A polymorphism in XKR4 is significantly associated with serum prolactin concentrations in beef cows grazing tall fescue.

Fescue toxicosis is a common syndrome of poor growth and reproductive performance of beef cattle grazing endophyte-infected tall fescue infected with Lolium arundinaceum Schreb. Together with decreased feed intake, decreased growth rates and tissue necrosis due to vasoconstriction, depressed circulating serum prolactin concentrations are typically observed in cattle afflicted with fescue toxicosis. Polymorphisms within the XK, Kell blood group complex subunit-related family, member 4 (XKR4) gene located on BTA14 have been previously reported to be associated with rump fat thickness, residual feed intake, average daily feed intake and average daily gain in cattle. Associations also have been reported between XKR4 genotype and effectiveness of the dopamine antagonist iloperidone as a treatment of schizophrenia in humans. Domperidone, a related dopamine antagonist, mediates effects of fescue toxicosis on livestock, including restoring depressed concentrations of prolactin. A mixed-breed population of 592 beef cattle grazing endophyte-infected tall fescue was used to examine the association between XKR4 genotype and circulating prolactin concentrations. The SNP rs42646708 was significantly (P = 0.0002) associated with serum prolactin concentrations and explained 2.45% of the phenotypic variation. Effect of genotype at the SNP was tested across five breeds, with significant associations within both Angus (P = 0.0275) and Simmental (P = 0.0224) breeds. These results suggest XKR4 may play a role in mediating the negative effects of fescue toxicosis, and polymorphisms within this gene may be useful markers for selection for genetic resistance to the debilitating effects of endophyte-infected tall fescue.

Tasco-Forage: I. Influence of a seaweed extract on antioxidant activity in tall fescue and in ruminants.

Seaweed (Ascophyllum nodosum) is a known source of plant growth regulators, and application to turfgrasses has increased activity of the antioxidant superoxide dismutase (SOD) and specific vitamin precursors. Increased antioxidant activity in both plants and animals diminishes oxidative stress. Two pasture experiments investigated effects of Tasco-Forage (a proprietary seaweed-based product) applied to tall fescue (Festuca arundinacea) on antioxidant activity in plants and in ruminants that grazed the forage. In Exp. 1, fescue was 70 to 100% infected with the endophyte fungus Neotyphodium coenophialum ([Morgan-Jones and Gams] Glenn, Bacon, and Hanlin). Twenty-four wether lambs (initial BW 41 kg; SD = 5) grazed fescue treated with 0, 1.7, or 3.4 kg Tasco/ha applied in April and July, 1994, with four replications per treatment. Grazing occurred for 26 d beginning April 21 and for 22 d beginning July 19. In July, there was a linear increase in daily gains (P < 0.05), and serum vitamin A (P < 0.13) and whole-blood Se (P < 0.10) tended to increase in lambs grazing Tasco-treated fescue. In Exp. 2,48 Angus and Angus x Hereford steers (initial BW 245 kg; SD = 20) grazed infected or uninfected tall fescue in Virginia that was treated (3.4 kg/ ha) or untreated with Tasco in April and July, 1995. Steers that grazed infected tall fescue had lower (P < 0.02) serum vitamin A and E and tended (P < 0.07) to have lower whole-blood Se in September compared with steers that grazed uninfected tall fescue. Tasco decreased (P < 0.06) serum vitamin E but tended to increase whole-blood Se (P < 0.10) in September and serum vitamin A in July (P < 0.12). During 1996 and 1997, the experiment was repeated in Virginia with Angus steers and was replicated at Prairie, MS, where 1/4 Brahman x 3/4 Angus steers were used. Forty-eight steers were included at each location in each year (n = 192 total steers for 1996 and 1997). Steers that grazed infected tall fescue in Mississippi had lower (P < 0.05) serum vitamin E by the end of the grazing season. At both locations Tasco increased (P < 0.05) activity of superoxide dismutase in both infected and uninfected fescue. The endophyte in tall fescue seemed to decrease antioxidant activity in grazing steers, whereas Tasco seemed to increase antioxidant activity in both the forage and the grazing ruminant. Tasco may provide opportunities to reduce oxidative stress in plants and animals.

