Randy Wilde

Enhanced early-life nutrition promotes hormone production and reproductive development in Holstein bulls

Holstein bull calves often reach artificial insemination centers in suboptimal body condition. Early-life nutrition is reported to increase reproductive performance in beef bulls. The objective was to determine whether early-life nutrition in Holstein bulls had effects similar to those reported in beef bulls. Twenty-six Holstein bull calves were randomly allocated into 3 groups at approximately 1 wk of age to receive a low-, medium-, or high-nutrition diet, based on levels of energy and protein, from 2 to 31 wk of age. Calves were on their respective diets until 31 wk of age, after which they were all fed a medium-nutrition diet. To evaluate secretion profiles and concentrations of blood hormones, a subset of bulls was subjected to intensive blood sampling every 4 wk from 11 to 31 wk of age. Testes of all bulls were measured once a month; once scrotal circumference reached 26cm, semen collection was attempted (by electroejaculation) every 2 wk to confirm puberty. Bulls were maintained until approximately 72 wk of age and then slaughtered at a local abattoir. Testes were recovered and weighed. Bulls fed the high-nutrition diet were younger at puberty (high=324.3 d, low=369.3 d) and had larger testes for the entire experimental period than bulls fed the low-nutrition diet. Bulls fed the high-nutrition diet also had an earlier and more substantial early rise in LH than those fed the low-nutrition diet and had increased concentrations of insulin-like growth factor-I (IGF-I) earlier than the bulls fed the low-nutrition diet. Furthermore, we detected a temporal association between increased IGF-I concentrations and an early LH rise in bulls fed the high-nutrition diet. Therefore, we inferred that IGF-I had a role in regulating the early gonadotropin rise (in particular, LH) and thus reproductive development of Holstein bulls. Overall, these results support our hypothesis that Holstein bull calves fed a high-nutrition diet reach puberty earlier and have larger testes than those fed a low-nutrition diet, and they provide clear evidence that nutritional modulation of Holstein bull calves during early life has profound effects on reproductive development.

Testicular ultrasonogram pixel intensity during sexual development and its relationship with semen quality, sperm production, and quantitative testicular histology in beef bulls

This study was conducted to evaluate testicular ultrasonogram pixel intensity during sexual development in bulls and to determine its relationship with semen quality, sperm production, and quantitative testicular histology. Beef bulls (N = 152) were examined from 14 - 26 to 70 - 74 wk of age in four different years. Testicular echogenicity increased during sexual development, but the pattern of change differed among years. Echogenicity increased between 26 and 42 to 46 wk of age in 2 yr, but increased considerably earlier in the other 2 yr, reaching maximum values at 34 wk of age. Because increased echogenicity was likely associated with testicular changes leading to initiation of spermatogenesis, these differences were difficult to explain considering that age at puberty did not differ significantly among years. When data were evaluated according to age normalized to puberty, echogenicity started to increase 16 to 12 wk before puberty and reached maximum values 4 wk before or at puberty. These results indicate that a certain developmental stage of the testicular parenchyma must be reached before puberty and that the composition of the parenchyma remained consistent after puberty. Testicular echogenicity was associated with sperm production, seminiferous tubule and epithelium area, and sperm morphology, but the associations were not consistent. Testicular echogenicity was a good indicator of pubertal and mature status, but was not superior to scrotal circumference. In conclusion, although testicular ultrasonogram pixel intensity analysis might be useful for research purposes, clinical application of this technology in the present form for bull breeding soundness evaluation is not justifiable.

Moribund sperm in frozen-thawed semen, and sperm motion end points post-thaw and post-swim-up, are related to fertility in Holstein AI bulls.

