David L. Kreider

Testosterone Cycles and Reproductive Energetics: Implications for Northern Range Limits of the Cottonmouth (Agkistrodon piscivorus leucostoma)

Abstract To assess the possibility of thermal effects on reproductive function as a range-limiting mechanism in cottonmouths, we investigated the effects of temperature/photoperiod regimes on monthly male testosterone levels in three groups. The first was a field group, the second was a lab control group that received natural temperature/photoperiod conditions, and the third was an experimental lab group that received temperature/photoperiod conditions of a region north of the current range limit. The field and lab control groups exhibited a single testosterone peak in August (34.4 and 14.1 ng ml−1, respectively) that coincided with observed reproductive activities in Northwestern Arkansas. The experimental group also exhibited a single peak (11.7 ng ml−1), but the peak was delayed by one month. We coupled energetic calculations with environmental temperature, the timing of reproductive events, and the time available for foraging to demonstrate how pre- and postcopulation reproductive failure may serve as a sublethal range-limiting mechanism. North of their current range limit, the reduced time for energy acquisition may not allow for sufficient juvenile recruitment into the population to replace losses. Therefore, cottonmouths may be prevented from establishing a more northern range limit due to their reproductive physiology.

Episodic Gonadotropin Secretion in the Mature Fowl: Serial Blood Sampling from Unrestrained Male Broiler Breeders (Gallus domesticus)

Abstract Forty-week-old male broiler breeders were used in two experiments. Males were reared as recommended by the breeder, housed in individual cages, and cannulated to facilitate blood sampling. In experiment 1, blood samples were collected at 10- min intervals for 4 h commencing the day of cannulation (Day 0) and for 12 h on each of Days 1 and 2. In experiment 2, blood samples were collected at 10-min intervals for 8 h on Day 1. After centrifugation, plasma was stored at −20°C until LH, FSH (experiment 1 and 2), testosterone, and corticosterone (experiment 1) concentrations were determined by RIA. Different statistical methods used to identify hormone secretion profiles revealed a characteristic pulsatile pattern of LH and FSH in plasma. However, LH pulses were more frequent and had greater amplitude than FSH pulses. Less than 32% of the FSH pulses were associated with LH episodes. Conversely, the association between LH and testosterone pulses averaged 83% in birds with testis weight greater than 10 g. Concentrations of corticosterone tended to increase after cannulation and remained elevated for only 3–4 h. Our data indicate that LH, FSH, and testosterone secretion is pulsatile in male broiler breeders. Additionally, LH pulses are associated with testosterone episodes but not with FSH pulses. The pulsatile pattern of FSH secretion, which is unique from those of LH, in adult males suggests that FSH secretion is independently regulated in the adult male fowl.

Testis development and gonadotropin secretion in broiler breeder males

One-day-old chicks were used to evaluate testis development and concentrations of luteinizing hormone, follicle-stimulating hormone (FSH), and testosterone during ontogenesis. Males on a conventional breeder program (control) were reared on a 15L:9D photoperiod and ad libitum food and water intake for 2 wk. On the third week, males were placed on a restricted diet and the photoperiod was reduced to 8L:16D. Males on a pedigree breeder program (broilerized) were reared on a 23L:1D photoperiod and unrestricted food and water intake for 6 wk. At 7 wk, males were placed on a restricted diet and the photoperiod was reduced to 8L:16D. On wk 18, both treatment groups were photostimulated (16L:8D) until the end of the experiment (50 wk). After photostimulation, there was an exponential increase in testis weight (TW), FSH, and testosterone concentrations. At 28 wk, TW from broilerized males were significantly heavier than those from control birds, and concentrations of luteinizing hormone, FSH, and testosterone were maximal at that time. After 28 wk, there was a significant decrease in FSH and testosterone concentrations that were associated with reduced TW. No correlation was observed between BW and TW. However, TW was highly correlated with FSH concentrations and daily sperm production. Our data suggest that management and photoperiod had a profound effect on testicular function that was associated with FSH concentrations in male broiler breeders.

The Immune Response and Performance of Calves Supplemented with Zinc from an Organic and an Inorganic Source1

Abstract Two experiments were conducted to determine the effects of supplemental zinc (Zn) from an organic and an inorganic source on growth performance, serum Zn concentrations, and immune response of beef calves. Treatments consisted of: i) control (no supplemental Zn), ii) Zn sulfate, or iii) Zn-amino acid complex. Zinc sources were supplemented to provide 360 mg of Zn/d. Experiment 1 was a 28-d study using 84 steers (240 ± 1.5 kg) fed bermudagrass hay (21 mg Zn/kg DM) with 1.8 kg/d of the appropriate corn-based supplement. In Exp. 2, 75 heifers (176 ± 2.5 kg) were fed bermudagrass hay (38 mg Zn/kg DM) and the supplements for 140 d. In Exp. 1, ADG was greater (P 0.10) among treatments for the entire 28-d study. In Exp. 2, there was no effect (P>0.10) on ADG as a result of Zn supplementation. In Exp. 2, Zn-supplemented heifers had a greater response (P=0.06) tophytohemagglutinin 24 h after an intradermal injection. In Exp. 2, calves supplemented with Zn-amino acid complex had a greater antibody response to a second vaccination for bovine respiratory syncytial virus than did control or Zn sulfate-supplemented calves (treatment by day interaction, P=0.06). There was not a consistent benefit of supplemental Zn on growth of calves, but there was a positive impact of supplemental Zn on some immune response measurements.

