Depo-Provera increases neural activity in the central amygdala of reindeer bulls.

Reindeer bulls are difficult to manage and dangerous to handlers during the rutting period. Progesterone agonists have been used anecdotally in the field to favorably influence behavior, but effects on reproductive signaling have not been determined. The objective of this study was to determine the effects of Depo-Provera (medroxyprogesterone acetate) on neural activity in the amygdala of reindeer bulls in the early (n = 4) and full (n = 4) rut. Treated bulls (n = 4) were injected with a single injection of Depo-Provera (400 mg i.m.) approximately 2 wk before rut was initiated. Control bulls were untreated. Bulls were exsanguinated and brains collected. Neural activity in the amygdala was determined using c-fos immunohistochemistry. Neural activity did not differ by treatment (P ≥ 0.5), collection period (P ≥ 0.5), or their interaction (P ≥ 0.3) in the medial and cortical amygdala nuclei. A treatment × time interaction (P = 0.009) was observed in the central amygdala. The amygdala nuclei are interconnected allowing for integration of sensory stimuli with a direct connection between the medial amygdala and the olfactory bulb. The central amygdala is responsible for alerting, fear, and initiating a state of arousal towards nonspecific stimuli in the surrounding environment. In wildlife, the central amygdala has a role in recognizing threats in the environment such as predators. During the rut, bulls normally have a decreased sense of fear and elevated aggressive behavior with Depo-Provera treatment seemly able to diminish that aggression. Although it is unlikely that this observed change in neural activity fully explains the decreased aggressive behavior noted in bulls treated with Depo-Provera, neural networks of aggression include the amygdala. It is possible that further changes in c-fos activity will be noted in other areas of the brain known to be necessary for processing social cues. Bulls treated with Depo-Provera maintain sexual interest and have offspring. Depo-Prevera increases the neural activity within the central amygdala and may partially account for their altered aggressive behavior during the rut.

Gestation length in farmed reindeer.

Reindeer (Rangifer tarandus tarundus) are the only cervids indigenous to the arctic environment. In Alaska, reindeer are a recognized agricultural species and an economic mainstay for many native populations. Traditionally raised in extensive free-ranging systems, a recent trend toward intensive farming requires a more in-depth knowledge of reproductive management. Reported gestation length in reindeer varies, ranging from 198 to 229 d in studies performed at the University of Alaska Fairbanks. A switchback study that manipulated only breeding date demonstrated a mean increase in gestation length of 8.5 d among females bred early in the season. The negative correlation between conception date and gestation length is consistent with reindeer research at other locations and reports of variable gestation length in a growing number of domestic and non-domestic species. This paper reviews the phenomenon in reindeer and discusses some of the factors known to affect gestation length as well as possible areas for future research.

Variation in gestation length among captive reindeer (Rangifer tarandus tarandus).

An estimated 90% of reindeer females are mated in a 10- to 21-d interval and give birth in an equally synchronized manner. Reported gestation length in reindeer is highly variable (range, 203 to 240 d), almost twice the reindeer estrous cycle length. Previously, we identified a significant, negative relationship between gestation length and conception date in a small group of reindeer. In the current study, the negative relationship was investigated in a switchback design, where reindeer were divided into two groups synchronized for early and late mating over a 2-yr trial. Regression analysis of 11 paired observations produced a negative (P<0.001) association between gestation length and conception date (slope= -0.31). Dam weight at breeding and prior to parturition, calf birth weight, and calf sex were not significant variables in the regression. Regression analysis of a larger data set from two University of Alaska Fairbanks reindeer herds, where conception date (verified by systemic progesterone) and gestation length were recorded (historical data set), supported previous conclusions (n=70; slope= -0.37; P<0.001). Although the calf sex ratio did not differ with gestation length, there was a positive relationship (r(2)=0.19; P=0.014) between male birth weight and gestation length in the larger data set. The negative relationship between conception date and gestation length enhanced calving synchrony, though the limits of gestation plasticity and underlying mechanisms are not clear. The potential role of photoperiod on early embryonic development is discussed.

Steroid hormone secretion during the ovulatory cycle and pregnancy in farmed Alaskan reindeer.

Seasonal endocrine changes in 5 non-bred and 10 pregnant Alaskan reindeer have been documented. Blood samples were collected from early September until early May, spanning the breeding season, gestation, or the anovulatory period. Plasma was analyzed by RIA for progesterone (P4), estradiol-17beta, estrone, and estrone sulfate. Elevated P4 in 80% of the reindeer at the onset of the study indicated that ovarian activity had been initiated. The median date for the onset of the first recorded full-length ovulatory cycle was September 23. In nonbred reindeer, the mean ovulatory cycle length from September to May was 24 +/- 1 d (range 18 to 29 d). Nonbred females continued to cycle throughout the winter, displaying 6 to 8 ovulatory cycles after the beginning of blood sampling. Cycle length (mean 22 to 24 d) did not vary between individuals (P = 0.170) or over the course of the winter (P = 0.244). In early April, ovulatory cycles ceased with normal demise of the corpus luteum in 2 females, whereas the remaining 3 females formed apparently persistent corpora lutea. Natural service breeding occurred between September 10 and October 2, and P4 profiles indicated that all breeding females conceived to the first mating. Concentrations of P4 rose steadily after conception and remained elevated throughout gestation, with mean concentrations not varying significantly (P = 0.104) from 4 to 28 wk of gestation. Estrogens all followed patterns similar to each other, remaining at baseline concentrations until approximately 24 wk of gestation and rising coincidently as P4 declined just before parturition. There was a continual overlap throughout the winter in peak P4 concentrations observed in cycling and pregnant reindeer. Calving occurred between April 8 and May 2, resulting in a mean gestation length of 211 +/- 2.2 d (range 198 to 221 d). Information from this study can be used by Alaskan reindeer producers to improve management and profitability of reindeer production.