The objectives were to compare testicular physical characteristics and post-thaw sperm characteristics and their associations with fertility in Holstein bulls used for AI. Ten Holstein bulls (4-5 y old) were classified as either high-fertility (HF) or low-fertility (LF; n = 5 each), based on adjusted 56-d non-return rates [non-return rate (NRR); range (mean ± SD): 55.6 ± 4.6 to 71.8 ± 1.3%). Testicular physical characteristics were not significantly different between the two groups. Four ejaculates were collected from each bull and cryopreserved. Several indexes of sperm motion (based on computer-assisted sperm analysis) at post-thaw and post-swim-up were correlated with NRR. Sperm from HF bulls were in transition to a hyperactivated motility pattern, whereas those from LF bulls had only a forward progressive motility pattern. In HF vs LF bulls, there was a greater percentage of viable sperm after thawing (60.6 ± 9.7 vs 49.5 ± 8.0%, P < 0.05) and after swim-up (70.9 ± 11.0 vs 63.0 ± 8.8%, P < 0.01); these two end points were positively correlated with fertility (r = 0.45, P < 0.01 and r = 0.78; P < 0.01, respectively). Furthermore, in HF vs LF bulls, the ratio of sperm recovered after swim-up to viable sperm in post-thaw semen was higher (P < 0.001), and the proportion of moribund sperm expressed as a percentage of live sperm differed (12.6 ± 3.4 vs. 16.4 ± 3.1%, P < 0.001) and was negatively correlated (r = -0.33, P < 0.05) with fertility. In conclusion, fertility of Holstein bulls maintained in a commercial AI center was not predicted by testicular physical characteristics, but it was associated with differences in moribund sperm in the inseminate, as well as characteristics of sperm post-thaw and after swim-up.

Short communication: Prepartum plasma insulin-like growth factor-I concentrations based on day of insemination are lower in cows developing postpartum diseases

Because peripartal production diseases are prevalent in dairy cows, early recognition is crucial. Several studies reported metabolic variables as risk predictors for subsequent diseases. To improve on-farm testing and application of those methods, the sampling procedure should take into account variation in gestation length. Furthermore, additional variables indicating cows at risk of any production disease should be sought. Therefore, the objective was to characterize differences between cows with and without postpartum production disease (retained fetal membranes, ketosis, hypocalcemia, abomasal displacement, metritis, mastitis) by prepartum measurement of serum nonesterified fatty acid (NEFA) and plasma insulin-like growth factor (IGF)-I concentrations relative to the artificial insemination (AI) that established pregnancy. Blood was collected from 41 Holstein Friesian cows on 235 to 241, 242 to 248, 249 to 255, 256 to 262, 263 to 269, 270 to 276, 277 to 283, and 284 to 290 d after AI. Health status was assessed daily for 3 wk after calving; 25 cows (66%) had at least one production disease. Cows developing postpartum diseases had higher mean serum NEFA concentrations (450 ± 26 μmol/L; mean ± SE) and lower plasma IGF-I concentrations (78 ± 6 ng/mL) prepartum compared with healthy cows (259 ± 19 μmol/L and 117 ± 8 ng/mL, respectively). In conclusion, because of substantial variation among cows in gestation length, blood samples should be collected and studies performed on risk prediction relative to AI rather than expected date of calving. As the somatotropic axis is one of the key regulators of metabolic adaption for onset of lactation, IGF-I might be a useful variable to differentiate between cows susceptible to production diseases and cows that are able to adapt adequately within the transition period and remain healthy.

Arterial blood flow is the main source of testicular heat in bulls and higher ambient temperatures significantly increase testicular blood flow

Two experiments were done in bulls to determine: total testicular blood flow, testis oxygenation and heat, and effects of ambient temperature on testicular temperatures and blood flow. In Experiment 1, arterial blood flow to testes and testicular oxygenation and heat were determined in Angus bulls (n = 8). Blood temperature and hemoglobin O2 saturation were both greater (P < 0.0001) in the testicular artery than in the testicular vein (39.2 ± 0.2 vs 36.9 ± 0.4 °C and 95.3 ± 0.7 vs 42.0 ± 5.8%, respectively; mean ± SEM). Based on testicular blood flow of 12.4 ± 1.1 mL/min and an arterial-venous temperature differential of 2.3 °C, blood contributed 28.3 ± 5.1 cal/min of heat to the testis, whereas heat produced by testicular metabolism was estimated at 5.8 ± 0.8 cal/min (based on O2 consumption of 1.2 ± 0.2 mL/min). In Experiment 2, effects of three ambient temperatures (5, 15 and 35 °C) on testicular blood flow and temperatures were determined in 20 Angus bulls. At 35 versus 5 °C, there was greater testicular blood flow (8.2 ± 0.9 versus 4.9 ± 0.7 mL/min/100 g of testicular tissue, P < 0.05), and higher scrotal subcutaneous and intratesticular temperatures (P < 0.01). In conclusion, arterial blood flow was the main source of testicular heat, testes were close to hypoxia, and increased ambient temperature significantly increased scrotal subcutaneous and intratesticular temperatures, as well as testicular blood flow. These studies gave new insights into scrotal/testicular thermoregulation in bulls; they confirmed that testes are nearly hypoxic, but challenged the long-standing paradigm that testicular blood flow does not increase when testes become warmer.