Response to elemental sulfur by calves and sheep fed purified diets.

Free amino acid profiles in plasma and liver as well as body, organ and gastrointestinal growth were compared in 20 weanling bulls (four per treatment) fed diets deficient (.04%), excessive (.94 and 1.72%) or adequate (.34%) in S. Body, organ and gastrointestinal comparisons also were made with yearling rams fed .04 and .34% S diets. The .34% S diet was fed at two levels, one ad libitum, the other in amounts equal on a body weight.75 basis to that consumed by animals fed the .04% S diet ad libitum. Animals were allowed to consume other diets ad libitum. The calves fed the .04% S diet had negative S, but slightly positive N, balance and were unable to maintain body weight. As dietary S content was increased, plasma and liver methionine increased linearly. An increased histidine in plasma of calves fed the .04% S diet may be due to reduced intake because the calves restricted-fed the .34% S diet also had high plasma histidine. Plasma citrulline, cystine, serine and total nonessential amino acids decreased markedly as dietary S intake became adequate. Intermediate S diets resulted in reduced concentrations of plasma alanine, serine, proline and total nonessential amino acids. Calves restricted-fed the .34% S diet were the most efficient in retaining N with less urinary N. Excesses of S were not detrimental to growth, but plasma valine increased linearly as S intake increased. The S deficiency in calves reduced the ratio of the rumen-reticulum tissue to body weight, and in rams it reduced the ratio of gastrointestinal tissue and preintestinal tissue to body weight. Per kilogram of intestinal-free body weight, there was a linear decrease in liver and testes but an increase in adrenals as S was decreased for calves. The kidney, adrenals and pituitary were increased by S deficiency in rams. Of the amino acids assayed, only methionine from the plasma and liver in calves reflected both an excess and a deficiency of S independent of feed intake effects.

Sulfur influences on rumen microorganisms in vitro and in sheep and calves.

When continuously cultured ruminal microbes were given orchardgrass hay and sufficient sulfuric acid or hydrochloric acid to maintain a pH of 5.5, fermentation and numbers of protozoa were reduced compared with cultures whose pH was controlled with phosphoric acid. Likewise, when sulfur-deficient, purified diets were supplied to cultures, less methane (mmol X liter-1 X d-1), 3.2 vs 32.6, was produced and fewer cellulolytic bacteria (log10/ml), 5.8 vs 7.2 were present than when cultures were given the same diet supplemented with .3% elemental sulfur. The rumen of sheep fed the .04% sulfur diet had reduced digesta weights (1.69 vs 3.2 kg) compared with sheep fed the diet with .34% sulfur at the same intake. There also was reduced methanogenesis 12.3 vs 25.8 mmol X liter-1 X d-1) and reduced numbers of cellulolytic bacteria (7.4 vs 8.4 log10/ml) in sulfur-deficient sheep in comparison to sulfur-supplemented sheep. In growing calves, the same types of bacteria predominated in the rumen, but more facultative anaerobic bacteria were isolated from calves fed .04% sulfur than from calves fed diets with .34 to 1.72% sulfur. None of the dietary levels of sulfur appeared toxic. Regardless of treatment, volatile fatty acids were more predominant than lactic acid as end-products of fermentation of ruminal microbes in fermenters, sheep and calves. The greater methanogenesis and the greater cellulolytic bacterial numbers of sulfur-supplemented sheep compared with sulfur-deficient in vitro cultures, is interpreted to be the result of recycling of sulfur to the rumen in sheep where it is efficiently scavengered by ruminal bacteria.

Effects of feeding level on growth, composition of gain, carcass quality and mature body size in steers at ages up to six years.

Tissue gain and efficiency and carcass characteristics of seventy-eight Angus steers were compared on three feed intake regimens and serially slaughtered at 6 months to 6 years. The regimens were: (A) continuous ad ad libitum feeding, (B) restricted to gain about 0.45 kg daily and (C) restricted as in B until 6 months before slaughter then fed ad libitum. Steers, regardless of feeding regimen, made their greatest gains up to 12 months of age and became less efficient after that time. Steers fed ad libitum had the highest percentage of fat but the lowest percentage of lean and bone when compared with steers fed for restricted gain. Carcasses of the steers fed ad libitum contained more lean and fat at each slaughter age. Average daily gain, feed efficiency and percentage of lean and bone decreased with age; and feed intake, slaughter grade, dressing percent, taste panel desirability and percent of fat tended to increase with age. All steers reached their maximum growth in height at withers, depth of chest and length of body at about 3 years. Steers that were restricted up to 6 months before slaughter showed compensatory growth during their ad libitum feeding period and during the first 12 months of the study; protein and fat were produced most efficiently by this growth. It would appear that it is possible to modify fat deposition by changing feed intake level.

Who should regulate the care of farm animals used in research? an opinion of USDA scientists and administrators.

The humane treatment and care of farm animals used for research purposes is the responsibility of every person associated with their use. Farm animal research is vastly different from laboratory animal research and, therefore, rigid standards and regulations for treatment and care will be difficult to define and administer. The present system of "self regulation" used at USDA farm animal research centers if providing an acceptable method of ensuring adequate animal treatment and care.