Update on key diet considerations and nutritional requirements

Recent years have seen significant changes in the dog and cat pet food market that should have stimulated practices to review their internal processes and advice they give to their clients.

This article highlights some of the recent issues of most concern to animal health and suggests how practices could approach them.

Marketplace changes

While the majority of pet owners still feed commercially manufactured “complete” wet or dry foods, interest has been growing in novel types of food, mimicking trends in human nutrition.

Perhaps surprisingly, some veterinary practice staff also hold polarised opinions on the value of, at one extreme, feeding raw meat diets; and at the other extreme, vegan diets.

• Implications for practices: we have to be aware that our clients may hold strong, sometimes irrational, views about how they want to feed their pets. However, our overriding professional obligation is to ensure the health of each pet, by advising against feeding practices that we know may be harmful to it, or to other animals or people.

Client education on best practice in nutrition is essential through all life stages, but especially during pregnancy and growth periods, and a detailed nutritional history should be a routine part of clinical history recording.

When making dietary recommendations to our clients, just two key considerations exist.

Is the food safe if fed exclusively over a period of time?

• Serious concerns exist about the potential for dogs and cats fed raw meats to carry zoonotic pathogens (notably Campylobacter, Salmonella, Listeria and Shiga toxin‑producing Escherichia coli [STEC]) that can be shed and cause serious disease in humans as well as other animals (Davies, 2020; Davies, 2018; Freeman et al, 2013). Pet food recalls because of microbiological contamination are almost all raw products. Visit https://bit.ly/3xu2ACy for cases in the UK and https://bit.ly/3zA1M0M for cases in the US. In the US, pet foods may be randomly screened for pathogens by state authorities, and between 1 January 2020 and 12 April 2021 25 pet food recalls were recorded by the US Food and Drug Administration (FDA) because of microbiological contamination (Table 1). Raw meat-based foods accounted for 76% of all reports – and given that prepared dry or wet foods dominate market sales, this represents a huge increased risk by feeding raw foods.

Table 1. Pathogenic microorganisms and pet food recalls recorded by the US Food and Drug Administration (January 2020 to 12 April 2021)
Infectious agent	Dry food	Wet food (can/pouch)	Raw food
Salmonella	2	3	6
Listeria monocytogenes	0	1	8
Salmonella and Listeria	0	0	3
Salmonella and Shiga toxin‑producing Escherichia coli	0	0	1
Clostridium botulinum	0	0	1
Total	2	3	19

• Pet foods can be dangerous if contaminated with toxins. During 2020-21 many pet foods had to be recalled from around the world following deaths due to aflatoxin contamination of corn. Cases in the US are listed at https://bit.ly/3zA1M0M
• Clinical signs of nutrient deficiency or excess can occur if imbalanced foods are given – a recent example is thiamine; deficiency – see further on.
• Consumers should be able to rely on a pet food declared to be “complete” to provide safe levels of ingredients, but they often do not – see further on.
• Unfortunately, feeding home‑made recipes is not the answer to the problem of non‑compliance with guidelines by commercial producers, as all studies looking at home‑made recipes have concluded they are not reliable (Wilson et al, 2019; Davies, 2014; Larsen et al, 2012) and potentially harmful because of deficiencies or imbalances.

Does the food provide appropriate energy and essential nutrients that the animal needs?

• Pet foods sold as being “complete” in the UK should comply with European Pet Food Industry (FEDIAF) Nutritional Guidelines, and in the US with Association of American Feed Control Officials (AAFCO) Guidelines. However, studies have shown many do not in fact meet the guidelines for essential nutrients, including minerals (Davies et al, 2017; Kazimierska et al, 2020; Zafalon et al, 2020).
  • Implications for practices: only recommend foods from trusted sources and have foods independently analysed to check for compliance when clinical signs could be due to nutritional errors.
• Home‑made recipes do not comply with minimum nutritional requirements. In all published studies, home‑made rations are inadequate – for example, of 114 home‑made recipes for cats, none met recommended allowances and the nutrients most frequently below AAFCO guidelines were choline, iron, thiamine, zinc, manganese, vitamin E and copper (in 89.7%, 76.6%, 62.8%, 61.7%, 57.4%, 57.4% and 45.7% of recipes, respectively; Wilson et al, 2019).
  • Implications for practices: do not recommend home‑made recipes unless you are sure they comply with minimum nutritional guidelines.
• National Research Council (NRC) energy calculations are inaccurate. Growing evidence exists that the energy calculations recommended by the NRC overestimate the energy needed by many dogs and cats, and predisposes them to develop obesity (Klein et al, 2019; Alexander et al, 2017; Dobenecker et al, 2013; Hawthorne et al, 2004; Kienzle and Rainbird, 1991). For this reason, some companies are formulating their foods to comply with AAFCO or FEDIAF guidelines, but they are then recommending lower energy feeding rates in their feeding guides. This is in an attempt to reduce the prevalence of overweight and obese pets in society, and takes into consideration the fact many owners provide energy‑dense treats to their pet in addition to the main ration. This practice is fine if the level of reduced energy is what is actually required because the proportions of essential nutrients needed should be directly related to the energy requirement. However, if the reduced energy and feeding rate is incorrect it could result in weight loss and nutrient deficiency. Claims by some manufacturers that their recipe is more digestible than other formulations need to be supported by controlled feeding trials using the compounded food they are selling.

