The influence of added niacin (0, 0.5 or 1 g per animal per day) and different crude protein contents (9.2 to 12.0% of DM) or the supply of various N-sources (urea, rape seed meal, soya bean meal, fish meal) were investigated on rumen fermentation, blood parameters, feed intake, weight gain and dry matter (DM) intake per weight gain in three individual feeding experiments with 156 growing bulls weighing between 175 and 300 kg per animal. Niacin supplementation did not significantly influence (P > 0.05) investigated parameters of rumen fermentation and blood. Ruminal propionate concentration increased insignificantly (from 18.9 to 19.5 moles per 100 moles on the average), inorganic P of blood serum somewhat decreased (from 2.98 to 2.82 mmol per 1) when niacin was added (P > 0.05). Protein level did not significantly influence rumen fermentation and blood parameters except an increased urea concentration in the blood of cattle fed with diets richer in protein. The DM intake of control bulls and niacin supplemented animals amounted to 6.35 and 6.46 kg per animal per day on average. Influence of niacin on DM intake varied in dependence on protein source. The daily weight gain increased from 1003 (control) to 1040 g per animal per day (+ niacin, P > 0.05). Niacin increased weight gain of bulls of urea (+ 43 g) and rape seed or soya bean meal added rations (+ 60 g per animal per day), but did not influence the weight gain in fish meal added rations. Increased weight gain resulted from ruminal and metabolic effects (about 2/3) as well as enhanced feed intake of bulls (about 1/3). Feed efficiency mostly improved.
Five experiments with 18 to 36 male calves each of the black and white dairy cattle breed (age: 14-21 days, initial live weight: approximately 45 kg per animal) were carried out in order to investigate the influence of various vitamin A supply (0-80,000 IU per 100 kg LW and day) on dry matter intake and weight gain as well as the vitamin A status of liver and blood plasma over 84 days. The calves consumed a diet free of carotene and vitamin A consisting of milk replacer, concentrate and chopped wheat straw. The calves were fed in three experiments for a longer time in order to observe the further vitamin A depletion. Nine animals consumed an unsupplemented ration, nine other one got 10,000 IU vitamin A per 100 kg LW and day. Biopsies of liver and plasma samples were taken from 4 animals per group every four weeks. The various vitamin A supplementation did not significantly influence the dry matter intake (Mean: 1.67; 1.48 to 1.80 kg DM per animal and day) and the weight gain of calves (Mean: 702, 599 to 770 g per animal and day). First vitamin A deficiency symptoms (reduced feed intake, decreased weight gain, diarrhoea etc.) were observed in animals of unsupplemented group after 100 days of experiments. After 84 days the vitamin A concentration of liver of animals of unsupplemented groups decreased to 1.3-32.2% compared with the begin of experiments (60.6-155.7 mumol/kg fresh matter). Up to 51% of initial concentration were found when 10,000 IU vitamin A per 100 kg LW and day were fed. About 25,000 IU vitamin A per 100 kg LW and day were required in order to keep the initial level of vitamin A concentration of liver. The plasma vitamin A concentration is unsuitable for estimation of vitamin A status of calves. The concentration of vitamin A of liver and plasma amounted to 114 mumol per kg and 0.25 mumol per litre at the begin of experiments. The vitamin A concentration of liver of unsupplemented group decreased to 20 mumol per kg, that of plasma increased to 0.28 mumol per 1 at the end. A strong vitamin A deficiency (liver concentration: less than 10 mumol/kg) may cause a decrease of vitamin A concentration of blood.
Five individual feeding experiments with male calves were conducted to investigate variou influencing factors on t h retirzol plasma level and the vitamin-A-depot of liver Liver vitamin-A-depot of calves depends on carotene or vitamin-A-intake of cows an,d vitamin,-A-concentration of milk, respectively. ?Eoo to three weeks old calves born during the summer contained more liver-vitamin-A (>lo0 IU g-') than animals born during the winter season. Feeding of first colostrurn improves vitamin A supply of calves because of the decrease of vitamin A in milk with following milkings (1st milking: loo%, 2nd : 74%, 3rd : 41%). Besides the vitamin-A-depot of liver of calves carotene content of feeds and vitamin-A-supply influ.enced the vitamin-A-status of growing cattle. About 25000 IU vitamin A per 100 kg body weight per day wefe necessary to keep the liver vitamin A depot on a constant level (= 100 IU g-). The results show a homeostasis of retinol in plasma of calves. The concentration of retinol in plasma was regulated very exactly, i f the liver stores of calves were higher than 25 IU g-'. Therefore, the plasma level in,dicates the status of vitamin A storage only i f there is an extreme depletion of vitamin A. At marginal depletion, howevel; there is damage to peripheral tissu.e before changes in the vitamin-A-level in serum occur The determination of vitamin A in serum or plasma gives no information on the adequacy of liver reserves for ju&ng the necessity of a vitamin A su,bstitution.
Three long time individual feeding experiments (greater than 258 days) with 48 beef cattle each (dairy breed and beef breed, 50% each) were carried out in order to measure the influence of various vitamin A supply (0, 2,500, 5,000 and 10,000 IU vitamin A per 100 kg body weight and day) on fattening and slaughtering performance, vitamin A concentration of liver and serum as well as carotene concentration of serum. The bulls consumed corn silage (experiments 1 and 2; 9.4 and 18.3 mg carotene per kg dry matter) or NaOH-treated and pelleted straw (experiment 3; no carotene). The roughages were supplemented with 2 (exp. 1 and 2) and 3 kg (exp. 3) concentrate per day. The vitamin A supply of corn silage diet did not significantly influence the dry matter intake (exp. 1: means: 6.95; 6.91 to 7.05; exp. 2: means: 6.54; 6.53 to 6.54 kg dry matter per animal and day) and the daily weight gain of bulls (exp. 1: means: 1076; 1028 to 1157; exp. 2: means: 1058; 1041 to 1057 g per animal). The bulls consumed 8.87 kg dry matter per day, the daily weight gain amounted to 1030 g per animal and day in experiment 3. The bulls of unsupplemented group reduced feed intake and weight gain after 150 days, an additional vitamin A supply was necessary. At the end of experiments 1 and 2 the liver vitamin A concentration of unsupplemented groups amounted to 38.8 and 65.9 mumol/kg, it increased after vitamin A supply (up to 153.4 mumol/kg). Feeding of pelleted straw effected a liver vitamin A concentration lower than 10 mumol/kg except the group supplemented with 10,000 IU vitamin A per 100 kg body weight and day (35.7 mumol per kg fresh matter of liver). The vitamin A concentration of blood is unsuitable for evaluation of vitamin A status of cattle. The carotene content of feeds and level of vitamin A supply determined the carotene concentration of blood. Recommendations for a suitable vitamin A supply of ration of growing cattle were given depending on body weight and type of diet.
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