Molds are parasitic plants that are ubiquitous in livestock feedstuffs. Even though molds themselves reduce the quality of grains, their synthesis of chemical substances termed mycotoxins causes the greatest monetary loss to the animal industry. Five major mycotoxins that impair growth and reproductive efficiency in North America are aflatoxins, zearalenone, deoxynivalenol, ochratoxin, and ergot. Aflatoxins are produced by Aspergillus flavus and Aspergillus parasiticus. Consumption of grains containing aflatoxins by swine affects reproduction indirectly by reducing feed intake and growth. In swine, aflatoxins impair liver and kidney function, delay blood clotting, increase susceptibility to bruising, and interfere with cellular humoral immune systems. Ruminants are comparatively resistant to aflatoxicosis, but presence of aflatoxins in milk of dairy cows is closely monitored for human safety. Depending on environmental conditions, Fusarium roseum can produce either zearalenone or deoxynivalenol. Days 7 to 10 postmating seem to be a critical period of gestation for zearalenone to exert its detrimental actions on early embryonic development. Presence of deoxynivalenol in swine feedstuffs decreases feed intake, causes feed refusal, and induces occasional vomiting. Several species of Penicillium and Aspergillus produce ochratoxin, a mycotoxin that causes necrosis of kidney tissue. Ergot alkaloids produced by Claviceps purpurea on wheat can cause reproductive problems and are associated with lactational failure in swine. Various methods have been developed to remove mycotoxins from infected feedstuffs. Chemical analyses in laboratories as well as diagnostic kits suitable for use at the elevator or farm can be used successfully to identify which mycotoxins are present in suspect feedstuffs.

Interrelationships among concentrations and maturation of intramuscular collagen, serum concentration of hydroxyproline and testosterone and meat tenderness were determined in growing bulls and steers. Sixty-four Charolais X Angus bulls were assigned to sex treatment groups (intact or castrate) and slaughter groups (9, 12, 15 or 18 mo of age). Animals were bled at 30-min intervals via intrajugular catheters between 0600 and 1400 beginning 48 h before slaughter. Serum concentrations of testosterone were determined in each sample from bulls and from four samples from steers; serum hydroxyproline was determined in the last sample from both sexes. Testosterone mean values for the collection period were calculated. Samples of the longissimus, semitendinosus and infraspinatus muscles secured within 45 min postmortem were analyzed for intramuscular collagen concentration, percent soluble collagen and collagen thermal shrinkage temperature. Tenderness of loin steaks was determined by Warner-Bratzler shear test. Serum concentrations of hydroxyproline and testosterone were higher (P less than .01) in bulls than steers. Age effects were noted for both hydroxyproline (P less than .01) and testosterone (P less than .06). Total intramuscular collagen was greater (P less than .01) in bulls than steers and was different (P less than .01) among muscles, but the muscle differences were not uniform over all ages (P less than .05). Percent soluble collagen declined (P less than .01) with age and was different (P less than .01) among muscles. Interaction of age and muscle (P less than .01) and age and sex (P less than .05) also were noted for percent soluble collagen.(ABSTRACT TRUNCATED AT 250 WORDS)

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Mature beef cows were slaughtered at 5 (n = 6), 10 (n = 6), 20 (n = 6) or 30 (n = 5) d after calving to identify endocrine events that may affect the duration of postpartum anestrus. Additional cows (n = 6) were slaughtered 12 to 14 d after their first postpartum estrus (luteal phase cows). Anterior pituitary concentrations of luteinizing hormone (LH) were low at d 5 (383-+ 69/2g/g), averaged 445-+ 103 and 682 + 207 gtg/g at d 10 and 20, respectively, and were elevated (P<.05) by d 30 (1,097 +-174 gig) to a concentration similar to luteal phase cows (1,208 + 148 gtg/g). Concentrations of folliclestimulating hormone (FSH) averaged 12.4 +

Sixty-four crossbred gilts were assigned randomly to one of four treatments at 9 to 11 wk of age: supplemental lighting and boar exposure, supplemental lighting without boar exposure, no supplemental lighting with boar exposure and no supplemental lighting and no boar exposure. Gilts in all treatment groups received natural daylight through windows of a growing and finishing house from February to July (Exp. 1) or from August to January (Exp. 2). Gilts in treatment groups 1 and 2 received supplemental lighting from a 250 w incandescent bulb (300 lx) from 0520 and 0830 h and from 1630 to 2020 h, for a total daily photoperiod of 15 h. No differences in weight gain or feed efficiency were found among any of the treatments. In Exp. 1, the proportion of gilts displaying estrus by 8 mo of age were 77, 13, 79 and 31% for treatments 1, 2, 3 and 4, respectively. As expected, the proportion of gilts that reached puberty was greater (P less than .01) in gilts that had received boar exposure than gilts that did not receive boar exposure. However, supplemental lighting given during periods of increasing natural daylength did not increase (P less than .05) the proportion of pubertal gilts or reduce the age of puberty. In Exp. 2, the proportion of gilts displaying estrus by 8 mo of age were 75, 7, 80 and 12% for treatments 1, 2, 3 and 4, respectively. Boar exposure increased the proportion of gilts reaching puberty by 8 mo of age.(ABSTRACT TRUNCATED AT 250 WORDS)