During infancy, appropriate nutrition is required for normal growth and development. There is now substantial evidence to indicate that early nutrition also has fundamental implications for long-term health by programming aspects of ensuant cognitive function, preventing obesity and anaemia, as well as reducing the risk of serious diseases such as diabetes, cardiovascular disease, osteoporosis, cancer and atopy (Lucas, 1998; WHO, 2003; SACN, 2011). To achieve these outcomes, breastfeeding is recommended (AAP, 2012).
Where breastfeeding is not possible or breast milk is insufficient (although this is a rarity), infant formulas are used. Traditionally, infant formulas made with cow’s milk are the first line choice for formula-fed infants, so until recently most of the internationally published conclusive studies in human infants have been limited to the evaluation of cow’s milk or soy protein-based infant formulae. This status quo has been largely maintained even though proteins from the milk of other animals or from various plant sources have been considered potentially suitable for use in infant formulae (Koletzko et al, 2005; CODEX, 2007).
The use of goat’s milk formula is a case in point. The suitability and safety of this milk has only recently been approved, despite the fact that goat’s milk has a history of use for human nutrition in many cultures (Silanikove et al, 2010; Haenlein, 2004; Razafindrakoto, 1994) and that there has always been demand for goat’s milk infant formulas, with reports of home-made goat formula and raw goat’s milk being used (Ziegler et al, 2005; Basnet et al, 2010; Taitz & Armitage, 1984; Baur & Allen, 2005).
Since March 2014, goat milk’s infant formula is now allowable throughout the EU. This decision was made when the Dietetic Products, Nutrition and Allergies of European Food Safety Authority (EFSA) panel concluded that protein from goat’s milk is suitable as a protein source for infant and follow on formulae, as long as the final products comply with the compositional criteria as per the EU Directive 2006/141/EC (EFSA, 2012).
How does it differ from cow’s milk formula?
Table 1 outlines the main differences between cow’s milk and goat’s milk formulae. Although there are some similarities, there are also different compositional components between both milks. These are:
Milk secretion process
In the mammary gland, milk is produced by forming minute droplets, containing proteins, lactose, vitamins and minerals. They are released by two different processes: merocrine and apocrine secretion. In goat’s milk, the apocrine process plays a greater role compared to cow’s milk (Wooding et al, 1970). It is similar to human milk in that it contains numerous cytoplasmic particles that are broken off from the cell during apocrine secretion (Boutinaud & Jammes, 2002). It is this that is proposed to naturally endow goat and human milk with cellular components, such as free amino acids and nucleotides.
Medium chain fatty acids
In goat’s milk there is a higher content of medium chain fatty acids (MCFA) compared to cow’s milk (Ceballos et al, 2009). Infant formula with goat’s milk fat contains 10–20% MCFA (Prosser et al 2010), while human milk contains up to 15% MCFA (Koletzko et al, 2001), depending on the mother’s diet.
In young infants, rapid growth can increase the need for nucleotides, which are important constituents of RNA and DNA. It is well documented that nucleotide supplementation increases weight gain and head growth in formula-fed infants. Therefore, nucleotides may be conditionally essential for optimal infant growth in some formula-fed populations (Singhal et al, 2010). Cow’s milk infant formulas are now routinely supplemented with nucleotides. However, goat’s milk formula already contains an array of nucleotides and so requires no supplementation (Prosser et al, 2008).
Protein and amino acids
Goat’s milk infant formula has amino acids in amounts similar to human milk reference values, when expressed on a per-energy basis (Rutherford et al, 2008).
The protein content of infant formula has, in the past, been set higher than human milk. This was due to concerns regarding protein quality and insufficient amounts of some amino acids. However, there now exists evidence that the protein content has been set too high, resulting in a greater than normal weight gain and stress on a young infant’s immature kidneys (Koletzko et al, 2009; Escribano et al, 2012).
This ‘growth acceleration hypothesis’ (a suggestion that early and rapid growth during infancy programs the infant metabolic profile to be susceptible to obesity and other components of metabolic syndrome) means it is essential that any infant formulas are brought in line with human milk reference values.
In infants fed goat formula, it has also been shown that their blood urea levels are closer to infants fed human milk and were actually 11% lower compared to those fed cow’s milk formula (Zhou et al, 2011). This confirms that there is an adequate supply of amino acids from goat formula and less excess amino acids compared to a cow’s milk formula with added whey proteins.
Infant milk formulas often have whey proteins added to improve the quality of protein available as essential and semi-essential amino acids (Janas et al, 1987; Janas et al, 1985).
Goat’s milk infant formulas, however, have been shown to have sufficient quantities of all essential and semiessential amino acids, without added whey proteins and so have an amino acid profile compatible with international standards for infant formula (Rutherford et al, 2006). The amino acid digestibility and absorption properties of this type of goat’s milk formula are similar to those of a cow’s milk infant formula, with added whey, in an animal model (Rutherford et al, 2006). It has also been demonstrated that the amount and bioavailability of the amino acids in goat’s milk infant formula, made from whole goat’s milk, provides less excess amino acids and is adequate for the growth of the infant (Zhou et al, 2011). It could therefore be concluded that there is no evidence to support any advantage in adding extra whey proteins to goat’s milk infant formulas.
