David K. Beede

Copyright © 2012. . © 2012 Beede

Diet fermentability influences lactational responses to feeding corn distillers grains (CDG) to dairy cows. However, some measures of diet fermentability are inherently related to the concentration and characteristics of corn-based ingredients in the ration. Corn-based feeds have poor protein quality, unable to meet the essential AA requirements of lactating cows. We conducted a meta-analysis of treatment means (n=44) from the scientific literature to evaluate responses in milk yield (MY) and milk true protein concentration and yield to dietary CDG. The test variable was the difference in response between the CDG diet mean and the control diet mean (0% CDG) within experiment. Fixed variables were CDG concentration of the diet [% of dietary dry matter (DM)] and crude protein (CP) concentration and fractions of CP based on origin (corn-based versus non-corn-based feeds) of control and CDG diets. Diets with CDG ranged from 4 to 42% CDG, DM basis. Non-corn-based dietary CP averaged 6.3±3.32% of total DM. Milk yield and milk true protein yield responses to added CDG were maximized when approximately 8.5% of the total dietary DM was non-corn-based CP. Milk yield response peaked for higher-producing cows (>30.0 kg MY/cow per day) at 4.3% dietary corn-based CP, but decreased linearly for lower-producing cows (<30.0 kg MY/cow per day) as corn-based dietary CP increased. Milk true protein yield response decreased as corn-based dietary CP concentration increased but milk true protein concentration response was not decreased when CDG diets had more than 6.5% dietary non-corn-based CP. Overall, 8.5% dietary non-corn-based CP was necessary in lactation diets to maximize lactational responses to dietary CDG. The necessity of dietary non-corn-based CP to maximize milk and milk protein yields limits the amount of dietary corn-based CP, including that from CDG, which can be included in rations without overfeeding N.

Increasing supply of corn distillers grains (CDG) raises questions about the extent to which they can be used in diets of lactating dairy cows. A database of treatment means (n=44) reported in 16 peer-reviewed journal articles published from 1985 to 2008 was developed. The database included response (within study) to a CDG diet compared with the control (no CDG) for milk yield (MY), milk fat concentration and yield, CDG content of the diet, and dietary composition of control and CDG diets (% of dietary dry matter). Additionally, corn grain fermentability was classified as high moisture (n=7) or dry (n=37). Data from studies with diets including more than one grain source (n=8) had been eliminated from the analysis. Dietary concentrations of CDG ranged from 4.2 to 42% across studies. Dietary concentrations in diets containing CDG were 16.8±1.91% (mean±standard deviation) crude protein, 36±15.5% corn silage, 23±8.8% corn grain, and 28±5.8% starch. Responses to CDG were 0.5±2.10 kg/cow per day (mean±standard deviation) for MY, 0.05±0.178 percentage units for milk fat concentration, and 26±77.6 g/cow per day for milk fat yield. Only MY response was related to increasing concentrations of CDG in diets and peaked at 1.2 kg/cow per day for 21% CDG. Diet fermentability was associated with responses. The greatest MY response to CDG was with 24% corn silage or 23% starch, and concentrations greater than 47% corn silage or 32% starch resulted in negative MY responses. Responses in MY differed by level of MY and were often more evident in higher- (>30.0 kg MY/d) than in lower-producing cows. Milk fat concentration response was not related to dietary CDG, but was correlated linearly with milk fat concentration of cows fed the control diet. Milk fat concentration greater than 3.6% for the control treatment was related to a negative milk fat concentration response to CDG, regardless of dietary concentration of CDG. Partially replacing high-moisture corn with CDG increased milk fat concentration by 0.16 percentage units compared with that from dry corn. When formulating diets with CDG, diet fermentability and level of MY (higher vs. lower) must be considered. Concentrations of corn silage and starch must be moderate to optimize lactational responses to CDG. Overall, lactational response to CDG in this database was dependent on diet fermentability and milk fat concentration in the control.

