There is no doubt breastfeeding is the gold standard of infant feeding. There is extensive evidence of its nutritional benefits for the infant alongside health benefits for both the infant and the mother (Horta et al, 2007; Ip et al, 2007). To ensure optimal nutritional and health benefits for infants, it is highly recommended that breastfeeding should be the infant feeding method of choice, and exclusive breastfeeding should be continued for a minimum of 6 months (Department of Health, 2003; World Health Organization (WHO), 2001).
There are instances when mothers are unable to breastfeed for medical, social or psychological reasons, and require a safe alternative method of feeding the infant. The requirement for alternatives to breastfeeding is not a new phenomenon, but has existed for countless centuries. This paper is not in any way intended to undermine the importance nor the value of breastfeeding, but will: review the historical use of animal milks as an alternative method of infant nutrition when maternal breastfeeding was not possible; consider the rise in the use of infant formula milk; explore the features and advantages of goat milk formula compared with cows' milk formula; and identify the use of goat milk formula as a safe alternative when mothers are unable to breastfeed.
History of goat milk
For many centuries, the choice of alternatives to breastfeeding was limited, and the most favoured and safest choice was considered to be the wet-nurse (Battersby, 2006). In addition to the use of wet-nurses, there is also evidence that animal milks were in relatively common use as far back as 2000 BC (Wickes, 1953). By the late 18th century, animal milks became more common and alongside human milk, the milk of ass, goat, cow and sheep were in regular use. Goat milk was more widely used as a source of infant nutrition outside of the UK. In France, the direct suckling of foundlings by goats was initiated in Aix by Alphonse Le Roy in 1775 (Hardyment, 2007). By the late 18th century, the ‘scientific revolution’ began to create advances that shaped our understanding of infant nutrition, and the advent of chemical physiology was to underpin the creation of human milk alternatives.
The development of infant formula
The first infant formula was accredited to Justin von Liebig, a pioneer of analytical chemistry, in the 1850s (Schwab, 1996). This formula, although it went on public sale, did not appear to suit newborn babies. This did not deter others, and Philippe Biedert, in Germany, was one of the first to experiment with various mixtures of cows' milk, and the humanisation of mammalian milk was commenced (Weaver, 2006). By the late 19th century, Henri Nestlé patented his own baby milk and the advent of infant formula had arrived. In the UK, it became tradition to use cows' milk for infant formulas.
Goat milk formula in the UK and Europe
Despite cows' milk being the dominant component of infant formulas, there has been a parental demand for goat milk infant formulas and there have been reports of the use of raw goat milk and homemade formula. Instructions for making homemade formula are readily available on the internet (Stout, 2015). However, these practices can have highly dangerous consequences for the infant. Outside the EU, goat milk formulas have been widely used in more than 20 countries for over 25 years, and countries such as Australia and New Zealand have a long history of goat milk formula use. Within the EU, the suitability and safety of goat milk formula has been questioned, and it was only following a double-blind randomised trial, comparing the growth and nutritional status of infants fed a whole goat milk (80: 20) formula with those of infants fed a typical whey-based (60: 40) cows' milk infant formula, that its use has been approved (European Food Safety Authority (EFSA), 2012). The research was a comparison of the two different types of formula and a reference group of breastfed infants was also included in the study (Zhou et al, 2014).
In 2013, in England, the Infant Formula and Follow-on Formula (England) Regulations 2007 were amended to allow the use of goat milk as a source of protein in formula milks from March 2014 (Gov.UK, 2013). This decision was taken after the clinical trials on whole goat milk formula were presented for scientific opinion to the EFSA (2012). The EFSA concluded that the growth and nutritional outcomes provided by whole goat milk formula (80: 20 casein: whey) did not differ from those provided by a standard whey-based cows' milk formula (60: 40 whey: casein). The proviso was that the final product must comply with the compositional criteria laid down in Directive 2006/141/EC, which governs the composition of all infant formulas and follow-on formulas produced within the EU, including the UK. This proviso ensures the quality of infant formula throughout the EU and, as such, should be a reassurance to parents and health-care advisors.
Differences between mammalian milk and human milk
With all infant formula, it is impossible to exactly replicate breast milk, which not only can vary from mother to mother but from feed to feed, and from the commencement of the feed to end of the feed. Breast milk also has numerous intrinsic therapeutic attributes that are difficult or impossible to replicate. It is important, therefore, that in the absence of breast milk infants receive a formula for the first 12 months of life which delivers, as closely as possible, the same nutritional and health outcomes as those of breastfed babies. Mammalian milk used as a breast milk substitute will require modification, and the amount of modification will depend on the milk's inherent constituents.
At a basic level, goat milk—like cows' milk—differs from human milk because it has a higher protein level and lower lactose level (NANNYcare, 2014; Crawley and Westland, 2015). Also, similar to unmodified cows' milk, unmodified goat milk lacks an adequate amount of certain constituents and, to comply with the compositional criteria laid down in Directive 2006/141/EC, these are adjusted for during manufacture.