Tasco-Forage: II. Monocyte immune cell response and performance of beef steers grazing tall fescue treated with a seaweed extract.

Effects of applying Tasco-Forage, an Ascophyllum nodosum seaweed-based product prepared by a proprietary process, to endophyte (Neotyphodium coenophialum [Morgan-Jones and Gams] Glenn, Bacon, and Hanlin)-infected and endophyte-free tall fescue (Festuca arundinacea Schreb.) were studied in each of 3 yr (1995, 1996, and 1997) in Virginia and in 1996 and 1997 in Mississippi. There were 48 steers at each location in each year (n = 240) in a 2 x 2 x 2 factorial arrangement with two replications at each location. Steers in Virginia were Angus and Angus x Hereford with initial weights of 245 kg (SD = 20), 234 kg (SD = 9), and 265 kg (SD = 5) in yr 1, 2, and 3, respectively. Steers in Mississippi were 3/4 Angus and 1/4 Brahman and weighed 230 kg (SD = 8) and 250 kg (SD = 2) in yr 2 and 3, respectively. Tasco (3.4 kg/ha) was dissolved in water and applied to pastures in April before grazing was begun and again in July at the same rate. The grazing period was from mid-April to late September or mid-October. Total gains were higher (P < 0.05) for steers grazing uninfected than for those grazing endophyte-infected tall fescue. Rectal temperatures were increased (P < 0.05) due to endophyte infection at both locations; Tasco application decreased temperature of steers grazing infected fescue in Virginia (interaction, P < 0.07) but increased temperatures of steers grazing infected fescue in Mississippi (interaction, P < 0.05). Presence of the endophyte resulted in rough hair coats and loss of hair color, but the effect was partially offset (P < 0.05) by Tasco application in Virginia in 1995. Both monocyte phagocytic activity (all years and locations) and major histocompatibility complex class II expression (1995 only) were decreased (P < 0.05) in steers due to endophyte infection, but this effect was reversed (P < 0.05) by application of Tasco to pastures. Application of the extract from A. nodosum seems to have use in alleviating adverse effects of endophyte on immune function and may improve hair coat condition in cattle grazing infected fescue, but effects on rectal temperature varied due to location.

Tasco-Forage: III. Influence of a seaweed extract on performance, monocyte immune cell response, and carcass characteristics in feedlot-finished steers.

Tall fescue (Festuca arundinacea Schreb.) infected with the endophyte Neotyphodium coenophialum ([Morgan-Jones and Gams] Glenn, Bacon, and Hanlin) causes fescue toxicosis in cattle grazing the forage, but effects of the endophyte were considered to be abated soon after removal of the animals from pastures. Tasco-Forage, a proprietary extract from the brown seaweed Ascophyllum nodosum, is a known source of cytokinins and has increased antioxidant activity in both plants and the animals that graze the forage. Tasco was applied at 0 and 3.4 kg/ha to infected and uninfected tall fescue pastures in Virginia and Mississippi. Forty-eight steers grazed the pastures at each location during each of 2 yr (n = 192) before being transported to Texas for feedlot finishing. On arrival at the feedlot, steers from Tasco-treated pastures had higher (P < 0.01) monocyte phagocytic activity and tended (P < 0.07) to have higher major histocompatibility complex class II expression than steers that grazed the untreated pastures. A depression (P < 0.05) in monocyte immune cell function due to grazing infected fescue was detected throughout the feedlot finishing period but was reversed by Tasco. Rectal temperatures were elevated (P < 0.07) in steers that had grazed the infected tall fescue when they arrived in Texas, but by d 14 no difference was detected. However, by d 28 the temperature effects of infected tall fescue were reversed. Steers that had grazed infected fescue had lower (P < 0.01) rectal temperatures on d 112 of the feedlot period, demonstrating a much longer-lasting effect of the endophyte on thermoregulatory mechanisms than previously thought. Steers that had grazed Tasco-treated pastures had higher (P < 0.01) rectal temperatures on d 56 than steers that had grazed untreated fescue. Steers that had grazed the Tasco-treated pastures had higher marbling scores (P < 0.05) regardless of the endophyte, but no effect of Tasco or endophyte on gain was measured. Our data suggest that Tasco application to tall fescue pastures alleviated some of the negative effects of tall fescue toxicity.