The objective was to evaluate estimates of the inevitable fecal loss component of the P maintenance requirement of lactating Holstein cows consuming differing amounts of a low-P diet. The maintenance requirement for P is the sum of inevitable (e. g., unavoidable) endogenous fecal P plus endogenous urinary P when an animal is fed near its true P requirement (i.e., zero P balance). Urinary excretion of P is normally very low in healthy cattle. Inevitable fecal P is the main part of the total P maintenance requirement; it can be expressed as grams of fecal P/kilogram of dry matter intake (DMI). Twenty-one multiparous lactating Holstein cows (55 to 253 +/- 6 d in milk, range +/- SD; 0 to 171 +/- 64 d pregnant) with a wide range of pretrial milk yields (25.3 to 47.3 +/- 1.23 kg/cow per day) were selected to achieve a range in DMI and assigned to treatment groups of low, medium, and high DMI. To obtain an even greater range in DMI, rations fed to cows in the low and medium treatment groups were restricted to 75 and 50% of their pretrial ad libitum intakes, respectively. Dry matter intakes during the experiment averaged 11.3 (low), 15.3 (medium), and 25.1 (high) kg/cow per d, respectively. All cows were fed the same low-P diet (0.26% P, dry basis) throughout the experiment. Phosphorus balances of cows in all treatments were not different from zero and unaffected by DMI. Average daily total inevitable fecal P excretion was 15.3, 18.2, and 26.3 g/cow for low, medium, and high DMI, respectively. Inevitable fecal P excretion was 1.36, 1.19, and 1.04 g/kg of DMI for low, medium, and high and decreased linearly with increasing DMI. The regression equation to estimate inevitable fecal P excretion across the range of DMI was: (g/d) = [0.85 +/- 0.070 (g/d)] x DMI (kg/d) + [5.30 +/- 1.224 (g/d)]; (R-2 = 0.90). This equation can be used to estimate the inevitable fecal P component of the total P maintenance requirement of lactating Holstein cows.

The objective was to determine if exercise training improves physical fitness of nonlactating, late-pregnant and nonpregnant multiparous Holstein cows and alters acid-base homeostasis during an exercise test on a treadmill. Twenty-six pairs (each pair having 1 late-pregnant and 1 nonpregnant) of cows were assigned to treatments of exercise training or no exercise. Exercise training was walking (1.25 to 1.5 h at 3.25 km/h) every other day in an outdoor mechanical walker for 70 d. Cows completed treadmill exercise tests on d 0, 30, and 60 of the experiment or about d 70, 40, and 10 before expected parturition of the pregnant cow of each pair. On d 0, physical fitness was similar among all cows based on durations of treadmill tests, heart rates, and acid-base measurements at given workloads (21.1 +/- 0.6 min; 144 +/- 2.2 beats per min; plasma lactate 3.1 +/- 1.9 mmol/L; and venous blood pH 7.44 +/- 0.0035, respectively). After 60 d of training, exercised cows walked longer during treadmill exercise tests compared with nonexercised cows (23.7 vs. 18.3 +/- 0.85 min, respectively), indicating greater physical fitness (pooled across pregnancy status). Heart rates and plasma lactate concentrations at given workloads were less (144 vs. 156 +/- 2.7 beats per min; and 1.4 vs. 3.2 +/- 0.24 mmol/L for exercised compared with nonexercised cows, respectively). Additionally, exercised cows more effectively maintained acid-base homeostasis during treadmill tests compared with nonexercised cows. Metabolic, endocrine, and nutritional demands associated with late pregnancy did not affect responses differently to exercise training for late-pregnant compared with nonpregnant cows. Overall, exercise training of late-pregnant and nonpregnant cows for 60 d improved physical fitness.

While research demonstrates that most agricultural producers prefer to receive research and other educational information in printed forms, such as newsletters and magazines, acceptance of the Internet is increasing.

Objectives were to develop a system to administer exercise training to dairy cows, to measure potential physiological indicators of fitness, and to assess physical fitness. Nonlactating, nonpregnant multiparous Holstein cows (n = 19) were in one of three exercise training treatments: no exercise; 1-h exercise; or 2-h exercise by walking 3 km/h every other day for 60 d in a mechanical walker. Treadmill tests on d 15, 30, 45, and 60 consisted of walking (5 km/h) with 1.6% increases in slope at 3-min intervals until heart rates reached 180 beats per minute (experimentally specified maximum) or until cows refused to walk. Fitness indices analyzed in tests as single datum points at maximal heart rates were length of time of test, heart rate, and plasma L-lactate concentration at end of the test, and change in heart rate and lactate concentration during the test. Exercised (1 or 2 h) cows had longer times to end of tests than nonexercised cows. Maximal and change in heart rates or plasma lactate during tests did not indicate improved physical fitness. However, when all data were evaluated as repeated measures of day and minute of tests, reductions of heart rates and plasma lactate concentrations were greatest on d 60 between exercised and nonexercised cows indicating improved fitness. Acid-base measurements were not found useful in this study. Changes of heart rates and plasma lactate concentrations over time (repeated measures) of treadmill tests quantified the physical fitness of dairy cows and can be used to compare potential responses to different exercise training treatments in this system.