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Item Physiological effects of dietary moisture in cats (Felis catus) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science, Massey University, Palmerston North, New Zealand(Massey University, 2022) Hekman, MargreetThere is no system in the mammalian body that does not depend on water. Water is an essential nutrient and comprises approximately two thirds of a domestic cat’s body weight. It is recommended that sufficient water is provided to domestic cats to allow self-regulation of intake, encompassing both voluntary drinking and intake of dietary moisture. Understanding the role of dietary moisture in health and disease in domestic cats, however, has thus far been neglected, and any physiological differences between cats consuming either high moisture (HM) or low moisture (LM) diets, have been assumed unimportant. Therefore, to fill this gap in the literature this thesis investigates the effects of consuming HM and LM diets in healthy cats and cats diagnosed with chronic kidney disease. By feeding cats diets which were created to differ in dietary moisture content only, this work aimed to determine if single or multiple meal feeding of a LM food influenced total water intake (TWI), urine concentration and pH, plasma osmolality (POsm), blood pressure (BP), water balance, and activity in cats when compared to free access HM food feeding (Chapters 2 and 3). Then the effect of a single meal and a single simulated meal on post-prandial BP and heart rate using the same diets was investigated (Chapter 4). Further, using these diets, the molecular weight distribution of urinary proteins was quantified and described (Chapter 6), and the effects of a meal on post-prandial vasopressin (VP) and copeptin concentrations were investigated (Chapter 7). Lastly the diets were used to compare the effects of consuming a HM and LM diet on urine concentration and pH, POsm, plasma VP, and BP, in cats recently diagnosed with chronic kidney disease (Chapter 8). Additionally, due to the difficult and inaccurate nature of VP hormone analysis, several alternative methods to quantitate the VP proxy copeptin were investigated, however these were unsuccessful (Chapter 5). It was found that TWI and output were significantly lower when healthy cats were fed LM diets compared to HM diets and increasing meal frequency of LM diets did not increase TWI. This difference in TWI did not result in a difference in BP or total urinary protein content. However, lower TWI did lead to a decrease in water turnover rate, and increased urine concentration, POsm, and plasma VP levels. Therefore, varying dietary moisture has meaningful physiological effects in the cat. In addition, the results may indicate increasing adverse effects on health when TWI is low, with particularly detrimental effects to the kidney. Furthermore, there were modest indications that additional adverse effects such as increasing urine protein to creatinine ratio appeared when older cats were fed LM diets. Therefore, it is proposed that the role of dietary moisture is significant for the health of domestic cats, especially as they age, and that primarily feeding a LM diet and allowing self-regulation of water intake through voluntary drinking does potentially not secure a high enough TWI for their long-term health. Feeding a HM diet ensures a high TWI, which may have clinical implications for rehydration of ill cats, especially in cats diagnosed with chronic kidney disease, and potentially may even prevent or delay progression of disease in healthy cats. Feeding a HM diet should primarily be considered when a greater water intake is required to counter dehydration, or in the treatment of diseases that benefit from an increase in water intake.Item Identifying drivers of palatability in beef and lamb ingredients used in commercial pet food : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Palmerston North, New Zealand EMBARGOED until 13 March 2026(Massey University, 2023) Watson, PavineePalatability is an important criterion in pet food research and development and involves examining a pet’s liking for certain foods by assessing intake. In a sense, palatability is very much a human concept that has been applied to pet food research to assess the success or failure of a product. Whether a pet eats a food or not can alter an owner’s future repurchasing habits of pet foods. Within pet care, pet food makes up the largest proportion of the sector. In cats, domestication has placed great importance on pet food, as compared to their carnivorous ancestors, domestic cats obtain most (if not all) their daily nutrition from commercial pet food. However, as a species, cats have retained much of their ancestral traits particularly in terms of their nutritional requirements and are still known as obligate carnivores. Cats preferentially choose diets high in protein and palatability of food is known to be positively associated with the amount of protein, particularly if ingredients of animal origin are included. Nevertheless, there are few studies on the palatability of meat and its by-products