Tasco-Forage: IV. Influence of a seaweed extract applied to tall fescue pastures on sensory characteristics, shelf-life, and vitamin E status in feedlot-finished steers.

Tasco-Forage is an Ascophyllum nodosum seaweed-based product that has increased antioxidant activity in both plants and animals. Endophyte (Neotyphodium coenophialum ([Morgan-Jones and Gams] Glenn, Bacon, and Hanlin)-infected and uninfected tall fescue (Festuca arundinacea Schreb.) pastures in Virginia and Mississippi during 1997 were treated or not with 3.4 kg Tasco/ha in April and July. There were two replications of each treatment at each location. Forty-eight steers (6/replication) grazed pastures at each location (n = 96) from April to October prior to transportation to Texas Tech, Lubbock, for finishing during a 160-d period in the feedlot. Blood (antemortem) and liver (postmortem) samples were collected. After slaughter and chilling, the left strip loins (IMPS #180) were collected from three randomly selected steers from within each pasture replication (n = 48). Strip loins were vacuum-packaged and stored at 2 degrees C. At postmortem d 7, 14, 21, and 28, strip loins were removed from packaging and fabricated into 2.54-cm steaks. Following each fabrication day postmortem, the strip loins were repackaged and stored at 2 degrees C until the following postmortem time. After the prescribed fabrication, steaks were overwrapped with polyvinyl chloride film, subjected to simulated retail display at 2 degrees C for up to 3 d, and subjective and objective color were evaluated daily by a trained panel. Steaks from Mississippi steers that had grazed Tasco-treated fescue retained higher (P < 0.05) CIE a* color scores throughout retail display. Steaks were more uniform and had less discoloration and less browning (P < 0.05) if they were from steers that had grazed Tasco-treated fescue, and the effect was greatest for steers from Mississippi (location x Tasco interaction; P < 0.05). The endophyte in tall fescue may decrease uniformity and increase lean discoloration and two-toning of beef steaks when removed from vacuum packaging on or beyond d 21 postmortem (endophyte x Tasco x postmortem day interaction: P < 0.05). Vitamin E in liver was increased (P < 0.06) and serum vitamin E was decreased (P < 0.09) in steers that had grazed the treated pastures. These experiments indicated that Tasco applied to tall fescue during the grazing season can improve color stability and extend beef shelf-life, particularly in cattle grazing infected tall fescue. The mode of action of Tasco is not clear, but antioxidants and specific vitamins may be involved.

Nutritional management of replacement beef heifers: a review.

Systems to produce replacement heifers to calve initially at 2 yr of age and at 12-mo intervals thereafter require integrated forage-animal management plans. The process of developing heifers as replacements must begin during the cow-calf production phase. Age and weight at puberty are affected by several factors, including breed of livestock. Generally, breeds of a larger size at maturity are older and heavier when reaching puberty. Heifers that are kept as replacements must be weaned at relatively heavy weights in comparison to their expected mature body size without becoming obese. Excessive adipose tissue in heifers during the preweaning phase may result in reduced subsequent performance of these animals. Several management techniques were reviewed that can be used both pre- and postweaning, including using anthelmintics, anabolic growth implants, and ionophores. Anabolic growth implants can increase heifer rates of gain and increase pelvic size. In addition, there are indications that these implants may alter mammary gland development, which may subsequently increase milk production. Ionophores were shown to increase growth rates, particularly in grazing heifers but more importantly to decrease age at puberty. Age and weight at puberty have been shown to be affected by level of nutrition. It is preferable for heifers to reach puberty one or two estrous cycles before the breeding season, and the breeding season for heifers should begin > or = 21 d before the breeding season of the mature cow herd. This time difference allows for the generally longer postpartum interval for primiparous cows than for multiparous cows. Because of the limited opportunities (every 12 mo) for cows to calve, optimum efficiency must be pursued.

Postweaning growth and reproduction of beef heifers exposed to calve at 24 or 30 months of age in spring and fall seasons.

