Ultrasonographic measurements of localized fat accumulation in Shetland pony mares fed a normal v. a high energy diet for 2 years

Abstract

Health risks associated with obesity are more likely a factor of the localization of fat excess, rather than of elevated BW per se. The aim of this randomized controlled clinical trial was to determine the effect of a long-term high energy diet on BW, fat accumulation and localization. Eight Shetland pony mares, 3 to 7 years old, were randomly divided into a control and a high energy (HE) diet group fed either maintenance or double maintenance energy requirements (200% net energy (NE)) for two consecutive summers, with a low energy diet in the winter in between. Body condition score (BCS) did not differ between the groups at the onset of the study (control 5.6±0.75 v. HE 6.3±0.5). From 12 weeks after starting the diet, ultrasonography of five different locations (retroperitoneal, axillary, withers, intercostal and rump) for adipose deposition, BCS and BW were measured monthly during the period that ponies received different diets. Statistical analysis was performed using a linear mixed-effects model with post hoc Bonferroni testing. P values <0.05 were considered significant. At week 12 after the onset of the diet, fat thickness in the HE group was significantly greater than in the control group. During the monitoring period, the HE group showed a significant increase in mean (±SE) BW (+52%, 265±13.94kg) and BCS (+70%; to 9.0±0.4), while the control group was unchanged (BW 160±13.98 kg; BCS 3.8±0.4). At all locations, the fat depth in the HE group increased significantly, with the highest increase noted for retroperitoneal deposits. The conclusions were that a 200% NE diet induced subcutaneous and retroperitoneal fat accumulation, with the greatest increase in intra-abdominal deposits. The moderate increase of the subcutaneous fat depth followed by a plateau phase suggests the existence of a limit of adipose tissue expandability, as in man.

Alterations of serum vitamin E and vitamin A concentrations of ponies and horses during experimentally induced obesity

“…As expected, the hypercaloric intake over two years induced significant increases in BW, BCS, CNS and fasting serum insulin in ponies and horses. However, the achieved BW gain was less than expected in the context of previous research by Carter, McCutcheon, et al (2009) and Siegers, de Ruijter‐Villani, van Doorn, Stout, and Roelfsema (2018) in which the excess energy intake was provided by approximately 60% concentrate and 40% roughage. In contrast, the energy intake in the current study was provided by 40% concentrate and 60% roughage.…”

Effect of long‐term overfeeding of a high‐energy diet on glucose tolerance in Shetland pony mares

“…The decrease in mean BCS of the control group by 1 unit during year 1, despite a mean ± SD increase in BW of 6.2% ± 2.1%, could be explained by growth in the young group of ponies and possibly loss of muscle mass because of decreased exercise during the experimental period. A previous study reported measuring fat depths SC and retroperitoneally in some of the ponies used in our study, and found no significant changes in ultrasound detectable fat reserves in year 1, suggesting that the decrease in BCS in control ponies might not be related to fat loss alone 15 . However, the first measurements in that study were performed 12 weeks after starting the diet, and it possible that some fat loss preceded this first measurement.…”

“…Mean ± SD BCS of the HE group did, however, decrease by 1 unit from BCS 8 ± 1 to 7 ± 1 over the winter period. A previous study reported a decrease in withers and axillary fat thickness in the HE group over the winter period 15 . However, retroperitoneal fat depth did not decrease appreciably.…”

“…The BCS of each pony was graded by a single evaluator at the start and end of both study years, using a 9‐point scale 13 . Ultrasonographic fat depth measurements were performed on some of the ponies and were reported previously 15 …”

Peer Review #1 of "Impact of body weight gain on hepatic metabolism and hepatic inflammatory cytokines in comparison of Shetland pony geldings and Warmblood horse geldings (v0.1)"

“…Despite the differences between ponies and horses, the majority of our equines did not develop steatosis within two years of BW gain. It has been described in Shetland ponies that subcutaneous tissue expandability is limited, while the expansion of the retroperitoneally adipose tissue proceeds (Siegers et al, 2018). It is one possible explanation that the expandability limit of the subcutaneous adipose tissue was not reached in the present study and therefore, fat was not stored extraordinary in retroperitoneal and intraabdominal sites like the liver.…”