Effect of a low chloride diet on lactating Holstein cows.

Twenty primiparous lactating Holstein cows were fed diets supplemented with either .5% sodium chloride or .75% sodium bicarbonate. Those fed the latter diet conserved chloride by reducing the chloride concentration in urine, feces, and, to a small but nonsignificant amount, in milk. The low chloride diet did not affect consumption of feed dry matter and water or milk production and composition. There was no indication of pica or other aberrant taste behavior. One half of the cows in each diet group was given free choice salt block of trace elements. Those fed the low chloride diet consumed more salt (337 versus 149 g/cow per wk). When chloride requirements have been established and data on chloride composition become more widely available, it will be possible to include both sodium and chloride in diet formulations and omit salt. This will reduce the amount of salt needed as either a sodium or chloride supplement.

Use of urea by early postpartum Holstein cows.

Thirty-nine lactating Holstein cows were fed high-energy complete rations ad libitum with crude protein: 1) 11.7% (negative control); 2) 13.9% (1% urea); 3) 16.6% (1% urea); or 4) 16.6% (positive control) in a continuous 12-wk study beginning at wk 5 postpartum. Milk production of 27.7, 31.8, 34.0, and 30.4 kg/day showed the use of urea nitrogen by groups 2 and probably 3. Two digestion-nitrogen balance trials with each cow also provided evidence that urea nitrogen was used for milk secretion. Energy digestibility averaged 59.4, 64.2, 65.4, and 65.8; and lower for the negative control diet. Nitrogen solubility in the diets was 28, 36, 32, and 21%, which reflects the objective of selecting ingredients with low nitrogen solubility for use in urea diets. Concentrations of ammonia nitrogen before and after feeding were 1.1, 3.3, 3.5, 4.2, and 2.2, 11.2, 11.9, and 9.3 mg/100 ml of rumen fluid. The prefeeding amounts were probably too low for maximum microbial growth. Urea-nitrogen concentrations in plasma were 8.65, 10.32, 18.00, and 17.03 mg/100 ml. These results lend support to the postulate that lactating cows in early lactation can use urea nitrogen when high-energy complete rations with ingredients of low nitrogen solubility are fed ad libitum.

Effects of a low calcium diet on feed intake, milk production, and response to blood calcium challenge in lactating Holstein cows.

Twenty-four lactating cows were fed a normal-calcium (.75% of dry matter) diet plus free-choice dicalcium phosphate supplement for 8 wk, a low-calcium (.25% of dry matter) diet for 9 wk, and a low-calcium (.25% of dry matter) diet plus free-choice supplement for 4 wk. The low-calcium diet did not appear to affect adversely feed intake, milk production, or plasma ions. Depression of plasma calcium by sequestration with a chelating agent was less following low intake of calcium than following adequate calcium intake. Presumably, lower calcium intake increased parathyroid hormone which resulted in a larger and more responsive calcium pool immediately mobilizable. Changes in plasma phosphorus and magnesium were similar among treatments. Low calcium intake for short times apparently will not affect intake or production and may increase resistance to calcium stress such as hypocalcemia and parturient paresis.

Effect of urea form and method of feeding on rumen ammonia concentration.

Rumen ammonia was compared in six rumen fistulated, lactating Holstein cows fed urea twice daily in a concentrate mixture, urea fed once per day in a complete ration, and a gelatinized starch-urea product fed twice daily in the concentrate mixture. Samples were taken during 24-h intervals at the end of each 3 wk. Sharp and similar peaks in rumen ammonia followed feeding of urea and gelatinized urea-starch product twice daily in the concentrate mixture. A much lower ammonia peak followed the once daily feeding of the complete ration. Use of complete rations offered ad libitum eliminates the need for products with sustained ammonia release.

Effects of silage diets on health, reproduction, and blood metabolites of dairy cattle.

Forty-eight Hostein dairy cows were assigned uniformly by parity and calving date to three forage treatments for three lactations. Forage treatments were corn silage (F-I), corn silage plus Hay-crop silage (-f-II), and corn silage plus hay (F-III). Records of health and reproductive data were kept to evaluate dietary effects. During the third lactation six animals in each treatment were blood-sampled on a 4-day interval from 24 days prepartum to 60 days postpartum to determine metabolites. Reproductive traits were similar among the treatment groups as were occurrences of mastitis. Corn silage and hay-crop silage cows had more ketosis than hay cows. Corn silage cows had more parturient paresis than the other two groups, and abomasal displacement occurred only in the corn silage group. There were differences in concentrations of plasma metabolites among treatments; however, they appeared to be within normal ranges, and no pathological implications were obvious. Blood pH, blood packed cell volume, blood alkaline reserve, and pH values were similar among treatment groups. Histological evaluation of hepatic and endocrine tissues revealed no treatment effects.