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PAPER
Impact of diet on incisor growth and attrition and the development of dental disease in pet rabbits A. L. Meredith, J. L. Prebble and D. J. Shaw Royal (Dick) School of Veterinary Studies and The Roslin Institute, University of Edinburgh, Easter Bush Campus, Midlothian, EH25 9RG J.L. Prebble was employed on a KTP partnership between the Royal (Dick) School of Veterinary Studies and Burgess Pet Care, Victory Mill, Priestman’s Lane, Thornton-Le-Dale, Pickering, North Yorkshire, YO18 7RU. Current address: Askham Bryan College, Askham Bryan, York, YO23 3FR
OBJECTIVES: To assess the impact of four rabbit diets (hay only; extruded diet with hay; muesli with hay; muesli only) on length and curvature of cheek teeth and eruption and attrition rates of incisors. MATERIALS AND METHODS: Thirty-two Dutch rabbits, randomly divided into four diet groups, had length and saggital plane curvature of the first cheek teeth measured radiographically at 1, 9 and 17 months. Eruption/attrition of the left upper incisor was directly measured at weeks 30, 32 and 35. RESULTS: Eruption rates matched attrition rates in all groups, but were higher in the hay only group than in both groups fed muesli. By month 9, a greater degree of tooth curvature was present in rabbits fed muesli only than in those fed hay only and extruded diet with hay. After 17 months, rabbits fed muesli only and muesli with hay had longer lower first cheek teeth and larger interdental spaces between the first two molars than rabbits fed extruded diet and hay and hay only. Three rabbits fed muesli only developed evidence of dental disease. CLINICAL SIGNIFICANCE: Presence of increased tooth length, curvature and interdental spaces indicated early dental pathology in rabbits fed muesli. Muesli diets cannot be recommended for pet rabbits. Journal of Small Animal Practice (2015) 56, 377–382 DOI: 10.1111/jsap.12346 Accepted: 2 February 2015; Published online: 19 March 2015
INTRODUCTION Despite rabbits being the third most popular mammalian pet in the UK (PDSA 2011), their dietary requirements are not fully understood. Diet is frequently implicated in the development of acquired dental disease in pet rabbits (Harcourt-Brown 1996, Crossley 2003, Meredith 2007, Okuda et al. 2007); however, its exact role in the aetiology of dental disease remains unclear. The prevalence of dental disease in pet rabbits has been reported to be 29–38·1% (Mullan & Main 2006, Jekl et al. 2008), but these reports may underestimate the true prevalence as radiography was not performed and early cases may have been undetected (Jekl et al. 2008). Rabbits have continuously growing elodont teeth (Shadle 1936). The upper incisors erupt at a rate of approximately 2 mm/ week and the lower at 2·4 mm/week (Shadle 1936), and incisor eruption rate and length vary widely between individuals (Shadle 1936, Ness 1956). The growth rates of the cheek teeth (premolars Journal of Small Animal Practice
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Vol 56
•
June 2015
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and molars) have been reported to be approximately 3 mm a month (Crossley 2005, Meredith 2007, Lord 2012), but more recent studies have reported growth rates of 1·4–3·2 mm/week (Müller et al. 2014). Tooth length is maintained by the abrasive nature of the diet, tooth on tooth action during chewing and grinding of the teeth during periods of rest (Shadle 1936, Crossley 2005). The functional differences between incisors and cheek teeth indicate that different diets affect each type of tooth differently (Müller et al. 2014). Eruption rates change to match rates of attrition (Wolf et al. 1993); taking the incisors out of occlusion by shortening them increases eruption rates (up to 0·7 mm/day) until the tooth returns to occlusion (Ness 1956). Tooth length, wear and growth are also linked to dietary abrasiveness, which is caused by the dietary content of both internal (plant phytolith) and external abrasives such as sand (Müller et al. 2014). In addition to diet, age and pregnancy may also influence the rate of eruption of teeth (Shadle 1936, Ness 1956, Wolf et al. 1993).
