FROM THE TESTES TO THE OVARIES


Table 1. Breeding Soundness Examination Findings for Stallion 1 Between 20 and 24 Years of Age Age, y Book PR/C SPR TTV DSO Effic %MN %PM Mean COMP Test Est LH FSH Inh Test Res 19


20 21 22 23 24


79 55% 86% NE NE NE NE NE NE NE NE NE NE NE NE NE 73 30% 67% 382 5.80 73% 43% 40% NE NE NE NE NE NE NE NE 63 31% 70% 380 3.48 43% 45% 30% 241 16% NE NE NE NE NE NE 53 21% 45% 312 2.09 32% 50% 25% 239 16% 650 275 2.0 2.1 NE 1300 40 25% 48% 308 2.06 32% 25% 15% 257 31% 784 156 11.0 10.2 NE 1126 20 7% 15% 260 1.74 32% 25% 15% 286 31% 650 156 NE NE NE 980


NEindicates not examined; Book, number of mares bred in season; PR/C, pregnancy rate per cycle, %; SPR, seasonal pregnancy rate, %; TTV, total testicular volume, cc; DSO, daily sperm output, 109


; Effic, spermatogenic efficiency, %; %MN, percentage of


morphologically normal sperm; %PM, percentage of progressively motile sperm, SCSA values; Mean, Mean-t; COMP, %COMP-t (percentage of cells outside the main population); Test, circulating testosterone concentration, pg/mL (normal range, 500–2000); Est, circulating total estrogens concentration, pg/mL (normal range, 150–400); LH, circulating luteinizing hormone concentration, ng/mL (normal range, 0.5–5.0); FSH, circulating follicle-stimulating hormone concentration, ng/mL (normal range, 0.5–15.0); Inh, circulating inhibin concentration, ng/mL (normal range, 2.2–3.4); Test Res, highest concentration of testosterone within 2 hours of GnRH administration, pg/mL (normal increase 100% within 2 hours).


changes were associated with a decrease in percent- age of morphologically normal and progressively mo- tile sperm in ejaculates, sperm chromatin structure assays did not reveal prominent changes in sperm DNA integrity. It was only late in the course of progression of testicular dysfunction (last 2 years of breeding) that sperm DNA integrity began to de- teriorate. Baseline hormonal concentrations usu- ally did not differ from reported normal ranges until after spermatogenic efficiency had declined to 40%, DSO approximated 2 billion, total number PMMN sperm at DSO was 500 million, and the average PR/C diminished to33%. Sperm motility and morphology values typically but not always de- teriorated from those found when each horse was still achieving normal pregnancy rates. Low total estrogen concentration was sometimes noted in the last 1 to 3 years of breeding (ie, two of three stal- lions). We also noted a low circulating concentra- tion of testosterone in two stallions during this same time period (ie, 116–403 pg/mL), and some-


times testosterone did not achieve the lower limit of reported normal circulating concentration (ie, 500 pg/mL) within 2 hours of GnRH administra- tion in one of three stallions. Total testicular vol- ume during the last year at stud decreased to approximately 50% of the previous size when the stallions were several years younger. At this late stage of testicular dysfunction, variations from nor- mal endocrine values were more likely to include low estrogen, testosterone and inhibin concentra- tions, and, in some instances, high FSH and LH concentrations.


4. Discussion


These findings support the premise that age-related testicular dysfunction follows a progressive pattern of deterioration. First, a decline in sperm output, including total number of normal motile sperm, is observed in ejaculates. This may be detected dur- ing pre-season breeding soundness examination but sometimes is found later during the breeding sea-


Table 2. Breeding Soundness Examination Findings for Stallion 2 Between 18 and 27 Years of Age Age, y Book PR/C SPR TTV DSO Effic %MN %PM Mean COMP Test Est LH FSH Inh Test Res 17


18 19 21 22 23 24 25 26 27


88 70% 97% NE NE NE NE NE NE NE NE NE NE NE NE NE 103 68% 88% 514 8.22 75% 47% 45% 232 18% NE NE NE NE NE NE 108 67% 85% 508 8.53 78% 45% 45% 250 20% NE NE NE NE NE NE 112 55% 84% NE NE NE NE NE NE NE NE NE NE NE NE NE 92 52% 86% NE NE NE NE NE NE NE NE NE NE NE NE NE 81 48% 83% 459 3.41 35% 49% 55% 234 9% 460 276 0.05 0.05 1.96 750 76 57% 88% 442 3.77 40% 43% 50% 231 15% 593 235 0.5 0.08 NE 645 78 34% 68% 360 1.73 23% 41% 30% 252 20% 274 231 1.8 0.8 4.19 494 61 19% 44% 346 1.50 21% 47% 25% 295 19% NE NE NE NE NE NE 26 0% 0% 299 1.00 17% 42% 25% 275 42% 116 128 2.8 0.8 3.99 370


NEindicates not examined; Book, number of mares bred in season; PR/C, pregnancy rate per cycle, %; SPR, seasonal pregnancy rate, %; TTV, total testicular volume, cc; DSO, daily sperm output, 109


; Effic, spermatogenic efficiency, %; %MN, percentage of


morphologically normal sperm; %PM, percentage of progressively motile sperm, SCSA values; Mean, Mean-t; COMP, %COMP-t (percentage of cells outside the main population); Test, circulating testosterone concentration, pg/mL (normal range, 500–2000); Est, circulating total estrogens concentration, pg/mL (normal range, 150–400); LH, circulating luteinizing hormone concentration, ng/mL (normal range, 0.5–5.0); FSH, circulating follicle-stimulating hormone concentration, ng/mL (normal range, 0.5–15.0); Inh, circulating inhibin concentration, ng/mL (normal range, 2.2–3.4); Test Res, highest concentration of testosterone within 2 hours of GnRH administration, pg/mL (normal increase 100% within 2 hours).


534 2013  Vol. 59  AAEP PROCEEDINGS


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