% fat and 25.0% CP; diet B contained 39.9% lactose, 2.8% fat ad 20.9% CP; diet C contained 11.6% lactose, 14.4% fat and 21% CP). This is because high levels of lactose can overwhelm the absorptive capacity of the gastrointestinal tract, which increases the carbohydrate load entering the lower intestinal tract. The increase in carbohydrates results in increased gut lumen osmolality and creates a water gradient into the intestines. The impact of higher levels of lactose in CMR has also been shown to have an impact on glucose homeostasis (Hugi et al, 1997; Pantophlet et al, 2016), but this does not appear to affect the DLWG (Pantophlet et al, 2016; Wilms et al, 2020).

Impact of higher fat content in CMR

The impact of high fat inclusion in CMR (30–40% of DM vs 16–22% DM) has been associated with potential health benefits and future production implications. One study reported a decreased number of disease events that required treatment for bovine respiratory disease (BRD) for calves fed high fat CMR (one BRD event per calf) compared with those fed high lactose CMR (2.25 events per calf) (Berends et al, 2020). The impact of a high fat CMR was hypothesised to result in increased fat deposition in tissues, including the mammary gland, which impaired mammary development. While this is true for the post-weaning period, this hypothesis has not been supported for the pre-weaning period within the literature. Research has highlighted that calves have a hard time accumulating fat in the first 70 days of life, so feeding high fat CMR is not detrimental to the calf (Pantophlet et al, 2016). One study reported that calves fed WM (29% fat) had an increased DLWG at weaning (10% increase) and increased milk production (10.2% increase), when compared with lower fat percentage CMR (13% fat in CMR vs 29.4% in WM) (Moallem et al, 2010).

The composition of fats within CMR

Research has highlighted that CMRs have different fat compositions (fatty acid profile) and structure, including globule size. These differences are a result of the fat sources used in CMR, which are a combination of blended vegetable fats for energy sources. The fats included in CMRs have a decreased digestibility in comparison to butter fat in WM, as indicated in Table 2. The idea behind using blended fats is to incorporate a mixture of short and medium chain fatty acids. Long chain fatty acids (LCFA), such as palmitic and stearic fatty acids found in lard and tallow, should be avoided as pancreatic lipase is required for emulsification and digestion of LCFA, which are not present until 2 weeks of age (Bauchart et al, 1996). The differences between the fat composition of WM and CMR can also impact the absorption rates of fats. One of the key aspects is the lack of a milk fat globule membrane on the fat particles in CMR, as these are coated in casein and milk proteins instead (Lopez et al, 2015). The fats in CMRs can undergo a process of homogenisation and encapsulation. The homogenisation process is designed to create an optimal fat globule size, similar to cows' milk, for improved solubility and stability in solution. The homogenisation of fat is reported to result in increased digestibility by of the fats. The encapsulation process is designed to cover the fat molecules with dairy products to improve the absorption and increase intake.

Milk feeding: what about proteins for lean growth?

The composition of milk replacer is important in terms of digestibility and the ability to utilise the proteins, a full review of this is outside of the scope of the article (suggested reading Cooper and Watson, 2013). CMRs utilising vegetable or non-milk protein sources (such as soya), which have a lower digestibility, can result in an increased osmotic pressure in the gut lumen and result in osmotic diarrhoea (Wilms et al, 2019). Different CMRs have different inclusion rates of CP (20–28% DM), with typically WM containing between 24.5 and 28.8%. Research has highlighted that calf DLWG was directly related to intake of CMR energy when dietary protein was not a limiting factor (Diaz et al, 2001). Feeding higher levels of CP (16% versus to 26% CP) resulted in increased DLWG and deposition of lean tissue. However, obtaining the correct protein to energy ratio is important, as if protein intake is less than required for lean tissue growth, excess dietary energy will be stored as fat. If protein intake exceeds requirements for lean tissue growth relative to energy intake, then the protein will be diverted and utilised as an energy source (Bartlett et al, 2006). Therefore, it is the balance of protein and energy that is important to consider.

Milk feeding: what is the correct feeding rate for milk powder?

