Monensin for lactating dairy cows grazing mixed-alfalfa pasture and supplemented with partial mixed ration.

The effect of monensin on milk production was evaluated in 58 lactating Holstein cows (48 multiparous; 10 primiparous) grazing a mixed-alfalfa pasture and supplemented with a partial mixed ration in a completely randomized design with repeated measurements. Cows were paired by calving date, lactation number, previous lactation milk production, body weight, and body condition score and were assigned to one of 2 treatments: control or monensin. Cows on the monensin treatment received 2 monensin controlled-release capsules (335 mg/d for 90 d), one 30 d before the expecting calving date and the other 60 d after calving. Short-term (0 to 150 d in milk) and long-term (305-d adjusted lactation) effects of monensin were evaluated. Pasture (measured by difference between pre- and postgrazing pasture mass), supplements, and total dry matter intake did not differ between treatments and averaged 8.7, 14.1, and 22.9 kg/d, respectively. In the short-term, monensin increased milk production (27.7 vs. 26.6 kg/d) and milk protein yield (0.890 vs. 0.860 kg/d); milk fat yield was not affected (0.959 kg/d). Monensin decreased milk fat content (3.51 vs. 3.60%) with no changes in milk protein content (3.25%). In the long term, milk production and milk protein yield were also increased by monensin: 214 and 7 kg, respectively. Monensin reduced the loss of body condition score and increased percentage of pregnancy at first service (44.8 vs. 20.7%). Monensin improves production and reproduction performance of dairy cows grazing a mixed-alfalfa pasture and supplemented with a partial mixed ration.

Fatty acid and triglyceride composition of milk fat from lactating Holstein cows in response to supplemental canola oil.

The objective was to determine the influence of dietary lipid on total and sn-2 fatty acid composition and triglyceride structure of milk fat in lactating Holstein cows. Five primiparous Holstein cows surgically fitted with ruminal and duodenal cannulas were used in a 4 x 5 incomplete Latin square. All cows received a basal diet. Treatments consisted of a basal diet with no supplemental canola oil (control), basal diet with canola oil added to the concentrate portion of the diet to provide 1.6% fat, basal diet with 330 g of canola oil infused directly into the rumen, and basal diet with 330 g of canola oil infused directly into the abomasum. Canola oil treatments decreased palmitic acid and increased oleic acid content of milk fat compared with the control. Stearate was higher when canola oil was rumen available compared with control and abomasal infusion. Abomasal infusion increased linoleic and linoleic acids in milk fat compared with the other treatments. The sn-2 fatty acid composition reflected total fatty acid composition. All canola oil treatments reduced palmitic acid and increased oleic acid content at the sn-2 position. Changes in sn-2 composition reflect specificity of the acyl transferases and substrate concentration. Triglyceride composition reported as carbon number was altered by canola oil. Triglycerides in carbon number C50, C52, and C54 were increased while C32, C34, and C36 were decreased.

Influences of saturation ratio of supplemental dietary fat on digestion and milk yield in dairy cows.

Four multiparous, ruminally and duodenally cannulated Holstein cows in midlactation were utilized in a 4 x 4 Latin square to evaluate the effects of supplemental fat from sources varying in proportions of unsaturated and saturated fatty acids on nutrient digestion and lactation performance. All diets (45% alfalfa hay) contained 12% whole cottonseed (as-fed); treatments were no supplemental fat (control, 3% total fatty acids, dry matter basis) or additional 2% tallow, 2% yellow grease, or 2% blend (60% tallow: 40% yellow grease). The unsaturated to saturated fatty acid ratios were 1:1 for tallow and 2.5:1 for yellow grease. Dry matter intake, apparent ruminal and total tract digestibilities of organic matter, neutral detergent fiber, acid detergent fiber, N, and fatty acids, and microbial efficiency were similar across treatments. Microbial N flow to the duodenum was increased by yellow grease. Supplemental fat reduced the postruminal digestibility of fatty acids, primarily the saturated fatty acids; increasing saturation of the fat source magnified the reduction. Total volatile fatty acid concentrations and ruminal fluid pH were unaffected by fat supplementation or saturation level. Blend decreased ruminal pH and acetate to propionate ratio. Yields of milk and milk fat increased with fat supplementation. Concentrations and yields of trans vaccenic acid in milk increased linearly with the unsaturated fatty acid content of the fat supplement. Modest supplementation using highly unsaturated fats to diets containing whole cottonseed can increase milk production without disturbing rumen function, evident by the similar VFA concentrations, nutrient digestibilities, and milk composition.

