The role of energy and weight: from conception to adulthood

Growth is a key stage in a kitten and puppy's life and is a time for both great exploration and physiological changes. The foundations that are laid down in growth can impact the long-term health of the animal. Nutrition, and specifically energy intake and bodyweight play a vital role in supporting growth; and this starts from before mating.

The impact of bodyweight on reproduction

Adipose tissue is an active organ that produces a large range of hormones and protein factors called adipokines. One such hormone is leptin, which plays a pivotal role in reproduction. Leptin levels have been found to be higher in dogs with an increased body condition score (Ishioka et al, 2007) and while studies in cats and dogs are limited, in human medicine it has been demonstrated that increased levels of leptin may negatively impact fertility (Brannian et al, 2001).

Breeding from queens and bitches at ideal bodyweight and shape will therefore help to support successful mating.

Energy levels during pregnancy and lactation

It is not just the bodyweight of the queen or bitch pre-mating that needs to be considered. The weight of the queen and bitch should be monitored throughout gestation and lactation to ensure they are not gaining too much weight, and careful consideration should be taken to meet their nutritional needs.

Five key nutrients to consider during gestation are protein, fat, carbohydrate, calcium and phosphorus. Proteins are the building blocks of the body, essential for the development and maintenance of hair, skin, eyes, organs and muscles, so it makes sense that pregnancy would increase nutritional demand. Fats provide almost twice as much energy (kcal) per gram than protein and carbohydrate (Greco, 2008). A high fat content means the diet fed will be energy dense, ensuring they can consume all the calories needed in a small feeding volume. This is ideal for the late stages of pregnancy, when stomach and digestive capacity might be limited because of the large uterus size. Carbohydrates are even more important as an energy source during gestation. Fetuses obtain more than 50% of their energy from glucose. Feeding a carbohydrate-free diet to pregnant bitches has been found to reduce the puppies' survival rate and contribute to weight loss in the bitch (Jones and Ackerman, 2016). Calcium and phosphorus are important for the development of fetal skeletons, while the amounts needed increase during pregnancy, it is essential to ensure feeding in the appropriate ratios.

During gestation, queens may gain up to 38% body-weight (Root Kustritz, 2006), but it is advised that the bitch's weight should not exceed their pre-breeding weight by more than 25–30% (Malandain, 2006).

Owners of pregnant pets might expect an increase in energy needs, which may lead to over-feeding. Overweight bitches are more prone to dystocia (Fontaine, 2012), which is thought to be as a result of excess fat tissue around the birth canal (German, 2006). Maternal obesity in queens has also been found to be linked to kitten mortality (Gunn-Moore, 2006).

It is therefore important to understand the difference in energy levels required for bitches and queens throughout pregnancy and lactation. While the length of gestation is very similar for both, feeding is very different.

Queens gain weight as soon as they become pregnant (Wichert et al, 2009), which is not only as a result of an increase in fetus size, but their requirement to build fat stores. This is an essential step for queens — without this energy store they may not meet the energy demands of lactation (Malandain, 2006). Feeding a diet high in energy formulated to support gestation and lactation is recommended from the start of pregnancy in queens, and their energy intake should be increased around 10% each week (Fontaine, 2012).

In comparison, bitches have a limited weight gain with-in the first 40 days (Moser, 1992; Malandain, 2006). Fetal growth mostly occurs during the last 3–4 weeks of gestation, whereby the bitch's weight will increase 15–25% (Fontaine, 2012). For this reason, a high energy diet formulated to support gestation and lactation is recommended after 42 days of pregnancy.

The diet fed to pregnant queens and bitches should meet the minimum levels set out by the European Pet Food industry (FEDIAF). Owners need to ensure they follow feeding guidelines and monitor their pet's weight to ensure weight gain does not exceed recommended values. Appropriate nutrition and energy intake during gestation will help to support the development of puppies and kittens, support optimal birthweight and influence the quality of colostrum and milk produced during lactation; all of which are key factors for neonate survival.

The influence of birthweight on survival in neonates

Neonates is a term referring to kittens within the first 4 weeks of life, and puppies within the first 3 weeks of life (Gunn-Moore, 2006; Chastant and Mila, 2019). During this time, neonatal mortality rates are surprisingly high; with kitten mortality rates reported between 15–30%, and around 10% for puppies (Gunn-Moore, 2006; Chastant and Mila, 2019).

An essential part of supporting survival in these early stages is to identify at-risk puppies early. Apgar scoring is widely used in human medicine and an adapted score has been developed to assess new born puppies and identify those at risk (Veronesi et al, 2009). Each puppy in the litter should receive an individual score within 8 hours of birth. Puppies that have an Apgar score of 6 or under are at higher risk of mortality and steps should be taken to provide additional support.