Adding whey also reduces the casein proteins in formula but increases beta lactoglobulin, resulting in higher levels of protein in whey-enhanced formulas not found in human milk (Lien, 2003). The lower levels of alpha s1 casein and absence of added whey proteins in goat’s milk means that the levels of non-human proteins are lower than either whey enhanced or casein dominated cow’s milk formula. This may be an important factor as these two proteins, alpha s1 casein and beta lactoglobulin, are known to induce allergic reactions in people sensitised to milk (Restani et al, 1999).
As well as meeting international compositional standards, it is also essential that the suitability and nutritional adequacy of infant formulas containing new sources of protein are established (Koletzko et al, 2005; Koletzko et al, 2002).
Until recently there has only been one previous randomised controlled trial using a goat’s milk infant formula to feed infants (Grant et al, 2005), demonstrating that the growth in 30 infants fed a goat’s milk formula was similar to that of 32 infants fed a whey-based cow milk formula, but the study was criticised for lack of blood biochemical data and numbers (EFSA, 2004).
However, a study published in 2014 demonstrated that in infants, the growth and nutritional outcomes provided by the goat’s milk formula did not differ from those provided by a standard whey-based cow’s milk formula. The study of 285 infants fed goat or cow formula or breast milk, provided the necessary evidence leading to the recent change allowing goat milk as a base in infant formula (Zhou et al, 2014).
This study also found some interesting differences in weight and weight for length z-scores when comparing a formula-fed with a breast-fed group. Their findings were consistent with other studies comparing the growth of formula and breast-fed infants (Kramer et al, 2004; Dewey et al, 1992; Agostoni et al, 1999). They found that while the differences in weight or weight for length z-scores continued at 12 months between the breast-fed infants and cow’s milk formula-fed infants, there were no differences between the goat’s milk formula-fed infants and the breast-fed infants. Zhou et al (2014) used the same formula with a lower protein content for goat’s and cow’s milk formulas (2g/100kcals and 2.1g/100 kcals for goat’s and cow’s milk formulas respectively) until 12 months, rather than changing to a follow on formula at six months, which contains a higher protein content, as had been done in the other three studies. This might partly explain the difference observed between the findings of Zhou et al and the other three formula studies, as it has been demonstrated that weight for length z-score at 24 months in infants fed a low-protein formula did not differ to that of breast-fed infants, while infants fed a high-protein formula (2.9g/100kcals) had higher z-scores.
An earlier study by Zhou et al (2011) highlighted an interesting aspect, in that they measured how many times an infant was offered an alternative formula or non-formula foods before the age of four months, as a measure of compliance. In the group randomised to receive the cow’s milk formula, almost 40% of the infants were offered either another formula or a non-formula food for more than 12 days before the age of four months. The rates in the infants fed the goat’s milk formula were far less, and more similar to the breast milk-fed infants.
When parents change their baby’s formula or introduce solids earlier than the recommendation, a common reason given is because they feel that the baby is not satisfied. This does need to be investigated further but could possibly suggest that they were more satisfied on the goat’s milk formula.
Development and maintenance of the protective gut barrier is of particular importance in the immature infant gut, especially when allergic symptoms are often associated with increased intestinal permeability between the ages of six to 12 months of age (Kalach et al, 2001). Research has demonstrated that goat’s milk prevents the loss of intestinal barrier function following heat stress in animals (Prosser et al, 2004), indicating the presence of factors that help to maintain intestinal health.
So what about cow’s milk protein allergy?
The World Allergy Organisation estimates that 1.9% to 4.9% of children suffer from cow’s milk protein allergy (Fiocchi et al, 2010). It has previously been suggested that goat’s milk could be used as a possible nutritional alternative to cow’s milk for these infants. However, clinical studies have demonstrated a risk of crossreactivity between the proteins in cow’s milk and in goat’s milk (Ballabio et al, 2011; Infante Pina et al, 2003). There have also been reported cases of infants with cow’s milk allergy developing anaphylaxis after the ingestion of goat’s milk (Pessler & Nejat, 2004).
The 2012 EFSA publication concluded that ‘there are insufficient data on the allergenicity of goat milk protein, with no convincing data to support the conclusion that the incidence of llergic reactions is lower when feeding goat milk-based infant formula when compared with cow’s milk-based infant formula’ (EFSA, 2012). They also concluded that ‘substituting goat milk protein for cow’s milk protein in infant formula intended for cow’s milk allergic infants cannot be considered safe, unless proven to be so in clinical and in vitro studies’.
Government advice at present is therefore that, ‘Goat milk infant formula and follow-on formula is not suitable for infants with a cow’s milk protein allergy unless directed by a healthcare professional’.
Optimum nutrition during infancy is not only important for normal growth and development but also for long term health. Where breast milk is not available, it is essential that infant formulas can provide, as closely as possible, the equivalent nutritional and health outcomes as breast milk.
Until recently, most of the conclusive studies in human infants published in the international literature have been limited to the evaluation of cow’s milk or soy protein based infant formulae. However, there is now published evidence that goat’s milk infant formula is a safe and suitable alternative to cow’s and soy-based formulas and is approved for use. Goat’s milk has several features that have greater similarity to human breast milk than cow’s milk. There is no evidence to suggest that there is any advantage to including extra whey proteins in goat’s milk infant formula.
Goat’s milk infant formula, however, is not suitable for infants with a cow’s milk protein allergy, unless directed by a healthcare professional.