Antibiotic sensitivity of an Argentine strain collection of Moraxella bovis.

The antimicrobial susceptibility of 88 isolates of Moraxella bovis of Argentine origin was evaluated for 12 antimicrobials by broth microdilution procedures. The isolates had a minimum inhibitory concentration (MIC90) of < or = 0.06 microg/mL to enrofloxacin; < or = 0.12 microg/mL to ceftiofur; < or = 0.25 microg/mL to ampicillin; < or = 0.5 microg/mL to florfenicol and gentamicin; < or = 1.0 microg/mL to tilmicosin, erythromycin, and oxytetracycline; < or = 4.0 microg/mL to tylosin; < or = 8.0 microg/mL to spectinomycin; < or = 0.25/4.75 microg/mL to trimethoprim/sulfamethoxazole; and > or = 32 microg/mL to lincomycin. Modal MIC values for these antimicrobials were as follows: enrofloxacin, 0.03 microg/mL; ceftiofur, 0.06 pg/mL; ampicillin, 0.25 microg/mL; florfenicol, gentamicin, erythromycin, and oxytetracycline, 0.5 microg/mL; tilmicosin, 1.0 microg/mL; tylosin and spectinomycin, 4.0 microg/mL; lincomycin and erythromycin, 16 microg/mL; and trimethoprim/ sulfamethoxazole, < or = 0.25/4.75 microg/mL. These data show that all antimicrobials except lincomycin have MICs suggestive of sensitivity in vitro, though confirmation of clinical efficacy can only be properly assessed based on pharmacologic and/or clinical data to support the MIC values.

Effects of dietary nitrogen manipulation on ammonia volatilization from manure from Holstein heifers.

Decomposition of livestock manure produces gaseous ammonia. Dietary manipulation is one means to reduce N in manure and ammonia volatilization. The effects of dietary crude protein concentration on N intake, N and urinary urea-N excretion, and ammonia volatilization were measured. Eight Holstein heifers (body weight = 260 to 488 kg) were fed a total mixed ration containing either 9.6 or 11.0% crude protein in a crossover design. Oatlage and concentrate were fed at 77:23 (dry matter basis), and soybean meal was used to alter total dietary crude protein. Seven-day adjustment periods preceded 5-d collection periods. Indwelling urinary catheters were inserted 2 d prior to the collection periods. Daily feces and acidified urine were collected, stirred, and subsampled for total Kjeldahl N, urinary urea N, dry matter, P, K, and ash. Urine collection tubes were split during period 2 to allow for collection of unacidified samples for urea N and total N determinations. Unacidified urine and fecal samples were combined (1:1.3) for collection of volatilized ammonia. Remaining slurries were extracted for total and urea N. Increased dietary crude protein concentration increased N intake, N excretion, urea-N excretion, and N excreted in the urine by the heifers. Dietary manipulation of N intake by reduction of 14.0% (dry matter basis) resulted in a 28.1% decrease in ammonia emission and decreases in the urea N, total N, and percentage N excreted in the urine of 29.6, 19.8, and 7.4%, respectively. Ammonia volatilization was dependent on N quantity and form in the urine.

Influence of processed corn grain in diets of dairy cows on digestion of nutrients and milk composition.

