Showing papers in "Journal of Animal Science in 1978"

Puberty in beef bulls: hormone concentrations, growth, testicular development, sperm production and sexual aggressiveness in bulls of different breeds.

Abstract: SUMMARY Postweaning growth and pubertal traits were studied in Hereford, Angus, Red Poll, Brown Swiss, Hereford-Angus crossbred (HXA) and Angus-Hereford crossbred (AX H) bulls from 7 through 13 months of age. Pubertal factors characterized included body weight, testicular size, hormone concentrations, sexual aggressiveness and sperm production. Puberty was defined as the age at which a bull first produced an ejaculate containing at least 50 x 106 spermatozoa with a minimum of 10% motility. Average pubertal age in days was 264 -+ 9 for Brown Swiss, 283 -+ 9 for Red Poll, 295 -+ 9 for Angus, 296 + 9 for AX H, 300 + 8 for HX A and 326 + 9 for Hereford bulls. Brown Swiss bulls were heaviest (295 kg), while Red Poll and Hereford bulls were lightest (258 and 261 kg) in body weight at puberty. Concentrations of serum luteinizing hormone (LH) and testosterone (T), averaged across all bulls, increased linearly (P<.01)from 7 through 13 months of age. Breed differences in LH concentration were not observed from 7 months of age through puberty. Breed groups with high average T concentrations between 7 and 13 months of age reached puberty earlier than breed groups with low T concentrations. Bulls exhibited first sexual interest approximately 3 weeks before reaching puberty, and attained mating ability approximately 6 weeks after reaching puberty. Brown Swiss bulls were

Molybdenum toxicity and hypocuprosis in ruminants: a review.

Abstract: Elevated Mo intakes depress Cu availability and may produce a physiological Cu deficiency in ruminants. Total sulfur or sulfate in the ration generally potentiates the effect of Mo. The ratio of Cu to Mo in feed is important regardless of the absolute amount of each. For this reason, and because of the importance of the S content of the diet, it is impossible to define safe dietary limits for Cu and Mo. Physiological Cu deficiencies are produced by four classes of feeds: (1) high Mo, generally above 100 ppM, (2) low Cu:Mo ratio, 2:1 or less, (3) Cu deficiency, below 5 ppM, and (4) high protein, 20 to 30% protein in fresh forage. The latter situation probably results from higher levels of sulfide produced from sulfur amino acids during rumen fermentation. Copper sulfide is largely unabsorbed. Future instances of hypocuprosis in the US are most likely to occur from marginal copper deficiencies in forages.

Relationship of rumen gram-negative bacteria and free endotoxin to lactic acidosis in cattle.

Abstract: Feeding grain to animals not adapted to grain resulted in a marked increase in the . / . concentration of free endotoxln m the rumen. Endotoxin concentration increased 15 to 18 times within 12 hr after lactic acidosis was induced through grain engorgement. The increase was accompanied by a shift from predominantly gram-negative to gram-positive bacteria. Data from in vitro fermentations showed that the increase in free endotoxin concentration was not accompanied by a decrease in the number of gram-negative bacteria. The absorption of endotoxin from the rumen was not apparent by the actinomycin D assay procedure because no difference was observed in mice lethality of plasma from control and post-engorgement samples. However, the significant granulocytosis that accompanied acidosis was suggestive of systemic action of rumen bacterial endotoxin. (

Influence of dietary energy intake on bovine pituitary and luteal function.

Abstract: Three experiments were conducted to measure the effect of dietary energy intake on pituitary and luteal function. Intact cows and heifers and spayed cows were administered injections of gonadotropin releasing hormone (GnRIt) following a prolonged period of either dietary energy restriction (low energy) or adequate energy (high energy) intake to determine if energy intake influenced the pituitary responsiveness to GnRH. In addition to measuring luteinizing hormone (LH) release following GnRtt, peripheral serum concentrations of progesterone, luteal progesterone content and the pituitary Llq content of cows fed low and high energy levels were compared. Low energy increased the LH release after a GnRH injection in intact heifers but not in intact cows. Peripheral serum progesterone concentrations tended to be reduced in low energy heifers and cows. Low energy spayed cows released more LH in response to GnRH than adequate energy spayed