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Five experiments (five different locations) with a total of 1,230 pigs (135 pens) were conducted in Minnesota, Missouri and Indiana to study the effects of supplementary bambermycins (2.2 ppm) and tylosin (44 or 22 ppm) in swine diets. The antibiotics were fed during the growing and finishing periods, and effects on rate of gain and efficiency of feed conversion were measured. A significant improvement in ADG and F:G over the control pigs was observed with the bambermycins treatment. A numerical but nonsignificant improvement in ADG and a significant improvement in F:G over control were observed with the tylosin treatment. The performance was divided into growing and finishing periods. In the growing period, bambermycins and tylosin numerically but nonsignificantly improved ADG and F:G over control pigs. The finishing period response to bambermycins was significantly improved for ADG and F:G. The tylosin finisher response was numerically but nonsignificantly improved for ADG and F:Gover negative control. Significant location effects were observed. This result would be expected due to variation in genetic background of the experimental animals and differences in housing, environment and management.

Six experiments were conducted at three geographic locations to determine the effect of 0 and 2 g of bambermycins5per ton of complete feed upon ADG and F/G in growing-finishing swine from 35 kg body weight to market. A 6.6% significant improvement in ADG and a 6.1% significant improvement in F/G over the control pigs was observed with the 2 g bambermycins treatment. The performance was divided into growing and finishing periods. In the growing period, bambermycins significantly improved ADG and F/G by 4.3 and 5.1%, respectively. The finishing period response was significant at 8.1 and 7.4% for ADG and F/G, respectively. The percentage improvement in ADG and F/G was greater in the finishing period than during the growing period in these studies.

Three experiments were conducted with eight lactating Angus cows to study the effects of dietary magnesium levels at early, mid- and late lactation. The individual experiments consisted of two consecutive 15-day trials. Each trial consisted of a 5-day adjustment period and a 10-day experimental period. During the experimental periods the total magnesium content of the four rations averaged 9.7, 20.6, 31.0 and 42.4 gm. per day. Blood and urine samples were taken at the end of the adjustment periods and on alternate days during the experimental periods. Generally, increasing the level of dietary magnesium significantly increased blood serum magnesium during the three stages of lactation but did not influence serum calcium or inorganic phosphorus values. In general, urinary magnesium per unit of creatinine was significantly increased as the level of dietary magnesium increased. As calculated from the regression equations obtained at each stage of lactation for the effect of dietary magnesium on serum magnesium, 20.9, 22.1 and 18.0 gm. per day of dietary magnesium would be required to maintain serum magnesium levels of 2.0 mg. per 100 ml. during early, mid- and late lactation, respectively.

Three experiments were conducted with eight gestating Angus cows to study the effects of feeding different magnesium levels at 145, 200 and 255 days gestation. Each trial consisted of a 5-day adjustment period and a 10-day experimental period. The average daily magnesium intake for the cows fed the basal ration was 3.4 grams. Supplemental magnesium was added at levels of 0, 4.1, 8.2 and 16.4 g per day. Blood and urine samples were taken at the end of the adjustment periods and on alternate days during the experimental periods.At the three stages of gestation, increases in dietary magnesium significantly increased serum magnesium levels. Serum calcium and inorganic phosphorus levels were not consistently altered by the dietary magnesium level. Increases in dietary magnesium significantly increased urinary magnesium values per unit of creatinine. As calculated from regression equations obtained at each stage of gestation for the effect of dietary magnesium on serum magnesium, 8.5, 7.0, and 9.0 g of dietary magnesium would be required per day to maintain serum magnesium levels of 2.0 mg per 100 ml at 155, 200, and 255 days gestation, respectively.