While many factors can influence survival rates, birth-weight, weight gained after birth and colostrum intake are particularly important.

Studies have found that litter size (Lawler, 2008) may influence birthweight in kittens and puppies, and breed size is an influencing factor in dogs (Gunn-Moore, 2006; Royal Canin, 2016); whereby the higher the bitch's weight, the higher the neonate puppies' weight. Because weight varies between bitches of the same breed, it is important to define a low birth weight for different sizes of dog (Table 1).

Kittens with a low birth weight are at an increased mortality risk (Gunn-Moore, 2006). Birth weight has been associated with neonate deaths in puppies, especially within the first 2 days of life (Mila et al, 2015), but was not found to influence mortality rates between 2–21 days. Growth rate in the first 2 days was found to influence mortality rates in puppies between 2–21 days old, with those with a low growth rate after 2 days of life being at increased risk of mortality (Mila et al, 2015).

After birth, nutrition is no longer provided through the placenta, instead it is provided through colostrum and milk (Figure 1). Colostrum is often referred to as ‘first milk’ and plays an essential role in survival as it has a high concentration of immunoglobulins and energy (Royal Canin: Neo-Care Center Toulouse National Veterinary School, 2016).

Unlike humans, placental transference of immunoglobulins is limited in kittens and puppies. Rather, they gain most of their passive immunity from the immunoglobulins in colostrum (Royal Canin: NeoCare Center Toulouse National Veterinary School, 2016).

Neonates have limited fat stores and a reduced ability to generate glucose, meaning there is an increased risk of developing hypoglycaemia (Gunn-Moore 2006; Mila et al, 2015). This is important when neonates with a low birth weight are considered, that then have a marked reduction in maintaining temperature and blood glucose level. Colostrum intake in 2-day old piglets was evaluated, a positive association was found between rectal temperature and glucose concentration. This highlights the importance of colostrum intake in helping newborns regulate temperature and glucose levels (Mila et al, 2015).

Colostrum plays a vital role in the survival of neonates; therefore a substitute is needed immediately if there is not enough available. Ideally this should contain immunoglobulins, but at least a milk replacer that provides energy and other essential nutrients. The replacement colostrum/milk product should be species-specific as puppies and kittens require high fat and high protein milk. Alternative sources, such as cow's milk, do not meet their nutritional needs (Table 2). Any puppies with a low birth weight or identified at risk should be supplemented with a colostrum/milk replacer.

Neonates should be encouraged to suckle within 2 hours of birth, ensuring an optimal intake of colostrum. They should be weighed daily for the first 2 weeks and then every 3 days until the puppy or kitten is 1 month old (Alves, 2020), to monitor weight gain. Regular weight assessment should continue throughout the pet's life to help maintain an ideal weight.

Weaning

Weaning is the process of puppies and kittens transitioning from maternal milk to solid food. This normally starts between 3–4 weeks of age and coincides with the eruption of the first set of teeth, when energy needs start to exceed what the mother's milk can provide. Diets should be energy dense and easy to eat, to support a limited stomach and digestive capacity.

Regular assessment of weight should continue through-out weaning to ensure enough calories, but after weaning, the focus switches to ensuring weight gain is not happening too quickly. Unfortunately, there are limited studies looking at ideal growth rates and weight gain in neonatal and weaning puppies, which can make it difficult to determine if the nutrition provided is meeting the needs of the growing animal. Research in this area is developing though, with one recent study looking at the development of growth curves for neonates up to 3 weeks of age (Alves, 2020). While more research is undertaken to develop growth curves for these essential early stages, the maintenance energy requirement (MER) calculations for growing animals recommended by FEDIAF should be referred to.

Growth rates after weaning

While puppies and kittens undergo a fast growth rate during the first 6–8 weeks of life, after weaning is when a rapid growth rate occurs.

After weaning, growing puppies need approximately twice the energy intake per unit of bodyweight compared with adult dogs of the same weight (National Research Council, 2006). When they reach about 40–50% of their adult weight, energy requirements reduce to about 1.6 times maintenance rates. By the time they reach 80% of their adult bodyweight energy requirements are about 1.2 times maintenance (Case et al, 2011).