Both goat and cows' milk formulas require supplementation with refined lactose, vitamins and minerals (NANNYcare, 2014). The naturally occurring fatty acids in goat milk are supplemented with essential fatty acids from selected vegetable oils. Importantly, unlike standard cows' milk formula, goat milk formula does not need to have whey added. The clinical study by Zhou et al (2014) demonstrated the health and nutritional outcomes of babies fed a whole goat milk (80: 20) formula were equivalent to those of babies fed a whey-based (60: 40) cows' milk formula. This study was the basis on which the European Directive was amended.
Features of whole goat milk formula
There are various differences and advantages of whole goat milk formula (80: 20 casein: whey) versus whey-adjusted cows' milk formula (60: 40 whey: casein) (Table 1).
| Goat milk: |
|---|
| Is synthesised by the apocrine process similar to that of human milk (Wooding et al, 1970) |
| Has lower levels of αs1-casein than cows' milk formula and is more in line to the human milk casein profile (Martin et al, 2002) |
| Contains higher levels of nucleotides and taurine and therefore does not require supplementation like cows' milk formula (Prosser et al, 2008) |
| Decreases gut damage and leakiness caused by heat stress (Prosser et al, 2004) |
| Contains proteins that are digested more completely than cows' milk proteins (Pintado and Malcata, 2000) |
| There is no need to add whey proteins to goat milk formula (Rutherfurd et al, 2006) |
Differences in the secretion process
The first important feature of goat milk is that the secretion process is nearer to that which occurs in the human breast than that which occurs in cows' milk synthesis (Wooding et al, 1970). Milk is produced in the mammary glands by forming minute droplets that contain proteins, lactose, vitamins and minerals, and bioactives.
There are two different processes by which this can occur—merocrine and apocrine secretion:
The apocrine process is central to human milk synthesis. In goat milk synthesis, the apocrine process is more dominant than in cows' milk synthesis (Wooding et al, 1970). The dominance of the apocrine process means that more cytoplasmic particles are present in goat milk similar to those in human milk (Boutinaud and Jammes, 2002), and this is thought to provide human milk and goat milk with a range of cellular components such as nucleotides and free amino acids. Therefore, goat milk—like human milk—benefits from higher levels of naturally occurring bioactives.
Nucleotides, which are important constituents of RNA and DNA, are essential for rapid growth that occurs in infants and the nucleotides present in human milk are essential for the infant's optimal growth (Schaller et al, 2007) and the development of the immune system (Pickering et al, 1998). Cows' milk infant formulas are routinely supplemented with nucleotides; whole goat milk formula, however, already contains a range of nucleotides five times greater than cows' milk formula, so does not require supplementation (Prosser et al, 2008).
Taurine, a sulphonated amino-acid, is another important ingredient of infant formula and is involved in bile salt formation, osmoregulation, antioxidation, calcium transport and in the central nervous system (Redman et al, 1998). It is one of the main free amino acids in goat milk and is up to 20-fold higher than in cows' milk (Mehaia and Al Kanhal, 1992).
The free amino acids present in goat milk are similar to human milk reference values, when expressed on a per-energy basis (Rutherfurd et al, 2006). In the past, the levels of protein in cows' milk formula have been set higher than human milk because of concerns over the low levels of amino acids and the quality of the protein. These higher protein levels have been shown to be detrimental to the infant because of greater-than-normal weight gain and also the stress on the immature kidneys (Koletzko et al, 2009; Escribano et al, 2012). There is a proposition that early and rapid growth in infancy can manipulate the infant's metabolic profile to be susceptible to obesity and other components of metabolic syndrome. This highlights the necessity to adjust the amino acid levels in any infant formulas to align as close as possible with human milk reference values.
Zhou et al (2014) demonstrated that infants fed with whole goat milk formula had blood urea levels that were more in line with those of breastfed infants, and these levels were 11% lower than those in infants who were fed cows' milk formula. Combined with the plasma amino acid and infant growth data, the urea levels demonstrate the adequacy of amino acids in whole goat milk formula. There is currently no equivalent data on any other form of goat milk formula e.g. a whey-based goat milk formula.
Differences in casein levels and non-human proteins
The second area where goat milk formula differs from cows' milk formulas is in the casein profile. The casein profile of goat milk is closer to human milk than is cows' milk. Human milk contains β-casein, κ-casein alongside α-lactalbumin, immunoglobulins (antibodies) and lactoferrin. Cows' milk and goat milk both contain these proteins but also two additional casein proteins—αs1-casein and αs2-casein—as well as the whey protein β-lactoglobulin. Goat milk formula, however, has significantly less αs1-casein than cows' milk formula and its protein profile is more in line with the casein profile of human milk (Martin et al, 2002)
It is common practice to add whey proteins to formula in an attempt to copy the casein: whey ratio of human milk. However, adding whey protein alters the balance of other ingredients. For example, while adding whey reduces casein proteins, at the same time it significantly increases the levels of non-human β-lactoglobulin. The lower levels of αs1-casein in goat milk, together with the absence of added whey in whole goat milk formula, means that the non-human proteins are lower in whole goat milk formula than in either whey-enhanced or casein-dominant cows' milk formula. This could be very important, as αs1-casein and β-lactoglobulin are two proteins known to induce allergic reactions in people sensitised to milk (Restani et al, 1999). However, it could be argued that the allergic reaction in a sensitive infant will be the same whether there is a small or large amount of the protein.
