C. G. Hart

Environmental stressors influencing hormones and systems physiology in cattle

Environmental stressors undoubtedly influence organismal biology, specifically the endocrine system that, in turn, impact cattle at the systems physiology level. Despite the significant advances in understanding the genetic determinants of the ideal dairy or beef cow, there is a grave lack of understanding of the systems physiology and effects of the environmental stressors that interfere with the endocrine system. This is a major problem because the lack of such knowledge is preventing advances in understanding gene-environment interactions and developing science-based solutions to these challenges. In this review, we synthesize the current knowledge on the nature of the major environmental stressors, such as climate (heat, cold, wind, and humidity), nutrition (feeds, feeding systems, and endocrine disruptors) and management (housing density and conditions, transportation, weaning practices). We summarize the impact of each one of these factors on cattle at the systems level, and provide solutions for the challenges.

Effect of 2 corpora lutea on blood perfusion, peripheral progesterone, and hepatic steroid-inactivating enzymes in dairy cattle

The luteal structure that develops postovulation is critical to the facilitation and maintenance of pregnancy in dairy cattle. The objectives of this experiment were to determine if the induction of an accessory corpus luteum (CL), via human chorionic gonadotropin, altered blood perfusion of CL, peripheral concentrations of progesterone, or hepatic steroid-inactivating enzymes. Twenty-eight late-lactation Holstein cows were synchronized using the Ovsynch protocol and randomly assigned to 1 of 2 treatment groups. Cows received either an injection of human chorionic gonadotropin (1,000IU, i.m.) to induce an accessory CL (cows had exactly 2CL in 1 ovary) or no treatment (cows had exactly 1CL). Corpora lutea were examined daily from d 10 to 18 (d 0 was induced ovulation) via Doppler ultrasonography and a blood sample was collected. Volume of the CL was recorded, as well as images and videos of each CL, which were analyzed for blood perfusion. On d 13, a liver biopsy was performed to analyze hepatic steroid-inactivating enzymes. Cows with 1 or 2CL had similar peripheral concentrations of progesterone. Cows with 2CL had similar luteal volumes to cows with 1CL but cows with 2CL had greater total luteal blood perfusion. Hepatic enzyme [cytochrome P450 (CYP) 1A, 3A, and 2C, aldo-keto reductase 1C, and uridine diphosphate glucuronosyltransferase] activities did not differ between cows with 1 and 2CL. Overall, the observed increase in total luteal blood perfusion in cows with 2CL did not correspond to differences in peripheral concentrations of progesterone or clearance of progesterone measured by the hepatic enzyme activity. This could indicate that induction of an accessory CL would not affect concentrations of progesterone necessary to maintain pregnancy.

Maternal nutrient restriction alters uterine artery hemodynamics and placentome vascular density in Bos indicus and Bos taurus

The objective was to examine uterine artery blood flow (UBF) as well as macroscopic and microscopic placentome vascular density in nutrient-restricted Angus and Brahman heifers. Angus (n = 6) and Brahman (n = 6) heifers were bred to a single sire and pregnancy confirmed at 30-d postbreeding. Heifers were randomly assigned to 1 of 2 dietary treatments consisting of 100% (control-fed; CON; n = 6) or 60% (total nutrient-restricted; RES; n = 6) based from net energy requirements for gestating heifers. Nutritional treatments were imposed from days 50 to 180 of gestation. On day 175 of gestation, UBF was collected ipsilateral and contralateral to the conceptus via Doppler ultrasonography. Heifers underwent Cesarean sections for collection of 2 adjacent placentomes on day 180 of gestation. The primary cotyledonary artery of 1 placentome was perfused with Alexa Fluor 647 Con A conjugate to examine macroscopic cotyledonary vascular density via an in vivo imaging system. The second placentome was fixed for microscopic immunofluorescence labeling of capillaries and separated into maternal (caruncle) and fetal (cotyledon) components for determination of angiogenic factor mRNA expression. Main effects of nutritional treatment and breed are reported in the absence of a significant nutritional treatment by breed interaction. Ipsilateral UBF was decreased (P < 0.05) by 48% in RES vs. CON, whereas breed did not influence ipsilateral UBF. Contralateral UBF was not different between nutritional treatments; however, contralateral UBF was decreased (P < 0.05) by 63% in Brahman vs. Angus cattle. Macroscopic cotyledonary vascular density was increased (P < 0.05) by 36% in RES vs. CON and 82% in Brahman vs. Angus heifers. Percent capillary area and capillary perimeter were increased (P < 0.05) in RES vs. CON and increased (P < 0.05) in Brahman vs. Angus heifers. Dietary treatments did not alter angiogenic factor expression; however, transcript abundance of caruncle and cotyledon ANGP1, FLT1, and KDR was increased (P < 0.05) in Brahman vs. Angus heifers. In summary, these data indicate compensatory responses in macroscopic and microscopic placentome blood vessel density during maternal nutrient restriction-induced reductions in UBF. Moreover, a greater macroscopic density of cotyledonary blood vessels was observed in Brahman vs. Angus heifers.