Development of Replacement Heifers Using Programmed Feeding1

This experiment was conducted to determine the effects of diet and pattern of gain on reproductive performance. On November 24, 80 spring-born Angus- and Brangus-sired heifers (BW = 230 ± 23 kg) were allotted by breed and BW to one of four treatments (two replicates per treatment). Heifers were program-fed to gain 0.68 kg/d until April 14 (134 d, MODERATE ), grazed wheat (cv. Hickory, Triticum aestivum L.) and ryegrass (cv. Marshall, Lolium multiflorum Lam.) interseeded into bermudagrass pasture ( GRAZED ), or were program-fed to gain 0.23 kg/d until February 4 (71 d) and then program-fed to gain 0.91 kg/ d (63 d, SLOW-FAST ) or grazed wheat and ryegrass pastures ( SLOW-GRAZED ). On February 4, MODERATE heifers were heavier (P 0.70) among treatments. Pregnancy rate tended to be less (P=0.16), conception date was later (P SUN ) tended to be greater (P=0.14) for GRAZED and SLOW-GRAZED heifers than for MODERATE and SLOW-FAST heifers. Program feeding can be a valuable tool for developing replacement heifers as long as BW goals pre-breeding are reached. Grazing heifers on cool-season annuals during breeding may impair reproduction as a result of the high forage N concentrations, causing reduced fertility.

The Effects of a Modified Glucomannan on the Performance of Stocker Cattle Grazing Endophyte-Infected Tall Fescue1

To evaluate a modified glucomannan to mitigate fescue toxicosis, 45 steer calves (BW = 281 ± 7.0 kg) grazed nine 2-ha pastures of endemic endophyte-infected tall fescue (Festuca arundinacea) for 133 d begininning in March of each year (2 yr; 5 steers/pasture). The 3 treatments were nonsupplemented (control), self-fed liquid supplement (QLF Inc., Dodgeville, WI; SUP), or SUP containing the glucomannan (FEB-200, Alltech Inc., Nicholasville, KY; MGL). Target intake of the supplements was 0.9 to 1.4 kg/d so that MGL would deliver 10 to 20 g of glucomannan daily. Steer BW was measured every 28 d, supplement intake was measured every 7 d, and behavior was monitored every other Thursday. Data were analyzed as a mixed model, with treatment as the fixed effect and year and pasture as random effects. Least squares means were separated using contrasts. Over the 133 d, MGL steers gained BW (0.54 kg/d) more quickly (P = 0.03) than SUP steers (0.41 kg/d), but ADG of SUP steers did not differ (P = 0.94) from that of control steers (0.50 kg/d). On d 133, BW of the supplemented cattle did not differ (P = 0.96) from that of control steers; the BW of MGL steers was 6% greater (P ≤ 0.03) than that of SUP steers. The control steers spent a greater (P < 0.05) percentage of time grazing than the SUP steers. Overall, there were no observed benefits for liquid-feed supplement with steers grazing endemic endophyte-infected tall fescue, but the inclusion of glucomannan to the supplement seemed to enhance BW gain.

Timed Insemination in Beef Heifers After Synchronization of Estrus with Controlled Intravaginal Drug Releasing Device and Melengestrol Acetate1

Two progestin estrous synchronization programs with timed AI (TAI) were used to compare effects on conception to TAI and overall pregnancy rates in beef heifers. Angus-cross heifers in two herds were sorted by age of heifers, body condition score (BCS), and BW then randomly assigned to a treatment. Treatments were 1) MPGG [melengestrol acetate (MGA®; Pfizer Animal Health, New York, NY) at 0.5 mg per head for 14 d followed by prostaglandin F2α (PGF2α) 17d after MGA® withdrawal and a gonadotropin-releasing hormone (GnRH) injection 48 h after PGF2α or 2) CIDR [a new controlled intravaginal drug-releasing (CIDR®) device inserted for 6 d with GnRH at CIDR insertion, PGF2α: at CIDR removal, and a second GnRH injection 48 h later. All heifers in both treatments were bred 18 h after the second GnRH injection.] Bulls were placed with heifers 10 d following TAI for approximately 50 d. Age of heifers, BCS, and BW in Herd 1, Herd 2, or the combined herds were not different (P≥0.25) between treatments. Across treatments, there was a difference between herds in BCS and BW (P<0.0001), but no difference in age of heifers (P=0.51). Conception rates (CR) and overall pregnancy rates (OP) were not different between herds, or between treatments in Herd 1, Herd 2, or in the combined groups (P≥0.40). The results in this study demonstrate similarities between MPGG and CIDR estrous synchronization protocols on conception rates to TAI and overall pregnancy rates in beef heifers.