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.

Forty-four Holstein calves were fed a direct-fed microbial (DFM) and 1 of 2 milk replacers to evaluate calf performance and growth. Treatments were (1) a control milk replacer [22:20; 22% crude protein (CP) and 20% fat], (2) an accelerated milk replacer (27:10; 27% CP and 10% fat), (3) the control milk replacer with added DFM (22:20+D), and (4) the accelerated milk replacer with added DFM (27:10+D). Dry matter intake, rectal temperatures, respiration scores and rates, and fecal scores were collected daily. Body weight, hip and withers height, heart girth, blood, and rumen fluid samples were collected weekly. Effects of treatment, sex, week, and their interactions were analyzed. Calves fed an accelerated milk replacer, regardless of DFM supplementation, consumed more CP and metabolizable energy in the milk replacer. No treatment differences were found for starter intake or intake of neutral detergent fiber or acid detergent fiber in the starter. Calves fed the accelerated milk replacer had greater preweaning and weaning body weight compared with calves fed the control milk replacer. Average daily gain was greater during the preweaning period for calves fed the accelerated milk replacer, but the same pattern did not hold true during the postweaning period. Feed efficiency did not differ among treatments. Hip height tended to be and withers height and heart girth were greater at weaning for calves fed the accelerated milk replacer compared with calves fed the control milk replacer. Fecal scores were greatest in calves fed DFM. Overall acetate, propionate, butyrate, and n-valerate concentrations were lower in calves fed the accelerated milk replacer, but DFM did not have an effect. Rumen pH was not different. Blood metabolites were unaffected by DFM supplementation, but calves fed the accelerated milk replacer had increased partial pressure of CO2, bicarbonate, and total bicarbonate in the blood. Direct-fed microbial supplementation did not appear to benefit the calf in this trial.

The objectives of the experiments were to compare ovarian responses, pregnancy per artificial insemination, and pattern of insemination of 2 estrus detection-based presynchronization protocols before first artificial insemination (AI) during heat stress. In experiment 1, primiparous lactating dairy cows (n=1,358) from 3 dairies were assigned randomly to 2 treatments at 60±3 (±SD) DIM (study d 0): (1) treatment with 100 µg of GnRH on study d 0 (Gpresynch), or (2) no treatment on study d 0 (control). In experiment 2, multiparous lactating dairy cows (n=1,971) from 3 dairies were assigned randomly to 2 treatments at 49±3 (±SD) DIM (study d 0), similar to experiment 1. In both experiments, PGF2α injections were administered 14 d apart starting on study d 7 for all cows. Cows not inseminated after detection of estrus were submitted to a timed artificial insemination protocol at study d 35. In a subgroup of cows from 2 dairies, concentrations of progesterone were determined from blood samples collected on study d 0 and 7. Furthermore, ovaries were examined by ultrasonography on study d -14, 0, and 7 to determine cyclic status and ovulation in response to GnRH treatment. In experiment 1, progesterone concentration was not different on d 0, but progesterone was increased for Gpresynch compared with control cows on study d 7 (3.6±0.3 vs. 2.7±0.4 ng/mL), respectively. Ovulation risk from study d 0 to 7 was increased for Gpresynch compared with control (50.6 vs. 15.2%). Control cows were inseminated at a faster rate than Gpresynch cows [adjusted hazard ratio (AHR)=0.89, 95% confidence interval=0.80 to 1.00], and the interaction between treatment and dairy affected pregnancy per artificial insemination at 36 and 94 d post-artificial insemination. In experiment 2, concentrations of progesterone did not differ on study d 0 or 7, despite ovulation risk from study d 0 to 7 being greater in Gpresynch than control cows (46.9 vs. 23.8%). The interaction between treatment and dairy affected hazard of insemination with Gpresynch cows from dairy 1 (AHR=1.21; 1.05 to 1.41) being inseminated faster than control cows. Hazard of pregnancy was affected by treatment because Gpresynch cows became pregnant at a faster rate than control cows (AHR=1.25; 1.04 to 1.50). In conclusion, GnRH-based presynchronization protocols initiated before the end of the voluntary waiting period may have benefits in reproductive efficiency of estrus detection-based programs during heat stress. In addition, treatment with GnRH decreased the prevalence of anovular cows at the initiation of PGF2α injections.

