J.W. Evans

Physiologic and metabolic response of exercising horses to added dietary fat

Summary Six mature Quarter Horse-type geldings were used in a replicated 3 × 3 Latin square experiment to determine the effects of adding 5 or 10% feed-grade rendered animal fat to the concentrate diet fed to performance horses. The experiment was conducted over a 14-day pre-trial period to acquaint horses to the experimental apparatus, a 28-day conditioning period and 3 diet treatment periods of 21 days, each conducted in a Latin square arrangement. The horses were exercised on a dirt track and diet effects were evaluated during and following a submaximal exercise test (SET) on an equine treadmill. Physiological responses to the SET were determined following each experimental period. Relative to the control, the horses required 21% and 25% less of the concentrate feed (P

Lactation and reproductive performance of mares fed added dietary fat during late gestation and early lactation

Summary Eighteen pregnant mares were randomly allotted to one of two treatment groups. The control group was fed a conventional concentrate and the fat group was fed a concentrate containing 5% feed-grade rendered fat. Both concentrates had the same nutrient:calorie ratio and were fed in amounts required to maintain zero change in percent body fat of the mares. During the study, which began 60 d prior to expected foaling date and ended 60 d postpartum, mares were monitored for feed intake, body weight, rump fat thickness, ration digestibility, plasma glucose and lipid concentrations, milk composition and reproductive efficiency. Birth weight, growth rate, and plasma glucose and lipid concentrations were also measured in foals. Mares fed fat consumed less concentrate (P

Growth and feed utilization by yearling horses fed added dietary fat

Summary Twenty-four yearlings were used to evaluate the efficacy of feeding feed-grade fat to growing horses. All horses were started on trial at 13-months-of-age and were fed for 112 days. The experimental diets, containing similar nutrient-to-calorie ratios, were: 1) control (no added fat; 2) 5% added fat and; 3) 10% added fat. There was a trend for yearlings fed the 10% added fat diet to grow faster and eat less feed than those on the control diet. Data from this study indicate that feed-grade fat can be safely fed to growing horses. Feeding fat to yearlings stimulated growth and efficiency of feed utilization initially, but these effects were not maintained as the yearlings grew toward maturity.

Digestible energy requirements for work and maintenance of horses fed conventional and fat-supplemented diets**

Summary A control and a 10% fat-supplemented diet were fed to exercising horses maintained in two different body conditions, during both temperate and hot weather, to determine the efficacy of fat as dietary aid to reduced energy requirements for thermal regulation in exercising horses. Horses were worked 7.2 km daily, 5 d/w, and in each season were fed sufficient energy to maintain constant body weight and body fat content at each assigned level of body condition. In both seasons and in both body conditions, digestible energy intake was lower (P

Influence of body fat content on digestible energy requirements of exercising horses in temperate and hot environments

Summary Six mature horses were used to determine the energy requirements of exercising horses during different seasons and in different body conditions. Horses were conditioned to work 7.2 km in 30 min 5 d/wk and fed to either a fleshy or moderate body condition during both hot (temperature mean 32.4 C, with a 23.9–36.1 C range) and temperate (temperature mean 17.4 C, with a 3.9–27.8 C range) seasons. Horses were fed average quality Bermuda grass hay at .75% of body weight sufficient concentrate to maintain body weight and condition. During each combination of body condition and season when body weight, condition and feed intake were stable for 14 d horses were declared at energy equilibrium and a digestion trial was conducted. Horses in fleshy body condition (7.5) required 2.3 kg/d more total feed than horses in moderate (5.2) body condition. When expressed in terms of digestible energy (DE) intake, fleshy horses required 11.12 kcal/kgBW/d more than horses in moderate flesh. When DE for maintenance (DEM) was calculated as the difference between DE intake and DE for work (DEW), DEM for horses in fleshy condition exceeded that of horses in moderate condition by 11.3 kcal/kgBW/d (P

Growth, nutrient utilization, radiographic bone characteristics and postprandial thyroid hormone concentrations in weanling horses fed added dietary fat

Summary Thirty, 19-week-old Quarter Horses were utilized in a 112-d study to compare growth, nutrient utilization and post prandial thyroid hormone concentrations in weanling horses fed fat-supplemented or conventional diets. Concentrates were formulated to contain the same nutrient-calorie ratios and were fed with Coastal Bermuda grass hay in a 70:30 concentrate:hay ratio. Initially and at 28-d intervals the horses were weighed and measured for height, heart girth circumfer ence and subcutaneous fat thickness over the rump and ribs. Radiographs were taken of the right carpal and metacarpal phalangealjoints at the beginning and end of the experimental period for evaluation of bone density and physeal maturation. A digestion trial was conducted on each horse 10 d prior to completion of the study. On d 70, blood samples were col lected from 6 females in each treatment group over a 6-h collection period for evaluation of postprandial insulin, T4 and T3 concentrations in response to the diets. Horses in both groups consumed an average of 2.6% of body weight daily of total feed (Dry Matter). Weanlings consuming the fat-supplemented concentrate tended to have higher (P = .10) average daily weight gains (.80 vs .74 kg) and lower (P