The recommended percentage of solids of CMR fed in a litre of milk is stated on the CMR label. Altering the percentage of solids fed impacts the osmolality of the solution. Whole milk is an isosmotic feed which is around 300 mOsm/kg (Davies and White, 1960), while most commercial CMR have osmolalities between 400–600 mOsm/kg (Berends et al, 2020). There is limited research on the impact that the osmolality of CMR has on calves. However it has been researched in other areas of veterinary medicine and human medicine, with results showing that increased osmolality resulted in delayed gastric emptying in children (Pearson et al, 2013), damage to the intestinal villus cells in piglets (Norris, 1973) and impacted on water absorption resulting in an increased incidence of diarrhoea (Glosson et al, 2015). The main research study conducted in 30 calves investigated the impact of different osmolalities (range 439–611 mOsm/kg) on the permeability of the gastrointestinal tract using standard permeability tests (lactulose-D-mannitol and Cr-EDTA). The results showed a greater absorption of the larger molecules occurred with solutions with increased osmolalities, indicating potentially diminished intestinal barrier function (Wilms et al, 2019). Research in calves has suggested that fluids with osmolalities greater than 600 mOsm/kg should be avoided as the absorption in the small intestine is inhibited because of a decrease in efficacy of the concentration gradient, potentially resulting in osmotic diarrhoea (McGuirk and Steps, 2003; Floren et al, 2016). Osmolalities greater than 600 mmol/litre have been reported to increase abomasal luminal pH and decrease abomasal emptying, which can result in abomasal bloat and facilitate the colonisation of the intestine with enteropathogenic bacteria (Burgstaller et al, 2016). Therefore care should be taken when increasing the percentage solids of CMR fed, in terms of increasing percent of solids per litre fed, with increasing the volume fed being the preferred option for increasing the energy fed.

What about energized calf milk?

Energized calf milk (ECM) has been designed to replicate whole milk as closely as possible, with the aim of helping heifers achieve lifetime potential in terms of both yield and longevity through superior growth during the pre-weaned period. A comparison of ECM to a good whey-based CMR is highlighted in Table 3 and the benefits of ECM are highlighted in Figure 1.

One of the largest differences between ECM and CMRs in the decrease in lactose content, increase in fat content and optimisation of the protein digestibility. Increasing the fat content by reducing the lactose content has been shown to result in increased DLWG (0.679 kg/day vs 0.402 kg/day for high fat and high lactose CMR) and feed conversion efficiency, as well as slowing abomasal emptying with minor alterations in glucose homeostasis (Stahel et al, 2019; Welboren et al, 2021).

The inclusion of more fat in the CMR results in an increased energy content of ECM (20.3 MJ/kg) compared with the standard CMR (activator = 18.8 MJ/kg). A difference of 1.5 MJ/kg is the equivalent 0.63 litres of that standard CMR fed at 125 g/litre. at 12.5% solids. The feeding of the extra energy in ECM resulted in higher predicted DLWGs for calves at both 40 kg and 60 kg at 10°C, in comparison to standard CMR (Figure 2). One of other the key differences between the ECM and CMR is the concentration at which the powders are fed, with ECM being fed at 13.5% solids, compared with 12.5%, which equates to 0.20 MJ per extra 1% solids fed (equivalent of 1.2 MJ for 6 litre). However, neither the ECM nor the CMR provide enough theoretical energy for the 60 kg animal to grow at 0.8 kg/day when fed at 6 litres per day. ECM is recommended to be fed at an elevated plane of nutrition and as close to ad lib as possible during early life; this is often seen as feeding at 8 litres per day from 3 weeks of age, which would results in a predicted DLWG of 0.88 kg/day for a 60 kg calf in an environment of 10°C (equivalent of 22.06 MJ fed per day). Feeding ECM at 8 litres/day to a 60 kg calf should result in a DLWG of 0.81 kg/day at 5°C and 0.72 kg/d at 0°C. Feeding CMR at 8 litres results in 20.6 MJ of energy, which is the equivalent of a predicted DLWG of 0.69 kg/day, 0.62 kg/day and 0.55 kg/day for 10°C, 5°C and 0°C respectively. These data suggest that ECM fed at the recommended rate is one method of potentially reducing the impact of cold stress on DLWG during the first month of life.