• • Implications for practices: only use feeding guides as a starting point. I recommend starting in the middle of a range (if given). It is imperative owners then weigh their pet regularly (weekly during growing periods) and measure body condition score (BCS). Food intake should be adjusted up or down as appropriate to maintain optimum body condition, which is four to five on a validated nine‑point BCS scale. For growing animals, BCS scales have not been validated, so the rate of weight gain should be measured against published scales where they exist (for example, https://bit.ly/3cRtrQZ) and excessively fast growth rates should be avoided, especially in large and giant breeds of dog in which rapid weight gain is associated with increased risk of developmental skeletal diseases.

Novel products

Feeding novel foods to dogs or cats is becoming increasingly popular – for example, feeding unusual and sustainable plant‑based protein sources.

The use of citrus fibre in pet foods jumped 437% in the year ending March 2019, and the use of apple and cranberry has increased (Mintel Global New Products Database). However, this trend is potentially problematic for several reasons:

• Foods that are quite safe for humans to consume can cause illness or even be fatal for dogs and cats. Examples include nuts, grapes, raisins and chocolate. The FDA is investigating a possible association between feeding some grain-free food recipes containing legumes and the occurrence of dilated cardiomyopathy in atypical dog breeds.
• For many novel foods, insufficient data exists to show whether the nutrients they contain are bioavailable and what nutritional benefits they actually provide for a species.
  • Implications for practices: only recommend diets containing novel ingredients if you are satisfied about their safety and efficacy – ideally they would have undergone feeding trials to ensure nutritional adequacy and safety.

Pet food recalls

When health risks are identified after pet foods have been distributed to the retail sector, they are recalled from the market.

Practices should appoint someone to monitor product recalls because early awareness about emerging issues can prevent exposure. Visit https://bit.ly/3xu2ACy for cases in the UK and https://bit.ly/3zA1M0M for cases in the US.

Excess vitamin D content (Crossley et al, 2017; Mellanby et al, 2005)

During 2020 many companies had to withdraw their products because of excessive vitamin D that had been added to the foods accidentally due to human error.

• Implications for practices: clinicians should take a complete dietary history and rule out – or in – hypervitaminosis D when pets present with any of the following signs:
  • persistent hypercalcaemia
  • soft tissue mineralisation
  • polydipsia
  • polyuria
  • renal failure
  • death

Inadequate thiamine (vitamin B₁) in cat foods (Kritikos et al, 2017; Markovitch et al, 2013)

Implications for practices

Clinicians should rule in or out thiamine deficiency when a dog or cat shows signs of arrhythmia, ataxia, blindness, death, dyspnoea (cats), nystagmus, paraparesis, proprioceptive deficits, delayed pupillary light response, recumbency, seizures, tachycardia or ventroflexion of the neck (cats).

Early signs may include anorexia, hyporexia, lethargy, vomiting and weight loss.

Salmonella, Listeria and STEC

Contamination with serious zoonotic pathogens is almost exclusively in raw pet foods, and this accounts for most product recalls in the UK and US.

• Implications for practices: all dogs and cats fed raw meats should be considered a potentially serious health risk to other animals and people who come into contact with them or their environment. This includes practice staff and animals on veterinary premises. Raw-fed animals should be handled wearing protective clothing, ideally not allowed on to veterinary premises, not allowed into contact with high‑risk people or animals (young, elderly, immune compromised or pregnant), or not allowed on to premises with high‑risk individuals (such as hospitals and care homes). Raw-fed animals should be regularly tested to ensure they are not carrying dangerous pathogens.

Mycotoxin recalls

In January 2021, pet foods manufactured by Midwestern Pet Foods in the US were withdrawn worldwide following 110 pet deaths due to contamination of foods with aflatoxins. The fungus grew on corn due to the exceptionally arid conditions during growth.

• Implications for practices: monitoring global pet food recall issues early in the roll‑out of this problem could have prevented many deaths worldwide before the affected products (which were all linked to a single manufacturer in the US) were withdrawn.

The gastrointestinal microbiome, diet and disease

Microbiome research continues, and an excellent review of the relationships between the microbiome of dogs and cats in disease was published last year (Wernimont et al, 2020).

Essentially, we now know certain foods can alter the microorganisms in the gut (microbiome), and that these and their metabolites impact on digestion and absorption of nutrients; and specific microbiome profiles can be associated with diseases including obesity, gastrointestinal disease, renal disease and diabetes.

Microbiome-modifying nutrients are now being incorporated into various therapeutic diets.

Genomic testing is now available in the UK, so patients’ microbiomes can be analysed from a single faecal sample.

Conclusions

The pet food industry is continually evolving and many of these changes will impact on veterinary practice. It would be useful to appoint someone in your practice to monitor the market and act as a sentinel to feed back relevant changes to the rest of the practice team.