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The objective of the study was to investigate the relationships between vaginal temperature during the dry-period and health, milk production, and reproduction in the subsequent lactation of cows during the warm season. A total of 105 nonlactating Holstein cows from 2 dairies were enrolled in the study during summer. At enrollment, cows were between 250 and 260 d of gestation. Vaginal temperature (VT) and corral ambient temperature and humidity were recorded every 5 min for 4 consecutive days starting at enrollment. Cows were categorized as presenting high (HT) or low temperature (LT) based on the median values of average VT and were followed until 300 d in milk (DIM) of the subsequent lactation to evaluate health disorders, culling rate, milk yield, and reproductive efficiency. Cows that became pregnant were followed until subsequent calving. Cows were monitored for uterine diseases (UTD) and mastitis (MAST) by farm personnel. Individual milk yield was recorded monthly until 300 DIM. Cows classified as HT had shorter ( < 0.01) gestation length (273.9 ± 0.9 vs. 278.7 ± 1.0 d) and spent fewer ( < 0.01) days in the close-up pen (14.3 ± 0.8 vs. 19.4 ± 1.0 d) than LT cows. Hazard to UTD or MAST in the first 60 DIM was greater for HT than LT cows (adjusted hazard ratio [AHR] = 5.15, 95% CI = 1.91 to 13.86). Cows classified as HT had greater hazard to MAST in the first 300 DIM compared with LT cows (AHR = 2.39; 1.03 to 5.56). Vaginal temperature was not associated with milk yield. In contrast, the interaction between VT category and month of lactation tended to influence milk yield. This interaction was observed because cows categorized as LT had greater ( < 0.01) milk yield in the first month of lactation compared with HT cows (39.2 ± 1.6 vs. 33.7 ± 1.5 kg), whereas milk yield tended ( = 0.07) and was greater ( = 0.05) for HT cows in the ninth (32.7 ± 1.6 vs. 28.5 ± 1.9 kg) and tenth (29.9 ± 1.7 vs. 25.0 ± 2.0 kg) month of lactation, respectively. Pregnancy per AI at first service, interval from calving to pregnancy, and percentage of cows calving in the subsequent lactation did not differ between HT and LT cows. In conclusion, VT assessed between 20 and 30 d before expected calving is associated with health outcomes and milk production in the subsequent lactation. In addition, cows susceptible to be affected by postpartum disorders after calving may be identified during the summer by evaluating VT temperature at 250 to 260 d of gestation.

