A study was carried out to determine whether the addition of rumen-protected Lys and Met to ration formulations allowed a reduction in dietary crude protein (CP) without jeopardizing total milk or milk protein yields. Eighteen multiparous Holstein cows were randomly assigned to treatment sequences in a replicated 3 x 3 Latin square design. Total mixed rations were balanced according to degradation and rates of passage of protein and carbohydrates using the Cornell Net Carbohydrate and Protein System. Rations differed in percentages of CP (18.3, 16.7, and 15.3% for rations 1, 2, and 3, respectively), but energy was held constant. Rations 2 and 3 were supplemented with rumen-protected Lys and Met. Milk, blood, and rumen fluid samples were taken during the 2nd and 3rd wk of each 28-d experimental period. Total collection of urine and feces occurred during the last 5 d of each experimental period. Cows fed ration 1 had a higher milk yield (34.2 vs. 32.8 kg/d) and DMI than did cows fed rations 2 or 3, but milk protein output was not different among groups. Nitrogen efficiency, milk N as a percentage of intake N, improved as percentages of CP in the rations were reduced. Blood urea N values were 15.9, 12.9, and 10.0 mg/dl for cows fed rations 1, 2, and 3, respectively. Apparent digestibilities of CP and urinary N excretion decreased as the percentages of CP in the rations decreased. Results indicated that it is possible to make more efficient use of CP by using rumen-protected amino acids. This procedure may result in less than maximum milk yield, but milk protein output can be maintained.

Altering feeding strategies for dairy cattle (Bos taurus) may reduce manure N excretion and NH3 emission from the manure. We determined the effect of dietary formulation on NH3 emission immediately following manure excretion and the availability of manure N for plant growth. Manure (urine and feces) was collected from dairy cattle fed diets containing crude protein levels of 16.4% (T1High), 15.3% (T1Med), and 12.3% (T1Low) in trial 1, and 18.3% (T2High), 16.7% (T2Med), and 15.3% (T2Low) in trial 2. Ammonia emission was measured in the laboratory for up to 48 h. Emissions during the first 24 h following manure excretion were 38 and 23% of the total manure N from Diets T1High and T1Low, and 22, and 15% of the total manure N from Diets T2High and T2Low. Manure NH+4 concentration and pH were positively related to the dietary crude protein level. Manure from cattle‐fed diets T1Med and T1Low were applied to soil at two rates to determine short‐term N availability for three plantings of corn (Zea mays L.) grown for 30 d each in the greenhouse. The recovery of manure and fertilizer N in the plants and the soil for the first two plantings was 48, 31, and 103% for the T1Med, T1Low, and inorganic N treatments, respectively. Whole farm N utilization for diets T2High and T2Low were estimated at 18 and 23%, respectively. Feeding diets lower in crude protein increases efficiency of N on the dairy farm, decreases NH3 emissions following excretion but also decreases the short‐term N availability of the manure.

This experiment used 18 lactating Holstein cows in a 3 x 3 Latin square replicated 6 times to determine the effectiveness of processing with moist heat or moist heat combined with lignosulfonate (LSO3) for increasing the ruminal undegradable fraction of canola meal for use as a protein supplement for lactating dairy cows. Diets were formulated to be isonitrogenous and contained one of 3 forms of canola meal; untreated canola meal (UCM), heat-treated canola meal (HTCM) or heat-and LSO3-treated canola meal (LSO3CM). Total collection of urine and feces was taken from each cow during the last 5 d of each 42-d experimental period. Milk production was greater for cows fed the LSO3CM diet (36.6 kg/d) than for cows fed the UCM diet (34.8 kg/d) but did not differ from cows fed the HTCM diet (35.3 kg/d). Digestibility of crude protein was lower for cows supplemented with LSO3CM and they had reduced concentrations of ruminal ammonia N, blood urea N, and milk urea N compared with cows supplemented with UCM or HTCM. Dry matter intake and apparent digestibilities of neutral and acid detergent fiber were increased in cows fed the LSO3CM diet. Urinary N excretion (as % of N intake) was reduced in cows fed the LSO3CM diet. These results indicate that moist heat combined with LSO3 treatment of canola meal was effective in increasing the proportion of crude protein digested in the lower digestive tract of lactating cows and was therefore used more effectively as a source of protein than UCM or HTCM.

. 1994. Effect of level of dietary potassium on the absorption and excretion of calcium and magnesium by lactating cows. Can. J. Anim. . This study was undertaken lith the objective of providing more-basic information on ihe absorption and excretion of calcium (Ca) and magnesium (]\!e) bV lactating co*, *h.n high levels 5f potassium (K) are fed. Employingpotassium carbonate as the source of supplemental K total mixed rations were f6rmulated to contain i.O [ow), 3.t lm6dirim;1ia q.en ftigh) K. The three rations were fed to 15 For personal use only.

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