The male effect, mounting behavior, and the onset of estrus in farmed muskoxen.

Muskox farming is an emerging industry in Alaska. For such an endeavor to succeed, it is necessary to develop fundamental husbandry tools specifically for this species. This study examined the role of the bull in the onset of seasonal ovarian activity and the synchrony of estrus and tested the efficacy of a radiotelemetric estrus detection system. Twenty parous female muskoxen, ranging in age from 4 to 15 yr, were divided into three groups (balanced by age and body weight). Groups received early bull exposure (EBE; August 1, n = 7), late bull exposure (LBE; August 22, n = 6), or remained physically isolated from a bull (NBE; n = 7). Just before bull introduction, radiotelemetry transmitters were attached to the rump of muskox cows in the EBE and LBE groups. Plasma samples were collected from all the cows twice weekly and analyzed for progesterone (P4). The mean date of onset of seasonal ovarian activity was earlier in the EBE and LBE groups than in the NBE group (P < 0.001) and was earlier in EBE (P < 0.021) than in LBE. All EBE and LBE cows conceived to the first fertile cycle, giving 100% fertility. The time interval for the onset of ovarian activity between the first and last cow within each group was 7 d in the EBE group, 12 d in the LBE group, and 24 d in the NBE group. Radiotelemetry correctly identified estrus 95% of the time (18 of 19 instances). Mean length of estrus for each cow, calculated from the time of first mount until last mount, was 771 +/- 98 min (range = 4 to 1,508 min). Mean number of mounts during estrus was 8.89 +/- 1.29 (range = 3 to 25 mounts). Length of estrus at the first short cycle did not differ from the length of the first fertile estrus between, or within, individuals. Estrous behavior was initiated more frequently during the night (2300 to 0500; P < 0.05). Bull introduction can be used as a simple, low-cost management tool for synchronizing estrus in farmed muskoxen. Radiotelemetry was an effective tool for identifying breeding behavior in this species.

Reindeer bull introduction affects the onset of the breeding season.

Reindeer are seasonally polyestrus, short day breeders, with estrous cycles of approximately 20 days in length. The objective of this study was to investigate the effects of reindeer bull exposure on the onset of the reindeer cow breeding season and to investigate whether cows with calving experience responded differently than cows with no previous reproductive experience. During year 1, blood samples were collected weekly beginning 14 July and continuing until 15 September (n = 8) or 30 September (n = 8) in order to determine the onset of the breeding season, based on ovarian function, with no bull present. Plasma was stored frozen for later assay of progesterone (P(4)) following the conclusion of sample collection. Eight randomly selected cows were allowed to breed with a bull during year 1. The mean onset of ovarian activity in the first year was 15 September (range: 8-29 September). The bull was removed from cows more than 2 months prior to the start of the experimental period during year 2 and housed at a separate facility approximately 2 km distant. Blood samples were collected during year 2 from 14 cows 3x weekly beginning on 11 August (day 1) and continuing until 29 September (day 50) and plasma was stored frozen for later assay of P(4) following the conclusion of sample collection. On day 6, cows were divided into two groups such that group 1 (early bull exposure; EBE), consisted of four cows that had calved the previous spring and four cows that had no reproductive experience (n = 8). Group 2 (late bull exposure; LBE), consisted of three cows that had calved the previous spring and three cows that had no reproductive experience (n = 6). EBE experienced bull introduction on day 13, 23 days earlier than the average onset of ovarian activity during year 1. LBE experienced bull introduction on day 46, 10 days later than the average onset of ovarian activity during year 1. Progesterone concentrations were analyzed by ANOVA procedures for repeated measures. Bull presence was not requisite for the onset of ovarian activity during either year. Previous reproductive status had no effect on the onset of ovarian activity within EBE (P = 0.61) or within LBE (P = 0.92). Time of bull introduction had a significant effect on the onset of ovarian activity when EBE was compared to LBE (P<0.001). The first sustained increase in mean P(4) concentration above 1 ng/ml occurred on day 25 in EBE reindeer and day 41 in LBE reindeer. EBE reindeer initiated ovarian activity 12 days after bull introduction while LBE reindeer initiated ovarian activity 5 days before bull introduction. All cows penned with the bull conceived during both breeding seasons, demonstrated by production of live calves during the subsequent spring. Cows bred during year 1 all calved within a 9 day-period. During year 2, EBE displayed a more synchronous calving period compared to LBE (P<0.05). Results indicate that bull management affects the onset of the breeding season in reindeer cows, regardless of previous reproductive experience.