© 2015 British Small Animal Veterinary Association
377
A. L. Meredith et al.
Prevention of eruption does not stop growth from the germinal centre at the apex of the tooth and growth continues with enough force to distort the structure of the tooth and cause remodelling of the surrounding alveolar bone (Ness 1956). Whilst dental disease may occur as a result of trauma, congenital abnormalities and neoplasia, dietary factors are generally considered to play a major role (Crossley 2003, Okuda et al. 2007, Harcourt-Brown 2009). Wild rabbits consume a diet of grasses, tree shoots and other plant material (Williams & Wells 1974, Bhadresa 1977, Martins & Milne 2002, Okuda et al. 2007). In contrast, pet rabbits frequently consume a diet consisting largely of concentrate foods (monocomponent nuggets or mixed mueslis) with no or limited roughage intake (Harcourt-Brown 1996, Mullan & Main 2006, Schepers et al. 2009, PDSA 2011). Whilst inadequate or incorrect diet is widely expected to cause dental disease, several theories describing the possible aetiopathogeneses have been proposed including a lack of attrition (Crossley 2003, Crossley 2005) and calcium/phosphorus imbalance (HarcourtBrown 1996, Jekl et al. 2011a,b, Gumpenberger et al. 2012). The aim of this study was to determine the effect of four different dietary regimes on tooth length and curvature and incisor eruption and attrition rates.
MATERIALS AND METHODS This study was conducted as a part of a long-term study to assess the effect of diet on the health and welfare of pet rabbits, as previously described by Prebble & Meredith (2014) and Prebble et al. (2014). Study design and methodology was approved by the Ethical Review Committees of the Royal (Dick) School of Veterinary Studies and the Food and Environment Research Agency (FERA). The rabbits were housed in a facility licensed by the Home Office; however, a project licence under the Animals (Scientific Procedures) Act 1986 (ASPA) was not required for this study. The study was continually monitored by the FERA Ethics Committee and Home Office inspector throughout its duration. Diets On arrival, the rabbits were acclimatised over 40 days (days –54 to –14) by maintaining their weaning diet of 50 g per rabbit of an extruded diet (Burgess® Excel-Junior and Dwarf Rabbit; Burgess Pet Care, Thornton Le Dale, North Yorkshire, UK) once a day plus ad lib Timothy Hay provided in wall-mounted hayracks. Water was provided ad lib in 700 ml bottles. At Day –14, the rabbits were randomly allocated to one of four diet groups: 1. Hay only (HO) – ad lib supply of Timothy hay (n=8); 2. Extruded diet and hay (EH) – 50 g per rabbit Burgess ExcelAdult Rabbit (Burgess Pet Care, Thornton Le Dale, North Yorkshire, UK) with ad lib supply of hay (n=8); 3. Muesli and hay (MH) – 60 g per rabbit Russell Rabbit Complete Muesli (Supreme Petfoods Limited, Ipswich, Suffolk, UK) with ad lib hay (n=8); 4. Muesli only (MO) – ad lib supply (125 g per rabbit) of Russell Rabbit Complete Muesli (Supreme Petfoods Limited, Ipswich, Suffolk, UK) (n=8). 378
The rabbits were gradually transitioned on to the new diet over a 2-week period (Day –14 to 0) and they remained on that diet for 17 months. The nutritional composition of the four diets offered is detailed in Table 1. A rabbit in the EH group died suddenly on day 209, but the cause of death was not evident on post-mortem examination. A rabbit in the MO group was removed at month 7 following the development of clinical dental disease. It showed signs of weight loss and reduced food intake. Dental examination revealed elongated curved cheek teeth and maloccluded incisors. Elongation of the apices of the cheek teeth and remodelling of the alveolar bone and ventral mandibular cortex were observed on radiography. Data from these two rabbits were not included in any analyses. In an additional two rabbits in the MO group, radiographic