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Neutering and weight gain in cats – what’s the evidence?

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01 April 2016, at 1:00a.m.

Lee Danks in the 3rd of his series for Royal Canin looks at further issues surrounding obesity.

AS MENTIONED IN OUR PREVIOUS ARTICLE, OBESITY CONTINUES TO BE A CONCERN within the pet population. An estimated 40% of pets are now considered overweight. 

It’s our collective role to examine the contributory factors – including our interventions – which can put the pet at a higher risk of weight gain. In this article, we will be turning our attention to the feline population to assess the evidence supporting the link between neutering and weight gain. 

Lifestyle changes within the human population and increasing urbanisation have resulted in a correlating increase in the number of cats kept indoors, with an estimated 24% of cats living an indoor-only lifestyle in 2015, compared to 15% in 2011.

In addition, most owners either provide food ad lib or feed two to three large meals per day4, which is at odds with the feline behavioural preference to “trickle feed”, taking many small meals throughout the day.

These lifestyle changes have occurred alongside significant levels of neutering. The 2015 PDSA Pet Animal Wellbeing report notes that 92% of cat owners de-sex their pets and we are frequently recommending early neutering. These trends may partly explain the increase in the incidence of obesity; studies have shown a clear correlation between neutering and an increased risk of weight gain.

Gonadal hormones (i.e. oestradiol, progesterone and testosterone) not only control the production of reproductive cells but are also recognised to have an effect on general metabolism and food intake. Other hormones, such as prolactin and leptin, are also thought to be involved.

With the interruption of gonadal hormone production and release which happens after neutering, levels of pituitary hormones increase. Following neutering, prolactin (synthesised in the pituitary gland) is also shown to increase as does leptin (which is synthesised in the liver) and hyperleptinaemia has been found to induce obesity.

An increase in food intake appears to be the most significant contributor when it comes to post-neutering weight gain. In a study of 12 pairs of female kittens offered free access to a dry diet until the age of one year, it was demonstrated that neutering directly affected feeding behaviour, resulting in a period of increased food intake following the procedure.

Reduction in oestrogen levels has 4 been cited as the cause of this increase and linked to the sensation of satiety. This effect is of course exacerbated where ad lib feeding is practised, particularly where a diet is high in fat and energy-dense.

Practitioners should refer to this knowledge when advising owners on neutering and the re ex changes to feeding, exercise and play that we should make. With preventive measures in mind, early signposting is of course best.

As well as discussing each pet’s welfare requirements at the first vaccination course (including the provision of an appropriate diet), we should be mindful to balance the benefits of neutering with a word about the variations which can occur to nutritional requirements.

Tailored diets for the neutered cat are formulated for both gender and life stage, realising that these factors as well as reproductive status have an influence on maintenance energy requirements.

Within the consultation room and beyond, monitoring body condition is essential and can be easily performed by the owner with adequate training. Coaching on BCS is particularly important where our feline patients are less enamoured with a visit to the veterinary practice. 

Figure 1 shows a useful take-home reference for monitoring changes in body condition, allowing owners to seek advice when they notice changes. Practitioners should also discuss the importance of environmental enrichment and encouraging play in cats throughout their entire lifetime.

The clear link between neutering and weight gain means we need to be prudent in our nutritional advice during this important time. As most of the pets presented to us in practice are neutered, it seems that our collective efforts to control the pet population and improve overall health in this manner have been effective.

To continue in the vein of preventive health, early conversations about the changing nutritional needs of the cat following neutering are essential.

References and further reading

  1. Butera, P. C. (2001) Estradiol and the control of food intake. Physiology & Behaviour 99 (2): 175-180. 
  2. Cave, N. J., Backus, R. C., Marks, S. L. et al (2007) Oestradiol but not genistein is associated with an increase in lean body mass. Journal of Animal Physiology and Animal Nutrition 91: 400-410. 
  3. Diez, M. and Nguyen, P. (2006) The epidemiology of canine and feline obesity. Veterinary Focus 16 (1): 2-8.
  4. German, A. (2012) Weight control and obesity in companion animals. Veterinary Focus 22 (2): 38-46.
  5. Kopelman, P.G. (2000) Physiopathology of prolactin secretion in obesity. International Journal of Obesity & Related Metabolic Disorders 2: S104-S108.
  6. Alexander, L., Salt, C., Thomas, G. and Butterwick, R. (2011) Effects on neutering on food intake, body weight and body composition in growing female kittens. British Journal of Nutrition 106: S19-S23.
  7. Martin, L. and Siliart, B. (2005) Hormonal consequences of neutering in cats. Waltham Focus 15 (3): 32-35
  8.  Nyugen, P. G. et al (2004) Effects of dietary fat and energy on body weight and composition after gonadectomy in cats. American Journal of Veterinary Research 65 (12).
  9. www.pdsa.org.uk: PDSA PAW Report 2015 [online] available at https://www.pdsa.org.uk/ get-involved/our-current-campaigns/pdsa- animal-wellbeing-report [accessed 09 February 2016]. 
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