as individual components. Additionally, reasons for differences in palatability between by-products have yet to be determined in detail. Research is particularly limited in new and emerging food formats such as air-dried and freeze-dried, which are of great interest to pet owners as providing nutrition to pets that has undergone minimal processing. With this being considered, this thesis examined the palatability of air-dried by-products (lung, heart, kidney, tripe, mechanically deboned meat (MDM), liver and spleen) from ovine and bovine sources and then examined potential nutrient drivers responsible for observed differences in palatability between the by-products. Finally, it aimed to understand whether inclusion of low- or highly- palatable ingredients would affect macronutrient selection in the cat. Firstly, Chapter 2 details the methodology used to manufacture air-dried by-products for testing in Chapters 3 and 4. Following the method development, three experimental trials using a designated panel of eight cats were conducted to make up Chapters 3, 4 and 5, respectively. Chapter 3 examined the within- and between-species differences in palatability between air-dried beef and lamb by-products. This was carried out to compare the same series of by-products that I investigated previously in their raw state to an air-dried state, to determine the influence of heat-treatment on palatability. The results reflected similar findings to previous research of raw by-products where greater amounts of organ meats were consumed over MDM and lamb was preferentially consumed over the equivalent beef by-products. In terms of the between species finding, lamb was also preferred over the same beef by-product. Furthermore, when compared on a dry matter basis, heat-treatment via air-drying had a negative impact on by-product palatbility compared to raw. Chapter 4 examined within species effects on palatability of by-products from young and old animals from ovine and bovine sources. Cats showed preferential consumption of organ meats from calves over beef and a general preference for lamb over mutton (except for mutton lung and tripe which were preferred from older animals), and no differences were observed between the liver of different ages. Metabolomic analysis of the by-products was also used as a tool to understand their metabolite composition and revealed that key compounds were associated with palatability in cats, particularly amino acids relating to umami taste, specifically glutamic acid, and kokumi dipeptides showed greater levels in the more palatable by-products. Whereas, dipeptides associated with lean meat, carnosine and anserine, were higher in the least palatable by-product MDM. These results highlight that although cats have a biological need for animal proteins, the type of by-product selected has a great influence on palatability. From here, I developed a series of high and low palatability diets varying in protein fat and carbohydrate content with limited ingredients, formulated with lamb kidney as the ingredient of high palatability and sheep heart as the ingredient of low palatability. These were used to examine the macronutrient selection by cats when presented in a geometric framework study. The highly palatable series did show greater intake, but both sets of diets were highly palatable with cats consuming greater than 100% of the maintenance energy requirements throughout the two phases. When the intake patterns were compared, the high palatability series saw cats consume similar metabolisable energy percentages from fat to the low palatability series but more protein and less carbohydrate. Whereas cats seemed to maximise their carbohydrate intake to reach the carbohydrate ceiling on the low palatability diet and consumed less protein. From this research, I have identified potential compounds of interest from Chapter 4 to undergo more controlled experimental protocols. Glutamic acid and the two γ-glutamyl dipeptides could be investigated further to determine the levels for inclusion in palatability enhancers and/or digests or in pet food formulations. Additionally, I have also discussed how further work could be done to reformulate the diets from the geometric framework study in Chapter 5 to achieve more variable protein, fat, and carbohydrate targets. The differences between the predicted and measured values for the series of diets with the consistent high fat contents of the diets across the study, need to be modified by using different or varying levels of meat ingredients to those selected. The study clearly demonstrated the variability of meat by-products and the challenges of using them in a controlled study. With the high utilisation of meat and by-products in pet food both locally in New Zealand and worldwide, the work carried out in this thesis highlights the importance of these ingredients at a fundamental level. This thesis also explores the known drivers of palatability in cats and their links to individual ingredients and begins to determine reasons for differences between by-products that have not be reported in the literature to date.