changes were observed at 17 months, with evidence of intrusion of tooth roots into the ventral cortex in one rabbit and elongated curved cheek teeth and stepping of the dental arcade that were visible on dental examination in the other. Data collection Notches were placed in the enamel of the left upper incisor in weeks 30, 32 and 35 using a low-speed drill with a diamond-cutting disc according to a previously described methodology (Wolf et al. 1993, Wolf et al. 2003). The distances between the gingival margin and the notch (E) and the notch and the end of the tooth (A) were measured with digital callipers (Fig 1). As the gingival margin comes across the tooth at an angle, measurements were taken along the lateral tooth margin. Measurements were taken at the time of notching (E1 and A1) and repeated seven days later (E2 and A2). The rate of eruption was calculated by (E2−E1)/7. The rate of attrition was calculated by (A1−A2)/7. Lateral skull radiography were performed at months 1, 9 and 17. The rabbits were restrained conscious in a towel and placed at a consistent distance in front of a digital x-ray plate. A horizontal x-ray beam was used to obtain the radiograph. Images were viewed and measured using efilm viewer lite (Merge Healthcare, Chicago,IL). Measurements taken were: • Height (h) of the upper (hu) and lower first cheek tooth (hl) measured as a line from the caudal edge of the top of the tooth to the apex (Fig 2a; black line) Table 1. Nutritional composition of the diets offered with values expressed as %DM Crude protein (%) Fat (%) Crude fibre (%) Ash (%) NDF‡ (%) ADF§ (%) Calcium (%) Phosphorus (%) Ca:P ratio
Timothy hay
Extruded nugget*
Muesli†
9 2 29 6·5 60 33 0·3 0·22 1·36
13 3 19 5·5 38 21 0·6 0·51 1·18
14 2·5 14 5 29 20 0·6 0·4 1·5
*Burgess Excel-Adult Rabbit (Burgess Pet Care, Goole, East Yorkshire, UK) † Russell Rabbit-Complete Muesli (Supreme Petfoods Limited, Ipswich, Suffolk, UK) ‡ Neutral detergent fibre § Acid detergent fibre
Journal of Small Animal Practice
•
Vol 56
•
June 2015
•
© 2015 British Small Animal Veterinary Association
Diet and dental disease in rabbits
border of the mandible, was performed every six weeks (without the use of anaesthesia). Uneaten muesli was collected from the MH and MO groups and separated into its components. These were subtracted from the amounts of each component fed, which gave the quantity of each component consumed. The quantities consumed and the amount of calcium and phosphorus in each component were entered into Best Mix Feed Formulation Software (© adifo software, Maldegem, Belgium) to determine the calcium and phosphorus content of the diet consumed.
FIG 1. Schematic diagram demonstrating the measurement of eruption and attrition rates of the incisor. A notch (grey line) was placed on the left upper incisor and the distances from the lateral gingival margin (E) to the notch and the notch to the end of the tooth (A) were measured
• Perpendicular distance between the above line and the middle of the tooth, for both upper (au) and lower (al) first cheek tooth (Fig 2a; blue line) Using these measurements, the tooth length was estimated, assuming that tooth shape formed an arc of a circle, using the following equation: 2xa sin–1 ______ 2 2 2 x +a x + a2 _____ __________ Tooth Length = p a 180
(
)
)
(
where x = 0·5h The degree of curvature in the saggital plane of the first cheek tooth was assessed by placing a line along the tangent of the erupted tooth and the unerupted tooth. The angle of interception of these lines was measured (Fig 2b). The degree of splaying of the lower arcade was assessed by measuring the angle of the interdental space between the first and the second lower molars (third and fourth cheek teeth) (Fig 2b). A routine dental examination, comprising visual oral examination with the aid of an otoscope and palpation of the ventral