Angus and Angus x Hereford heifer calves born in spring or fall seasons were allotted by weight at weaning to be exposed to bulls for calving at either 24 or 30 mo of age. Comparisons were made 1) within birth season--heifers born in the same season were first exposed to bulls at either 14 to 16 or 19 to 22 mo of age and 2) within breeding season--heifers born in different but consecutive seasons (spring-fall or fall-spring) were exposed to bulls during the same season but at different ages. Spring-born heifers exposed for 30-mo calving were heavier (336 vs 302 kg) and taller (P less than .01) at breeding than those exposed for 24-mo calving. Also, more were observed in estrus and became pregnant (P less than .01) during a 21-d AI breeding period, but season-long (63 d) pregnancy rates were not different (86%). Fall-born heifers exposed for 24- or 30-mo calving were similar for weight, hip height, and body condition score (BCS) at breeding, but season-long pregnancy rates were 71 and 94%, respectively (P less than .01). Although fall-born heifers were heavier at weaning (P less than .01), spring-born heifers were heavier, taller, and had higher BCS at breeding (P less than .01), regardless of age. Within spring breeding seasons, breeding weight and initial reproduction were not affected by heifer age. Within fall breeding seasons, older heifers were larger (P less than .01) and had greater reproductive performance (P less than .05) than younger heifers. Age at breeding, irrespective of season, consistently affected (P less than .01) both hip height (116 vs 113 cm) and pelvic area (209 vs 178 cm2) for older vs younger heifers, respectively. These data indicate that heifers exposed for 30-mo first calving are heavier, taller, have larger pelvic area, and have greater reproductive performance than those exposed for 24-mo first calving.

Growth and sexual characteristics of suckling beef calves as influenced by age at castration and growth implants.

A 2-yr study using crossbred male calves (n = 228) evaluated castrating at birth or at 4 mo of age and use of anabolic growth implants (none, zeranol or estradiol-17 beta). Angus, Hereford and Brahman crossbred calves produced in seven cow-calf units that varied by breed component, stocking rate and calving season were allotted to treatment at birth in a 2 x 3 factorial arrangement. Growth implants decreased (P less than .01) testicular weight and expression (P less than .05) of male secondary sex characteristics in suckling bull calves at 4 mo. Implanted calves were shorter (P less than .05) at the hips and had shorter front legs (P less than .01) at both 4 mo and at weaning. Cannon bone circumference at weaning was increased (P less than .05) by growth implants. Age at castration did not affect (P greater than .05) calf performance or body characteristics. Calves given growth implants had higher (P less than .05) rates of gain from birth to 4 mo than did nonimplanted calves (.75 vs .71 kg/d). Implanted calves were heavier (P less than .01) at weaning and had higher (P less than .01) ADG from 4 mo to weaning than did nonimplanted calves. These data indicate no benefit from delaying age at castration, but implanting increased weaning weight an average of 8.2 kg.

Effects of salinomycin on ruminal characteristics and performance of grazing beef steers.

Grazing trials were conducted for 2 yr using weanling Brahman crossbred beef steers to evaluate graded levels of salinomycin (0, 50, 100 or 150 mg. head-1.d-1) for 161 d and to evaluate salinomycin in a free-choice mineral supplement (99 d). The 40 and 48 steers in trials 1 and 2 had average initial weights of 198 and 285 kg, respectively. In trial 1, steers were group-fed to consume either 0, 50, 100 or 150 mg of salinomycin.head-1.d-1 in .9 kg ground corn while grazing bermudagrass pastures. Both linear (P less than .01) and quadratic (P less than .05) effects were observed for steer performance as salinomycin level increased from 0 to 150 mg.head-1.d-1. Linear increases (P less than .01) in ruminal NH3-N (mg/100 ml) and in the molar proportion of propionate and decreases (P less than .01) in butyrate and acetate/propionate were detected. In trial 2, mineral supplements with and without salinomycin were fed free-choice to steers on bermudagrass pasture. The mean salinomycin intake of 38 mg.head-1.d-1 was lower than anticipated as a result of the instability of salinomycin in the mineral supplement and the slightly lower intake (65 g/d) than anticipated (75 g/d). Performance of steers was not influenced by salinomycin supplementation in trial 2. The ionophore salinomycin at intakes over 50 mg.head-1.d-1 appears to increase the performance of steers grazing bermudagrass pasture.