Influence of milk production potential on forage dry matter intake by multiparous and primiparous Brangus females

Brangus cows (n = 29) were used in three experiments to evaluate the effects of parity (multiparous vs. primiparous) and potential genetic merit for milk production (high vs. low) on forage intake during late gestation, early lactation, and late lactation. Cows were selected for milk production based on their sire's EPD for milk production (MEPD). Cows had ad libitum access to (130% of previous 2-d average intake) low-quality hay (5.3% CP and 76% NDF), and cottonseed meal was supplemented to ensure adequate degradable intake protein. All females were adapted to diets for at least 7 d, and individual intake data were collected for 9 d. During the lactation trials, actual milk production was determined using a portable milking machine following a 12-h separation from calves. During late gestation, multiparous cows consumed 24% more (P = 0.01) forage DM (kg/d) than primiparous cows; however, parity class did not influence forage intake when intake was expressed relative to BW. Furthermore, MEPD did not influence forage intake during late gestation. During early lactation, multiparous cows produced 66% more (P < 0.001) milk than primiparous cows, and high MEPD tended (P = 0.10) to produce more milk than low MEPD. Multiparous cows consumed 19% more (P < 0.0001) forage DM than did primiparous cows when expressed on an absolute basis, but not when expressed on a BW basis. High-MEPD cows consumed 8% more (P < 0.05) forage DM than did low-MEPD cows. During late lactation, multiparous cows produced 84% more milk than primiparous cows, although MEPD did not influence (P = 0.40) milk yield. In addition, multiparous cows consumed 17% more (P < 0.01) forage DM per day than primiparous cows, but when intake was expressed relative to BW, neither parity nor MEPD influenced forage DMI during late lactation. Milk yield and BW explained significant proportions of the variation in forage DMI during early and late lactation. Each kilogram increase in milk yield was associated with a 0.33- and 0.37-kg increase in forage DMI for early and late lactation, respectively. Results suggest that multiand primiparous cows consume similar amounts of low-quality forage DM, expressed per unit of BW, during late gestation and lactation. Selecting beef cows for increased genetic merit for milk production increases forage DMI during early lactation.     

Evaluation of renal gentamicin depletion kinetic properties in sheep, using serial percutaneous biopsies

Tissue drug residue research often involves the killing of an animal every time tissue concentrations are determined. To decrease the number of animals required to perform tissue depletion studies and to circumvent the statistical problems associated with determining tissue depletion kinetic properties, using multiple animals, the renal depletion profile of gentamicin from individual sheep was studied, using a bilateral renal translocation technique. Seven ewes were surgically altered, allowed to stabilize, and then allocated into 2 groups; group-1 sheep (n = 4) were given 3 mg of gentamicin/kg, IM, q 12 h for 10 days, and group-2 sheep (n = 3) were not given gentamicin. The kidneys from all ewes were biopsied 9 times over 74 days after the termination of gentamicin treatment. The renal concentrations of gentamicin were measured by use of a validated tissue digestion procedure coupled with a liquid-phase fluorescence polarization immunoassay. On days 75 and 77 after the end of gentamicin treatment, all ewes were euthanatized and necropsied. The concentrations of gentamicin in the biopsy specimens ranged from 71.9 to 183 micrograms/g on days 1 and 2 after dosing, and decreased to concentrations ranging from 3.99 to 7.35 micrograms/g on days 73 and 74 after the end of dosing. The decrease in renal gentamicin concentrations was best described by a biexponential equation. The early phase half-life was 2.8 days, whereas the terminal phase half-life was 59 days (harmonic means). There was no difference in the appearance or histologic features of the kidneys from groups 1 and 2. The only lesions noticed were linear fibroses that were attributed to the biopsy procedure.     

Probenecid infusion in mares: effect on para-aminohippuric acid clearance

Para-aminohippuric acid (PAHA, 0.1 mg/min/kg of body weight) was infused IV into 2 mares, followed by concurrent IV infusion of PAHA and probenecid (0.075, 0.15, 0.25, or 0.35 mg of probenecid/min/kg). Probenecid infusion reduced the clearance of PAHA at serum probenecid concentrations greater than 55 micrograms/ml. At 12-hour intervals, probenecid (in 5 repeated doses - 50, 75, 100, or 200 mg/kg) was administered by gavage to 2 mares. Mean serum probenecid concentration was greater than 55 micrograms/ml for all dosages. At dosages less than 200 mg/kg, accumulation of probenecid in the serum was minimal from the 1st to the 5th dose. At a dosage of 200 mg/kg, probenecid accumulated in the serum from the 1st to the 5th dose. Intragastric administration of 5 doses of probenecid (75 mg/kg) at 12-hour intervals to 6 mares reduced the clearance of PAHA by 50%. Bioavailability of probenecid was 117 and 102% for 2 mares after a single intragastric dose, compared with a single IV dose.     

Characterization of tick antigens inducing host immune resistance. II. Description of rabbit-acquired immunity to Amblyomma americanum ticks and identification of potential tick antigens by Western blot analysis

Feeding by adult Amblyomma americanum ticks induced a level of immunity in rabbits to subsequent tick feeding that resulted in a significant decrease in tick feeding success and fecundity. Histological analysis of tick feeding sites in hosts expressing resistance revealed a predominant eosinophil response, with weak basophil and neutrophil infiltrates. While the basophil was never the dominant granulocyte at the tick feeding sites in resistant hosts, this cell exhibited the greatest increase in density (tenfold) over levels observed in hosts experiencing their first infestation; eosinophils and neutrophils exhibited increases of five- and twofold, respectively. Serum from animals that expressed resistance was tested for the presence of anti-tick antibodies to tick-derived salivary gland substances (SGA) by Western blotting. Western blot analysis of female-derived SGA compared to male-derived SGA, using the Avidin/Biotin technique, resulted in the identification of approximately 25 proteins from the female preparation, but only seven from the male. The use of 125I labeled protein-A as the probe for anti-tick antibody in Western blot analysis resulted in fewer recognized proteins. Serum from rabbits immunized with A. americanum-derived SGA emulsified with complete (CFA) Freund's adjuvant recognized most of the proteins identified by active serum, whereas serum from animals immunized with SGA in incomplete (IFA) Freund's adjuvant did not. Furthermore, both sera recognized a multiplicity of proteins from extracts of larval A. americanum Dermacentor variabilis and Boophilus microplus ticks, suggesting the presence of common antigens between these distantly related ticks. The results from this study demonstrate that rabbits acquire a strong immunity to A. americanum ticks characterized by the production of antibody. Furthermore, ticks secrete a number of substances into rabbits during feeding, as seen by Western blot analysis but only three may be crucial to the induction of host immunity; proteins at 41, 40 and 39 kDa. The purified anti-tick antibody will be used for subsequent isolation and characterization of crucial antigens.     

Immunohistochemical characteristics of canine aortic and carotid body tumours

In an immunohistochemical study of 25 canine chemodectomas, 17 tumours were stained with antisera to neurone specific enolase and the same number were stained for synaptophysin; a single tumour was stained for S100. Staining for Ki-67 occurred in 18 cases; the Ki-67-labelling index and the intensity of immunostaining was increased in more pleomorphic and malignant tumours, as assessed on histological grounds. Immunohistochemistry did not aid in recognition of less well-differentiated tumours.