Statistical analysis Data were analysed using Minitab (v16.1.1 © 2010 Minitab Inc.) and R software (v2.15.1 © 2012 The R Foundation for Statistical Computing). For most of the measurements, data from each time point were analysed using standard analysis of variance (ANOVA) also taking the sex of the rabbit into account, using standard Tukey’s post-hoc tests to assess pair-wise differences between the groups where overall differences were obtained. Residuals were examined for adequate normality before analysis. For the al measurement, the lack of adequacy in the residuals necessitated the use of the non-parametric Kruskal–Wallis and associated DwassSteel-Fligner-Critchlow post hoc test. Degrees of freedom are indicated in subscripts. A Pearson product moment correlation was carried out to assess the relationship between eruption and attrition rates. P0·154). In addition, the height of the lower first cheek tooth (hl) was not statistically significantly different between groups at any time point (P>0·093). In contrast, whilst not different at months 1 and 9 (P>0·133), the distance between the line (h), from the caudal edge of the top of the tooth to the apex and the centre of
FIG 2. (a) Measurement of the height of the first cheek tooth (hu and hl) indicated by black lines and the distance between these lines and the centre of the tooth (au and al) indicated by blue lines. (b) Measurement of the angle of curvature in the saggital plane of the first lower cheek tooth (red arc) and that of the interdental space between the first and second molars (light blue arc) Journal of Small Animal Practice
•
Vol 56
•
June 2015
•
© 2015 British Small Animal Veterinary Association
379
A. L. Meredith et al.
FIG 3. Boxplots of radiographic differences measured from lateral skull radiographs of Dutch rabbits (n=30) fed four diets, ad lib Timothy hay (HO), extruded nugget and hay (EH), muesli and hay (MH) and ad lib muesli (MO): (a) Length of the first lower premolar (mm) at the end of the trial period (month 17); (b) angle of the interdental space between the first and second lower molar teeth (°) at 17 months; angle of curvature of the first lower premolar at (c) 9 and (d) 17 months. The horizontal bar represents the median, the box is the interquartile range and whiskers represent the range of values. **statistically significant at P
PAPER
Impact of diet on incisor growth and attrition and the development of dental disease in pet rabbits A. L. Meredith, J. L. Prebble and D. J. Shaw Royal (Dick) School of Veterinary Studies and The Roslin Institute, University of Edinburgh, Easter Bush Campus, Midlothian, EH25 9RG J.L. Prebble was employed on a KTP partnership between the Royal (Dick) School of Veterinary Studies and Burgess Pet Care, Victory Mill, Priestman’s Lane, Thornton-Le-Dale, Pickering, North Yorkshire, YO18 7RU. Current address: Askham Bryan College, Askham Bryan, York, YO23 3FR
OBJECTIVES: To assess the impact of four rabbit diets (hay only; extruded diet with hay; muesli with hay; muesli only) on length and curvature of cheek teeth and eruption and attrition rates of incisors. MATERIALS AND METHODS: Thirty-two Dutch rabbits, randomly divided into four diet groups, had length and saggital plane curvature of the first cheek teeth measured radiographically at 1, 9 and 17 months. Eruption/attrition of the left upper incisor was directly measured at weeks 30, 32 and 35. RESULTS: Eruption rates matched attrition rates in all groups, but were higher in the hay only group than in both groups fed muesli. By month 9, a greater degree of tooth curvature was present in rabbits fed muesli only than in those fed hay only and extruded diet with hay. After 17 months, rabbits fed muesli only and muesli with hay had longer lower first cheek teeth and larger interdental spaces between the first two molars than rabbits fed extruded diet and hay and hay only. Three rabbits fed muesli only developed evidence of dental disease. CLINICAL SIGNIFICANCE: Presence of increased tooth length, curvature and interdental spaces indicated early dental pathology in rabbits fed muesli. Muesli diets cannot be recommended for pet rabbits. Journal of Small Animal Practice (2015) 56, 377–382 DOI: 10.1111/jsap.12346 Accepted: 2 February 2015; Published online: 19 March 2015