Effect of chronic melatonin supplementation during mid to late gestation on maternal uterine artery blood flow and subsequent development of male offspring in beef cattle

The objective of the current study was to examine the effects of supplemental melatonin implants on uterine artery blood flow from mid to late gestation in beef cattle and subsequent development of their male offspring. Commercial beef heifers (n = 32) and cows (n = 25) were bred via artificial insemination and assigned to 1 of 2 groups supplemented with melatonin implants (MEL) or without (CON) at day 180, 210, and 240 of gestation. Uterine artery blood flow was determined using color Doppler ultrasonography. A subset of 12 crossbred heifers (n = 6 MEL; n = 6 CON) underwent Cesarean sections on day 243 ± 2 of gestation to allow for placentome collection. Maternal and fetal serum were collected to analyze melatonin concentrations. The remaining cattle were allowed to calve and at weaning (195 ± 2 d of age), bull calves (n = 15) were castrated and testicular tissue harvested for seminiferous tubule analysis. Heifer uterine artery blood flow was increased (P = 0.009) at day 240 of gestation in MEL compared with CON heifers. Cow uterine artery blood flow was increased (P = 0.003) in MEL compared with CON cows irrespective of gestational day. Maternal and fetal concentrations of melatonin were increased (P < 0.05) in MEL compared with CON heifers. The percent of placentome capillary area per mm2 was decreased (P = 0.019) in MEL compared with CON heifers, while cotyledonary ANGPT1 mRNA tended to increase (P = 0.095) in MEL compared with CON heifers. At weaning, body weight of male offspring and their scrotal circumference were increased (P < 0.05) in calves born to MEL compared with CON dams, while seminiferous tubule diameter and area were not different (P > 0.40) between treatments. In summary, melatonin supplementation increased uterine artery blood flow in mid to late gestating cattle, but this was not accompanied by an increase in fetal weight. Alterations in postnatal development of bulls, including increased body weight and scrotal circumference, warrants future investigations related to attainment of puberty and subsequent fertility of offspring born to melatonin supplemented dams.

Endometrial blood perfusion as assessed using a novel laser Doppler technique in Angus cows

Previous studies have characterized ovarian steroid synthesis which directly affects uterine environment and blood flow. Clearance of steroids occurs primarily in hepatic tissues, however, it was discovered that there is an abundant activity of the phase II steroid metabolizing enzyme UDP-glucuronosyltransferase (UGT) in uterine biopsies. No minimally invasive techniques for collecting endometrial perfusion, which is affected by steroids and indicative of reproductive health, have been developed for livestock. The objective of the present study was to characterize UGT activity and endometrial blood perfusion during a normal estrous cycle of cattle. It was hypothesized that there would be increased steroid metabolism during the luteal phase of the estrous cycle and in the uterine horn ipsilateral to the corpus luteum (CL). During the first synchronized estrous cycle, progesterone and UGT activity increased on Day 6 compared with 0 and 3, with the first day of estrus being considered Day 0 of the study. Endometrial perfusion was greater ipsilateral to the CL compared with contralateral on Day 12, and was less ipsilateral to the CL compared with contralateral on Day 18. Similar to perfusion results, nitric oxide metabolites (nitrites) were greatest in the endometrium ipsilateral as compared with contralateral to the CL. Moreover, there was a positive correlation (ru202f=u202f0.28; Pu202f=u202f.04) between endometrial perfusion and nitrite concentration. It is concluded that activity of UGT within the endometrium is affected by the contralateral or ipsilateral location of the CL, and collection of endometrial perfusion data using a laser Doppler probe could be a viable measurement technique as indicated by associated nitrite concentrations in the present study.