Clinical observations on changes in concentrations of hormones in plasma of two stallions with thermally-induced testicular degeneration

Summary To investigate effects of thermally-induced testicular degeneration on hormonal and seminal parameters in stallions, the scrotum was insulated for 36 hours in two mature (5-year-old mixed breed and 11-year-old Throughbred) stallions. Semen was collected daily for 10 days (DSO) prior to, and at intervals after, scrotal insulation. When DSO determinations were not being made, semen was collected 3 times weekly. Jugular blood samples were collected at 15-minute intervals for 6 hours from each stallion prior to, and at intervals after, scrotal insulation. A mouse interstitial cell testosterone assay was modified to quantify biologic activity of equine luteinizing hormone (BLH) in plasma samples. Immunoactive luteinizing hormone (ILH) and testosterone (T) concentrations were determined in plasma samples by routine RIA procedures. Percentages of progressively motile and morphologically normal spermatozoa began to decrease by 1 to 2 weeks postinsulation, reached nadir values at 3 to 3-1/2 weeks postinsulation, and returned to preinsulation values by 7 weeks postinsulation. Total number of spermatozoa and total number of progressively motile, morphologically normal spermatozoa in ejaculates at DSO returned to normal by 8 weeks postinsulation in stallion 2 and 12 weeks postinsulation in stallion 1. Concentrations of BLH and ILH increased, and while T concentrations decreased, immediately postinsulation. The increase in ILH concentrations was greater than the increase in BLH concentrations, resulting in a decrease in the BLH:ILH (B:I) ratio. Following the peak in LH secretion immediately postinsulation, LH concentrations gradually decreased while T concentrations increased. The B:I ratio was elevated from 1 to 13 weeks postinsulation compared to immediately postinsulation. In addition to changes in spermatozoal quality in ejaculates, stallion response to scrotal insulation included increased secretion of luteinizing hormone and impaired Leydig cell function (as determined by reduced testosterone concentration in circulating plasma). The proportion of biologically active LH secreted in response to thermal testicular injury increased during the recovery phase.

Milk yield and composition in the multiparous mare fed to obesity

Summary Eighteen multiparous Quarter Horse mares were utilized in a study to determine whether nutritionally-induced obesity, initiated during gestation, would adversely affect milk yield and milk composition. Mares were assigned to one of two treatment groups during gestation: 1) control (n=11): fed to maintain a moderate degree of body fatness (mean postpartum condition score ± SE = 6.1 ± 0.2) and 2) obese (n=7): fed to achieve (prepartum) and then maintain (postpartum) an extremely high degree of body fatness (mean postpartum condition score ± SE = 8.8 ± 0.2). Foal growth was monitored at weekly intervals until the study was terminated on Day 63 of lactation. Foals were not allowed access to supplemental feed. A weigh-suckle-weigh technique was used to estimate milk yield on Days 30 and 60 of lactation. Samples for laboratory analysis of milk composition were collected on Days 31 and 61 of lactation. The 63-d total gain in body weight, heart girth, and third metacarpal bone circumference was greater (p 0.05). Milk yield tended to be greater in control as compared to obese mares (14.4 vs 13.0 kg/d, SE=0.5, p

Follicular, estrus, gonadotropin and ovulation responses in anestrous mares treated with a GnRH analogue (CH 690030)

Summary A total of 54 mares in seasonal anestrus were assigned to 5 groups to receive depots containing 0, 0.9, 1.8, 3.6, and 5.4 mg/mare of a GnRH analogue (CH 690030 or goserelin acetate) on January 28. Five mares, three classified as transitional mares and two classified in anestrus, when depots were given ovulated between 11 and 21 days after the onset of treatment and subsequently formed a corpus luteum. Reciprocal changes between an increased LH concentration and a decreased FSH concentration commenced 6 days before ovulation, when rapid follicle growth was initiated. Mares that ovulated showed a gradual rise in LH concentration with a 5-day duration of high LH concentrations, reaching a peak during the peri-ovulatory period and followed by a slow decline without returning to the pre-treatment value at the end of the 30-day post-treatment period. The change in FSH was first a rapid rise then an obvious drop with a nadir 3-5 days before ovulation and then a low level maintained until the end of the study. Mares receiving a dose of 3.6 mg had a lower mean post-treatment FSH concentration and a lower mean FSH peak value than the controls (P Results of this trial did not show any encouragement for giving goserelin depots to anestrous mares in late January to stimulate ovulation. The low LH concentrations in the majority of the mares that failed to ovulate and an early date of onset of treatment in the present study may account for the low ovulation rate. The adverse weather conditions (heavy rain and low temperatures) at the time of study may also have contributed to the failure of the mares to ovulate.

Evaluation of three techniques (follicular aspiration, follicular aspiration and flushing and slicing of the ovaries) for recovery of equine oocytes from excised ovaries

Summary The objective of this study was to compare three different methods of oocyte recovery from equine ovaries obtained from an abattoir. The techniques used were a) aspiration of follicles, b) aspiration plus flushing of the follicles and c) slicing of the ovaries in a grid pattern. The number of oocytes recovered from each of the three methods was different (P