INTRODUCTION Despite rabbits being the third most popular mammalian pet in the UK (PDSA 2011), their dietary requirements are not fully understood. Diet is frequently implicated in the development of acquired dental disease in pet rabbits (Harcourt-Brown 1996, Crossley 2003, Meredith 2007, Okuda et al. 2007); however, its exact role in the aetiology of dental disease remains unclear. The prevalence of dental disease in pet rabbits has been reported to be 29–38·1% (Mullan & Main 2006, Jekl et al. 2008), but these reports may underestimate the true prevalence as radiography was not performed and early cases may have been undetected (Jekl et al. 2008). Rabbits have continuously growing elodont teeth (Shadle 1936). The upper incisors erupt at a rate of approximately 2 mm/ week and the lower at 2·4 mm/week (Shadle 1936), and incisor eruption rate and length vary widely between individuals (Shadle 1936, Ness 1956). The growth rates of the cheek teeth (premolars Journal of Small Animal Practice
•
Vol 56
•
June 2015
•
and molars) have been reported to be approximately 3 mm a month (Crossley 2005, Meredith 2007, Lord 2012), but more recent studies have reported growth rates of 1·4–3·2 mm/week (Müller et al. 2014). Tooth length is maintained by the abrasive nature of the diet, tooth on tooth action during chewing and grinding of the teeth during periods of rest (Shadle 1936, Crossley 2005). The functional differences between incisors and cheek teeth indicate that different diets affect each type of tooth differently (Müller et al. 2014). Eruption rates change to match rates of attrition (Wolf et al. 1993); taking the incisors out of occlusion by shortening them increases eruption rates (up to 0·7 mm/day) until the tooth returns to occlusion (Ness 1956). Tooth length, wear and growth are also linked to dietary abrasiveness, which is caused by the dietary content of both internal (plant phytolith) and external abrasives such as sand (Müller et al. 2014). In addition to diet, age and pregnancy may also influence the rate of eruption of teeth (Shadle 1936, Ness 1956, Wolf et al. 1993).
© 2015 British Small Animal Veterinary Association
377
A. L. Meredith et al.
Prevention of eruption does not stop growth from the germinal centre at the apex of the tooth and growth continues with enough force to distort the structure of the tooth and cause remodelling of the surrounding alveolar bone (Ness 1956). Whilst dental disease may occur as a result of trauma, congenital abnormalities and neoplasia, dietary factors are generally considered to play a major role (Crossley 2003, Okuda et al. 2007, Harcourt-Brown 2009). Wild rabbits consume a diet of grasses, tree shoots and other plant material (Williams & Wells 1974, Bhadresa 1977, Martins & Milne 2002, Okuda et al. 2007). In contrast, pet rabbits frequently consume a diet consisting largely of concentrate foods (monocomponent nuggets or mixed mueslis) with no or limited roughage intake (Harcourt-Brown 1996, Mullan & Main 2006, Schepers et al. 2009, PDSA 2011). Whilst inadequate or incorrect diet is widely expected to cause dental disease, several theories describing the possible aetiopathogeneses have been proposed including a lack of attrition (Crossley 2003, Crossley 2005) and calcium/phosphorus imbalance (HarcourtBrown 1996, Jekl et al. 2011a,b, Gumpenberger et al. 2012). The aim of this study was to determine the effect of four different dietary regimes on tooth length and curvature and incisor eruption and attrition rates.