Five primiparous Holstein cows (55 d in milk) that were fitted with ruminal and duodenal cannulas were used in a 4 x 5 incomplete Latin square to determine the effects of blends of steam-flaked and dry-rolled corn on site and extent of nutrient digestion and milk yield and composition. Diets were fed as total mixed rations and consisted of 45% forage and 55% concentrate; each diet contained 27% corn grain. Dietary treatments were composed of blends of dry-rolled and steam-flaked corn in ratios of 100:0, 67:33, 33:67, and 0:100. Intake of dry matter; digestibilities of dry matter, organic matter, acid detergent fiber, cellulose, neutral detergent fiber, fatty acids, and N; and microbial efficiency were unaffected by diet. Ruminal, postruminal, and total tract digestion of starch increased linearly, and starch passage to the duodenum decreased linearly, as the proportion of dry-rolled corn in the diet decreased. Ruminal propionate and valerate increased linearly, and acetate, butyrate, isovalerate, and the acetate to propionate ratio decreased linearly, as proportions of dry-rolled corn in the diet decreased; however, no changes in total volatile fatty acid concentrations in ruminal fluid were observed. Ruminal fluid pH was similar across diets. A decrease in dry-rolled corn decreased ruminal ammonia N and plasma urea N linearly. Milk yield and composition, as well as milk N fractions, were similar across diets. Although changes in fatty acid composition of milk fat were small, linear decreases in percentages of trans-C16:1 and cis-9- and cis-10-C18:1, as well as a linear increase in the percentage of C18:2 occurred as the proportion of dry-rolled corn in the diet decreased. An increased proportion of dry-rolled corn in the diet decreased digestion of starch in the rumen, and patterns of volatile fatty acid concentrations shifted accordingly. However, no effects on lactational parameters were observed.

Ash content of detergent fibers in feeds, digesta, and feces and its relevance in fiber digestibility calculations.

The influence of insoluble ash in diet, digesta, and fecal samples was evaluated. Ash-free values of neutral detergent fiber (NDF) and acid detergent fiber (ADF) for feed, digesta, and fecal samples were compared with uncorrected values of NDF and ADF in two digestibility experiments. Six feed samples were selected at random along with four duodenal and two fecal samples; the latter two were a part of two digestion studies. The silica composition of feed samples was low with the exception of oat hay and rice straw. Ash-free values of NDF and ADF for digesta and fecal samples were lower than uncorrected values of NDF and ADF, and silica accounted for the majority of the differences. The use of ash-free values of NDF and ADF in both digestibility experiments with dairy cows resulted in more realistic digestibility estimates and reduced the amount of variability associated with the calculation of the digestibility of NDF and ADF in the rumen and total digestive tract. The source of the insoluble ash was not identified but could have come from individual feedstuffs or the consumption of sand. Sample contamination by silica and other ash components may influence NDF and ADF composition if the fiber residues are not ashed prior to calculation of NDF and ADF.

Effects on nutrient digestion of wheat processing and methods of tallow addition to the diets of lactating dairy cows.

Five multiparous Holstein cows in midlactation that were fitted with ruminal and duodenal cannulas were used in a 3 x 5 incomplete Latin square. The objective of this study was to examine the effects on nutrient digestion of wheat processing and method of tallow addition to the diets of lactating dairy cows. Diets consisted of 45% forage and 55% concentrate, and each diet contained 20% wheat and 2% tallow (as-fed basis). Treatments were dry-rolled wheat with tallow added to the concentrate, steam-rolled wheat with tallow added to the concentrate, and steam-rolled wheat with tallow added first to the wheat. The dry matter intake; digestion of starch, fiber, and fatty acids; ammonia N concentration; and molar proportions of volatile fatty acids in ruminal fluid were not affected by treatments. The apparent digestibility in the total tract of organic matter and nitrogenous compounds was significantly higher for the steam-rolled treatment with tallow added first to the wheat. Mean ruminal fluid pH was similar across treatments; however, cows fed the diet containing steam-rolled wheat with tallow added first to the wheat had the smallest pH change from 0 to 2 h postfeeding. Milk yield did not differ, regardless of cow diet. Method of tallow addition had marked effects on the apparent digestibility of organic matter and N in the total tract of lactating dairy cows.