R.J. Harmon

Salt- and pyrophosphate-induced structural changes in myofibrils from chicken red and white muscles

Myofibrils isolated from post-rigor chicken Pectoralis major (PM, white) and Gastrocnemius (Gas, red) muscles were irrigated with various concentrations of NaCl (0.1–1.0 M) with or without 10 mM sodium pyrophosphate at pH 5.5 and 6.0. Structural changes were examined using phase contrast microscopy. PM myofibril samples tended to show more definitive H-zones but obscure Z-lines compared to Gas myofibrils. Significant myofibril swelling, accompanied by a pronounced protein extraction, occurred in 0.5 M NaCl solution. The extent of swelling as well as protein extraction increased with the NaCl concentration up to about 0.8 M. Addition of pyrophosphate facilitated myofibril swelling and reduced the minimal NaCl concentration for swelling to 0.4 M. Without pyrophosphate, protein extraction for both PM and Gas myofibrils occurred along the A-band, sometimes starting from the centre, but when pyrophosphate was added, the extraction began from the ends of the A-band. At pH 5.5, protein extraction was similar for PM and Gas, but at pH 6.0, PM myofibrils were more extractable and their architecture changed more extensively than Gas myofibrils, especially when pyrophosphate was present. The results may explain the different water-imbibing abilities of white and red meat when processed with salt and phosphate. © 2000 Society of Chemical Industry

Mastitis in Heifers

Udder health is typically overlooked but critically important in heifers. Mastitis pathogens of the contagious as well as environmental groups have been implicated in mastitis in heifers. Procedures considered for control of heifer mastitis include prepartum treatment in primigravid heifers, separating preweaned calves to prevent suckling, fly control, and segregation of pregnant heifers from dry cows. Further investigation is needed before general recommendations can be made relative to prepartum treatment of primigravid heifers. An improved understanding of the epidemiology and pathogenesis of heifer mastitis will aid in expanding and improving control measures.

Estimating US dairy clinical disease costs with a stochastic simulation model

A farm-level stochastic model was used to estimate costs of 7 common clinical diseases in the United States: mastitis, lameness, metritis, retained placenta, left-displaced abomasum, ketosis, and hypocalcemia. The total disease costs were divided into 7 categories: veterinary and treatment, producer labor, milk loss, discarded milk, culling cost, extended days open, and on-farm death. A Monte Carlo simulation with 5,000 iterations was applied to the model to account for inherent system variation. Four types of market prices (milk, feed, slaughter, and replacement cow) and 3 herd-performance factors (rolling herd average, product of heat detection rate and conception rate, and age at first calving) were modeled stochastically. Sensitivity analyses were conducted to study the relationship between total disease costs and selected stochastic factors. In general, the disease costs in multiparous cows were greater than in primiparous cows. Left-displaced abomasum had the greatest estimated total costs in all parities (

Effect of dietary copper source on response to coliform mastitis in dairy cows

432.48 in primiparous cows and

Comparison of buffers on rumen functions, turnover rate and gastric secretions in Holstein steers

639.51 in multiparous cows). Cost category contributions varied for different diseases and parities. Milk production loss and treatment cost were the 2 greatest cost categories. The effect of market prices were consistent in all diseases and parities; higher milk and replacement prices increased total costs, whereas greater feed and slaughter prices decreased disease costs.

Physiology of Mastitis and Factors Affecting Somatic Cell Counts

The effect of organic or inorganic dietary Cu on Escherichia coli mastitis was investigated in first-lactation heifers. Twenty-eight primigravid Holstein heifers were assigned to 3 treatments in a completely randomized block design with 10 blocks of 3 animals grouped by expected calving date. Treatments were as follows: basal diet [7.1 mg Cu/kg of dry matter (DM); CON] and diets supplemented with Cu (10 mg/kg of DM) as Cu sulfate (CUS) or as Cu proteinate (CUP). Treatments were fed individually from 60 d prepartum through 49 d of lactation. All heifers were marginally deficient at the onset of the experiment (liver Cu of 60 mg/kg) and did not differ between groups. Mean liver Cu concentrations were about 3-fold greater in CUS and CUP compared with CON at d 0, 21, and 42 of lactation. At d 34 postpartum, one pathogen-free quarter per cow was infused with Escherichia coli strain 727. Copper supplementation did not lower peak responses to challenge; however, CUP tended to offer some benefits: milk bacterial count with CUP was lower compared with CON at 24, 48, and 72 h and lower than CUS at 24 and 96 h, and postchallenge milk production tended to be greater for CUP. Clinical udder score was lower at 12 h for CUP and CUS compared with CON, and at 144 h CUP had lower clinical scores compared with CUS or CON. Somatic cell count, dry matter intake, plasma Cu, and plasma ceruloplasmin did not differ between treatments. Compared with the control diet or Cu sulfate supplement, supplementation with Cu proteinate tended to improve the clinical status of cows after live E. coli intramammary challenge.

Influence of addition of yeast culture supplement to diets of lactating cows on ruminal fermentation and microbial populations.

Abstract Five Holstein steers (276 kg) fitted with ruminal and duodenal cannulae were used to study the effect of buffers on rumen parameters, turnover and abomasal gastric secretions. In a 5 × 5 Latin square design, treatments were control, 0.8% magnesium oxide, 0.8% sodium bicarbonate, 0.96% limestone and 0.8% magnesium oxide + 0.8% sodium bicarbonate. Dietary addition of buffers decreased plasma glucose. Addition of 0.8% magnesium oxide and 0.8% sodium bicarbonate increased plasma magnesium. Rumen pH was significantly increased by addition of 0.8% magnesium oxide, either alone or with 0.8% sodium bicarbonate. Buffer addition had no influence on duodenal pH. Dietary addition of magnesium oxide and sodium bicarbonate, either alone or together, increased water intake which caused a significant increase in total rumen fluid outflow, increased estimated rumen volume and caused a faster rumen digesta disappearance rate, especially for the combined buffers. Estimated dry matter volume of rumen and dry matter disappearance was significantly increased by the addition of magnesium oxide. Buffered diets caused a 2-fold increase in gastric secretion. Results suggest that buffers not only alter rumen functions and flow rate, but may also influence digestion in the small intestine by increasing gastric secretions.