MATERIALS AND METHODS This study was conducted as a part of a long-term study to assess the effect of diet on the health and welfare of pet rabbits, as previously described by Prebble & Meredith (2014) and Prebble et al. (2014). Study design and methodology was approved by the Ethical Review Committees of the Royal (Dick) School of Veterinary Studies and the Food and Environment Research Agency (FERA). The rabbits were housed in a facility licensed by the Home Office; however, a project licence under the Animals (Scientific Procedures) Act 1986 (ASPA) was not required for this study. The study was continually monitored by the FERA Ethics Committee and Home Office inspector throughout its duration. Diets On arrival, the rabbits were acclimatised over 40 days (days –54 to –14) by maintaining their weaning diet of 50 g per rabbit of an extruded diet (Burgess® Excel-Junior and Dwarf Rabbit; Burgess Pet Care, Thornton Le Dale, North Yorkshire, UK) once a day plus ad lib Timothy Hay provided in wall-mounted hayracks. Water was provided ad lib in 700 ml bottles. At Day –14, the rabbits were randomly allocated to one of four diet groups: 1. Hay only (HO) – ad lib supply of Timothy hay (n=8); 2. Extruded diet and hay (EH) – 50 g per rabbit Burgess ExcelAdult Rabbit (Burgess Pet Care, Thornton Le Dale, North Yorkshire, UK) with ad lib supply of hay (n=8); 3. Muesli and hay (MH) – 60 g per rabbit Russell Rabbit Complete Muesli (Supreme Petfoods Limited, Ipswich, Suffolk, UK) with ad lib hay (n=8); 4. Muesli only (MO) – ad lib supply (125 g per rabbit) of Russell Rabbit Complete Muesli (Supreme Petfoods Limited, Ipswich, Suffolk, UK) (n=8). 378
The rabbits were gradually transitioned on to the new diet over a 2-week period (Day –14 to 0) and they remained on that diet for 17 months. The nutritional composition of the four diets offered is detailed in Table 1. A rabbit in the EH group died suddenly on day 209, but the cause of death was not evident on post-mortem examination. A rabbit in the MO group was removed at month 7 following the development of clinical dental disease. It showed signs of weight loss and reduced food intake. Dental examination revealed elongated curved cheek teeth and maloccluded incisors. Elongation of the apices of the cheek teeth and remodelling of the alveolar bone and ventral mandibular cortex were observed on radiography. Data from these two rabbits were not included in any analyses. In an additional two rabbits in the MO group, radiographic changes were observed at 17 months, with evidence of intrusion of tooth roots into the ventral cortex in one rabbit and elongated curved cheek teeth and stepping of the dental arcade that were visible on dental examination in the other. Data collection Notches were placed in the enamel of the left upper incisor in weeks 30, 32 and 35 using a low-speed drill with a diamond-cutting disc according to a previously described methodology (Wolf et al. 1993, Wolf et al. 2003). The distances between the gingival margin and the notch (E) and the notch and the end of the tooth (A) were measured with digital callipers (Fig 1). As the gingival margin comes across the tooth at an angle, measurements were taken along the lateral tooth margin. Measurements were taken at the time of notching (E1 and A1) and repeated seven days later (E2 and A2). The rate of eruption was calculated by (E2−E1)/7. The rate of attrition was calculated by (A1−A2)/7. Lateral skull radiography were performed at months 1, 9 and 17. The rabbits were restrained conscious in a towel and placed at a consistent distance in front of a digital x-ray plate. A horizontal x-ray beam was used to obtain the radiograph. Images were viewed and measured using efilm viewer lite (Merge Healthcare, Chicago,IL). Measurements taken were: • Height (h) of the upper (hu) and lower first cheek tooth (hl) measured as a line from the caudal edge of the top of the tooth to the apex (Fig 2a; black line) Table 1. Nutritional composition of the diets offered with values expressed as %DM Crude protein (%) Fat (%) Crude fibre (%) Ash (%) NDF‡ (%) ADF§ (%) Calcium (%) Phosphorus (%) Ca:P ratio
Timothy hay
Extruded nugget*
Muesli†
9 2 29 6·5 60 33 0·3 0·22 1·36
13 3 19 5·5 38 21 0·6 0·51 1·18
14 2·5 14 5 29 20 0·6 0·4 1·5
*Burgess Excel-Adult Rabbit (Burgess Pet Care, Goole, East Yorkshire, UK) † Russell Rabbit-Complete Muesli (Supreme Petfoods Limited, Ipswich, Suffolk, UK) ‡ Neutral detergent fibre § Acid detergent fibre
Journal of Small Animal Practice
•
Vol 56
•
June 2015
•
© 2015 British Small Animal Veterinary Association
Diet and dental disease in rabbits
border of the mandible, was performed every six weeks (without the use of anaesthesia). Uneaten muesli was collected from the MH and MO groups and separated into its components. These were subtracted from the amounts of each component fed, which gave the quantity of each component consumed. The quantities consumed and the amount of calcium and phosphorus in each component were entered into Best Mix Feed Formulation Software (© adifo software, Maldegem, Belgium) to determine the calcium and phosphorus content of the diet consumed.