Another method that has been suggested for reducing the impact of cold stress as well as increasing the volume of milk fed to the calf, is to increase the concentration of milk replacer fed to 15%. Increasing the CMR to 15%, results in feeding 2.82 MJ/litre (equivalent of 16.9 MJ in 6 litre). Feeding premium CMR at a rate of 15% potentially increases the energy content to more than the energy provided in 6 litres of ECM. However, it will have the impact of increasing the osmolality of the CMR as the solution becomes more concentrated, which increases the risk of osmotic diarrhoea as the hydroscopic lactose increases the osmotic pressure in the gastrointestinal tract.

None of the calculations above take into the account that ECM contains a specific fatty acid profile alongside homogenised fats that have been encapsulated, both of which increase the digestibility of the fats and could also influence the DWLGs of the calves (Echeverry-Munera et al, 2021).

The economics of milk replacer feeding

One of the major considerations of feeding CMR is the financial cost. The mean cost of pre-weaning heifer rearing in the UK has been reported as £3.14 per day (range: £1.68 to £6.11), with 37.3±9.4% of those costs being attributed to milk feeding (range 18.0–66.8%), with the mean cost of milk fed being 0.26 ± 0.10 £/litre (range 0.13 to 0.80) (Boulton et al, 2015).

While the cost of CMR is high and contributes to more than a third of pre-weaning heifer costs, farmers can see a return in their investment, because of the high feed conversion efficiency in preweaned calves. Table 4 highlights the associated costs with different stages of heifer rearing, as well as the feed conversion efficiency (FCE). The daily cost of rearing heifers depends on the DLWG of the heifers, because faster growing heifers require more feed on a daily basis, with increased energy and protein requirements (Tozer, 2000). While the cost of rearing is highest during the pre-weaned period, the FCE is the highest, with 55–60% of 100 g feed converted into carcass, and therefore the kg of growth increasing the DLWG in pre-weaned calves can be more economically efficient. Therefore a higher daily cost may not result in a higher total feed cost, as there will be a shorter rearing period to reach a specified bodyweight (Tozer, 2000). This was highlighted by a study in 2017, which reported that while 46% of total heifer rearing costs were a result of feed cost and that total cost increased as milk allotment increased, the cost per kg of gain decreased because of increased DLWG (Hawkins et al, 2019). The results of this study are high-lighted in Table 5.

Improved DLWG in the pre-weaned period has been high-lighted within the research to be associated with an improved efficiency of rearing, reduced calving to conception interval and increased first lactation yields (Bach and Ahedo, 2008; Boulton et al, 2017). Acceleration of growth of pre-weaned heifers has been shown to allow breeding size to be achieved earlier and therefore has a potential to decrease age at first calving (AFC) and rearing costs (Davis Rincker et al, 2008; Raeth-Knight et al, 2009). This was also reported with lower AFC reported, with an increase in bodyweight and girth measurements at 1 month of age (Brickell et al, 2009). A lower AFC has been reported to result in increased survival within the herd, alongside improved health and fertility performance during the first lactation (Sherwin et al, 2016; Eastham et al, 2018). Research has also shown that 5% variation of future milk production can be explained by DLWG in the first 2 months of life (Bach and Ahedo, 2008), with an additional 226 kg milk per 100 g increase in DLWG. This is hypothesised to be related to there being a higher concentration of oestrogen within the mammary gland cells. Therefore the economic benefits of increased DLWG in the pre-weaning period occur throughout the heifer's life.

The balance between economics and adequate DLWG can be difficult to achieve. A study assessed the impact of feeding 6 litres/day and 8 litres/day (25% CP, 19% fat and 21.7 ME per kg, fed at 125 g/litre) and reported that both groups of calves had very similar DLWG at the end of the study, suggesting that there might be an economic limit, as well as a physiological ceiling in terms of feeding a high plane of nutrition. The DLWG during the pre-weaning stage (up to 52 days old) was highest in calves fed 8 litres/day, compared with those fed 6 litres/day. However the DLWG during the weaning period (52–73 days) was greatest in calves fed 6 litres/day (0.977 kg/day) compared with those fed 8 litres/day (0.857 kg/day), because of increased starter intake and improved rumen development (Bach et al, 2013). These results suggest that milk feeding is only one component of what drives DLWG and needs to be considered alongside other management aspects.

Would I recommend using ECM to my dairy clients?

