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.

193 EVALUATION OF A NOVEL ELECTRONIC ESTRUS DETECTION DEVICE IN RECIPIENTS SYNCHRONIZED FOR EMBRYO TRANSFER

The ability to detect estrus in cattle is an important aspect for both successful artificial insemination (AI) and successful embryo transfer (ET). The use of estrus detection devices has allowed producers to more precisely determine when to breed their cattle. There have been many types of devices including chin-ball marking harnesses, dye patches, and even electronic devices that monitor the animal's activity. With the growing popularity in timed AI and ET, these devices have again become of great interest. The latest tool for estrus detection is the multi-use TattleTale" Heat Detector (Microdyne Co., LLC., St. Joseph, MO, USA). The TattleTale" is an electronic device that is placed in a patch and affixed to the tail head. It is activated by a 3-s mount with subsequent mounts recorded per h through 12 h. Twelve hours after activation the device flashes indicating that the animal is ready for breeding. Such devices may allow breeders to determine exactly when estrus began as well as identify the peak estrus period, resulting in more accurate determination of optimal time for AI or ET. The objective of this study was to compare the accuracy of estrus detection devices when analyzing detection records and pregnancy rates. Cows from the Dixon Springs Agricultural Center (Simpson, IL, USA) were randomly separated into two groups based on estrus detection devices, one group receiving Kamar� patches (Kamor, Inc., Steamboat Springs, CO, USA) and the other receiving TattleTales. Both groups were synchronized using the OvSynch protocol (Syntex, Buenos Aires, Argentina). Cows were checked twice each day for four consecutive days, with a fifth day occurring a week later when the embryos were transferred. Estrus results were analyzed using a PROC UNIVARITE and GLM analyses with differences between treatment means determined by the LSD method of SAS (SAS Institute, Inc., Cary, NC, USA). The TattleTale detected a higher percentage (P < 0.05) of the cows in estrus (92 vs. 70%) than the Kamar� patch. Further, the TattleTale detected more asynchronous recipients (in estrus >48 h before expected) and synchronous recipients (in estrus <24 h than expected), although not significant with this sample size. In the present study, the TattleTale was more accurate in detecting estrus (i.e. fewer pregnancies were observed without estrus detected). Using the TattleTale information, a breeder would be able detect more animals in estrus and determine the most accurate time to breed or transfer embryos. Practically, the use of estrus detection devices in combination with timed AI and ET could allow for the exclusion of animals not in estrus in the optimal time windows for AI or ET, thus saving valuable semen and embryos that would be otherwise wasted on asynchronous females. The advantages of this device to producers include improved pregnancy rates based on timed breeding, lower herd management costs due to reduced quantities of wasted semen or embryos and fewer cows being resynchronized. This device also records any mounting activity missed by visual observation alone. This work was supported by USDA RRF W-1171.

159 TWIN vs. SINGLE TRANSFER OF IVP HOLSTEIN HEIFER EMBRYOS TO BEEF RECIPIENTS

Use of sexed semen in conjunction with in vitro embryo production is a potentially efficient means of obtaining offspring of predetermined sex. Here we evaluate a production scheme involving single and bilateral twin transfer of Holstein female embryos to beef cattle recipients. Holstein oocytes were fertilized with the X-bearing fraction of gender-sorted Holstein semen. Cumulus cells were removed with aid of a vortex or microfluidic device (μFD). Half of the vortexed embryos were cultured in KSOMaaBSA (control), as were all μFD embryos. The remaining vortexed embryos were cultured in control medium with 6% avian white yolk (WY). Embryo production and transfer occurred across five replicates. Cows (n = 475) were synchronized using an Ovsynch protocol. They were administered GnRH on Day −9, PGF on Day −2, and GnRH on Day 0. Half of the cows received a CIDR (1.38 g progesterone) with the 1st GnRH injection. The CIDR was removed at the time of PGF treatment. Day 7 Grade 1 blastocysts were transferred fresh 7 days after the 2nd GnRH injection. Control and WY embryos were transferred as ipsilateral singles and bilateral twins; μFD embryos were transferred singly. Pregnancy was diagnosed with ultrasound between 41–46 days and confirmed between 60–90 days; fetal sexing confirmed that 95% of fetuses were female. Effects on embryo survival were analyzed by logistic regression. Chi-square analysis was applied to survival rates. Replication affected embryo survival (P < 0.05). There was no effect of cumulus removal, medium, or CIDR use. Fetal loss between ultrasounds was greater for twin vs. single transfers (30% vs. 15%, respectively; P < 0.01). Probability of embryo survival was estimated to increase ∼0.006 with each increasing day postpartum. Five cases of hydrallantois were detected during the 5th month of gestation for 1 control twin, 1 WY single, and 3 WY twin transfers, originating from 3 replicates. On a production per transfer basis, the proportion of fetuses obtained for single and twin transfers was 30% and 55%, respectively (P < 0.001). Although there was greater embryonic loss for twin compared to single transfers, a higher percentage of cows receiving twins established and maintained pregnancy. Large-scale transfer of IVP Holstein heifer embryos to beef recipients is a feasible production scheme. Table 1. Embryo survival and pregnancy rates

Long term perifusion of rabbit ovarian follicles

Preovulatory follicles were dissected from ovaries of estrous rabbits. Four follicles were placed in each chamber of a perifusion system. Medium 199, containing 10% rabbit serum and antibiotics, eluted through the chambers at a rate of 1 ml/10 min. Every 6 h for 36 h, 1 microgram of LH and 50 ng of FSH were injected into each chamber. P4, T and E2 were measured in the medium. P4 exhibited a peak after each of the injections at 6, 12, 18, 24 and 30 h. E2 and T gave major peaks after the injection at 0 time, with minor peaks after the injection at 6 h; thereafter T and E2 secretion gradually decreased to levels below those of baseline.