Energy is the most important nutrient in growth (Case et al, 2011). If too much energy is fed, growth rates speed up. However, there is no benefit to speeding up growth rates, and this may in fact cause long-term health effects in large and giant breed dogs (Larsen, 2010). One study looked at the impact of feeding a high energy diet to giant breed puppies and found it resulted in skeletal abnormalities (Hedhammer et al, 1974). Conversely, slowing the growth rate may have positive impacts for long-term health. In one study, Great Dane puppies were either fed ad-libitum or limit fed to 60–70% of ad-libitum. The limit fed puppies grew slower with a dramatic reduction in skeletal abnormalities compared with the ad-libitum fed group (Dämmrich, 1991).

The variation in dog sizes means canine growth rates vary greatly (Figure 2). Cats and small breed dogs reach maturity between 9–12 months of age, whereas large and giant breed dogs will not reach maturity until 18–24 months (Case et al, 2011). Energy needs of each breed therefore vary greatly.

This means energy requirements and the feeding ration likely changes throughout growth, and owners should be advised to regularly review feeding guidelines to ensure the appropriate feed amount. Owners should be encouraged to weigh their pet's daily food ration daily using digital scales. Measuring cups should be avoided, research suggests they may lead to over-feeding by as much as 80% (German et al, 2010), which may contribute to obesity.

Obesity

Obesity in cats and dogs is one of the most common diseases in veterinary practice (Cave et al, 2012; O'Neil et al, 2014). It is estimated that 65% of adult dogs and 39% cats in the UK are overweight (Courcier et al, 2010; German et al, 2018). The links between obesity and an increased incidence of conditions such as joint disease, diabetes mellitus, urinary disease, skin disease and tumours are well documented (German, 2006). While the importance of balanced nutrition and maintaining a healthy weight is an essential part of supporting the overall health of adult cats and dogs, more and more we are seeing reports that obesity in puppies and kittens is a risk factor for predicting the likelihood of obesity in adulthood.

Risk factors for obesity

In a letter to the editor of Veterinary Record in 2018, Professor Alexander German indicated that 37% of dogs less than 2 years of age were overweight or obese. The importance of this cannot be ignored. Research has indicated that a high body condition score at 7 months of age may be a predictive factor of obesity in adult dogs (Leclerc et al, 2017). In fact, Glickman et al in 1995 found that female dogs that were obese between 9 and 12 months of age were 1.5 times more likely to be obese as an adult. There are similar findings in cats.

Cats whose owners reported them as being overweight or obese by 1 year of age were found to be over 10 times more likely to be reported as overweight or obese at 2 years of age (Rowe et al, 2017). This is not the only study that reports this finding. Serisier et al in 2013 found that an increased bodyweight at 1 year of age was a risk factor for obesity in adult cats. However importantly, growth rate between 3 and 12 months of age (measured by bodyweight changes) has also been identified as an important risk factor for bodyweight at 1 year of age (Serisier et al, 2013).

It is therefore vital that as part of tackling the obesity epidemic, optimal growth rates for kittens and puppies are maintained. One way to monitor this is through plotting growth curves.

Growth charts

Growth charts are commonplace in human medicine, allowing healthcare professionals to monitor the growth of an individual and compare it to that of a healthy reference population. Recent advances in veterinary research have led to the development of growth curves for puppies (Salt et al, 2017) and kittens (Figures 3 and 4). There are different growth charts for male and female kittens and puppies, as well as different size charts available for puppies, which allows for the different growth rates of different sized dogs to be accommodated.

Weight is plotted against the current age of the puppy or kitten. An increase or decrease beyond two centiles are indications that there may be growth disturbances. A change in direction upwards may indicate that the kitten or puppy is gaining too much weight and is therefore at risk of obesity. A downward trend might indicate a slow growth rate and could be a sign of failure to thrive. Essentially, the charts allow for early identification of those that may be at risk and allow veterinary professionals to intervene early in order to ensure optimal growth rates are maintained.

Growth charts allow the puppy or kitten's growth to be tracked until they reach maturity ensuring optimal growth throughout and ultimately helping to reduce the number of overweight puppies and kittens. Growth charts can also help to support conversations with pet owners on the appropriate time to transition puppies and kittens from a growth diet to an adult formulation.

Conclusions

The journey from conception to adulthood plays an important role in the long-term health of cats and dogs. It is important to have an understanding of different energy needs throughout each stage and the importance of monitoring bodyweight to identify those at risk; whether that is lack of weight gain in neonates or excessive weight gain in the post-weaning growth phase.

KEY POINTS

• Growth represents a vital period in the life of a puppy or kitten.
• Appropriate energy intake from conception to adulthood helps to support healthy growth and a heathy weight.
• Utilising new tools can help to identify those at risk of low or increased weight gain and allows for early intervention.