The first thing to consider when deciding if you would recommend using ECM on a specific farm, is to decide what you are hoping to achieve by using ECM, in comparison to another CMR. The higher energy density of ECM and higher feed rate, as well as improved digestibility, will result in higher DLWGs in the same situation, when compared with standard CMRs. While the target DWLG has been reported as 0.8 kg/day, research has highlighted significant variations in DLWG between farms in the UK, with variations in one study of 50 farms reporting a range of pre-weaning DLWG of 0.49–1.06 kg/day (Bazeley et al, 2016; Hyde et al, 2021). A variety of risk factors have been implemented in affecting DLWG within and between farms. A summary of how some of these factors are associated with DLWG is highlighted in Figure 3; these findings are taken from a study of 50 British farms in 2019–2020 investigating the impact of different factors on DLWG (Hyde et al, 2021). The results of this study, and other studies, highlights that milk feeding is only one factor in a multifactorial situation. However, milk feeding is one of the easiest factors out of all of the factors to alter and keep consistent on a day-to-day basis and therefore ECM could be used to help improve DLWG on farms which have suboptimal environmental conditions, which do not have an easy fix. However if there are issues with areas such as colostrum feeding, then ECM may not be the best option for this farm, until the other ‘big wins’ have been achieved.

Another potential reason for choosing ECM compared with a standard CMR is the potential protective effect it has for clinical BRD and decreased incidence of osmotic diarrhoea, because of the high fat content (25% compared with 18–20%) and low lactose content (Table 2). BRD has been highlighted to decrease DLWG by 0.066 kg/day during the first month of life, with each additional week of BRD reducing the DLWG by 0.014 kg/day (Virtala et al, 1996). This is hypothesised to be because of decreased intakes and altered behaviours, as well as energy siphoned away from growth to the immune response. The feeding of a higher plane of nutrition during the pre-weaned period has been hypothesised to influence calf health because of alterations in leukocyte responses to pathogen challenges, which suggests that there are epigenetic effects that are currently not fully understood (Ballou, 2012; Ballou et al, 2015). The long-term impact on DLWG and production of BRD is related to decreased lung capacity as a result of BRD injury and its chronicity. Chronic BRD results in a decreased oxygen exchange capacity, which leads to a decreased efficiency of metabolism and ability to extract energy from the diet (Bach, 2011). Therefore minimising the incidence and chronicity of BRD is essential for optimising DLWG and future production of heifers.

Economics will always play a substantial role in choosing CMRS and is an individual farm's choice. An estimate on the economics of ECM, compared with two whey-based CMRs is given in Table 6 to act as a helpful guide.

Conclusions

The discussion above highlights that ECM has been designed to mimic whole milk as closely as possible, because of the increased fat content, decreased lactose content and the digestibility of the milk fats present, as well as the osmolality (as summarised in Figure 2). The research behind the reasons why ECM has been designed in this manner highlights potential health benefits, as well as improved production outcomes, suggesting that there are welfare and economic benefits present when using ECM. However as research has shown, milk feeding is not the only factor on farms that impacts the health, welfare and DLWG of pre-weaned calves, and therefore ECM cannot be expected to compensate for issues in other areas of pre-weaning calf rearing. The decision as to whether investing in using ECM is the correct decision for a specific farm will depend on the individual farm, with a holistic herd health approach required to aid a farmer in making this decision.

KEY POINTS

• Energized calf milk (ECM) has been designed to mimic whole milk, with a higher fat content and increased digestibility in comparison to commercial milk replacers (CMR) to provide more energy per kg fed.
• ECM has a lower lactose content and lower osmolality compared with CMR. Increased lactose content or increased osmolality (often through increasing the percentage CMR per litre fed), results in an increased osmotic pressure in the small intestine and an increased the risk of diarrhoea.
• While the cost of pre-weaning liquid feeding can be high, it is an investment that can pay off because of the increased feed conversion efficiency resulting in elevated daily live weight gain (DLWG). Elevated DLWGs are associated with improved future production and survivability.
• The amount of CMR required for target DLWGs can easily be calculated across different CMRs, for different calf bodyweights and at different environmental temperatures. This is important for ensuring target DLWGs are met and an environmental issues are compensated for.
• Milk feeding is not the only factor on farms that impacts the health, welfare and DLWG of pre-weaned calves, and therefore ECM cannot be expected to compensate for issues in other areas of pre-weaning calf rearing.