FIG 1. Schematic diagram demonstrating the measurement of eruption and attrition rates of the incisor. A notch (grey line) was placed on the left upper incisor and the distances from the lateral gingival margin (E) to the notch and the notch to the end of the tooth (A) were measured
• Perpendicular distance between the above line and the middle of the tooth, for both upper (au) and lower (al) first cheek tooth (Fig 2a; blue line) Using these measurements, the tooth length was estimated, assuming that tooth shape formed an arc of a circle, using the following equation: 2xa sin–1 ______ 2 2 2 x +a x + a2 _____ __________ Tooth Length = p a 180
(
)
)
(
where x = 0·5h The degree of curvature in the saggital plane of the first cheek tooth was assessed by placing a line along the tangent of the erupted tooth and the unerupted tooth. The angle of interception of these lines was measured (Fig 2b). The degree of splaying of the lower arcade was assessed by measuring the angle of the interdental space between the first and the second lower molars (third and fourth cheek teeth) (Fig 2b). A routine dental examination, comprising visual oral examination with the aid of an otoscope and palpation of the ventral
Statistical analysis Data were analysed using Minitab (v16.1.1 © 2010 Minitab Inc.) and R software (v2.15.1 © 2012 The R Foundation for Statistical Computing). For most of the measurements, data from each time point were analysed using standard analysis of variance (ANOVA) also taking the sex of the rabbit into account, using standard Tukey’s post-hoc tests to assess pair-wise differences between the groups where overall differences were obtained. Residuals were examined for adequate normality before analysis. For the al measurement, the lack of adequacy in the residuals necessitated the use of the non-parametric Kruskal–Wallis and associated DwassSteel-Fligner-Critchlow post hoc test. Degrees of freedom are indicated in subscripts. A Pearson product moment correlation was carried out to assess the relationship between eruption and attrition rates. P0·154). In addition, the height of the lower first cheek tooth (hl) was not statistically significantly different between groups at any time point (P>0·093). In contrast, whilst not different at months 1 and 9 (P>0·133), the distance between the line (h), from the caudal edge of the top of the tooth to the apex and the centre of
FIG 2. (a) Measurement of the height of the first cheek tooth (hu and hl) indicated by black lines and the distance between these lines and the centre of the tooth (au and al) indicated by blue lines. (b) Measurement of the angle of curvature in the saggital plane of the first lower cheek tooth (red arc) and that of the interdental space between the first and second molars (light blue arc) Journal of Small Animal Practice
•
Vol 56
•
June 2015
•
© 2015 British Small Animal Veterinary Association
379
A. L. Meredith et al.
FIG 3. Boxplots of radiographic differences measured from lateral skull radiographs of Dutch rabbits (n=30) fed four diets, ad lib Timothy hay (HO), extruded nugget and hay (EH), muesli and hay (MH) and ad lib muesli (MO): (a) Length of the first lower premolar (mm) at the end of the trial period (month 17); (b) angle of the interdental space between the first and second lower molar teeth (°) at 17 months; angle of curvature of the first lower premolar at (c) 9 and (d) 17 months. The horizontal bar represents the median, the box is the interquartile range and whiskers represent the range of values. **statistically significant at P