Using an activity monitoring system (AMS) equipped with an accelerometer, 2 experiments were conducted to test the hypotheses that (1) enhancing progesterone before inducing luteolysis or (2) exposing cows to estradiol cypionate (ECP) or testosterone propionate (TP) after luteolysis would increase occurrence and intensity of estrus. Our goal was to determine if more cows could be detected in estrus by an AMS compared with other estrus-detection aids. In experiment 1, cows (n=154) were fitted with both an AMS collar and a pressure-sensitive, rump-mounted device (HeatWatch; HW) and assigned to 3 treatments: (1) no CL + progesterone insert (CIDR) for 5d, (2) CL only, or (3) CL + 2 CIDR inserts for 5d to achieve a range in concentrations of progesterone. Prostaglandin F was administered to all cows upon CIDR insert removal or its equivalent. Progesterone concentration up to 72h posttreatment was greatest in CL + 2 CIDR, followed by CL only, and no CL + CIDR cows. Estrus occurred 14 to 28h earlier in no CL + CIDR compared with CL-bearing cows. Estrus intensity was greater for CL + 2 CIDR than for CL-only cows. The AMS and HW detected 70 and 59% of cows defined to be in estrus, respectively. In experiment 2, cows (n=203) were equipped with both an AMS and a friction-activated, rump-mounted patch (Estrotect patch) and assigned to receive 1mg of ECP, 2mg of TP, or control 24h after PGF. Concentrations of estradiol 24 and 48h after treatment were greater in ECP cows compared with controls. Estrus expression detected by AMS or patches in cows defined to be in estrus tended to be greater or was greater for ECP compared with controls, respectively. Compared with controls and in response to TP or ECP, estrus occurred 8 to 18h earlier and was of greater intensity for ECP cows, respectively. The AMS and patches determined 73 and 76% of cows defined to be in estrus, respectively. Of cows exposed to the AMS, HW, or patches, 70, 61, and 75%, respectively, were detected in estrus and more than 93% of these subsequently ovulated. In contrast, of the residual cows not detected in estrus, 62 to 77% ovulated in the absence of detected estrus. Only ECP was successful in inducing more expression and intensity of estrus, and proportions of cows detected in estrus exceeded 80%. Given the large proportion of cows equipped with AMS collars ovulating in the absence of estrus, further research is warranted to determine if more pregnancies can be achieved by inseminating those cows not detected in estrus at an appropriate time when PGF is administered to induce luteolysis.

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We hypothesized (1) that neither duration of the Ovsynch program nor dose frequency of PGF would change the proportion of cows with complete luteolysis (progesterone <0.4 ng/mL 72 h after PGF) and (2) that the additional GnRH treatment administered as part of a presynchronization program would not alter the proportion of anovulatory cows starting the timed artificial insemination (AI) program compared with an alternative shorter presynch program including only 1 GnRH treatment. Lactating Holstein cows (n = 406) were milked 3 times daily and enrolled in a 2 × 2 × 2 factorial experiment consisting of 8 treatments before the first postpartum AI. Treatments were used to test ovulatory, luteal, and luteolytic outcomes to 3 main effects: (1) 2 GnRH-PGF presynchronization programs (PG-3-G vs. Double Ovsynch), (2) 2 Ovsynch program durations [5 d: GnRH (GnRH-1)-5 d-PGF-24 h-PGF-32 h-GnRH (GnRH-2)-16 h-timed AI; 7 d: GnRH-1-7 d-PGF-56 h-GnRH-2-16 h-timed AI], and (3) 2 PGF dose frequency treatments (2 × 25 mg) 24 h apart versus 1 dose (1 × 50 mg) of PGF administered 72 h before timed AI. The presynchronization treatments of PG-3-G and Double Ovsynch had no effect on the proportion of cows with luteal function at the onset of the Ovsynch treatments (87.9 vs. 86.2%). Although ovulatory responses were similar after GnRH-1 (>60%), Double Ovsynch cows tended to have greater ovulatory responses than PG-3-G after GnRH-2 (95.3 vs. 90.6%). The 2 × 25-mg doses of PGF and the 1 × 50-mg dose induced luteolysis in both Ovsynch treatment durations, but the 1 × 50-mg dose was less effective in the 5-d program. More pregnancy per AI (P/AI; 49.2%) tended to occur in the PG-3-G cows in the 7-d program compared with the other treatment combinations (range: 32.4-37.4%; Ovsynch × presynch interaction). In addition, an Ovsynch × PGF dose frequency interaction resulted in cows receiving the 1 × 50-mg dose in the 7-d program having the greatest P/AI (46.1%) and cows receiving the 1 × 50-mg dose in the 5-d program having the least P/AI (30.6%). We conclude that complete luteolysis was less effective in the 5-d program when the 1 × 50-mg dose was applied, but both PGF dose frequencies (1 × 50 mg and 2 × 25 mg 24 h apart) effectively induced complete luteolysis in the 7-d program. Treatments producing complete luteolysis tended to be related to subsequent pregnancy outcomes.