Estrogen concentrations in milk at estrus and ovulation in dairy cows.

The objective of this study was to determine the efficacy of using milk estradiol-17beta (E(2)) sampled during regular milking periods as a predictor of estrus in dairy cows. Twenty-three primiparous Holstein cows received radiotelemetric transmitters on day 16 of the estrous cycle (day 0 = estrus) for continuous monitoring of behavioral estrus. Milk and blood samples were collected every 12h at each milking, from day 18 of the estrous cycle until the fourth milking after the onset of estrus, for radioimmunoassay of E(2). Onset of estrus was indicated by the first standing event identified by radiotelemetry. Ultrasound examination of ovaries was conducted daily in a subset of cows (n = 17) from day 18 until ovulation was confirmed. Statistical analysis involved utilization of Pearson correlation to observe any association of mean plasma and milk E(2) concentrations. Intervals from highest measured plasma and highest measured milk E(2) until the first expression of standing behavior and intervals from highest measured plasma and highest measured milk E(2) until ovulation were compared using Student's t-test. Repeated measures were utilized to evaluate the effect of day and time on milk E(2) concentration. Chi-square procedures were utilized to detect differences in actual time of onset of estrus compared to the expectation of random time of onset of estrus throughout the 24 h day. Mean duration from highest measured milk E(2) until onset of standing behavior was 21+/-3.7h and until ovulation was 46.7+/-5.3h. Mean duration from onset of standing behavior until ovulation was 26.4+/-4.2h. Mean milk E(2) concentrations increased (P<0.01) from the fourth milking period before estrus to the milking period immediately before the first expression of standing behavior, followed by a reduction (P<0.01) in mean concentrations at the milking immediately after the onset of estrus.

Effects of bull exposure on postpartum ovarian activity of dairy cows.

The effects of bull exposure on postpartum reproduction have been previously studied in beef, but not in dairy cattle. The objective of this experiment was to investigate effects of bull exposure on postpartum reproductive characteristics during early lactation in high-producing Holstein dairy cattle. Forty-five multiparous dairy cows (9764 +/- 140 kg milk/lactation) were randomly grouped at the time of calving. Treatment 1 (NBE) was never exposed to the bull, treatment 2 (2 x BE) experienced fenceline contact with a mature Holstein bull twice daily during routine detection of oestrus, and treatment 3 (CBE) was in continuous proximity to the bull. All cows were observed for oestrous behaviour twice daily for 1/2 h following milking. Blood samples were collected every other day for progesterone (P4) assay. Postpartum ovarian reactivation, indicated by the occurrence of the first sustained rise in P4, was later (P = 0.02) during the postpartum period in both bull-exposed (2 x BE, CBE) treatments compared to the NBE treatment. Time postpartum until completion of the first ovarian cycle tended (P = 0.08) to be shorter in NBE cows compared to bull-exposed cows. Peak P4 concentrations were higher (P = 0.05) in NBE cows compared to bull-exposed cows prior to the second postpartum ovulation. Results indicate an extended period to ovarian reactivation in dairy cattle exposed to a bull, but bull exposure had no effect on long-term reproductive performance of exposed cows.

Altering conception of dairy cattle by gonadotropin-releasing hormone preceding luteolysis induced by prostaglandin F2 alpha.

The objective of these experiments was to determine the effect on fertility of GnRH when used in conjunction with one or two injections of PGF2alpha. In Experiment 1, GnRH was administered 7 d before the second of two injections of PGF2alpha (14 d apart). The control group received two injections of PGF2alpha without GnRH. Conception was reduced from 63.5% for 74 controls to 48.7% for the 79 heifers and cows that had been treated with GnRH, but estrus detection and pregnancy rates were similar. In Experiment 2, 85 heifers and cows received GnRH at a random stage of the estrous cycle, followed in 7 d by PGF2alpha. Thirty to 32 h after PGF2alpha, a second dose of GnRH was given to induce ovulation of the preovulatory follicle, followed by one fixed-time insemination 18 to 19 h later (treatment designated as GnRH, PGF2alpha, and GnRH). Controls (n = 85) were given PGF2alpha and inseminated at estrus. Although conception rate was not different, one fixed-time insemination after the GnRH, PGF2alpha, and GnRH treatment tended (35.3%) to reduce fertility compared with effects of the control (47.1%). It is unclear how an injection of GnRH during the intervening week between two injections of PGF2alpha reduced fertility in Experiment 1. However, in Experiment 2, when GnRH was given 7 d before one injection of PGF2alpha and when ovulation was induced with a second GnRH injection, one fixed-time insemination seemed to produce acceptable fertility in dairy cows but probably less than that when inseminations were based on detected estrus.