Differences in digestibility and need to add whey
A further reason why whey proteins were initially added to cows' milk formula was to reduce the formation of hard curds in the infant's stomach (Schreiner et al, 1982). The newborn's digestive tract is immature and, as such, requires proteins and fats in formula to be easily digestible. Cows' milk forms firmer, harder casein curds than goat milk (Park, 2007). These can be difficult to digest and the addition of whey reduces the number of these harder curds. In contrast, goat milk behaves more like breast milk in the infant stomach, forming looser, softer and more porous curds which assist digestion. Further, the digestion and absorption of the amino acids in infant formula based on whole goat milk is comparable to a cows' milk infant formula with added whey (Rutherfurd et al, 2006). This highlights that it is not necessary to modify the casein: whey ratio of goat milk to optimise digestibility.
Pintado and Malcata (2000) also found that the stomach enzyme trypsin broke down 96% of goat casein compared to only 76-90% of cow casein. One reason why goat casein proteins may be better digested is the larger size of casein micelles, (minute casein proteins that are suspended in milk). The digestive juices in the human stomach cause casein micelles to form into curds and whey. The curds in goat milk behave more like those formed when human milk is digested; they are a loose, more porous curd than standard cows' milk formula. It is hypothesised that this type of curd allows digestive enzymes easier access to the milk proteins, assisting with their digestion. At the same time, nearly threefold more β-lactoglobulin in goat milk is digested by human digestive juices compared to β-lactoglobulin in cows' milk (Almaas et al, 2006). Both the studies by Pintado and Malcata (2000) and Almaas et al (2006) were based on in vitro studies of goat milk and not goat milk formula.
Differences in amount of processing
When modifying whole goat milk formula, a blend of goat milk fat and vegetable oils is used, rather than extensively modified fats often used in other formulas. This provides whole goat milk formula with a triglyceride structure similar to cows' milk formula with modified vegetable oils but with far less processing (Prosser et al, 2010).
Goat milk may also assist intestinal health. Prosser et al (2004) demonstrated that goat milk was able to prevent the loss of intestinal barrier function following heat stress tests in animals. The development and maintenance of the barrier is important in regard to symptoms of allergy. This is an area that requires further investigation; the EFSA publication recommends against the use of goat milk formula in cases of cows' milk allergy and the government advice is that ‘goat milk formula and follow-on formula is not suitable for infants with a cow milk allergy’ (EFSA, 2012: 8).
Zhou et al (2014) demonstrated that the parents of infants fed goat milk formula were less likely to switch formula or to introduce early weaning; only 27% of infants fed with goat milk formula were offered alternative formula or additional weaning foods compared to 40% of infants fed with cows' milk formula. Many parents who choose to change their infant's formula usually do so because they feel that their infant is not satisfied. From the evidence presented by Zhou et al (2014), it may be surmised that parents felt their infants were more satisfied when fed on goat milk formula; however, this would require further investigation.
Conclusion
Breastfeeding remains the best way for infants to receive optimum nutrition to ensure normal growth and development, as well as long-term health. For those mothers unable to breastfeed their infants, the new recommendation by the EFSA and the amendment of the Infant Formula and Follow-on Formula (England) Regulations now means that parents can, if they so wish, use goat milk formula as an alternative to cows' milk formula. This means that for both parents and health professionals, there needs to be a better awareness of goat milk formula and also of the advantages that it has over cows' milk formula.
In summary, the advantages that goat milk formula has for infants over cows' milk formula include the fact that it is secreted by a process that is similar to that of human milk and also that its casein profile is near to human breast milk, having a lower level of αs1-casein and a smaller proportion of β-lactoglobulin. Other advantages are that goat milk also contains naturally higher levels of nucleotides and taurine, both of which are important for the health and wellbeing of the infant. In animal research, it has been shown to decrease gut damage and leakiness caused by heat stress. Finally, milk proteins are more readily digested because of the larger micelles, which contribute to a softer curd in the infant's stomach.
Clinical studies have shown that formula based on whole goat milk provides equivalent outcomes to a whey-based cows' milk formula, confirming goat milk formula is a safe alternative to cows' milk formula when breastfeeding is not possible. Moreover, it also has some advantages over cows' milk formula. Importantly, there is no need to add whey proteins to goat milk formula.