The wide variance in anatomical characteristics among heifers born co-twin to a bull make diagnosis of freemartinism by measurements of vaginal length or the distance between the anus and vulva unreliable. Change in serum luteinizing hormone (LH) in response to injection of estrogen or gonadotropin releasing hormone (GnRH) is different in freemartins compared to normal heifers but is also an unreliable predictor of freemartinism. Presently, the most conclusive way to establish freemartinism in a heifer born co-twin to a bull is to measure the percentage of XX and XY chromosomes in cells from whole blood, which is a specialized and expensive procedure.
Conception rates and subsequent calving dates were compared between cows synchronized with Syncro-Mate-B® and inseminated by appointment and nonsynchronized cows bred by natural service. Average conception date was seven days earlier in the synchronized cows.
High ambient temperature (34.4 C degrees and 60-65% relative humidity (RH failed to maintain optimum embryonic and/or foetal survival rate in ovariectomized pregnant rats given exogenous progesterone and oestrone injections. A still higher ambient environment (36.6 C degrees and 70-75% RH) did not affect the decidual cell response (DCR) in psuedo-pregnant rats. Heat stress did not result either in insufficiency or lack of progesterone and hence the latter two are not factors for the heat stress causing embryonic and/or foetal loss. The possibility of the failure of oestrone being converted to oestradiol or an intrinsic interference of RNA synthesis to be the factors responsible for embryonic and/or foetal loss caused by heat stress has been examined.
Fertility during the first two breeding seasons was not affected by the dam's weaning weight, but lightest heifers at weaning reached puberty later, had smaller pelvic areas at calving, more difficult deliveries, had more calves die, and weaned a smaller percentage of their calves.
Heifers with faster gain the first and second winter (weaning to yearling and 18 months to 2 years old) had better production and reproduction than heifers with low or moderate gains. Gains during the first winter (weaning to yearling) had more influence on future performance than gains during the second winter as bred heifers.
Expanded use of artificial insemination in the beef cattle industry depends on successful application of treatments designed to synchronize estrus. Regulation of estrous cycles is associated with control of the corpus luteum (CL), whose life span and secretory activity are subject to trophic and lytic mechanisms. The advantages of melengestrol acetate (MGA) in estrous synchronization incorporate ease of administration, lower cost relative to other estrous synchronization products, and potential for use to induce estrus in prepubertal heifers. Treatments first designed to synchronize estrous cycles of normally cycling heifers by feeding MGA were imposed daily for 14 to 18 d at levels of .5 to 1 mg. The minimal daily effective dose required to inhibit ovulation was .42 mg. Longer feeding periods of MGA were associated with low fertility at the first synchronized estrus, but at the second estrus, conception was normal. Low fertility at the synchronized estrus resulted in development of alternative treatment practices, which combined feeding of MGA with injections or implants of estradiol-17β estradiol cypionate, luteinizing hormone, human chorionic gonadotropin, pregnant mare serum gonadotropin, or oxytocin. Estrus was synchronized after MGA and estradiol-17β or estradiol cypionate treatments, but fertility was low. Short-term feeding of MGA (5 to 7 d) combined with prostaglandin F2α or its analogs (PGF) on the last day of MGA reduced fertility at the synchronized estrus. The reduced conception at first service occurred in animals that began treatment after d 12 of the estrous cycle. However, feeding MGA for 14 d and then injecting PGF 17 d later avoided problems with reduced conception. Fertility of animals after this treatment was similar to that of contemporaries synchronized with Syncro-Mate-B. However, the length of the treatment period creates a need for increased management and may extend management beyond practical limits. Further research is warranted to address problems associated with reduced fertility after short-term treatment with MGA.
High ambient temperature (34.4 C degrees and 60-65% relative humidity (RH) did not affect foetal survival when bred female rats were exposed between day-8 and -18 (Day-0=day of breeding). Heat-stress at this intensity given on day-0 was critical for embryonic and/or foetal survival rate and more so, if the ambient temperature was increased to 36.6 C degrees and 70-75% RH than on day-1. Postimplantation foetal survival was reduced due to heat-stress given only during early gestation period.
The effectiveness of alfaprostol in inducing abortion was tested in 93 pregnant heifers. Alfaprostol was injected intramuscularly, .7 mg per 100 pounds body weight. Twenty-four heifers were injected when they averaged 83 days (range 64 to 86) pregnant, while 23 were injected when 138 days (range 119-143) pregnant. A control injection of the Alfaprostol carrier, propylene glycol, was given 23 heifers averaging 81 or 134 days pregnant. By 14 days after the Alfaprostol injection 79% of the heifers 83 days pregnant and 96% of the heifers 138 days pregnant had aborted. Two of the 83-day controls and none of the 138 day controls aborted. Since Alfaprostol (5.4 mg) was very effective up to at least 140 days of pregnancy, but somewhat less effective earlier, the dosage may need to be increased for lighted or earlier pregnancy heifers. No serious side effects were noted in aborted heifers.
Twenty-six, Hereford x Angus, suckled cows were utilized to determine patterns of follicular development and associated changes in reproductive hormones during postpartum anestrus and first estrous cycles. Ultrasonography per rectum was used to monitor follicular size and detect ovulation. Dietary energy and(or) body condition influenced patterns of follicular development during postpartum anestrus. Follicular growth occurred in waves during this period in cows that were in adequate body condition and adequately fed, and follicular development appeared to be related to serum concentrations of luteinizing hormone and estradiol. Two distinct characteristics were associated with follicular development before the first postpartum ovulation. First, diameter of dominant follicles increased with successive follicular waves. Second, a large dominant follicle was present for an extended time before development of the first ovulatory follicle and appeared to be involved in the mechanism that initiates the first ovulation after calving.
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